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© 2002 Frame Relay Option for Service Providers - QoS Mechanisms and SLA Pre-conference workshop International IT Conference 2002 Colombo, Sri Lanka 4 th October 2002 R. Jayanthan. Team Leader – Design & Consultancy Bsc.Eng.(Hons), MIEEE, AMIEE, AMIE(SL) MCP, CCNA, NNCDS, NNCAS
© 2002Objectives At the end of this workshop you will be able to: Define how Frame Relay defers from other communication technology Describe the features & benefits of Frame Relay technology Explain the Quality of Service mechanism built-in to Frame Relay technology Discuss the Service Level Agreement Parameters and Measurements related to Frame Relay
© 2002 What is not Frame Relay ? Frame Relay is not a networking protocol ! Frame Relay Is an Interface Protocol used in wide area networking Frame Relay User - Network Interface (UNI) Frame Relay Network - Network Interface (NNI)
© 2002 Frame Relay Interfaces CPE Frame Relay Network FR-UNI Frame Relay Network FR-NNI UNI – Between Customer and Operator NNI – Between two Operators
© 2002 Leased Line based Network Multiple Interfaces, DSU/CSUs and Links Router
© 2002 Leased Line based Network Advantages Simple Totally Managed by the Customer organization The links are ‘private’ to the organization Considered to be secure Disadvantages Not optimum in bandwidth utilization High number of links & physical ports required. Hence expensive to the customer Confined to LAN traffic (IP/IPX) Does not provide extensive QoS features
© 2002 Frame Relay based Network FRAD DTE Virtual Circuits Single Physical Link FRAD DTE FRAD DTE FRAD DTE FRAD DTE Frame Relay Switch DCE Frame Relay Switch DCE Frame Relay Switch DCE Frame Relay Switch DCE Frame Relay Switch DCE Frame Relay UNI
© 2002 A Shared Network Frame Relay Switch DCE Frame Relay Switch DCE Frame Relay Switch DCE Frame Relay Switch DCE Frame Relay Switch DCE Network Trunk Link Access Link
© 2002 Frame Relay based Network Network bandwidth is shared Single physical port at CPE Virtual Circuits are configured through software Built-in QoS mechanism Less frame overhead hence fast switching Support for switched virtual circuit enables on- demand services viz. voice & video calls
© 2002 TDM vs. Frame Relay TDM ApproachVirtual Circuit Approach
© 2002 Types of Virtual Circuits Permanent Virtual Circuits Switch Virtual Circuits CPE LAN SVC PVC
© 2002FR-UNI Physical Link Permanent Virtual Circuits PVC Frame Relay Switch DCE
© 2002DLCI Data Link Control Identifier Identifies each PVC within a FR-UNI Router DTE DLCI 16 DLCI 17 DLCI 18 DLCI 19 Frame Relay Switch DCE FR-UNI Frame Relay Network
© 2002 DLCI (Cont…) Assigned unique to each logical channel (PVC) within one FR-UNI DLCI has only local significance DLCI values has to be provided by the Network Operator Can be from 16 to 1023 in value (DLCI are reserved)
© 2002 Frame Relay Frame Structure FlagHeaderI fieldFCSFlag 1 byte 2 bytesVariable byte2 bytes1 byte DLCI DLCI FECN BECN DE EA C/R LAPF Frame C/RCommand /Response EAAddress Extension FECNForward Explicit Congestion Notification BECNBackward Explicit Congestion Notification DEDiscard Eligible Frame Relay supports 2, 3 or 4 byte headers resulting in more DLCI’s per FR-UNI. However 2 byte header is the most commonly implemented.
© 2002 Need for Congestion Management Input buffer Output buffer Subscriber Frame Handler Switch Node
© 2002 Congestion Management No congestion Mild congestion Severe congestion Throughput Delay Offered Load Throughput or Delay ITU Recommendation I.370 defines the frame relay congestion
© 2002 Congestion Control Techniques Discard Strategy Providing guidance to the network regarding which frames to discard; by way of CIR and DE bit. Congestion Avoidance Providing guidance to the end systems about the congestion in the network; by way of FECN, BECN and CLLM. This is called explicit control. Congestion Recovery End system infers congestion from frame loss; by way of higher level protocol function. This is called implicit control.
© 2002 FECN / BECN Frame Relay Network User data FECN=0 / BECN=0 User data FECN=1 / BECN=0 User data FECN=0 / BECN=0 User data FECN=0 / BECN=1 Client Server Congestion Congestion in the direction of Server The end stations (or Transport protocol such as TCP) shall take care of FECN/BECN to avoid congestion
© 2002 CLLM Message Consolidated Link Layer Management message Is a variation of BECN Used when no reverse traffic is available Carries congestion information of multiple virtual circuits
© 2002 Implicit Control When a higher layer protocol detects frame discards, it can adapt rate control such as using sliding window technique. This function is independent of Frame Relay technology and usually handled by transport layer protocol like TCP.
© 2002 Service Parameter Definition CIR - T c - B c - B e - Committed Information Rate: The guaranteed throughput provided by the network for the user traffic under normal operation Committed Burst Size: The maximum amount of data the network agrees to transfer, under normal conditions, over the measurement interval of T c Excess Burst Size: The maximum amount of data in excess of B c the network will attempt to transfer, over a period of T c TcTc # of Bits Transmitted Time BcBc B c + B e CIR Access Rate Committed Rate Measurement Interval or Bandwidth Interval
© 2002 Example Service Parameters Access Rate = Mbps T c = s CIR = 128 kbps Permits a burst rate B c = 144 kbps These parameters are defined per virtual circuit Though the CIR is 128 kbps, user data is fed in to the network at Mbps resulting in low latency; 15 times faster in this example. A single physical link can carry several virtual circuits and the service parameters are configured according to the: Type of traffic, viz. real-time, transaction, database backup & replication, etc. Bandwidth required
© 2002 Measurement Intervals CIRBcBc BeBe TcTc >0 T c = (B c /CIR) >0 =0T c = (B c /CIR) =0 >0T c = (B e /access rate)
© 2002 Discard Eligible (DE) bit DE=0: The frame is guaranteed to be delivered. DE=1: The frame delivered if possible The DE bit is used to mark a frame as Discard Eligible at the ingress port of the Frame Relay switch first Frame Relay switch if the input data rate exceed the committed burst rate Frame Relay Network CPE FR Switch FR Switch DE=1 CPE Ingress port Egress Port
© 2002 Traffic Management using CIR and DE bit # of Bits Transmitted Time TcTc BcBc B c + B e CIR Access Rate Frame 1 DE = 0 Frame 2 DE = 0 Frame 3 DE = 1 Frame 4 Discarded
© 2002 CIR Gauge 0 Access Rate CIR Maximum Rate Current Rate Guaranteed transmission Transmission if possible Discard all excess
© 2002 Leaky Bucket Algorithm Limit C = B c +B e Discard any incoming data while C is at its threshold Decrement C by MIN [C, B c ] every T c time units B c CIR = T c BcBc B e (set DE=1 and forward) C C = Counter; increases with incoming data Input data
© 2002 Service Level Agreement Compare different service providers Measure the quality of specific service Enforce contractual commitments Frame Relay service offerings are available from multiple service providers. Each provider describes the offering by specifying user information transfer parameters. End-users of the service utilize these parameters to:
© 2002 FRF.13 Implementation Agreement Frame Relay Forum Implementation Agreement FRF.13 specifies the SLA parameters that describes frame service performance Frame Transfer Delay ( FTD ) The time required to transfer data through the network Frame Delivery Ratio ( FDR,FDR c, FRD e ) Effectiveness in transporting offered load in one direction in a single virtual circuit Data Delivery Ratio ( DDR, DDR c, DDR e ) Effectiveness in transporting payload Service Availability ( FRVCA, FRMTTR, FRMTBSO )
© 2002 FRF.13 Connection Components Frame Relay Network Frame Relay Network Frame Relay Network FR-DTE Access Circuit Section Access Network Section Internetwork Circuit Section Transit Network Section Internetwork Circuit Section Access Network Section Access Circuit Section FR-UNI FR-NNI FR-NNII FR-UNI
© 2002 FRF.13 Reference Points Intermediate Nodes L1/L2 Function Traffic Policing Function Egress Queue Function Egress Node Ingress Node Public Frame Relay Network Source FR-DTE (Optional) Measurement Function Frame Relay End System Destination FR-DTE (Optional) Measurement Function Frame Relay End System SrcRP TpRP IngRP EqiRP EqoRP DesRP
© 2002 FRF.13 Scopes Public Frame Relay Network (s) FR-DTE Private FR Network FR-UNI FR-UNI / NNIFR-UNI Edge-to-edge Queue Scope Edge-to-edge Interface Scope End-to-end Scope
© 2002Delay Frame Transfer Delay FTD = t 2 – t 1 t 1 – time when the frame left the source (ms) t 2 – time the frame arrived at the destination (ms) Measurement DomainSourceDestination End-to-end SrcRPDesRP Edge-tp-edge Interface IngRPEqoRP Edge-to-edge Egress Queue IngRPEqiRP
© 2002 Frame Delivery Ratio ( FDR ) FDR = = FDR c = FDR e = (FramesDelivered c + FramesDelivered e ) (FramesOffered c + FramesOffered e ) (FramesDelivered c+e ) (FramesOffered c+e ) (FramesDelivered c ) (FramesOffered c ) (FramesDelivered e ) (FramesOffered e ) [FDR for load consisting of frames within CIR] [FDR for load in excess of CIR]
© 2002 Data Delivery Ratio ( DDR ) DDR = = DDR c = DDR e = (DataDelivered c + DataDelivered e ) (DataOffered c + DataOffered e ) (DataDelivered c+e ) (DataOffered c+e ) (DataDelivered c ) (DataOffered c ) (DataDelivered e ) (DataOffered e ) [FDR for load consisting of frames within CIR] [FDR for load in excess of CIR] Data = Frame – Header - FCS
© 2002 Service Availability Frame Relay virtual connection availability FRVCA = IntervalTime - ExcludedOutageTime – OutageTime IntervalTime - ExcludedOutageTime * 100 Frame Relay mean time to repair for virtual connection when OutageCount > 0 FRMTTR = OutageTime OutageCount Frame Relay mean time between service outage for virtual connection when OutageCount > 0 FRMTBSO = IntervalTime – ExcludedOutageTime – OutageTime OutageCount When OutageCount = 0, then FRMTTR = 0 and FRMTBSO = 0
© 2002Summary Frame Relay standards only define Interface Protocols. It enables network sharing and bandwidth optimization. The Frame Relay UNI & NNI have traffic management And congestion control mechanisms built-in. SLA parameters are defined to measure the network performance on a per virtual circuit basis.
© 2002Reference Further reading: Uyless Black: Frame Relay Networks, McGraw-Hill, 1998 William Stallings: ISDN and Broadband ISDN with Frame Relay and ATM, Prentice Hall, 2000 Configuring Frame Relay Services: BayRS documentation- WAN Suite Protocols. Nortel MAGELAN Training Manual: Network Engineering Volume 1 & 2 Frame Relay Forum web site
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