[SR-Users] Is this idea even feasible?

Antony Stone Antony.Stone at kamailio.open.source.it
Tue Aug 17 23:22:49 CEST 2021

On Tuesday 17 August 2021 at 22:39:49, Fred Posner wrote:

> On 8/17/21 4:22 PM, Antony Stone wrote:
> > 
> > Can you point me at anything which documents how this could be possible?
> Asterisk was just one possibility of course. I don't know your case in
> detail and probably best to direct that question to an Asterisk group of
> course...

I have.  The answer is "Asterisk as a SIP client is extremely basic and it 
cannot do what you want".

> This said, Asterisk if as a b2bua you may want to look at
> moh_passthrough and ARI.

I *really* cannot help feeling I still have not explained my question well.

I have a very basic SIP client application, which can make and receive phone 
calls, and that's it.

It is registering to a PBX system which can do all the usual fancy things like 
putting calls on hold, playing music, transferring calls, conferencing... 
*provided* it gets the SIP commands from a phone/client telling it to do these 

What I am looking for is something which can sit in the network connection 
between this very basic SIP client, and the very capable SIP server, and can 
send commands to the server which the client is incapable of generating, such 
as "place this call on hold", "resume this held call", "transfer this call", 

It obviously needs to sit in the network connection between client and server, 
so that it sees the INVITEs and the OKs, and can keep track of the Call-IDs, 
sequence numbers, To and From headers, etc, and then re-use those when it 
needs to send a request to the server which the client doesn't know how to do.

Because of this, I tend to think of what I'm looking for as a SIP proxy, 
because it's in between the client and the server, relaying messages between 
the two.

Maybe that's the wrong name for it, if so I apologise.

I am definitely *not* looking for a SIP server which can act as a PBX, routing 
calls and putting them on hold.  I already have that.

What I need is something which can *tell* such a PBX that a call needs to be 
put on hold, when the client which originally initiated the call cannot do 
that for itself.

This thing (proxy) which can send the instruction to put a call on hold could 
be told to do so by a simple web interface, for example, where I place a web 
page side-by-side on screen with the rather dumb SIP client, showing buttons 
labelled "Hold", "Resume", "Transfer", "Conference", etc., and these send the 
instructions to my "proxy" between the dumb client and the capable server, so 
that the server can be told to do the appropriate thing.

I hope that helps.


"Measuring average network latency is about as useful as measuring the mean 
temperature of patients in a hospital."

 - Stéphane Bortzmeyer

                                                   Please reply to the list;
                                                         please *don't* CC me.

More information about the sr-users mailing list