[Asterisk-Users] Asterisk as SIP <-> PSTN gateway

[John Todd]

Answers and opinions in-line:

>Hi,
>
>I'm new to Asterisk and have a couple of basic questions.
>
>We're interested in using * simply as a SIP <-> PSTN gateway using
>a T400P connected to one or more ISDN PRI lines (instead of using
>a Cisco box which would cost more and come with no hackable source
>code :-)
>
>First, is Asterisk's SIP stack up to date and fully functional
>with respect to the SIP protocol? Are there any known limitations
>that would cause problems in this application? Is there a general
>'to-do' list for SIP support?

No.  Yes.  No.  :)

Asterisk is "mostly" functional as a SIP endpoint but it is not a 
proxy, if that's what you're after.  Anything that is 
out-of-the-ordinary is not well-handled by Asterisk's current SIP 
implementation, but that's not to say it can't be fixed.  It's a very 
"pragmatic" solution right now, and things that break for people get 
fixed if you have adequate debugging and reasonable patch usefulness 
to argue for the community.  If you are looking to use "plain-jane" 
SIP termination, it works quite well and is stable.  If you are 
looking for exotic instant-message handling or redirection and 
re-INVITEs, then you will have some debugging ahead of you.

There is no list of issues presently, though that is being worked on too.

>E.g., it doesn't seem that chan_sip.c supports SUBSCRIBE/NOTIFY
>DTMF events, which some Cisco boxes seem generate for DTMF (?).

As far as I know, it does not support NOTIFY as a method for DTMF 
events.  It does, however, support the INFO trigger for DTMF - is 
this what you mean?

>Secondly, roughly what kind of CPU/system horsepower would required to
>support transferring 96 channels of voice data between SIP/Ethernet and
>the PRI if:
>
>   (a) if no transcoding were being performed (i.e., both the
>       RTP pkts and PRI B-channels were carrying ulaw data); and
>   (b) transcoding from e.g. ulaw on the PRI <-> GSM in the RTP.

I'll make wild, unsubstantiated guesses (yes, yes, I'm still working 
on the hardware list):

a) a single 2ghz machine
b) a dual 2ghz machine, maybe

JT


>Thanks,
>-Archie
>
>__________________________________________________________________________
>Archie Cobbs     *    Halloo Communications    *     http://www.halloo.com