SDP descriptors for ALC

Hi All,

I was reading the new version of the "SDP Descriptors for FLUTE" I-D and
figured out that there is no counterpart for this specification to
describe ALC sessions. 
As most of the parameters and descriptors should be identical for ALC
and FLUTE transport protocols, my proposal is to create a separate
section in the proposed I-D to describe SDP descriptors for ALC.

I included below a proposal on how to modify the new version of the I-D
to fulfill this purpose.
Any comments or alternative proposals? 

Best Regards,
Imed Bouazizi

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Abstract

   This document specifies the use of SDP to describe the parameters
   required to begin, join, receive data from, and/or end FLUTE
   sessions.  It also provides a Composite Session SDP media grouping
   semantic for grouping media streams into protocol-specific sessions,
   such as multiple-channel FLUTE sessions. General SDP for ALC session 
   is also specified, mostly by reusing FLUTE descriptors.

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1.  Introduction

<3rd paragraph, 3rd sentence is new>

   This document defines a new protocol identifier for File Delivery
   over Unidirectional Transport (FLUTE) protocol [1] and other required
   SDP attributes for initiating a FLUTE session.  The formal ABNF
   syntax [5] is used for the attributes.  A protocol identifier and 
   other SDP attributes are also provided for general underspecified 
   ALC-based sessions, reusing the majority of syntax specified for 
   FLUTE session descriptions. This SDP syntax is
   independent of Any Source Multicast (ASM) or Source Specific
   Multicast (SSM) is used to route the media.

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<new section>

5.  ALC Descriptors

   The ALC specification [XX] describes the underspecified ALC transport

protocol on which FLUTE is based. Many session characteristics of ALC
are 
the same as FLUTE, as both originate from LCT session semantics [XX].
Hence, 
to aid the session description of a fully-specified ALC-based transport 
protocol, and ensure the minimum of difference in SDP descriptors for
similar 
parameters, the following rules apply to ALC-based transport protocols
other 
than FLUTE.

The descriptors for these parameters for ALC sessions SHALL be identical
to 
those for FLUTE sessions, as specified in section 3:
   o  Source IP Address
   o  Session Timing Parameters
   o  FEC Object Transmission Information
   o  Content Description Pointer
   o  Bandwidth Specification
   o  Composite Session Semantics

The descriptors for these ALC parameters differs from those of FLUTE and
are 
according to the specification of the following subsections:
   o  Number of channels
   o  Transport Session Identifier
   o  Protocol Id

5.1.  ALC Protocol Identifier

   A new value for the "proto" sub-field for ALC media is defined:
ALC/UDP.  The
   ALC/UDP protocol identifier specifies that the session being
   described will use the underspecified ALC [XX] protocol on top of a
UDP connection.

   The remainder of ALC session media line syntax is the same as for
FLUTE 
(section >>3.1<<), with respect to: the fmt (format) list and the use of
a "*" 
character; and, describing more than one ALC session may be described by
a single 
SDP using the Composite Session mechanism.

5.2.  Transport Session Identifier

   The TSI MUST be described by the "alc-tsi" attribute. Otherwise, ALC
Transport 
Session Identifier syntax for ALC SHALL be the same as for FLUTE as
specified in 
section >>3.4<<.

   The syntax for the attribute in ABNF is given below:

      alc-tsi-line = "a=alc-tsi:" tsi CRLF

5.3.  Channelisation Descriptors

   Destination IP address and port number for ALC channels shall be
according to 
the same specification as FLUTE (section >>3.6<<) with the one exception
that the 
number of channels MAY be signalled using an "alc-ch" attribute that
behaves exactly 
like the "flute-ch" attribute (section >>3.6.1<<).

   The syntax for the attribute in ABNF is given below:

      alc-channel-line = "a=alc-ch:" ch CRLF

5.4.  Fully-specified ALC-based Protocols other than FLUTE

Specification of fully-specified ALC-based protocols is beyond the scope
of this 
document, as is the specification of descriptors specific to such
protocols, other 
than FLUTE.

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6.2.  Attribute Names

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   SDP Attribute ("att-field"):
     Attribute name:     alc-tsi
     Long form:          Underspecified ALC Transport Session Identifier
     Type of name:       att-field
     Type of attribute:  Session level or media level
     Subject to charset: No
     Purpose:            See this document
     Reference:          This document
     Values:             See this document

   SDP Attribute ("att-field"):
     Attribute name:     alc-ch
     Long form:          Number of Channels in an Underspecified ALC
Session
     Type of name:       att-field
     Type of attribute:  Session level or media level
     Subject to charset: No
     Purpose:            See this document
     Reference:          This document
     Values:             See this document

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