1. ETE405 :: Lecture 9 Chapter 9. Quality of Service Dr. Mashiur Rahman

5. QoS Network Toolkit

7. Bandwidth Limitations The first issue of major concern when designing a VoIP network is bandwidth constraints. Depending upon which codec you use and how many voice samples you want per packet, the amount of bandwidth per call can increase drastically. For an explanation of packet sizes and bandwidth consumed, see Table After reviewing this table, you might be asking yourself why 24 kbps of bandwidth is consumed when you're using an 8-kbps codec. This occurs due to a phenomenon called " The IP Tax." G.729 using two 10-ms samples consumes 20 bytes per frame, which works out to 8 kbps. The packet headers that include IP, RTP, and User Datagram Protocol (UDP) add 40 bytes to each frame. This "IP Tax" header is twice the amount of the payload.

8. cRTP To reduce the large percentage of bandwidth consumed by a G.729 voice call, you can use cRTP. cRTP enables you to compress the 40-byte IP/RTP/UDP header to 2 to 4 bytes most of the time

17. IP Header and ToS Field IP Precedence refers to the three bits in the ToS field in an IP header, as shown in Figure.

21. Generic Traffic Shaping (GTS) GTS applies on a per-interface basis and can use access lists to select the traffic to shape. It works with a variety of Layer 2 technologies, including Frame Relay, ATM, Switched Multimegabit Data Service (SMDS), and Ethernet.