Frame relay traffic shaping

Frame relay

 

1. Setting the CIR or MinCIR to the access rate should be avoided because those values does not consider the overhead bytes of flag and CRC and hence would lead to oversubscription of the links and cause packet drops. Shaping at access rates is not recommended. At a max, you should shape at 95% of the access rate.
2. Frame relay traffic shaping is enabled on the main interface and it applies to all DLCI’s on that interface. You can apply different traffic shaping values using the map class statements. If you do not apply any shaping to one DLCI, then it would match the default map class with a CIR of 56000

 

CIR	Average rate Higher than guaranteed rate Lower than access rate Allows for bursting When using VoIP/VoFR, must be same as the guaranteed rate. Same as MinCIR Default: 56000 bps
MinCIR	Guaranteed rate Default: half of CIR
Bc	Amount of data send per Tc For Data = CIR/8 so Tc = 125 ms For Voice = CIR/100 so Tc = 10ms
Be	Amount of excess data to be send during the first Tc interval once credit is build up Used only if CIR is less than Access rate For voice, set Be to 0 Default = 0
BECN	When it receives a BECN, the traffic rate is dropped by 25% For each BECN (one per time interval), the rate is dropped by 25%, until it reaches the MinCIR value It must allow 16 intervals of no BECN, before it traffic rate is increased The rate is increased by the byte limit/16. Hence it takes much longer to get back to CIR level