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SIPRECMSRP Recording
(draft-yan-siprec-msrp-recording-01)
IETF 90, July 25, 2014Authors:
Michael Yan, Paul Kyzivat
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Intro
• Now have a partially complete proposal for how to handle MSRP recording:– draft-yan-siprec-msrp-recording-01
• There has been productive discussion on the mailing list
• Have identified a number of issues.• Want to get sense of the group on these.
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Issues Identified
• How much detail to record?• Recording CS REPORT messages• Recording MSRP errors• Distinguishing CPIM wrappers added by SRC from those
already present• When adding CPIM, what From/To URIs should be used?• Preserving MESSAGE-IDs• Recording CS MSRP URIs• Compatibility of max-size on CS and RS• How to handle nicknames
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How much detail to record?
• What are we recording?– the user experience, or– the binary structure of the CS MSRP session?
• Can we draw valid analogies from RTP recording?– For RTP we allow the SRC to take a variety of roles.
• Some preserve more than others. • Some may preserve very little
– neither SSRC, CNAME, nor Codec.
– For MSRP we don’t have these defined roles.• If we want them we must define them.
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Recording CS REPORT messages
• Which reports to record?– Success Reports– Failure Reports?
• Should SRC request reports, or just pass through participant requests?
• How to convey reports in RS? – (Can’t be as a REPORT)– Special content type?
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Recording MSRP Errors
• (This hasn’t been considered yet.)• How to convey in RS?– Special content type?
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Recording CS MSRP URIs
• Is there any value in having these in the recording?
• If so, how to convey?
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Distinguishing CPIM wrappers added by SRC from those already present
• If message in CS MSRP session has no CPIM wrapper then – the sender and receiver of the message are implicit. – That isn’t good enough in the RS MSRP session, because it is
multiplexing.• Some possibilities for dealing with this:– Add CPIM wrapper if one isn’t already present
• Must we mark it some way to indicate it was added by SRC?
– Always add a CPIM wrapper• Then the outer wrapper is always the SRC’s view• Makes all the messages bigger• May make playback harder
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When adding CPIM, what From/To URIs should be used?
• One of the participant URIs from the stream metadata?
• The MSRP URIs from the CS?
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Preserving MESSAGE-IDs
• MSRP allows a message to be sent (perhaps partially) in one MSRP session, and then resent/resumed in another MSRP session. The message is identified as the same by MESSAGE-ID.
• Do we want to preserve this behavior in the RS?– Recommend: YES
• But don’t require the SRS to do the correlation.
• To accomplish this we can:– Use same MESSAGE-IDs in CS and RS– Map CS IDs to RS IDs. (e.g., a prefix)
• Concern: will this work with redundant SRCs or SRSs?– Easier if we use the same MESSAGE-IDs
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Compatibility of max-size on CS and RS
• Max-size is declared by receiver (in SDP), not negotiated• It is a hint, non-binding on sender• How does SRS decide on max-size to declare in RS?
– Proposal: local policy• How does SRC decide on max-size to declare in CS?
– Should it take RS max-size into account when doing this?– Proposal:
• Do not consider RS max-size• If is an endpoint, use local policy• If is a middle box solely for recording, make as large as possible
• What should SRC do if it has a message to record that exceeds max-size on the RS session?– Proposal: SRC MAY drop these messages– Should we define a small message to send as placeholder for large message that was
dropped?
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How to handle nicknames
• Nicknames defined in draft-ietf-simple-chat-18• Problems
– Nickname usage is bound to an MSRP session by the focus– Not sent with each message– Conveyed to participants by conference event package
• Ideas– Expect SRS to subscribe to conference event package on SRC– Send NICKNAME requests to SRS to rebind as needed– Update MSRP to allow nickname to be sent in each message.
• Revision to draft-ietf-simple-chat-18
– Extend CPIM wrapper to carry nickname.
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The End
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