You can find an example for Call Hold in RFC5359 chapter 2.1.
To take a call off hold the UA has to send a message with attribute
a=sendrecv. In message F16 this attribute is omitted, so the default
value of sendrecv is assumed (RFC4566 chapter 6).
If the offer contains a=recvonly, as in your example of the Re-Invite
without SDP, the answer must contain a=sendonly or a=inactive. This is
described in RFC3264 chapter 6.1. Sending a=sendrecv in the answer is
against protocol and will most likely not have the other UA start
sending a media stream.
Best regards,
Richard
On 19-12-2018 12:25, Amarnath Kanchivanam wrote:
Thanks All for your response.
I did try to send Ack with "sendrecv" attribute, but still it doesn't
work.
Do we have any RFC describing call flow for various scenarios?
Regards,
Amarnath
On Wed, Dec 19, 2018 at 2:08 PM Olle E. Johansson <o...@edvina.net
<mailto:o...@edvina.net>> wrote:
> On 19 Dec 2018, at 09:28, Richard Phernambucq
<r.phernamb...@cuperus.nl <mailto:r.phernamb...@cuperus.nl>> wrote:
>
> Hi Amarnath,
>
> A Re-Invite without SDP is called a late offer and isn't the
same as resuming a call that was placed on hold.
>
> If 'UAS' wanted to resume the call it should have sent an SDP
body with sendrecv attribute.
I don’t agree. The UA sending re-invite without SDP is asking the
other side “what is your
opinion on the state right now.”
Hold is a state that can exist separately on both sides, it
doesn’t really apply to the call.
/O
>
> Best regards,
> Richard
>
>
> On 19-12-2018 06:28, Amarnath Kanchivanam wrote:
>> Hi,
>>
>> I have below call flow and would like to know the correct behavior.
>>
>> UAC UAS
>> INVITE ----------------->
>> <---------------200 OK
>> Ack ---------------------->
>>
>> Now UAS puts call on Hold
>>
>> <---------------Re-Invite with send-only
>> attribute
>> 200 OK ----------> recv-only
>> <--------------Ack
>>
>> Now UAS does Un-Hold
>> <-------------Re-Invite* without SDP*
>> 200 OK ----------> recv-only
>> <----------------Ack with SDP
>>
>> In final Ack there is no SDP attribute (sendrecv or send-only).
With this
>> call flow UAC failed to Un-Hold and continue to be on hold
operation.
>> I would like you to share your comments which would help to
understand the
>> correct behavior.
>>
>> Regards,
>> Amarnath
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