8.4 Frame Relay Traffic Shaping
8.4.1 Overview
Frame Relay service providers use a parameter called committed information rate (CIR) to provision network resources to a Frame Relay user and regulate usage according to the assigned parameters. A mechanism written for the Frame Relay protocol exists for letting Frame Relay users know that congestion has been encountered within the Frame Relay network. This mechanism relies on the Forward Explicit Congestion Notification (FECN)/Backward Explicit Congestion Notification (BECN) bits in the Q.922 header of the frame. The network or the user can selectively set the discard-eligible (DE) bit in frames, and then drop these frames when congestion is encountered.

The traffic shaping-over-Frame Relay feature provides the following capabilities:

  • Rate enforcement on a per-virtual-circuit basis - You can configure a peak rate to limit outbound traffic to either the CIR or some other defined value, such as the excess information rate (EIR).
  • Generalized BECN support on a per-VC basis - The router can monitor BECNs and throttle traffic based on BECN-marked packet feedback from the Frame Relay network.
  • Priority/Custom/Weighted Fair Queuing (PQ/CQ/WFQ) support at the VC level - This allows for finer granularity in the prioritization and queuing of traffic, thus giving you more control over the traffic flow on an individual VC.