02 IK IESYS e Introduction to Industrial Ethernet

Automation and Drives

Introduction to Industrial Ethernet

SITRAIN IK-IESYS / Ethernet basics

Page 1

03/2007 © Siemens AG 2007 - Subject to change without prior notice

Contents Page Indu Indust stri rial al auto automa mati tion on leve levels ls,, hor horiz izon onta tall .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 2 Indu Indust stri rial al auto automa mati tion on leve levels ls,, ver verti tica call .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 3 Unif Un ifor orm m bus bus syst system em for for all all leve levels ls .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .. 4 Industria Industriall environ environmen ment.... t.......... ........... .......... ........... ........... .......... ........... ............ ............ ............ ............ ........... ........... ............ ............ ............ ........... .......... .......... ........... .......... .... 5 Indust Ind ustria riall Ethern Ethernet et (IE) (IE) ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ..... .. 6 ISO ISO 7 lay layer model, el, part 1 ..... ...... .... ........ ...... .... ....... ....... ...... .... ........ ...... ........ ...... .... .... .... .... ........ ...... .... .... .... .... .... .... .... ........ ...... ........ ...... .... .... .... .... .... .. 7 ISO ISO 7 lay layer model, el, part 2 ..... ...... .... ........ ...... .... ....... ....... ...... .... ........ ...... ........ ...... .... .... .... .... ........ ...... .... .... .... .... .... .... .... ........ ...... ........ ...... .... .... .... .... .... .. 8 Develop Developmen mentt timeline timeline ...... ........... .......... .......... .......... ........... ........... .......... .......... ........... ............ ............ ........... .......... ........... ............ ........... ........... ........... .......... .......... .......... ..... 9 Industri Industrial al Etherne Ethernett – basic basic layout, layout, previous previously ly ...... ............ ........... .......... ........... ............ ............ ........... .......... .......... .......... .......... .......... ........... ........... ..... 10 Examp Example le of of Ether Etherne nett config configur urati ation on,, 200 2006 6 ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ..... .. 11 Classific Classificatio ation n of differen differentt types types of Ethernet Ethernet ............... .................... .......... .......... ........... ........... .......... ........... ........... .......... .......... ........... ........... ......... ........ .... 12 Etherne Ethernett variants variants,, Etherne Ethernett naming naming convent conventions ions...... ........... .......... .......... .......... .......... ........... ............ ........... .......... .......... .......... .......... ........... ........... ..... 13 Thic Thick k Ethe Ethern rnet et 10Ba 10Base se5 5 .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 14 Thin Thin Ethe Ethern rnet et 10Ba 10Base se2 2 .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .. 15 Twis Twiste tedd-pa pair ir Ethe Ethern rnet et 10Ba 10Base seT T .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... 16 Fiber Fiber-o -opti ptic c Ether Etherne nett 10Ba 10Base seF F ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ... 17 Fast Fast Ether Etherne nett 100B 100Base aseT T ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ... 18 Giga Gigabi bitt Ethe Ethern rnet et 1000 1000Ba Base seX X .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .. 19 Acces Access s me metho thods ds are are ...... ........ ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ..... 20 CSMA/C CSMA/CD D access access me metho thod, d, bus bus stru structu cture re ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ..... 21 CSMA CS MA/C /CD D acces access s me meth thod od,, proce process ss flow flow .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .. 22 CSMA/C CSMA/CD D ac acces cess s me meth thod od,, co colli llisio sion n dom domain ain ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ... 23 CSMA/CD CSMA/CD access access method, method, real-tim real-time e respons response e ..... .......... ........... ............ ........... ........... ........... .......... .......... .......... ........... ............ ........... .......... ....... .. 24 The The hub, hub, mu multi ltipo port rt repe repeate aterr ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ..... 25 The swi switch tch ..... ...... .... .... .... .... .... .... .... ........ ...... .... ........ ...... .... .... .... .... .... .... ........ ...... .... .... .... .... ........ ...... .... .... .... .... .... .... .... .... ........ ...... .... ........ ...... .... .... .... .... .... .... .. 26 Hub Hu b comp compar ared ed to swit switch ch .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .. 27 Shar Shared ed LAN LAN comp compar ared ed to to switc switche hed d LA LAN N .... ...... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .... .. 28 Switchin Switching g technolo technology, gy, part part 2 ...... ............ ........... .......... ........... ........... .......... .......... .......... ........... ........... .......... .......... ........... ............ ............ ........... .......... .......... ........ ... 29 Switchin Switching g netw network: ork: Spanni Spanning ng tree ..... .......... .......... .......... .......... ........... ............ ........... .......... .......... .......... .......... .......... .......... ........... ............ ........... .......... ........ ... 30 Network Network components components in the OSI model: model: Repeate Repeater, r, hub/bridge hub/bridge,, switch...................................... switch............................................... ......... 31 Network Network components components in the OSI model: Router and gateway........................... gateway................................................................32 .....................................32 SITRAIN traini training ng for Automation and Industrial Solutions

Page 1

IK-IESYS Ethernet basics


Industrial Industrial automation automation levels, levels, horizontal horizontal

Data management level

Managing Archiving Visualizing

Open-loop control Closed-loop control

Control level

Measuring Positioning Switching

Field level


Page 2


Industrial automation levels Industrial automation encompasses many segments. The tasks of these segments and the flow of information between them can be described using a simplified level model. Components within one level communicate over bus systems that are customized and and optimized for the functional functional requirements requirements of that level.

SITRAIN traini training ng for Automation and Industrial Solutions

Page 2



Industrial Industrial automation automation levels, levels, horizontal horizontal




Control level


Field level


Page 2


Industrial automation levels Industrial automation encompasses many segments. The tasks of these segments and the flow of information between them can be described using a simplified level model. Components within one level communicate over bus systems that are customized and and optimized for the functional functional requirements requirements of that level.


Page 2



Industrial Industrial automatio automation n levels, levels, vertical vertical




Control level


Field level


Page 3


Vertical communication communication There also needs to be vertical communication between the levels. Production specifications are passed down to the lower levels. Conversely, process-related information from the lower levels is verified and archived at the management level. However, optimal flow of information is ensured only if the networks of the individual levels work together in an optimal manner.


Page 3



Uniform bus system for all levels Internet


Control level

Field level


Page 4


Uniform bus system across all levels A largely uniform bus system is required to ensure optimal data flow across levels. The Ethernet version previously used in a commercial (office) environment with the CP/IP protocol forms the basis for this type of data integration. The automation network can be seamlessly linked to the company network and the INTERNET.

SITRAIN training for Automation and Industrial Solutions

Page 4



Industrial environment

Electrical and magnetic interference (EMC)

Vibrations

Large temperature ranges SITRAIN IK-IESYS / Ethernet basics

Corrosive atmospheres Page 5


Industrial environment Ethernet-based networking technology was developed for communication in the commercial sector. However, for installations used in the industrial rather than the office environment, additional considerations must be taken into account.


Page 5



Industrial Ethernet (IE)

High temperature compatibility of network components

Rugged mechanics and industry-standard cables and connections

EMC immunity through special shielding and the use of fiber-optic conductors

Industrial Ethernet

Increased availability through redundant network structures

Compliance with real-time requirements through appropriate network segmentation and the use of switching technology


Page 6


Industrial Ethernet Through the use of special network components, Industrial Ethernet takes the strict requirements of production/the process environment into account. However, interaction with conventional Ethernet components is also ensured.


Page 6



ISO 7 layer model, part 1 7: Application layer This layer encompasses the applicationspecific services of the various communication applications. These include basic services and protocols such as FTP file transfer, e-mail, virtual terminals, etc.

6: Presentation layer This layer ensures the independence of the different data formats used.

5: Session layer This layer organizes the dialog between the communicating partners.


Page 7


ISO 7 layer model The tasks and functions performed by communication systems are varied and complex. This is why ISO developed the OSI reference model. This 7-layer architecture specifies which protocols and services can be implemented in the individual layers. 7: Application layer This layer encompasses the application-specific services of the various communication pplications. These include basic services and protocols such as FTP file transfer, e-mail, virtual terminals, etc. 6: Presentation layer This layer ensures the independence of the different data formats used. During sending, the data to be transferred is converted to a uniform intermediate format so that it can be interpreted correctly by the connected computers. When the data is received, the intermediate format is converted to the format required by the individual computers. 5: Session layer This layer organizes dialog between the communicating partners. It establishes, maintains and clears the connection and synchronizes the flow of data between the application processes.


Page 7



ISO 7 layer model, part 2 4: Transport layer This layer is primarily concerned with ensuring that data actually arrives at its destination. 3: Network layer This layer is responsible for transferring data packets between the source and destination. This includes routing, addressing of other networks and data flow control.

2: Data link layer This layer transfers bits between two systems. This includes controlling access to the transmission medium (access method), as well as detection and elimination/signaling of transmission errors.

1: Physical layer This layer is responsible for the correct transmission of individual bits over the physical channel. The main activities involved here are the encoding of signals and specification of the transmission medium and transmission devices.


Page 8


4: Transport layer This layer is primarily concerned with ensuring that data actually arrives at its destination. It is able to trigger data retransmission if data were lost.

3: Network layer This layer is responsible for transferring data packets between the source and destination. This includes routing, addressing of other networks and data flow control. 2: Data link layer This layer transfers bits between two systems. This includes controlling access to the transmission medium (access method), as well as detection and elimination/signaling of transmission errors. 1: Physical layer This layer is responsible for correct transmission of individual bits over the physical channel. The main activities involved here are the encoding of signals and specification of the transmission medium and transmission devices.


Page 8



Development timeline

Industrial Ethernet bus system SINEC H1

1985

Optical Industrial Ethernet SINEC H1FO

1989


OLM/ELM Twisted-pair cabling/FOC Web server

Fast Ethernet switches FC cabling MOBIC WLAN

1996

GIGABIT Modular switches Industrial security Real-time Ethernet fieldbus/PROFINET IWLAN Rapid roaming

2000

Page 9

2005 03/2007 © Siemens AG 2007 - Subject to change without prior notice

History 1985

Ethernet in industrial applications for SIMATIC and PC/PG

1991

PROFIBUS products for SIMATIC S5 and PC/PG

1993

Fiber-optic cables for PROFIBUS

1994

AS-Interface for SIMATIC and PC/PG

1994

Flexible fiber-optic-cable networks for PROFIBUS by means of OLM

1995

Industrial twisted pair cables for Ethernet

1996

Flexible FOC/ITP networks for Ethernet via optical/electrical link module

1998

FastConnect cable system for PROFIBUS

1998

Internet technology used in automation: Market launch of the first IT CPs for SIMATIC S7

1999:

Switching technology and high-speed redundancy for Industrial Ethernet via OSM/ORM

1999

Fast Ethernet for SIMATIC and PC/PG

2000

FastConnect cable system for Industrial Ethernet

2001

First industrial WebPad on the market: MOBIC T8 Mobile Industrial Communicator

2001

PROFINET: Distributed and open automation solutions based on Industrial Ethernet

2003

Industrial wireless LAN in the industrial environment


Page 9



Industrial Ethernet – basic layout, previously

Triaxial cable

Fan-out unit

Star coupler KYDE Fiber-optic cable


Page 10


Technical data Standard

Ethernet to IEEE 802.3/ISO 8802.3 or Ethernet Blue Book

Access method

CSMA/CD (Carrier Sense Multiple Access/Collision Detection)

Transmission rate

10/100 Mbit/s

Transmission

Electrical: Double-shielded coaxial cable, industrial twisted pair

medium

Optical:

Max. no. of nodes

Over 1,000

Fiber-optic cable (glass)

Approx. network range Electrical: 1.5 km Optical:

4.5 km, 150 km, or 1300 km if switches are used

Topology

Line, tree, star, redundant ring

Automation

Management and cell levels

level


Page 10



Example of Ethernet configuration, 2006 MES level Computer

Production master computer

Service computer

Data server Firewall

Office network Workstation computer Server

HMI

Automation network

Automation cells

Service computer



Page 11

Page 11




Classification of different types of Ethernet Ethernet

Fast Ethernet

Gigabit Ethernet

IEEE standard

802.3

802.3u

802.3z

Data rate

10 Mbit/s

100 Mbit/s

1,000 Mbit/s

Duration of one bit

0.1 microsecond

0.01 microsecond

0.001 microsecond

Slot time (cable action period)

After 512 bits;

After 512 bits;

After 4,096 bits;

Length of collision domain

2,000 m

200 m

20 m

Access methods

CSMA/CD

CSMA/CD

CSMA/CD

Largest data packet

1,518 bytes

1,518 bytes

1,518 bytes

Smallest data packet

64 bytes

64 bytes

64 bytes

Length of address field

48 bits

48 bits

48 bits

Topology

Star, tree, line

Star, tree, line

Star, tree, line

Supported media

Coaxial: 10 Base5 Twisted pair:10 BaseT Fiber optic: 10 Base-FL

Twisted pair: 10 BaseT Fiber optic: 10 Base-FL

Twisted pair: 10 BaseT Fiber optic: 10 Base-FL

Network components

Bus coupler (transceiver) Optical link module, electrical link module, active star coupler, mini UYDE, MINI OTDE

OSM, ESM

SCALANCE

Max. length of a TP path

100 m

100 m

100 m

Max. length of a fiber-opticcable path

Multimode: 300 m

Multimode: 3,000 m Single mode: 26 km

Multimode: 3,000 m Single mode: 26 km


Page 12


IEEE standard 802.3 The international Institute of Electrical and Electronic Engineers (IEEE) defined the first Ethernet standard, 10BASE5, in 1985. This standard, which was based on a coaxial cable transmission medium, laid the foundations for the first Industrial Ethernet. This network, which went under the name SINEC H1 and was improved by the introduction of a triaxial cable for the industrial environment, has been used successfully in process and production automation for many years. Since the very beginning, both the IEEE standard and the SIMATIC NET product range have constantly been updated with the latest technologies, which further improve the flexibility and performance capability of Ethernet networks. This includes the introduction of transmission via fiber-optic and twisted-pair cables and the tenfold increase of the transmission rate by means of Fast Ethernet. All versions are based on baseband transmission and the CSMA/CD access method. Baseband transmission technology Ethernet to IEEE 802.3 uses baseband transmission technology. This means that data is transferred to the transmission medium (e.g., connecting cable) unmodulated, in a pulse shape. The transmission medium forms a single transmission channel, which must share its capacity with the connected data terminals. All connected data terminals receive the data transmitted via the medium at the same time. Only one data terminal may send data at any one time. If several data terminals send data at the same time, this will lead to data collision on the transmission medium. The data signals of the senders concerned will destroy one another. Transmission rights need to be assigned in order to regulate access to the shared transmission medium by the data terminals. The IEEE 802.3 standard regulates access in accordance with the CSMA/CD method. SITRAIN training for Automation and Industrial Solutions

Page 12



Ethernet variants, Ethernet naming conventions Transmission medium

Standard 10 Mbit/s systems 10Base5

Coaxial cable (3/8 inch)

10Base2

Coaxial cable (3/16 inch)

10BaseT

Fiber-optic cable

100 Mbit/s systems 100BaseT

Fiber-optic/Twisted pair

1,000 Mbit/s systems 1000BaseX


Fiber-optic/Twisted pair

Page 13


Ethernet naming conventions Standard IEEE 802.3 defines several Ethernet versions, whose main differences lie in their transmission rates and the cabling technology they use. The naming conventions shown were laid down in order to distinguish between the different versions. Data rate in Mbit/s This field indicates the applicable data rate in Mbit/s. It can range from 10 Mbit/s to 10,000 Mbit/s. The original data rate of 3 Mbit/s and the 1 Mbit/s version are no longer used. Transmission method Base (baseband) In a baseband, digital signals are fed directly into the cable as pulses, i.e., the signals are transported unmodulated (10Base5). Broad (broadband) In a broadband system, multiple carrier frequencies are used and the signal to be transmitted is modulated up to these carrier frequencies. This enables multiple messages to be transmitted simultaneously and independently (10Broad36). Max. length/Cable type The data in this field can have different meanings. It can be used to specify the maximum cable length per segment, in 100 m (10Base5 = 500 m). It can also indicate the cable type. The name 10BaseT is used for twisted pair cables and 10BaseF is used for fiber-optic cables.


Page 13



Thick Ethernet 10Base5


Page 14


Thick Ethernet 10Base5 The figure above shows the original cabling of an Ethernet network segment. In this bus structure, the Ethernet coaxial cable is routed via every station and every station is connected via a short connecting cable.

Coaxial cable (yellow cable) Ethernet 10Base5 uses a 3/8-inch, 50-ohm coaxial cable. Due to emission and attenuation, the maximum length for a cable segment is 500 m. This type of cable is more uncommon today as it is not particularly easy to use. Terminator A coaxial segment must be terminated at each end with 50-ohm terminators. This prevents reflections and associated signal corruption. Controller The Ethernet controller executes the functions of the MAC layer. These include data compilation, the calculation of checksums for sent frames, and the checking of checksums for received frames. The controller is connected to the transceiver by means of the transceiver cable. Transceiver Data terminals are connected to the coaxial cable by means of transceivers, which are also known as MAUs (Medium Attachment Units). There are two different designs, which use a different type of connector. Coaxial cable connector and vampire terminal connection. SITRAIN training for Automation and Industrial Solutions

Page 14



Thin Ethernet 10Base2

Coaxial cable

BNC T fitting

BNC connector

Exterior insulation

Dielectric Dielectric

Ethernet controller

Ground

Central conductor

50-ohm terminating resistor


Shielding Shielding

Page 15


Thin Ethernet 10Base2 This version uses a thin coaxial cable. Although this type of cable does lead to decreased attenuation and is less immune to interference, it is more than adequate for smaller networks. As this version does not cost as much as that using the yellow cable, it is known as Cheapernet.


Page 15



Twisted-pair Ethernet 10BaseT


Page 16


Twisted-pair Ethernet 10BaseT 10BaseT refers to Ethernet networks based on twisted pair cabling. The bus topology is a star topology. A hub (multiport repeater) forms the central point from which twisted cable pairs lead to the individual stations. These networks are very common and cost-effective. Twisted pair:

A twisted pair usually consists of a four-core copper cable twisted in pairs. A distinction is made between shielded (STP) and unshielded (UTP) cables. The maximum transmission length depends on the shielding; however, it must not exceed 100 m.

Cable category:

UTP and STP describe the cable's design, but UTP cables are further broken down into categories defining the requirements of the cable and plug-in connector. Cables used for 10BaseT must meet the specifications for category UTP-3 as a minimum.

Plug-in connector:

Conventional twisted pair Ethernet cabling uses 8-pin (Western) connectors. There is a wide range of different types of these connectors, such as the new RJ45 plug connector.

Hub:

Hubs are characteristic of networks with star or tree topologies. A hub has numerous ports for connecting stations and other devices. If signals are sent, the hub copies these signals and passes them on to ALL the connected stations.


Page 16



Fiber-optic Ethernet 10BaseF Fiber-optic cable


Page 17


Fiber-optic Ethernet 10BaseF 10BaseF refers to a series of standards that use fiber-optic cables as a transmission medium. Due to the long-range transmission paths, these systems are often used to connect distant network segments.

Fiber-optic cables

In fiber-optic cables, information is transmitted over thin glass fibers using extremely short light pulses. The cable contains two glass fibers, enabling simultaneous sending and receiving (FD = full duplex).


Page 17



Fast Ethernet 100BaseT

Transmission medium

Standard

Max. distance

100BaseTX

2 pairs, category 5 UTP

100 m

100BaseFX

Multi-mode fiber

400 m

100BaseT4

4 pairs, min. category 3 UTP

100 m

100BaseT2

2 pairs, min. category 3 UTP

100 m


Fast Ethernet

Page 18


Fast Ethernet is an LAN standard for a transmission rate of 100 Mbit/s. It is a natural expansion of 10BaseT and the two are compatible. New capabilities, such as full duplex, have also been added. There are several versions of 100BaseT, which have different physical layers and, as a result, different transmission media.


Page 18



Gigabit Ethernet 1000BaseX Transmission medium

Standard

Max. distance

1000BaseTX

4 pairs, category 5 UTP

100 m

1000BaseCX

2 pairs, STP

25 m

1000BaseSX

Multi-mode fiber (short wave)

1000BaseLX

Mono-mode/Multi-mode fiber (long wave)


Page 19

275 m

5,000/550 m


Gigabit Ethernet Gigabit Ethernet technology provides a data transfer rate of 1,000 Mbit/s. This LAN system is also based on the CSMA/CD method, but is uses optimized physical transmission and logical signal encoding. Gigabit Ethernet is compatible with the 802.3 standard and provides seamless integration into existing networks.


Page 19



Access methods are .......

Deterministic Deterministic (can (canbe bepredicted) predicted)

Stochastic Stochastic (random) (random)

Central Central


Distributed Distributed

Page 20


Stochastic access (random) The station wishing to transmit data transfers it to a free channel without first seeking permission to do so. Resolving issues arising from collisions, e.g., if a transmission is repeated following a random delay time - Simple - Fast if there is not much traffic - Delay time fluctuates randomly with no upper limit - CSMA/CD for local networks (Carrier Sense Multiple Access with Collision Detection) Deterministic access (can be predicted) An explicit order is defined, in accordance with which stations transmit data to free channels. Stations are permitted to transmit data in a specific order (e.g., cyclically) - The need to seek permission minimizes the delay time - An upper limit can be specified for the delay time, priorities if necessary Important examples: Token method for LAN polling method


Page 20



CSMA/CD access method, bus structure

Carrier Sensing (CS):

All stations continuously listen to the transmission medium.

Multiple Access (MA):

Equal competing access of all stations wishing to send data.

Collision Detection (CD): Listening to the medium during the transmission process, detection of any collisions.


Page 21


Ethernet bus structure In conventional Ethernet technology, all stations are attached to the same cable line (linear bus, linear structure). The Ethernet stations are completely independent, they are not synchronized by a higher-level network master (as with PROFIBUS DP ) or by a token that is passed around (as with PROFIBUS). So, the stations compete to access the bus, meaning that access control is needed. Access control Access control is the responsibility of the data link layer (layer 2). This layer has to detect when two or more stations are attempting to send data at the same time. To this end, Ethernet uses the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method. Carrier Sensing (CS)

All stations continuously listen to the transmission medium.

Multiple Access ( MA) Equal competing access of all stations wishing to send data.

Collision Detection (CD) Listening to the medium during the transmission process, detection of any collisions.


Page 21



CSMA/CD access method, process flow

1

2

3


Page 22


Carrier Sensing (CS)Before sending, a station first listens to the line to determine whether data exchange is already taking place between stations. Points 1 and 2:

If the transmission medium is available, the station begins its transmission. However, because other stations can also transmit at the same time (MA), the sender listens to the transmission in order to detect any possible collisions. If transmission takes places with no collisions, station 3 recognizes from the receiver address inside the data packet that it is the intended recipient and accepts the data. All other stations ignore the packet.

Point 3:

A certain execution time must be taken into account for all lines. For example, station 2 may erroneously consider the bus to be available because it has not yet received the signal sent by station 1. If station 2 now starts sending, a collision occurs. If a sending station detects a collision, it immediately stops transmission and sends a collision signal (4 to 6 bytes with a special bit pattern). All sending stations then stop transmission, and the line is quiet.

After receiving a collision signal, the stations wishing to send wait a random delay time and then attempt to resend the data. If this new attempt also fails, the delay time becomes longer. After 16 collisions in succession, the access algorithm is aborted and the higher-level software must decide how to proceed. This flowchart again provides an overview of how the CSMA/CD access method works. SITRAIN training for Automation and Industrial Solutions

Page 22



CSMA/CD access method, collision domain


Page 23


Collision domain A collision domain is a network area in which collisions may occur between sending stations as a result of the CSMA/CD method. It also includes all Ethernet segments connected to the collision domain over a repeater (signal amplifier).


Page 23



CSMA/CD access method, real-time response Average delay

Network loading


Page 24


Real-time response This graph shows that, if CSMA/CD is used and the load on the bus increases, transmission times increase sharply too, as there is a greater risk of collisions. A real-time response can, therefore, not be guaranteed. This means that the network must be appropriately segmented in order to reduce the likelihood of a collision.


Page 24



The hub, multiport repeater


Page 25


The hub Functionally, the hub is the counterpart of the repeater in a twisted-pair cabled network with a star topology. As it features multiple ports, it is also known as a multiport repeater. Like repeaters, hubs are used as a simple way of increasing the expansion of a network. • Hubs work on the physical layer (layer 1) of the OSI model. • Their sole function is to work as a distributor. All stations connected to a hub share the entire bandwidth made available via the hub (e.g., 10 Mbit/s or 100 Mbit/s). • The connection between the computer and the hub only has access to this bandwidth temporarily. • A hub accepts a data packet and sends it to all other ports. This procedure results in all ports being occupied. This technology is not particularly effective, but it does have the advantage that hubs of this type are easy and cheap to manufacture. • Two hubs are connected via an uplink port on a device or by means of a crossover cable (the transmission and reception cables are crossed).

• Special stackable hubs are also available, which, depending on the make, can be cascaded with connecting cables. • The number of possible stations can be increased by connecting several hubs. However, there is a limit to the number of stations which can be connected (repeater rule on previous slide).


Page 25



The switch Collision domain 1

Collision domain2 Collision domain 3


Page 26


The switch The switch is a high-speed packet-switching system used to divide local networks into segments. Like the bridge, the switch operates on layer 2 of the ISO/OSI reference model. Every port of a switch forms a separate network segment with its own collision domain. This enables a switch to not only increase the performance capability of the network as a whole, but also that of each individual segment. Function

Within the switch, a particular port is assigned to each MAC address in a routing table. An incoming data packet is transmitted directly to the port of the receiver, based on its destination address. A switch can establish multiple connections simultaneously between pairs of ports, thus considerably decreasing collision overhead.


Page 26



Hub compared to switch Hub

A

Switch

A D G

B

If A transmits data to B, this data is also forwarded to all the other users connected to the hub.

General

B

C

F

The switch transfers a frame to a certain port, based on its destination address. It also enables multiple connections to be established between ports simultaneously. Every port can access the full Ethernet bandwidth and work in, among others, full-duplex mode.

The 10 Mbit/s Ethernet bandwidth is equally available to all nodes, which must share it.


H E

Page 27


The individual ports on a switch can send and receive data independently of one another. The ports are interconnected via an internal high-speed bus (backplane). As far as possible, data buffers ensure that data frames are not lost. Packets/frames can be forwarded in a switch in the operating modes below, which differ in terms of their delay times and error compensation:

Cut through

This is a very fast method, which is primarily used by better switches. The switch only looks at the MAC destination address of the received frame, makes a decision as regards forwarding and forwards the frame accordingly. The frame is not checked for errors, in order to save time. Therefore, the switch also forwards damaged frames, which must then be picked up by other layer-2 devices or higher network levels.

Store and forward

This is the most basic, but also the slowest switching method, which can be performed by every switch. The switch makes a forwarding decision based on the MAC destination address as usual, then uses the frame to calculate a checksum, which it compares to the CRC value stored at the end of the packet. If there is any discrepancy, the frame is rejected. This ensures that no faulty frames are distributed in the LAN. Store and forward is the only switching method which can be used if the sender and receiver are working at different transmission rates or with duplex modes, or if they are using different transmission media.

Spanning tree

Bridges and switches communicate via the (rapid) spanning tree algorithm (IEEE 802.3d,w) to prevent data packets looping endlessly within a network. In a meshed system, various connections are temporarily switched to standby mode in order to create a tree topology.


Page 27



Shared LAN compared to switched LAN

Data traffic

Shared LAN

Switched LAN

•

•

• • •

All network nodes share the available bandwidth, e.g., 10 Mbit/s Liable to collisions All frames pass through all segments Repeaters, hubs, optical link modules, etc., require compliance with configuration rules and restrict the maximum range SITRAIN IK-IESYS / Ethernet basics

Fragment free

• •

Each individual collision domain has access to the entire bandwidth Local data traffic remains local, so the load is separated Maximum range for each collision domain

Page 28


This is faster than Store and Forward, but slower than Cut Through. It is more commonly found on better switches. It checks whether a frame reaches the minimum length of 64 bytes required by the Ethernet standard and then transmits it to the destination port immediately, without carrying out a cyclic redundancy check. Fragments below 64 bytes are usually "debris" created by a collision, which no longer represent a meaningful packet.

Advantages of switches • If two network nodes receive data simultaneously there are no collisions (see CSMA/CD), as the switch can internally transfer both transmissions simultaneously via the backplane. If data arrives at an output port faster than it can be forwarded over the network, it is buffered. If possible, flow control is used to prompt the sender(s) to send the data more slowly. • If eight computers are connected via an 8-port switch and two computers are both sending data to one another at full speed, so that four full-duplex connections are established, in theory you have eight times the speed you would achieve with a corresponding hub where all the devices would share the maximum bandwidth - 4 * 200 Mbit/s as opposed to 100 Mbit/s. However, two aspects contradict this theoretical calculation: For one thing, the internal processors are not designed to run all ports at full speed and a hub with multiple computers will never reach 100 Mbits either, as the more collisions that occur, the more load the network is subjected to, which in turn restricts the bandwidth. • The switch records in a table which station can be reached via which port. During continuous operation, the MAC sender addresses of the forwarded frames are saved. Data is then only forwarded to the port where the receiver is actually located. Packets with unknown MAC destination addresses are treated as broadcasts and forwarded to all ports, with the exception of the source port.


Page 28



Switching technology, part 2 Cut through The switch only looks at the MAC destination address of the received frame, makes a decision as regards forwarding and forwards the frame accordingly. The frame is not checked for errors in order to save time. Therefore, the switch also forwards damaged frames, which must then be picked up by other layer-2 devices. Store and forward This is the most basic, but also the slowest switching method, which can be performed by every switch. The switch makes a forwarding decision based on the MAC destination address as usual, then uses the frame to calculate a checksum, which it compares to the CRC value stored at the end of the packet. If there is any discrepancy, the frame is rejected. This ensures that no faulty frames are distributed in the LAN. Store and Forward is the only switching method which can be used if the sender and receiver are working at different transmission rates or with duplex modes, or if they are using different transmission media. Spanning tree Bridges and switches communicate via the (rapid) spanning tree algorithm (IEEE 802.3d,w) to prevent data packets looping endlessly within a network. In a meshed system, various connections are temporarily switched to standby mode in order to create a tree topology.


Page 29


General

The individual ports on a switch can send and receive data independently of one another. The ports are interconnected via an internal high-speed bus (backplane). As far as possible, data buffers ensure that data frames are not lost. Packets/frames can be forwarded in a switch in the operating modes below, which differ in terms of their delay times and error compensation:

Cut through

This is a very fast method, which is primarily used by better switches. The switch only looks at the MAC destination address of the received frame, makes a decision as regards forwarding and forwards the frame accordingly. The frame is not checked for errors, in order to save time. Therefore, the switch also forwards damaged frames, which must then be picked up by other layer-2 devices or higher network levels.

Store and forward

This is the most basic, but also the slowest switching method, which can be performed by every switch. The switch makes a forwarding decision based on the MAC destination address as usual, then uses the frame to calculate a checksum, which it compares to the CRC value stored at the end of the packet. If there is any discrepancy, the frame is rejected. This ensures that no faulty frames are distributed in the LAN. Store and Forward is the only switching method which can be used if the sender and receiver are working at different transmission rates or with duplex modes, or if they are using different transmission media.

Spanning tree

Bridges and switches communicate via the (rapid) spanning tree algorithm (IEEE 802.3d,w) to prevent data packets looping endlessly within a network. In a meshed system, various connections are temporarily switched to standby mode in order to create a tree topology.


Page 29



Switching network: Spanning tree

Fiber-optic cable


Page 30


Spanning tree In order to prevent data packets from looping in the network, various connections are switched to standby with closed machines so that a tree topology is created. Bridges and switches communicate over the spanning tree protocol (IEEE 802.1d) or the rapid spanning tree protocol (IEEE 802.1w). Their message frames are represented in yellow. Switches of the SCALANCE X400 product range offer the time-optimized variant. In the event of an error, they only require a few seconds to reconfigure new trees.


Page 30



Network components in the OSI model: Repeater, hub/bridge, switch Repeater/hub (star hub) - "Refreshes" and forwards the incoming signals - Immediately forwards the information to all partners connected to the repeater/hub. - No filtering, load separation or intervention in communication - The use of repeaters/hubs is restricted to a single collision domain.

Application

Application

Presentation

Presentation

Session

Session

Transport

Transport

Network Data Link Physical

Network Repeater / Hub Physical

Physical

Data Link Physical

Bridge/switch - Connects collision domains. The maximum extension is only limited by the delay of the data packets between two nodes. - Load separation: Data traffic can be spread over different subsegments. - Data traffic is not interrupted if individual stations fail. - Parallel communication SITRAIN IK-IESYS / Ethernet basics


Page 31

Page 31

Application

Application

Presentation

Presentation

Session

Session

Transport

Transport

Network

Bridge / Switch

Network

Data Link

Data Link

Data Link

Data Link

Physical

Physical

Physical

Physical



02 IK IESYS e Introduction to Industrial Ethernet

Recommend Documents