Mitel 5560 IPT none Specifications download pdf (Page 200)

Engineering Guidelines

186

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 186

• “3300 ICP controllers and compression” on page 187

• “Internal 3300 ICP devices and compression” on page 187

• “IP applications and compression” on page 187

• “IP networking routes and compression” on page 188

• “Compression zones” on page 188

• “IP trunk routes and compression” on page 190

• “IP networking and compression licenses” on page 190

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.

Other IP phones, however, do not support compression. Calls to and from these devices are

restricted to G.711 only. The following IP phones have this restriction:

• 4015 and 4025

• 5001 and 5005

• 5201, 5205, and 5207

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Mitel 5560 IPT none Specifications Page 200