SCONE Working Group D. Druta Internet-Draft E. Halepovic Intended status: Informational T. Karagioules Expires: 3 August 2025 AT&T 30 January 2025 Video Session Data Rate for SCONE protocol draft-druta-scone-video-session-data-rate-00 Abstract The SCONE protocol requires a semantically consistent way for CSPs to convey a throughput advice. The Video Session Data Rate (VSDR) describes the formula to be applied both for setting the limit on the CAP side as well as for the CSP to validate conformance with the policy. 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 3 August 2025. Copyright Notice Copyright (c) 2025 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Druta, et al. Expires 3 August 2025 [Page 1] Internet-Draft VSDR January 2025 Table of Contents 1. Motivation and Drivers . . . . . . . . . . . . . . . . . . . 2 2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Details . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Benefits and Uses . . . . . . . . . . . . . . . . . . . . . . 4 6. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 6 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 1. Motivation and Drivers The SCONE working group has started to work on a protocol allowing CSPs (Communication Service Providers) to pass throughput advice to CAPs (Content and Application Providers) for the purpose of enforcing network policies associated with video throughput limits in a self- regulatory fashion. While the actual SCONE mechanism has not been defined yet, a simple, standard semantic representation of the throughput advice is necessary in order to have a common baseline measure to track overall video session data consumption. This draft addresses the formula of metric to be used for the SCONE protocol advise. Since a significant percentage of the internet traffic consists of video and specifically Adaptive Bitrate Video, the focus is on video sessions and their impact on the subscription limits. For most, the active stream being displayed on the screen is the only one delivered. That being said, many video services use QUIC HTTP/3 as a delivery mechanism and take advantage of the multiplexing capabilities provided by the protocol. Therefore, at any given point in time it is possible to have multiple video streams delivered over the same connection. In other words, the requirement is to establish a measurement that represents the Aggregate Bitrate of all the active video flows associated with a particular 4 tuple. An additional requirement is to establish an easily computable metric by both CSPs and CAPs that can be compared and measured by both sides. Druta, et al. Expires 3 August 2025 [Page 2] Internet-Draft VSDR January 2025 2. Objectives On the CSP side, since most of the internet traffic is end-to-end encrypted, the main objective is to be able to characterize video sessions from network data in the absence of application-layer metrics. In addition to that, there is a need to estimate customer experience and network support for video delivery while assessing how is video service using available bandwidth. On the CAP side, using the same formula to compute the data usage for video delivery allows for a proactive implementation of video optimization delivery techniques in compliance and alignment with the network policies set for the subscription. 3. Definitions A video session, from the network perspective is the set of IP flows carrying video (and audio and metadata, as appropriate), which are separated from other such flows by a timeout T. Data is the total volume of all flows in the session per direction of transmission, typically downlink for streaming video, and both downlink and uplink for video conferencing. Duration is the period from the earliest data transmission and the latest data transmission across all flows in the video session, eliminating idle times at the beginning and end of the flows, if exclusion is possible. 4. Details Figure 1 below illustrates three video sessions, comprised of different video streams (three active ones with some idle periods representing a typical video delivery scenario with a main video being displayed and others being queued or pre-fetched in the background. Druta, et al. Expires 3 August 2025 [Page 3] Internet-Draft VSDR January 2025 Session A | Delta_t > T |Session B |Delta t > T Video Session C | | | | | | | |<--------->|<----------->|<-------->|<------>|<---|------|------->| Flow #1 |XXXX | o|OOOOOOOOO| | | | ######| Flow #2 | XXXXXX|XX / | OOO | | | |####### | Flow #3 | XXXX | \ / | | |####| | | |<--------->| \ / | | | |<---->| | | | \ / | | | | | | Duration D Idle period Delta t < T (excluded) Figure 1: Three flow traffic for Video Session Data Rate The Video Session Data Rate or VSDR is ratio (expressed in Kbit/s or Mbit/s) of Data (Cumulative data transmitted over all the video flows) and duration D. 5. Benefits and Uses There are several benefits to defining a standard VSDR. For once, expressing the metric using the above-described formula provides simplicity of expression and calculation. In addition to that, it enables robustness against certain types of abuse. Since this measure is an aggregate bitrate of active video flows, it should be able to provide some correlation with encoding bitrate. Additionally, VSDR is easily computable by both CAPs and CSPs and therefore induces very little extra compute cycles in the process. VSDR is robust to some forms of miscalculation. First, it reflects the true overall data rate of the session compared to averaging or otherwise summarizing flow throughputs. Therefore, it is robust to outliers resulting from very short flows or flows with very little data. Second, it is robust to some form of miscalculation. By establishing a sensible timeout T, session concatenation is discouraged for long periods of time resulting in artificially lower VSDR values. This method reflects more accurately the video delivery behavior and is measurable based on IP traffic patterns observed on the wire. Examples of computation: Druta, et al. Expires 3 August 2025 [Page 4] Internet-Draft VSDR January 2025 CSP can compute VSDR using high-level flow records that contain start and end times, and data volume per direction. No packet-level data is required. Therefore, a simple accumulation of flow records can provide for quick computation of session start and end time for duration, and data volume summation, while separating sessions based on the timeout. This can be done in near real time as well as later. CAP can compute the same VSDR using more than one method. At the CDN edge note, flow monitoring towards different ASNs or subnets can compute VSDR in the same way as the CSP. Web server logs can be used as well where multiple request/response pairs will comprise each flow. VSDR can be used in the following ways: For the purpose of SCONE, it provides a flexible and versatile vehicle to convey throughput advice or a target rate: A CSP can use VSDR to express to the CAP the maximum rate of delivery of the data. Depending on CSP network or subscription policy, it can be used as per-session, per-minute, or even as a percentile (e.g., 95% of sessions or daily data should be delivered in sessions under the certain VSDR). VSDR). Quality of delivery estimation: As a proxy for overall delivery, its increase or decrease can be used as a proxy for improvement or degradation of the delivery of content. Slower sessions can represent impact of network load and congestion, and reaction of a video service to it. 6. Assumptions In order to measure the VSDR, on the network side it is necessary to correctly and accurately identify video flows. Since the majority of the video traffic over the internet is end to end encrypted, the identification of flows is commonly based on heuristics and other techniques. Although CSPs can identify the video flows, applying traffic shaping filters in the network can negatively impact the Quality of Experience for the video service as there is no video delivery optimization possible. By allowing the CAP to adjust and optimize within the VSDR limit, the expectation is that not only the network policies are enforced but the video streams are efficiently distributed to provide users with a good user experience. Druta, et al. Expires 3 August 2025 [Page 5] Internet-Draft VSDR January 2025 7. Limitations Since the VSDR is a measure relative to the individual CAP connections, it is not always representative of customer experience. That is because at any given time, especially on mobile connections, congestion can be a factor. In addition to that, individual CAP traffic cannot be completely isolated from the rest of the traffic on the same device. A background download for a software update, for example could have an impact on the overall connection throughput. Changes in VSDR value are comparable within each video service across network conditions under uniform use assumption, but not comparable across different video services. For example, if we assume that a user population behavior of one video service is uniform across geographic and network locations (meaning that the distribution of video bitrates and general usage are comparable), then differences in VSDR can indicate difference in performance and QoE across network locations, within that video service. However, due to differences in user behavior, stream design and other factors, VSDR differences are generally not comparable between different video services. An example may be the use of the more efficient codec in one video service vs another. Acknowledgements Thanks to Abhishek Tiwari for providing input and feedback. Authors' Addresses Dan Druta AT&T Email: dd5826@att.com Emir Halepovic AT&T Email: emir@research.att.com Theo Karagioules AT&T Email: theo@research.att.com Druta, et al. Expires 3 August 2025 [Page 6]