[SIPForum-techwg] comments on Interoperability Draft 3

[Maria Yndefors]

Hi, 
I havent read the whole doc yet, but so far looks great.
Just like to send a comment on echo.
An IP conference phone and also a headsets can cause echo from my experience. I think it is good to keep the echo cancelation in all devices, so that it is possible to cancel the echo as close to the source as possible.
Regards Maria

> 
> Section 14.4:
> Why must all devices support echo cancellation? E.g. If a SIP phone
> calls another SIP phone, there is no echo (generated by the 
> technology).
> If the same SIP phone calls to a SIP/PSTN gateway there may be echo
> generated in the PSTN. This echo should be removed by gateway. Thus,
> wouldn't it be sufficient if echo cancellation support is 
> mandatory only
> for devices which use technologies were echo may happen (i.e. 
> gateways,
> ATAs)?
> 
> 
> Chapter 15.1:
> In Austria, if I dial an unallocated number from the PSTN, there is no
> Reorder Tone, but the SIT. If this is also outside Austria, I suggest
> using the SIT instead of Reorder Tone for response codes 604 and 404.
> 
> Section 15.2: Cause Code 1,2 and 3 map to 404. I'm not an SS7 expert,
> but after Cause Code 1, I would think that there is no reason why the
> PBX should try this number using another route. But after reception of
> Cause Code 2 or 3 I would think the PBX may try another route 
> (e.g. via
> another service provider). Thus, wouldn't it be better to use another
> SIP response code, e.g. 604 for cause code 1?
> 
> regards
> klaus
> 
> 
> 
> 
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