270 Chapter 9: Frame Relay Connection Controlling Traffic Flow
Frame Relay Traffic Shaping
Frame Relay traffic shaping is a means of controlling the output of traffic across the Frame
Relay network. Whether the goal is to meet service contract obligations or to control output
speed to slower links, traffic shaping can provide granular control of outbound data. Traffic
shaping can provide per-VC rate enforcement, BECN support, and queuing (WFQ, PQ, or CQ)
at the VC level.
Frame Relay traffic shaping is supported only on fast switching and process switching paths.
Therefore, to use it, other switching methods must be disabled on all interfaces that send traffic
to the serial interface.
Frame Relay Traffic Parameters
To properly understand the concepts of traffic shaping, it is important to have a firm grasp of
the various traffic parameters in the Frame Relay Network. In particular, you should know that
some (such as CIR and Be (Excessive Burst)) are commonly used, but misunderstood.
Table 9-2 details the traffic parameters.
Table 9-2
Frame Relay Traffic Parameters
Parameter
Description
CIR
The average rate you want to transmit. This is generally not the
same as the CIR provided by the telco. This is the amount you
want to send in periods of noncongestion.
Be (Excessive Burst)
The amount of excess data allowed to be sent during the first
interval once credit is built up. Transmission credit is built
during periods of no transmission. The credit is the burst size.
Full credit is typically CIR
ч 8.
Bc (Committed Burst)
The amount of data to send in each Tc interval.
Tc (Committed Rate Measurement
Interval)
The Bc
ч CIR time interval. The time interval shouldn't exceed
125 ms (almost always 125 ms).
MinCIR (Minimum CIR)
The minimum amount of data to be sent during periods of
congestion. This is usually what you get from the telco.
MinCIR defaults to one-half of CIR.
PIR (Peak Information Rate)
Highest possible rate of transmission on a given interface.
MIR (Minimum Information Rate)
Slowest rate of transmission on a given interface.
Interval
Bc
ч CIR. The maximum is 125 ms, or 1/8 second.
Byte Increment
Bc
ч 8. This value must be greater than 125.
Limit
Byte Increment + Be
ч 8 (in bytes).