Frame Relay Qos Implemented - 3Com MSR 50 Series Configuration Manual

1710 C 91: F
HAPTER RAME
Frame Relay QoS
Implemented
R Q S C
ELAY O ONFIGURATION
Excess Burst Size (EBS): the maximum that packet traffic of frame relay network
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could exceed the CBS within the interval of a Tc. Upon network congestion,
this part of excess traffic will be first discarded. Therefore, frame relay network
does not ensure this part of traffic could be certainly sent successfully.
Frame Relay traffic shaping
The Frame Relay traffic shaping limits traffic of packets sent from a virtual circuit
(VC) and of burst packets, so that they can be transmitted at relatively average
rates.
In a Frame Relay network, the bottleneck will often occur at the boundary of
segments if the bandwidths of different segments do not match. As shown in
Figure 487, Router B transmits packets to Router A at the rate of 128 kbps
whereas the maximum interface rate of Router A is only 64 kbps. In this case, the
bottleneck will occur at the place where Router A is connected to the Frame Relay
network, and thereby resulting in the congestion that prevents the data from
normal transmitting.
If the Frame Relay traffic shaping is applied on the egress interface Serial 2/0 on
Router B, the interface will be able to transmit packets at 64 kbps, a relatively
average rate, so as to avoid the network congestion. Even if the congestion occurs
to the network, Router B can still transmit packets at 32 kbps.
Figure 487 Frame Relay traffic shaping
128 Kbps
S2/0
Router B
DTE
CIR ALLOW = 64 Kbps
Frame Relay traffic shaping (FRTS) is applied on the egress interface on a device. It
can provide for the users the parameters like CIR ALLOW, CIR, CBS and EBS. Frame
Relay PVCs can transmit packets at the rate of CIR ALLOW and azFRTS allows the
PVCs to transmit packets at a rate exceeding CIR ALLOW in case of the burst.
The FRTS of our company is implemented using token bucket. The meanings of
the parameters in the protocol are modified in accordance to the actual algorithm
and fundamentals.
Data flow direction
Frame relay
network
CIR = 32 Kbps
Figure 488 illustrates the fundamentals of token bucket.
64 Kbps
S2/ 0
Router A
DTE
Frame relay
network