--- 1/draft-ietf-rmcat-sbd-09.txt 2018-02-16 08:13:57.497794056 -0800 +++ 2/draft-ietf-rmcat-sbd-10.txt 2018-02-16 08:13:57.585796139 -0800 @@ -1,53 +1,52 @@ RTP Media Congestion Avoidance Techniques D. Hayes, Ed. Internet-Draft Simula Research Laboratory Intended status: Experimental S. Ferlin -Expires: May 30, 2018 +Expires: August 20, 2018 M. Welzl K. Hiorth University of Oslo - November 26, 2017 + February 16, 2018 Shared Bottleneck Detection for Coupled Congestion Control for RTP Media. - draft-ietf-rmcat-sbd-09 + draft-ietf-rmcat-sbd-10 Abstract This document describes a mechanism to detect whether end-to-end data flows share a common bottleneck. It relies on summary statistics that are calculated based on continuous measurements and used as input to a grouping algorithm that runs wherever the knowledge is - needed. This mechanism complements the coupled congestion control - mechanism in draft-ietf-rmcat-coupled-cc. + needed. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on May 30, 2018. + This Internet-Draft will expire on August 20, 2018. Copyright Notice - Copyright (c) 2017 IETF Trust and the persons identified as the + Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as @@ -86,22 +85,22 @@ 4.1.2. Improving the Response of the Variability Estimate . 19 4.2. Removing Oscillation Noise . . . . . . . . . . . . . . . 19 5. Measuring OWD . . . . . . . . . . . . . . . . . . . . . . . . 20 5.1. Time-stamp Resolution . . . . . . . . . . . . . . . . . . 20 5.2. Clock Skew . . . . . . . . . . . . . . . . . . . . . . . 20 6. Expected Feedback from Experiments . . . . . . . . . . . . . 20 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 9. Security Considerations . . . . . . . . . . . . . . . . . . . 21 10. Change history . . . . . . . . . . . . . . . . . . . . . . . 21 - 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 - 11.1. Normative References . . . . . . . . . . . . . . . . . . 22 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 + 11.1. Normative References . . . . . . . . . . . . . . . . . . 23 11.2. Informative References . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 1. Introduction In the Internet, it is not normally known if flows (e.g., TCP connections or UDP data streams) traverse the same bottlenecks. Even flows that have the same sender and receiver may take different paths and may or may not share a bottleneck. Flows that share a bottleneck link usually compete with one another for their share of the @@ -164,22 +163,24 @@ Flows that share a common bottleneck may traverse different paths, and these paths will often have different base delays. This makes it difficult to correlate changes in delay or loss. This technique uses the long term shape of the delay distribution as a base for comparison to counter this. 2. Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", - "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this - document are to be interpreted as described in RFC 2119 [RFC2119]. + "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and + "OPTIONAL" in this document are to be interpreted as described in BCP + 14 [RFC2119] RFC2119 [RFC2119] RFC8174 [RFC8174] when, and only when, + they appear in all capitals, as shown here. Acronyms used in this document: OWD -- One Way Delay MAD -- Mean Absolute Deviation RTT -- Round Trip Time SBD -- Shared Bottleneck Detection @@ -381,76 +382,75 @@ control mechanisms. 3.1.1. Feedback When All the Logic is Placed at the Sender Having the sender calculate the summary statistics and determine the shared bottlenecks based on them has the advantage of placing most of the functionality in one place -- the sender. For every packet, the sender requires accurate relative OWD measurements of adequate precision, along with an indication of lost - packets (or the proportion of packets lost over an interval). These - can be provided by [I-D.ietf-avtcore-cc-feedback-message]. + packets (or the proportion of packets lost over an interval). An + method to provide such measurement data with RTCP is described in + [I-D.ietf-avtcore-cc-feedback-message]. Sums, var_base_T and skew_base_T are calculated incrementally as relative OWD measurements are determined from the feedback messages. When the mechanism has received sufficient measurements to cover the T base time interval for all flows, the summary statistics (see Section 3.2) are calculated for that T interval and flows are grouped (see Section 3.3.1). The exact timing of these calculations will depend on the frequency of the feedback message. 3.1.2. Feedback When the Statistics are Calculated at the Receiver and SBD Performed at the Sender This scenario minimizes feedback, but requires receivers to send selected summary statistics at an agreed regular interval. We envisage the following exchange of information to initialize the system: o An initialization message from the sender to the receiver will contain the following information: - * A protocol identifier (SBD=01). This is to future proof the - message exchange so that potential advances in SBD technology - can be easily deployed. All following initialization elements - relate to the mechanism outlined in this document which will - have the identifier SBD=01. - * A list of which key metrics should be collected and relayed back to the sender out of a possibly extensible set (pkt_loss, var_est, skew_est, freq_est). The grouping algorithm described in this document requires all four of these metrics, and receivers MUST be able to provide them, but future algorithms may be able to exploit other metrics (e.g. metrics based on explicit network signals). * The values of T, N, M, and the necessary resolution and precision of the relayed statistics. o A response message from the receiver acknowledges this message with a list of key metrics it supports (subset of the senders list) and is able to relay back to the sender. This initialization exchange may be repeated to finalize the agreed - metrics should not all be supported by all receivers. + metrics should not all be supported by all receivers. It is also + recommendable to include an identifier for the SBD algorithm version + in the initialization message from the sender, so that potential + advances in SBD technology can be easily deployed. For reference, + the mechanism outlined in this document has the identifier SBD=01. After initialization the agreed summary statistics are fed back to the sender (nominally every T). 3.1.3. Feedback When Bottlenecks can be Determined at Both Senders and Receivers - This type of mechanism is currently beyond the scope of SBD in RMCAT. - It is mentioned here to ensure more advanced sender/receiver - cooperative shared bottleneck determination mechanisms remain - possible in the future. + This type of mechanism is currently beyond the scope of the SBD + algorithm described in this document. It is mentioned here to ensure + more advanced sender/receiver cooperative shared bottleneck + determination mechanisms remain possible in the future. It is envisaged that such a mechanism would be initialized in a similar manner to that described in Section 3.1.2. After initialization both summary statistics and shared bottleneck determinations should be exchanged, nominally every T. 3.2. Key Metrics and Their Calculation Measurements are calculated over a base interval, T and summarized @@ -479,21 +479,21 @@ 3.2.2. Skewness Estimate Skewness is difficult to calculate efficiently and accurately. Ideally it should be calculated over the entire period (M * T) from the mean OWD over that period. However this would require storing every delay measurement over the period. Instead, an estimate is made over M * T based on a calculation every T using the previous T's calculation of mean_delay. The base for the skewness calculation is estimated using a counter - initialized every T. It increments for one way delay samples (OWD) + initialized every T. It increments for one way delay (OWD) samples below the mean and decrements for OWD above the mean. So for each OWD sample: if (OWD < mean_delay) skew_base_T++ if (OWD > mean_delay) skew_base_T-- The mean_delay does not include the mean of the current T interval to enable it to be calculated iteratively. @@ -562,23 +562,24 @@ pkt_loss = sum_NT(lost packets) / sum_NT(total packets) Note: When pkt_loss is small it is very variable, however, when pkt_loss is high it becomes a stable measure for making grouping decisions. 3.3. Flow Grouping 3.3.1. Flow Grouping Algorithm - The following grouping algorithm is RECOMMENDED for SBD in the RMCAT - context and is sufficient and efficient for small to moderate numbers - of flows. For very large numbers of flows (e.g. hundreds), a more + The following grouping algorithm is RECOMMENDED for use of SBD with + coupled congestion control for RTP media [I-D.ietf-rmcat-coupled-cc] + and is sufficient and efficient for small to moderate numbers of + flows. For very large numbers of flows (e.g. hundreds), a more complex clustering algorithm may be substituted. Since no single metric is precise enough to group flows (due to noise), the algorithm uses multiple metrics. Each metric offers a different "view" of the bottleneck link characteristics, and used together they enable a more precise grouping of flows than would otherwise be possible. Flows determined to be transiting a bottleneck are successively divided into groups based on freq_est, var_est, skew_est and @@ -859,72 +860,80 @@ clock offsets should be approximately constant over the measurement periods, the offset is subtracted out in the calculation. 5.1. Time-stamp Resolution The SBD mechanism requires timing information precise enough to be able to make comparisons. As a rule of thumb, the time resolution should be less than one hundredth of a typical path's range of delays. In general, the coarser the time resolution, the more care that needs to be taken to ensure rounding errors do not bias the - skewness calculation. Timing information described by - [I-D.ietf-avtcore-cc-feedback-message] should be sufficient for the - sender to calculate relative OWD. + skewness calculation. Frequent timing information in millisecond + resolution as described by [I-D.ietf-avtcore-cc-feedback-message] + should be sufficient for the sender to calculate relative OWD. 5.2. Clock Skew Generally sender and receiver clock skew will be too small to cause significant errors in the estimators. Skew_est and freq_est are the most sensitive to this type of noise due to their use of a mean OWD calculated over a longer interval. In circumstances where clock skew is high, basing skew_est only on the previous T's mean and ignoring freq_est provides a noisier but reliable signal. A more sophisticated method is to estimate the effect the clock skew is having on the summary statistics, and then adjust statistics accordingly. There are a number of techniques in the literature, including [Zhang-Infocom02]. 6. Expected Feedback from Experiments The algorithm described in this memo has so far been evaluated using simulations and small scale experiments. Real network tests using - RMCAT congestion control algorithms will help confirm the default - parameter choice. For example, the time interval T may need to be - made longer if the packet rate is very low. Implementers and testers - are invited to document their findings in an Internet draft. + RTP Media Congestion Avoidance Techniques (RMCAT) congestion control + algorithms will help confirm the default parameter choice. For + example, the time interval T may need to be made longer if the packet + rate is very low. Implementers and testers are invited to document + their findings in an Internet draft. 7. Acknowledgments This work was part-funded by the European Community under its Seventh Framework Programme through the Reducing Internet Transport Latency (RITE) project (ICT-317700). The views expressed are solely those of the authors. 8. IANA Considerations This memo includes no request to IANA. 9. Security Considerations The security considerations of RFC 3550 [RFC3550], RFC 4585 [RFC4585], and RFC 5124 [RFC5124] are expected to apply. Non-authenticated RTCP packets carrying OWD measurements, shared bottleneck indications, and/or summary statistics could allow attackers to alter the bottleneck sharing characteristics for private - gain or disruption of other parties' communication. + gain or disruption of other parties' communication. When using SBD + for coupled congestion control as described in + [I-D.ietf-rmcat-coupled-cc], the security considerations of + [I-D.ietf-rmcat-coupled-cc] apply. 10. Change history + XX RFC ED - PLEASE REMOVE THIS SECTION XXX + Changes made to this document: + WG-09->WG-10 : AD review addressed. + WG-08->WG-09 : Removed definitions that are no longer used. Added pkt_loss definition. Refined c_s recommendation. WG-07->WG-08 : Updates addressing https://www.ietf.org/mail- archive/web/rmcat/current/msg01671.html Mainly clarifications. WG-06->WG-07 : Updates addressing https://mailarchive.ietf.org/arch/msg/ rmcat/80B6q4nI7carGcf_ddBwx7nKvOw. Mainly @@ -1025,20 +1034,24 @@ [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February 2008, . [RFC6817] Shalunov, S., Hazel, G., Iyengar, J., and M. Kuehlewind, "Low Extra Delay Background Transport (LEDBAT)", RFC 6817, DOI 10.17487/RFC6817, December 2012, . + [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC + 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, + May 2017, . + [Zhang-Infocom02] Zhang, L., Liu, Z., and H. Xia, "Clock synchronization algorithms for network measurements", Proc. the IEEE International Conference on Computer Communications (INFOCOM) pp160-169, September 2002, . Authors' Addresses David Hayes (editor)