/mcpbandwidth guarantees are met. Not suitable for voice. 1. Needs bandwidth guaranteed for voice. 2. Needs latency to be taken care of. 3. Sufficient for voice. 4. Serialization Delay Even if queuing works at its best and prioritizes voice traffic, there are times when the priority queue is empty and a packet from another class is serviced. Packets from guaranteed bandwidth classes must be serviced based on their configured weight. If a priority voice packet arrives in the output queue while these packets are being serviced, the voice packet can wait a significant amount of time before it is sent. Voice packets experience serialization delay when they have to wait behind larger data packets. Serialization delay can introduce the worst form of jitter for voice packets. If the voice packets have to wait behind a data packet that is as large as 1500 bytes, on a slower link, this translates to a huge delay. The serialization delay is vastly different if the data packet is 80 bytes, as shown in this example: Serialization delay on a 64 kbps link due to a 1500 bytes packet = 15008/64000 = 187.5 ms. • Serialization delay on a 64 kbps link due to a 80bytes packet = 808/64000 = 10 ms. • Therefore, a voice packet potentially has to wait up to 187.5 ms before it is sent if it gets stuck behind a single 1500−byte packet on a 64 kbps link. On the other hand, another voice packet has to wait for only 10 ms at the destination gateway. This results into a huge jitter that occurs due to the variance in the inter−packet delay. On the originating gateway, voice packets are usually sent every 20 ms. With an end−to−end delay budget of 150 ms and strict jitter requirements, a gap of more than 180 ms is unacceptable. Introduce a mechanism of fragmentation that ensures that the size of one transmission unit is less than 10 ms. Any packets that have more than 10 ms serialization delay need to be fragmented into 10 ms chunks. A 10 ms chunk or fragment is the number of bytes that is sent over the link in 10 ms. Calculate the size by using the link speed, as shown in this example: Fragmentation size = (0.01 seconds * 64,000 bps) / (8 bits/byte) = 80 bytes • It takes 10 ms to send an 80−byte packet or fragment over a 64 kbps link. In case of multiple ATM or Frame Relay Permanent Virtual Circuits (PVCs) on a single physical interface, configure fragmentation values (on all PVCs) based on the PVC that has the lowest bandwidth available. For example, if there are three PVCs that have a guaranteed bandwidth of 512 kbps, 128 kbps, and 256 kbps, then configure all three PVCs with a fragment size of 160 bytes (the lowest speed is 128 kbps that requires a 160−byte fragment size). These values are recommended for different link speeds: Link Speed (kbps) Fragmentation Size (bytes) 56 70 64 80 128 160 256 320 512 640 768 960 1024 1280 1536 1920