Re: MSRP chat: 'chatroom' attribute ABNF

On Dec 15, 2011, at 8:08 AM, Miguel A. Garcia wrote:

> I was doing some editorial fixes to the MSRP chat document, and then I went to validate the ABNF of the 'chatroom' attribute in SDP and the "Use-Nickname" header in MSRP.
> 
> When doing this, I noticed an open area, for which I would like to get input from the working group.
> 
> The current ABNF of the chatroom attribute is:
> 
>          attribute        /= chatroom-attr
>          chatroom-attr     = chatroom-label ":" chat-token
>                              *(SP chat-token)
> 
> The problem is that the syntax above always require a chat-token. So, it is not possible to write an SDP line without tokens:
> 
>        a=chatroom
> 
> However, the text has text that may lead to this case, for example:
> 
>   A conference focus that includes the 'nicknames' token in the session
>   description is signaling that the MSRP switch supports and the chat
>   room allows to use the procedures specified in Section 7.  A
>   conference focus that includes the 'private-messages' in the SDP
>   description is signaling that the MSRP switch supports and the chat
>   room allows to use the procedures specified in Section 6.2.
> 
> So, one can derive that if a conference focus does not have support for nicknames nor for private messages, it should write an empty attribute: a=chatroom
> 
> The standalone a=chatroom signals that the MSRP switch understand this draft, in particular the convention to use Message/CPIM wrappers for sending regular messages.
> 
> So, I suggest to modify the ABNF to support a standalone attribute in the following way:
> 
>           attribute         =/ chatroom-attr
>           chatroom-attr     = chatroom-label [":" chat-token
>                               *(SP chat-token)]
> 
> This accommodates both standalone and non-standalone attributes, such as:
> 
> a=chatroom
> a=chatroom:private-messages
> a=chatroom:nickname private-messages
> 
> I also suggest to add a couple of paragraphs indicating that it is fine to include a standalone 'chatroom' attribute:
> 
>   An example of a 'chatroom' attribute for an MSRP media stream where
>   the endpoint, e..g, an MSRP switch, does not allow neither nicknames
>   nor private messages.
> 
>             a=chatroom
> 
>   The 'chatroom' attribute
>   without further modifiers (e.g., tokens) indicates that the endpoint
>   supports the procedures described in this document for transferring
>   MSRP messages to/from a multi-party conference.
> 
> 
> Does anyone have concerns with the above proposal?
> 

Not at all. Sounds correct.


Regards,

-- 
Saúl Ibarra Corretgé
AG Projects