Table 13.1 Frame Relay Congestion Control Techniques by qyz12567

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									            Table 13.1 Frame Relay Congestion Control Techniques



     Technique                Type                Function            Key Elements
Discard control       Discard strategy      Provides guidance to   DE bit
                                            network concerning
                                            which frames to
                                            discard
Backward explicit     Congestion avoidance Provides guidance to BECN bit or CLLM
Congestion                                 end systems about     message
Notification                               congestion in network
Forward explicit      Congestion avoidance Provides guidance to FECN bit
Congestion                                 end systems about
Notification                               congestion in network
Implicit congestion   Congestion recovery   End system infers      Sequence numbers in
notification                                congestion from        higher-layer PDU
                                            frame loss
          Table13.2 Traffic Control and Congestion Control Functions




                                                              Congestion Control
      Response Time        Traffic Control Functions              Functions

Long Term                •Resource management using
                           virtual paths

Connection Duration      •Connection admission control
                           (CAC)

Round-Trip Propagation   •Fast resource management       •Explicit forward congestion
Time                                                       indication (EFCI)

                                                         •ABR flow control

Cell Insertion Time      •Usage parameter control        •Selective cell discard
                           (UPC)

                         •Priority control

                         •Traffic shaping
       Table 13.3 Traffic Parameters Used in Defining VCC/VPC Quality of Service


         Parameter                     Description               Traffic Type
Peak Cell Rate (PCR)          An upper bound on the traffic       CBR, VBR
                              that can be submitted on an
                              ATM connection.
Cell Delay Variation (CDV)    An upper bound on the               CBR, VBR
                              variability in the pattern of
                              cell arrivals observed at a
                              single measurement point with
                              reference to the peak cell rate.
Sustainable Cell Rate (SCR)   An upper bound on the                  VBR
                              average rate of an ATM
                              connection, calculated over
                              the duration of the connection.
Burst Tolerance               An upper bound on the                  VBR
                              variability in the pattern of
                              cell arrivals observed at a
                              single measurement point with
                              reference to the sustainable
                              cell rate.

CBR = constant bit rate
VBR = variable bit rate
               Table 13.4 Procedures Used to Set Values of
                       Traffic Contract Parameters



                                                             Implicitly Specified
               Explicitly Specified Parameters                  Parameters
      Parameter Values Set at      Parameter Values         Parameter Values Set
      Connection-Setup Time     Specified at Subscription    Using Default Rules
                                          Time
      Requested by User/NMS                Assigned by Network Operator

SVC          signaling                by subscription       network-operator default
                                                                     rules

PVC            NMS                    by subscription       network-operator default
                                                                     rules

 SVC = switched virtual connection
 PVC = permanent virtual connection
 NMS = network management system

								
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