Frame relay

A Virtual Circuit is a circuit used in transportation of data over a packet switch networks.

Virtual Circuit appears as if there is a physical path established between and source and destination so that all packets(data) can be routed over that path during the transmission

1. Frame Relay
Dr R Jegadeesan Prof-CSE
Jyothishmathi Institute of Technology and
Science, karimnagar

2. •AVirtualCircuitisacircuitusedin
transportationofdataoverapacketswitch
networks.
•VirtualCircuitappearsasifthereisa
physicalpathestablishedbetweenandsource
anddestinationsothatallpackets(data)can
beroutedoverthatpathduringthe
transmission.

3. •FrameRelayisavirtual-circuitwide-area
networkthatwasdesignedinthelate1980s
•FrameRelayoperatesatahigherspeed
44.376Mbps
•FrameRelayallowsburstydata.
•Framerelayoperatesinjustthephysicaland
DataLinklayersandcaneasilybeusedasa
backbonenetworktoprovideservicesto
higherlayerprotocols,suchastheInternet
Protocol.

4. •FrameRelayallowsaframesizeof9000bytes,
whichcanaccommodatealllocalareanetwork
framesizes.
•FrameRelayislessexpensivethanother
traditionalWANslikeDSL,cableTV.
•FrameRelayhaserrordetectiononlybutnot
correctionatthedatalinklayer.Thereisnoflow
control.
•Thereisnotevenaretransmissionpolicyifa
frameisdamaged;itissilentlydropped.

5. Frame Relay Architecture

6. •FigureshowsanexampleofaFrameRelay
networkconnectedtotheInternet.
•TheroutersareusedtoconnectLANsand
WANsintheInternet.
•Inthefigure,theFrameRelayWANisused
asonelinkconnectedtoglobalInternet

7. •FrameRelayisavirtualcircuitnetwork.
•AvirtualcircuitinFrameRelayisidentified
byanumbercalledaDataLinkConnection
Identifier(DLCI)
•Frame Relay provides
➢Permanent Virtual Circuits
➢Switched Virtual Circuits

8. Permanent Virtual Circuits
•Asourceandadestinationmaychoosetohave
aPermanentVirtualCircuit(PVC).
•Theconnectionsetupissimple.
•The corresponding table entry is recorded for
all switches by the administrator electronically

9. •AnOutgoingDLCIisgiventothesourceandan
IncomingDLCIisgiventothedestination.
•PVC connections have two drawbacks.
•First, they are costly because two parties pay for
the connection all the time even when it is not in
use.
•Second,aconnectioniscreatedfromonesource
toonesingledestination.Ifasourceneeds
connectionswithseveraldestinations,itneedsa
PVCforeachconnection.

10. Switched Virtual Circuit (SVC)
•TheSVCcreatesatemporary,shortconnectionthat
existsonlywhendataarebeingtransferredbetween
sourceanddestination.
•Itrequirestwophasesmainlyestablishmentphase
andterminationphase.
•Thereisatableforeachswitchtoroutetheframes
bymatchingincomingportDLCIwithanoutgoing
portDLCI.

11. Switches
•Each switchin a Frame Relay network has a
table to route frames.
•The table matches an incoming port-DLCI
combination with an outgoing port-DLCI
combination.
•The only difference is that VCIs are replaced
by DLCIs

12. Layers of Frame relay
•Frame Relay has only physical and data link
layers.

13. Physical Layer
•Nospecificprotocolisdefinedforthe
physicallayerinFrameRelay.
•FrameRelaysupportsanyoftheprotocols
recognizedbyANSI.

14. Data Link Layer
•Frame Relay uses a simple protocol that does
not support flow or error control.
•It only has an error detection mechanism.
•Figure below shows the format of a Frame
Relay frame

16. Address (DLCI) field
•Theaddressfieldisdividedintotwoparts1
st
byte
2
nd
byte.
•Thefirst6bitsofthefirstbytemakesupthefirst
partoftheDLCI.
•ThesecondpartoftheDLCIusesthefirst4bits
ofthesecondbyte.
•Thesebitsarepartofthe10-bitdatalink
connectionidentifier

17. Command/response (CIR)
Thecommand/response(C/R)bitisprovidedto
allowupperlayerstoidentifyaframeaseithera
commandoraresponse.ItisnotusedbytheFrame
Relayprotocol.
Extendedaddress(EA)
Theextendedaddress(EA)bitindicateswhetherthe
currentbyteisthefinalbyteoftheaddress.AnEA
of0meansthatanotheraddressbyteistofollow.An
EAof1meansthatthecurrentbyteisthefinalone.

18. ForwardExplicitCongestionNotification
(FECN)
➢FECNbitcanbesetbyanyswitchtoindicate
thattrafficiscongested.
➢Thisbitinformsthedestinationthat
congestionhasoccurred.
➢Inthisway,thedestinationknowsthatit
shouldexpectdelayoralossofpackets.

19. Backwardexplicitcongestionnotification
(BECN)
•BECNbitisset(inframesthattravelinthe
otherdirection)toindicateacongestion
probleminthenetwork.
•Thisbitinformsthesenderthatcongestion
hasoccurred.
•Inthisway,thesourceknowsitneedstoslow
downtosenddatainordertopreventtheloss
ofpackets.

20. Discard eligibility (DE)
•The discard eligibility (DE) bit indicates the
priority level of the frame.
•In emergency situations, switches may have to
discard frames to relieve bottlenecks and keep
the network from collapsing due to overload.
•When set (DE=1), this bit tells the network to
discard this frame if there is congestion.
•This bit can be set either by the senderof the
frames (user) or by any switchin the network

21. FRADs
•Tohandleframesarrivingfromother
protocols,frameRelayusesadevicecalleda
FrameRelayassembler/disassembler
(FRAD)
•AFRADassemblesanddisassemblesframes
comingfromotherprotocolstoallowthemto
becarriedbyFrameRelayframes.
•AFRADcanbeimplementedasaseparate
deviceoraspartofaswitch

23. VOFR
•FrameRelaynetworksofferanoptioncalledVoiceOver
FrameRelay(VOFR)thatsendsvoicethroughthenetwork.
•VoiceisdigitizedusingPCMandthencompressed.The
resultissentasdataframesoverthenetwork.
•Thisfeatureallowstheinexpensivesendingofvoiceover
longdistances.
•However,notethatthequalityofvoiceisnotasgoodasvoice
overacircuit-switchednetworksuchasthetelephone
network

24. LocalManagementInformation(LMI)
•LMI is a protocol added recently to the Frame Relay
to provide more management features.
•In particular LMI can provide
➢Akeep-alivemechanismtocheckifdataareflowing.
➢Amulticastmechanismtoallowalocalendsystemto
sendframestomorethanoneremoteendsystem.
➢Amechanismtoallowanendsystemtocheckthe
statusofaswitch(e.g.,toseeiftheswitchis
congested).

25. Asynchronous Transfer Mode

26. ATM
•Asynchronous Transfer Mode (ATM) is the
protocol designed by the ATM Forum and
adopted by the ITU-T.
•ThecombinationofATMandSONETwill
allowhigh-speedinterconnectionofallthe
world'snetworks.

27. ATM Architecture

28. •ATMisaswitchingnetworkinwhichthedatais
transmittedfromsourcetodestination.
•Sourceanddestinationarereferredastheendpoints
whichareuseraccessdevices.
•Theendpointsareconnectedtotheswitches
throughaninterfacecalleduser-to-network
interface(UNI)
•Theswitchesareconnectedthroughnetwork-to-
networkinterfaces(NNIs)

29. •ATMprovidesconnectionorientedservices
suchtypeofservicesareknownasVirtual
Connection.
•Connectionbetweentwoendpointsis
accomplishedthrough
•Transmissionpaths(TPs)
•Virtualpaths(VPs)
•Virtualcircuits(VCs).

30. •Atransmissionpath(TP)isthephysical
connection(wire,cable,satellite,andsoon)
betweenanendpointandaswitchorbetween
twoswitches.
•Thinkoftwoswitchesastwocities.A
transmissionpathisthesetofallhighways
thatdirectlyconnectthetwocities.

31. •Atransmissionpathisdividedinto
severalvirtualpaths.
•Avirtualpath(VP)providesa
connectionorasetofconnections
betweentwoswitches.
•Thinkofavirtualpathasahighway
thatconnectstwocities.
•Eachhighwayisavirtualpath;theset
ofallhighwaysisthetransmissionpath.

32. •Cellnetworksarebasedonvirtualcircuits
(VCs).
•Allcellsbelongingtoasinglemessagefollow
thesamevirtualcircuitandremainintheir
originalorderuntiltheyreachtheir
destination.
•Thinkofavirtualcircuitasthelanesofa
highway(virtualpath).

33. FigureshowstherelationshipbetweenVPVC
TP

34. ATM Cells
•ATMtransmits,switchesandmultiplexes
informationinfixedlengthcells.
•ItisthebasicdataunitinanATMnetwork
•Acellisonly53byteslongwith5bytesallocated
totheheaderand48bytescarryingthepayload
(userdatamaybelessthan48bytes).
•Themainideaforusingsmalldatacellsisthatit
reducesjitter(asavariationinthedelayof
receivedpackets)

35. ATM layers
•TheATMstandarddefinesthreelayers.
Theyarefromtoptobottom,
Application Adaptation Layer (AAL)
ATM layer
physical layer

36. •Physical layer
Thislayerspecifiescertainrulesof
howasignalshouldbeencodedandalso
specifyphysicalmediumandtransmission
characteristics(e.g.,modesoftransmission)

37. ATM layer
•TheATMlayerprovidesrouting,traffic
management,switching,andmultiplexing
services.
•Itprocessesoutgoingtrafficbyaccepting48-
bytesegmentsfromtheAALlayerand
transformingtheminto53-bytecellsbythe
additionofa5-byteheader

38. AAL
•ThisApplicationAdaptationLayerdefineshow
tosegmentandreassemblehigher-layerpackets
intoATMcells,andhowtohandlevarious
transmissionaspectsintheATMlayer.
•ThemainservicesprovidedbyAAL(ATM
AdaptationLayer)are:
•Segmentationandreassembly
•Handlingoftransmissionerrors
•Handlingoflostandmisinsertedcellconditions
•Timingandflowcontrol

39. Thank you