Re: [xrblock] Adam Roach's No Objection on draft-ietf-xrblock-rtcweb-rtcp-xr-metrics-09: (with COMMENT)
Adam Roach <adam@nostrum.com> Tue, 22 May 2018 03:20 UTC
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To: "Huangyihong (Rachel)" <rachel.huang@huawei.com>, The IESG <iesg@ietf.org>
Cc: "xrblock-chairs@ietf.org" <xrblock-chairs@ietf.org>, "draft-ietf-xrblock-rtcweb-rtcp-xr-metrics@ietf.org" <draft-ietf-xrblock-rtcweb-rtcp-xr-metrics@ietf.org>, "shida.at.ietf@gmail.com" <shida.at.ietf@gmail.com>, "xrblock@ietf.org" <xrblock@ietf.org>
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From: Adam Roach <adam@nostrum.com>
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Subject: Re: [xrblock] Adam Roach's No Objection on draft-ietf-xrblock-rtcweb-rtcp-xr-metrics-09: (with COMMENT)
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Thanks! Your proposed resolutions look good to me. /a On 5/21/18 10:18 PM, Huangyihong (Rachel) wrote: > Hi Adam, > > Thanks for the comments. Please see inline. > > BR, > Rachel > >> -----Original Message----- >> From: Adam Roach [mailto:adam@nostrum.com] >> Sent: Tuesday, May 22, 2018 8:56 AM >> To: The IESG >> Cc: draft-ietf-xrblock-rtcweb-rtcp-xr-metrics@ietf.org; Shida Schubert; >> xrblock-chairs@ietf.org; shida.at.ietf@gmail.com; xrblock@ietf.org >> Subject: Adam Roach's No Objection on >> draft-ietf-xrblock-rtcweb-rtcp-xr-metrics-09: (with COMMENT) >> >> Adam Roach has entered the following ballot position for >> draft-ietf-xrblock-rtcweb-rtcp-xr-metrics-09: No Objection >> >> When responding, please keep the subject line intact and reply to all >> email addresses included in the To and CC lines. (Feel free to cut this >> introductory paragraph, however.) >> >> >> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html >> for more information about IESG DISCUSS and COMMENT positions. >> >> >> The document, along with other ballot positions, can be found here: >> https://datatracker.ietf.org/doc/draft-ietf-xrblock-rtcweb-rtcp-xr-metrics/ >> >> >> >> ---------------------------------------------------------------------- >> COMMENT: >> ---------------------------------------------------------------------- >> >> Thanks to the authors and contributors on this document. I have two >> substantive >> comments, and a handful of minor nits. >> >> --------------------------------------------------------------------------- >> >> §5.3.1: >> >>> application can use these metrics to calculate the Mean Opinion Score >>> (MoS) values or Media Delivery Index (MDI) for their services. >> "...calculate Estimated Mean Opinion Score (eMOS) values..." >> >> (MOS scores necessarily require human subjective evaluation of audio under >> carefully controlled circumstances -- any computer-generated metrics are >> inherently estimations, and should not be called MOS scores.) >> > [Rachel]: You're right. Will change to "estimated Mean Opinion Score (MOS)" in the next version. > >> --------------------------------------------------------------------------- >> >> §5.3.1: >> >>> Error-resilience mechanisms, like RTP retransmission or FEC, are >>> optional in RTCWEB because the overhead of the repair bits adding to >>> the original streams. >> This is a little misleading. draft-ietf-rtcweb-rtp-usage says: >> >> WebRTC endpoints MUST follow the recommendations for FEC use given in >> [I-D.ietf-rtcweb-fec]. >> >> And, in turn, draft-ietf-rtcweb-fec says: >> >> To support the functionality recommended above, implementations MUST >> be able to receive and make use of the relevant FEC formats for their >> supported audio codecs, and MUST indicate this support, as described >> in Section 4. Use of these formats when sending, as mentioned above, >> is RECOMMENDED. >> >> Rather than trying to reiterate this somewhat nuanced situation in *this* >> document, I recommend removing the entire sentence and fixing the rest of >> the >> paragraph. If you choose to keep it, please make sure it more clearly explains >> the level of FEC support required of RTCWEB implementations. >> > [Rachel]: Your concern makes sense to me. I'll delete it as following: > > OLD > > " > Error-resilience mechanisms, like RTP retransmission or FEC, are > optional in RTCWEB because the overhead of the repair bits adding to > the original streams. But they do help to greatly reduce the impact > of packet loss and enhance the quality of transmission. Web > applications could support certain repair mechanism after negotiation > between both sides of browsers when needed. > " > > NEW > " > Web applications could support certain RTP error-resilience mechanisms following the recommendations specified in [draft-ietf-rtcweb-rtp-usage]. > " > >> ================================================================ >> =========== >> >> The remainder of my comments are grammatical or editorial nits that should >> be >> fixed before progressing the document. >> >> --------------------------------------------------------------------------- >> >> §3: >> >>> The RTCP Sender Reports (SRs) and Receiver Reports (RRs) [RFC3550] >>> exposes the basic metrics... >> "expose" >> >>> However, these metrics provides... >> "provide" >> >> >>> For example, it may be useful to distinguish between >>> packets lost and packets discarded due to late arrival, even though >>> they have the same impact on the multimedia quality, it helps in >>> identifying and diagnosing issues. >> This is a run-on sentence. Suggest: "...due to late arrival. Even though..." >> >>> The WebRTC application extracts the statistic from the browser by >>> querying the getStats() API [W3C.WD-webrtc-20161124], but the browser >>> currently only reports the local variables i.e., the statistics >>> related to the outgoing RTP media streams and the incoming RTP media >>> streams. >> I don't think the "currently" in this sentence is actually true any longer; and >> I expect it to get increasingly less true as time goes on. Consider rephrasing. >> >>> [I-D.ietf-rtcweb-rtp-usage] does not mandate the use of >>> any RTCP XRs and since their usage is optional. >> This is not a sentence. Maybe remove "since"? >> >> --------------------------------------------------------------------------- >> >> §4: >> >>> For example, an application may choose >>> to poll the stack for statistics every 1 second, in this case the >>> underlying stack local will return the current snapshot of the local >>> statistics (for incoming and outgoing media streams). >> This is a comma splice. Consider: "...every second. In this case..." >> >>> However it may >>> return the same remote statistics as before for the remote >>> statistics >> Add a comma after "However". >> >> --------------------------------------------------------------------------- >> >> §5: >> >>> Since following metrics are all defined in RTCP XR which is not >>> mandated in WebRTC, all of them are local. >> "Since the following..." >> ^^^ >> >> "...RTCP XR, which is..." >> ^ >> >>> However, if RTCP XR is >>> supported by negotiation between two browsers, following metrics can >>> also be generated remotely and be sent to local by RTCP XR packets. >> "...two browsers, the following..." >> ^^^ >> >>> Following metrics are classified into 3 categories: network impact >> "The following metrics..." >> ^^^ >> >> >>> viewpoint of application, e.g., bit rate, frames rate or jitter >> "...frame rate..." >> >>> WebRTC >>> application can use these metrics to calculate the Mean Opinion Score >> "applications" >> >> >> --------------------------------------------------------------------------- >> >> §5.1.1: >> >>> lost and duplicated packets. Lost packets counts are useful for >> "Lost packet counts..." >> >> --------------------------------------------------------------------------- >> >> §5.1.3: >> >>> the two run length vectors to identify congestion-related losses, >>> i.e., a router queue became overloaded causing delays and then >> Replace "i.e." ("that is") with "e.g." ("for example"). >> >> --------------------------------------------------------------------------- >> >> §5.2.1: >> >>> The metric reports the cumulative size of the packets discarded in >>> the interval, it is complementary to number of discarded packets. >> "...the interval. It is complementary..." >> >> --------------------------------------------------------------------------- >> >> §5.2.2: >> >>> For >>> audio streams, a single RTP packet may contain one or multiple audio >>> frames, each of which has a fixed length. >> I don't think this is generally true. Even in the case of WebRTC, I believe the >> default mode of operation for Opus is VBR, which results in frame sizes that >> vary from frame to frame. >> >>> The metrics in this category includes: number of discarded key >> "...category include:..." >> >> --------------------------------------------------------------------------- >> >> >> §5.3.1: >> >>> The un-repaired packets count and repaired loss count defined in >> "...unrepaired packet count..." >> >>> packets to lost packets. Including this kind of metrics helps the >> Choose either "...these kinds of metrics..." or "...this kind of metric..." >> >> --------------------------------------------------------------------------- >> >> §5.3.2: >> >>> related losses, i.e., a router queue became overloaded causing delays >> Replace "i.e." with "e.g." >> >> --------------------------------------------------------------------------- >> >> §6: >> >>> identifiers relevant to RTP media in WebRTC. These group of >>> identifiers are defined on a ReportGroup corresponding to an >>> Synchronization source (SSRC). In practice the application need to >> "This group of identifiers..." >> ^^^^ >> >> "...corresponding to a synchronization source..." >> ^ >> >> "...the application needs to..." >> ^^^^^ >> >>> For XR metrics, it depends on >>> two factors: 1) if it measured at the endpoint, 2) if it reported by >>> the endpoint in an XR report. >> "...if it is measured..." >> ^^ >> >> "...if it is reported..." >> ^^ >> >> --------------------------------------------------------------------------- >> >> §11.2: >> >>> [W3C.WD-webrtc-20161124] >>> Sporny, M. and D. Longley, "WebRTC 1.0: Real-time >>> Communication Between Browsers", World Wide Web >> Consortium >>> WD WD-webrtc-20161124, November 2016, >>> <https://www.w3.org/TR/2016/WD-webrtc-20161124>. >> The authorship of this document is incorrect (neither Sporny nor Longley are >> authors on WebRTC). >> >> The URL points to an outdated version of the specification. Please update to >> https://www.w3.org/TR/2017/CR-webrtc-20171102/ >> >> >>> [W3C.WD-webrtc-stats-20161214] >>> Alvestrand, H. and V. Singh, "Identifiers for >>> WebRTC's Statistics API", World Wide Web Consortium >>> WD WD-webrtc-stats-20161214, December 2016, >>> <https://www.w3.org/TR/2016/WD-webrtc-stats-20161214>. >> Please replace "'" with an apostrophe. >> >> Please update the URL to >> https://www.w3.org/TR/2018/WD-webrtc-stats-20180519/ >> > [Rachel]: They'll be fixed in the next version. Thanks.
- [xrblock] Adam Roach's No Objection on draft-ietf… Adam Roach
- Re: [xrblock] Adam Roach's No Objection on draft-… Adam Roach
- Re: [xrblock] Adam Roach's No Objection on draft-… Huangyihong (Rachel)
- Re: [xrblock] Adam Roach's No Objection on draft-… Adam Roach
- Re: [xrblock] Adam Roach's No Objection on draft-… Ben Campbell
- Re: [xrblock] Adam Roach's No Objection on draft-… Huangyihong (Rachel)