[SR-Users] Can only tranfer (refer) a call one time

[Grzegorz Stanislawski]

it is just bypass to enable call transfers for users connected to sipx, 
when uplink ITSP doesn't support REFER.
sipxbridge works as SBC in b2bua mode, it stays in path of all calls to 
and from Your uplink ITSP and when it receives REFER i just makes new 
call (using INVITE) to Your ITSP, and then bridges new call with proper 
leg of previous call and disconects other one.
so inside sipx 'domain' you can use call transers using refer, and from 
Your ITSP side there are only invites byes and cancels.
in ex. in case when someone from outside calls you inside sipx, and you 
forward it back outside - from ITSP point of view there will be 2 calls, 
one to and one from your sipx, and he would have no idea that those 
calls are related.

drawback is of course that rtp streams are going back and forth through 
your internet uplink and AFAIR deaf silence at some point of transfer, 
but at least it works with all lousy ITSP's.

You should check sipx documentation or sipx mailing list, this thread is 
getting off-topic.

and REFER is not only for blind transfers ;-)

Grzegorz Stanislawski


W dniu 2011-02-27 20:35, Youngjin Park pisze:
>
>     Hi,
>
>     Can you tell me what advantage on INVITE has against REFER?
>
>     REFER is a kind of blind transfer and INVITE in sipXbridge is 3PCC?
>
>     Thanks in advance.
>
>     Youngjin
>
>
>     On Sun, Feb 27, 2011 at 6:40 AM, Grzegorz Stanislawski
>     <stangrze at netitel.pl <mailto:stangrze at netitel.pl>> wrote:
>
>         Hi.
>         We have proverb for this, i don't know english version but it
>         goes like this:
>         "When it isn't known what it's all about, it's about money"
>
>         Your ITSP had troubles with proper handling second transfer for
>         billing purposes so decided to disable it.
>         Proxy doesnt participate in call transfer, but ITSP it must
>         charge users properly: Alice should pay just for call to Bob,
>         Bob for "his" call to Charlie and so on.
>         If You are using sipX You should use sipXbridge, it replaces
>         REFER with INVITE and bridges calls.
>
>         Grzegorz Stanislawski
>
>
>
>         W dniu 2011-02-25 11:40, niklas rehnberg pisze:
>
>             Hi,
>             Thank for the quick response.
>             The issue occur only when the Alice is a PSTN client.
>             My ITSP says that they only supporting one call transfer
>             (very strange).
>             They can not explain why etc...
>             PSTN client:              Alice
>             MGW/MGC(ITSP):     Cisco/SER
>             Our sip server:           SIPX
>
>             BR Niklas
>             2011/2/25 Iñaki Baz Castillo <ibc at aliax.net
>             <mailto:ibc at aliax.net> <mailto:ibc at aliax.net
>             <mailto:ibc at aliax.net>>>
>
>                 2011/2/25 niklas rehnberg <niklas.rehnberg at gmail.com
>             <mailto:niklas.rehnberg at gmail.com>
>             <mailto:niklas.rehnberg at gmail.com
>             <mailto:niklas.rehnberg at gmail.com>>>:
>              > Hi,
>              > Have following issue:
>              >
>              > Alice calling Bob.
>              > Bob make call transfer to Charlie  (works fine)
>              > Charlie transfer Alice to David.    (the call break)
>              >
>              > Why is not possible to transfer the call more than one time?
>              > Is it any parameters?
>              >
>              > My ITSP use SER together with Cisco MGW.
>
>                 Niklas, nothing in SIP protocol neither in SER/Kamailio
>             makes your
>                 scenario to fail. It must be a problem in your custom
>             setup. Try
>                 identifying the problem capturing SIP traces.
>                 Also take into account that a proxy doesn't participate
>             at all in the
>                 process of a "call transfer". It's just a transparent
>             mechanism for a
>                 proxy.
>
>                 --
>                 Iñaki Baz Castillo
>             <ibc at aliax.net <mailto:ibc at aliax.net> <mailto:ibc at aliax.net
>             <mailto:ibc at aliax.net>>>
>
>
>
>
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>
>
>
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>
>
>
>
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