3Com 10014299 manual Rate

			Configure Frame Relay QoS 259
Figure 82 Frame Relay traffic shaping
		Data flow direction
	128 kbps		64 kbps
	S0	Frame-relay network	S0
Router B	DTE		DTE	Router A

CIR ALLOW = 64kbps

CIR = 32kbps

If the Frame Relay traffic shaping is applied on the outgoing interface Serial 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.

Frame Relay traffic shaping is applied on the outgoing interface on a router. It can provide for the users the parameters like Committed Information Rate Allowed (CIR ALLOW), Committed Information Rate (CIR), Committed Burst Size (CBS) and Excess Burst Size (EBS).

When the network is in normal, the Frame Relay PVCs can transmit packets at the rate of CIR ALLOW. In this case, the packet traffic transmitted at an interval of Tc is CBS. Furthermore, the Frame Relay traffic shaping allows the PVCs to transmit packets at a rate exceeding CIR ALLOW in case of the burst, and the traffic exceeding the CBS can be EBS at maximum.

When the network congestion occurs, if the Frame Relay switch device has been configured with the function of congestion management, it will notify the router of network congestion. Upon receiving the notification, the router will eventually slow down the transmit rate to the CIR, so as to ease the congestion, then users can transmit data at the rate of CIR. After this, if no notifications of network congestion are received within a certain period of time, the router will eventually raise the transmit rate from the CIR back to the CIR ALLOW.

Figure 83 Fundamentals of Frame Relay traffic shaping

RATE
CI R ALLOW+EI Rº£ 128 Kbps
CI R ALLOWº£ 64 kbps
CI Rº£ 32 kbps
0s	1s	2s	3s	4s	5s	6s	TI ME

As shown in Figure 83, the parameters of Frame Relay traffic shaping are respectively set to be: CIR ALLOW= 64 kbps, CIR = 32 kbps, CBS = 64000 bit, EBS

=64000 bit, and interval Tc = CBS / CIR ALLOW = 1s. Within the first interval Tc, the PVC-transmitting burst traffic size equals to CBS+EBS. Beginning from the second Tc, the transmitted traffic size within each interval Tc becomes CBS. At the 3s, the router receives the Frame Relay packet whose backward explicit congestion