Subject: Re: Regarding SDP Media level description

From: Arjun RC <[email-masked]>
Date: Wed, 14 Apr 1999 15:28:50 +0530 (IST)

Hi Kartick,
According to the SDP specification and the grammar specified, the
m= field is mandatory within any media-level description. 
What that means is that for each SDP message, 

v,o,s are mandatory and if you specify a media description field, 
m is mandatory.

Now according to the grammar (App. A),

media-descriptions =  *( media-field
                         information-field
                         *(connection-field)
                         bandwidth-fields
                         key-field
                         attribute-fields )

which means it can be empty too as you suggested. However, I am yet to see
an example/ think of a case in which I send a SDP packet without
specifying m= field.

Could anyone give inputs on when such a case might happen ?

Thx
Cheers
ARC

On Wed, 14 Apr -1, Kartick wrote:

Kartic> hi! I have a doubt regarding Media Level description The
Kartic> RFC 2327 states that
Kartic>    "An announcement consists of a session-level section
Kartic>  followed by zero

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From: Arjun RC <[email-masked]>
Date: Thu, 15 Apr 1999 12:14:56 +0530 (IST)

Hi Kartick,
the m field is mandatory only if you are specifying the media level
description. However, if you look at the whole grammar in the appendix,
you will see that you could leave out the entire media level description
(which starts with m= line).

In short, m is a mandatory field if you want to specify a media
description. However, you dont have to necessarily specify a media
description. i.e m is stated as optional as its container (media level
description) is optional.

Hope this clarifies the siuation.
Cheers
ARC

On Thu, 15 Apr -1, Kartick wrote:

K> Some lines in each description are required and some
K>    are optional but all must appear in exactly the order given here (the
K>    fixed order greatly enhances error detection and allows for a simple
K>    parser). Optional items are marked with a `*'.
K> Media description
K> m= (media name and transport address)
K> i=* (media title)
K> c=* (connection information - optional if
K> here "m" does not have a star before it hence it
K> is mandatory or that is what I feel
K> 
K> regards
K> kartick

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