Re: [MMUSIC] Thoughts on draft-ietf-mmusic-dtls-sdp-10 semantics

[Justin Uberti <[e-mail]>]

Keep in mind that this id value isn't actually sent anywhere. So it's not
like the ICE ufrag that needs a certain amount of entropy. It can just as
easily be a monotonically increasing number.

IOW, a string with a 1-byte minimum seems right.

On Mon, Mar 7, 2016 at 10:26 AM, Roman Shpount <[e-mail]> wrote:

>
> On Mon, Mar 7, 2016 at 12:21 PM, Paul Kyzivat <[e-mail]>
> wrote:
>
>> On 3/7/16 12:12 PM, Roman Shpount wrote:
>>
>>> On Mon, Mar 7, 2016 at 11:52 AM, Paul Kyzivat <[e-mail]
>>> <mailto:[e-mail]>> wrote:
>>>
>>>     On 3/7/16 11:26 AM, Christer Holmberg wrote:
>>>
>>>         I suggest dtls-association-id. In my opinion there is no longer
>>>         the same
>>>         need to be aligned with the name of the connection attribute.
>>>
>>>
>>>     This seems plausible. But I want to reserve judgement until the
>>>     detailed semantics of the attribute are worked out:
>>>
>>> I wanted to model this attribute on ICE ufrag
>>>
>>>     - is it numeric, or a token?
>>>
>>>
>>> I was thinking something like this:
>>> dtls-association-id-attr = "dtls-association-id" ":" dtls-association-id
>>>
>>> dtls-association-id = 4*256dtls-association-id-char
>>>
>>> dtls-association-id-char = ALPHA / DIGIT / "+" / "/"
>>>
>>
>> Why this in particular? Is it your intent to reuse values that were
>> generated for another purpose? Or to reuse code that is also used for
>> another purpose?
>
>
> This is reusing the definition (and generation code) from ice-ufrag
> attribute (https://tools.ietf.org/html/rfc5245#section-15.4).
>
>     - any rules for how the value chosen?
>>>
>>>
>>> The dtls-association-id attributes MUST be chosen randomly when new DTLS
>>> association is requested.  The dtls-association-id attribute MUST
>>> contain at least 24 bits of randomness.  This means that
>>> the dtls-association-id  attribute will be at least 4 characters
>>> long since the grammar for this attribute allows for 6 bits of
>>> randomness per character.  The attribute MAY be longer than 4
>>> characters, respectively, of course, up to 256 characters.  The upper
>>> limit allows for buffer sizing in implementations.  Its large upper
>>> limit allows for increased amounts of randomness to be added over time.
>>>
>>
>> What is the reason for using random values, rather than some well defined
>> sequence of values? (Where the sequence might start with a random value, or
>> perhaps every sequence would start with 0.)
>>
>
> We are dealing with multiple end points which can be reconnected in more
> or less random order. Each end point needs to detect when it is talking to
> a new end point or to a new DTLS association. This is why I picked a random
> value. Once again, if this works for ICE, should work for DTLS just as well.
>
> Let me know if you have a better idea for ID generation.
>
> Regards,
> _____________
> Roman Shpount
>
>