Subject: [Sip] Music On Hold

From: "Suha Cubukcuoglu" <[email-masked]>
Date: Tue, 3 Feb 2004 11:20:19 -0000

Hi,

During an attended call transfer attempt, the transferred party
(A-Party) is put on 'hold' by the transferor (B-Party) - i.e. no media
stream flows from B to A and vice versa. While the A-Party is on hold,
the B-Party can INVITE a third party to play 'Music on Hold' tune to the
A-Party until the transfer attempt succeeds. We think that there are
complications in this approach. Firstly, the SIP Proxy must now where to
route the new INVITE generated by the B-Party. If the destination URI is
[email-masked]', the SIP Proxy must either do a DNS query or use
its IP dial-plans to know where to route the call. Secondly, the B-Party
might eventually end-up receiving the music tune whereas it was
initially intended for the A-Party - we've had problems in the past
because of this. This is all dependent on how the third party MOH server
handles/established/terminates requests. 

We think that third party invitation is a bad idea, and it would rather
be more suitable to have a dedicated server (IVR unit perhaps) which the
SIP Proxy Server can transfer calls to/from upon request for a MOH
service. Could you tell us your opinions about this please?

Thanks.

Regards,    

Suha Cubukcuoglu
nplusone
t: +44 131 514 2000
d: +44 131 514 4037

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