Signaling Use Cases for Collaborative Traffic Differentiation

Signaling Use Cases for Collaborative Traffic Differentiation Cloud Software Group Holdings, Inc.

United States of America sridharan.girish@gmail.com

Cloud Software Group Holdings, Inc.

United States of America danwing@gmail.com

Orange

France mohamed.boucadair@orange.com

Nokia

India kondtir@gmail.com

Web and Internet Transport Transport and Services Working Group user experience bandwidth priority enriched feedback media streaming realtime media QoS 5G Wi-Fi WiFi diffserv Host-to-network (and vice versa) signaling can improve the user experience by informing the network which flows are more important and which packets within a flow are more important without having to disclose the content of the packets being delivered. The differentiated service may be provided at the network (e.g., packet discard preference), the sender (e.g., adaptive transmission or session migration), or through cooperation of both the host and the network. This document outlines a set of use-cases that highlight the need for a mechanism to share metadata about flows between a host and its network in order to enable different traffic treatment. Such a mechanism is typically implemented using a signaling protocol between the host and a set of trusted netwrok elements. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Transport and Services Working Group Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction Bandwidth constraints exist most predominantly at the access network (e.g., radio access networks). Users who are serviced via these networks use various hosts which run various applications; each having different connectivity needs for an optimal user experience. These needs are not frozen but change over time depending on the application and even depending on how an application is used (e.g., user's preferences). The simple network diagram below shows where such bandwidth and performance constraints usually exist with a "B" (for Bottleneck). Other network bottlenecks may be experienced in other segments not shown in the figure, such as interconnection links or the infrastructure that hosts the service (e.g., flash crowds). A bottleneck may be limited in time, present or not regular patters, etc. Complications that are induced by such phenomena may be eliminated by adequate dimensioning and upgrades. However, such upgrades may not be always immediately possible or economically justified. Complementary mitigations are thus needed to soften these complications by introducing some collaboration between hosts and networks to adjust their behaviors. For traffic sent in either direction, the network network elements that terminate a bandwidth constraining link (or located few hops next to that element) can be fed with flow metadata. Such augmentation allows those network elements to make autonomous decisions to prioritize, delay, or drop packets, especially when performing reactive resource management. Absent such metadata, these network elements have no means to guide the enforcement of the reactive resource policy. There are several challenges with this metadata augmentation:

for hosts: which data to share without privacy breach or lowering confidentiality.
for network elements:
- Deciding which metadata to trust
- Tradeoff between the extra cost (including processing) vs. expected benefits
- Impact on the network operations

The metadata signals from a content provider are more likely to be authentic (if adequate authorization/validation are in place) but the metadata signals from other hosts may be "wrong", undesired by the peer host, or maliciously contain improper metadata. Attempts to automate identification of content providers have included HTTP "Host" header inspection and TLS SNI inspection which are expected to fail as encrypted SNI and privacy-enhancing proxies become more prevalent. Another mechanism to authorize metadata signals from a content provider is to configure the ISP equipment with the content network's source IP addresses (or other labels that may be visible on the packets) and provide a differentiated service to the traffic that match these criteria. However, such an arrangement may have scalability issues. An approach to mitigate these issues is to limit the target contents networks and networks that would put in place these arrangements. Such limitations would benefit large players (large ISPs and large content network) and disadvantages small players (and new players). A more egalitarian approach would provide the same benefit to all parties -- large and small -- and also provide richer signaling to further improve user experience and metadata interoperability. This would allow all parties to become part of the "Internet fast lane". The authorization problem exists with technologies as relatively simple as DiffServ and the problem persists with many other recently discussed metadata signaling mechanisms, including embedding information in the UDP payload (), UDP options (), overloading the IPv6 Flow Label (, and Hop-by-Hop Options. One mechanism suggested occasionally is to encrypt or integrity protect the metadata with a key; such a key could be established using a signaling protocol, see . There is some consensus that applications can benefit by collaborative signaling the network (, ). This document provides use-cases to further detail the need of such signaling.

Scope & Running Experiments This document does not intend to define any signaling protocol nor call whether a new signaling protocol, a new extension, one or more signaling protocols are needed. However, this document provides a reference to digest the intended benefits for enabling collaborating between hosts and networks. These benefits are yet to be backed up with more evidence. Some experimental work would be reasonable to be endorsed by the IETF to solicit more feedback and collect assess the benefits under various setups.

Conventions and Definitions

Intentional Management:: network policy such as (monthly) bandwidth quota or bandwidth limit, or quality (delay and/or jitter)) assurances.
Reactive Management:: network reactions to congestion events, with very short to very long durations (e.g., varying wireless and mobile air interface conditions).

Various Approaches for Collaborative Signaling depicts examples of approaches to establish channels to convey and share metadata between hosts, networks, and servers. Metadata exchanges can occur in one single direction or both directions of a flows.

Use Cases

Generic Cases

Priority Between Flows (Inter-Flow) of The Same Host Certain flows being received by a host (or by an application on a host) are less or more important than other flows of the same host. For example, a host downloading a software update is generally considered less important than another host doing interactive audio/video or gaming. By signaling the relative importance of flows to a network element, the network element can (de-)prioritize those flows to best accomodate the needs of the various applications (on a same host) and between hosts on a network.

Priority Within a Flow (Intra-Flow) Interactive Audio/Video has long been using which runs over UDP. As described in , there is value in differentiating between voice, video and data. Today's video streaming is exclusively over TCP but will migrate to QUIC and eventually is likely to support unreliable transport (, ). With unreliable transport of video in RTP or QUIC, it is beneficial to differentiate the important video keyframes from other video frames. Other applications such as gaming and remote desktop also benefit from differentiating their packets to the network. Many of these flows do not originate from a content provider's network. Thus, the flows originate from an IP address that is not known before connection establishment, so there needs to be a way for the client to authorize the network elements to receive and hopefully to honor the metadata of those packets.

Detailed Use Cases

Video Streaming Streaming video contains the occasional key frame ("i-frame") containing a full video frame. These are necessary to rebuild receiver state after loss of delta frames. The key frames are therefore more critical to deliver to the receiver than delta frames. Streaming video also contains audio frames which can be encoded separately and thus can be signaled separately. Audio is more critical than video for almost all applications, but its importance (relative to other packets in the flow) is still an application decision. In the example below, the audio is more important than video (importance=high, PT=keep, RU=reliable), video key frames have middle importance (importance=low, PT=discard, RU=reliable), and both types of video delta frames (P-frame and B-frame) have least importance (importance=low, PT=discard, RU=unreliable). Video Streaming Metadata: Example Values for Video Streaming Metadata

Traffic type	Importance	PacketNature	PacketType
video I-frame (key frame)	low	realtime	reliable
video delta P-frame	low	discard	unreliable
video delta B-frame	low	discard	unreliable
audio	high	realtime	reliable

Interactive Media Examples: VoIP, gaming. Requirement: Signal the flow needs low jitter and low delay. However, the network can only provide a limited amount of low jitter/low delay to each host, maybe as few as one. This requires signaling feedback indicating that low jitter and low delay flows are already subscribed to other hosts. In response, the user and the application will likely continue, occasionally re-attempting to get the desired quality of service from the network. In many scenarios a game or VoIP application will want to signal different metadata for the same type of packet in each direction. For example, for a game, video in the server-to-client direction might be more important than audio, whereas input devices (e.g., keystrokes) might be more important than audio. Both gaming (video in both directions, audio in both directions, input devices from client to server) and interactive audio/video (VoIP, video conference) involves important traffic in both directions -- thus is a slightly more complicated use-case than the previous example. Additionally, most Internet service providers constrain upstream bandwidth so proper packet treatment is critical in the upstream direction. Metadata: Based on metadata types listed in the , the host to network metadata parameters for interactive media type will as given below. Interactive A/V, downstream Metadata: Example Values for Interactive A/V, downstream

Traffic type	Importance	PacketNature	PacketType
video key frame	low	realtime	reliable
video delta frame	low	discard	unreliable
audio	high	realtime	reliable

Example Values for Interactive A/V, upstream

Traffic type	Importance	PacketNature	PacketType
video key frame	low	realtime	reliable
video delta frame	low	discard	unreliable
audio	high	realtime	reliable

Many interactive audio/video applications also support sharing the presenter's screen, file, video, or pictures. During this sharing the presenter's video is less important but the screen or picture is more important. This change of imporance can be conveyed in metadata to the network, as in the table below: Interactive A/V, upstream Metadata: Example Values for Interactive A/V with picture sharing, upstream

Traffic type	Importance	PacketNature	PacketType
video key frame	low	realtime	reliable
video delta frame	low	discard	unreliable
audio	high	realtime	reliable
picture sharing	high	realtime	reliable

In many scenarios a game or VoIP application will want to signal different metadata for the same type of packet in each direction. For example, for a game, video in the server-to-client direction might be more important than audio, whereas input devices (e.g., keystrokes) might be more important than audio. Todo: this section on cooperation needs editing.

Bulk Data Transfer Examples: backup/restore, software update, RSS feed update, email, printing to a print server Requirement: Signal the flow as below best-effort. Metadata:

Traffic type	Importance	PacketNature	PacketType	Comments
File copy	low	bulk	reliable
Printing	high	bulk	reliable

Mixed Traffic Examples: Desktop Virtualization, Office software in the cloud (editing local files, typing is interactive while save operation is bulk transfer) Requirement: Signal flow will vary depending on the nature of the packet. With variety of traffic going through the session, some packets can contain interactive traffic while the others contain bulk transfer. There can be combination of reliable and unreliable traffic within the same session through multiple streams. Host-to-network signaling plays a vital role in effectively routing mixed traffic for ideal user interactivity and network performance. Example packet metadata for Desktop Virtualization (like Citrix Virtual Apps and Desktops - CVAD) application. This is shown in two tables, client-to-server traffic () and server-to-client traffic (). Remote Desktop Virtualization Metadata: Example Values for Remote Desktop Virtualization Metadata, client to server

Traffic type	Importance	PacketNature	PacketType	Comments
User typing	high	realtime	reliable
Mouse click/End Position	high	realtime	reliable	The start and endpoint of the pointer movement is vital to ensure user action is completed correctly. So, the endpoints have to be reliably transmitted with real-time priority. **
Interactive audio	high	keep	unreliable
Authentication - Finger print, smart card	low	realtime	reliable
Interactive video key frame	low	keep	unreliable	Video key frames form the base frames of a video upon which the next 'n' timeframe of video updates is applied on. These frames, are hence, critical and without them, the video would not be coherent until the next critical frame is received. Retransmits of these are harmful to the UX. ***
Mouse position tracking	low	discard	unreliable	When the pointer is moved from one point to another, the coordinates of the pointers between the two points can be lost without much of an impact to the UX as long as the start and endpoint reaches. This would ensure the user action is completed, even if the experience seems glitchy.
Interactive video delta frame	low	discard	unreliable

Example Values for Remote Desktop Virtualization Metadata, server to client

Traffic type	Importance	PacketNature	PacketType	Comments
Glyph critical	high	realtime	reliable	The frames that form the base for the image is more critical and needs to be transmitted as reliably as possible. Retransmits of these are harmful to the UX.**
Interactive (or streaming) audio	high	keep	unreliable
Haptic feedback	high	discard	unreliable	Virtualizing haptic feedback is real-time and high importance although the feedback being delivered late is of no use. So dropping the packet altogether and not retransmitting it makes more sense
Interactive (or streaming) video key frame	low	keep	unreliable	Video key frames form the base frames of a video upon which the next 'n' timeframe of video updates is applied on. These frames, are hence, critical and without them, the video would not be coherent until the next critical frame is received. Retransmits of these are harmful to the UX. ***
File copy	low	bulk	reliable
Interactive (or streaming) video predictive frame	low	discard	unreliable	Video predictive frames can be lost, which would result in minor glitch but not compromise the user activity and video would still be coherent and useful. The reception of subsequent video key frame would mitigate the loss in quality caused by lost predictive frames.
Glyph smoothing	low	discard	Unreliable	The smoothing elements of the glyph can be lost and would still present a recognizable image, although with a lesser quality. Hence, these can be marked as loss tolerant as the user action is still completed with a small compromise to the UX. Moreover, with the reception of the next glyph critical frame would mitigate the loss in quality caused by lost glyph smoothing elements.

*** A video key frame should be handled differently by the network depending on a streaming application versus a remote desktop application. The video streaming application's primary and only nature of traffic is video and audio. In contrast, a remote desktop application might be playing a video and its associated audio while at the same time the user is editing a document. The user's keystrokes and those glyphs need to be prioritized over the video lest the user think their inputs are being ignored (and type the same characters again). Hence, the values are different even for the same nature of traffic but a different application.

Assisted Offload There are cases (crisis) where "normal" network resources cannot be used at maximum and, thus, a network would seek to reduce or offload some of the traffic during these events -- often called 'reactive traffic policy'. An example of such sue case is cellular networks that are overly used (and radio resources exhausted) while alternative network attachment networks are available to host. Network-to-host signals are useful to put in place adequate traffic distribution policies (e.g., prefer the use of alternate paths, offload a network).

Operational Considerations

Abuse and Constraints It is important that not every flow be prioritized; otherwise, the network devolves into the best-effort network that existed prior to metadata signaling. It is a requirement that mechanisms exist to prevent this occurrence. Such a mechanism might be simple, for example, a cellular network might allow one flow from a subscriber to declare itself as important; other flows with that subscriber are denied attempts to prioritize themselves. The mechanism might be more complex where authentication and authorization is performed by an enterprise network which, itself, decides which flows are important based on its policy and only the enterprise network communicates flow priorities to the ISP network. The enterprise might prioritize certain users (e.g., IT staff), certain equipment (audio/video equipment in a conference room), or whatever its policies it might want.

Key Establishment Various proposals have suggested establishing a key to validate per-packet metadata or to decrypt per-packet metadata. However, most proposals have not specified how this key would be established. A signaling protocol from the receiving host to its ISP could establish such a key. The host can then convey the key to the sending host to use to integrity protect or encrypt the per-packet metadata.

Note: The CPU overhead of validating or decrypting such per-packet metadata needs to be carefully considered (and further assessed via experiments) by the signaling protocol proposing such keying. Also, the required operational setup should be documented.

Metadata Version/Capability Exchange The sender has to convey metadata in a way that is understood by the various network elements on the path -- each of which might be operated by different entities and have different capabilities. For example, the Wi-Fi access point might be operated by an enterprise network, hotel, or home user, whereas the upstream router is operated by the ISP. Each of those might support different versions of the same metadata, or might need the metadata expressed in different ways. The signaling protocol would provide a way to learn the needs of those networks, and provide metadata signaling satisfying most or all of their needs.

On the Use of Fast Path TBC

Impacts of Nested Congestion Controls TBC

Requirements Summary TODO summary.

Security Considerations TODO Security

IANA Considerations This document has no IANA actions.

Informative References Content Classification for Traffic Optimization Path Layer UDP Substrate Specification ETH Zurich ETH Zurich This document specifies a common Path Layer UDP Substrate (PLUS) wire image for encrypted transport protocols carried over UDP. The base PLUS header carries information for driving a minimal state machine at middleboxes described in [I-D.trammell-plus-statefulness], and provides optional exposure of additional information to devices along the path using the mechanism described in [I-D.trammell-plus-abstract-mech]. Media Handling Considerations for Wireless Networks Futurewei Cisco Tencent America LLC Wireless networks like 5G cellular or Wi-Fi experience significant variations in link capacity over short intervals due to wireless channel conditions, interference, or the end-user's movement. These variations in capacity take place in the order of hundreds of milliseconds and is much too fast for end-to-end congestion signaling by itself to convey the changes for an application to adapt. Media applications on the other hand demand both high throughput and low latency, and may adjust the size and quality of a stream to network bandwidth available or dynamic change in content coded. However, catering to such media flows over a radio link with rapid changes in capacity requires the buffers and congestion to be managed carefully. Wireless networks need additional information to manage radio resources optimally to maximize network utilization and application performance. This draft provides requirements on metadata about the media transported, its scalability, privacy, and other related considerations. Use of the IPv6 Flow Label for WLCG Packet Marking Energy Sciences Network Jisc University of Michigan CERN This document describes an experimentally deployed approach currently used within the Worldwide Large Hadron Collider Computing Grid (WLCG) to mark packets with their project (experiment) and application. The marking uses the 20-bit IPv6 Flow Label in each packet, with 15 bits used for semantics (community and activity) and 5 bits for entropy. Alternatives, in particular use of IPv6 Extension Headers (EH), were considered but found to not be practical. The WLCG is one of the largest worldwide research communities and has adopted IPv6 heavily for movement of many hundreds of PB of data annually, with the ultimate goal of running IPv6 only. Considerations on Application - Network Collaboration Using Path Signals This document discusses principles for designing mechanisms that use or provide path signals and calls for standards action in specific valuable cases. RFC 8558 describes path signals as messages to or from on-path elements and points out that visible information will be used whether or not it is intended as a signal. The principles in this document are intended as guidance for the design of explicit path signals, which are encouraged to be authenticated and include a minimal set of parties to minimize information sharing. These principles can be achieved through mechanisms like encryption of information and establishing trust relationships between entities on a path. RTP: A Transport Protocol for Real-Time Applications This memorandum describes RTP, the real-time transport protocol. RTP provides end-to-end network transport functions suitable for applications transmitting real-time data, such as audio, video or simulation data, over multicast or unicast network services. RTP does not address resource reservation and does not guarantee quality-of- service for real-time services. The data transport is augmented by a control protocol (RTCP) to allow monitoring of the data delivery in a manner scalable to large multicast networks, and to provide minimal control and identification functionality. RTP and RTCP are designed to be independent of the underlying transport and network layers. The protocol supports the use of RTP-level translators and mixers. Most of the text in this memorandum is identical to RFC 1889 which it obsoletes. There are no changes in the packet formats on the wire, only changes to the rules and algorithms governing how the protocol is used. The biggest change is an enhancement to the scalable timer algorithm for calculating when to send RTCP packets in order to minimize transmission in excess of the intended rate when many participants join a session simultaneously. [STANDARDS-TRACK] Web Real-Time Communication Use Cases and Requirements This document describes web-based real-time communication use cases. Requirements on the browser functionality are derived from the use cases. This document was developed in an initial phase of the work with rather minor updates at later stages. It has not really served as a tool in deciding features or scope for the WG's efforts so far. It is being published to record the early conclusions of the WG. It will not be used as a set of rigid guidelines that specifications and implementations will be held to in the future. An Unreliable Datagram Extension to QUIC This document defines an extension to the QUIC transport protocol to add support for sending and receiving unreliable datagrams over a QUIC connection. RUSH - Reliable (unreliable) streaming protocol Facebook Facebook Facebook Facebook RUSH is an application-level protocol for ingesting live video. This document describes the protocol and how it maps onto QUIC. Discussion Venues This note is to be removed before publishing as an RFC. Discussion of this document takes place on the mailing list (), which is archived at . Source for this draft and an issue tracker can be found at https://github.com/afrind/draft-rush. *** BROKEN REFERENCE ***

Acknowledgments TODO acknowledge.