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Tony

Thanks for getting back to me.

The SBC is an Acme Packet. The way we have it set up; in
relation to sipXecs is as follows:

The SBC has 'access'; 'peer' and 'core' realms.

When an IP phone registers; it does it through the 'access'
realm; which performs NAT traversal and routes the call to
sipXecs via its core realm. sipXecs sees the device as not
behind NAT.

When calling voicemail or conference bridge on sipXecs;
there is only one session going from the IP phone though the
SBC to sipXecs.

When I dial a PSTN number; the call has the same flow as
above except that sipXecs proxies the INVITE to the SBC on
its 'peer' realm. The SBC in turn transparently delivers the
call to the appropriate PSTN trunk.
sipXecs sees the peer realm as a gateway; as in there are no
registrations.

The SBC is configured to anchor media from the IP phone to
sipXecs, but it doesn't anchor media on the peer realm.

So let's say we have a call established as:

IP Phone -> [SBC access] -> [SBC core] -> sipXecss -> [SBC
peer] -> SIP Trunk provider

media is anchored at the SBC: The IP phone sees [SBC access]
media address and everything else after that sees media
coming from [SBC core]. Both of these are routable IPs; so
this suits the needs.

Now the IP phone initiates an unattended transfer to another
PSTN number.

the REFER shows the same path as above; but [SBC peer] is
configured to reject the REFER because [SIP Trunk provider]
does not allow the REFER method; so the REFER cannot be
completed. My expectation; after using other software like
FreeSHITCH; was that sipXecs would consume the REFER and in
turn generate another INVITE towards PSTN number [SBC peer].
Seems I'm mistaken in my expectation here.

For MOH; what I, perhaps naively; though it would happen is
that if sipXecs receives a ReINVITE originated from the IP
phone where its SDP contains 'a=sendonly'; it would ReINVITE
the PSTN leg to its IVR which is playing MOH. Once the IP
phone sends another ReINVITE with 'a=sendrecv'; sipXecs then
forwards that SDP so its IVR in no longer on the call.

my questions in regards to sipXecs is what is the expected
behavior in this case when it receives a REFER or the
On-hold signal from the IP phone.

Thanks
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