Unit
– I
CIM: Introduction to CIM, CIM Wheel, Evolution, Benefits, Trends. Computers in Manufacturing: Factory tasks for Computer Integration Needs of CIM, CIM Hardware and Software, Workstations Fundamentals of Communication: Communications Matrix – Matrix – Types. Types. Representation of data, Coding, Transmission, Medium Types of Communication Lines and Hardware. Network Architectures: The seven layers OSI Model , LAN, MAP and Network Topologies.
2 1 2 2 2 1 2 (12 hours)
Introduction to Computer Integrated manufacturing Computer Integrated Manufacturing (CIM) encompasses the entire range of product development and manufacturing activities with all the functions being carried out with the help of dedicated software packages. The data required for various functions are passed from one application software to another in a seamless manner. For example, the product data is created during design. This data has to be transferred from the modeling software to
manufacturing
software without any loss of data. CIM uses a common database wherever feasible and communication technologies to integrate design, manufacturing and associated business functions that combine the automated segments of a factory or a manufacturing facility. CIM reduces the human component of manufacturing and thereby relieves the process of its slow, expensive and errorprone component. CIM stands for a holistic and methodological approach to the activities of the manufacturing enterprise in order to achieve vast improvement in its performance.
This methodological approach approach is applied applied to all activities activities from the design of the product to methods,
customer support in an integrated way, using various
means
and
techniques
in
order
to
achieve
production
improvement, cost reduction, fulfillment of scheduled delivery dates, quality 1
improvement and total flexibility in the manufacturing system. CIM requires all those associated with a company to involve totally in the process process of product development and manufacture. In such a holistic approach, economic, social and human aspects have the same importance as technical aspects. CIM also encompasses the whole lot of enabling technologies including total quality management, workflow
business
process
automation,
reengineering, concurrent engineering,
enterprise
resource
planning
and
flexible
manufacturing.
The challenge challenge before the manufacturi manufacturing ng engineers engineers is illustrated in Fig. 1
Figure 1 1 - Challenges in manufacturing
Manufacturing industries strive to reduce the cost of the product continuously to remain competitive in the face of global competition. In addition, there is the need to improve the quality and performance levels on a continuing basis. Another important requirement is on time delivery. In the context of global outsourcing
and
long
supply
chains
cutting
across
several
international
borders, the task of continuously reducing delivery times is really an arduous 2
improvement and total flexibility in the manufacturing system. CIM requires all those associated with a company to involve totally in the process process of product development and manufacture. In such a holistic approach, economic, social and human aspects have the same importance as technical aspects. CIM also encompasses the whole lot of enabling technologies including total quality management, workflow
business
process
automation,
reengineering, concurrent engineering,
enterprise
resource
planning
and
flexible
manufacturing.
The challenge challenge before the manufacturi manufacturing ng engineers engineers is illustrated in Fig. 1
Figure 1 1 - Challenges in manufacturing
Manufacturing industries strive to reduce the cost of the product continuously to remain competitive in the face of global competition. In addition, there is the need to improve the quality and performance levels on a continuing basis. Another important requirement is on time delivery. In the context of global outsourcing
and
long
supply
chains
cutting
across
several
international
borders, the task of continuously reducing delivery times is really an arduous 2
task. CIM has several software tools to address the above needs.
Manufacturing engineers are required to achieve the following objectives to be competitive in a global context.
•
Reduction in inventory
•
Lower the cost of the product
•
Reduce waste
•
Improve quality
•
Increase flexibility flexibility in manufacturing to achieve immediate and an d rapid response to: •
Product changes
•
Production changes
•
Process change
•
Equipment change
•
Change of personnel
CIM technology is an enabling technology to meet the above challenges to the manufacturing. Definition of CIM
Joel Goldhar, Goldhar, Dean, Illinois Illinois Institute Institute of Technology Technology gives CIM as a computer computer system in which the peripherals are robots, machine tools and other processing equipment.
Dan Appleton, President, DACOM, Inc. defines CIM is a management philosophy, not a turnkey product. 3
Jack Conaway Conaway,, CIM Marketing Marketing manager, manager, DEC, defines defines CIM CIM is nothing nothing but a data data management and networking problem.
The computer computer and automated automated systems systems association association of the society society of Manufacturing Engineers (CASA/SEM) defines CIM is the integration of total manufacturing
enterprise
by
using
integrated
systems
and
data
communication coupled with new managerial philosophies that improve organizational and personnel efficiency.
CIM is recognized as Islands of Automation. They are
1. CAD/CAM/CAE/GT 2.
Manufacturing Planning and Control.
3.
Factory Automation
4.
General Business Management
CIM wheel CASA/SME s CIM CIM Wheel is as shown in figure 2 ’
4
Figure 2- CASA/ SME
’
s
CIM Wheel
Conceptual model of manufacturing
`The computer has had and continues to have a dramatic impact on the development of production automation technologies. Nearly all modern production systems are implemented today using computer systems. The term computer integrated manufacturing (CIM) has been coined to denote the pervasive use of computers to design the products, plan the production, control the operations, and perform the various business related functions needed in a manufacturing firm. CAD/CAM (computer-aided design and computer-aided manufacturing) is another term that is used almost synonymously with CIM.
Let us attempt to define the relationship between automation and CIM by developing a conceptual model of manufacturing. In a manufacturing firm, the physical activities related to production that take place in the factory can be distinguished from the information-processing activities, such as product design 5
and production planning, that usually occur in an office environment. The physical activities include all of the manufacturing processing, assembly, material handling, and inspections that are performed on the product. These operations come in direct contact with the product during manufacture. They touch the product. The relationship between the physical activities and the informationprocessing activities in our model is depicted in Figure 5. Raw materials flow in one end of the factory and finished products flow out the other end. The physical activities
(processing,
handling,
etc.)
take
place
inside
the
factory.
The
information-processing functions form a ring that surrounds the factory, providing the data and knowledge required to produce the product successfully. These information-processing functions include (1) certain business activities (e.g., marketing and sales, order entry, customer billing, etc.), (2) product design, (3) manufacturing planning, and (4) manufacturing control. These four functions form a cycle of events that must accompany the physical production activities but which do not directly touch the product.
Now consider the difference between automation and CIM. Automation is concerned with the physical activities in manufacturing. Automated production systems are designed to accomplish the processing, assembly, material handling, and inspecting activities with little or no human participation.
)
6
In the above figure
Model of manufacturing, showing (a] the factory as a
processing pipeline where the physical manufacturing activities are performed, and (b) the information-processing activities that support manufacturing as a ring that surrounds the factory concerned more with the informationprocessing functions that are required to support the production operations. CIM involves the use of computer systems to perform the four types of information-processing functions. Just as automation deals with the physical activities, CIM deals with automating the information-processing activities in manufacturing.
EVOLUTION OF COMPUTER INTEGRATED MANUFACTURING
Computer Integrated Manufacturing (CIM) is considered a natural evolution of the technology of CAD/CAM which by itself evolved by the integration of CAD and CAM. Massachusetts Institute of Technology (MIT, USA) is credited with pioneering the development in both CAD and CAM. The need to meet the design and manufacturing requirements of aerospace industries after the Second World War necessitated the development these technologies. The manufacturing technology available during late 40's and early 50's could not meet the design and manufacturing challenges arising out of the need to develop sophisticated aircraft and satellite launch vehicles. This prompted the US Air Force to approach MIT to develop suitable control systems,
drives
and
programming
techniques
for
machine
tools
using
electronic control.
The
first
major
innovation in machin e control is the Numerical 7
Control (NC), demonstrated at MIT in 1952. Early Numerical Control Systems were all basically hardwired systems, since these were built with discrete systems or with later first generation integrated chips. Early NC machines used paper tape as an input medium. Every NC machine was fitted with a tape reader to read paper tape and transfer the program to the memory of the machine tool block by block. Mainframe computers were used to control a group of NC machines by mid 60's. This arrangement was then called Direct Numerical Control (DNC) as the transfer
the
program
data
computer
to
the
bypassed
the
tape
reader
to
machine controller. By late 60's mini
computers were being commonly used to control NC machines. At this stage NC became truly soft wired with the facilities of mass program storage, offline editing and software logic control and processing. This development is called Computer Numerical Control (CNC). Since 70's, numerical controllers are being designed around microprocessors, resulting in compact CNC systems. A further development to this technology is the distributed numerical control (also called DNC) in which processing of NC program is carried out in different computers operating at different hierarchical levels typically
from
mainframe
host
computers
to
plant
computers
to
the
machine controller. Today the CNC systems are built around powerful 32 bit and
64
bit
microprocessors.
PC
based
systems
are
also
becoming
increasingly popular.
Manufacturing
engineers
also
started
using
computers
for
such
tasks like inventory control, demand forecasting, production planning and control etc. CNC technology was adapted in the development of co-ordinate measuring machine's (CMMs) which automated inspection.
Robots
were
introduced to automate several tasks like machine loading, materials handling, welding, painting and assembly. All these developments led to the evolution of flexible manufacturing cells and flexible manufacturing systems in late 70's. 8
Evolution of Computer Aided Design (CAD), on the other hand was to
cater
to
the geometric modeling needs of automobile and aeronautical
industries. The developments in computers, design workstations, graphic cards, display devices and graphic input and output devices during the last ten years have been phenomenal. This coupled with the development of operating system with graphic user interfaces and powerful interactive (user friendly) software packages for modeling, drafting, analysis and optimization provides the necessary tools to automate the design process.
CAD in fact owes its development to the APT language project at MIT in early 50's. Several clones of APT were introduced in 80's to automatically develop NC codes from the geometric model of the component. Now, one can model, draft, analyze, simulate, modify, optimize and create the NC code to manufacture a component and simulate the machining operation sitting at a computer workstation.
If we
review t h e m a n u f a c t u r i n g s c e n a r i o d u r i n g 8 0 ’ s
we
will
find t h a t t h e manufacturing is characterized by a few islands
of automation. In the case of design, the task is well automated. In the case of manufacture, CNC machines, DNC systems, FMC, FMS etc provide tightly controlled
automation
implemented
in
systems.
several
areas
Similarly like
computer
manufacturing
control resource
has
been
planning,
accounting, sales, marketing and purchase. Yet the full potential of computerization could not be obtained.
COMPUTER-INTEGRATED MANUFACTURING CONCEPT
9
There are three major challenges to development of a smoothly operating computer-integrated manufacturing system: Integration of components from different suppliers : When different machines, such as CNC, conveyors and robots, are using different communications protocols. In the case of AGVs, even differing lengths of time for charging the batteries may cause problems. Data integrity: The higher the degree of automation, the more critical is the integrity of the data used to control the machines. While the CIM system saves on labor of operating the machines, it requires extra human labor in ensuring that there are proper safeguards for the data signals that are used to control the machines. Process control: Computers may be used to assist the human operators of the manufacturing facility, but there must always be a competent engineer on hand to handle circumstances which could not be foreseen by the designers of the control software.
10
Computer_Integrated_Manufacturing_control_system Subsystems in computer-integrated manufacturing A computer-integrated manufacturing system is not the same as a "lights-out" factory , which would run completely independent of human intervention, although it is a big step in that direction. Part of the system involves flexible manufacturing, where the factory can be quickly modified to produce different products, or where the volume of products can be changed quickly with the aid of computers. Some or all of the following subsystems may be found in a CIM operation: Computer-aided techniques: CAD (computer-aided design) CAE (computer-aided engineering) CAM (computer-aided manufacturing) CAPP (computer-aided process planning) CAQ (computer-aided quality assurance) PPC (production planning and control) ERP (enterprise resource planning) A business system integrated by a common database. Devices and equipment required: CNC, Computer numerical controlled machine tools DNC, Direct numerical control machine tools PLCs, Programmable logic controllers Robotics Computers 11
Software Controllers Networks Interfacing Monitoring equipment Technologies: FMS, (flexible manufacturing system) ASRS, automated storage and retrieval system AGV, automated guided vehicle Robotics Automated conveyance systems Others: Lean manufacturing CIMOSA CIMOSA (Computer Integrated Manufacturing Open System Architecture), is a 1990s European proposal for an open system architecture for CIM developed by the AMICE Consortium as a series of ESPRIT projects.[4][5] The goal of CIMOSA was "to help companies to manage change and integrate their facilities and operations to face world wide competition. It provides a consistent architectural framework for both enterprise modeling and enterprise integration as required in CIM environments".[6] CIMOSA provides a solution for business integration with four types of products:[7]
12
The CIMOSA Enterprise Modeling Framework, which provides a reference architecture for enterprise architecture CIMOSA IIS, a standard for physical and application integration. CIMOSA Systems Life Cycle, is a life cycle model for CIM development and deployment. Inputs to standardization, basics for international standard development. CIMOSA according to Vernadat (1996), coined the term business process and introduced the process-based approach for integrated enterprise modeling based on a cross-boundaries approach, which opposed to traditional function or activity-based approaches. With CIMOSA also the concept of an "Open System Architecture" (OSA) for CIM was introduced, which was designed to be vendorindependent, and constructed with standardised CIM modules. Here to the OSA is "described in terms of their function, information, resource, and organizational aspects. This should be designed with structured engineering methods and made operational in a modular and evolutionary architecture for operational use".[6] Application There are multiple areas of usage: In mechanical engineering In electronic design automation (printed circuit board (PCB) and integrated circuit design data for manufacturing)
unless all the segments of manufacturing are integrated, permitting the transfer of data across various functional modules. This realization led to the concept of computer integrated manufacturing. Thus the implementation of CIM required the development of whole lot of computer technologies related to hardware and software.
13
CIM HARDWARE AND CIM SOFTWARE
CIM Hardware comprises the following:
i. Manufacturing equipment such as CNC machines or computerized work centers, robotic work cells, DNC/FMS systems, work handling and tool handling devices, storage devices, sensors, shop floor data collection devices, inspection machines etc. ii. Computers, controllers, CAD/CAM systems, workstations / terminals, data entry terminals, bar code reader s, RFID tags, printers, plotters and other peripheral devices, modems, cables, connectors etc.,
CIM software comprises computer programmes to carry out the following functions: •
Management Information System
•
Sales
•
Marketing
•
Finance
•
Database Management
•
Modeling and Design
•
Analysis
•
Simulation
•
Communications
•
Monitoring
•
Production Control 14
•
•
Manufactur ing Area Control Job Tr acking
•
Inventory Control
•
Shop Floor Data Collection
•
Order Entry
•
Materials Handling
•
Device Drivers
•
Process Planning
•
Manufacturing Facilities Planning
•
Work Flow Automation
•
Business Process Engineering
•
Network Management
•
Quality Management
NATURE AND ROLE OF THE ELEMENTS OF CIM SYSTEM Nine major elements of a C IM system are in Figure 2 they are,
•
Marketing
•
Product Design
•
Planning
•
Purchase
•
Manufacturing Engineering
•
Factory Automation Hardware
•
Warehousing 15
•
Logistics and Supply Chain Manageme nt
•
Finance
•
Infor mation Management
Figure 2 Major elements of CIM systems
i. Marketing : The need for a product is identified by the marketing division . The
specifications
of
the
product,
the
projection
of
manufacturing
quantities and the strategy for marketing the product are also decided by the marketing department. Marketing also works out the manufacturing costs to assess the economic viability of the product.
ii. Product Design: The design department of the company establishes the initial database for production of a proposed product. In a CIM system this is accomplished through activities such as geometric modeling and computer aided design while considering the product requirements and concepts generated by the creativity of the design engineer. Configuration 16
management is an important activity in many designs.
Complex designs are usually carried out by several teams working simultaneously, located often in different parts of the world. The design process is constrained by the costs that will be incurred
in
production
production
and
by
the
capabilities
of
the
available
actual
equipment and processes. The design process creates the database required to manufacture the part.
iii. Planning: The planning department takes the database established by the design department and enriches it with production data and information to produce a plan for the production of the product. Planning involves several subsystems dealing with materials, facility, process, tools, manpower, capacity, scheduling, outsourcing, assembly, inspection, logistics etc. In a CIM system, this planning process should be
constrained
by
the
production
costs
and
by
the
production
equipment and process capability, in order to generate an optimized plan.
iv. Purchase: The purchase departments is responsible for placing the purchase orders and follow up, ensure quality in the production process of the vendor, receive the items, arrange for inspection and supply the items to the stores or arrange timely delivery depending on the production schedule for eventual supply to manufacture and assembly.
v. Manufacturing Engineering: Manufacturing Engineering is the activity of carrying out the production of the product, involving further enrichment of the database with performance data and information about the production equipment and processes. In CIM, this requires activities like 17
CNC programming, simulation and computer aided scheduling of the production activity. This should include online dynamic scheduling and control based on the real time performance of the equipment and processes to assure continuous production activity. Often, the need to meet fluctuating market demand requires the manufacturing system flexible and agile.
vi. Factory Automation Hardware: Factory automation equipment further enriches the database with equipment and process data, resident either in the operator or the equipment to carry out the production process. In CIM
system
this
consists
of computer controlled process machinery
such as CNC machine tools, flexible manufacturing systems (FMS), Computer controlled robots, material handling systems, computer controlled assembly systems, flexibly automated inspection systems and so on. vii.
Warehousing: Warehousing is
the
function
involving storage
and
retrieval of raw materials, components, finished goods as well as shipment of items. In today's complex outsourcing s c e n a r i o just-in-time
supply
of
components
and t h e
need
for
and subsystems, logistics and
supply chain management assume great importance.
viii. Finance: Finance deals with the resources pertaining to money. Planning of investment, working capital, and cash flow control, realiza tion of receipts, accounting and allocation of funds are the major tasks of the finance departments .
TYPES OF COMMUNICATION LINES AND HARDWARE: Power line communication or power line carrier (PLC), also known as power line digital subscriber line (PDSL), mains communication, power line telecom 18
(PLT), power line networking (PLN), or broadband over power lines (BPL) are systems for carrying data on a conductor also used for electric power transmission. A wide range of power line communication technologies are needed for different applications, ranging from home automation to Internet access. Electrical
power
is
transmitted
over
long
distances
using
high
voltage
transmission lines, distributed over medium voltages, and used inside buildings at lower voltages. Most PLC technologies limit themselves to one set of wires (such as premises wiring within a single building), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically transformers prevent propagating the signal, which requires multiple technologies to form very large networks. Various data rates and frequencies are used in different situations. A number of difficult technical problems are common between wireless and power line communication, notably those of spread spectrum radio signals operating in a crowded environment. Potential interference, for example, has been a long concern of amateur radio groups. CIM IMPLEMENTATION AND DATA COMMUNICATION CIM and company strategy Does that mean the starting point for CIM is a network to link all the existing islands of automation and software? Or is it the integration of the existing departmental functions and activities as suggested by the CIM wheel? The answer to both the questions just posed is no. the starting point for CIM is not islands of automation or software, not is it the structure presented by the CIM wheel, rather it is a company’s business strategy. CIM open system architecture (CIMOSA) CIMOSA was produced as generic reference architecture for CIM integration as part of an ESPRIT project. The architecture is designed to yield executable models or parts of models leading to computerized implementations for managing an enterprise. 19
Manufacturing enterprise wheel T he new manufacturing enterprise wheel’s focus is now the customer at level 1, and it identifies 15 key processes circumferentially at level 4. These are grouped
under
the
headings
of
customer
support,
product/process
and
manufacturing. CIM ARCHITECTURE CIM Architecture Overview To develop a comprehensive CIM strategy and solutions, an enterprise must begin with .solid foundations such as CIM architecture. A CIM architecture is an information systems structure that enables industrial enterprises integrate information and business processes It accomplishes this first by establishing the direction integration will take; and second, by defining the interfaces between the users and the providers of this integration function.The chart (Figure 2.1) illustrates how a CIM architecture answers the enterprise’s integration needs. As you can see here, a CIM architecture provides a core of common services. These services support every other area of the enterprise — from its common support functions to its highly specialized business processes. Three key building blocks The information environment of an industrial enterprise is subject to frequent changes in systems configuration and technologies. A CIM architecture can offer a flexible structure that enables it to react to these changes. This structure relies on a number of modular elements that allow systems to change more easily to grow along with enterprise needs. And as you can see from the chart on the facing page, the modular elements that give a CIM architecture its flexible structure are based on three key building blocks: • Communications — the communication and distribution of data. • Data management — the definition, storage and use of data 20
• Presentation — the presentation of this data to people and devices throughout the enterprise
Data dictionary
Data repository and store
A layered structure
Repository builder
Product data management (PDM): CIM implementation software The four major modules typically contained within the PDM software are
Process models
Process project management
Data management
Data and information kitting
The PDM environment provides links to a number of software packages used by a company. They are 21
A CAD package
A manufacturing/production management package
A word processing package
Databases for various applications
Life-cycle data
COMMUNICATION FUNDAMENTALS
A frequency
An amplitude
A phase which continuously changes
A bandwidth
An introduction to baseband and broadband
Telephone terminology Digital communications
Local area networks
Signal transmission, baseband and broadband
Interconnection media
Topology
Star topology
Ring topology
Bus topology
Tree topology
LAN implementations
Client server architecture 22
Networks and distributed systems
Multi-tier and high speed LANs
Network management and installation
Security and administration
Performance
Flexibility
User interface
Installation
OPEN SYSTEM AND DATABASE FOR CIM Open system interconnection (OSI) model
The physical layer
The data link layer
The network layer
The transport layer
The session layer
The presentation layer
The application layer
Manufacturing automation protocol and technical office protocol Basic database terminology
Database management system
Database system 23
Data model
Transaction
Schema
Data definition language
Data manipulation language
Applications program
Host language
Database administrator
The architecture of a database system
Internal schema
External schema
Conceptual schema
Data modeling and data associations Data modeling is carried out by using a data modeling method and one of a number of graphic representations to depict data groupings and the relationship between groupings. Data associations
One-to-One
One-to-Many
Many-to-One
Many-to-Many
Relational databases The terms illustrated are relation, tuple, attribute, domain, primary key and foreign key. 24
Database operators
Union
Intersection
Difference
Product
Project
Select
Join
Divide
NETWORK ARCHITECTURES: OSI model and its 7 layers The Open Systems Interconnection model (OSI model) is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar communication functions are grouped into logical layers. An instance of a layer provides services to its upper layer instances while receiving services from the layer below. For example, a layer that provides error-free communications across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that make up the contents of that path. Two instances at one layer are connected by a horizontal connection on that layer. OSI 7 Layers Reference Model For Network Communication 25
Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different vendors. It is now considered the primary
architectural
model
for
inter-computing
and
internetworking
communications. Most of the network communication protocols used today have a structure based on the OSI model. The OSI model defines the communications process into 7 layers, which divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers.
Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers. The OSI 7 layers model has clear characteristics. Layers 7 through 4 deal with end to end communications between data source and destinations. Layers 3 to 1 deal with communications between network devices. On the other hand, the seven layers of the OSI model can be divided into two groups: upper layers (layers 7, 6 & 5) and lower layers (layers 4, 3, 2, 1). The upper layers of the OSI model deal with application issues and generally are implemented only in software. The highest layer, the application layer, is closest to the end user. The lower layers of the OSI model handle data transport issues. The physical layer and the data link layer are implemented in hardware and software. The lowest layer, the physical layer, is closest to the physical network medium (the wires, for example) and is responsible for placing data on the medium. The specific description for each layer is as follows:
26
Layer 7:Application Layer Defines interface to user processes for communication and data transfer in network Provides standardized services such as virtual terminal, file and job transfer and operations Layer 6:Presentation Layer Masks the differences of data formats between dissimilar systems Specifies architecture-independent data transfer format Encodes and decodes data; Encrypts and decrypts data; Compresses and decompresses data Layer 5:Session Layer Manages user sessions and dialogues Controls establishment and termination of logic links between users Reports upper layer errors Layer 4:Transport Layer Manages end-to-end message delivery in network Provides reliable and sequential packet delivery through error recovery and flow control mechanisms Provides connectionless oriented packet delivery Layer 3:Network Layer 27
Determines how data are transferred between network devices Routes packets according to unique network device addresses Provides flow and congestion control to prevent network resource depletion Layer 2:Data Link Layer Defines procedures for operating the communication links Frames packets Detects and corrects packets transmit errors Layer 1:Physical Layer Defines physical means of sending data over network devices Interfaces between network medium and devices Defines optical, electrical and mechanical characteristics There are other network architecture models, such as IBM SNA (Systems Network Architecture) model . Those models will be discussed in separate documents. The OSI 7 layer model is defined by ISO in document 7498 and ITU X.200, X.207, X.210, X.211, X.212, X.213, X.214, X.215, X.217 and X.800. The protocols defined by ISO based on the OSI 7 layer mode are as follows:
Application
ACSE: Association Control Service Element CMIP:
Common Management 28
Information Protocol CMIS:
Common Management
Information Service CMOT: CMIP over TCP/IP FTAM: File Transfer Access and Management ROSE: Remote Operation Service Element RTSE:
Reliable
Transfer
Service
Element
Protocol VTP: ISO Virtual Terminal Protocol X.400: Message Handling Service (ISO email transmission service) Protocols X.500:
Directory
Access
Service
Protocol
(DAP) Presentation Layer
ISO-PP: OSI Presentation Layer Protocol
ASN.1: Abstract Syntax Notation One Session Layer Transport Layer
Network Layer
ISO-SP: OSI Session Layer Protocol ISO-TP: OSI Transport Protocols: TP0, TP1, TP2, TP3, TP4 ISO-IP:
CLNP:
Connectionless
Network
Protocol
29
CONP: Connection-Oriented Network Protocol ES-IS: End System to Intermediate System Routing Exchange protocol IDRP: Inter-Domain Routing Protocol IS-IS: Intermediate System to Intermediate System Data Link
HDLC: High Level Data Link Control protocol LAPB: Link Access Procedure Balanced for X.25
A local area network (LAN) is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building. The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased telecommunication lines. ARCNET, Token Ring and other technology standards have been used in the past, but Ethernet over twisted pair cabling, and Wi-Fi are the two most common technologies currently used to build LANs. Definition: A local area network (LAN) supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet or other WAN. Most local area networks are built with relatively inexpensive hardware such as Ethernet cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware options also exist. 30
Specialized operating system software may be used to configure a local area network. For example, most flavors of Microsoft Windows provide a software package called Internet Connection Sharing (ICS) that supports controlled access to LAN resources. The term LAN party refers to a multiplayer gaming event where participants bring their own computers and build a temporary LAN.
Examples: The most common type of local area network is an Ethernet LAN. The smallest home LAN can have exactly two computers; a large LAN can accommodate many thousands of computers. Many LANs are divided into logical groups called subnets. An Internet Protocol (IP) "Class A" LAN can in theory accommodate more than 16 million devices organized into subnets. Manufacturing automation protocol (MAP) The launch of the MAP initiates the use of open systems and the movement towards the integrated enterprise. Product related activities of a company 31
1. Marketing Sales and customer order servicing 2. Engineering Research and product development Manufacturing development Design Engineering release and control Manufacturing engineering Facilities engineering Industrial engineering 3. Production planning Master production scheduling Material planning and resource planning Purchasing Production control 4. Plant operations Production management and control Material receiving Storage and inventory Manufacturing processes Test and inspection Material transfer Packing, dispatch and shipping Plant site service and maintenance 32
5. Physical distribution Physical distribution planning Physical distribution operations Warranties, servicing and spares 6. Business and financial management Company services Payroll Accounts payable, billing and accounts receivable NETWORK TOPOLOGY: Network topology is the layout pattern of interconnections of the various elements (links, nodes, etc.) of a computer or biological network. Network topologies may be physical or logical. Physical topology refers to the physical design of a network including the devices, location and cable installation. Logical topology refers to how data is actually transferred in a network as opposed to its physical design. In general physical topology relates to a core network whereas logical topology relates to basic network. Topology can be understood as the shape or structure of a network. This shape does not necessarily correspond to the actual physical design of the devices on the computer network. The computers on a home network can be arranged in a circle but it does not necessarily mean that it represents a ring topology. Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. The study of network topology uses graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical. 33
A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN has one or more links to one or more nodes in the network and the mapping of these links and nodes in a graph results in a geometric shape that may be used to describe the physical topology of the network. Likewise, the mapping of the data flow between the nodes in the network determines the logical topology of the network. The physical and logical topologies may or may not be identical in any particular network. Topology There are two basic categories of network topologies: Physical topologies Logical topologies The shape of the cabling layout used to link devices is called the physical topology of the network. This refers to the layout of cabling, the locations of nodes, and the interconnections between the nodes and the cabling. The physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits. The logical topology, in contrast, is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices. A network's logical topology is not necessarily the same as its physical topology. For example, the original twisted pair Ethernet using repeater hubs was a logical bus topology with a physical star topology layout. Token Ring is a logical ring topology, but is wired a physical star from the Media Access Unit. The logical classification of network topologies generally follows the same classifications as those in the physical classifications of network topologies but 34
describes the path that the data takes between nodes being used as opposed to the actual physical connections between nodes. The logical topologies are generally determined by network protocols as opposed to being determined by the physical layout of cables, wires, and network devices or by the flow of the electrical signals, although in many cases the paths that the electrical signals take between nodes may closely match the logical flow of data, hence the convention
of
using
the
terms
logical
topology and
signal
topology
interchangeably. Logical topologies are often closely associated with Media Access Control methods and protocols. Logical topologies are able to be dynamically reconfigured by special types of equipment such as routers and switches. The study of network topology recognizes seven basic topologies: Point-to-point Bus Star Ring Mesh Tree Hybrid Daisy chain Point-to-point The simplest topology is a permanent link between two endpoints. Switched point-to-point topologies are the basic model of conventional telephony. The value of a permanent point-to-point network is unimpeded communications between the two endpoints. The value of an on-demand point-to-point connection is proportional to the number of potential pairs of subscribers, and has been expressed as Metcalfe's Law. Permanent (dedicated) 35
Easiest to understand, of the variations of point-to-point topology, is a point-to-point communications channel that appears, to the user, to be permanently associated with the two endpoints. A children's tin can telephone is one
example
of
a physical
dedicated channel.
Within
many
switched
telecommunications systems, it is possible to establish a permanent circuit. One example might be a telephone in the lobby of a public building, which is programmed to ring only the number of a telephone dispatcher. "Nailing down" a switched connection saves the cost of running a physical circuit between the two points. The resources in such a connection can be released when no longer needed, for example, a television circuit from a parade route back to the studio. Switched: Using circuit-switching or packet-switching technologies, a point-to-point circuit can be set up dynamically, and dropped when no longer needed. This is the basic mode of conventional telephony. Bus
Bus network topology In local area networks where bus topology is used, each node is connected to a single cable. Each computer or server is connected to the single bus cable. A signal from the source travels in both directions to all machines connected on the bus cable until it finds the intended recipient. If the machine address does not match the intended address for the data, the machine ignores the data. Alternatively, if the data matches the machine address, the data is accepted. Since the bus topology consists of only one wire, it is rather inexpensive to implement when compared to other topologies. However, the low cost of 36
implementing the technology is offset by the high cost of managing the network. Additionally, since only one cable is utilized, it can be the single point of failure. If the network cable is terminated on both ends and when without termination data transfer stop and when cable breaks, the entire network will be down. Linear bus The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has exactly two endpoints (this is the 'bus', which is also commonly referred to as the backbone, or trunk) – all data that is transmitted between nodes in the network is transmitted over this common transmission medium and is able to be received by all nodes in the network simultaneously .[1] Note: The two endpoints of the common transmission medium are normally terminated with a device called a terminator that exhibits the characteristic impedance of the transmission medium and which dissipates or absorbs the energy that remains in the signal to prevent the signal from being reflected or propagated back onto the transmission medium in the opposite direction, which would cause interference with and degradation of the signals on the transmission medium. Distributed bus The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has more than two endpoints that are created by adding branches to the main section of the transmission medium – the physical distributed bus topology functions in exactly the same fashion as the physical linear bus topology (i.e., all nodes share a common transmission medium). Notes: 1. All of the endpoints of the common transmission medium are normally terminated using 50 ohm resistor.
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2. The linear bus topology is sometimes considered to be a special case of the distributed bus topology – i.e., a distributed bus with no branching segments. 3. The physical distributed bus topology is sometimes incorrectly referred to as a physical tree topology – however, although the physical distributed bus topology resembles the physical tree topology, it differs from the physical tree topology in that there is no central node to which any other nodes are connected, since this hierarchical functionality is replaced by the common bus. Star
Star network topology In local area networks with a star topology, each network host is connected to a central hub with a point-to-point connection. The network does not necessarily have to resemble a star to be classified as a star network, but all of the nodes on the network must be connected to one central device. All traffic that traverses the network passes through the central hub. The hub acts as a signal repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.
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1. A point-to-point link (described above) is sometimes categorized as a special instance of the physical star topology – therefore, the simplest type of network that is based upon the physical star topology would consist of one node with a single point-to-point link to a second node, the choice of which node is the 'hub' and which node is the 'spoke' being arbitrary. 2. After the special case of the point-to-point link, as in note (1) above, the next simplest type of network that is based upon the physical star topology would consist of one central node – the 'hub' – with two separate point-to-point links to two peripheral nodes – the 'spokes'. 3. Although most networks that are based upon the physical star topology are commonly implemented using a special device such as a hub or switch as the central node (i.e., the 'hub' of the star), it is also possible to implement a network that is based upon the physical star topology using a computer or even a simple common connection point as the 'hub' or central node. 4. Star networks may also be described as either broadcast multiaccess or non broadcast multi-access (NBMA), depending on whether the technology of the network either automatically propagates a signal at the hub to all spokes, or only addresses individual spokes with each communication. Extended star A type of network topology in which a network that is based upon the physical star topology has one or more repeaters between the central node (the 'hub' of the star) and the peripheral or 'spoke' nodes, the repeaters being used to extend the maximum transmission distance of the point-to-point links between the central node and the peripheral nodes beyond that which is supported by the transmitter power of the central node or beyond that which is supported by the standard upon which the physical layer of the physical star network is based. If the repeaters in a network that is based upon the physical extended star topology 39
are replaced with hubs or switches, then a hybrid network topology is created that is referred to as a physical hierarchical star topology, although some texts make no distinction between the two topologies. Distributed Star A type of network topology that is composed of individual networks that are based upon the physical star topology connected together in a linear fashion – i.e., 'daisy-chained' – with no central or top level connection point (e.g., two or more 'stacked' hubs, along with their associated star connected nodes or 'spokes'). Ring
Ring network topology A network topology that is set up in a circular fashion in which data travels around the ring in one direction and each device on the right acts as a repeater to keep the signal strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The network is dependent on the ability of the signal to travel around the ring.
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Mesh The value of fully meshed networks is proportional to the exponent of the number of subscribers, assuming that communicating groups of any two endpoints, up to and including all the endpoints, is approximated by Reed's Law. Fully connected
Fully connected mesh topology The number of connections in a full mesh = n(n - 1) / 2. Note: The physical fully connected mesh topology is generally too costly and complex for practical networks, although the topology is used when there are only a small number of nodes to be interconnected (see Combinatorial explosion). Partially connected
Partially connected mesh topology 41
The type of network topology in which some of the nodes of the network are connected to more than one other node in the network with a point-to-point link – this makes it possible to take advantage of some of the redundancy that is provided by a physical fully connected mesh topology without the expense and complexity required for a connection between every node in the network. Note: In most practical networks that are based upon the partially connected mesh topology, all of the data that is transmitted between nodes in the network takes the shortest path between nodes,[ except in the case of a failure or break in one of the links, in which case the data takes an alternative path to the destination. This requires that the nodes of the network possess some type of logical 'routing' algorithm to determine the correct path to use at any particular time. Tree
Tree network topology The type of network topology in which a central 'root' node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the second level nodes and the top level central 'root' node, while each of the second level nodes that are connected to the top level central 'root' node will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central 'root' node being the only node that has no other node above it in the hierarchy (The 42
hierarchy of the tree is symmetrical.) Each node in the network having a specific fixed number, of nodes connected to it at the next lower level in the hierarchy, the number, being referred to as the 'branching factor' of the hierarchical tree. This tree has individual peripheral nodes. 1. A network that is based upon the physical hierarchical topology must have at least three levels in the hierarchy of the tree, since a network with a central 'root' node and only one hierarchical level below it would exhibit the physical topology of a star. 2. A network that is based upon the physical hierarchical topology and with a branching factor of 1 would be classified as a physical linear topology. 3. The branching factor, f, is independent of the total number of nodes in the network and, therefore, if the nodes in the network require ports for connection to other nodes the total number of ports per node may be kept low even though the total number of nodes is large – this makes the effect of the cost of adding ports to each node totally dependent upon the branching factor and may therefore be kept as low as required without any effect upon the total number of nodes that are possible. 4. The total number of point-to-point links in a network that is based upon the physical hierarchical topology will be one less than the total number of nodes in the network. 5. If the nodes in a network that is based upon the physical hierarchical topology are required to perform any processing upon the data that is transmitted between nodes in the network, the nodes that are at higher levels in the hierarchy will be required to perform more processing operations on behalf of other nodes than the nodes that are lower in the hierarchy. Such a type of network topology is very useful and highly recommended. Definition: Tree topology is a combination of Bus and Star topology.
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Hybrid Hybrid networks use a combination of any two or more topologies in such a way that the resulting network does not exhibit one of the standard topologies (e.g., bus, star, ring, etc.). For example, a tree network connected to a tree network is still a tree network topology. A hybrid topology is always produced when two different basic network topologies are connected. Two common examples for Hybrid network are: star ring network and star bus network A Star ring network consists of two or more star topologies connected using a multistation access unit (MAU) as a centralized hub. A Star Bus network consists of two or more star topologies connected using a bus trunk (the bus trunk serves as the network's backbone). While grid and torus networks have found popularity in high-performance computing applications, some systems have used genetic algorithms to design custom networks that have the fewest possible hops in between different nodes. Some of the resulting layouts are nearly incomprehensible, although they function quite well. A Snowflake topology is really a "Star of Stars" network, so it exhibits characteristics of a hybrid network topology but is not composed of two different basic network topologies being connected together. Definition :Daisy chain Except for star-based networks, the easiest way to add more computers into a network is by daisy-chaining, or connecting each computer in series to the next. If a message is intended for a computer partway down the line, each system bounces it along in sequence until it reaches the destination. A daisy-chained network can take two basic forms: linear and ring. A linear topology puts a two-way link between one computer and the next. However, this was expensive in the early days of computing, since each
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