Requirements for Host-to-Network Collaboration Signaling
draft-kwbdgrr-tsvwg-net-collab-rqmts-04
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | John Kaippallimalil , Dan Wing , Sri Gundavelli , Sridharan Rajagopalan , Spencer Dawkins , Mohamed Boucadair | ||
| Last updated | 2024-10-14 | ||
| Replaces | draft-rwbr-tsvwg-signaling-use-cases | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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| Send notices to | (None) |
draft-kwbdgrr-tsvwg-net-collab-rqmts-04
Transport and Services Working Group J. Kaippallimalil
Internet-Draft Futurewei
Intended status: Informational D. Wing
Expires: 17 April 2025 Cloud Software Group
S. Gundavelli
Cisco
S. Rajagopalan
Cloud Software Group
S. Dawkins
Tencent America LLC
M. Boucadair
Orange
14 October 2024
Requirements for Host-to-Network Collaboration Signaling
draft-kwbdgrr-tsvwg-net-collab-rqmts-04
Abstract
Collaborative signaling from host-to-network (i.e., client-to-network
and server-to-network) can improve the user experience by informing
the network about the nature and relative importance of packets
(frames, streams, etc.) without having to disclose the content of the
packets. Moreover, the collaborative signaling may be enabled so
that clients and servers are aware of the network's treatment of
incoming packets. Also, client-to-network collaboration can be put
in place without revealing the identity of the remote servers. This
collaboration allows for differentiated services at the network
(e.g., packet discard preference), the sender (e.g., adaptive
transmission), or through cooperation of server/client and the
network.
This document lists some use cases that illustrate the need for a
mechanism to share metadata and outlines host-to-network
requirements. The document focuses on signaling information about a
UDP transport flow (UDP 4-tuple).
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-kwbdgrr-tsvwg-net-collab-
rqmts/.
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This Internet-Draft will expire on 17 April 2025.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Rationale for Per-packet Metadata . . . . . . . . . . . . . . 5
4. Requirements Definition . . . . . . . . . . . . . . . . . . . 7
4.1. Server-to-Network (S2N) . . . . . . . . . . . . . . . . . 7
4.2. Client-to-Network (C2N) . . . . . . . . . . . . . . . . . 8
4.3. API . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.4. System Considerations . . . . . . . . . . . . . . . . . . 8
5. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. Media Streaming . . . . . . . . . . . . . . . . . . . . . 9
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5.2. Interactive Media . . . . . . . . . . . . . . . . . . . . 10
5.3. Metadata Negotiation Support . . . . . . . . . . . . . . 11
6. On-path Metadata Requirements . . . . . . . . . . . . . . . . 12
6.1. Client-Network Metadata . . . . . . . . . . . . . . . . . 13
6.1.1. Client-Network Flow Authorization and Negotiation . . 13
6.2. Server-Network Metadata . . . . . . . . . . . . . . . . . 13
6.2.1. Packet Priority . . . . . . . . . . . . . . . . . . . 14
6.2.2. Tolerance to Delay . . . . . . . . . . . . . . . . . 15
7. System Considerations . . . . . . . . . . . . . . . . . . . . 15
7.1. Privacy Considerations . . . . . . . . . . . . . . . . . 15
8. Non-Requirements . . . . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10. Security Considerations . . . . . . . . . . . . . . . . . . . 16
11. Informative References . . . . . . . . . . . . . . . . . . . 17
Appendix A. Extended Requirements Definition . . . . . . . . . . 19
Appendix B. Extended Use-Cases . . . . . . . . . . . . . . . . . 21
B.1. Media Streaming Extended . . . . . . . . . . . . . . . . 21
Appendix C. Extended System Considerations . . . . . . . . . . . 21
C.1. Redundant Functions and Classification Complications . . 21
C.2. Session Continuity . . . . . . . . . . . . . . . . . . . 21
C.3. Multiple Bottlenecks . . . . . . . . . . . . . . . . . . 22
C.4. Scalability . . . . . . . . . . . . . . . . . . . . . . . 22
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
Wireless networks, including 5G and WLAN, inherently experience large
variations in link quality over sub-RTT (round-trip time) intervals
and on the other hand, applications such as interactive media demand
both low latency and high bandwidth.
Superior service during adverse network events can be achieved by the
sender conveying packet behavior preferences to the network for
packets within a single UDP 4-tuple flow. During adverse network
events this allows the network to be informed about the least-
impactful packets to drop (or delay) in the same UDP 4-tuple flow.
Without such signaling, the network can only indiscriminately drop
(or delay) packets. With such capability, loss-tolerant and delay-
tolerant transport protocols such as RTP [RFC3550], QUIC [RFC9000],
and Unreliable QUIC [RFC9221] can inform the network and provide a
superior end user experience.
Some of the complications that are induced by adverse network events
may be eliminated by adequate dimensioning and upgrades. However,
such upgrades may not be always (immediately) possible or justified.
Complementary mitigations are thus needed to soften these
complications by introducing some collaboration between endpoints and
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networks to adjust their behaviors. This document focuses on host-
to-network collaboration, which covers both client-to-network (C2N)
and server-to-network (S2N) directions.
Section 3 discusses the rationale for per-packet metadata.
Section 5 outlines use cases to illustrate the issues and the need
for additional information per flow to allow the network to optimize
its handling. Section 6 describes the requirements for on-path media
collaboration signals.
Section 7 provides operational constraints in the network.
2. Definitions
The document makes use of the following terms:
Host: Refers to an endpoint that is connected to a network (called,
client) or a server that delivers a service to a client.
Per-Flow Metadata: Refers to metadata that doesn't change often
during the lifetime of a connection and thus can be exchanged once
or as needed. This is communicated per flow (i.e., UDP 4-tuple)
between client and network.
Examples of such metadata are client request to honor per-packet
metadata and preferences.
Per-Packet Metadata: Refers to metadata that varies packet to packet
within the same flow, often capturing the nature and
characteristics of the traffic each packet carries. This needs to
be communicated on a per packet basis.
Examples of such metadata are Packet Priority and tolerance to
delay
Reactive Management: Network management actions that are undertaken
as a reaction to unplanned overload events. Concretely, this
includes policies which react to congestion events with very short
to very long durations (e.g., varying wireless and mobile air
interface conditions) or protection policies to soften the impact
of ongoing attacks.
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3. Rationale for Per-packet Metadata
Maximizing network utilization and enhancing user experience under
adverse conditions are challenging. Wireless networks face issues
like channel condition changes, cell interference, and user mobility.
These variations can occur in milliseconds [_5G-Lumos], while
congestion control takes tens of milliseconds (more than one RTT) to
estimate data rate. Application servers encoding live or interactive
content also take time to adjust to network rates. End-to-end
congestion control algorithms (CCAs) are suboptimal when link quality
varies in sub-RTT timeframes and applications need low latency and
high bandwidth (e.g., Section 2.1 of [RFC6077]). Applications settle
for lower throughput when prioritizing latency or higher throughput
with higher delays.
Feedback-based rate control for a flow (UDP 4-tuple) cannot adapt to
sub-RTT wireless channel changes. Application servers can provide
per-packet information for network shapers to allocate resources
effectively. Heuristics can build an “implicit signal” from
unencrypted packets to prioritize flows, but this leads to protocol
ossification [RFC9419]. Encrypted packets make implicit signals
unviable.
Bandwidth constraints are most prominent in access networks (e.g.,
radio access networks). Users, serviced via these networks, use
clients with varying connectivity needs for optimal experiences,
which change over time based on application usage. Explicit signals
to clients can help manage bandwidth better.
Interactive media applications and likewise demand high throughput
and low latency, sometimes carrying different streams (e.g., audio
and video) in a single connection (e.g., WebRTC [RFC8825]).
With RTP [RFC3550], media type could be used as an implicit signal
for determining relative priority. However, [RFC9335] encrypts RTP
header extensions and Contributing sources (CSRCs). Fully encrypted
transport (e.g., QUIC [RFC9000]) does not expose media header
information for network decisions.
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:
3GPP/mobile network
+--------------------:----------------------+
| +------+ : +-----+ +-----+ |
| |client+-----------B---+radio+----+ CN | |
| +------+ : +-----+ +--+--+ |
+--------------------:-----------------|----+
: |
Wireless home/ISP network |
+--------------------:-----------+ | : :
| +------+ +----+ : +------+ | +---+--+ : +------+ : +------+
| |client+-B-+WLAN+--B--+router+---+router+---+router+---+server|
| +------+ +----+ : +------+ | +------+ : +------+ : +------+
+--------------------:-----------+ : :
: : :
: : Transit : Content
User device/Network : MNO/ISP Network : Network : Network
Figure 1: E2E Media Transport Overview
Figure 1 shows where such bandwidth and performance constraints
usually exist with a "B" (for Bottleneck) in 3GPP/mobile networks and
WLAN/ISP networks. When a bottleneck exists temporarily, the network
has no choice but to discard or delay packets -- which can harm
certain flows and, thus, lead to suboptimal perceived experience. In
this document, this is termed 'Reactive Management'.
(A) Application signaling (client - server)
+--------------------------------------------------------+
/ \
+--+---+ +------------+ +--+---+
| | (C) C2N | | | |
| |<------------>| +--------+ | | |
| | | | Network| | downstream packet | |
| |<=============+=+ Shaper +<+=========================+ |
| | | +--------+ | (B) on-path S2N metadata| |
+------+ +------------+ +------+
Client Router Server
Figure 2: Metadata and Network Shaping
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Figure 2 shows a bottleneck (access) router on the Server to Client
path. A network shaper in the router manages QoS of multiple users’
flows and can buffer, discard, or apply other flow control rules.
Application layer signaling and feedback between Client and Server (A
- in the figure) adjust transmission rate over several RTTs using
feedback and CCAs, settling to a steady rate to avoid excessive
packet loss. In networks where link conditions (between Client and
Router) vary significantly at sub-RTT timescales, this results in
unused bandwidth at short timescales.
Research (e.g., [_5G-Octopus]) indicates that media applications can
achieve better QoE when sending at a higher rate (less conservative
than current CCA) and tolerating some packet loss or delay of low
priority packets. Packet priority and tolerance to delay in such
cases would be provided on-path in a side channel associated with the
downstream packet (B). The requirements for this server-to-network
(S2N) metadata are described in Section 6.2.
The client may provide information to an (access) router to drop
'lower priority'-marked packets of a flow (UDP 4-tuple) temporarily
which can in turn allocate available bandwidth to other flows of that
network attachment, especially during a reactive management event.
Network shapers observe flows and apply policies to maximize
performancebut are unaware underlying flows belinging to the same
user and network attachment (e.g., a subscriber connection, a 3GPP
PDU Session). Clients may provide information to an (access) router
to drop 'lower priority'-marked packets of a flow (UDP 4-tuple)
temporarily during congestion, allowing bandwidth allocation to other
flows of the same network attachment.
In summary, the rapid variation of wireless link quality and/or
bandwidth limitations in networks along with interactive applications
that demand low latency and high throughput can lead to suboptimal
user experience.
4. Requirements Definition
4.1. Server-to-Network (S2N)
REQ-PACKET-PRIORITY: Server indicates the importance of a packet
within a flow. This allows the network to prioritize based on
requirement and during a Reactive Management event. This priority
value may also be used to indicate loss tolerance and the network
elements may drop loss tolerant packets during Reactive Management
events.
This is a per-packet metadata requirement.
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REQ-PACKET-DELAY: Metadata to indicate whether the packet can
tolerate delay.
This is a per-packet metadata requirement.
4.2. Client-to-Network (C2N)
REQ-CLIENT-DECIDES: User/Client indicating to the network to honor
the application's metadata signaling.
This is a per-flow metadata requirement.
REQ-PAYLOAD-CLIENT-DECIDES: The ability of the receiver to change
the priority by communicating to the network to prioritize one
payload(metadata) over another within the flow -- without
cooperation of the sender. Gives the sender the ability to have
same metadata for all the connections without having to change
based on the user preference, aids in scalability.
This is a per-flow metadata requirement.
4.3. API
REQ-API-FRAMEWORK: API framework to facilitate signaling for
applications.
Signaling from client to network (Section 6.1.1) and server to
network (Section 6.2)) is best facilitated by Application
Programming Interfaces (APIs). Signaling and retrieval of the
signals may not be performed at a single layer (although not
encouraged). Hence, for server to network signaling, a framework
is required to abstract the underlying per-packet metadata
protocol(s) and allow the application(s) to retrieve/send signals
using a single or a set of APIs independent of the channels that
are used to convey the signals. The API framework is required
even if one single channel is used so that any application on a
client can consume the signals.
The API framework uses the medium negotiated under Section 5.3 to
send/receive the signals.
4.4. System Considerations
REQ-PRIVACY-ADDITIONAL: An on-path observer obtains (or gleans) no
additional information about the IP packet.
REQ-SIGNALING-AVOIDANCE: Leveraging previous experience [RFC9049],
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the following is not required to make use of the collaborative
signaling:
* Reveal the application identity.
* Expose the application cause (or 'reason') to signal metadata.
* Reveal the server identity.
* Inspect client-to-server encrypted payload by network elements.
5. Use Cases
5.1. Media Streaming
Streaming video contains the occasional key frame ("I-frame")
containing a full video frame. These frames 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.
Examples: live broadcast, on-demand video streaming.
Use cases:
1. The majority of streaming traffic is Audio and Video traffic.
Audio traffic is more critical than video for many applications
and vice-versa for some. This differences in priority needs to
be indicated to the network to ensure network (de)prioritizes (or
even drop if deemed necessary) traffic appropriately.
Requirement: REQ-PACKET-PRIORITY.
Impact: With the above requirement met, better quality of service
could be maintained in resource-constrained networks and during
Reactive Management events ensuring better user experience.
2. The server (or relay) sends the same stream to many receivers,
including the same metadata (especially with media over QUIC).
Different clients have different priorities for different types
of traffic. This would result in change in priorities for the
same type of traffic that a single server sends, based on the
user/client.
Requirement: REQ-PAYLOAD-CLIENT-DECIDES.
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Impact: With the above requirement met, each client/user
preferences are prioritized accordingly while maintaining
scalability on the server, since the metadata that the server
sends still remains the same for all the connections.
3. In loss-prone networks or during Reactive Management events, if
all packets of an application flow (UDP 4-tuple) such as live
broadcast or on-demand video streaming are treated the same, it
limits the ability to maximize network utilization and use the
transiently available bandwidth. Dropping or delaying of (media)
packets randomly is likely to lower network utilization and
application performance.
Requirement: REQ-PACKET-PRIORITY, REQ-PACKET-DELAY.
Impact: By identifying packets that tolerate being dropped,
congestion can be reduced leading to improved performance/quality
of service.
5.2. Interactive Media
Interactive media includes content that a user can actively engage
with and results in input and response actions that can be highly
delay-sensitive. This can also include mixed traffic based on the
user activity and interaction.
Examples: VoIP (Peer-to-Peer (P2P), group conferencing), gaming,
Remote Desktop Virtualization, eXtended Reality (XR).
Use cases:
1. A mobile/roaming user prioritizes audio over video during a VoIP
call to have a seamless meeting experience.
Requirement: REQ-PAYLOAD-CLIENT-DECIDES.
Impact: With the above requirement met, each client/user
preferences are prioritized accordingly while maintaining
scalability on the server.
2. A remote desktop user prioritizes graphics updates over an on-
going file copy operation. A user types in/interacts with a
document/file after triggering a save file operation, while save
operation is on-going.
Requirement: REQ-PACKET-PRIORITY, REQ-PACKET-DELAY.
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Impact: By prioritizing graphic updates/interactive traffic, user
interactivity is improved with lesser jitter.
3. A game or VoIP application may want to signal different metadata
for the same type of packet in each direction. One user, in a
VoIP conference call, wants to prioritize the slide deck being
shared while the other wants to prioritize audio and other wants
to prioritize video of the speaker. Each user's varied
preferences can be catered with same type of metadata originating
from the server.
Requirement: REQ-PACKET-PRIORITY, REQ-PAYLOAD-CLIENT-DECIDES.
Impact: With the above requirement met, each client/user
preferences are prioritized accordingly while maintaining
scalability on the server.
4. A network glitch while user is in an eXtended Reality
application. The traffic comprises of haptic, video, audio,
graphics update and keystrokes. During such a Reactive
Management event, some packets need to be deprioritized/dropped
to maintain interactivity.
Requirement: REQ-PACKET-PRIORITY, REQ-PACKET-DELAY.
Impact: By prioritizing high priority traffic, user's interactive
experience is improved with lesser jitter.
5.3. Metadata Negotiation Support
Currently, some flows are granted higher priority over other flows
because of a contractual agreement between the ISP and the content
provider. These contracts could be extended to also allow per-packet
metadata within a single UDP 4-tuple, as desired by this document
(Section 6.1.1). However, these sorts of agreements favor large
content providers and major ISPs, disfavoring smaller providers and
smaller ISPs while also preventing other network topologies such as
peer-to-peer networking (e.g., VoIP) as that traffic does not
originate from a contracted content provider.
For all applications to benefit from per-packet prioritization within
a single UDP 4-tuple, the client needs to communicate with the ISP to
determine which per-packet markings are supported by the ISP's
network (e.g., encoded into IPv6 Flow Label, UDP Option, or DSCP).
Then it can indicate to the ISP's network that a certain UDP 4-tuple
will have those markings and instruct the server to generate those
per-packet metadata markings.
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There might be many channels to signal the Server-to-Network per-
packet metadata such as (non-exhaustive list):
* TCP options [RFC9293]
* UDP Options [I-D.ietf-tsvwg-udp-options]
* IPv6 Hop-by-Hop Options (Section 4.3 of [RFC8200])
* QUIC CID mapping
* ICMP messages
Requirements: REQ-API-FRAMEWORK and REQ-CLIENT-DECIDES.
Impact: By signaling ISPs to honor the metadata for a particular
flow, the client facilitates identifying important packets to the ISP
enhancing packet delay or drop decisions during Reactive Management
events.
Client ISP router
| |
|-------------------------------------------------->|
| Network Collaboration Capabilities? |
| |
|<--------------------------------------------------|
| my Network Collaboration capabilities |
| |
|-------------------------------------------------->|
| Server will mark packets using "method #4" |
| |
|<--------------------------------------------------|
| ok |
Figure 3: API Framework: Client learns ISP capabilities and
signals how incoming IP packets will signal network collaboration
6. On-path Metadata Requirements
There are various approaches for collaborative signaling between the
server/client and network including out-of-band signaling, client-
centric metadata sharing and proxied connections. The requirements
here focus on proxied metadata connections on path with the data
traffic.
The path signals below should follow the principles of intentional
distribution, protection of information, minimization and limiting
impact as described in [RFC9419] and [RFC8558]. Leveraging previous
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experience ([RFC9049]), the metadata signals do not need application
identity, application cause (or 'reason'), server identity or the
inspection of client-to-server encrypted payload.
The metadata connections may be between server and network (in either
direction) or between client and network (in either direction).
Some use cases benefit from server-network metadata exchanges
(Section 6.2) after first performing a client-network metadata
exchange (Section 6.1.1).
For the requirements that follow, the assumption is that the client
agrees to the exchange of metadata between the server and network, or
between the client and network.
6.1. Client-Network Metadata
Client-to-network metadata is critical in both identifying the flow
that contains metadata as well as negotiate the medium of signaling
of metadata.
6.1.1. Client-Network Flow Authorization and Negotiation
By signaling the ISP, a client can authorize the ISP to honor
incoming per-packet metadata for a certain flow (UDP 4-tuple).
This same signal also allows negotiating capabilities discussed in
Section 5.3) and sharing the keys necessary for encrypting or
obfuscating server-to-network per- packet metadata recommended in
Section 7.1.
REQ-CLIENT-DECIDES is satisfied by signaling Client Flow
Authorization as part of client-to-network signal.
6.2. Server-Network Metadata
Application flows (UDP 4-tuple) for live media, eXtended Reality
(XR), and gaming require high bandwidth and low latency. In wireless
networks, some bandwidth cannot be scheduled using feedback-based
rate control due to significant link variations at sub-RTT
timescales. Congestion control algorithms settle to a steady rate to
avoid excessive packet loss. Feedback via ECN/L4S [RFC9331] provides
an accurate signal but lacks finer resolution information of
instantaneous bandwidth available.
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If application packets can tolerate delay or some loss of lower
priority packets, the network traffic shaper and scheduler can use
this information to provide higher application quality of service
[_5G-Octopus].
The metadata in Section 6.2.1 should satisfy constraints identified
in Section 7. Privacy Section 7.1 requires that metadata should not
provide additional information to identify the application or user.
The application server can decide on metadata values that provide the
best handling for packets and may not reflect exact priority values.
This metadata is advisory, and network traffic policy that restricts
its use would not result in additional issues. Other constraints
include scale (Appendix C.4) and continuity (Appendix C.2).
Realizing the additional bandwidth potential with these metadata may
require a higher sending rate for the transport flow, which is not
specified in this document. Network shapers and schedulers can use
the metadata in Section 6.2.1, but further details are out of scope.
Previous work in [TR.23.700-70-3GPP] has identified the general
problem, but the solution in [TS.23.501-3GPP] is specific to a 5G
network. The metadata sent from a dedicated 5G application server
identifies PDU set information and end-of-burst signals, which are
not understood by non-3GPP systems such as Wi-Fi or DOCSIS. Further,
3GPP functions and policy configurations are required since this is a
5G specific solution. The metadata disclosed in the 5G solution also
identifies frame boundaries and does not fully conform to the
constraints for privacy or minimality of data identified in
Section 7.
6.2.1. Packet Priority
Per-packet priority information provides the priority level of one
packet relative to other packets within a transport flow (UDP
4-tuple). When a packet is marked with high priority, the
expectation is that during a Reactive Management event, the network
will give high importance to forwarding the packet compared to a
packet marked with low priority. The application server can decide
on the priority or importance values that provide the best handling
for the packets of the transport flow. When more than one
application stream (e.g., video, audio) is sent on the same transport
flow, the application server decides the best allocation of priority
values across the different streams of the flow.
Per-packet priority or importance determines the drop priority of a
packet.
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REQ-PACKET-PRIORITY is satisfied by signaling Packet Priority as part
of server-to-network metadata.
6.2.2. Tolerance to Delay
Some packets of a media flow (UDP 4-tuple) can tolerate more delay
over the wire than others (e.g., packets carrying live media frames
require very low latency while packets carrying a background image
for augmented reality can tolerate more delay). The objective of
this metadata is to indicate that these packets can tolerate a
limited amount of delay when there is severe congestion or limited
bandwidth. Similar to the LE PHB [RFC8622] for flows, the
expectation is that in this case, each packet marked with this
metadata is dropped during a Reactive Management event. As with per-
packet priority in Section 6.2.1, the application server can decide
on the metadata values that provide the best handling for the packets
of the transport flow.
REQ-PACKET-DELAY is satisfied by signaling Tolerance to Delay as part
of server-to-network metadata.
7. System Considerations
Traffic policing and shaping are enforced in ingress/egress network
points for various reasons (protect the network against attacks,
ensure conformance with a traffic profile, etc.). Out-of-profile
traffic may be discarded or assigned another class (e.g., using Lower
Effort Per-Domain Behavior (LE PDB) [RFC3662]) a bandwidth limit
among others. The exact behavior is policy-based and deployment-
specific.
The entire set of operations to manage traffic is beyond the scope of
this document. This section focuses on operational constraints that
impact server-network, and client-network modes of sending metadata.
7.1. Privacy Considerations
Media flows are vulnerable to traffic analysis even without per-
packet metadata (see, e.g., [traffic-analysis]). The security
aspects of the media payload / transport are not in the scope of this
document; these are mentioned here only to provide context for
metadata privacy.
Protocols such as TLS, SRTP, and QUIC offer some mitigations (like
padding) but are vulnerable to traffic analysis
([traffic-analysis-2]).
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Per-packet metadata can aid in traffic analysis. Hence, it is
recommended to encrypt or obfuscate the metadata information so it is
only available to the server, client, and authorized network
elements. However, encryption/obfuscation of per-packet metadata is
ineffective if the threat resides in the same network entity with
keys to decrypt the metadata. The method of encryption or
obfuscation is out of scope. To best preserve privacy,
implementations might also consider less granular per-packet marking,
for example marking all audio and video packets the same and only
marking a background data transfer with different metadata.
Analysis to ensure that metadata exposure does not compromise user
privacy or allow unauthorized entities to infer sensitive
information, while maintaining minimal resource consumption is
crucial. There is a tension between resource consumption of such
encryption and the user's privacy (Section 7.4 of [RFC6973]).
REQ-PRIVACY-ADDITIONAL and REQ-SIGNALING-AVOIDANCE are satisfied by
not revealing any information that could identify the application's
identity, reason to signal, server identity, and securing the
metadata.
8. Non-Requirements
Application feedback with measurements of packets lost and delay
incurred may affect the sending rate and other behavior of the
application. The requirements and specification to mitigate these
aspects are not in the scope of this document.
9. IANA Considerations
None.
10. Security Considerations
Security aspects for the metadata are discussed in Section 7.1. The
principles outlined in [RFC8558], [RFC9049], and [RFC9419] contain
security considerations and are referenced in Section 6.
Per-packet metadata can be vulnerable to modification in transit by
on-path attackers, who can corrupt checksums, drop packets, or modify
metadata. Such changes can be detected by the receiver.
Since the document focuses only on priorities within a flow (not
specifying inter-flow priority), the document does not induce
concerns related to a specific user or client declaring all flows or
a subset of them as being more important. Such abuse concerns are
thus not applicable.
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Privacy-related considerations are discussed in Section 7.1.
11. Informative References
[app-measurement]
Gurel, Z. and A. C. Begen, "Bandwidth measurement for
QUIC", 2024, <https://datatracker.ietf.org/doc/slides-119-
moq-bandwidth-measurement-for-quic/>.
[I-D.ietf-tsvwg-udp-options]
Touch, J. D. and C. M. Heard, "Transport Options for UDP",
Work in Progress, Internet-Draft, draft-ietf-tsvwg-udp-
options-37, 13 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-tsvwg-
udp-options-37>.
[I-D.kaippallimalil-tsvwg-media-hdr-wireless]
Kaippallimalil, J., Gundavelli, S., and S. Dawkins, "Media
Handling Considerations for Wireless Networks", Work in
Progress, Internet-Draft, draft-kaippallimalil-tsvwg-
media-hdr-wireless-05, 10 August 2024,
<https://datatracker.ietf.org/doc/html/draft-
kaippallimalil-tsvwg-media-hdr-wireless-05>.
[I-D.rwbr-tsvwg-signaling-use-cases]
Rajagopalan, S., Wing, D., Boucadair, M., and T. Reddy.K,
"Host to Network Signaling Use Cases for Collaborative
Traffic Differentiation", Work in Progress, Internet-
Draft, draft-rwbr-tsvwg-signaling-use-cases-02, 17 March
2024, <https://datatracker.ietf.org/doc/html/draft-rwbr-
tsvwg-signaling-use-cases-02>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/rfc/rfc3550>.
[RFC3662] Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort
Per-Domain Behavior (PDB) for Differentiated Services",
RFC 3662, DOI 10.17487/RFC3662, December 2003,
<https://www.rfc-editor.org/rfc/rfc3662>.
[RFC6077] Papadimitriou, D., Ed., Welzl, M., Scharf, M., and B.
Briscoe, "Open Research Issues in Internet Congestion
Control", RFC 6077, DOI 10.17487/RFC6077, February 2011,
<https://www.rfc-editor.org/rfc/rfc6077>.
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[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/rfc/rfc6973>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/rfc/rfc8200>.
[RFC8558] Hardie, T., Ed., "Transport Protocol Path Signals",
RFC 8558, DOI 10.17487/RFC8558, April 2019,
<https://www.rfc-editor.org/rfc/rfc8558>.
[RFC8622] Bless, R., "A Lower-Effort Per-Hop Behavior (LE PHB) for
Differentiated Services", RFC 8622, DOI 10.17487/RFC8622,
June 2019, <https://www.rfc-editor.org/rfc/rfc8622>.
[RFC8825] Alvestrand, H., "Overview: Real-Time Protocols for
Browser-Based Applications", RFC 8825,
DOI 10.17487/RFC8825, January 2021,
<https://www.rfc-editor.org/rfc/rfc8825>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[RFC9049] Dawkins, S., Ed., "Path Aware Networking: Obstacles to
Deployment (A Bestiary of Roads Not Taken)", RFC 9049,
DOI 10.17487/RFC9049, June 2021,
<https://www.rfc-editor.org/rfc/rfc9049>.
[RFC9221] Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", RFC 9221,
DOI 10.17487/RFC9221, March 2022,
<https://www.rfc-editor.org/rfc/rfc9221>.
[RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/rfc/rfc9293>.
[RFC9331] De Schepper, K. and B. Briscoe, Ed., "The Explicit
Congestion Notification (ECN) Protocol for Low Latency,
Low Loss, and Scalable Throughput (L4S)", RFC 9331,
DOI 10.17487/RFC9331, January 2023,
<https://www.rfc-editor.org/rfc/rfc9331>.
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[RFC9335] Uberti, J., Jennings, C., and S. Murillo, "Completely
Encrypting RTP Header Extensions and Contributing
Sources", RFC 9335, DOI 10.17487/RFC9335, January 2023,
<https://www.rfc-editor.org/rfc/rfc9335>.
[RFC9419] Arkko, J., Hardie, T., Pauly, T., and M. Kühlewind,
"Considerations on Application - Network Collaboration
Using Path Signals", RFC 9419, DOI 10.17487/RFC9419, July
2023, <https://www.rfc-editor.org/rfc/rfc9419>.
[TR.23.700-70-3GPP]
"Study on XR (Extended Reality) and media services
(Release 19)", August 2024.
[traffic-analysis]
Alwhbi, I. A., Zou, C. C., and R. N. Alharbi, "Encrypted
Network Traffic Analysis and Classification Utilizing
Machine Learning", 2024,
<https://www.mdpi.com/1424-8220/24/11/3509>.
[traffic-analysis-2]
"A real-world dataset of netflix videos and user watch-
behavior", 2021, <https://www.gnan.ece.gatech.edu/archive/
ICC_2021_Netflix_Insights.pdf>.
[TS.23.501-3GPP]
"3rd Generation Partnership Project; Technical
Specification Group Servies and System Aspects; System
architecture for the 5G System (5GS); Stage 2 (Release
18)", March 2023.
[_5G-Lumos]
"Lumos5G: Mapping and Predicting Commercial mmWave 5G
Throughput, Arvind Narayanan et al., ACM Internet
Measurement Conference (IMC '20),
https://dl.acm.org/doi/10.1145/3419394.3423629", October
2020.
[_5G-Octopus]
"Octopus: In-Network Content Adaptation to Control
Congestion on 5G Links, Yongzhou Chen et al., ACM/IEEE
Symposium on Edge Computing (SEC '23),
https://dl.acm.org/doi/10.1145/3583740.3628438", December
2023.
Appendix A. Extended Requirements Definition
REQ-MEDIA-AV-SEPARATE: Audio can be prioritized differently than
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video.
This requirement may be generalized to non-media packet types.
This is an enhanced requirement that requires e2e application
layer signaling (out of scope here) to identify of frame
boundaries and may not be suitable in cases which are sensitive to
traffic analysis (see REQ-SIGNALING-AVOIDANCE and [RFC9049]). If
the application provides frame boundaries, the client signals the
enhanced application priority values in REQ-PAYLOAD-CLIENT-
DECIDES.
This is a per-flow metadata requirement.
REQ-MEDIA-KEYFRAME: Video contains prediction frames and full
frames, which need to be distinguished so that full frames can be
indicated to the network.
This is an enhanced requirement that requires e2e application
layer signaling (out of scope here) to identify of frame
boundaries and may not be suitable in cases which are sensitive to
traffic analysis (see REQ-SIGNALING-AVOIDANCE and [RFC9049]). If
the application provides frame boundaries, the client signals the
enhanced application priority values in REQ-PAYLOAD-CLIENT-
DECIDES.
This is a per-packet metadata requirement.
REQ-CONTINUITY: Handover from one radio or router to another should
continue to provide same service level.
REQ-MULTIPLE-BOTTLENECKS: Signaling should support Multiple
bottlenecks.
The network must identify multiple bottlenecks, including those
within the ISP and subscriber networks, ensuring all bottlenecks
benefit from network/client collaboration to enhance overall
performance.
REQ-SINGLE-CHANNEL: The network should use a single channel for
sharing metadata to simplify the process and avoid the need for
redundant functions.
REQ-ISP-SCALE: The metadata and other state information that a
router has to maintain for each additional flow it handles should
be kept to a minimum or eliminated altogether.
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Appendix B. Extended Use-Cases
B.1. Media Streaming Extended
Streaming video contains the occasional key frame ("I-frame")
containing a full video frame. These frames 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.
Examples:
1. Audio is more critical than video for many applications and
should be prioritized differently than video.
Requirement: REQ-MEDIA-AV-SEPARATE.
2. Video contains prediction frames and full frames, which need to
be distinguished so that full frames can be indicated to the
network.
Requirement: REQ-MEDIA-KEYFRAME.
Appendix C. Extended System Considerations
C.1. Redundant Functions and Classification Complications
If distinct channels are used to share the metadata between a host
and a network, a network that engages in the collaborative signaling
approach will require sophisticated features to classify flows and
decide which channel is used to share metadata so that it can consume
that information.
Likewise, the network will require to implement redundant functions;
for each signaling interface.
_As such, application- and protocol-specific signaling channels are
suboptimal._ (REQ-SINGLE-CHANNEL)
Requirement: REQ-SINGLE-CHANNEL is preferred.
C.2. Session Continuity
The frequency of handovers increases when a user moves faster or when
the media session lasts longer. During handovers, there should be
minimal delay incurred during handover in configuring/setting up the
metadata of a media session in progress.
Requirement: REQ-CONTINUITY.
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C.3. Multiple Bottlenecks
Whereas models often show a single bottleneck, there are frequently
two (or more) bottlenecks: the ISP network and within the subscriber
network (e.g., Wi-Fi link). As such, all bottlenecks near the
subscriber should be able to benefit from network/client
collaboration.
Requirement: REQ-MULTIPLE-BOTTLENECKS.
C.4. Scalability
There may be a large number of flows handled by the server and
wireless/access router. Per flow information (state) at a wireless
router for optimizing the flow can negate the advantages offered as
the number of flows handled increases.
Requirement: REQ-ISP-SCALE.
Acknowledgments
This document is a merge of [I-D.rwbr-tsvwg-signaling-use-cases] and
[I-D.kaippallimalil-tsvwg-media-hdr-wireless].
T. Reddy contributed text and ideas to this document.
Acknowledgments from
[I-D.kaippallimalil-tsvwg-media-hdr-wireless]: Xavier De Foy and the
authors of this draft have discussed the similarities and
differences of this draft with the MoQ draft for carrying media
metadata.
The authors wish to thank Mike Heard, Sebastian Moeller and Tom
Herbert for discussions on metadata fields, fragmentation and
various transport aspects.
The authors appreciate input from Marcus Ilhar and Magnus
Westerlund on the need to address privacy in general and Dan Druta
to consider a common transport across various client/server to
network signaling when possible. Ruediger Geib suggested that
limiting the amount of state information that a wireless router
has to keep for a flow should be minimized.
Ingemar Johansson's suggestions on fast fading (which L4S handles)
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and dramatic drops in wireless accesses have been helpful to
identify the issues. Thanks to Hang Shi for the review and
comments on client-to-network signaling. Thanks to Luis Miguel
Contreras, Colin Kahn, Marcus Ilhar and Tianji Jiang for their
review and comments.
Authors' Addresses
John Kaippallimalil
Futurewei
Email: john.kaippallimalil@futurewei.com
Dan Wing
Cloud Software Group Holdings, Inc.
Email: danwing@gmail.com
Sri Gundavelli
Cisco
Email: sgundave@cisco.com
Sridharan Rajagopalan
Cloud Software Group Holdings, Inc.
Email: Sridharan.girish@gmail.com
Spencer Dawkins
Tencent America LLC
Email: spencerdawkins.ietf@gmail.com
Mohamed Boucadair
Orange
35000 Rennes
France
Email: mohamed.boucadair@orange.com
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