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Re: [rtcweb] DTLS, DTLS-SRTP, and 5-tuples

Iñaki Baz Castillo <ibc@aliax.net> Thu, 05 March 2015 13:44 UTC

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From: Iñaki Baz Castillo <ibc@aliax.net>
Date: Thu, 05 Mar 2015 14:44:18 +0100
Message-ID: <CALiegfncHuqiUbCjWi4BN=OG--=nri5-AEUtNFNspwUApcRHNg@mail.gmail.com>
To: "Makaraju, Maridi Raju (Raju)" <Raju.Makaraju@alcatel-lucent.com>
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Subject: Re: [rtcweb] DTLS, DTLS-SRTP, and 5-tuples
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2015-03-05 14:26 GMT+01:00 Makaraju, Maridi Raju (Raju)
<Raju.Makaraju@alcatel-lucent.com>:
>>
>> - A sends USE-CANDIDATE requests in parallel.
>> - A receives the ok response from one of them.
>> - A sends DTLS ClientHello.
>
> <Raju>
> This is not allowed by http://tools.ietf.org/html/rfc5245#section-8.1.1.2 , unless webrtc overrides it.
> A can only send DTLS once final nomination, which happens after all valid pairs are found, is done.
> </Raju>


   However, because the agent included the USE-CANDIDATE
   attribute in all of its checks, another check may yet
   complete, causing another valid pair to have its nominated flag set.
   ICE always selects the highest-priority nominated candidate pair from
   the valid list as the one used for media.  Consequently, the selected
   pair may actually change briefly as ICE checks complete, resulting in
   a set of transient selections until it stabilizes.


Also consider the case in which the ICE-CONTROLLING agent is not the
DTLS client. This is:

- A sends USE-CANDIDATE requests in parallel.
- B replies OK to the first one.
- B decides that it is the selected-pair (common in ICE-Lite servers).
- B sends DTLS ClientHello.
- A replies DTLS ServerHello etc.
- A continues sending USE-CANDIDATE requests.
- After a while another pair may be selected but "media" already started.


-- 
Iñaki Baz Castillo
<ibc@aliax.net>

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