RTP
Issue 3.4.1 June 2005
325
Application perspective
Table 75: Anatomy of 20-ms G.729 audio packet
shows the anatomy of a 20-ms G.729 audio
packet, which is recommended for use across limited bandwidth WAN links. Notice that
two-thirds of the packet is consumed by overhead (IP, UDP, and RTP), and only one-third is
used by the actual audio.
It is important to understand that all 20-ms G.729 audio packets, regardless of the vendor, are
constructed like this. Not only is the structure of the packet the same, but the method of
encoding and decoding the audio itself is also the same. This sameness is what allows an
Avaya IP Telephone to communicate directly with a Cisco IP Telephone, or any other IP
Telephone, when using matching codecs. The packets from the application perspective are
identical.
Network perspective
RTP header compression is a mechanism that routers use to reduce the 40 bytes of protocol
overhead to approximately 2 to 4 bytes. Cisco routers use this mechanism, as does the Avaya
X330WAN router, which is a module for the P330 chassis. RTP header compression can
drastically reduce the IP Telephony bandwidth consumption on a WAN link when using 20-ms
G.729 audio. When the combined 40-byte header is reduced to 4 bytes, the total IP packet size
is reduced by 60% (from 60 bytes to 24 bytes). This equates to reducing the total IP Telephony
WAN bandwidth consumption by roughly half, and it applies to all 20-ms G.729 audio packets,
regardless of the vendor.
Recommendations for RTP header compression
Enterprises that deploy routers that are capable of this feature might be able to benefit from it.
However, Cisco recommends caution in using RTP header compression on its routers because
it can significantly tax the processor if the compression is done in software. Depending on the
processor load before compression, enabling RTP header compression can significantly slow
down the router, or cause the router to stop completely. For best results, use a hardware/IOS/
interface module combination that permits the compression to be done in hardware.
Table 75: Anatomy of 20-ms G.729 audio packet
IP header
UDP header
RTP header
20 ms of G.729 audio
20 B
8 B
12 B
20 B
Содержание Application Solutions
Страница 1: ...Avaya Application Solutions IP Telephony Deployment Guide 555 245 600 Issue 3 4 1 June 2005 ...
Страница 20: ...About This Book 20 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 21: ...Issue 3 4 1 June 2005 21 Section 1 Avaya Application Solutions product guide ...
Страница 22: ...22 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 74: ...Avaya Application Solutions platforms 74 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 106: ...Call processing 106 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 124: ...Avaya LAN switching products 124 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 139: ...Issue 3 4 1 June 2005 139 Section 2 Deploying IP Telephony ...
Страница 140: ...140 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 186: ...Traffic engineering 186 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 204: ...Security 204 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 214: ...Voice quality network requirements 214 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 228: ...Avaya Integrated Management 228 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 239: ...Reliability Issue 3 4 1 June 2005 239 Figure 69 S8700 Media Server in a high reliability configuration ...
Страница 274: ...Reliability and Recovery 274 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 275: ...Issue 3 4 1 June 2005 275 Section 3 Getting the IP network ready for telephony ...
Страница 276: ...276 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 350: ...Implementing Communication Manager on a data network 350 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 356: ...Network recovery 356 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 366: ...Network assessment offer 366 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 367: ...Issue 3 4 1 June 2005 367 Appendixes ...
Страница 368: ...Appendixes 368 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 394: ...Access list 394 Avaya Application Solutions IP Telephony Deployment Guide ...
Страница 414: ...DHCP TFTP 414 Avaya Application Solutions IP Telephony Deployment Guide ...