QoS Traffic Requirements Videoconferencing

• Minimum priority bandwidth guarantee required is:

- For example, a 384-kbps stream would require 460 kbps of bandwidth

*One-way requirements

Module Summary

This topic summarizes the key points discussed in this module.

This topic summarizes the key points discussed in this module.

The different link efficiency mechanisms available in Cisco IOS software include class-based TCP and RTP header compression, Layer 2 payload compression, MLP link fragmentation and interleaving (MLP LFI), and Frame Relay Fragmentation (FRF. 12). You can use these QoS mechanisms on slower WAN links, such as 768 kbps and slower, to improve the link efficiency by increasing the throughput and decreasing the overall delay.

Class-based TCP and RTP header compressions are configured using the MQC method to reduce the protocol header overhead. Header compression is most effective for packets with small payload size.

Layer 2 payload compression is not used much because of the software compression delay overhead. Using a hardware compression module can help reduce the software compression delay.

For MLP LFI is supported on a leased-line interfaces, while FRF. 12 (for VoIP) and FRF. 11 Annex C (for VoFR) are supported on Frame Relay interfaces. LFI is used to reduce the serialization delay of large packets. Serialization delay is based on the link speed and packet size. To ensure high voice quality, the recommended serialization delay is 10 to 15 ms maximum. As a general rule, a fragment size of 80 bytes for every 64 kbps of link speed is recommended.

For additional information, refer to these resources:

■ For more information on link efficiency mechanisms, refer to Link Efficiency Mechanisms Overview at this URL:

http : //www.cisco. com/univercd/ cc/td/ doc/product/software/ios 122/122cgcr/fqos_c/fqcprt6/ qcflem.htm

■ For more information on Layer 2 payload compression, refer to Understanding Data Compression at this URL: http://www.cisco.com/warp/public/116/compress_overview.html

■ For more information on TCP and RTP header compression, refer to these RFCs:

— RFC 2508 (RTP header compression)

— RFC 1144 (TCP header compression)

— RFC 2507 (IP header compression)

■ For more information on FRF. 12 and DTS configuration, refer to Frame Relay Traffic Shaping With Distributed QoS on the Cisco 7500 Series at this URL: http://www.cisco.com/warp/public/105/distribfrts.html#topic2°/o20URL

■ For information on FRF. 11 Annex C, refer to VoFR Encapsulation and Fragmentation at these URLs:


http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121newft/121limi t/121e/121e2/vofvip/vofr3vip.htm

■ For more information on Cisco class-based TCP and RTP header compression, refer to Class-Based RTP and TCP Header Compression at this URL:

http : //www.cisco. com/univercd/ cc/td/ doc/product/software/ios 122/122newft/122t/ 122t13/ft hdrcmp.htm#wp1044256

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