[SIPForum-discussion] SIP Call Control

[Jamie Chen]

Hi there,

First of all, many thanks for people's feedbacks in the other email thread
with subject "Controlling SIP UA from the application". I learned a lot from
your response. I have the further questions in term of SIP Call Control.

Let's say the end user has a SIP hard phone and you want your application to
monitor it and controlling it from your application. For example, when there
is an inbound call arrives, the SIP hard phone shows the inbound call. And
your application also shows the inbound call too. But the end user can
answer the call from your application. The call is then connected to the
user's hard phone and the RTP voice stream is sent to this SIP hard phone.

Can we achieve this through having a SIP soft phone in the application? But
it seems that both of SIP soft phone and hard phone cannot co-exist because
they are 2 UAs. So I am wondering whether we can use SIP to do call control
on the other one. In this case, can we use some form of SIP soft phone to
control the SIP hard phone.

Some people were saying this has to do with "SIP Forking". But after my
research, it seems that SIP Forking is meant to fork multiple SIP Requests
(e.g. INVITE) and expect one response back. But in this case, we are
actually cloning each SIP requests and each SIP responses to both UAs. If I
think deeper, I don't think a regular SIP server can do this and I am not
sure if this is part of SIP spec.

Thanks again for your advice.
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