Re: [MMUSIC] Empty candidate lists in ice-sip-sdp offers and answers

Christer Holmberg <> Sat, 27 April 2019 18:02 UTC

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From: Christer Holmberg <>
To: Roman Shpount <>, mmusic WG <>
Thread-Topic: Empty candidate lists in ice-sip-sdp offers and answers
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Date: Sat, 27 Apr 2019 18:02:13 +0000
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Subject: Re: [MMUSIC] Empty candidate lists in ice-sip-sdp offers and answers
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>NOTE: Since it is possible that no candidates were provided in the offer,  or that all candidates in the offer 
>where skipped due to unsupported address type or FQDN name resolution failure, ICE nomination process 
>can start with no remote candidates. This,  however, does not indicate an immediate ICE nomination failure. 
>See <<draft-holmberg-ice-pac>> for more details.
>In the Receiving the Initial Answer section I have added the following: 
>NOTE: Since it is possible that no candidates were provided in the answer, or that all candidates in the answer 
>where skipped due to unsupported address type or FQDN name resolution failure, ICE nomination process can 
>start with no remote candidates. This,  however, does not indicate an immediate ICE nomination failure. 
>See <<draft-holmberg-ice-pac>> for more details. 

I think the text is confusing, because it starts talking about the ICE nomination process. There are other things that happen before, including the creation of candidate pairs.

So, I think the text should say that the agent will not be able to create candidate pairs, and it will not be able to start sending connectivity checks. Instead it will wait for the peer agent to start sending connectivity checks, that the agent will then process as peer reflexive candidates.

>I wanted to get the group's opinion regarding:
>1. Allowing offers and answers with no candidates

I am ok with the principle. There seem to be use-cases for it, so...

>2. Adding a reference to draft-holmberg-ice-pac regarding how such session descriptions or session descriptions where all candidates were rejected are handled.

The reference in the text above is misleading, because to me it sounds like PAC describes how to process offers/answers without candidates. PAC is only about a timer.