Mitel MiVOICE BUSINESS, Engineering Manualline

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Bandwidth, Codecs and Compression
189
COMPRESSION – INTRODUCTION
Generally when compression is mentioned, it is usually mentioned with a CODEC, for example,
“G.729 Compression.” This just refers to the ability to reduce the amount of data that needs to
be carried across the IP infrastructure.
In the case of CODEC compression, this works by reducing the amount of data that needs to
be carried in the voice payload. However, the IP header information still needs to be added, so
although there is a reduction in required bandwidth, the gain isn’t always as much as might be
expected.
Other forms of data compression also exist in the network. It is possible to do a level of header
compression on certain fixed links, e.g. RFC 1993. Other data compression techniques include
Compressed RTP (RFC 2508 or Enhanced CRTP-RFC 3545), or they may only compress up
to the IP layer. Data and header compression is typically used for lower speed links, less than
1.5 Mbps, where every last bit per second counts. Since the link is point-to-point, the header
information is simply repeat information and is redundant. In this case, much of the information
can be established before the data is sent, and the far end router re-applies this data before it
is sent onwards. Although this can work well for data, it adds delay to the transmission as well
as using valuable router resources.
3300 ICP COMPRESSION GUIDELINES
Compression affects a number of call connection types. These include:
• IP phone to IP phone
• IP phone to TDM and vice versa
• IP phone at a remote site back to TDM or IP
• IP connection across an IP trunk route
Compression affects other aspects of the 3300 ICP as well. These include IP phones, the 3300
ICP, 3300 ICP devices, IP applications, IP networking routes and trunk routes, and licenses.
See the following topics for more information.
• “IP Phones and compression” on page 189
• “3300 ICP controllers and compression” on page 190
• “Internal 3300 ICP devices and compression” on page 190
• “IP applications and compression” on page 191
• “IP networking routes and compression” on page 192
• “Compression zones” on page 192
• “IP trunk routes and compression” on page 193
• “IP networking and compression licenses” on page 193
IP Phones and compression
Some IP phones include compression capability and licenses. If required, these devices can
stream directly with compressed voice without 3300 ICP intervention.