Multicast Extension for QUIC
draft-jholland-quic-multicast-00
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| Authors | Jake Holland , Lucas Pardue , Max Franke | ||
| Last updated | 2022-05-13 | ||
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draft-jholland-quic-multicast-00
QUIC Working Group J. Holland
Internet-Draft Akamai Technologies, Inc.
Intended status: Experimental L. Pardue
Expires: 14 November 2022
M. Franke
TU Berlin
13 May 2022
Multicast Extension for QUIC
draft-jholland-quic-multicast-00
Abstract
This document defines a multicast extension to QUIC to enable the
efficient use of mullticast-capable networks to send identical data
streams to many clients at once, coordinated through individual
unicast QUIC connections.
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
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and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 14 November 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Multicast Channel . . . . . . . . . . . . . . . . . . . . . . 3
3. Transport Parameter . . . . . . . . . . . . . . . . . . . . . 5
4. Extension Overview . . . . . . . . . . . . . . . . . . . . . 6
4.1. Channel Management . . . . . . . . . . . . . . . . . . . 6
4.2. Client Response . . . . . . . . . . . . . . . . . . . . . 7
4.3. Data Carried in Channels . . . . . . . . . . . . . . . . 7
4.4. Stream Processing . . . . . . . . . . . . . . . . . . . . 8
5. Flow Control . . . . . . . . . . . . . . . . . . . . . . . . 8
6. Congestion Control . . . . . . . . . . . . . . . . . . . . . 9
7. Data Integrity . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Packet Hashes . . . . . . . . . . . . . . . . . . . . . . 9
8. Packet Scheduling . . . . . . . . . . . . . . . . . . . . . . 9
9. Stateless Reset . . . . . . . . . . . . . . . . . . . . . . . 10
10. Implementation and Operational Considerations . . . . . . . . 10
11. New Frames . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. MC_CHANNEL_ANNOUNCE . . . . . . . . . . . . . . . . . . 10
11.2. MC_CHANNEL_PROPERTIES . . . . . . . . . . . . . . . . . 12
11.3. MC_CHANNEL_JOIN . . . . . . . . . . . . . . . . . . . . 15
11.4. MC_CHANNEL_LEAVE . . . . . . . . . . . . . . . . . . . . 16
11.5. MC_CHANNEL_INTEGRITY . . . . . . . . . . . . . . . . . . 16
11.6. MC_CHANNEL_STREAM_BOUNDARY_OFFSET . . . . . . . . . . . 17
11.7. MC_CHANNEL_ACK . . . . . . . . . . . . . . . . . . . . . 17
11.8. MC_PATH_RESPONSE . . . . . . . . . . . . . . . . . . . . 18
11.9. MC_CLIENT_LIMITS . . . . . . . . . . . . . . . . . . . . 18
11.10. MC_CHANNEL_RETIRE . . . . . . . . . . . . . . . . . . . 19
11.11. MC_CLIENT_CHANNEL_STATE . . . . . . . . . . . . . . . . 19
12. Frames Carried in Channel Packets . . . . . . . . . . . . . . 21
13. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 23
14. Security Considerations . . . . . . . . . . . . . . . . . . . 23
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
16.1. Normative References . . . . . . . . . . . . . . . . . . 23
16.2. Informative References . . . . . . . . . . . . . . . . . 24
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
This document specifies an extension to QUIC version 1 [RFC9000] to
enable the use of multicast IP transport of identical data packets
for use in many individual QUIC connections.
The multicast data can only be consumed in conjunction with a unicast
QUIC connection. When support for multicast is negotiated, the
server can optionally advertise existence of one or more multicast
channels that contain unidirectional data streams from server to
client, and the client can optionally join the multicast channel and
verify from integrity data the server provides that correct data is
being received, then acknowledge the data from the multicast
channel(s) over the unicast connection.
Enabling this can provide large scalability benefits for popular
traffic over multicast-capable networks.
This document does not define any multicast transport except server
to client and only includes semantics for source-specific multicast.
## Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Commonly used terms in this document are described below.
(S,G): A tuple of IP addresses identifying a source-specific
multicast channel, as described in [RFC4607].
2. Multicast Channel
A QUIC multicast channel (or just channel) is a one-way network path
that a server can use as an alternate path to send QUIC connection
data to a client.
Multicast channels are designed to leverage multicast IP and to be
shared by many different connections simultaneously for
unidirectional server-initiated data. One or more servers can use
the same QUIC multicast channel to send the same data to many
clients, as a supplement to the individual QUIC connections between
those servers and clients.
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Each QUIC multicast channel has exactly one associated (S,G) that is
used for the delivery of the multicast packets on the IP layer.
Channels do not support any-source multicast semantics. This however
does not impose a requirement on how the underlying network stack has
to handle the forwarding and delivery of multicast packets.
QUIC connections are defined in Section 5 of [RFC9000] and are not
changed in this document; each connection is a shared state between a
client and a server.
Channels carry only 1-RTT packets. Packets associated with a channel
contain a Channel ID in place of a Destination Connection ID. (A
Channel ID cannot be zero length.) This adds a layer of indirection
to the process described in Section 5.2 of [RFC9000]} for matching
packets to connections upon receipt. Incoming packets received on
the network path associated with a channel use the Channel ID to
associate the packet with a joined channel.
A client with a matching joined channel always has at least one
connection associated with the channel. If a client has no matching
joined channel, the packet is discarded.
Since the network path for a channel is unidirectional, packets
associated with a channel are acknowledged with MP_CHANNEL_ACK frames
Section 11.7 instead of with ACK frames. Each channel has an
independent packet number space.
The use of any particular channel is OPTIONAL for both the server and
the client. It is recommended that applications designed to leverage
the multicast capabilities of this extension also provide graceeful
degradation for endpoints that do not or cannot make use of the
multicast functionality.
The server has access to all data transmitted on any multicast
channel it uses, and could optionally send this data with unicast
instead.
No special handling of the data is required in a client application
that has enabled multicast. A datagram or any particular bytes from
a server-initiated unidirectional stream can be delivered over the
unicast connection or a multicast channel transparently to the
client.
Client applications should have a mechanism that disables the use of
multicast on connections with enhanced privacy requirements for the
privacy-related reasons covered in
[I-D.draft-krose-multicast-security].
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3. Transport Parameter
Support for multicast extesnsions in a client is advertised by means
of a QUIC transport parameter:
* name: multicast_client_params (TBD - experiments use 0xff3e800)
If a multicast_client_params transport parameter is not included,
servers MUST NOT send any frames defined in this document. (Given
that a server never sends any MC_CHANNEL_JOIN frames, the clients
also will never send any frames in this document so only the client-
to-server advertisement is necessary.)
The multicast_client_params parameter has the structure shown below
in Figure 1.
multicast_client_params {
Capabilities Field (i),
Max Aggregate Rate (i),
Max Channel IDs (i),
Hash Algorithms Supported (i),
AEAD Algorithms Supported (i),
Hash Algorithms List (16 * Hash Algorithms Supported),
AEAD Algorithms List (16 * AEAD Algorithms Supported)
}
Figure 1: multicast_client_params Format
Capabilities Flags is a bit field structured as follows:
* 0x1 is set if IPv4 channels are permitted
* 0x2 is set if IPv6 channels are permitted
A server MUST NOT send MC_CHANNEL_PROPERTIES with addresses using an
IP Family that is not supported according to the Capabilities in the
multicast_client_params, unless and until a later MC_CLIENT_LIMITS
frame adds permission for a different address family.
The Capabilities Field, Max Aggregate Rate, and Max Channel IDs are
the same as in MC_CLIENT_LIMITS frames (Section 11.9) and provide the
initial client values.
The AEAD Algorithms List field is in order of preference (most
preferred occuring first) using values from the registry below. It
lists the algorithms the client is willing to use to decrypt data in
multicast channels, and the server MUST NOT send a MC_CHANNEL_JOIN to
this client for any channels using unsupported algorithms:
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* https://www.iana.org/assignments/aead-parameters/aead-
parameters.xhtml (https://www.iana.org/assignments/aead-
parameters/aead-parameters.xhtml)
The Hash Algorithms List field is in order of preference (most
preferred occurring first) using values from the registry below. It
lists the algorithms the client is willing to use to check integrity
of data in multicast channels, and the server MUST NOT send a
MC_CHANNEL_JOIN to this client for any channels using unsupported
algorithms:
* https://www.iana.org/assignments/named-information/named-
information.xhtml#hash-alg (https://www.iana.org/assignments/
named-information/named-information.xhtml#hash-alg)
4. Extension Overview
A client has the option of refusal and the power to impose upper
bound maxima on several resources (see Section 5), but otherwise its
join status for all multicast channels is entirely managed by the
server.
* A client MUST NOT join a channel without receiving instructions
from a server to do so
* A client MUST leave joined channels when instructed by the server
to do so
* A client MAY leave channels or refuse to join channels, regardless
of instructions from the server
4.1. Channel Management
The client tells its server about some restrictions on resources that
it is capable of processing with the initial values in the
multicast_client_params transport parameter (Section 3) and later can
update these limits with MC_CLIENT_LIMITS Section 11.9 frames.
Servers ensure the set of channels the client is currently requested
to join remains within these advertised client limits as covered in
Section 5.
The server asks the client to join channels with MC_CHANNEL_JOIN
(Section 11.3) frames and to leave channels with MC_CHANNEL_LEAVE
(Section 11.4) frames.
The server uses MC_CHANNEL_PROPERTIES (Section 11.2) frames before
any join or leave frames for the channel to describe the channel
properties to the client, including values the client can use to
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ensure the server's requests remain within the limits it has sent to
the server, as well as the keys necessary to decode packets in the
channel.
When the server has asked the client to join a channel, it also sends
MC_CHANNEL_INTEGRITY frames (Section 11.5) to enable the client to
verify packet integrity before processing the packet. A client MUST
NOT decode packets for a channel for which it has not received an
applicable set of MC_CHANNEL_PROPERTIES (Section 11.2) frames
containing the full set of data required, or for which it has not
received a matching packet hash in an MC_CHANNEL_INTEGRITY
(Section 11.5) frame.
The server ensures that in aggregate, all channels that the client
has currently been asked to join and that the client has not left or
declined to join fit within the limits indicated by the initial
values in the transport parameter or last MC_CLIENT_LIMITS
(Section 11.9) frame the server received.
4.2. Client Response
The client sends back information about how it has responded to the
server's requests to join and leave channels in
MC_CLIENT_CHANNEL_STATE (Section 11.11) frames.
MC_CLIENT_CHANNEL_STATE frames are only sent for channels after the
server has requested the client to join the channel, and are
thereafter sent any time the state changes.
Clients that receive and decode data on a multicast channel send
acknowledgements for the data on a unicast connection using
MC_CHANNEL_ACK (Section 11.7) frames. Channels also will
periodically contain PATH_CHALLENGE ([RFC9000] Section 19.17) frames,
which cause clients to send MC_PATH_RESPONSE (Section 11.8) frames on
the unicast connection in addition to their MC_CHANNEL_ACK frames.
4.3. Data Carried in Channels
Data transmitted in a multicast channel is encrypted with symmetric
keys so that on-path observers without access to these keys cannot
decode the data. However, since potentially many receivers receive
identical packets and identical keys for the multicast channel and
some receivers might be malicious, the packets are also protected by
MC_CHANNEL_INTEGRITY (Section 11.5) frames transmitted over a
separate integrity-protected path.
A client MUST NOT decode packets on a multicast channel for which it
has not received a matching hash in an MC_CHANNEL_INTEGRITY frame
over a different integrity-protected communication path. The
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different path can be either the unicast connection or another
multicast channel with packets that were verified with an earlier
MC_CHANNEL_INTEGRITY frame.
4.4. Stream Processing
Stream IDs in channels are restricted to unidirectional server
initiated streams, or those with the least significant 2 bits of the
stream ID equal to 3 (see [RFC9000] Section 2.1).
Since a server has access to all data in channels it uses, a server
can always avoid stream ID collisions with the stream IDs carried in
channels, and can usually (depending on the timing) avoid allowing
channels to exceed the client's max_streams_uni by requesting that
clients leave channels before their limits would be exceeded.
However, since clients can join later than a channel began, clients
supporting the multicast extensions to QUIC should be prepared to
handle stream IDs that do not begin at early values, since by the
time a client joins a channel in progress the stream id count might
have been increasing for a long time. Clients should therefore begin
with a high initial_max_streams_uni or send an early MAX_STREAMS type
0x13 value (see Section 19.11 of [RFC9000]) with a high limit.
MC_CHANNEL_PROPERTIES can provide a recommended value for
max_streams_uni to allow for uninterrupted transport using the
multicast channel.
Servers also can send MC_CHANNEL_STREAM_BOUNDARY_OFFSET
(Section 11.6) frames to indicate an application-layer boundary in a
stream carried inside a channel. These frames enable new clients
joining a channel to start receiving application data from the
indicated stream as though the stream data at that offset had an
offset of 0.
5. Flow Control
The values used for unicast flow control cannot be used to limit the
transmission rate of a multicast channel because a single client with
a low MAX_STREAM_DATA or MAX_DATA value that did not acknowledge
receipt could block many other receivers if the servers had to ensure
that channels responded to each client's limits.
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Instead, clients advertise resource limits that the server is
responsible for staying within via MC_CLIENT_LIMITS (Section 11.9)
frames and their initial values from the transport parameter
(Section 3). The server advertises the expected maxima of the values
that can contribute toward client resource limits within a channel in
MC_CHANNEL_PROPERTIES (Section 11.2) frames.
If the server asks the client to join a channel that would exceed the
client's limits with an up-to-date Client Limit Sequence Number, the
client should send back a MC_CHANNEL_STATE_CHANGE with "Declined
Join" and reason "Property Violation". If the server asks the client
to join a channel that would exceed the client's limits with an out-
of-date Client Limit Sequence Number or a Channel Property Sequence
Number that the client has not yet seen, the client should instead
send back a "Declined Join" with "Desynchronized Limit Violation".
If the actual contents sent in the channel exceed the advertised
limits from the MC_CHANNEL_PROPERTY, clients SHOULD leave the stream
with a PROTOCOL_ERROR/Limit Violated state change.
6. Congestion Control
The server maintains a full view of the traffic received by the
client via the ACK frames coupled with the MC_CHANNEL_ACK
(Section 11.7) frames.
Under sustained persistent loss, the server SHOULD instruct the
client such that the aggregate rate of joined channels remains under
the data rate successfully received by the client in the recent past.
7. Data Integrity
TODO: import the [I-D.draft-krose-multicast-security] explanation for
why extra integrity protection is necessary (many client have the
shared key, so AEAD doesn't provide authentication against other
valid clients on its own).
7.1. Packet Hashes
TODO: explanation and example for how to calculate the packet hash.
Note that the hash is on the unencrypted packet because it checks
against a specific packet number, which is protected by AEAD. (This
approach also may help make better use of crypto hardware offload.)
8. Packet Scheduling
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9. Stateless Reset
As clients can unilaterally stop the delivery of multicast packets by
leaving the relevant (S,G), channels do not need stateless reset
tokens. Clients therefore do not share the stateless reset tokens of
channels with the server. Instead, if an endpoint receives packets
addressed to an (S,G) that it can not associate with any existing
channel, it MAY take the necessary steps to prevent the reception of
further such packets, without the need to signal to the server that
it should stop sending.
If a server or client somehow still detect a stateless reset for a
channel, they MUST ignore it.
10. Implementation and Operational Considerations
11. New Frames
11.1. MC_CHANNEL_ANNOUNCE
Once a server learns that a client supports multicast through its
transport parameters, it can send one or multiple MC_CHANNEL_ANNOUNCE
frames (type=TBD-11..TBD-22) to share information about available
channels with the client. The MC_CHANNEL_ANNOUNCE frame contains the
static properties of a channel that do not change during its
lifetime.
MC_CHANNEL_ANNOUNCE frames are formatted as shown in Figure 2.
MC_CHANNEL_ANNOUNCE Frame {
Type (i) = TBD-11..TBD-12 (experiments use 0xff3e811/0xff3e812),
ID Length (8),
Channel ID (8..160),
Source IP (32..128),
Group IP (32..128),
UDP Port (16),
Header AEAD Algorithm (16),
Header Key Length (i),
Header Key (..),
}
Figure 2: MC_CHANNEL_ANNOUNCE Frame Format
Frames of type TBD-10 are used for IPv4 and both Source and Group
address are 32 bits long. Frames of type TBD-11 are used for IPv6
and both Source and Group address are 128 bits long.
MC_CHANNEL_ANNOUNCE frames contain the following fields:
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* ID Length: The length in bytes of the Channel ID field.
* Channel ID: The channel ID of the channel that is getting
announced.
* IP Family: Unset indicates IPv4, Set indicates IPv6 for both
Source IP and Group IP.
* Source IP: The IP Address of the source of the (S,G) for the
channel. Either a 32-bit IPv4 address or a 128-bit IPv6 address,
as indicated by IP Family.
* Group IP: The IP Address of the group of the (S,G) for the
channel. Either a 32-bit IPv4 address or a 128-bit IPv6 address,
as indicated by IP Family.
* UDP Port: The 16-bit UDP Port of traffic for the channel.
* Header AEAD Algorithm: A value from
https://www.iana.org/assignments/aead-parameters/aead-
parameters.xhtml (https://www.iana.org/assignments/aead-
parameters/aead-parameters.xhtml), used to protect the header
fields in the channel packets. The value MUST match a value
provided in the "AEAD Algorithms List" of the transport parameter
(see Section 3).
* Header Key Length: Provides the length of the Key field. It MUST
match a valid key length for the Header AEAD Algorithm.
* Header Key: A key for use with the Header AEAD Algorithm for
protecting the header fields of 1-RTT packets in the channel as
described in [RFC9001].
- *Author's Note:* I assume it's not better to use a TLS
CipherSuite because there is no KDF stage for deriving these
keys (they are a strict server-to-client advertisement), so the
Hash part would be unused? (https://www.iana.org/assignments/
tls-parameters/tls-parameters.xhtml#tls-parameters-4
(https://www.iana.org/assignments/tls-parameters/tls-
parameters.xhtml#tls-parameters-4))
A client MUST NOT use the channel ID included in the
MC_CHANNEL_ANNOUNCE frame as a connection ID for the unicast
connection. If it is already in use, the client should retire it as
soon as possible. As the server knows which connection IDs are in
use by the client, it MUST wait with the sending of a MC_CHANNEL_JOIN
frame until the channel ID associated with it has been retired by the
client.
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As the properties in MC_CHANNEL_ANNOUNCE frames are immutable during
the lifetime of a channel, a server SHOULD NOT send a
MC_CHANNEL_ANNOUNCE frame for the same channel more than once to each
client.
A server SHOULD send an MC_CHANNEL_ANNOUNCE frame for a channel
before sending a MC_CHANNEL_PROPERTIES or MC_CHANNEL_JOIN frame for
it.
11.2. MC_CHANNEL_PROPERTIES
An MC_CHANNEL_PROPERTIES frame (type=TBD-01) is sent from server to
client, either with the unicast connection or in an existing joined
multicast channel. The MC_CHANNEL_PROPERTIES frame consists of the
properties of a channel that are mutable and might change during the
course of its lifetime.
A server can send an update to a prior MC_CHANNEL_PROPERTIES frame
with a new sequence number increased by one.
It is RECOMMENDED that servers set an Until Packet Number and send
regular updates to the MC_CHANNEL_PROPERTIES before the packet
numbers in the channel exceed that value.
MC_CHANNEL_PROPERTIES frames are formatted as shown in Figure 3.
MC_CHANNEL_PROPERTIES Frame {
Type (i) = TBD-01 (experiments use 0xff3e801),
ID Length (8),
Channel ID (8..160),
Properties Sequence Number (i),
From Packet Number (i),
Until Packet Number (i),
AEAD Algorithm (16),
Key Length (i),
Key (..),
Integrity Hash Algorithm (16),
Max Rate (i),
Max Idle Time (i),
Max Streams (i),
ACK Bundle Size (i),
}
Figure 3: MC_CHANNEL_PROPERTIES Frame Format
MC_CHANNEL_PROPERTIES frames contain the following fields:
* ID Length: The length in bytes of the Channel ID field.
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* Channel ID: The channel ID for the channel associated with this
frame.
* Properties Sequence Number: Increases by 1 each time the
properties for the channel are changed by the server. The client
tracks the sequence number of the MC_CHANNEL_PROPERTIES frame that
set its current value, and only updates the value and the packet
number range on which it's applicable if the Properties Sequence
Number is higher.
* From Packet Number, Until Packet Number: The values in this
MC_CHANNEL_PROPERTIES frame apply only to packets starting at From
Packet Number and continuing for all packets up to and including
Until Packet Number. If Until Packet Number is omitted it
indicates the current property values for this channel have no
expiration at (equivalent to the maximum value for packet numbers,
or 2^62-1). If a packet number is received outside of any prior
(From,Until) range, it has no applicable channel properties and
MUST be dropped.
* AEAD Algorithm: A value from https://www.iana.org/assignments/
aead-parameters/aead-parameters.xhtml
(https://www.iana.org/assignments/aead-parameters/aead-
parameters.xhtml). The value MUST match a value provided in the
"AEAD Algorithms List" of the transport parameter (see Section 3).
* Key Length: Provides the length of the Key field. It MUST match a
valid key length for the AEAD Algorithm.
* Key: Used to protect the packet contents of 1-RTT packets for the
channel as described in [RFC9001], with length given by Key
Length. To maintain forward secrecy and prevent malicious clients
from decrypting packets long after they have left or were removed
from the unicast connection, servers SHOULD periodically send key
updates using only unicast.
* Integrity Hash Algorithm: The hash algorithm used in integrity
frames.
- *Author's Note:* Several candidate iana registries, not sure
which one to use? Some have only text for some possibly useful
values. For now we use the first of these:
o https://www.iana.org/assignments/named-information/named-
information.xhtml#hash-alg
(https://www.iana.org/assignments/named-information/named-
information.xhtml#hash-alg)
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o https://www.iana.org/assignments/tls-parameters/tls-
parameters.xhtml#tls-parameters-18
(https://www.iana.org/assignments/tls-parameters/tls-
parameters.xhtml#tls-parameters-18)
o (text-only): https://www.iana.org/assignments/hash-function-
text-names/hash-function-text-names.xhtml
(https://www.iana.org/assignments/hash-function-text-names/
hash-function-text-names.xhtml)
* Max Rate: The maximum rate in Kibps of the payload data for this
channel.Channel data MUST NOT exceed this rate over any 5s window,
if it does clients SHOULD leave the channel with reason Max Rate
Exceeded.
* Max Idle Time: The maximum expected idle time of the channel. If
this amount of time passes in a joined channel without data
received, clients SHOULD leave the channel with reason Max Idle
Time Exceeded.
* Max Streams: The maximum stream ID that might appear in the
channel. If a client joined to this channel can raise its Max
Streams limit up to or above this value it SHOULD do so, otherwise
it SHOULD leave or decline join for the channel with Max Streams
Exceeded.
* ACK Bundle Size:nThe minimum number of ACKs a client should send
in a single QUIC packet. If the max_ack_delay would force a
client to send a packet that only consists of MC_CHANNEL_ACK
frames, it SHOULD instead wait with sending until at least the
specified number of acknowledgements have been collected.
However, the Client MUST send any pending acknowledgements at
least once per Max Idle Time to prevent the Server from perceiving
the channel as interrupted.
From Packet Number and Until Packet Number are used to indicate the
packet number (Section 17.1 of [RFC9000]) the 1-RTT packets received)
over which these values are applicable.
A From Packet Number without an Until Packet Number has an
unspecified termination.
If new property values appear and are different from prior values,
the From Packet Number implicitly sets the Until Packet Number of the
prior property value equal to one below the new From Packet Number
for all the changed properties.
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The properties of a channel MAY change during its lifetime. As such,
a server SHOULD NOT send properties for channels except those the
client has joined or will be imminently asked to join.
11.3. MC_CHANNEL_JOIN
An MC_CHANNEL_JOIN frame (type TBD-02) is sent from server to client
and requests that a client join the given transport addresses and
ports and process packets with the given Channel ID according to the
corresponding MC_CHANNEL_PROPERTIES.
A client cannot join a multicast channel without first receiving a
MC_CHANNEL_ANNOUNCE and MC_CHANNEL_PROPERTIES frame which together
set all the values for a channel.
If a client receives a MC_CHANNEL_JOIN for a channel for which it has
not received both, it MUST respond with a MC_CLIENT_CHANNEL_STATE
with State "Declined Join" and reason "Missing Properties". The
server MAY send another MC_CHANNEL_JOIN after retransmitting the
MC_CHANNEL_PROPERTIES and receiving an acknowledgement indicating
receipt of the MC_CHANNEL_ANNOUNCE.
MC_CHANNEL_JOIN frames are formatted as shown in Figure 4.
MC_CHANNEL_JOIN Frame {
Type (i) = TBD-02 (experiments use 0xff3e802),
MC_CLIENT_LIMIT Sequence Number (i),
MC_CLIENT_CHANNEL_STATE Sequence Number (i),
MC_CHANNEL_PROPERTIES Sequence Number (i),
ID Length (8),
Channel ID (8..160)
}
Figure 4: MC_CHANNEL_JOIN Frame Format
The sequence numbers are the most recently processed sequence number
by the server from the respective frame type. They are present to
allow the client to distinguish between a broken server that has
performed an illegal action and an instruction that's based on
updates that are out of sync (either one or more missing updates to
MC_CHANNEL_PROPERTIES not yet received by the client or one or more
missing updates to MC_CLIENT_LIMITS or MC_CLIENT_CHANNEL_STATE not
yet received by the server).
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A client MAY perform the join if it has the sequence number of the
corresponding channel properties and the client's limits will not be
exceeded, even if the client sequence numbers are not up-to-date. If
the client does not join, it MUST send a MC_CLIENT_CHANNEL_STATE with
"Declined Join" and a reason.
11.4. MC_CHANNEL_LEAVE
An MC_CHANNEL_LEAVE frame (type=TBD-03) is sent from server to client
in either the unicast connection or a channel.
MC_CHANNEL_LEAVE frames are formatted as shown in Figure 5.
MC_CHANNEL_LEAVE Frame {
Type (i) = TBD-03 (experiments use 0xff3e803),
MC_CLIENT_CHANNEL_STATE Sequence Number (i),
ID Length (8),
Channel ID (8..160),
After Packet Number (i)
}
Figure 5: MC_CHANNEL_LEAVE Frame Format
If After Packet Number is nonzero, wait until receiving that packet
or a higher valued number before leaving.
11.5. MC_CHANNEL_INTEGRITY
MC_CHANNEL_INTEGRITY frames are sent from server to client and are
used to convey packet hashes for validating the integrity of packets
received over the multicast channel as described in Section 7.1.
MC_CHANNEL_INTEGRITY frames are formatted as shown in Figure 6.
MC_CHANNEL_INTEGRITY Frame {
Type (i) = TBD-04..TBD-05 (experiments use 0xff3e804/0xff3e805),
ID Length (8),
Channel ID (8..160),
Packet Number Start (i),
[Length (i)],
Packet Hashes (..)
}
Figure 6: MC_CHANNEL_INTEGRITY Frame Format
For type TBD-05, Length is present and is a count of packet hashes.
For TBD-04, Length is not present and the packet hashes extend to the
end of the packet.
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The first hash in the Packet Hashes list is a hash of a 1-RTT packet
with the Channel ID equal to the Channel ID in the
MC_CHANNEL_INTEGRITY frame and packet number equal to the Packet
Number Start field. Subsequent hashes refer to the packets for the
channel with packet numbers increasing by 1.
Packet hashes MUST have length with an integer multiple of the length
indicated by the Hash Algorithm from the Channel Properties.
See Section 7.1 for a description of the packet hash calculation.
11.6. MC_CHANNEL_STREAM_BOUNDARY_OFFSET
MC_CHANNEL_STREAM_BOUNDARY_OFFSET frames are formatted as shown in
Figure 7.
MC_CHANNEL_STREAM_BOUNDARY_OFFSET Frame {
Type (i) = TBD-06 (experiments use 0xff3e806),
ID Length (8),
Channel ID (8..160),
Stream ID (i),
Stream Offset (i)
}
Figure 7: MC_CHANNEL_STREAM_BOUNDARY_OFFSET Frame Format
Clients must discard data before Stream Offset, and should start
accepting stream data at Stream Offset as though it's a new stream
with offset 0.
A server must ensure that data beginning at the given stream offsets
could equivalently begin a new stream, and are safe for clients to
start processing in order to use this. (Well-suited for boundaries
of http server push objects, for example, which otherwise would need
to start a new stream per object in order to be usable by late
joiners.)
11.7. MC_CHANNEL_ACK
Client->Server on unicast connection.
(TODO: Is it possible to reuse the multiple packet number space
version of ACK_MP from Section 12.2 of
[I-D.draft-ietf-quic-multipath], defining channel id as the packet
number space? at 2022-04-12 they're identical.)
MC_CHANNEL_ACK frames are formatted as shown in Figure 8.
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MC_CHANNEL_ACK Frame {
Type (i) = TBD-07 (experiments use 0xff3e807),
ID Length (8),
Channel ID (8..160),
Largest Acknowledged (i),
ACK Delay (i),
ACK Range Count (i),
First ACK Range (i),
ACK Range (..) ...,
[ECN Counts (..)],
}
Figure 8: MC_CHANNEL_ACK Frame Format
11.8. MC_PATH_RESPONSE
MC_PATH_RESPONSE frames are sent from client to server in a unicast
connection in response to an PATH_CHALLENGE received in a channel.
Like PATH_RESPONSE but includes a channel id.
MC_PATH_RESPONSE frames are formatted as shown in Figure 9.
MC_PATH_RESPONSE Frame {
Type (i) = TBD-08 (experiments use 0xffe38008),
ID Length (8),
Channel ID (8..160),
Data (64)
}
Figure 9: MC_PATH_RESPONSE Frame Format
11.9. MC_CLIENT_LIMITS
MC_CLIENT_LIMITS frames are formatted as shown in Figure 10.
MC_CLIENT_LIMITS Frame {
Type (i) = TBD-09 (experiments use 0xff3e809),
Client Limits Sequence Number (i),
Capabilities Flags(i),
Max Aggregate Rate (i),
Max Channel IDs (i),
Max Joined Count (i),
}
Figure 10: MC_CLIENT_LIMITS Frame Format
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The sequence number is implicitly 0 before the first MC_CLIENT_LIMITS
frame from the client, and increases by 1 each new frame that's sent.
Newer frames override older ones.
Capabilities Flags is a bit field structured as follows:
* 0x1 is set if IPv4 channels are permitted
* 0x2 is set if IPv6 channels are permitted
For example, a Capabilities Flags value of 3 (0x11) indicates that
both IPv4 and IPv6 channels are permitted.
Max Aggregate Rate allowed across all joined channels is in Kibps.
Max Channel IDs is the count of channel IDs that can be reserved and
have properties. Retired Channel IDs don't count against this value.
Max Joined Count is the count of channels that are allowed to be
joined concurrently.
11.10. MC_CHANNEL_RETIRE
MC_CHANNEL_RETIRE frames are formatted as shown in Figure 11.
MC_CHANNEL_RETIRE Frame {
Type (i) = TBD-0a (experiments use 0xff3e80a),
ID Length (8),
Channel ID (8..160)
}
Figure 11: MC_CHANNEL_RETIRE Frame Format
Retires a channel by id. (We can't use RETIRE_CONNECTION_ID because
we don't have a coherent sequence number.)
11.11. MC_CLIENT_CHANNEL_STATE
MC_CLIENT_CHANNEL_STATE frames are formatted as shown in Figure 12.
MC_CLIENT_CHANNEL_STATE Frame {
Type (i) = TBD-0b (experiments use 0xff3e80b),
Client Channel State Sequence Number (i),
ID Length (8),
Channel ID (8..160),
State (i),
Reason (0..i)
}
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Figure 12: MC_CLIENT_CHANNEL_STATE Frame Format
State has these defined values:
* 0x1: Left
* 0x2: Declined Join
* 0x3: Joined
If State is Joined, the Reason field is absent.
If State is Left or Declined Join, the Reason field is set to one of:
* 0x0: Unspecified Other
* 0x1: Left as requested by server
* 0x2: Administrative Block
* 0x3: Protocol Error
* 0x4: Property Violation
* 0x5: Unsynchronized Properties
* 0x6: ID Collision
* 0x10: Held Down
* 0x11: Max Idle Time Exceeded
* 0x12: Max Rate Exceeded
* 0x13: High Loss
* 0x14: Spurious Traffic
* 0x1000000-0x3fffffff: Application-specific Reason
A client might receive multicast packets that it can not associate
with any channel ID. If these are addressed to an (S,G) that is used
for reception in one or more known channels, it MAY leave these
channels with reason "Spurious traffic".
(TODO: Or should we try to reuse PATH_ABANDON and/or PATH_STATUS? I
don't think they're sufficient, but maybe?): -
[I-D.draft-ietf-quic-multipath] -
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https://datatracker.ietf.org/doc/html/draft-liu-multipath-quic-
04#section-9.1 (https://datatracker.ietf.org/doc/html/draft-liu-
multipath-quic-04#section-9.1)
The things server needs to know for state changes _could_ maybe be
inferred from ack responses but explicit seems better, allowing for a
more proactive response under strain?
12. Frames Carried in Channel Packets
MC Channels will contain normal QUIC 1-rtt data packets (see
Section 17.3.1 of [RFC9000]) except using the Channel ID instead of a
Connection ID. The packets are protected with the keys from
MC_CHANNEL_PROPERTIES for the corresponding channel.
Data packet hashes will also be sent in MC_CHANNEL_INTEGRITY frames,
as keys cannot be trusted for integrity due to giving them to too
many receivers, as in [I-D.draft-krose-multicast-security].
The 1-rtt packets in multicast channels will have a restricted set of
frames. Since the channel is strictly 1-way server to client, the
general principle is that broadcastable shared server->client data
frames can be sent, but frames that make sense only for
individualized connections cannot.
Permitted:
* PADDING Frames ([RFC9000] Section 19.1)
* PING Frames ([RFC9000] Section 19.2)
* RESET_STREAM Frames ([RFC9000] Section 19.4)
* STREAM Frames ([RFC9000] Section 19.8)
* DATAGRAM Frames (both types) ([RFC9221] Section 4)
* PATH_CHALLENGE Frames ([RFC9000] Section 19.17)
* MC_CHANNEL_PROPERTIES
* MC_CHANNEL_LEAVE (however, join must come over unicast?)
* MC_CHANNEL_INTEGRITY (not for this channel, only for another)
* MC_STREAM_BOUNDARY_OFFSET
* MC_CHANNEL_RETIRE
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Not permitted:
* 19.3. ACK Frames
* 19.6. CRYPTO Frames (crypto handshake does not happen on mc
channels)
* 19.7. NEW_TOKEN Frames
* Flow control is different:
- 19.5. STOP_SENDING Frames
- 19.9. MAX_DATA Frames (flow control for mc channels is by
rate)
- 19.10. MAX_STREAM_DATA Frames
- 19.11. MAX_STREAMS Frames
- 19.12. DATA_BLOCKED Frames
- 19.13. STREAM_DATA_BLOCKED Frames
- 19.14. STREAMS_BLOCKED Frames
* Channel ID Migration can't use the "prior to" concept, not
0-starting
- 19.15. NEW_CONNECTION_ID Frames
- 19.16. RETIRE_CONNECTION_ID Frames
* 19.18. PATH_RESPONSE Frames
* 19.19. CONNECTION_CLOSE Frames
* 19.20. HANDSHAKE_DONE Frames
* MC_PATH_RESPONSE
* MC_CLIENT_LIMITS
* MC_CLIENT_CHANNEL_STATE
* MC_CHANNEL_ACK
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13. Error Codes
14. Security Considerations
Mostly incorporate [I-D.draft-krose-multicast-security]. Anything
else?
e.g. if a different legitimate quic connection says someone else's
quic multicast stream is theirs, that's maybe a problem worth
protecting against. Maybe we need a periodic asymmetric challenge?
I'm thinking send a public key on the multicast channel and in the
unicast channels send an individualized MAC signed with the private
key and verify it with the public key, so that in addition to
validating that the unicast server knows the contents of the
multicast packets via the hashes it supplies, the multicast stream
provides a way for the client to validate that the unicast stream is
authorized to use it for data transport via proof they know the
private key corresponding to the public key that arrived on the
multicast channel. (Note this doesn't prevent unauthorized receipt
of multicast data packts, but does prevent a quic server from lying
when claiming a multicast data channel belongs to it, preventing
legit receivers from consuming it.)
(alternatively, can the multicast channel just periodically say what
domain name is expected for the quic connection and get the same
crypto guarantee of a proper sender via the domain's cert, which was
already checked on the unicast channel?)
15. IANA Considerations
TODO: lots
16. References
16.1. Normative References
[I-D.draft-ietf-quic-multipath]
Liu, Y., Ma, Y., Coninck, Q. D., Bonaventure, O., Huitema,
C., and M. Kuehlewind, "Multipath Extension for QUIC",
Work in Progress, Internet-Draft, draft-ietf-quic-
multipath-00, 2 February 2022,
<https://www.ietf.org/archive/id/draft-ietf-quic-
multipath-00.txt>.
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[I-D.draft-krose-multicast-security]
Rose, K. and J. Holland, "Security and Privacy
Considerations for Multicast Transports", Work in
Progress, Internet-Draft, draft-krose-multicast-security-
02, 31 January 2022, <https://www.ietf.org/archive/id/
draft-krose-multicast-security-02.txt>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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/info/rfc9000>.
[RFC9001] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/info/rfc9001>.
[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/info/rfc9221>.
16.2. Informative References
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<https://www.rfc-editor.org/info/rfc4607>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Jake Holland
Akamai Technologies, Inc.
Email: jakeholland.net@gmail.com
Lucas Pardue
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Email: lucaspardue.24.7@gmail.com
Max Franke
TU Berlin
Email: mfranke@inet.tu-berlin.de
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