Re: [MMUSIC] WGLC for draft-ietf-mmusic-udptl-dtls-06

[Paul Kyzivat <[e-mail]>]

I've had my say on this. I'll be satisfied with whatever you decide to 
do about it, including nothing.

	Thanks,
	Paul

On 3/28/14 2:25 PM, Christer Holmberg wrote:
>
> Hi,
>
>>>>> If a new DTLS association is to be established, is it well defined when
>>>>> to cut over to it? ISTM that some procedures are required here to ensure
>>>>> that data isn't lost, or replicated.
>>>>
>>>> I don't think we can define any exact procedures for that. DTLS-SRTP doesn't define any exact procedures either. RFC 5763 only says:
>>>>
>>>>    "Once the new session keys are established, the session can switch to using these and abandon the old keys."
>>>>
>>>> ...and I don't think we can say much more.
>>>>
>>>> In addition, I assume there are procedures on the fax application layer for avoiding lost data.
>>>>
>>>> Also, I think it will be rare that the keys and/or transport parameters change during a fax transmission. Or, if they do, perhaps a fax transmission failure is acceptable?
>>>
>>> Data loss prevention/recovery mechanisms are in place at the fax layer.
>>
>> The case I'm talking about is: A new O/A results in establishing a new
>> connection, replacing a prior one. At some point during that process
>> both the old and new connections are usable. Then, at some point the
>> sender stops sending to the old connection and starts sending to the new
>> one.
>
> Yes.
>
>> For the receiver to get all the data, it must keep reading from the old
>> one until it has received the last packet sent there, and must start
>> reading on the new connection soon enough to get the first data sent
>> there. And there is a possibility that the packets won't arrive in the
>> order sent, so ceasing to read from the new one once something has been
>> received from the old one could cause something to be lost. (Or course
>> these aren't reliable protocols, so something could be lost in the
>> network too.)
>>
>> Are you saying that the fax layer is sufficient to deal with this? (I
>> haven't looked at it.)
>
> Yes.
>
> I don't think the receiver should cease to read from the new one if it receives something from the old one.
>
> If it helps, we could add a sentence saying that the receiver needs to be prepared to receive data on both the new and old connections, as long as they are both alive.
>
>> I realize that this problem isn't unique here - it applies any time O/A
>> results in a change to the media path. I've wondered about it for a long
>> time, but have assumed it has typically been considered acceptable to
>> get a "glitch" in an audio or video stream in such a case. But it is
>> less acceptable for fax.
>
> It is not even introduced by this draft, as FoIP using SDP O/A has been around for many years.
>
> Regards,
>
> Christer
>
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