[tsvwg] Review of draft-tuexen-tsvwg-sctp-prpolicies-03.txt

["Michael Ramalho (mramalho)" <[e-mail]>]

[Everyone except Michael: I volunteered to be a reviewer on the SCTP "PR-policies" draft while at the IETF in London. This exchange between me and Michael Tuexen are a part of that review process.]



***



Michael (Tuexen),



Re: "...  the RTCWeb guys [don't want the combination of timed reliability and lifetime] "

AND

Re: " The current API allows you only to have a single parameter... So we would not define a "generic combination" of existing policies, but a single new policy having two parameters and having the semantics of combining two existing policies."



If the current API allows you only to have a single parameter, then I presume (by extension) that you cannot have priority (this draft) and timed reliability (RFC 3758) combination either.



I am SURE that if you asked the "RTCWeb guys" if they wanted that particular combination that they would have said YES!



Indeed, I was on a call just yesterday where priority within a PR-SCTP stream was discussed (where they assumed "timed-reliability" was in effect). This is of particular use for video (and video encoding in screen sharing modes).



So, I see we have (at present) three dimensions of PR policy:



1) Timed Reliability

2) Limited Retransmissions

3) Priority



For the record, I don't think people will come up with additional policies for a specific stream ... but there is something I don't like about your proposal to create another policy that is a combination of two or three of the existing ones because of the combinatorics involved (individual policies for 1&2, 2&3, 1&3, 1&2&3). One more policy and that gets untenable!



Since the "retransmission decision" is conditioned by policy ... (presumably a break from within an "if and if else" portion) ... I don't see the combination as being particularly hard in code.



Is the issue here simply that you don't want to make the new API a little more complex? Or backward compatibility?



I think the key point here is that at least "priority" and "timed reliability" are probably desired together. What do others think?



Michael Ramalho