[Asterisk-Users] Best codec for faxes?

[Julio Arruda]

Steve Underwood wrote:
> Julio Arruda wrote:
> 
>> Roger Schreiter wrote:
>>
>>> Matthew Boehm schrieb:
>>>
>>>> I'm not using asterisk as the "fax machine" a la rxfax and the like. 
>>>> I'm
>>>> using an ATA (linksys, grandstream, etc) plugged into a fax machine. 
>>>> I know
>>>> not to use 729 for faxing. Which 'should' I use?
>>>> ...
>>>
>>>
>>> Hi,
>>>
>>> use G.711, and you'll have ISDN quality!
>>> Tradidional analog adaptors for ISDN do the same,
>>> and (analog) faxing over ISDN is working fine, isn't it?
>>
>>
>>
>> I would expect FAX over ISDN to work better than fax over G.711 on 
>> some networks.
>> ISDN doesn't have the jitter/packet loss of IP networks (unless you 
>> control the whole path or has some nice SLA :-)). The price being, is 
>> a circuit switched technology.
>>
> Clue: G.711 is the codec used over ISDN :-)

I understand a voice switched PCM channel/DS0 is G.711 and this also is 
the b-channel 'unrestricted 64k' ISDN circuit.
What I'm saying is, with ISDN, you have a end-to-end circuit switched 
channel, with very low delay and jitter, with g.711 over VOIP, you have 
at least the additional sampling time (20ms ?), jitter buffers, variable 
delays in the routers in the path (queueing related).