updated 12/20011 Frame Relay Nirmala Shenoy Information Technology Department Rochester Institute of Technology

updated 12/20012 Frame Relay Purpose –Faster transmission Virtual circuit technology Data rates up to Kbps to the end user Network Data rates – Mbps – T3 lines Assumes smart end systems & reliable media No error & flow control in the network –High data rates at low costs

updated 12/20013 Frame Relay Purpose –Replacement for a number of leased T1 lines Virtual private networks Lower costs for similar resources –Wide Area coverage – interconnect LANs –Ideally suited to bursty traffic

updated 12/20014 Frame Relay Purpose –Bursty traffic

updated 12/20015 Frame Relay Advantages –High data rates & access rates –Lower 2 layers- ideal for backbone networks –Support bursty data –Maximum frame size – 9000 bytes –Less expensive technology –Can be used on lease or on requirement basis

updated 12/20016 Frame Relay Disadvantages –Not high enough data rates –Variable length frames –Not suited to time sensitive applications

updated 12/20017 Frame Relay Topology

updated 12/20018 Frame Relay Topology – virtual circuits

updated 12/20019 Frame Relay Topology – virtual circuits –At the Data link layer –DLCI – Data Link Connection Identifier –PVCs and SVCs –Different connections get different DLCI –Local significance –DLCIs within the network

updated 12/ Frame Relay Route table at FR switch

updated 12/ Layers Core data link function – LAPF –Simplified HDLC Frame Relay

updated 12/ LAPF – PDU –Flag –Address field DLCI C/R (command response bit) not used EA – extended address bit FECN BECN DE - Drop eligibility bit Frame Relay

updated 12/ LAPF – PDU –Information –FCS – Frame check sequence –Flag Frame Relay

updated 12/ LAPF – PDU EA bit – useful for extended address capability –0 signifies – another address byte to follow FECN –Forward explicit congestion notification Warning to receiver of message that there is congestion along the direction of flow Frame Relay

updated 12/ LAPF – PDU BECN – –Notify sender that there is congestion in a direction opposite to the information flow –Use response frames going in reverse direction –Use predefined DLCI connection 1023 FECN & BECN inform end systems of network congestion Frame Relay

updated 12/ FECN & BECN Frame Relay

updated 12/ Discard Eligibility bit –This frame can be dropped during congestion –A congestion control mechanism Frame Relay

updated 12/ Traffic Control - Attributes –Committed burst size – Bc Eg 400kbs for 4 seconds During the 4 second period – max traffic 400kbs –Committed information rate Average rate Bc/T (T –predefined period for burst) CIR = 400/4 = 100kbs/sec Frame Relay

updated 12/ Traffic Control - Attributes –Excess burst size – Be –Bits in excess of Bc that can be sent in T –May not be transferred under congestion Frame Relay

updated 12/ Traffic Control Frame Relay

updated 12/ Traffic Control Forwarding of traffic –Fast forward –Leaking CIR Traffic control via leaky bucket Frame Relay

updated 12/ Traffic Control –Control of output from leaky bucket – leak rate –Timer (  T) and counter for counting bits sent Frame Relay

updated 12/ Traffic Control – leaky bucket Frame Relay

updated 12/ Traffic Control Use of the DE bit –User setting –Network setting, based on Bc, Be –May not be used Policing & Traffic shaping Frame Relay

updated 12/ Service class categorization –Be only – all data can be dropped on congestion –CIR and Bc, User sets DE flag, network will discard these frames under severe network congestion if exceeding Bc –CIR, Bc and Be Network will tag Be traffic and drop if severe congestion Frame Relay

updated 12/ UNI NNI inter-working –ANSI T1.617 Frame Relay

updated 12/ UNI NNI inter-working –Messages –SE - Status Enquiry –S – Status –FS – full status on all PVCs –Use of Unnumbered Information frames of HDLC – DLCI = 0 Frame Relay

updated 12/ NNI operations –Adding a PVC notification –Detection of PVC deletion –UNI, NNI failures –PVC segment availability –Link verification –Node verification Frame Relay

updated 12/ Typical Bellcore PVC service Exchange Access Frame Relay XA-FR Defined between LEC (Local Exchange Carrier) and IC(Interchange Carrier) –FR-ICI interface Consistent service – end-to-end PVC, UNI to UNI Frame Relay

updated 12/ XA-FR topology Frame Relay

updated 12/ XA-FR Service parameters at FR-ICI –compliant frames Performance objective –Delay –Accuracy –Availability Frame Relay

updated 12/ XA-FR – delay –FR-UNI access rate –FR-ICI access rate –Frame size –Time the first bit placed on the UNI, till the last bit received at ICI < specified value for 95% of the frames Frame Relay

updated 12/ XA-FR – accuracy –Number of errored frames –Number of lost frames –Number of extra frames –Compute Frames not delivered ratio Errored frames ratio Extra frames ratio Frame Relay

updated 12/ XA-FR – availability –Scheduled hours of service –Service availability –MTTSR – mean time to service restoration –MTBSO – mean time between service outages –Fraction of time in non-congestion notification state –Mean time between congestion notification st Frame Relay

updated 12/ DLCI Values – two octet field –0 – in channel signaling –1-15 reserved – – assigned by FR connections – – layer management for bearer service – – reserved –1023 – in-channel layer management Frame Relay

updated 12/ DLCI Values – –Global addressing – unique destination address –Semi-broadcast – copied to multiple routers Frame Relay

updated 12/ Frame Relay SVC operation Frame Relay

updated 12/ Frame Relay SVC operation –Set up information –DLCI –An explicit address –Requested end-to-end delay –Max frame size –Requested throughput (incoming & outgoing) –Requested Bc (incoming & outgoing) –Requested Be (incoming & outgoing) Frame Relay

updated 12/ Quality of service options –Residual Error rate –Frame related –Switched virtual call establishment delay –Clearing delay –Premature disconnect Frame Relay

updated 12/ Features of emerging technologies? –Bursty data & high bit rate (not so high?!) –Quality of Service addressed –Frame based – real time suitability? –Flow control – implicit & minimal Drop traffic on congestion –Error control – no Drop traffic on error –Payload integrity management – no –Band width on demand Frame Relay

updated 12/ Summary –Extended use of HDLC technology –High speed WAN –Ideal to interconnect high speed LANs –Limitations Speed Frame size –Good backbone technology Frame Relay

updated 12/ Summary –Lower costs Operational End user –Better sharing of resources –New service offering Frame Relay