iso layers & ethernet basics

Overview of TopicsOverview of Topics Introduction to networksIntroduction to networks ISO OSI 7-layer Reference ModelISO OSI 7-layer Reference Model Ethernet and IEEE 802.3Ethernet and IEEE 802.3 TCP/IPTCP/IP Practical implementation informationPractical implementation information

Types of LANTypes of LAN ProprietaryProprietary

– e.g.. Geniuse.g.. Genius Ethernet - IEEE 802.3Ethernet - IEEE 802.3

– Most widely used networkMost widely used network MAP - IEEE 802.4MAP - IEEE 802.4

– MManufacturing anufacturing AAutomation utomation PProtocolrotocol IBM Token Ring - IEEE 802.5IBM Token Ring - IEEE 802.5

– 4 Mbit s4 Mbit s-1-1 token passing ring network token passing ring network FDDIFDDI

– FFibre ibre DDistributed istributed DData ata IInterfacenterface– 100 Mbit s100 Mbit s-1-1 token passing dual Fiber-optic ring network token passing dual Fiber-optic ring network

Network TopologiesNetwork Topologies

Star

Ring

Bus

Tree

Definition of the modelDefinition of the model Details of the function of each layerDetails of the function of each layer Sending data using the modelSending data using the model OSI terminologyOSI terminology

ISO OSI 7-layer Reference ISO OSI 7-layer Reference ModelModel

Definition of the 7-layer ModelDefinition of the 7-layer Model

The ISO (The ISO (IInternational nternational SStandards tandards OrganizationOrganization) defines the OSI () defines the OSI (OOpen pen SSystems ystems IInterconnection) reference model nterconnection) reference model as consisting of 7 layers:as consisting of 7 layers:

Layer 1Layer 2Layer 3Layer 4Layer 5Layer 6Layer 7

User Layer

Physical Link

Each layer specifies functions necessary to provide a Each layer specifies functions necessary to provide a defined set of services to the layer above itdefined set of services to the layer above it

Each layer requests and uses the services of the layer Each layer requests and uses the services of the layer below itbelow it

Each layer effectively isolates the details of implementation Each layer effectively isolates the details of implementation in the layers belowin the layers below

The characteristics of a layer may thus be changed without The characteristics of a layer may thus be changed without impacting other layersimpacting other layers

All layers are required for end-to-end connection of a link All layers are required for end-to-end connection of a link and the full transmission of a set of dataand the full transmission of a set of data

– i.e... an international telephone calli.e... an international telephone call

Definition of the 7-layer Model Definition of the 7-layer Model (cot...)(cot...)

Depending upon the network, layers may be Depending upon the network, layers may be small or non-existentsmall or non-existent

Layers are intended to be implemented as Layers are intended to be implemented as separate programsseparate programs

In practice, layers are often combined into In practice, layers are often combined into one program that achieves the functions of one program that achieves the functions of two or more layerstwo or more layers


Physical

Data Link

Network

Transport

Session

Presentation

Application

User

The layers of the 7-layer model are: The layers of the 7-layer model are:

Physical

Data Link

Network

Transport

Session

Presentation

Application

User

Host A Host B

Presentation protocol

Network protocol

Data Link protocol

Physical protocol

Application protocol

Transport protocol

Session protocol

LayerName of unitexchanged

7654321

A P D U

P P D U

S P D U

T P D U

Packet

Frame

Bit

D U = Data Unit


Layer 1Layer 1

Physical LayerPhysical Layer Responsible for sending a bit of data from Responsible for sending a bit of data from

one device to another deviceone device to another device Includes the physical link (hardware and Includes the physical link (hardware and

connectors) and the electronics necessary to connectors) and the electronics necessary to modulate the linkmodulate the link

Layer 2Layer 2Data Link LayerData Link Layer Responsible for transmitting data frames without Responsible for transmitting data frames without

errorserrors Solves problems caused by lost frames, corrupted Solves problems caused by lost frames, corrupted

frame and duplicated frames frame and duplicated frames Split into two actual layersSplit into two actual layers

–LLC - Logical Link ControlLLC - Logical Link Control Performs error detection and recoveryPerforms error detection and recovery

–MAC - Media Access ControlMAC - Media Access Control Performs transmission of packetsPerforms transmission of packets Different MAC for each network typeDifferent MAC for each network type

Layer 3Layer 3

Network LayerNetwork Layer Determines how a packet is routed from source to Determines how a packet is routed from source to

destinationdestination–Could be fixed for a simple networkCould be fixed for a simple network–Could be dynamically decided for each packet for a Could be dynamically decided for each packet for a

complex networkcomplex network Keeps a count of amount of data transmitted for billing Keeps a count of amount of data transmitted for billing

purposespurposes Translates network addresses where the destination is Translates network addresses where the destination is

on a different network to the sourceon a different network to the source

Layer 4Layer 4

Transport LayerTransport Layer Takes data from the session layer, splits it up into Takes data from the session layer, splits it up into

smaller pieces if required and passes these to the smaller pieces if required and passes these to the network layernetwork layer

Ensures that the data is received by the other deviceEnsures that the data is received by the other device May be responsible for multiplexing many data routes May be responsible for multiplexing many data routes

for improved speed in transmitting datafor improved speed in transmitting data Takes care of multi-programmed (i.e.... parallel Takes care of multi-programmed (i.e.... parallel

tasking) communications sessionstasking) communications sessions

Layer 5Layer 5Session LayerSession Layer Establishes sessions between two devicesEstablishes sessions between two devices

– i.e.... for transferring a filei.e.... for transferring a file Manages dialogue controlManages dialogue control

– i.e... one-way or two-way data flowi.e... one-way or two-way data flow Performs token managementPerforms token management

– i.e... to ensure that both sides do not attempt the i.e... to ensure that both sides do not attempt the same operation at the same timesame operation at the same time

Performs synchronizationPerforms synchronization– i.e... to ensure that data is not transmitted i.e... to ensure that data is not transmitted

redundantly, after a system crash for exampleredundantly, after a system crash for example

Layer 6Layer 6

Presentation LayerPresentation Layer Performs functions concerning syntax and Performs functions concerning syntax and

semantics of informationsemantics of information–These are functions requested frequently enough These are functions requested frequently enough

to warrant a specific solutionto warrant a specific solution–Examples are the data formatExamples are the data format

i.e... ASCII, floating point, integeri.e... ASCII, floating point, integer

May also perform data encryption and May also perform data encryption and compressioncompression

Layer 7Layer 7

Application LayerApplication Layer Contains a variety of protocols to allow Contains a variety of protocols to allow

communication of datacommunication of data– i.e... MMS, virtual terminal software, file transfer, i.e... MMS, virtual terminal software, file transfer,

SRTPSRTP

User LayerUser Layer

The User’s Application!The User’s Application! This is the program that the user is This is the program that the user is

concerned withconcerned with The application must communicate with The application must communicate with

another application on another machine, another application on another machine, thus requiring the services of the relevant thus requiring the services of the relevant protocol in the application layerprotocol in the application layer

Ethernet and IEEE 802.3Ethernet and IEEE 802.3

History of Ethernet and IEEE 802.3History of Ethernet and IEEE 802.3 What is Ethernet?What is Ethernet? TerminologyTerminology Introduction to EthernetIntroduction to Ethernet Extending EthernetExtending Ethernet

History of Ethernet/IEEE 802.3History of Ethernet/IEEE 802.3

Ethernet was co-developed by Digital Ethernet was co-developed by Digital Equipment, Intel and Xerox in 1980 (Robert Equipment, Intel and Xerox in 1980 (Robert Metcalf)Metcalf)

The IEEE developed the 802.3 standard in 1982, The IEEE developed the 802.3 standard in 1982, based on Ethernetbased on Ethernet

IEEE802.3 is based on Ethernet but is not IEEE802.3 is based on Ethernet but is not identicalidentical

Over 50% of currently installed networks use Over 50% of currently installed networks use IEEE802.3IEEE802.3

What is Ethernet?What is Ethernet? Ethernet is the bottom one and a half layers of the ISO Ethernet is the bottom one and a half layers of the ISO

OSI 7-layer reference modelOSI 7-layer reference model Layer 1 (Physical Layer) is defined as IEEE 802.3Layer 1 (Physical Layer) is defined as IEEE 802.3 Layer 2 (Data Link Layer) Medium Access Control Layer 2 (Data Link Layer) Medium Access Control

(MAC) is defined by IEEE 802.3(MAC) is defined by IEEE 802.3 Layer 2 (Data Link Layer) Link Layer Control (LLC) is Layer 2 (Data Link Layer) Link Layer Control (LLC) is

defined by IEEE 802.2defined by IEEE 802.2 Layers 3 to 7 are software and outside the scope of Layers 3 to 7 are software and outside the scope of

the Ethernet descriptionthe Ethernet description

Layer 1Layer 2

Physical Link

MACLLC

IEEE 802.3

IEEE 802.2

Ethernet TerminologyEthernet Terminology EthernetEthernet

– The cable that connects nodesThe cable that connects nodes TransceiverTransceiver

– A device that taps onto the Ethernet cableA device that taps onto the Ethernet cable– Usually a small box with some LEDs to indicate trafficUsually a small box with some LEDs to indicate traffic

Drop cableDrop cable– A cable to connect the transceiver to the nodeA cable to connect the transceiver to the node

HeartbeatHeartbeat– A false collision signal sent on the drop cable after A false collision signal sent on the drop cable after

transmitting datatransmitting data– Used to verify that the collision detection system is Used to verify that the collision detection system is

workingworking

IEEE terminologyIEEE terminology IEEE802.3IEEE802.3

– The standard that defines “Ethernet”The standard that defines “Ethernet” MAUMAU

– Media Access Unit - a transceiverMedia Access Unit - a transceiver AUIAUI

– Attachment Unit Interface - a 15 pin D connector that the drop Attachment Unit Interface - a 15 pin D connector that the drop cable plugs intocable plugs into

AUI cable AUI cable – A drop cableA drop cable

SQESQE– Signal Quality Error - heartbeat testSignal Quality Error - heartbeat test

AAUIAAUI– Apple Attachment Unit Interface - a 14 pin connector that the Apple Attachment Unit Interface - a 14 pin connector that the

drop cable plugs intodrop cable plugs into

Other TerminologyOther Terminology SegmentSegment

– A single section of Ethernet cableA single section of Ethernet cable PacketPacket

– An Ethernet message comprising data and control informationAn Ethernet message comprising data and control information FrameFrame

– The actual message sent on the LANThe actual message sent on the LAN ServerServer

– A device on a network that provides a service to other devicesA device on a network that provides a service to other devices ClientClient

– A device that requests services from a serverA device that requests services from a server

Introduction to EthernetIntroduction to Ethernet

Characteristics of EthernetCharacteristics of Ethernet Ethernet cable typesEthernet cable types

Characteristics of EthernetCharacteristics of Ethernet High speedHigh speed

–10 Mbits s10 Mbits s-1-1

CSMA/CD (non-deterministic)CSMA/CD (non-deterministic)–CCarrier arrier SSense ense MMultiple ultiple AAccess with ccess with CCollision ollision DDetectionetection

Devices sense a carrier and refrain from transmitting if the Devices sense a carrier and refrain from transmitting if the carrier is busycarrier is busy

Multiple devices have equal access to a single carrierMultiple devices have equal access to a single carrier If two devices transmit simultaneously a collision occurs - If two devices transmit simultaneously a collision occurs -

this is detected and both devices back offthis is detected and both devices back off

Wide variety of cable typesWide variety of cable types

Ethernet Cable TypesEthernet Cable Types

10Base5 - Thickwire10Base5 - Thickwire 10 Mbit s10 Mbit s-1-1, Baseband, Baseband Each segment may be up to 100 nodes, 500 metersEach segment may be up to 100 nodes, 500 meters Uses 50 ohm shielded coaxial cable, 10 mm outside Uses 50 ohm shielded coaxial cable, 10 mm outside

diameter.diameter. N Series connectors or “Vampire” connectorsN Series connectors or “Vampire” connectors Nodes must be spaced at 2.5 meter intervalsNodes must be spaced at 2.5 meter intervals

– or multiple of 2.5 metersor multiple of 2.5 meters Terminate 50 ohm at each endTerminate 50 ohm at each end Earth each segment at one point onlyEarth each segment at one point only

Ethernet Cable Types (cot...)Ethernet Cable Types (cot...)

10Base2 - Thinwire10Base2 - Thinwire 10 Mbit s10 Mbit s-1-1, Baseband, Baseband Also known as cheapernetAlso known as cheapernet Each segment may be up to 30 nodes, 185 metesEach segment may be up to 30 nodes, 185 metes Uses 50 ohm shielded coaxial cable, 5mm outside diameter. Uses 50 ohm shielded coaxial cable, 5mm outside diameter.

(RG58)(RG58) BNC connectorsBNC connectors Nodes must be spaced a minimum distance of 0.5 meters apartNodes must be spaced a minimum distance of 0.5 meters apart Terminate 50 ohm at each endTerminate 50 ohm at each end Earth each segment at one point onlyEarth each segment at one point only

Usual 10Base2 CablingUsual 10Base2 Cabling

The backbone of the LAN is a cableThe backbone of the LAN is a cable Nodes are connected directly to the cable Nodes are connected directly to the cable

via T connectors (must use a T or it will not via T connectors (must use a T or it will not work)work)

Device 1

I/F

Device 2

I/F

Ethernet cable

10BaseT - Twisted Pair10BaseT - Twisted Pair 10 Mbit s10 Mbit s-1-1, Baseband, Baseband Each segment may be up to 100 metersEach segment may be up to 100 meters Number of nodes limited by hubNumber of nodes limited by hub Uses unshielded twisted pair cable, c. 6mm Uses unshielded twisted pair cable, c. 6mm

outside diameter. Max (telephone cable)outside diameter. Max (telephone cable) RJ45 (telephone) connectors ( 8 wires)RJ45 (telephone) connectors ( 8 wires) Terminated in hubTerminated in hub Grounded in hubGrounded in hub


Twisted pair cableTwisted pair cable–Two insulated cables, twisted togetherTwo insulated cables, twisted together–Usually no shielding requiredUsually no shielding required– Immune to noise provided that twisting is regularImmune to noise provided that twisting is regular

Cable Terminology (cot...)Cable Terminology (cot...)

Conductor

Insulator

Usual 10BaseT CablingUsual 10BaseT Cabling

The backbone of the LAN is a hubThe backbone of the LAN is a hub Nodes are connected to the hub via a Nodes are connected to the hub via a

twisted pair drop cabletwisted pair drop cable One device at each end of the drop cableOne device at each end of the drop cable

Device 2

I/FDrop cable Drop cable

Hub

Device 1

I/F

10Broad3610Broad36 10 Mbit s10 Mbit s-1-1, Broadband, Broadband Each segment may be up to 1,023 nodes, Each segment may be up to 1,023 nodes,

3,800 metes3,800 metes TV and audio signals may coexist on the TV and audio signals may coexist on the

same cablesame cable Expensive - requires specialist installationExpensive - requires specialist installation


10BaseF - Fibre-optic10BaseF - Fibre-optic 10 Mbit s10 Mbit s-1-1, Fibre-optic, Fibre-optic Main type is FOIRL - Fibre Optic Interface Main type is FOIRL - Fibre Optic Interface

Repeater LinkRepeater Link–Used to link repeatersUsed to link repeaters–Up to 1km distanceUp to 1km distance


AUI/drop cableAUI/drop cable Connects node to networkConnects node to network 15 pin D to 15 pin D cable15 pin D to 15 pin D cable Up to 50 meters distanceUp to 50 meters distance Must be shielded (including connectors)Must be shielded (including connectors) Not included in distances for 10Base5, Not included in distances for 10Base5,

10Base2 10Base2


Extending EthernetExtending Ethernet

HubsHubs RepeatersRepeaters BridgesBridges RoutersRouters GatewaysGateways

A knowledge of the OSI 7-layer modelhelps understanding of the different

methods of extending Ethernet

HubsHubs Connects nodes when using 10BaseTConnects nodes when using 10BaseT

– May just be wiring concentrator (cheapest Ethernet May just be wiring concentrator (cheapest Ethernet solution)solution)

– May have intelligence to increase overall system May have intelligence to increase overall system bandwidthbandwidth

HubTwisted pair cables

One device perport

(may be a repeater)

RepeatersRepeaters

Connect two segments on the same network Connect two segments on the same network togethertogether

1234567

User

1234567

User

A A

Station onNetwork A

Station onNetwork B

Repeater

The two segments are still on thesame collision domain

Overall distance is limited to755 meters for 10Base2 and

1,700 meters for 10Base5

Repeaters (cot...)Repeaters (cot...)


Repeater

Multi-portRepeater

Multi-port RepeatersMulti-port Repeaters

Connect more than two segments on the same Connect more than two segments on the same network togethernetwork together

Used to overcome the node limits of a single Used to overcome the node limits of a single segmentsegment

Drop cables(10BaseT or 10Base2)

10BaseT/2 limits tonumber of devices

per port

Fiber-Optic Repeater LinksFiber-Optic Repeater Links


1234567

User

1234567

User

A A

Station onNetwork A

Station onNetwork B

Fibre-Optic Repeater

The two segments are still on thesame collision domain

Overall distance is limited bythe Fiber optic link distance

(typically 1,000 meters)

Fibre-Optic Link

Fibre-Optic Repeater Links Fibre-Optic Repeater Links (cot...)(cot...)


Repeater

Repeater

Fibre-optic linkUp to 1 km

12

1

Bridge

2MAC MAC

LLC

BridgesBridges

Links two networks using different MAC protocolsLinks two networks using different MAC protocols

1234567

User

1234567

User

Station onNetwork A

Station onNetwork B

i.e... Link Ethernet to MAP(layers 3 to 7 are the same)

RoutersRouters

Links two networks using different MAC protocols Links two networks using different MAC protocols and LLC layersand LLC layers

1 1 1234567

User

1234567

User

Station onNetwork A

Station onNetwork B

i.e... Link LANs to WANs(layers 4 to 7 are the same)

2 23

Router

3

GatewaysGateways

Links any network to any other networkLinks any network to any other network

1234567

User

1234567

User

Station onNetwork A

Station onNetwork B

1 12 23 34 45 56 67

Gateway

7

Application layer is the same

Protocol convertersProtocol converters

Links any network to any other networkLinks any network to any other network

1234567

User

1234567

User

Station onNetwork A

Station onNetwork B

1 12 23 34 45 56 6

Protocol converter

7 7User User

TCP/IPTCP/IP

Introduction to TCP/IPIntroduction to TCP/IP Why TCP/IP?Why TCP/IP? What is TCP/IP?What is TCP/IP? TCP/IP addressingTCP/IP addressing

Introduction to TCP/IPIntroduction to TCP/IP

Ethernet is hardware onlyEthernet is hardware only To send data you need a software protocolTo send data you need a software protocol

– layers 3 to 7 of the 7 layer modellayers 3 to 7 of the 7 layer model One option is to use a full OSI compliant One option is to use a full OSI compliant

stackstack– layers 3 to 7 all fully implementedlayers 3 to 7 all fully implemented

Other protocols also exist - the commonest Other protocols also exist - the commonest is TCP/IPis TCP/IP

Why TCP/IP?Why TCP/IP?

TCP/IP is faster than ISOTCP/IP is faster than ISO–There are fewer layers (2 rather than 4)There are fewer layers (2 rather than 4)–Typically TCP/IP is 2 to 6 times fasterTypically TCP/IP is 2 to 6 times faster

TCP/IP is cheapTCP/IP is cheap–Often supplied free with a computer or network Often supplied free with a computer or network

interfaceinterface Widely acceptedWidely accepted

–TCP/IP is becoming the de facto standard for TCP/IP is becoming the de facto standard for computer communicationscomputer communications

What is TCP/IP?What is TCP/IP?

TCP/IP stands for TCP/IP stands for TTransmission ransmission CControl ontrol PProtocol/rotocol/IInternet nternet PProtocolrotocol

TCP/IP only has four layersTCP/IP only has four layers Easiest way to see what TCP/IP looks like is Easiest way to see what TCP/IP looks like is

to compare it with the ISO 7 layer modelto compare it with the ISO 7 layer model

What is TCP/IP? (cot...) What is TCP/IP? (cot...)

Network AccessLayerLayer 1

Layer 2

Layer 3

Layer 4

Layer 5

Layer 6

Layer 7

OSI 7 layer

Ethernet

InternetLayer (IP)

Host-to-Host TransportLayer (TCP)

ApplicationLayer

TCP/IP

Ethernet

TCP/IP

ProtocolProtocol

What is TCP/IP? (cot...)What is TCP/IP? (cot...) Note that TCP/IP is the middle two layersNote that TCP/IP is the middle two layers The bottom layer is EthernetThe bottom layer is Ethernet TCP/IP does not fully conform to the ISO OSI 7 layer reference TCP/IP does not fully conform to the ISO OSI 7 layer reference

modelmodel– however, the model is still valid for considering bridges, Routers however, the model is still valid for considering bridges, Routers

etc..etc.. The top layer is a protocolThe top layer is a protocol

– not specified by TCP/IPnot specified by TCP/IP Common protocols used over TCP/IP includeCommon protocols used over TCP/IP include

– TELNET - Remote Terminal AccessTELNET - Remote Terminal Access– FTP - File Transfer ProtocolFTP - File Transfer Protocol– and many othersand many others

TCP/IP AddressingTCP/IP Addressing Each TCP/IP node on a network must have a unique IP Each TCP/IP node on a network must have a unique IP

(Internet Protocol) address(Internet Protocol) address The IP address identifies the host (device) on the networkThe IP address identifies the host (device) on the network IP addresses are 32 bits long and have a IP addresses are 32 bits long and have a net IDnet ID part and part and

a a hostedhosted part part net IDnet ID identifies the network identifies the network

– All hosts on the same physical network must have the All hosts on the same physical network must have the same same net IDnet ID

hostedhosted identifies the host identifies the host– All hosts on the same physical network must have a All hosts on the same physical network must have a

unique unique hostedhosted There are three classes of IP address - A, B and CThere are three classes of IP address - A, B and C

Expressing an IP AddressExpressing an IP Address

IP addresses are written as four decimal integersIP addresses are written as four decimal integers Each integer gives the value of one byte of the Each integer gives the value of one byte of the

IP addressIP address Integers are separated by periods (“.” - full stop)Integers are separated by periods (“.” - full stop) e.g... IP address 00000011 00010000 00010010 e.g... IP address 00000011 00010000 00010010

0010111100101111 is written as 3.16.18.47is written as 3.16.18.47

Class A IP AddressClass A IP Address

0 1 8 16 24 31

0

Range of first integer is 0 to 127

net ID hosted

net ID is 7 bits, hosted is 24 bits

Class B IP AddressClass B IP Address

0 1 8 16 24 31


net ID hosted01


Class C IP AddressClass C IP Address

0 1 8 16 24 31


net ID hosted011

2


Note that first integer values of 224 to 255 are reserved

GatewaysGateways Gateways connect individual physical networks into a system of Gateways connect individual physical networks into a system of

networksnetworks Gateways are also known as Routers using TCP/IP terminologyGateways are also known as Routers using TCP/IP terminology When a host on one network wishes to communicate with a host When a host on one network wishes to communicate with a host

on another network, the gateway forwards the data between the on another network, the gateway forwards the data between the two networkstwo networks

A

BGateway

Network 1

Network 2

Gateways (cot...)Gateways (cot...) For example, host B (IP address 128.2.0.1) wishes to For example, host B (IP address 128.2.0.1) wishes to

communicate with host Ccommunicate with host C C’s IP address indicates that it is on the same network so it C’s IP address indicates that it is on the same network so it

can communicate directlycan communicate directly

A

B CGateway

Network 1

Network 2

128.1.0.1

128.2.0.1 128.2.0.2128.2.0.3

128.1.0.2

Net ID

Net ID

Gateways (cot...)Gateways (cot...) Now suppose host B wishes to communicate with ANow suppose host B wishes to communicate with A B knows that A is on a different network since its B knows that A is on a different network since its net IDnet ID is different is different In order to communicate, B must know the IP address of the In order to communicate, B must know the IP address of the

gateway connecting the two networksgateway connecting the two networks Note that the gateway has two IP addresses, one for each networkNote that the gateway has two IP addresses, one for each network

A

B CGateway

Network 1

Network 2

128.1.0.1

128.2.0.1 128.2.0.2128.2.0.3

128.1.0.2

Net ID

Net ID

SubnetsSubnets Subnet addressing is an extension of the IP address Subnet addressing is an extension of the IP address

schemescheme It allows a site to use a single net ID for multiple It allows a site to use a single net ID for multiple

physical networksphysical networks Routing outside the site works as normal by dividing Routing outside the site works as normal by dividing

the IP address into a the IP address into a net IDnet ID and a and a hostedhosted as before as before Inside a site a Inside a site a subnet mask subnet mask is used to re-divide the is used to re-divide the

IP address into a custom IP address into a custom net IDnet ID portion and portion and hostedhosted portionportion

Subnets (cot...)Subnets (cot...) Consider taking the class B network 2 from the previous Consider taking the class B network 2 from the previous

example and adding another network example and adding another network Selecting the Selecting the subnet mask subnet mask 11111111 11111111

11111111 11000000 00000000 (255.255.192.0) adds two 11111111 11000000 00000000 (255.255.192.0) adds two additional additional net IDnet ID bits allowing up to four networks bits allowing up to four networks

In other words, two bits of the class B In other words, two bits of the class B hostedhosted have been have been used to extend the used to extend the net IDnet ID

So network 2.1 uses aSo network 2.1 uses a net ID net ID beginning 01 (64), network beginning 01 (64), network 2.2 uses a 2.2 uses a net IDnet ID beginning 10 (128) beginning 10 (128)

Further networks could use 00 and 11 (0 and 192)Further networks could use 00 and 11 (0 and 192)

Subnets (cot...)Subnets (cot...)

The new network becomes:The new network becomes:A

B CGateway 1

Network 1

Network 2.1

128.1.0.1

128.2.64.1 128.2.64.2128.2.64.3

128.1.0.2

B CGateway 2

Network 2.2128.2.128.1 128.2.128.2

128.2.128.3

128.2.64.4

To assure proper To assure proper communication:communication:

All devices on the network must have a unique IP addressAll devices on the network must have a unique IP address All devices wishing to communicate with each other on the All devices wishing to communicate with each other on the

same physical network must have the same same physical network must have the same net IDnet ID All devices wishing to communicate with other devices on All devices wishing to communicate with other devices on

different physical networks must know the IP address of the different physical networks must know the IP address of the gatewaygateway

All devices wishing to communicate with each other on the All devices wishing to communicate with each other on the same site should have the same same site should have the same subnet masksubnet mask

IP addresses and IP addresses and subnet maskssubnet masks are defined by a network are defined by a network administratoradministrator

Practical ImplementationPractical Implementation

Diagnosing LAN problemsDiagnosing LAN problems Network Timing ImplicationsNetwork Timing Implications Guidelines for Successful LAN Guidelines for Successful LAN

ImplementationImplementation

Diagnosing LAN ProblemsDiagnosing LAN Problems LAN problems arise from:LAN problems arise from:

– Faulty cablesFaulty cables– Faulty connectionsFaulty connections– NoiseNoise– Faulty devicesFaulty devices

To eliminate problems:To eliminate problems:– Check all cablesCheck all cables

use a continuity tester to check for shorts etc.use a continuity tester to check for shorts etc. use an Ohmmeter for checking termination'suse an Ohmmeter for checking termination's

– Use a TDR - Use a TDR - TTime ime DDomain omain RReflectometereflectometer an expensive device but invaluable for large networksan expensive device but invaluable for large networks

– Isolate the problem by removing and adding devices in turnIsolate the problem by removing and adding devices in turn only practical for small networksonly practical for small networks

– Use a SnifferUse a Sniffer

Network Timing Implications - Network Timing Implications - TCP/IPTCP/IP

The minimum time for a TCP/IP message to transfer The minimum time for a TCP/IP message to transfer from a local station to a remote station is approx... 25 from a local station to a remote station is approx... 25 millisecondsmilliseconds

Only a very short amount of time is spent using the Only a very short amount of time is spent using the networknetwork

Most time is spent in the TCP/IP stack on the moduleMost time is spent in the TCP/IP stack on the module Overhead of using larger message sizes is smallOverhead of using larger message sizes is small

– 1 register takes 25-40 milliseconds1 register takes 25-40 milliseconds– 100 registers take 25-40 milliseconds100 registers take 25-40 milliseconds– 1000 registers take 50-65 milliseconds1000 registers take 50-65 milliseconds

Send as much data per single message as possibleSend as much data per single message as possible– reduces message overheadreduces message overhead

Group data into contiguous blocksGroup data into contiguous blocks If possible, use unsolicited writes to send data rather than wait If possible, use unsolicited writes to send data rather than wait

for it to be requestedfor it to be requested– cuts down the amount of message trafficcuts down the amount of message traffic

Use separate Ethernet segments where possibleUse separate Ethernet segments where possible– Routers keep individual network traffic downRouters keep individual network traffic down– limit individual segment loading to 30% or lesslimit individual segment loading to 30% or less– above 30% loading collisions become commonabove 30% loading collisions become common– network performance reduces exponentiallynetwork performance reduces exponentially

To Optimize Communication To Optimize Communication TimeTime

5 Rules for Successful LAN 5 Rules for Successful LAN ImplementationImplementation

One qualified individual must be responsible for One qualified individual must be responsible for the LANthe LAN

He/she must be trained on all connected He/she must be trained on all connected productsproducts

Standards must be met in purchase and Standards must be met in purchase and installationinstallation

Experts should be contracted for special Experts should be contracted for special requirements such as broadband or redundancyrequirements such as broadband or redundancy

Discipline in LAN operation should be expected Discipline in LAN operation should be expected and encouragedand encouraged

iso layers & ethernet basics

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