Frame Relay Traffic Shaping 95% CIR

[mlitka]

I have been reading the QoS SRND Guide and they recommend to shape Frame Relay circuits to 95% of the CIR. The Frame Relay links we have in use are simply access links to a service provider MPLS network. Further on in the guide it recommends these procedures be used even in this scenario.

The question is: Will I be losing 5% of my bandwidth? And if so, is a 5% loss in bandwidth worth the performance gain?

[mohammedmahmoud · Accepted solution]

Hi,

The reason for this is that the shape rate does not take into account the overhead bytes of the flag and Cyclic Redundancy Check (CRC) fields. So, shaping at line rate is actually oversubscribing, and will cause interface congestion. Shaping at the access rate is not recommended. You should always shape the traffic at 95 percent of the access rate. More generally, the aggregate shaped rate should be no more than 95 percent of the access rate, accordingly it should affect the performance.

HTH, please rate if it does help,

Mohammed Mahmoud.