[SIPForum-discussion] Sdp attribute for Call hold

[Kovács György]

Hi,

It depends. For example here it is one possible solution from Cisco 7600
SBC Configuration Guide:

With SDP call hold interworking, there are two ways of setting up call
hold using SIP. Either the caller or callee can renegotiate the call
characteristics using SDP so that either:


•The connection line is set to the null address, c=IN IP4 0.0.0.0.
•Or the direction attribute for their endpoint so that it does not
receive media from the endpoint.


–If this was previously set to a=sendrecv, the endpoint putting the call
on hold sets it to a=sendonly.
–If this was previously set to a=recvonly, the endpoint putting the call
on hold sets it to a=inactive.


Some SIP endpoints support setting the connection line to the null
address, some support setting the direction, and some support both
approaches. Additionally, some endpoints only respect setting the
direction attribute to sendonly or inactive.


With SDP call hold interworking, the SBC supports interoperating with
SIP endpoints that support a subset of the above approaches. When the
SBC detects that a call is being put on hold in the SDP, it removes any
preexisting c=IN IP4 0.0.0.0 or a=direction lines and replaces them with
appropriate settings for the endpoint.


If the endpoint putting the call on hold was sendrecv or sendonly, then
the default behavior is to send


•c=IN IP4 0.0.0.0
•a=sendonly


If the endpoint putting the call on hold was recvonly or inactive, then
the default behavior is to send


•C=IN IP4 0.0.0.0
•a=inactive

Regards,
Gyorgy Kovacs


On Wed, 2013-06-19 at 11:26 +0530, ankur bansal wrote: 

> Hi All
> 
> 
> Can anyone explain why a=sendonly is sent in offer from side
> performing HOLD ?
> I think a=inactive should be right way of holding call .
> Any specific scenario which explain when to use sendonly and when
> inactive 
> 
> 
> Thanks & regards
> Ankur Bansal
> 
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