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| 8.7 |  | Traffic Shaping |
| 8.7.1 |  | Traffic shaping overview |

Traffic shaping allows rate control of traffic leaving an interface in order to match its flow to the speed of the remote target interface and to ensure that the traffic conforms to policies defined for it. Therefore, traffic adhering to a particular profile can be shaped to meet downstream requirements, eliminating bottlenecks in topologies with data-rate mismatches.

Traffic shaping prevents packet loss. Its use is important in Frame Relay networks because a Frame Relay switch cannot determine which packets take precedence, and which packets should be dropped when congestion occurs. It is of critical importance for real-time traffic, such as Voice over Frame Relay, that latency be minimized by bounding the amount of traffic and traffic loss in the data link network and by keeping the data in the router that is making the guarantees.

Retaining the data in the router, through the use of queuing, allows the router to prioritize traffic according to the guarantees it is making.

Cisco IOS QoS software has three types of traffic shaping:

- Generic Traffic Shaping (GTS)
- Class-Based
- Frame Relay Traffic Shaping (FRTS)

All three of these traffic shaping methods are similar in implementation, though the CLIs differ somewhat and they use different types of queues to contain and shape traffic that is deferred. The underlying code that determines whether enough credit is in the token bucket for a packet to be sent or whether that packet must be delayed is common to both features. If a packet is deferred, GTS and Class-Based Shaping use a weighted fair queue to hold the delayed traffic. FRTS uses either a custom queue or a priority queue for the same, depending on what has been configured.