Discussion:
[Sip-implementors] RTP start time in case of PRACK
Rajesh
2014-05-19 14:58:45 UTC
Permalink
Hi,

In the below call flow, when the UAC and UAS can start transmitting RTP
packets. I think RTP session can be started after UAS receives PRACK for
180 ringing. I would really appreciate your opinion on this. Thanks


UAC -> UAS (Invite)
UAS -> UAC (100 trying)
UAS -> UAC (180 Ringing Require 100rel header is set) includes SDP Body
UAC -> UAS (PRACK to 180 Ringing)
UAS -> UAC (200 OK to PRACK)
UAS -> UAC (200 OK to invite) No SDP
UAC -> UAS (ACK to 200 OK for invite)


Regards
Rajesh
Paul Kyzivat
2014-05-19 15:17:26 UTC
Permalink
Post by Rajesh
Hi,
In the below call flow, when the UAC and UAS can start transmitting RTP
packets. I think RTP session can be started after UAS receives PRACK for
180 ringing. I would really appreciate your opinion on this. Thanks
The use of 180rel doesn't alter when RTP can start. From the UAC's
perspective it can still start toward the UAC as soon as the INVITE is
sent. From the UAS perspective it can't start toward the UAC until the
UAS has received the offer (the INVITE). There is no reason why the UAS
must wait for the prack. However the UAS might *want* to wait for the
prack before starting to send, since that gives it more assurance that
things are in good shape.

For instance, if something in the middle is gating the flow of RTP in
both directions until the answer is received, then waiting for the prack
will avoid early media being dropped.

Thanks,
Paul
Post by Rajesh
UAC -> UAS (Invite)
UAS -> UAC (100 trying)
UAS -> UAC (180 Ringing Require 100rel header is set) includes SDP Body
UAC -> UAS (PRACK to 180 Ringing)
UAS -> UAC (200 OK to PRACK)
UAS -> UAC (200 OK to invite) No SDP
UAC -> UAS (ACK to 200 OK for invite)
Regards
Rajesh
_______________________________________________
Sip-implementors mailing list
Sip-implementors at lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
Rajesh
2014-05-19 15:26:47 UTC
Permalink
Thanks Paul. Sorry, i didn't get the point that "From the UAC's perspective
it can still start toward the UAC as soon as the INVITE is sent.". May i
know how UAC can start the RTP as it has not negotiated media parameters
with UAS and doesn't know the port. Please be informed that we have SDP in
INVITE.


UAC -> UAS (Invite) includes SDP offer
UAS -> UAC (100 trying)
UAS -> UAC (180 Ringing Require 100rel header is set) includes SDP answer
UAC -> UAS (PRACK to 180 Ringing)
UAS -> UAC (200 OK to PRACK)
UAS -> UAC (200 OK to invite) No SDP
UAC -> UAS (ACK to 200 OK for invite)

Regards
Rajesh
Post by Paul Kyzivat
Post by Rajesh
Hi,
In the below call flow, when the UAC and UAS can start transmitting RTP
packets. I think RTP session can be started after UAS receives PRACK for
180 ringing. I would really appreciate your opinion on this. Thanks
The use of 180rel doesn't alter when RTP can start. From the UAC's
perspective it can still start toward the UAC as soon as the INVITE is
sent. From the UAS perspective it can't start toward the UAC until the UAS
has received the offer (the INVITE). There is no reason why the UAS must
wait for the prack. However the UAS might *want* to wait for the prack
before starting to send, since that gives it more assurance that things are
in good shape.
For instance, if something in the middle is gating the flow of RTP in both
directions until the answer is received, then waiting for the prack will
avoid early media being dropped.
Thanks,
Paul
UAC -> UAS (Invite)
Post by Rajesh
UAS -> UAC (100 trying)
UAS -> UAC (180 Ringing Require 100rel header is set) includes SDP Body
UAC -> UAS (PRACK to 180 Ringing)
UAS -> UAC (200 OK to PRACK)
UAS -> UAC (200 OK to invite) No SDP
UAC -> UAS (ACK to 200 OK for invite)
Regards
Rajesh
_______________________________________________
Sip-implementors mailing list
Sip-implementors at lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
_______________________________________________
Sip-implementors mailing list
Sip-implementors at lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors
Paul Kyzivat
2014-05-19 16:51:17 UTC
Permalink
Post by Rajesh
Thanks Paul. Sorry, i didn't get the point that "From the UAC's
perspective it can still start toward the UAC as soon as the INVITE is
sent.". May i know how UAC can start the RTP as it has not negotiated
media parameters with UAS and doesn't know the port. Please be informed
that we have SDP in INVITE.
The UAC can't start to *send* until it has received an answer. But it
may start to *receive* RTP as soon as it has sent the offer. My point
about the UAC *perspective* is that it doesn't know about what is
happening on the wire or at the UAS, only what messages it has sent and
received. So while in fact there is a time window after it sends the
offer before there is a possibility of RTP being sent, it has no way of
knowing how big that window is.

Thanks,
Paul
Post by Rajesh
UAC -> UAS (Invite) includes SDP offer
UAS -> UAC (100 trying)
UAS -> UAC (180 Ringing Require 100rel header is set) includes SDP answer
UAC -> UAS (PRACK to 180 Ringing)
UAS -> UAC (200 OK to PRACK)
UAS -> UAC (200 OK to invite) No SDP
UAC -> UAS (ACK to 200 OK for invite)
Regards
Rajesh
On Mon, May 19, 2014 at 4:17 PM, Paul Kyzivat <pkyzivat at alum.mit.edu
Hi,
In the below call flow, when the UAC and UAS can start
transmitting RTP
packets. I think RTP session can be started after UAS receives PRACK for
180 ringing. I would really appreciate your opinion on this. Thanks
The use of 180rel doesn't alter when RTP can start. From the UAC's
perspective it can still start toward the UAC as soon as the INVITE
is sent. From the UAS perspective it can't start toward the UAC
until the UAS has received the offer (the INVITE). There is no
reason why the UAS must wait for the prack. However the UAS might
*want* to wait for the prack before starting to send, since that
gives it more assurance that things are in good shape.
For instance, if something in the middle is gating the flow of RTP
in both directions until the answer is received, then waiting for
the prack will avoid early media being dropped.
Thanks,
Paul
UAC -> UAS (Invite)
UAS -> UAC (100 trying)
UAS -> UAC (180 Ringing Require 100rel header is set) includes SDP Body
UAC -> UAS (PRACK to 180 Ringing)
UAS -> UAC (200 OK to PRACK)
UAS -> UAC (200 OK to invite) No SDP
UAC -> UAS (ACK to 200 OK for invite)
Regards
Rajesh
_________________________________________________
Sip-implementors mailing list
Sip-implementors at lists.cs.__columbia.edu
<mailto:Sip-implementors at lists.cs.columbia.edu>
https://lists.cs.columbia.edu/__mailman/listinfo/sip-__implementors
<https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors>
_________________________________________________
Sip-implementors mailing list
Sip-implementors at lists.cs.__columbia.edu
<mailto:Sip-implementors at lists.cs.columbia.edu>
https://lists.cs.columbia.edu/__mailman/listinfo/sip-__implementors
<https://lists.cs.columbia.edu/mailman/listinfo/sip-implementors>
Loading...