Description: Escaux G.729 codec appliance module

Document description

Escaux Code: XAG001
Document type: Item description

Description

Per-appliance module for the G729 transcoder. The G729 codec is a highly optimized codec for transferring speech over a low bandwidth channel. This module implements transcoding of ongoing calls to and from the G729 codec. If the project needs conversion to/from the G.729 codec, add one here.

Note that this license is valid per appliance. In case of a redundant setup with 2 appliances, each requiring 50 licenses, you need to order two times 50 licenses.

Quick evaluation method

Licenses are needed per SOP in an active/active or active/standby configuration
The amount of G.729 transcoding licenses depends essentially on:
- P1 is the amount of phones restricted to G.729
- P2 is the expected amount of phones restricted to G.729 simultaneously participating to conference calls

Evaluation per SOP

Number of G.729 phones (P1)	Number of G.729 licenses (A)
5	5 + P2
10	6 + P2
20	7 + P2
50	11 + P2
100	17 + P2
150	23 + P2
200	29 + P2

When should we use G.729 ?

G.729 codec can be used when we want to limit the bandwidth of VoIP calls on a connection.

This can occurs in two situations :

We have a main site with a sufficiently large upstream link to the telephony provider network and all phones on the main site use G.711. The infrastructure also has remote sites where the bandwidth is more of a concern. In this case, G.729 is a good option to reduce the bandwidth consumption on those small bandwidth links. If G.729 is used, we will not need a G.729 transcoding licence when an outside call directly reaches a remote phone (or the opposite). The G.729 transcoding license is only needed during certain scenarios where the SOP is directly communicating with the G.729 phone (see section on Cases).

We have a main site with a small upstream link to the telephony provider network. In this case, we can configure the phones and the SIP trunk to use G.729 as preferred codec. Communications between the phones and the upstream telephony provider network will occur in G.729. The G.729 transcoding license is only needed during certain scenarios where the SOP is directly communicating with the G.729 phone (see section on Cases).

How to size the number of codec licences to use ?

G.729 codec licences are used whenever a transcoding has to be done. A G.729 transcoding happens when a channel (phone, SIP trunk, etc.) on one side of the PBX use G.729 and use another codec for the channel on the other side. When an audio message is recorded through a G.729-codec channel, the audio file will also be in G.729 and a transcoding will also be necessary if the channel who wants to hear the message use another codec.

Cases

There is an ideal case where no G.729 codec licence should be necessary : For basic telephony without any audio file played or access to voicemail.

For other cases where G.729 is used, a minimal licences should be provided :

When someone calls an extension with a G.729 configured SIP trunk and reaches the voicemail, a licence is used when prompts are played and when the message is recorded. The message will not be recorded in the G.729 format so a licence can be used when listening to the voicemail with a G.729 configured phone.

For conversation with the G.729 codec end-to-end, consumes a G.729 codec when the call is put "on hold".

Whenever an audio file is played from a communication which is set up in G.729, a licence is needed to make the file audible in the other format (this include "Welcome message", IVR, etc.). Note that an audio file at the beginning of a callflow can change the negociation of the codec. For a communication between two endpoints which support G.729, if the caller A reach directly the caller B, they will use G.729 but if caller A reach first an audio file, it will use G.711 and keep G.711 even when connected to the other part which is codec in G.729. In the latter case, we will then need a licence for the duration of the conversation.

Transfer : When a call will be transfered from an uncompressed communication to a phone which support only G.729, a licence will be used for the duration of the communication even if the other part support G.729 (there will be no codec re-negociation). With an attended transfer, if we transfer a call from a G.729 communication to a G.711 phone, it can even use two licences for a short time. One to play a waiting music to the person on hold and one to transcode the communication for the two other parts.

Queue : The behavior in a queue depends on whether the queue uses the ringing tone or the music on hold. If the queue sends a ringing tone, the call will behave as if it was a direct call to the agent. If a music on hold was chosen, the behavior will be the same as if an audio message was played before calling the phone.

Conference bridge : Due to the functionality of the conference bridge, all channels need to be decoded, afterward be mixed with all other inputs and thus be encoded for each channel. This mean that even with all endpoints in G.729, a licence will be needed for every channel encoded in G.729.

Calculation method

Obviously, the licence need will depend on the usage of the endpoints using G.729 but we will do here a rough estimation.

When G.729 phones will be contacted directly, G.729 licences will hardly be used. Some should be provided for voicemail, music on hold, etc. One licence for twenty phones should be enough.

For communications to G729 phones after an audio message (see above) or transfered from a communication using G.711 (or in a conference bridge, etc.), the codec will be used during the length of the conversation. In this case, one licence for five phones using G.729 should be provided.

P1 is the amount of phones restricted to G.729
P2 is the expected amount of phones restricted to G.729 simultaneously participating to conference calls

A is the amount of required G.729 transcoding licences.

Basic telephony without IVR or voice prompts on incoming calls: A = 3+8/200*(P1-5)+P2
Average of 2 incoming calls playing an announcement or being transfered of 3 minutes duration during the busiest hour of traffic: A = 3+25/200*(P1-5)+P2

The minimum of 3 is there in order to be able to use the voicemail and change the status of the g.729 users.