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moq-lite-04: explicit hop IDs and exclude hop filter #21

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moq-lite-04: explicit hop IDs and exclude hop filter
kixelated Mar 31, 2026
7716cf1
moq-lite-04: clarify hop tracking semantics and fix editorial issues
kixelated Mar 31, 2026
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34 changes: 25 additions & 9 deletions draft-lcurley-moq-lite.md
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Original file line number Diff line number Diff line change
Expand Up @@ -64,8 +64,8 @@ moq-lite consists of:

- **Session**: An established QUIC connection between a client and server.
- **Broadcast**: A collection of Tracks from a single publisher.
- **Track**: An series of Groups, each of which can be delivered and decoded *out-of-order*.
- **Group**: An series of Frames, each of which must be delivered and decoded *in-order*.
- **Track**: A series of Groups, each of which can be delivered and decoded *out-of-order*.
- **Group**: A series of Frames, each of which must be delivered and decoded *in-order*.
- **Frame**: A sized payload of bytes within a Group.

The application determines how to split data into broadcast, tracks, groups, and frames.
Expand Down Expand Up @@ -132,7 +132,7 @@ The contents are opaque to the moq-lite layer.

# Flow
This section outlines the flow of messages within a moq-lite session.
See the section for Messages section for the specific encoding.
See the Messages section for the specific encoding.

## Connection
moq-lite runs on top of WebTransport.
Expand Down Expand Up @@ -306,7 +306,7 @@ Group age is computed relative to the latest group by sequence number.
A group is never expired until at least the next group (by sequence number) has been received or queued.
Once a newer group exists, a group is considered expired if the time between its arrival and the latest group's arrival exceeds `Max Latency`.
The arrival time is when the first byte of a group is received (subscriber) or queued (publisher).
An expired group SHOULD BE reset at the QUIC level to avoid consuming flow control.
An expired group SHOULD be reset at the QUIC level to avoid consuming flow control.

## Unidirectional Streams
Unidirectional streams are used for data transmission.
Expand Down Expand Up @@ -361,12 +361,17 @@ A subscriber sends an ANNOUNCE_PLEASE message to indicate it wants to receive an
ANNOUNCE_PLEASE Message {
Message Length (i)
Broadcast Path Prefix (s),
Exclude Hop (i),
}
~~~

**Broadcast Path Prefix**:
Indicate interest for any broadcasts with a path that starts with this prefix.

**Exclude Hop**:
If non-zero, the publisher SHOULD skip ANNOUNCE messages for broadcasts whose Hop ID entries contain this value.
This is used by relays to avoid routing loops in a cluster.

The publisher MUST respond with ANNOUNCE messages for any matching and active broadcasts, followed by ANNOUNCE messages for any future updates.
Implementations SHOULD consider reasonable limits on the number of matching broadcasts to prevent resource exhaustion.

Expand All @@ -384,7 +389,8 @@ ANNOUNCE Message {
Message Length (i)
Announce Status (i),
Broadcast Path Suffix (s),
Hops (i),
Hop Count (i),
Hop ID (i) ...,
}
~~~

Expand All @@ -397,10 +403,16 @@ A flag indicating the announce status.
**Broadcast Path Suffix**:
This is combined with the broadcast path prefix to form the full broadcast path.

**Hops**:
The number of hops from the origin publisher.
This is used as a tiebreaker when there are multiple paths to the same broadcast.
A relay SHOULD increment this value when forwarding an announcement.
**Hop Count**:
The number of Hop ID entries that follow.
A value of 0 means no Hop ID entries are present, indicating a fully unknown path (e.g. the announcement originated locally or was received from a peer that does not support hop tracking).
A receiver MUST close the stream with a PROTOCOL_VIOLATION if the Hop Count does not match the number of subsequent Hop ID entries.

**Hop ID**:
A unique identifier for each relay in the path from the origin publisher.
Each relay MUST append its own Hop ID and increment the Hop Count when forwarding an announcement, even if no prior Hop ID entries are present (e.g. when receiving from an older protocol version).
The Hop Count is used as a tiebreaker when there are multiple paths to the same broadcast.
A Hop ID value of 0 indicates an unknown or bridged relay hop (e.g. when bridging from an older protocol version that does not assign Hop IDs); the Hop Count still reflects the total number of entries including unknown hops.


## SUBSCRIBE
Expand Down Expand Up @@ -608,6 +620,10 @@ A generic library or relay MUST NOT inspect or modify the contents unless otherw

# Appendix A: Changelog

## moq-lite-04
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⚠️ Potential issue | 🟡 Minor

Fix heading style at Line 623 to satisfy markdownlint MD003.

## moq-lite-04 is ATX style, but the configured rule expects setext style. Please convert this heading to setext (or align rule config if ATX is intended globally).

🧰 Tools
🪛 markdownlint-cli2 (0.22.0)

[warning] 623-623: Heading style
Expected: setext; Actual: atx

(MD003, heading-style)

🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@draft-lcurley-moq-lite.md` at line 623, The heading "moq-lite-04" currently
uses ATX style ("## moq-lite-04") which violates markdownlint MD003; replace the
ATX line with a setext-style heading by removing the leading "##" and adding a
setext underline on the following line (for an H2 use a line of three or more
hyphens, e.g. place "moq-lite-04" on one line and "---" on the next). Ensure no
extra trailing spaces so the new setext heading (moq-lite-04 + ---) replaces the
original ATX heading.

- ANNOUNCE `Hops` count replaced with explicit `Hop ID` list for loop detection.
- Added `Exclude Hop` to ANNOUNCE_PLEASE for relay loop avoidance.

## moq-lite-03
- Version negotiated via ALPN (`moq-lite-xx`) instead of SETUP messages.
- Removed Session, SessionCompat streams and SESSION_CLIENT/SESSION_SERVER/SESSION_UPDATE messages.
Expand Down
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