/mcpQuality of Service for Voice over IP Traffic Shaping 14 QoSVoIP.mif FRF.12 Fragmentation and Interleaving Example The following configuration example shows how to configure fragmentation and interleaving using FRF.12: Traffic Shaping Traffic shaping is a QoS mechanism used to send traffic in short bursts at a configured transmission rate. It is most commonly used in Frame Relay environments where the interface clock rate is not the same as the guaranteed bandwidth or CIR. This section describes traffic shaping and includes the following subsections: • Traffic Shaping Overview • Frame Relay Traffic Shaping Example Traffic Shaping Overview Frame Relay traffic shaping is the most common traffic shaping application in VoIP environments. Frame Relay scenarios usually have a hub and spoke network where the hub link speed is higher than any of the remote link speeds. In some cases, the sum of the remote link speeds is higher than the hub link speed, causing oversubscription. Without Frame Relay traffic shaping, the hub may try to send at higher rates than the remotes can receive traffic, causing the Frame Relay network to arbitrarily drop traffic. However, the remotes could all send at an aggregate rate that is higher than what the hub can receive, again causing the Frame Relay network to arbitrarily drop traffic. When we refer to the Frame Relay network, we mean the service provider (SP) network of WAN switches that provide the end-to-end PVC connectivity. Because the WAN SP cloud has no Layer 3 or above intelligence, it can Configuration Example 7: Frame Relay Fragmentation (FRF.12) LFI interface Serial 0/1 no ip address encapsulation frame-relay frame-relay traffic-shaping ! interface Serial 0/1.64 point-to-point ip address 10.14.96.2 255.255.255.252 frame-relay interface-dlci 128 class voice ! map-class frame-relay voice frame-relay cir 256000 frame-relay fragment 320 In this example, Frame Relay traffic shaping is enabled on DLCI 128 and FRF.12 is configured with a fragmentation size of 320 bytes, which is 10 ms of the committed information rate (CIR). The fragmentation size should be 10 ms of the lower port speed at the endpoints of the PVC; this example assumes that the CIR and the lower port speed are the same: 256 kbps.