3Com MSR 50 Series Configuration Manual page 1713

Frame Relay packet whose backward explicit congestion notification (BECN) flag
bit is 1, indicating that congestion has occurred to the network, the token
addition speed is decreased to CIR, that is, 32 kbps, and the packet is sent at 32
kbps on the VC.
Frame Relay traffic policing
Frame Relay policing monitors the traffic that flows into the network from each
PVC, and restricts it in a certain range. If the traffic size on a PVC exceeds the
range set by the user, the device will adopt the measures like discarding the
packets, so as to protect the network resources.
Figure 491 Frame Relay traffic policing
192Kbps
64Kbps
S 2/0 S 2/0
DCE
DTE
Router A
CIR ALLOW=64Kbps
CBS=8000bit
EBS=8000bit
As shown in the above figure, Router A at the user side transmits packets at 192
kbps to Router B at the switching side. However, Router B only wants to provide
the 64 kbps bandwidth for Router A. In this case, you need to configure the Frame
Relay traffic policing at the DCE side of Router B.
Frame Relay traffic policing can only be applied on the DCE interface on a device.
It can monitor the traffic transmitted from the DTE side. When the traffic size is
smaller than CBS, the packets can be normally transmitted, and the device will not
process the packets. When the traffic size is larger than CBS and smaller than EBS
+ CBS, the packets can be normally transmitted. In this case, however, as for those
packets in the traffic exceeding CBS, the device will mark the flag bit of DE in the
Frame Relay packet headers to 1. When the traffic size is larger than CBS + EBS,
the device will transmit the traffic within CBS + EBS, and discard the traffic
exceeding CBS + EBS. As for the traffic of EBS which is the size exceeding CBS, the
device will mark the flag bit of DE in the Frame Relay packet headers to 1.
Figure 492 Fundamentals of Frame Relay traffic policing
150 Kbps
CIR ALLOW+EIR 128 Kbps
100 Kbps
CIR ALLOW 64 Kbps
As shown in the above figure, the parameters of Frame Relay traffic policing are
respectively set to be: CIR ALLOW = 64 kbps, CBS = 8000 bits, EBS = 8000 bits,
NNI
Router B
RATE
Transmit
0m 125m 250m 375m
s s s s
Frame Relay QoS Overview
Frame-Relay
network
Discarded
DE
500m 625m 750m
TIME
s s s
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