Filter
Top Products
Configure Frame Relay QoS 261
Figure 85 Frame Relay traffic policing
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 router. 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 router 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 router 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 router 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
router will mark the flag bit of DE in the Frame Relay packet headers to 1.
Figure 86 Fundamentals of Frame Relay traffic policing
As shown in the above figure, the parameters of Frame Relay traffic policing are
respectively set to be: CIR ALLOW = 64 kbps, CBS = 64000 bit, EBS = 64000 bit,
and interval Tc = CBS / CIR ALLOW = 1s.
When the interval is in the range of 0 to
2s, DTE will transmit packets to DCE at 64 kbps and DCE will normally forward
these packets at 64 kbps. When the interval is in the range of 2 to 4ms, DTE will
transmit packets at 100 kbps, and DCE will forward them at 100 kbps. In this case,
however, the flag bit of DE in the headers of packets exceeding
CBS will be set to
1. After 4 seconds, DTE will transmit the packets to DCE at 150 kbps, and DCE will
forward them at 128 kbps. As for the packets exceeding
CBS but within CBS +
EBS
, the flag bit of DE in their headers will be set to 1, and the packets exceeding
CBS + EBS will be discarded directly.
Frame-relay
network
Router
A
Router
B
192 kbps 64 kbps
DTE DCE
CIR ALLOW = 64 kbps
CBS = 8000 bit
EBS = 8000 bit
S0 S0
NNI
CI R ALLOW£º 64 Kbps
0ms 125ms 500ms375ms250ms750ms625ms
RATE
TI ME
CI R ALLOW+EI R£º 128 Kbps
100 Kbps
150 Kbps
DE
Discarded
Transmit