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| 8.7 |  | Traffic Shaping |
| 8.7.3 |  | Configuring GTS for an interface |

GTS can be configured to shape traffic for all traffic exiting an interface using the traffic-shape command:

> Router(config-if)#traffic-shape rate bit-rate [burst-size [excess-burst-size]]

Alternatively, traffic defined by an ACL can be shaped independently of other traffic exiting an interface using the command:

> Router(config-if)#traffic-shape group access-list-number bit-rate [burst-size [excess-burst-size]]

The bit-rate determines the average data rate that is permitted out of the specified interface. The burst-size is the number of bits that can be sent as a single burst within a time period. The instantaneous bit-rate can be much higher than the average bit-rate and the burst-size should be configured so that any peaks do not overwhelm the input queue of the destination interface. The time period (Tc) over which the bit-rate is measured is given by the formula:

> Tr =

> | burst–size bit–rate

From this formula it can be seen that the smaller the burst size, the shorter the measurement time period and consequently the smoother, or less bursty, the traffic flow. A small Tc will also ensure more consistent latency which is important for voice. For voice applications Tc should be as small as possible or around 10mS. This implies that the burst size should be no more than 100th of the average bit rate.

The excess-burst-size allows more traffic to be sent in a given time interval than the burst-size would allow if in a previous time period the maximum amount was not sent. Whenever less than the burst-size is sent during an interval, the remaining number of bits, up to the excess-burst-size, can be used to send more than the burst size in a later interval. Configuring the excess-burst-size to be the same as the burst-size effectively disables any excess burst capability.