Networking Concept.pdf

Networking Concepts (BTEC Higher National Diploma)

Introduction to Networking Group of computers and associate peripherals connected by communication channels, which is used to share resources and for communication.

A network consists of two or more computers that are linked in order to share resources (such as printers and CD-ROMs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams. Today every business in the world from banking to airlines offices, corporate organizations, postal services, universities and a even a home where there are two or more computers, need a network to communicate with other people.

Advantages of Network. • Speed. Networks provide a very rapid method for sharing and transferring files. Without a network, files are shared by copying them to floppy disks, then carrying or sending the disks from one computer to another. This method of transferring files is very time-consuming. • Cost. Network able versions of many popular software programs are available at considerable savings when compared to buying individually licensed copies. Besides monetary savings, sharing a program on a network allows for easier upgrading of the program. The changes have to be done only once, on the file server, instead of on all the individual workstations. • Security. Files and programs on a network can be designated as "copy inhibit," so that you do not have to worry about illegal copying of programs. Also, passwords can be established for specific directories to restrict access to authorized users. • Centralized Software Management. One of the greatest benefits of installing a network at a school is the fact that all of the software can be loaded on one computer (the file server). This eliminates that need to spend time and energy installing updates and tracking files on independent computers throughout the building. • Resource Sharing. Sharing resources is another area in which a network exceeds stand-alone computers. Most companies cannot afford enough laser printers, fax machines, modems, scanners, and CD-ROM S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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players for each computer. However, if these or similar peripherals are added to a network, they can be shared by many users. • Electronic Mail. The presence of a network provides the hardware necessary to install an e-mail system. E-mail aids in personal and professional communication for all school personnel, and it facilitates the dissemination of general information to the entire school staff. Electronic mail on a LAN can enable students to communicate with teachers and peers at their own institute. If the LAN is connected to the Internet, students can communicate with others throughout the world. • Flexible Access. Some networks allow students to access their files from computers throughout the institute. Students can begin an assignment in their classroom, save part of it on a public access area of the network, then go to the media center after school to finish their work. Students can also work cooperatively through the network.

• Workgroup Computing. Workgroup software (such as Microsoft BackOffice) allows many users to work on a document or project concurrently. For example, educators located at various locations within a county could simultaneously contribute their ideas about new curriculum standards to the same document and spreadsheets.

Disadvantages of Network • Expensive to Install. Although a network will generally save money over time, the initial costs of installation can be prohibitive. Cables, network cards, and software are expensive, and the installation may require the services of a technician. • Requires Administrative Time. Proper maintenance of a network requires considerable time and expertise. Many institute have installed a network, only to find that they did not budget for the necessary administrative support. • File Server May Fail. Although a file server is no more susceptible to failure than any other computer, when the files server "goes down," the entire network may come to a halt. When this happens, the entire company may lose access to necessary programs and files. • Cables May Break. Some of the configurations are designed to minimize the inconvenience of a broken cable; with other configurations, one broken cable can stop the entire network.

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Requirements to setting up a simple network 1. 2. 3. 4. 5.

Two computers with required hardware resources. Two network adapters. A physical connectivity media (cable). A network support operating system. Protocol.

S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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Scope of Network The scope of a network refers to its geographical size. It determined by the size of the organization or the distance between users on the network. The scope determines how the network is designed and what physical components are used in its construction. There are two general types of network scopes. 1. Local area networks (LANs) 2. Wide area networks (WANs)

Local Area Networks (LANs) A local area network (LAN) is a group of computers and network communication devices interconnected within a geographically limited area, such as a building or campus. A LAN tends to use only one type of transmission medium (cabling). LANs are characterized by the following:     

They transfer data at high speeds. They exist in a limited geographical area. Their technology is generally less expensive. Not share communication media. Use cabling as the transmission media (Wired Network)

Wide Area Networks (WANs) A wide area network (WAN) interconnects LANs. A WAN may be located entirely within a state or country, or it may be interconnected around the world. WANs are characterized by the following:       

They exist in an unlimited geographical area. They are more susceptible to errors due to the distances data travels. They interconnect multiple LANs. They are more sophisticated and complex than LANs. Their technology is expensive. They transfer data at low speeds. Share the communication media.

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WANs are often a natural outgrowth of the need to

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connect geographically separate LANs into a single network. For instance, a company might have several branch offices in different cities. Every branch would have its own LAN so that branch employees could share files and other resources, and all the branches together would be part of a WAN, a greater network that enables the exchange of files, messages, and application services between cities.


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Network Models: Comparing Server-Based and Peer-to-Peer Configurations PC networks generally fall within one of these two network types: 

Server-based. A server-based network consists of a group of user-oriented PCs (called clients) that request and receive network services from specialized computers called servers. Servers are generally higher-performance systems, optimized to provide network services to other PCs. (Some common server types include file servers, mail servers, print servers, fax servers, and application servers.)

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Peer-to-peer. A peer-to-peer network is a group of user oriented PCs that basically operate as equals. Each PC is called a peer. The peers share resources, such as files and printers, but no specialized servers exist. Each peer is responsible for its own security, and, in a sense, each peer is both a client (because it requests services from the other peers) and a server (because it offers services to the other peers). Small networks usually under 10 machines may work well in this configuration.

Server-Based Networking In a server-based network environment, resources are located on a central server or group of servers. A server is a computer that is specifically designated to provide services for the other computers on the network. A network client is a computer that accesses the resources available on the server. The server-based network model is more efficient for all but the smallest networks because hardware resources can be concentrated on relatively few highly-utilized network servers; client computers can be designed with minimal hardware configurations. A basic network client machine, for instance, might have a 486 processor and 8-16 megabytes of RAM. A typical server might have 32 megabytes of RAM (or more) and many gigabytes of file storage capacity.

Peer-to-Peer Networking In the peer-to-peer network environment, resources are distributed throughout the network on computer systems that may act as both service requesters and service providers. In a peer-to-peer network, the user of each PC is responsible for the administration and sharing of resources for his PC, which is known as distributed or workgroup administration. A peer-to-peer network sometimes is called a workgroup. Peer-to-peer networks are ideal for small organizations (fewer than ten users) where security is not of concern. Peer-to-peer networks also S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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provide a decentralized alternative for situations in which server administration would be too large or complex a task. Because a peer-to-peer network does not attempt to centralize security, and because peer-to-peer networks are generally much smaller and simpler than server-based networks, the software required to operate a peer-to-peer network can be much simpler. Several desktop operating systems, including the Microsoft operating systems Windows for Workgroups, Windows 95, and Windows NT Workstation, come with built-in peer-to-peer networking functionality.

Network Operating Systems The PCs in a network must have special system software that enables them to function in a networking environment. The early network operating systems were really add-on packages that supplied the networking software for existing operating systems, such as MS-DOS or OS/2. More recent operating systems, such as Windows 95 and Windows NT, come with the networking components built in. Client and server machines require specific software components. A computer that is in a peer-topeer network is functioning as both a client and a server and thus requires both client and server software. Operating systems, such as Windows NT, include dozens of services and utilities that facilitate networking. A network client must have a software component called a redirector. In a typical stand-alone PC, I/O requests pass along the local bus to the local CPU. The redirector intercepts I/O requests within the client machine and checks whether the request is directed toward a service on another computer. If it is, the redirector directs the request toward the appropriate network entity. The redirector enables the client machine to perform the following tasks:

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Log on to a network Access shared resources Access and participate in distributed applications

Other than that a network operating system will provide services like File Services, Printer Services, fax Services, Application Services, Directory Services and etc. A network operating system 1. 2. 3. 4.

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Enable computers to operate in a network. Co-ordinates the activities of the various devices. Provides clients with access to network resources. Ensure the security of data and devices.

Models of Network Computing After you have the necessary prerequisites for network communication, a structure must be put in place that organizes the way communication and sharing occur. Three methods of organization, or models, are generally recognized. The three models for network computing are as follows:   

Centralized computing. Distributed computing. Collaborative or cooperative computing. S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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Centralized Computing The earliest computer was large, expensive, and difficult to manage. Originally, these large mainframe computers were not networked in the sense you are familiar with today. Jobs were entered into the system by reading commands from card decks. The computer would execute one job at a time and generate a printout when the job was complete. Terminals, which came later, enabled users to interact with the centralized computer, but terminals were merely input/output devices that had no independent processing power. All processing still took place on the main frame, hence the name centralized computing. Networks, therefore, served little purpose other than to deliver commands to and results from the powerful centralized processing device.

Distributed Computing As personal computers were introduced to organizations, a new model of distributed computing emerged. Instead of concentrating computing to a central device, PCs made it possible to give each worker an independent, individual computer. Each of these PCs can process and store data locally, without assistance from another machine. This meant that groups who previously had found the cost of a mainframe environment prohibitive were able to gain the benefits of networking at a far reduced cost. Under the distributed computing model, networking has evolved to enable the many distributed computers to exchange data and share resources and services among themselves. Note that these machines need not be considered equals. A Windows NT file server, for instance, is considered to be a part of a distributed network. This server stores and retrieves files for other machines, but does not do the thinking for these machines as a mainframe would have done in the centralized computing model.

Collaborative Computing Also called cooperative computing, collaborative computing enables computers in a distributed computing environment to share processing power in addition to data, resources, and services. In a collaborative computing environment, one computer might “borrow” processing power by running a program on other computers on the network. Or, processes might be designed so that they can run on two or more computers. Obviously, collaborative computing cannot take place without a network to enable the various computers to communicate. Collaborative computing is exemplified in Microsoft networks by server-based products such as Exchange Server or SQL Server. With both of these products, requests srcinate from intelligent client software (which uses the processor power of the workstation it is running on) but then are serviced from server software running on an NT Server. The server processes the request using its own resources and then passes the results back to the client. Processor and memory resources on both the client and the server are utilized in the completion of the task. In summary, collaborative computing involves the following:   

Multiple computers cooperating to perform a task A network that enables the computers to exchange data and services Software designed to take advantage of the collaborative environment. S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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Roles of Computers in a network Computers in a network functions either as clients or as servers.

Client (Workstation) Client computers make requests for services or data on the network form computers referred to as servers.

Servers Servers are computers that provide services and data to client computers. In a complex network several servers are been assigned specific servers. Eg:- File and print servers, Application Servers, Fax Servers, Data Base Servers, Mail Servers.

File Services File services enable networked computers to share files. This capability was one of the primary reasons networking personal computers initially came about. File services include all network functions centering on the storage, retrieval, or movement of data files. A common feature of file services is access control and transaction logging. File services enable users to read, write, and manage files and data, but they also should restrict users to authorized file operations so that files aren’t accidentally overwritten or deleted. Two types of servers exist: 1. Dedicated Servers. 2. Non Dedicated Servers. Dedicated servers do nothing but fulfill requests to network clients. These are commonly found in client – server environments. Non Dedicated Servers do double duty by requesting and providing services, and they are the backbone of the peer-to-peer structure. Dedicated files Servers have the following benefits. i. ii. iii.

Central file servers can be managed more efficiently, with user and security data located in a single database. Central file servers can contain expensive, high-performance hardware that expedites file services and makes the file servers more reliable. The cost of specialized file server technology is shared by a large number of users. Centralized networks are more reliable.

The following drawbacks, however, should be considered with regard to centralized file services: 

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When all data is stored on a single server, a single point of failure exists. If the server fails, all data becomes unavailable, making proper design, management, and backup of the server essential. Because all clients contend for file services from a single source, average file access times might be slower with a centralized file server than when file are stored on individual, local drives.

Centralized file services generally are chosen for organizations that want to achieve the highest levels of protection for their data files. S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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Some key file services include: i. ii. iii. iv. v.

File transfer File storage File migration File archiving File-update synchronization

File Transfer Without a network, the options for transferring data between computers are limited. You can, of course, exchange files on floppy disks. This proc ess came to be called “sneaker -net” because it consisted of networking by physically running around and hand-delivering floppy disks from desk to desk. Otherwise, you can use communication software to dial another computer and transfer files via a modem or a direct serial connection. With a network, users have constant access to high-speed data transfer without leaving their desks or dialing anywhere. Moving a file is as easy as depositing it in a shared directory. When users transfer confidential files, the need for network security rises. You might need to limit file transfers to authorized users who are using password-controlled security systems, to assign file attributes that restrict the operations that may be performed with a file, or to encrypt files so they may be read only by authorized users. Each of these options is possible with networking. Another important file-management task of the NOS is to provide and regulate access to programs and data stored on the file server’s hard drive, which is kno wn as file sharing. File sharing is another main reason companies invest in a network. Companies save money by purchasing a single version anserver application ratherseveral than many Placing data files created bynetwork employees on a of file also serves othersingle-user purposes, versions. such as security, document control, and backup.

File Storage Most networks have some form of centralized file storage. For many years, companies have used the online storage approach to file storage. In the online storage scenario, data is stored on hard disks that are accessible on demand. The files that can be accessed on a server are limited to the amount of available hard drive space. Hard drives are fast, but even with drive prices decreasing in recent years, the cost to store a megabyte of data this way is still fairly high. Hard drives have another disadvantage; that is, generally, they cannot be removed for off-site storage or exchange or simply to build a library of files that are seldom required but must be fairly readily available. Almost all companies have large amounts of infrequently used data. For example, there is usually no need to keep all the financial reports from the previous year online. However, those reports must be stored somewhere in case questions arise or an audit occurs. Another common approach to file storage, therefore, is offline storage, which consists of removable media that is managed manually. After data is written to a tape or optical disk, the storage medium can be removed from the server and shelved. Users who require offline data might need to know which tape or optical disk to request. Some systems provide indexes or other aids that make requesting the proper offline storage element automatic. A system operator still has to retrieve the tape or disk and mount it on the server, however.


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When the slow response of offline storage is unacceptable, a near-line storage approach may be selected. Near-line storage employs a machine, often called a jukebox, to manage large numbers of tapes or optical disks automatically. The proper tape or disk is retrieved and mounted by the jukebox without human intervention. With near-line storage, huge amounts of data can be made available with only slight delays, but at a much lower cost than would be required to store the data on hard drives.

Data Migration Data migration is a technology that automatically moves less-used data from online storage to nearline or offline storage. The criteria for moving files can depend on when the files were last used, the owner of the files, file size, or a variety of other factors. An efficient data-migration facility makes locating migrated files easier for users.

Data migration.

File Archiving File archiving (also known as backup) is basically offline storage that is primarily geared to creating duplicate copies of online files. These backup copies serve as insurance against minor or major system failures by creating a redundant copy of important system and data files. Generally, network administrators enable file archiving from a centralized location. A single site, for example, can back up all the servers on a network. Many current backup systems also offer the capability to back up various client workstations, making it feasible to archive all files on the network to a central facility, whether the files are located on network servers or clients. This archive then is stored in a safe location, and a duplicate often is made and placed off the premises in case of disaster.

File-Update Synchronization In its simplest form, file-update synchronization is a means of ensuring that all users have the latest copy of a file. File-update synchronization services can manage files by monitoring the date and time stamps on files to determine which files were saved most recently. By tracking the users who access the file, along with the date and time stamps, the service can update all the copies of the file with the most recent version. File-update synchronization, however, can be considerably more involved. In a modern computing environment, it is not always feasible for all users to access all files in real time. A salesman, for example, might carry a notebook computer on which to enter orders. Dialing the central LAN every time an order was to be entered would be impractical, so the salesman would enter orders offline (while disconnected from the network) and store them in the laptop. That evening, he would call the central LAN, log in, and transmit all the day’s orders at once.


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During this process, files on the LAN must be updated to reflect new data in the salesman’s portable computer. In addition, the salesman’s PC might need to be updated, for example, with order confirmations or new pricing information. The process of bringing the local and remote files into agreement is also known as file-update synchronization. File-update synchronization becomes considerably more challenging when additional users are sharing data files simultaneously. Complex mechanisms must be in place to ensure that users do not accidentally overwrite each other’s data. In some cases, the system simply flags files that have multiple, conflicting updates and require a human to reconcile the differences. In Windows 95 and NT 4.0, the My Briefcase program provides this service.

Network Interface Card (NIC) A network adapter card is a hardware device that installs in a PC and provides an interface from a PC to the transmission medium.

Most PC networks, including Ethernet and Token Ring networks, use network adapter card. The network adapter card is thus as essential part of networking, and an understanding of network adapter cards is crucial for any networking professional. As the data passes through the cable to the network adapter, it is formatted into Packets.



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The physical topology of a network refers to the configuration of cables, computers, and other peripherals. A topology basically defines how the network has to be designed and provides a structure to the network. Physical Topology, when in the context of networking, refers to the physical layout of the devices connected to the network, including the location and cable installation. The Logical Topology refers to the way it actually operates (transfers data), as opposed to its layout. The five different kinds of topologies are Bus Ring Star Tree Mesh     

1.

Bus topology

A bus topology network is a network architecture in which a set of clients are connected via a shared communications line, called a bus. The bus topology is often referred to as a "linear bus" because the computers are connected in a straight line. This is the simplest and most common method of networking computers. Below figure shows a typical bus topology. It consists of a single cable called a trunk (also called a backbone or segment) that connects all of the computers in the network in a single line.

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Advantages and Disadvantages of a Bus Network Advantages 1. 2. 3. 4. 5. 6.

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Easy to implement and extend Well suited for temporary networks (quick setup) Typically the cheapest topology to implement Faster than a ring network. If any node on the bus network fails, the bus its self is not effected. Requires less cable than a Star network.

Disadvantages 1. Difficult to administer/troubleshoot S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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2. 3. 4. 5. 6.

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Limited cable length and number of stations A cable break can disable the entire network Performance degrades as additional computers are added or on heavy traffic Low security (all computers on the bus can see all data transmissions) Proper termination is required.(loop must be in closed path)

Ring topology

A ring network is a topology of computer networks where each node is connected to two other nodes, so as to create a ring. The ring topology connects computers on a single circle of cable. Unlike the bus topology, there are no terminated ends. The signals travel around the loop in one direction and pass through each computer, which can act as a repeater to boost the signal and send it on to the next computer. Following figure shows a typical ring topology with one server and four workstations. The failure of one computer can have an impact on the entire network.

One method of transmitting data around a ring is called token passing. (A token is a special series of bits that travels around a token-ring network. Each network has only one token.) The token is passed from computer to computer until it gets to a computer that has data to send. Below figure shows a token ring topology with the token. The sending computer modifies the token, puts an electronic address on the data, and sends it around the ring. Ring networks also carry the disadvantage that if one of the nodes in the network breaks down then the entire network will break down with it as it requires a full circle in order to function.

Advantages and Disadvantages of a Ring Network Advantages

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1. The transmission of data is relatively simple as packets travel in one direction only.

Disadvantages 1. Data packets must pass through every computer between the sender and recipient Therefore this makes it slower. 2. If any of the nodes fail then the ring is broken and data cannot be transmitted successfully. 3. It is difficult to troubleshoot the ring.

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Star topology

Star networks are one of the most common computer network topologies. In its simplest form, a star network consists of one central switch , hub or computer which acts as a router to transmit messages. S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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In the star topology, cable segments from each computer are connected to a centralized component called a hub or switch. Following figure shows four computers and a hub connected in a star topology. Signals are transmitted from the sending computer through the hub to all computers on the network. This topology srcinated in the early days of computing when computers were connected to a centralized mainframe computer.

The star network offers the advantage of centralized resources and management. However, because each computer is connected to a central point, this topology requires a great deal of cable in a large network installation. Also, if the central point fails, the entire network goes down. If one computer or the cable that connects it to the hub fails on a star network, only the failed computer will not be able to send or receive network data. The rest of the network continues to function normally.

Advantages and Disadvantages of a Star Network Advantages 1. Easy to implement and extend, even in large networks 2. Well suited for temporary networks (quick setup) 3. The failure of a non-central node will not have major effects on the functionality of the network. 4. No problems with collisions of Data since each station have its own cable to the server/hub. 5. Security can be implemented in the hub/switch. 6. The centre of a star i.e. the hub or switch is best place to find network faults. 7. It is easy to modify and add new computers to a star network without disturbing the rest of the network.

Disadvantages 1. Depending on the transmission media, length limitations may be imposed from the central location used 2. Failure of the central node can disable the entire network 3. Limited cable length and number of stations

4.

Tree Topology

A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.


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Advantages and Disadvantages of a Tree Network Advantages 1. Point-to-point wiring for individual segments. 2. Supported by several hardware and software venders.

Disadvantages 1. Overall length of each segment is limited by the type of cabling used. 2. If the backbone line breaks, the entire segment goes down. 3. More difficult to configure and wire than other topologies.

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Mesh topology

A mesh topology network offers superior redundancy and reliability. In a mesh topology, each computer is connected to every other computer by separate cabling. This configuration provides redundant paths throughout the network so that if one cable fails, another will take over the traffic. While ease of troubleshooting and increased reliability is definite pluses, these networks are expensive to install because they use a lot of cabling. Often, a mesh topology will be used in conjunction with other topologies to form a hybrid topology.

Advantages and Disadvantages of a mesh network Advantages 1. Provides redundant paths between devices. 2. The network can be expanded without disruption to current users.

Disadvantages 1. Requires more cable than the other LAN topologies. 2. Complicated implementation.


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Network media is the actual path over which an electrical signal travels as it moves from one component to another. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network. The following section describes the common types of network media, including twisted-pair cable, coaxial cable, fiber-optic cable, and wireless.

Twisted-Pair Cable Twisted-pair cable is a type of cabling that is used for telephone communications and most modern Ethernet networks. A pair of wires forms a circuit that can transmit data. The pairs are twisted to provide protection against crosstalk, the noise generated by adjacent pairs. When electrical current flows through a wire, it creates a small, circular magnetic field around the wire. When two wires in an electrical circuit are placed close together, their magnetic fields are the exact opposite of each other. Thus, the two magnetic fields cancel each other out. They also cancel out any outside magnetic fields. Twisting the wires can enhance this cancellation effect. Two basic types of twisted-pair cable exist: 

Unshielded twisted pair (UTP) and

Shielded twisted pair (STP). The following sections discuss UTP and STP cable in more detail. 

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Unshielded twisted pair (UTP) Cable

UTP cable is a medium that is composed of pairs of wires. UTP cable is used in a variety of networks. Each of the eight individual copper wires in UTP cable is covered by an insulating material. In addition, the wires in each pair are twisted around each other.

Unshielded Twisted-Pair Cable

UTP cable often is installed using a Registered Jack 45 (RJ-45) connector. The RJ-45 is an eight-wire connector used commonly to connect computers onto a local-area network (LAN), especially Ethernets.


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UTP cable offers many advantages. Because UTP has an external diameter of approximately 0.43 cm (0.17 inches), its small size can be advantageous during installation. Because it has such a small external diameter, UTP cable is easy to install and is less expensive than other types of networking media. UTP is considered the fastest copper-based medium today. The following summarizes the features of UTP cable: Speed and throughput

10 to 1000 Mbps

Average cost per node

Least expensive

Media and connector size

Small

Maximum cable length

100 m (short)

Commonly used types of UTP cabling are as follows: 

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Category 1—Used for telephone communications. Not suitable for transmitting data. Category 2—Capable of transmitting data at speeds up to 4 megabits per second (Mbps). Category 3—Used in 10BASE-T networks. Can transmit data at speeds up to 10 Mbps. Category 4—Used in Token Ring networks. Can transmit data at speeds up to 16 Mbps. Category 5—Can transmit data at speeds up to 100 Mbps. (100 BASE T) Category 5e —Used in networks running at speeds up to 1000 Mbps (1 gigabit per second [Gbps]).

Shielded Twisted-Pair Cable

Shielded twisted-pair (STP) cable combines the techniques of shielding, cancellation, and wire twisting. Each pair of wires is wrapped in a metallic foil. The four pairs of wires then are wrapped in an overall metallic braid or foil. As specified for use in Ethernet network installations, STP reduces electrical noise both within the cable (pair-to-pair coupling, or crosstalk) and from outside the cable (EMI and RFI). STP cabling also can use the same RJ connectors that UTP uses.

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Although STP prevents interference better than UTP, it is more expensive and difficult to install. In addition, the metallic shielding must be grounded at both ends. If it is improperly grounded, the shield acts like an antenna and picks up unwanted signals. Because of its cost and difficulty with termination, STP is rarely used in Ethernet networks. STP is primarily used in Europe.


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The following summarizes the features of STP cable: Speed and throughput

10 to 100 Mbps


Moderately expensive


Medium to large


100 m (short)

Coaxial Cable Coaxial cable consists of a hollow outer cylindrical conductor that surrounds a single inner wire made of two conducting elements. One of these elements, located in the center of the cable, is a copper conductor. Surrounding the copper conductor is a layer of flexible insulation. Coaxial cable supports 10 to 100 Mbps and is relatively inexpensive, although it is more costly than UTP on a per-unit length. However, coaxial cable can be cheaper for a physical bus topology because less cable will be needed. Coaxial cable can be cabled over longer distances than twisted-pair cable. For example, Ethernet can run approximately 100 meters (328 feet) using twistedpair cabling. Using coaxial cable increases this distance to 500m (1640.4 feet). Coaxial cable comes in a variety of sizes. The largest diameter (1 centimeter [cm]) referred to as Thicknet. (500m) The smallest diameter (0.35 centimeter [cm]) referred to as Thinnet. (185 m) The following summarizes the features of coaxial cables: Speed and throughput

10 to 100 Mbps


Inexpensive


Medium


500 m (medium)

BNC T-connectors are female devices for connecting two cables to a network interface card (NIC)

A BNC barrel connector facilitates connecting two cables together.

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Terminator is used to absorb signals so that they do not reflect back down the line. Ethernet networks require a terminator at both ends of the bus network.


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Fiber Optic Cable The fiber optics or optical fibers are long thin strands of very pure glass which have a diameter that of a human hair. These strands are arranged in bundles called optic cables, and used for transmitting light signals over long distances. When a single optical fiber is looked closely you will observe there is a core, which is a thin glass center, then there is cladding which is the outer optical material surrounding the core, then there is a buffer coating which protects the fiber from damage and moisture.

Generally fiber optic cable is categorized as either multimode cable, which is used for short-distance connections (LANs, campus networks, and short-distance metro networks), or single-mode cable that is used for long-distance (cross-country networks and intercontinental submarine links).

Single Mode Fiber cable (SMF) Single-mode fiber gives you a higher transmission rate and up to 50 times more distance than multimode, but it also costs more. Single-mode fiber has a much smaller core than multimode. The small core and single light-wave virtually eliminate any distortion that could result from overlapping light pulses, providing the least signal attenuation and the highest transmission speeds of any fiber cable type.

Multi-Mode Fiber cable (MMF) Multimode fiber gives you high bandwidth at high speeds (10 to 100MBS - Gigabit to 275m to 2km) over medium distances. Multi-mode fiber is thick enough for light to follow several paths through the code. Multi-mode fiber is best suited for use in short lengths, such as those used in Local Area Networks (LANs). Multi-mode fiber comes in two standard widths, 62.5 micron and 50 micron. A micron is one millionth of a meter.


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Comparing Media Types Following chart provides an overview of various media that you can use as a reference. The medium is possibly the single most important long-term investment made in a network. The choice of media type will affect the type of NICs installed, the speed of the network, and the capability of the network to meet future needs.

Media Type

Maximum Segment Length

Speed

Cost

UTP

100 m

10 Mbps to 1000 Mbps

Least expensive

STP

100 m

10 Mbps to 100 Mbps

More expensive than UTP

10 Mbps to 100 Mbps

Relatively inexpensive, but more costly than UTP

500 m (Thicknet) Coaxial 185 m (Thinnet)

FiberOptic

10 km and farther

100 Mbps to 100 Gbps

(single-mode)

(single mode) 100 Mbps to 9.92 Gbps (multimode)

Disadvantages

Easy to install; widely available and widely used Reduced crosstalk; more resistant to EMI than Thinnet or UTP

Susceptible to interference; can cover only a limited distance Difficult to work with; can cover only a limited distance Difficult to work with (Thicknet); limited bandwidth; limited application (Thinnet); damage to cable can bring down entire network

Less susceptible to EMI interference than other types of copper media Cannot be tapped, so security is better; can

Expensive 2 km and farther (multimode)

Advantages

be used over great distances; is not susceptible to EMI; has a higher data rate than coaxial and twistedpair cable

Difficult to terminate

Wireless Communication Wireless communication uses radio frequencies (RF) or infrared (IR) waves to transmit data between devices on a LAN. For wireless LANs, a key component is the wireless hub, or access point, used for signal distribution. To receive the signals from the access point, a PC or laptop must install a wireless adapter card (wireless NIC). Wireless signals are electromagnetic waves that can travel through the vacuum of outer space and through a medium such as air. Therefore, no physical medium is necessary for wireless signals, making them a very versatile way to build a network. The primary difference between electromagnetic waves is their frequency. Low-frequency electromagnetic waves have a long wavelength (the distance from one peak to the next on the sine wave), while high-frequency electromagnetic waves have a short wavelength.


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Some common applications of wireless data communication include the following:    

Accessing the Internet using a cellular phone Establishing a home or business Internet connection over satellite Beaming data between two hand-held computing devices Using a wireless keyboard and mouse for the PC



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Computer network devices also known as communication devices and they constitute a data communication network. These devices are NIC, routers, switches, hubs, LAN cards, gateway, modems, hardware firewall and transceivers. In an Ethernet or WAN network, the data communication cannot be performed without these devices. Being an IT professional or a network administrator, you must have the good understanding of these devices.

Network Interface Card (NIC) A network adapter card is a hardware device that installs in a PC and provides an interface from a PC to the transmission medium. Most PC networks, including Ethernet and Token Ring networks, use network adapter card. The network adapter card is thus as essential part of networking, and an understanding of network adapter cards is crucial for any networking professional. As the data passes through the cable to the network adapter, it is formatted into Packets.

Modem Short for modulator-demodulator. A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms. A modem is used to provide the connectivity with the internet.

Internal modem

External Modem

Wireless Modem

Hub The central connecting device in a computer network is known as a hub. Every computer is directly connected with the hub. When data packets arrives at hub, it broadcast them to all the LAN cards in a network and the destined recipient picks them and all other computers discard the data packets. Hub has five, eight, sixteen and more ports and one port is known as uplink port, which is used to connect with the next hub.


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Switches Like the router, a switch is an intelligent device that maps the IP address with the MAC address of the LAN card. Unlike the hubs, a switch does not broadcast the data to all the computers, it sends the data packets only to the destined computer. Switches are used in the LAN, MAN and WAN. In an Ethernet network, computers are directly connected with the switch via twisted pair cables.

Routers A router is a communication device that is used to connect two logically and physically different networks, two LANs, two WANs and a LAN with WAN. The main function of the router is to sorting and the distribution of the data packets to their destinations based on their IP addresses. Routers provides the connectivity between the enterprise businesses, ISPs and in the internet infrastructure, router is a main device. Cisco routers are widely used in the world. Every router has routing software, which is known as IOS. Router does not broadcast the data packets.

Bridge A bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or Token Ring).A bridge examines each message on a LAN, "passing" those known to be within the same LAN, and forwarding those known to be on the other interconnected LAN (or LANs). Bridges serve a similar function as switches. Switches are sometimes called "multi-port bridges" for this reason. A bridge only has one incoming and one outgoing port.



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Gateway A network gateway is an internetworking system capable of joining together two networks that use different base protocols. The gateway has two sides. The WAN side connects to your cable DSL modem and LAN side connects to your private network via a hub or switch. The main function of it is to route the traffic from computer to the Internet and back to the computer. A computer with the two NIC cards can act as a gateway. It routes the network traffic between two logically and physically different networks.

Repeater A network repeater is a device used to expand the boundaries of a wired or wireless (WiFi) local area network (LAN). In the past, wired network repeaters were used to join segments of Ethernet cable. The repeaters would amplify the data signals before sending them on to the uplinked segment, thereby countering signal decay that occurs over extended lengths of wire. A WiFi network repeater will pick up the signal from a wireless router and amplify it, propagating signal strength to boost distance and coverage of the WLAN.

Wireless Access Point (WAP) Wireless access points (APs or WAPs) are specially configured nodes on wireless local area networks (WLANs). Access points act as a central transmitter and receiver of WLAN radio signals. Access points used in home or small business networks are generally small, dedicated hardware devices featuring a built-in network adapter, antenna, and radio transmitter. Access points support Wi-Fi wireless communication standards.



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Devices in a wireless network are set up to either communicate indirectly through a central place — an access point — or directly, one to the other. The first is called "Infrastructure Mode" and the other is called "Ad Hoc" mode (it's also called peer-to-peer).

Media Converters Network media converters are used to interconnect different types of cables within an existing network. They receive data from one type of cable and convert the signals for transmission along another cable type.

PoE (Power over Ethernet) Power over Ethernet is a technology which enables to connect network devices through ethernet cable. PoE requires category 5 cable or higher for high power levels, but can operate with category 3 cable for low power levels. Therefore it is

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not necessary to use two individual lines for data connectivity and power supplying. One Ethernet line is sufficient. This technology is applicable for wide range of network products such as Access Points, Routers, IP cameras, modems, switches, embedded computers or other network products.


s t p e c n o C

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Definition: A network address serves as a unique identifier for a computer on a network. When set up correctly, computers can determine the addresses of other computers on the network and use these addresses to send messages to each other. One of the best known form of network addressing is the Internet Protocol (IP) address. IP addresses consist of four bytes (32 bits) that uniquely identify all computers on the public Internet. Another popular form of address is the Media Access Control (MAC) address. MAC addresses are six bytes (48 bits) that manufacturers of network adapters burn into their products to uniquely identify them. 

Internet Protocol (IP) address

An IP address is a logical address for a network adapter. The IP address uniquely identifies computers on a TCP/IP network. An IP address can be private - for use on a local area network (LAN) - or public - for use on the Internet or other wide area network (WAN). IP addresses can be determined statically (assigned to a computer by a system administrator) or dynamically (assigned by another device on the network on demand). Two IP addressing standards are in use today. The IPv4 standard is most familiar to people and supported everywhere on the Internet, but the newer IPv6 standard is planned to replace it and starting to be deployed. IPv4 addresses consist of four bytes (32 bits). Each byte of an IP address is known as an octet. Octets can take any value between 0 and 255. Various conventions exist for the numbering and use of IP addresses. IP addresses are broken into 4 octets (IPv4) separated by dots called dotted decimal notation. An octet is a byte consisting of 8 bits. The IPv4 addresses are in the following form: There are two parts of an IP address:  

Network ID Host ID

The various classes of networks specify additional or fewer octets to designate the network ID versus the host ID.



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Class A-E networks IPv4 Address Classes The IPv4 address space can be subdivided into 5 classes - Class A, B, C, D and E. Each class consists of a contiguous subset of the overall IPv4 address range. With a few special exceptions explained further below, the values of the leftmost four bits of an IPv4 address determine its class as follows: Class

Leftmost bits

Start address

Finish address

A

0xxx

0.0.0.0

126.255.255.255

B

10xx

128.0.0.0

191.255.255.255

C

110x

192.0.0.0

223.255.255.255

D

1110

224.0.0.0

239.255.255.255

E

1111

240.0.0.0

255.255.255.255

Network/Net mask specification Sometimes you may see a network interface card (NIC) IP address specified in the following manner: 192.168.1.1/24 The first part indicates the IP address of the NIC which is "192.168.1.1" in this case. The second part "/24" indicates the net mask value meaning in this case that the first 24 bits of the net mask are set. This makes the net mask value 255.255.255.0. If the last part of the line above were "/16", the net mask would be 255.255.0.0.

Subnet masks Sub netting is the process of breaking down a main class A, B, or C network into subnets for routing purposes. A subnet mask is the same basic thing as a net mask with the only real difference being that you are breaking a larger organizational network into smaller parts, and each smaller section will use a different set of address numbers. This will allow network packets to be routed between sub networks. Setting up subnets the following must be determined: Number of segments Hosts per segment  

Sub netting provides the following advantages:   

Network traffic isolation - There is less network traffic on each subnet. Simplified Administration - Networks may be managed independently. Improved security - Subnets can isolate internal networks so they are not visible from external networks.

One network ID is required by each of: Subnet WAN connection  


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One host ID is required by each of: Each NIC on each host. Each router interface.  

The role of the subnet mask Whenever you're dealing with subnets, it will come in handy to remember eight special numbers that reoccur when dealing with subnet masks. They are 255, 254, 252, 248, 240, 224, 192, and 128. You'll see these numbers over and over again in IP networking, and memorizing them will make your life much easier.

IPv6 IPv6 is 128 bits. It has eight octet pairs, each with 16 bits and written in hexadecimal as follows: 2b63:1478:1ac5:37ef:4e8c:75df:14cd:93f2



Media Access Control (MAC) address

Media Access Control assigns a unique number to each IP network adapter called the MAC address. A MAC address is 48 bits long. The MAC address is commonly written as a sequence of 12 hexadecimal digits as follows: 48-3F-0A-91-00-BC MAC addresses are uniquely set by the network adapter manufacturer and are sometimes called physical addresses. The first six hexadecimal digits of the address correspond to a manufacturer's unique identifier (OUI), while the last six digits correspond to the device's serial number. MAC addresses map to logical IP addresses through the Address Resolution Protocol (ARP).


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Finding Your Computer's IP & MAC Address Click on the Start Menu then select Run. Type cmd then click OK. In the Command Prompt box, type ipconfig /all then hit Enter. Note the Physical Address, this is also the MAC address.



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Network devices MAC Devices

: PC NIC, Router.

Non MAC Devices

: Hub, Switch, Bridge, Gateway, Media Converter,

What You Need: 1. 2. 3. 4. 5. 6.

Ethernet Cable 1. RJ45 Plugs Wire Cutters RJ45 Crimper 110 Punch Down Tool Cable Tester 4.

2.

3.

5.

6.

About the Cable You can find bulk supplies of Ethernet cable at many computer stores or most electrical or home centers. You want UTP (Unshielded Twisted Pair) Ethernet cable of at least Category 5 (Cat 5). Here is what the internals of the Ethernet cable look like:

Internal Cable Structure and Color Coding

Inside the Ethernet cable, there are 8 color coded wires. These wires are twisted into 4 pairs of wires, each pair has a common color theme. One wire in the pair being a solid or primarily solid colored wire and the other being a primarily white wire with a colored stripe.


Wiring diagram and pin out

RJ45 Plug and Jack Pin Out


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Ethernet Cable Pin Outs There are two basic Ethernet cable pin outs. 1. Straight through cable which is used to connect to MAC devices with Non MAC devices 2. Cross over cable which is used to connect to MAC devices with MAC devices or non MAC devices with non MAC devices. Generally all fixed wiring should be run as straight through. Some Ethernet interfaces can cross and un-cross a cable automatically as needed, a handy feature. Standard, Straight-Through Wiring Diagram (both ends are the same) RJ45 Pin (END 1) 1 2 3 4 5 6 7 8

Wire Color

Wire Diagram End #1

White/Green Green White/Orange Blue White/Blue Orange White/Brown Brown

RJ45 Pin (END 2) 1 2 3 4 5 6 7 8

Wire Color

Diagram End #2


Crossover Cable Wiring Diagram RJ45 Pin (END 1) 1 2 3 4 5 6 7 8

Wire Color White/Orange Orange White/Green Blue White/Blue Green White/Brown Brown

Diagram End #1

RJ45 Pin (END 2) 1 2 3 4 5 6 7 8

Wire Color

Diagram End #2




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OSI Reference Model The International Organization of Standardization (ISO) defined procedures for computer communications which was called Open System Interconnection (OSI) Reference Model or OSI Model for short. The OSI Model describes how data flows from one computer to another computer in a network. The OSI Model is defined as a protocol stack that consists of seven logical layers. Each layer has specific functions and handles a unique data format. When two computers communicate, data flows from the user-to-network interface (application) at the sending computer down through the protocol stack to the connecting physical medium (i.e. cable, radio, or infrared) and up through the protocol stack to the network-to-user interface (application) at the receiving computer. When data flows from an upper layer to a lower layer, it is converted to the lower layer data format and a lower layer header is added to it. This process is called encapsulation. Conversely, when data flows from a lower layer to an upper layer, it is converted to the upper layer data format and the lower layer header is discarded.

Upper layers

Lower layers

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Even though most computer network technologies do not follow strictly to the OSI Model in that they combine several OSI layers functions in one protocol, the OSI Model is still used as a reference and a guideline in network design. Understanding the OSI Model will help you understand how a network works.


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The OSI Model protocol stack is explained in the following table: Layer

Layer Name

Functions

Layer 7

Application Layer

application support

Layer 6

Presentation Layer

Layer 5

Session Layer

data format conversion, data compression, and encryption user identification; establishing, maintaining, and

Layer 4

Transport Layer

terminating a session end-to-end transport

Layer 3

Network Layer

addressing, routing

Layer 2

Data Link Layer

medium access control, error detection, retransmission

Layer 1

Physical Layer

electrical/optical signaling, cabling, connector pin assignment

Examples HTTP, FTP, Telnet, SMTP, SNMP, POP3, IMAP4

SIP TCP, UDP, RT P, RTCP IP, IPSec, IPX, NetBEUI, AppleTalk, ICMP Ethernet, Wi-Fi, HomePNA, HomePlug, PPP, PPTP, L2TP, ATM, Frame Relay, Token Ring, FDDI RF, UTP, STP, coax, fiber optic, connectors, signaling, voltages

The following table explains network components along with their functions and the corresponding layers in the OSI Model. Network Component Network Adapter Modem (Modulator & demodulator) Repeater (Regenerator)

Hub

Switch Access Point

Residential Gateway Gateway

Receives signal, amplifies it, then retransmits it. Connects networks with different Layer 2 protocols; divides a network into several segments to filter traffic. Connects computers in a network; receives a packet from a sending computer and transmits it to all other computers. Connects computers in a network; receives a

Bridge

Router

Functions Converts a computer message into electrical/optical signals for transmission across a network. Puts a message (baseband signal) on a carrier for efficient transmission; takes the baseband signal from the carrier.

packet from a sending computer and transmits it only to its destination. Connects computers in a wireless network; connects the wireless network to wired networks; connects it to the Internet. Forwards a packet to its destination by examining the packet destination network address. Connects a home network to the Internet; hides all computers in the home network from the Internet. Connects two totally different networks; translates one signaling/protocol into another.

OSI Model Physical (Layer 1)

Physical (Layer 1) Physical (Layer 1) Data Link (Layer 2)

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Physical (Layer 1)

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Data Link (Layer 2) Data Link (Layer 2) Network (Layer 3) Network (Layer 3) All layers


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Layer 7: The application layer This is the layer at which communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. (This layer is not the application itself, although some applications may perform application layer functions.)

Layer 6: The presentation layer This is a layer, usually part of an operating system, that converts incoming and outgoing data from one presentation format to another (for example, from a text stream into a popup window with the newly arrived text). Sometimes called the syntax layer.

Layer 5: The session layer This layer sets up, coordinates, and terminates conversations, exchanges, and dialogs between the applications at each end. It deals with session and connection coordination.

Layer 4: The transport layer This layer manages the end-to-end control (for example, determining whether all packets have arrived) and error-checking. It ensures complete data transfer.

Layer 3: The network layer This layertransmissions handles the routing of the data (sending it in the right direction the right on outgoing and receiving incoming transmissions at the packetto level). The destination network layer does routing and forwarding.

Layer 2: The data-link layer This layer provides synchronization for the physical level and does bit-stuffing for strings of 1's in excess of 5. It furnishes transmission protocol knowledge and management.

Layer 1: The physical layer This layer conveys the bit stream through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier.



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Application Layer

: HTTP FTP SMTP POP3 DNS DHCP IMAP IRC NTP SNMP Telnet

-

Hyper Text Transfer Protocol File Transfer Protocol Simple Mail Transfer Protocol Post Office Protocol Version3 Domain Name Services. Dynamic Host Configuration Protocol Internet Message Access Protocol Internet Relay Chat Network Time Protocol Simple Network Management Protocol Terminal Emulation Protocol -

Transport Layer

:

TCP UDP

Internet Layer

:

IGMP ICMP ARP -

Network Access Layer

:

Transmission Control Protocol User Datagram Protocol Internet Group Management Protocol Internet Control Message Protocol Address Resolution Protocol

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Ethernet Frame Relay ATM

-

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Asynchronous Transfer Mode


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What is a Protocol? A protocol is a set of rules that governs the communications between computers on a network. In order for two computers to talk to each other, they must be speaking the same language. Many different types of network protocols and standards are required to ensure that your computer (no matter which operating system, network card, or application you are using) can communicate with another computer located on the next desk or half-way around the world.

Common OSI & TCP Protocols

HTTP HTTP (Hypertext Transfer Protocol) is in widespread use today. HTTP is used to transfer Web pages from a Web server to a local Web browser. Those Web pages are created as HTML (Hypertext Markup Language) documents. HTTP also has a sister protocol called HTTP(S), which allows for secure transfer of documents. While HTTPS is slower due to the overhead generated by encryption methods, most would agree that it is essential for e-commerce and on-line banking transactions.

FTP FTP (File Transfer Protocol) is somewhat unique in that it is both a protocol and a program. As the name would indicate, it is used to transfer files. It is very powerful and flexible in its use. It can be configured to let users take files but not transmit them. This could be very advantageous in the case of limiting the transfer of files that may contain a virus. There is also a stripped down version of FTP called TFTP (Trivial File Transfer Protocol) which lacks some of the functionality of FTP in particular the ability to browse for files.

SMTP SMTP (Simple Mail Transfer Protocol) provides a mechanism to send email between dissimilar operating systems. It is SMTP’s ability to send email between different operating systems that makes it so useful on the Internet. An example of this would be composing an email message from a Windows 98 client, forwarding that to a local Microsoft Exchange Server which could then send it via the Internet to a server running the UNIX operating system.

P0P3 The POP3 (Post Office Protocol) version 3 is used to download email from various servers to an email client. Microsoft’s Outlook Express is an example of a client-side software that uses POP3 technology. Most ISPs (Internet Service Providers) that provide home service also use the POP3 protocol. This enables the ISP to download messages to the individual user’s computer rather than having to s tore them on the ISP’s servers.

TCP The main function of TCP is to establish and monitor connections between the sending and receiving devices. TCP is responsible for providing reliable connection-oriented data delivery. TCP functions at the Transport layer of the OSI model. When you are using TCP, you basically have an acknowledgement between sender and receiver that is maintained the entire length of the data transmission.


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IP Internet Protocol provides the mechanism for Internet addressing. IP functions at the Network layer of the OSI model. There are basically two parts to an IP address; the first part defines the network a device is attached to, and the second portion identifies the actual device itself. An IP address can be assigned by the network administrator or assigned by a DHCP (Dynamic Host Configuration Protocol) server.

UDP (User Datagram Protocol) User Datagram Protocol and is an integral part of Internet Protocol suite. it is used by programs that run on different computers, which are part of a network, in order to send or share short messages which are also called as datagrams. The user datagram protocol or UDP, unlike TCP, doesn’t guarantee the correct sequence of transferred data. Moreover, it also doesn’t guarantee any reliability of the data. The datagrams sent from one computer to another using UDP may become lost without getting into notice. Moreover, they may arrive in a different order as compared to their order when they were sent. Benefits of UDP: UDP can be used as it provides better speed as compared to TCP. (UDP doesn’t check whether the packet or the data has been delivered or not, therefore, it successfully avoids this overhead check.) Major Problems of using UDP: UDPerror can offer smooth network traffic. No control.

ARP Address Resolution Protocol Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol address (IP address) to a physical machine address that is recognized in the local network. For example, in IP Version 4, the most common level of IP in use today, an address is 32 bits long. In an Ethernet local area network, however, addresses for attached devices are 48 bits long. (The physical machine address is also known as a Media Access Control or MAC address.) A table, usually called the ARP cache, is used to maintain a correlation between each MAC address and its corresponding IP address. ARP provides the protocol rules for making this correlation and providing address conversion in both directions.

AppleTalk AppleTalk, a protocol suite developed by Apple Computer in the early 1980s, was developed in conjunction with the Macintosh computer. AppleTalk's purpose was to allow multiple users to share resources, such as files and printers. The devices that supply these resources are called servers, while the devices that make use of these resources (such as a user's Macintosh computer) are referred to as clients. Hence, AppleTalk is one of the early implementations of a distributed client/server networking system. This chapter provides a summary of AppleTalk's network architecture. AppleTalk was designed with a transparent network interface—that is, the interaction between client computers and network servers requires little interaction from the user. In addition, the actual operations of the AppleTalk protocols are invisible to end users, who see only the result of these operations. S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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Internet Message Access Protocol IMAP (Internet Message Access Protocol): IMAP is gradually replacing POP as the main protocol used by email clients in communicating with email servers. Using IMAP an email client program can not only retrieve email but can also manipulate message stored on the server, without having to actually retrieve the messages. So messages can be deleted, have their status changed, multiple mail boxes can be managed, etc.

Internet Control Message Protocol ICMP is a network protocol useful in Internet Protocol (IP) network management and administration. ICMP is a required element of IP implementations. ICMP is a control protocol, meaning that it does not carry application data, but rather information about the status of the network itself. ICMP can be used to report: errors in the underlying communications of network applications availability of remote hosts network congestion   

Internet Group Management Protocol The Internet Group Management Protocol (IGMP) is an Internet protocol that provides a means to automatically control and limit the flow of multicast traffic through the network. Applications that implement IGMP, on networks that support IGMP, effectively eliminate multicast traffic on segments that are not destined to receive this traffic. Multicasting allows one computer on the Internet to send content to computer's multiple other computers that have identified as interestedasinupdating receivingthe the srcinating content. Multicasting can be usedthemselves for such applications address books of mobile computer users in the field, sending out company newsletters to a distribution list, and "broadcasting" high-bandwidth programs of streaming media to an audience that has "tuned in" by setting up a multicast group membership.

Simple Network Management Protocol Simple Network Management Protocol (SNMP) is used as the transport protocol for network management. SNMP is now a part of TCP/IP suite of protocols, works over the internet, and can be used to manage virtually any device such as printers, switches, and wiring hubs. Its improved version (called remote network monitoring specification or RNMS) allows error alerts to be sent to network administrators.

Dynamic Host Configuration Protocol Short for Dynamic Host Configuration Protocol, a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses. Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address. Many ISPs use dynamic IP addressing for dial-up users.


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Telnet Telnet is a program for TCP/IP networks such as the Internet. The Telnet program runs on your computer and connects your PC to a server on the network. You can then enter commands through the Telnet program and they will be executed as if you were entering them directly on the server console. This enables you to control the server and communicate with other servers on the network. To start a Telnet session, you must log in to a server by entering a valid username and password. Telnet is a common way to remotely control Web servers.

Frame Relay Frame relay is a computer networking structure that allows for a quick and efficient way to transmit frames from one device to another. These frames, or packets of data, are usually sent between local area networks (LANs) within a wide area network (WAN). The way the frames are sent is like a relay

— data is passed from one router or node to another from where it's then sent to another node or router. It's a relatively inexpensive technology though alternative structures like virtual private networks (VPNs) or multiprotocol label switching (MPLS) are often preferred.

Asynchronous Transfer Mode Asynchronous transfer mode (ATM) is a switching technology that facilitates the movement of data from one point to another. It is one of the preferred technologies because of its efficiency of use, especially with different hardware components. Unlike other types of technology, the speed and efficiency used in asynchronous transfer mode makes it one of the most common network protocol standards in use today. The main advantage of asynchronous transfer mode technology is the ability to transfer many different types of data at the same time. This is because all bandwidth is utilized, as long as it is available.

Point-to-Point Protocol (PPP) PPP (Point-to-Point Protocol) is a protocol for communication between two computers using a serial interface, typically a personal computer connected by phone line to a server. For example, your Internet server provider may provide you with a PPP connection so that the provider's server can respond to your requests, pass them on to the Internet, and forward your requested Internet responses back to you. PPP is a full-duplex protocol that can be used on various physical media, including twisted pair or fiber optic lines or satellite transmission.


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Point to Point Protocol over Ethernet (PPPoE) Point to Point Protocol over Ethernet is a proposal specifying how a host personal computer (PC) interacts with a broadband modem (i.e. xDSL, cable, wireless, etc) to achieve access to the growing number of High speed data networks. PPPoE is used to allow Internet Service Providers (ISPs) the use of their existing Radius authentication systems from their Dial-Up service on a Broadband / Ethernet based service.

Layer Two (2) Tunneling Protocol (L2TP) Short for Layer Two (2) Tunneling Protocol, an extension to the PPP protocol that enables ISPs to operate Virtual Private Networks (VPNs). L2TP merges the best features of two other tunneling protocols: PPTP from Microsoft and L2F from Cisco Systems. Like PPTP, L2TP requires that the ISP's routers support the protocol.

Internetwork Packet Exchange (IPX) IPX stands for Internetwork Packet Exchange and it is a local area network communication protocol that is developed by Novell Systems. It is used to connect the computers that are using Novell Netware operating system. As it is a datagram protocol so it is used for the connectionless communications. IPX works at the network layer of the OSI layers model. In general IPX/SPX is a protocol stack that is supported by the Novell Netware operating systems. It does not require to establish or maintain the connection before the communication starts between the network computers. IPX doesn’t take the unnecessary network resources. Today computers are networks can support multiple communication protocols. Novell computers support TCP/IP and TCP/IP computers support Novell Netware. Today a computer can be mixture of multiple logical and physical networks. IPX addressing now has been replaced by the TCP/IP. It was previously used for the network games.

Sequenced Packet Exchange (SPX) Short for Sequenced Packet Exchange, a transport layer protocol (layer 4 of the OSI Model) used in Novell Netware networks. The SPX layer sits on top of the IPX layer (layer 3) and provides connection-oriented services between two nodes on the network. SPX is used primarily by client/server applications. Whereas the IPX protocol is similar to IP, SPX is similar to TCP. Together, therefore, IPX/SPX provides connection services similar to TCP/IP.



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Firewall A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.

Hardware Firewall: A Hardware Firewall is a physical piece of equipment that sits between the Internet and your computer. An example of a hardware firewall is a broadband router, a common form of Internet connection. The benefit of using a hardware firewall, is that it has the ability to protect multiple computer systems that are connected to it at the same time. This makes it an effective firewall for use in businesses that have multiple computers connected to the Internet, as well as in homes that have more than one computer system.

Software Firewall: Software Firewalls work in the same way as a hardware firewall, by monitoring and blocking information that comes to your computer via the Internet, however software firewalls must be installed as a program on your computer. These software firewalls can either be installed from a computer disk that you have purchased, or downloaded over the Internet. Software firewalls are the most common type of firewall. Programs such as Norton 360, Norton Internet Security, ESET Smart Security, and Kaspersky Internet Security all have a firewall bundled within them. There are several types of firewall techniques: 



Packet filter: Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing. Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation.



Circuit-levelOnce gateway: Applies security mechanisms when a TCP UDP connection established. the connection has been made, packets can flow or between the hosts is without further checking. 

Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses.

In practice, many firewalls use two or more of these techniques in concert. A firewall is considered a first line of defense in protecting private information. For greater security, data can be encrypted.


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Multiplexing Under the simplest conditions, a medium can carry only one signal at any moment in time. Many times, however, we want a medium to carry multiple signals at the same time. Technique of transmitting multiple signals over a single medium is multiplexing. Multiplexing is a technique performed at the physical layer of the OSI model or the interface layer of the Internet model. For multiple signals to share one medium, the medium must somehow be divided, giving each signal a portion of the total bandwidth. there are four basic ways to divide a medium: frequency division multiplexing, time division multiplexing, dense wavelength division multiplexing, and code division multiplexing.

Frequency Division Multiplexing Used in many fields of communications, including cable television, cellular telephones, broadcast television and radio, and pagers It is also one of the simplest multiplexing techniques. Frequency division multiplexing (FDM) is the assignment of non- overlapping frequency ranges to each “user” of a medium. So that multiple users can share a single medium, each user is assigned a channel. A channel is an assigned set of frequencies that is used to transmit the user’s signal. Frequency division multiplexing is used only with analog signals.

Time Division Multiplexing Frequency division multiplexing cannot be used with digital signaling techniques unless the digital signals are first converted to analog signals. In contrast, time division multiplexing directly supports digital signals. In time division multiplexing (TDM), sharing of the signal is accomplished by dividing available transmission time on a medium among users. A time division multiplexor calls on one input device after another, giving each device a turn at transmitting its data over a high-speed line. Suppose two users, A and B, wish to transmit data over a shared medium to a distant computer. We can create a rather simple time division multiplexing scheme by allowing user A to transmit during the first second, then user B during the following second, followed again by user A during the third second, and so on.


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Synchronous time division multiplexing Synchronous time division multiplexing (Sync TDM) gives each incoming source a turn to transmit, proceeding through the sources in round-robin fashion. Given n inputs, a synchronous time division multiplexor accepts one piece of data, such as a byte, from the first device, transmits it over a highspeed link, accepts one byte from the second device, transmits it over the high-speed link, and continues this process until a byte is accepted from the nth device. After the nth device’s first byte is transmitted, the multiplexor returns to the first device and continues in round robin fashion.

Since the high-speed output data stream generated by the multiplexor does not contain addressing information for individual bytes, a precise order must be maintained, so that the de multiplexor can disassemble and deliver the bytes to the respective owners in the same sequence as the bytes were input.

Statistical time division multiplexing Both frequency division multiplexing and synchronous time division multiplexing can waste unused transmission space. One solution to this problem is statistical time division multiplexing. Statistical time division multiplexing (Stat TDM, sometimes called asynchronous time division multiplexing) transmits data only from active users and does not transmit empty time slots. To transmit data only from active users, the multiplexor creates a more complex frame that contains data only from those input sources that have something to send.

Dense Wavelength Division Multiplexing With Internet access growing by more than 100 percent per year a single fiber optic line transmitting billions of bits per second is simply no longer sufficient. This inability of a single fiber optic line to meet users’ needs is called fiber exhaust. Dense wavelength division multiplexing (DWDM), or simply wave division multiplexing, multiplexes multiple data streams onto a single fiber optic line. Similarly to frequency division multiplexing, which assigns input sources to separate sets of frequencies, wave division multiplexing uses different wavelength (frequency) lasers to transmit multiple signals. The wavelength of each different colored laser is called the lambda. Thus, DWDM supports multiple lambdas. The technique takes each input source, assigns a uniquely colored laser to that source, and combines the multiple optical signals of the input sources, so that they can be amplified as a group and transported over a single fiber. S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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It is interesting that because of the properties of the signals, light, and glass fiber, each signal carried on the fiber can be transmitted at a different rate from the other signals. This means that a single fiber optic line can support simultaneous transmission speeds such as 51.84 Mbps, 155.52 Mbps, 622.08 Mbps, and 2.488 Gbps.

Code Division Multiplexing Code division multiplexing (CDM and also known as code division multiple access) is a relatively new technology and has been used extensively by both the military and cellular telephone companies. Whereas other multiplexing techniques differentiate one user from another by either assigning frequency ranges or interleaving bit sequences in time, code division multiplexing allows multiple users to share a common set of frequencies by assigning unique digital codes to each user.



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Connection-Oriented and Connectionless Services Two distinct techniques are used in data communications to transfer data. Each has its own advantages and disadvantages. They are the connection-oriented method and the connectionless method:

Connection-oriented Services Requires a session connection (analogous to a phone call)Itbe established any will dataarrive can beinsent. This method is often called a "reliable" network service. can guaranteebefore that data the same order. Connection-oriented services set up virtual links between end systems through a network, as shown in figure below. Note that the packet on the left is assigned the virtual circuit number 01. As it moves through the network, routers quickly send it through virtual circuit 01.

Given valid input parameters, the service:   

Establishes the connection. Allows me to utilize the connection. Tears down the connection when I'm done using it.

Connectionless Services Does not require a session connection between sender and receiver. The sender simply starts sending packets (called datagrams) to the destination. This service does not have the reliability of the connection-oriented method, but it is useful for periodic burst transfers. Neither system must maintain state information for the systems that they send transmission to or receive transmission from. A connectionless network provides minimal services.    

a message can be delayed to ensure another arrives first. widely different channels of communication can be used for transmitting messages. a message can be handed off to a trusted third party in the distribution network. a message can be intercepted by a third party, copied or logged, and passed on to the intended receiver.

Note: TCP (Transmission Control Protocol) is a connection-oriented transport protocol, while UDP (User Datagram Protocol) is a connectionless network protocol. Both operate over IP.


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Transmission Impairments Analog signal consist of varying a voltage with time to represent an information steam. If the transmission media were perfectly, the receiver could receive exactly the same signal that the transmitter sent. But communication lines are usually not perfect, so the receive signal is not the same as the transmitted signal. For digital data this difference can lead to errors. Transmission lines suffers from three major problems, 1. Attenuation 2. Delay distortion 3. Noise Impairments exist in all forms of data transmission:  

Analog signal impairments result in random modifications that impair signal quality. Digital signal impairments result in bit errors (1s and 0s transpose)

Attenuation Signal amplitude decrease along a transmission medium over distance. This is known as signal attenuation. 

Amplifiers (analog) or repeaters (Digital) are inserted at intervals along the medium to improve the received signal as closed as to it’s srcinal level. Attenuations and amplifications are measured in decibel (dB).

Delay distortion Velocity of a propagation of a signal through a guided medium varies with frequency. The varies frequency components in digitalof signal arrive at the with varyingtimes. delay,Effects resulting in delay distortion. Various components a signal arrive at receiver receiver at different digital more.


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Limited Bandwidth Every medium has a limit on its bandwidth. Bandwidth is the range of frequencies that the equipment or channel is capable of processing. If there is not enough bandwidth some of the frequencies will be lost, and the signal will be distorted.

Noise Noise is unwanted sound or an unwanted electrical interference on the signal wires. There are several types of noises.    

Thermal Intermediation Crosstalk Impulse

Thermal The noise caused by the increase of current carries in a resistor due a thermal increase in the device. Or it cause from thermal agitation of electrons.   

It present in all electronic devices. Known as white notice. Can’t be eliminated.

Inter modulation Noise Signals of different frequencies share a medium can produce a new frequency that is the sum or the difference of the srcinal frequency. Cross Talk Crosstalk is interference generated when magnetic fields or current nearby wires, interrupt electrical current in a wire. As electrical current travels through a wire, the current generates magnetic fields. Magnetic field from wires that are closed together can interfere each other. Shielding the wire and twisting wire pairs around each other help decrease crosstalk. NEXT -

Near end crosstalk s t p e c n o C

Interference in a wire at the transmitting end of a signal sent on a different wire. FEXT -

Far end crosstalk

Interference in a wire at the receiving end of a signal sent on a different wire. Impulse Noise Impulse noise caused by irregular pulse, high amplitude, non-continuous. More damaging to digital than analog and difficult to deal with.


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g n i k r o w t e N

IEEE Standards The Institute of Electrical and Electronics Engineers Standards Association (IEEE-SA) is an organization within IEEE that develops global standards in a broad range of industries, including: power and energy, biomedical and healthcare, information technology, telecommunications, transportation, nanotechnology, information assurance, and many more. IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks. The number 802 was simply the next free number IEEE could assign though “802” is sometimes associated with the date the first meeting was held — February 1980. Notable IEEE Standards committees and formats

IEEE 802 IEEE 802.1 IEEE 802.2 IEEE 802.3 IEEE 802.4 IEEE 802.5 IEEE 802.6 IEEE 802.7 IEEE 802.8 IEEE 802.9 IEEE 802.10 IEEE 802.11 IEEE 802.12 IEEE 802.14 IEEE 802.15.1 IEEE 802.15.4 IEEE 802.16

LAN/MAN Standards for LAN/MAN bridging and management and remote media access control (MAC) bridging. Standards for Logical Link Control (LLC) standards for connectivity. Ethernet Standards for Carrier Sense Multiple Access with Collision Detection (CSMA/CD). Standards for token passing bus access. Standards for token ring access and for communications between LANs and MANs Standards for information exchange between systems. Standards for broadband LAN cabling. Fiber optic connection. Standards for integrated services, like voice and data. Standards for LAN/MAN security implementations. Wireless Networking – "WiFi". Standards for demand priority access method. Standards for cable television broadband communications. Bluetooth Wireless Sensor/Control Networks – "ZigBee" Wireless Networking – "WiMAX"

IEEE 8802.11 Wi Fi The name of a popular wireless networking technology that uses radio waves to provide wireless high-speed Internet and network connections. The Wi-Fi Alliance, the organization that owns the WiFi (registered trademark) term specifically defines Wi-Fi as any "wireless local area network (WLAN) products that are based on the Institute of Electrical and Electronics Engineers' (IEEE) 802.11 standards."


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Advantages of WiFi 

It allows local area networks (LANs) to be setup with cabling.



Reducing the costs of network deployment and expansion.



Places where cables cannot be run, such as outdoor areas and historical buildings can use wireless LANs.



WiFi networks can support roaming. This allows mobile users with laptop computer to be



able to move from one access point to another. WiFi has a set of global standards. Not like the cellular carriers, the same WiFi users can work in different countries around the world at all time.





WiFi uses unlicensed radio spectrum and does not require regulatory approval for individual deployers. Wide range of WiFi products available in the market with (WiFi Protected Access2) WPA2 security method for wireless networks that provides stronger data protection and network access control.

Disadvantages of WiFi 

WiFi networks have limited range o Ex) WiFI Home router

-

45 m (150 feet) indoor 90m (300 feet) outdoor.



Initial cost may high.



The most common wireless encryptions can be breakable.





Access points could be used to steal personal confidential information transmitted from WiFi consumers. If Access point failure then all wireless hosts will be down.



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LAN Technologies Each computer in a LAN can effectively send and receive any information addressed to it. This information is in the form of data 'packets'. The standards followed to regularize the transmission of packets, are called LAN standards. There are many LAN standards as Ethernet, Token Ring , FDDI etc. Usually LAN standards differ due to their media access technology and the physical transmission medium. There are different types of LAN technologies available.

I.

Ethernet – A local-area network (LAN) architecture/technology uses a bus or star topology and supports data transfer rates of 10 Mbps. The Ethernet specification served as the basis for the IEEE 802.3 standard, which specifies the physical and lower software layers. Ethernet uses the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol to control access network. Ethernet Frame Format An Ethernet frame is a way of arranging sections of data for transfer over a computer network. The frame is the one of the key elements of the Ethernet system, one of the most popular types of local network. It is made up of three elements: a pair of addresses, the data itself, and an error checking field.

Preamble The preamble is a 64-bit (8 byte) field that contains a synchronization pattern consisting of alternating ones and zeros and ending with two consecutive ones. After synchronization is established, the preamble is used to locate the first bit of the packet. The preamble is generated by the LAN interface card. Destination Address The destination address field is a 48-bit (6 byte) field that specifies the station or stations to which the packet should be sent. Each station examines this field to determine whether it should accept the packet. Source Address The source address field is a 48-bit (6 byte) field that contains the unique address of the station that is transmitting the packet. Type field The type field is 16-bit (2 byte) field that identifies the higher-level protocol associated with the packet. It is interpreted at the data link level.


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Data Field The data field contains 46 to 1500 bytes. Each octet (8-bit field) contains any arbitrary sequence of values. The data field is the information received from Layer 3 (Network Layer). The information, or packet, received from Layer 3 is broken into frames of information of 46 to 1500 bytes by Layer 2. FCS (Frame check sequence) CRC Field The Cyclic Redundancy Check (CRC) field is a 32-bit error checking field. The CRC is generated based on the destination address, type and data fields.

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is the LAN access method used in Ethernet. When a device wants to gain access to the network, it checks to see if the network is free. If the network is not free, the device waits a random amount of time before retrying. If the network is free and two devices access the line at exactly the same time, their signals collide. When the collision is detected, they both back off and wait a random amount of time before retrying. Carrier Sense:

Carrier sense means that every Ethernet device listen to the Ethernet wire before it attempts to transmit. If the Ethernet device senses that another device is transmitting, it will wait to transmit.

Multiple Access:

Multiple access means that more than one other network device can be sensing (listening and waiting to transmit) at a time.

Collision Detection: Collision Detection means that when multiple Ethernet devices accidentally transmit at the same time, they are able to detect this error.

II.

Token Ring This is a 4-Mbps or 16-Mbps token-passing method, operating in a ring topology. Devices on a Token Ring network get access to the media through token passing. Token and data pass to each station on the ring. The devices pass the token around the ring until one of the computer who wants to transmit data, takes the token and replaces it with a frame. Each device passes the frame to the next device, until the frame reaches its destination. As the frame passes to the intended recipient, the recipient sets certain bits in the frame to indicate that it received the frame. The srcinal sender of the frame strips the frame data off the ring and issues a new token.


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III.

Fast Ethernet This is an extension of 10Mbps Ethernet standard and supports speed up to 100Mbps. The access method used is CSMA/CD. For physical connections Star wiring topology is used. Fast Ethernet is becoming very popular as an up gradation from 10Mbps Ethernet LAN to Fast Ethernet LAN is quite easy.

IV.

FDDI (Fiber Distributed Data Interface) FDDI provides data speed at 100Mbps which is faster than Token Ring and Ethernet LANs . FDDI comprise two independent, counter-rotating rings : a primary ring and a secondary ring. Data flows in opposite directions on the rings. The counter-rotating ring architecture prevents data loss in the event of a link failure, a node failure, or the failure of both the primary and secondary links between any two nodes. This technology is usually implemented for a backbone network.

In (a), the outer ring is used to transfer data. In (b), a station has failed and the adjacent stations detect the disconnection and reconfigure to use the reverse path to form a closed ring. This process of reconfiguring is called self-healing and FDDI is known as a self-healing network. s t p e c n o C g n i k r o w t e N


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WAN Technologies Wide Area Networks (WANs) are used to interconnect networks that are not physically close to each other, might be physically separated across the cities, across regions, or even across geography. Currently there are many WAN technologies available. Primary different between WAN technology and LAN technology is about the distance that separates the interconnected networks. WANs use different transmission media, hardware, and protocols. Data transfer rates are typically much lower for WAN communication when compared to LAN rates.

1. ATM ATM or Asynchronous Transfer Mode is a high bandwidth and high speed wide area network technology that operates at the speed of 155Mbps. ATM is also called cell relay and it supports multiple data types such as data, voice, video etc. ATM uses fixed sized packets for data communication that are also known as packets. Asynchronous Transfer Mode, or ATM, uses fiber optic cable to achieve speeds exceeding 600 Mbps, and is only used in large-scale, “backbone” operations. ATM can accommodate such varying technologies as traditional phone service, data service, and even VOIP service (Voice over IP).

2. ISDN Integrated Services Digital Network (ISDN) is a circuit-switching network used for voice, data, and video transfer over plain copper telephone lines. ISDN is a bit similar to the normal telephone system but it is faster, more reliable, and requires less time to setup a call. ISDN Network availability is widespread, but you can still find places where it is simply not available. One key reason to use dialed connections of any kind, including ISDN network, might be to send and receive data for only short periods of time. Routers frequently use ISDN network to create a backup link when their primary leased line or Frame Relay connection is lost. ISDN network includes two types of interfaces: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). ISDN BRI offers connection speeds up to 128 Kbps while ISDN PRI services offer connections ranging up to 2.048 Mbps (or 1.554 Mbps). Basic Rate Interface (BRI) ISDN BRI network includes two 64 Kbps channels (called B channel), and one 16 Kbps channel (called D channel). B channel carry data, digitalized voice, or digitalized video signals. The D channel is service channel used for both data and control information. ISDN BRI is ideal for home and small businesses that need data transfer rates higher than traditional modems. There are two scenarios you can use with this ISDN BRI network: 1. One B channel is dedicated to voice, and the other B channel is dedicated to data 2. Both B channels are dedicated to data for a total transfer rate of 128 Kbps The total bandwidth of an ISDN BRI line is 144 Kbps (two B channels and one D channel) with total data transfer rate is 128 Kbps.


52


ISDN BRI Practical Applications ISDN BRI is a relatively low-cost WAN service that is ideal for the following situations:  

Home office or telecommuters who need a relatively fast connection Businesses that need to periodically send data between sites (burst traffic pattern)

ISDN BRI offers the following benefits over dial-up modems and other WAN connection options.   

Faster data transfer rates (128Kbps) compared to dial-up modems (56Kbps maximum) Faster call establishment (dial-up) than modems Lower cost than other WAN solutions (users pay a monthly fee plus connection charges)

Primary Rate Interface (PRI) ISDN PRI network is used in businesses that require an “always on” high speed connection. PRI is an industrial ISDN line while the Basic Rate Interface, or BRI, is used to cater to home and small enterprises. A PRI is typically used to establish communication between a PBX, or a private branch exchange, which is a telephone exchange operated by the customer of a telephone company, and a Central Office of the telephone company or an Inter Exchange Carrier or IXC, a long distance telephone company. The advantage of primary rate interface or PRI is that the 23 or 30 B channels can be used in various combinations for specific data transmission needs, such as a videoconferencing, allowing bulk data transfer to be achieved more flexibly.

s t p e c n o C

3. Frame Relay Frame Relay is a high-performance WAN protocol that can provide digital internetwork WAN connections up to 2.048 Mbps (and sometimes higher) in many parts of the world. Frame relay uses virtual circuits to connect sites and provide scalability by the definition of guaranteed data pipes (using a committed information rate). Frame relay is so popular because its scalable bandwidth offerings across digital pathways. Using standard Frame Relay configurations is a simple way of minimizing connectivity problems in large Frame Relay networks.


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g n i k r o w t e N

The following is the main feature of frame relay: 1. 2. 3. 4. 5.

Frame relay provides error detection but not error recovery Frame relay can provide data transfer up to 1.54Mbps Frame relay have a variable packet size (called a frame) Frame relay can be used as backbone connection to LANs Frame relay can be implemented over a variety of connection lines.

4. X.25 X.25 is a standard suite of protocols used for packet switching across computer networks. Each X.25 packets contains up to 128 bytes of data. The X.25 network handles packet assembly at the source device, delivery, and then disassembly at the destination. X.25 packet delivery technology includes not only switching and network-layer routing, but also error checking and re-transmission logic should delivery failures occur. X.25 supports multiple simultaneous conversations by multiplexing packets and using virtual communication channels. X.25 was srcinally designed more than 25 years ago to carry voice over analog telephone lines (dialup networks). Typical applications of X.25 today include automatic teller machine networks and credit card verification networks. X.25 also supports a variety of mainframe terminal/server applications. 5.

Packet Switching

Packet-switched networks use two different technologies for sending messages and data from one point to another. 

  

In packet-based networks, the message gets broken into small data packets. These packets are sent out from the computer and they travel around the network seeking out the most efficient route to travel as circuits become available. This does not necessarily mean that they seek out the shortest route. Each packet may go a different route from the others. Each packet is sent with a ‘header address’. This tells it where its final destination is, so it knows where to go. The header address also describes the sequence for reassembly at the destination computer so that the packets are put back into the correct order. S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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 

One packet also contains details of how many packets should be arriving so that the recipient computer knows if one packet has failed to turn up. If a packet fails to arrive, the recipient computer sends a message back to the computer which srcinally sent the data, asking for the missing packet to be resent.

Advantages »

Security

» »

Bandwidth used to full potential Devices of different speeds can communicate Not affected by line failure (re diverts signal) Availability – do not have to wait for a direct connection to become available During a crisis or disaster, when the public telephone network might stop working, e-mails and texts can still be sent via packet switching

» » »

Disadvantages » » » »

Under heavy use there can be a delay Data packets can get lost or become corrupted Protocols are needed for a reliable transfer Not so good for some types data streams e.g real-time video streams can lose frames due to the way packets arrive out of sequence.

6.

Circuit Switching



Circuit switching was designed in 1878 in order to send telephone calls down a dedicated channel. This channel remained open and in use throughout the whole call and could not be used by any other data or phone calls. There are three phases in circuit switching: 1. Establish 2. Transfer 3. Disconnect The telephone message is sent in one go, it is not broken up. The message arrives in the same order that it was srcinally sent. In modern circuit-switched networks, electronic signals pass through several switches before a connection is established. During a call, no other network traffic can use those switches. The resources remain dedicated to the circuit during the entire data transfer and the entire message follows the same path.



   

  

Circuit switching can be analogue or digital With the expanded use of the Internet for voice and video, analysts predict a gradual shift away from circuit-switched networks. A circuit-switched network is excellent for data that needs a constant link from end-to-end. For example real-time video.


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Advantages: » » »

Circuit is dedicated to the call – no interference, no sharing Guaranteed the full bandwidth for the duration of the call Guaranteed Quality of Service

Disadvantages: » » » »

Inefficient – the equipment may be unused for a lot of the call, if no data is being sent, the dedicated line still remains open Takes a relatively long time to set up the circuit During a crisis or disaster, the network may become unstable or unavailable. It was primarily developed for voice traffic rather than data traffic.



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Virtual Private Network (VPN) A Virtual Private Network (VPN) is a network technology that creates a secure network connection over a public network such as the Internet or a private network owned by a service provider. Large corporations, educational institutions, and government agencies use VPN technology to enable remote users to securely connect to a private network. In order to gain access to the private network, a user must be authenticated using a unique identification and a password.

Protocols Used in VPN There are a number of VPN protocols in use that secure the transport of data traffic over a public network infrastructure. Each protocol varies slightly in the way that data is kept secure.

IP security (IPSec) is used to over the Internet. IPSec traffic can use either transport mode or tunneling to secure encryptcommunications data traffic in a VPN. Secure Sockets Layer (SSL) and Transport Layer Security (TLS) use cryptography to secure communications over the Internet. To successfully initiate a connection, an authentication process involving certificates is used. Point-To-Point Tunneling Protocol (PPTP) is another tunneling protocol used to connect a remote client to a private server over the Internet. PPTP is one of the most widely used VPN protocols because of it's straightforward configuration and maintenance and also because it is included with the Windows operating system. S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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Layer 2 Tunneling Protocol (L2TP) is a protocol used to tunnel data communications traffic between two sites over the Internet.

Advantages 

  

Allows you to be at home and access your company's computers in the same way as if you were sitting at work. A VPN is a inexpensive effective way of building a private network. Almost impossible for someone to tap or interfere with data in the VPN tunnel. If you have VPN client software on a laptop, you can connect to your company from anywhere in the world.

Disadvantages  



Setup is more complicated than less secure methods. Vendor interoperability is another potential disadvantage as VPN technologies from one vendor may not be compatible with VPN technologies from another vendor. The company whose network you connect to may require you to follow the company's own policies on your home computers



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Responsibilities of the network Administrator and the network users A network administrator is a person responsible for the maintenance of computer hardware and software that comprises a computer network. This normally includes deploying, configuring, maintaining and monitoring active network equipment. Every session communicates to a stage in the continuing of a network. The administrator might be accountable for all the stages. The Senior Network Administrator is responsible for all trouble shooting, maintenance of Existing WAN, LAN, WLAN and VPN communications as well as recommending and designing new DMZ,WAN, LAN, WLAN and VPN utilizing Cisco switches/ routers/ firewalls/ concentrators and environments at Cisco & Microsoft . He is also occasionally called upon to provide direction to the team. As a network Admin, he makes decisions and Takes action to help ensure the stability of Serendib’ network infrastructure.

KEY ROLES AND RESPONSIBILITIES 

Provide technical expertise and platform leadership in areas of Cisco WAN, LAN, WLAN, VPN and Firewall technologies.



Configure,

implement,

and

troubleshoot

a

variety

of

Cisco

Hardware/Software

Products, including: VPN Concentrators, Firewalls, Routers, WLAN and Switches. 

Proactively manage the service and security requirements of these systems to an Average of 99.99% uptime.

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On-Going Review of Cisco’ Router and Switches Infrastructure.

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Project Planning and documentation as required.

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Second/Third-Level Help Desk Ticket Resolution, including supporting the Business 7x24x365 and on-call support as needed.

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Perform advanced monitoring and reporting related to network systems.

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Develop tactical and strategic plans, standards, guidelines and policies for the

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Network resources based on growth, trends, available metrics, etc.

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Coordinate change planning and formal change control process to systems in order to Eliminate customer impact and to ensure that availability SLA's are met.

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Adherence to time and metric’s tracking.

Rights & Responsibilities of Users There are also responsibilities that must be met as part of the privilege of network access. Network users are expected to live up to these responsibilities. If you knowingly violate a network responsibility, your network access will be suspended. Depending on the seriousness of the violation, you could be referred through the University disciplinary procedure process. Violations that also violate federal or state laws can also result in referral to the appropriate legal authority. S.Kishokumar B.Sc (EUSL), PG Dip in IT (UPDN), MBCS. IDM Affiliated University College, Higher Studies Division, No: 11/7 Station Road, Batticaloa.

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You are responsible for the use of your network ID (Net ID) and all computer accounts that are assigned to you.

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You may not give anyone else access to your Net ID or computer accounts. .

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You may not misrepresent yourself or your data on the network.

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You are responsible for the security of your passwords. This includes changing passwords on a regular basis and making sure no one else knows them.

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You must not use NU's network resources to gain or attempt to gain unauthorized access to remote computers.

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You must not deliberately perform an act that will seriously impair the operation of computers, terminals, peripherals, or networks. This includes, but is not limited to, tampering with components of a local area network (LAN) or the high-speed backbone network, otherwise blocking communication lines, or interfering with the operational readiness of a computer.

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You must not run or install on any of NU's computer systems, or give to another, a program that could result in the eventual damage to a file or computer system and/or the reproduction of itself. This is directed towards, but not limited to, the classes of programs known as computer viruses, Trojan horses, and worms.

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You must not attempt to circumvent data protection schemes or exploit security loopholes or interfere with standard technical measures that identify and protect the rights of copyright owners.



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Networking Concept.pdf

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