- From: Harald Alvestrand <harald@alvestrand.no>
- Date: Mon, 15 Jan 2018 23:37:45 +0100
- To: Randell Jesup <randell-ietf@jesup.org>, public-webrtc@w3.org
Den 15. jan. 2018 20:52, skrev Randell Jesup: > On 1/15/2018 9:13 AM, Lennart Grahl wrote: >> On 15.01.2018 06:03, Bernard Aboba wrote: >>> 1. Competition between SCTP data channels and audio/video, due to building of queues. Currently, >>> data channel implementations use the default SCTP congestion control (loss-based, defined in RFC 4960), >>> and don't expose a way of selecting an alternative algorithm. One developer I talked to expressed an >>> interest in being able to use an algorithm like LEDBAT for a background file transfer, so I'm not clear >>> that a new cc algorithm needs to be standardized in IETF. >> I'm passing this on to Michael: Would it be feasible to do this with the >> existing API of usrsctp? > > This was expected - we had a number of discussions about how we could > split up bandwidth between media and data; limiting data rates to > something proportional to the media rates (to avoid data overwhelming > media). There are SCTP congestion algorithms (not necessarily in > usrsctp today) that are delay-based, per my memory of some of the early > proposals I made. > One issue would be what the relative priority/split "should" be, but the > browser can certainly make a default decision. The assumption was that > we'd do "something" here; either a forced split or a compatible CC > algorithm, or some variation on the shared-CC proposals. > > If you don't want to give (say) 1/2 the bandwidth to data during a > transfer, we'd need an API point anyways (QUIC or no QUIC), though maybe > you could add more semantics onto priorities I suppose. We do have a very coarse API point in the "priority" setting, which we defined to say "if it's 1 step higher in priority, it should get double the bandwidth when there's congestion". > >>> 2. Complexity of doing large file transfers on top of RTCDataChannel message implementations. >>> You've mentioned a number of the issues with this, and most of them seem solvable by fixing issues >>> in the existing specification, and perhaps adding some tests to make sure that implementations conform >>> to the new guidance. >> Indeed, I believe one of the most pressing issues is the impact of >> userland fragmentation/reassembly. > > Yeah... the original plan was for WebSocket-sized transfers for files, > with fragmentation/reassembly in the DC impl (PPID-fragmentation). > Application-level chunking forces a memory spike (and spike in > processing time) when combining data for delivery or writing to disk. > Direct large-Blob transfer allows/allowed the impl to append the data to > a temporary disk file as it was received, if it wanted to, or move it > there after some threshold. Yes, that's what Streams (the W3C API) is good for. > > Note this isn't a protocol issue really; it's an API issue. The > mechanism that the bytes use to cross the wire don't matter for this. > > -- > Randell Jesup -- rjesup a t mozilla d o t com > Please please please don't email randell-ietf@jesup.org! Way too much spam >
Received on Monday, 15 January 2018 22:38:12 UTC