Internet DRAFT - draft-gaoyang-sipcore-suspending-and-resuming
draft-gaoyang-sipcore-suspending-and-resuming
sipcore Y. Gao
Internet-Draft ZTE
Intended status: Standards Track August 25, 2009
Expires: February 26, 2010
Suspending and Resuming for Modification
draft-gaoyang-sipcore-suspending-and-resuming-00.txt
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Abstract
RFC3312 & 4032 has defined semantics of suspending and resuming for
session establishment. But suspending and resuming for session
modification needs clarification, especially for modification with
part of the streams with precondition. This text just aims for
giving out some use case for further analysis. And if we need do
some standard track for this issue, IMO, the "Re-INVITE Handling"
draft can be more proper and systematic.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Drawbacks of suspending and resuming for whole session . . . . 4
2.1. To delay using of new parameters for stream without
precondition may arose media clip problem . . . . . . . . . 4
2.2. Behavior of streams without precondition would be
depend on the existence of other streams . . . . . . . . . 4
2.3. Various streams are not controlled by the same entity,
so that coordination of when they take effect could be
problematic . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Normative references . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
RFC3312 & 4032 did not talk about session modification with
precondition for detail. And, there are two alternatives for this
issue here:
o suspending and resuming for whole session;
o suspending and resuming for streams with precondition separately;
Considering a use case, A and B has a audio only session. Then A
send a Re-INVITE for adding vedio stream( with precondition) and
changing codec or address for audio stream( without preconditon). If
suspending is effective for whole session, then streams without
precondition should use old parameters while in suspending state. If
suspending is effective for streams with precondition, the then
streams without preconditio can use new parameters after first O/A
during the Re-INVITE.
I will use some use cases to reveal the drawbacks of "suspending and
resuming for whole session".
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2. Drawbacks of suspending and resuming for whole session
2.1. To delay using of new parameters for stream without precondition
may arose media clip problem
Considering a use case, A and B has a audio only session. Then A
send a Re-INVITE(F1) for adding vedio stream(with precondition) and
changing codec or address for audio stream(without preconditon). If
suspending is effective for whole session, then streams without
precondition should use old parameters while in suspending state.
But sometimes, A has no way to use old parameters anymore, for
example session mobility. Then, it aroses media clip problem.
Media clip problem
A B
| session established |
|<===================>|
| |
| F1 re-INVITE (SDP) |
|-------------------->|
| F2 1xx-rel (SDP) |
|<--------------------|
| F3 UPDATE |
|-------------------->|
| F4 2xx UPT |
|<--------------------|
| |
| F5 180 ringing |
|<--------------------|
| |
| F6 2xx INV |
|<--------------------|
| F7 ACK |
|-------------------->|
| |
Figure 1
2.2. Behavior of streams without precondition would be depend on the
existence of other streams
Considering a use case, A and B has a audio only session. Then A
send a Re-INVITE(F1) for adding vedio stream and changing codec or
address for audio stream(without precondition). If suspending is
effective for whole session, then the behavior of audio stream would
be depend on the condition of vedio stream. The user will be
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confused. As:
If vedio stream is without preconditon too, B will send F2 with
answer at once. And B can use new parameters of audio stream just
after F2.
Vedio stream without preconditon
A B
| session established |
|<===================>|
| |
| F1 re-INVITE (SDP) |
|-------------------->|
| F2 2xx INV (SDP) |
|<--------------------|
| F3 ACK |
|-------------------->|
| |
Figure 2
If vedio stream is with preconditon, B can use new parameters of
audio stream after the time point of precondition met.
Vedio stream with preconditon
A B
| session established |
|<===================>|
| |
| F1 re-INVITE (SDP) |
|-------------------->|
| F2 1xx-rel (SDP) |
|<--------------------|
| F3 UPDATE |
|-------------------->|
| F4 2xx UPT |
|<--------------------|
| F5 2xx INV |
|<--------------------|
| F6 ACK |
|-------------------->|
| |
Figure 3
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2.3. Various streams are not controlled by the same entity, so that
coordination of when they take effect could be problematic
Considering a use case, A and B has a audio only session. Then A
send a Re-INVITE(F1) for adding vedio stream and changing codec or
address for audio stream(without precondition). And B is controller
of Media Servers. So, it will dispatch the offer(or part streams of
the offer) to media servers. As in Figure, the controller will send
audio stream to media server1 using Re-INVITE, and send vedio stream
to media server2 using INVITE.
If suspending is effective for whole session, then the new parameters
of audio stream should not be used. And it is complex or difficult
for controller to do so.
Coordination problem
A B(Controller) Media Server1 Media Server2
| session established | | |
|<=========================================>| |
| | | |
| F1 re-INVITE (SDP) | | |
|-------------------->| F2 re-INVITE (SDP) | |
| |-------------------->| |
| | F3 INVITE (SDP) | |
| |------------------------------------------>|
| | F4 2xx INV | |
| |<--------------------| |
| | F5 1xx-rel (SDP) | |
| |<------------------------------------------|
| F6 1xx-rel(SDP) | | |
|<--------------------| | |
| | | |
Figure 4
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3. Acknowledgment
Thanks Paul Kyzivat's suggestion.
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4. Normative references
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Author's Address
Gao yang
ZTE
CHINA
Email: gao.yang2@zte.com.cn
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