RE: Re: Signaling MIB - Draft 3 - Last Call - pktcSigDevCodecTable (Issue1)

Status: closed.

Based upon the feedback, there seems to be an agreement to indeed
include all possible combinations in the codec table. There has been a
suggestion to make it clear that an MTA MUST populate this table with
all possible combinations it supports for simultaneous execution, and to
provide an fully worked-out example.

Let's take and MTA with two endpoints, that supports PCMA, PCMU and
G729. All possible combinations of maximum codec instantiations for this
MTA can then be, for example:

  3 PCMA

  2 PCMA
  1 PCMU

  1 PCMA
  2 PCMU

  3 PCMU

  1 PCMA
  1 G729

  2 G729

  1 PCMU
  1 G729

This list is fixed by design, and is based upon architectural
limitations (DSP and memory resources) of the MTA. For examples, having
three G729 connections is not possible with this MTA, while you can have
three PCMA connections.

Translated to the pktcSigDevCodecTable, this would be:

pktcSigDevCodec(Combo)Index pktcSigDevCodecType pktcSigDevCodecMax
1                           pcma                3
2                           pcma                2
2                           pcmu                1
3                           pcma                1
3                           pcmu                2
4                           pcmu                3
5                           pcma                1
5                           g729                1
6                           g729                2
7                           pcmu                1
7                           g729                1

Note that groups 2 and 3 look similar, but are distinct. The idea is to
express that the MTA can have three instantiations of a G711 codec. In
this case, 2 PCMA and 1 PCMU or 2 PCMU and 1 PCMA. We cannot group this
into one group, because that would then have to be a group with 2 PCMA
and 2 PCMU, which would mean that the MTA can have two PCMA connections
AND two PCMU connections at the same time.

For clarifying that the MTA MUST in this table list all combinations it
*supports* at the same time, not all combinations that are
mathematically possible, we can extend the previous example.

Suppose now that the MTA also supports G728, but that G728 and G729 are
mutually exclusive for some reason. In this case, the
pktcSigDevCodecTable would be:

pktcSigDevCodec(Combo)Index pktcSigDevCodecType pktcSigDevCodecMax
1                           pcma                3
2                           pcma                2
2                           pcmu                1
3                           pcma                1
3                           pcmu                2
4                           pcmu                3
5                           pcma                1
5                           g729                1
6                           g729                2
7                           pcmu                1
7                           g729                1
8                           pcma                1
8                           g728                1
9                           g728                2
10                          pcmu                1
10                          g728                1

Note now that there is not a single group where g728 and g729 occur
together.


Thanks,

David

_____________________________________________________
David De Reu
tComLabs
Stapelplein 70/004 - 9000 Ghent - Belgium
Tel: +32 9 269 22 91 - Fax: +32 9 329 31 74
www.tComLabs.com
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