Intent to Experiment: Reverse Origin Trial for WebRTC's Plan B SDP semantics

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Henrik Boström

Feb 18, 2021, 5:05:38 AMFeb 18
to blink-dev
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WebRTC is a W3C Recommendation and multiple IETF standards:

The Session Description Protocol (SDP) used by WebRTC currently has two implementations:
  • "Unified Plan", the spec-compliant SDP format implemented by all browsers.
  • "Plan B", the non-standard SDP format that does not have a spec, is deprecated but not yet removed and is only implemented in Chromium-based browsers. JavaScript applications have access to it by using a non-standard API.
We want to remove the non-standard SDP format, "Plan B", from Chromium. Removal dates have already been announced, but in order to aid applications from migrating from Plan B to Unified Plan and to ensure we can keep the deadlines we have set, a Reverse Origin Trial is desired to give applications that opt-in more time to migrate.

Deadlines and rationale for Reverse Origin Trial were provided in the intent to deprecate. The target dates are:
  • M89 (Stable in February, 2021): Deprecation warning is added in the developer console.

  • M93 (Stable in August, 2021): Plan B is removed, with the option to extend this deadline by opting-in to a Reverse Origin Trial.

  • M96 (Stable in January, 2022): The extended deadline ends and Plan B is removed for everybody.

I would like to make the Reverse Origin Trial available as of M90 or M91 (when this CL lands).

Goals for experimentation
Unblock Plan B removal.

Experiment timeline

Any risk when the experiment finishes?
If Plan B is removed while still in use, some applications would experience incompatibility issues when attempting to set up audio or video channels, especially in multi-participant conferencing setups. 1:1 calling will still work for some applications.

Ongoing technical constraints
N/A. There were some Unified Plan bugs and performance issues discovered that have been addressed in M90.

When using Plan B you will get a deprecation warning in the JS console. It will look different depending on if you have opted in to the Reverse Origin Trial.

Will this feature be supported on all five Blink platforms supported by Origin Trials (Windows, Mac, Linux, Chrome OS, and Android)?

Link to entry on the feature dashboard
N/A, Unified Plan was shipped several years ago. Should I create an entry even for the Reverse Origin Trial?

Philip Jägenstedt

Feb 18, 2021, 5:13:24 AMFeb 18
to Henrik Boström, blink-dev
LGTM per the plan in the Intent to Deprecate.

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Joe Medley

Mar 2, 2021, 9:41:02 AMMar 2
to Henrik Boström, blink-dev
"Should I create an entry even for the Reverse Origin Trial?"

Yes, you should.
Joe Medley | Technical Writer, Chrome DevRel | | 816-678-7195
If an API's not documented it doesn't exist.

Joe Medley

Mar 2, 2021, 9:45:06 AMMar 2
to Henrik Boström, blink-dev
To be clear, Chrome Status isn't extra. It's a tool for creating intents and it tries to help you get everything needed for that. The option for Feature deprecation contains a stage for a reverse origin trial.


Joe Medley | Technical Writer, Chrome DevRel | | 816-678-7195
If an API's not documented it doesn't exist.

Henrik Boström

Mar 5, 2021, 10:41:12 AMMar 5
to blink-dev, Joe Medley, blink-dev, Henrik Boström

Joe Medley

Mar 5, 2021, 12:48:03 PMMar 5
to Henrik Boström, blink-dev, Henrik Boström
Thank you!

Joe Medley | Technical Writer, Chrome DevRel | | 816-678-7195
If an API's not documented it doesn't exist.

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