Specifications

IP Networking
143
Variable RTP Packet Rates
MCD 4.0 introduced capabilities to support the use of variable RTP packet rates between specific
phones, applications and the 3300 ICP. Previously, RTP packet rates were fixed at 20 ms.
Currently, the 3300 ICP has only one means of connecting to service providers via IP
technology: over SIP Trunks. Some service providers of SIP trunks may require packet rates
that are not 20 ms. In this case the installer can select packet rates for SIP trunks other than
the default value of 20 ms. Alternatively, the installer can use an MiVoice Border Gateway at
the edge of the customer network to adapt packet rates to what the service provider requires.
The bandwidth used by the IP media streams will vary according to the packet rate value chosen.
Relative to current usage, bandwidth usage will rise by 27% when using a 10 ms packet rate
for G.711 and by 80% when using G.729, but will decrease if the packet size chosen is greater
than 20 ms. Chapter 11, Bandwidth, Codecs and Compression provides specific details on
bandwidth requirements to support SIP trunks with different packet rates.
The working packet rate should be a multiple of the working CODEC frame rate. Chapter 12,
Network Configuration Concepts, provides specific details under the CODEC Selection heading
of CODEC frame rates.
MiVoice Business supports packet rates from 10ms to 80ms in steps of 10ms. MiVoice Border
Gateway goes up to 60ms (also in 10ms increments).
The following Mitel devices and applications will support variable RTP packet rates:
The 5302 SIP set will not fully support variable RTP packet rates. It is possible to configure a
5302 device to provide a non-default rate. However, if this is done the set will always provide
that packet rate, even on calls that do not include a SIP trunk to a service provider.
Constraints
At this time, a limited number of 3rd-party phones and applications will be compatible with a
non-default (i.e. 20 ms) packet rate.
Since the 3300 ICP does not support rate adaptation between media streams using different
packet rates, it will not be possible to connect a media stream between two service providers
that require different packet rates through the 3300 ICP.
•E2T
•5302
• 5304
•5215
•5220
• 5212/24
• 5312/24
•5235
• 5330/40
• 5550 IP Console
•5560
• MiVoice Border Gateway
(Teleworker)
• Mobile Extension