/mcpQuality of Service for Voice over IP VoIP QoS over Frame Relay Networks 38 QoSVoIP.mif To provide high quality to VoIP over Frame Relay, you need to configure the following features: • Frame Relay traffic shaping: – Set the frame-relay cir map-class configuration command to maximum transmit rate (it should be the negotiated guaranteed rate from the service provider). – Disable the frame-relay adaptive-shaping map-class configuration command and set the mincir command value to match the cir command value for best quality voice. – Set the frame-relay bc map-class configuration command to 1/100 of CIR to allow traffic shaping to service packets at least every 10 ms. • FRF.12 LFI—You need LFI only if the remote or hub end port speed is less than 1.2 Mbps; fragmentation size should be 10 ms, or 80 bytes multiplied by the number of DS0s (For example, for 4x64k, fragmentation size would be 4x80 = 320 bytes) • LLQ on Frame Relay PVC—LLQ is applied under the map class for Frame Relay traffic shaping. • cRTP—cRTP is applied under the Frame Relay subinterface; you should use cRTP only if the CPU utilization is low, and for a small number of calls, depending on platform. The following configuration example shows how to enable the QoS features described in the previous section: Configuration Example 16: QoS for VoIP over Frame Relay WAN Links Commands Description class-map voip match ip precedence 5 ! Creates the class voip for voice traffic that has been marked with IP Precedence 5 using one of the available marking methods. class-map webtraffic match ip precedence 3 ! Creates the class webtraffic for web traffic that has been marked with IP Precedence 3 using one of the available marking methods. policy-map llq class voip priority 64 class webtraffic bandwidth 64 class class-default fair-queue ! Defines the QoS policy map llq: Class voip traffic gets priority and is limited to 64 kbps during congestion; class webtraffic packets are guaranteed 64 kbps. All other traffic shares the remaining bandwidth. interface Serial 0/1 no ip address encapsulation frame-relay frame-relay traffic shaping ! Enables Frame Relay traffic shaping. You must enable Frame Relay traffic shaping to handle speed mismatches and oversubscription. (LLQ per Frame Relay PVC also requires 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 Attaches traffic shaping class voice to this Frame Relay PVC. frame-relay ip rtp header-compression ! Configures cRTP to reduce the bandwidth requirements of each voice call. map-class frame-relay voice no frame-relay adaptive-shaping Disables adaptive shaping. We do not recommend adaptive shaping for VoIP. frame-relay cir 256000 Sets the CIR or upper transmit rate at 256 kbps. frame-relay bc 2560 Sets the committed burst rate to 1/100 of CIR.