Re: [MMUSIC] JSEP Issue #394: What appears in m= lines.

Eric Rescorla <ekr@rtfm.com> Mon, 16 January 2017 13:18 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Mon, 16 Jan 2017 05:17:52 -0800
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To: Magnus Westerlund <magnus.westerlund@ericsson.com>
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Subject: Re: [MMUSIC] JSEP Issue #394: What appears in m= lines.
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On Tue, Jan 10, 2017 at 7:44 AM, Magnus Westerlund <
magnus.westerlund@ericsson.com> wrote:

> Den 2017-01-02 kl. 14:42, skrev Harald Alvestrand:
>
>> Den 22. des. 2016 18:30, skrev Eric Rescorla:
>>
>>>      __
>>>
>>>     Okay, I agree that having any rules for what you should offer here
>>>     based on what the actual outcome is not the best idea here. I think
>>>     the rules should be based on capability and intent. So if you only
>>>     are going offer TCP candidates, then you clearly should use TCP/…,
>>>
>>>
>>> I'm going to push on this. If we've already agreed that mismatches are
>>> normal, why should we do that? Wouldn't it be better to just effectively
>>> deprecate this field?
>>>
>>>
>> Concur with EKR.
>>
>> This field (the TCP/UDP part of the protocol field) was defined in a way
>> that makes its original purpose (to negotiate profiles) not only
>> impossible while using ICE, but actively harmful, because you end up
>> telling lies in very many cases, so people will have to accept things
>> that don't match reality.
>>
>> Make the world as simple for implementors as possible: Send a fixed
>> string, and accept all strings.
>>
>>
> Okay, can we please be precise with what is suggested here. Because what
> you write above, and what EKR proposed is not really the same thing. The
> issue proposed that it was fine to set either of the strings. You saying a
> fixed string. I want to ask you which UDP/... or TCP/..., or even
> ICE/DTLS/RTP/SAVPF?
>
> From a strict clarity issue using ICE/... would be my preferred. But, that
> is probably going to throw some implementations, especially gateways. It
> will also require us to actually go write the registration to explain what
> it is.
>
> Using UDP is likely the most compatible and will only fail in gateway
> cases where there are no UDP candidates and the gateway fail to pick that
> up.
>
> Using TCP when there are no TCP candidates are equally misleading to
> gateway cases.
>
> The above is why I proposed that implementation capabilities and any
> configuration to limit what functions being used would be an appropriate
> choice.
>
> I hope at least we can agree that an JSEP Answer MUST use the PROTO string
> of the OFFER?


Yes. I think implementations should offer UDP/ (ICE/ will cause problems)
and in the answer echo the offer.

-Ekr


>
>
> Cheers
>
> Magnus Westerlund
>
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