/mcpQuality of Service for Voice over IP VoIP QoS over Frame Relay Networks 37 QoSVoIP.mif Figure 10 VoIP QoS over Low Speed Frame Relay Links VoIP QoS over Frame Relay Recommended Solution You need to configure Frame Relay traffic shaping to ensure that speed mismatches at the remote and hub sites are handled correctly. For example, if the hub site has a T1 connection into the Frame Relay network and the remote site has a 128-kbps access speed, the hub site has the capability to send at T1 speeds toward this single remote. The Frame Relay switches will buffer this traffic to a small extent, but then arbitrarily drop anything over 128 kbps. You need to decide what should be dropped and what should be prioritized at the endpoints of the PVC. Frame Relay traffic shaping allows the routers to send traffic into the Frame Relay cloud below a preconfigured rate. Any traffic over this rate is queued, and a queueing algorithm such as LLQ can be used to make intelligent decisions on which packets should be sent. If the queues fill up, the packets simply will be dropped. However, if VoIP is given priority, and the total VoIP traffic is below the traffic-shaping rate, VoIP packets will be serviced with low latency and will not be dropped. For lower speed links less than 1.2 Mbps, you need to configure packet fragmentation to ensure that a VoIP packet need not wait behind a large packet. Fragmenting larger data packets to 10 ms of the link speed can bind the maximum waiting period. You can use cRTP to efficiently use bandwidth if the number of calls is not too large. Cisco 3640 voice gateway Ethernet switch Ethernet switch Ethernet switch Ethernet switch Ethernet switch Cisco 7206 Voice gateway Medium-Sized Branch Office Corporate HQ Cisco 2611 voice gateway Ethernet switch Small-Sized Branch Office PRI Frame Relay PVC Frame Relay switch Frame Relay PVC Frame Relay PVC PRI PRI PRI 54742