Re: [MMUSIC] BUNDLE: SDP Offer Types

Christer Holmberg <christer.holmberg@ericsson.com> Wed, 05 June 2013 06:03 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
To: Paul Kyzivat <pkyzivat@alum.mit.edu>
Thread-Topic: [MMUSIC] BUNDLE: SDP Offer Types
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Date: Wed, 5 Jun 2013 06:02:53 +0000
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Subject: Re: [MMUSIC] BUNDLE: SDP Offer Types
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Hi,

>>>>>> I'll throw the ball out with suggesting the following ones:
>>>>>>
>>>>>> -*Bundle restart offer* (different port value, currently referred 
>>>>>> to as "first offer")
>>>>>>
>>>>>> The reason I use "restart" wording is because this is used, no 
>>>>>> matter whether in the beginning of the session or mid-session, to 
>>>>>> (re-)negotiate the usage of BUNDLE, and the bundle address 
>>>>>> information selection.
>>>>>>
>>>>>> -*Bundle sync offer* (identical port value, currently referred to 
>>>>>> as "second offer")
>>>>>>
>>>>>> The reason I used "sync" wording is because this is used to ensure 
>>>>>> that intermediaries have correct address information for each m- line.
>>>>>>
>>>>>> Keep in mind that we may even need to split the sync offer into 
>>>>>> more sub types, when we get into the details of adding new m- 
>>>>>> lines etc, but I'd like to agree a base to start from :)
>>>>>
>>>>> Above seems like a good start, but I'm still grappling with some 
>>>>> things and don't know how to talk about concisely:
>>>>>
>>>>> I understand that the next offer after a Bundle Restart Offer will 
>>>>> typically be a Bundle Sync Offer. But if there is another offer 
>>>>> after a Bundle Sync Offer, and it doesn't change anything about the 
>>>>> bundle, then is it still a Bundle Sync Offer?
>>>>
>>>> Currently, yes.
>>>
>>> I agree that without adjusting the terminology this is the only right choice to make. But it is a little obscure. I'm not certain this needs to be improved, but I thought I would suggest that it might.
>>>>
>>>>> Also, I don't believe the above are mutually exclusive. If I send 
>>>>> an offer to add a new m-line to a bundle, and I give it distinct 
>>>>> address info so that the answerer may take it out of the bundle if 
>>>>> needed, then is that a Bundle Restart Offer or a Bundle Sync Offer? 
>>>>> It seems to be a bit of each. And of course there may be multiple 
>>>>> bundles described by the SDP, and these terms apply independently to each.
>>>>>
>>>>> Maybe we need a couple more terms for:
>>>>>
>>>>> - offer that adds a new m-line to bundle using the existing bundle
>>>>>     address info.
>>>>
>>>> Technically that is a Bundle Sync Offer, but I DO agree that the wording is not good in this case - as it's not only about synchronization.
>>>>
>>>>> - offer that adds a new m-line to an existing bundle using unique
>>>>>     address info.
>>>>
>>>> I agree that doesn't fit the current definitions.
>>>>
>>>> However, we will have to agree on whether we allow that in the first place, or whether the offerer will have to use 1) same address information or 2) different address information for ALL m- lines (Bundle Restart Offer).
>>>
>>> Yes, we need to settle on whether either or both of these are permitted.
>>>
>>> But I can think of reasons why I might wish to use either one, and no good reason not to allow both. So allowing both is my preference.
>>
>> I personally think we should allow BOTH 1) and 2).
>>
>> The question is whether we should allow 3), which is new m- line with unique address, while the other m- lines use the bundle address.
>
> I agree it is a valid question to ask.
> Again, I can see how it might be useful sometimes, and I can see no reason not to allow it. Its just a special case of the bundle restart offer.

We could modify the definition of bundle restart offer, to allow that some m- lines may use the same address information.

It needs to be very clear, though, that such m- lines cannot be moved out of the BUNDLE group by the Answerer, as they don't have a unique address to fallback to.

However, the Answerer MAY still change the address for such m- lines to the address of the added m- line - especially if the Offerer puts the mid value associated with the new m- line first in the SDP group:BUNDLE attribute mid value list.

> (Note, IMO it should be ok for the very first offer to propose a bundle with address info already shared among m-lines in the proposed bundle. 
> Using that trades off potential interop issues for speed in establishing the session.)

My intention (and, that's why I appreciate all feedback I can get :) is to make the procedures very generic, and not separate between initial and subsequent offers (other than in examples).

Regards,

Christer