URI%20List%20Index

1
URI List Index

• Lucent Technologies
• Tom Hiller
• Dean Willis
• Adam Roach

2
Background

• SIPPING has chartered work to specify how SIP
  uses URI lists
• URI lists can be stored on servers and referenced
  via a URI. This usage is called a server-stored
  list.
• URI lists can be contained in a request. This
  usage is called a request-contained list.
• Usage of both types of list is being defined for
  each request type.
• Server-stored lists can be arbitrarily long.
• We want to be able to have a request apply to a
  specific subset of the members of a list, with
  the subset indicated in the request.
• We want this subsetting operation to be extremely
  concise. This would make it very useful for
  mobile scenarios, especially Push to Talk.

3
Use Case

• Bob has a server-stored list which contains URIs
  for every member of his athletic club
• Bob wishes to invite three specific members
  (Bill, Joe, Alice) of his club to participate in
  a conference call.
• Bob constructs a SIP request that references the
  server-stored list and includes selection
  criteria for the three specific members.
• Bob request-handling server extracts the URIs for
  Bill, Joe, and Alice from Bobs list and sends
  the request to them.
• They chat.

4
Proposed Mechanism

• Extend resource list XML schema to include key
  values (membercodes) for each member
• Define new MIME types to include a list reference
  and a set of key values
• Use new MIME type as a cid body in a request, as
  request-contained usage does.
• The request-handling application retrieves list
  and applies membercodes to select intended target
  set.

5
Proposed MIME Types

• application/resource-lists-indices
• Only a few member of a relatively large list are
  included in the SIP request. Applies best for a
  sparse subset of the list.
• This MIME is just a list of membercodes
• application/resource-lists-bitmap
• Many or most of the members of a list are
  included in the SIP request. Applies best for a
  relatively dense subset of the list.
• This MIME is a binary array represented as hex
  digits. A bit in the array being set implies the
  member code of that value is included. Groups of
  four bits represent hex digits.

6
Example Resource List with Membercode
7
Examples

• application/resource-lists-indices
• Bob wishes to identify Bill in a SIP request .
  The MIME body based on the previous slide is
• athletic-club 2
• application/resource-lists-bitmap
• Bob wishes to identify many club members in a SIP
  request the membercodes of the individuals are
  2, 4, 5, 9, 19, 25, 36. The MIME body might be
• athletic-club 010110001000000000100001000000000010
  000

Or, as per current draft, something
like athletic-club A13BD
8
Issues and Further Steps

• Specific MIME format to use
• Addition of membercodes to resource list schema
• Requires modifying the schema to allow the
  addition of attributes
• Membercodes must be unique this requires XCAP
  handling for validation. (server rejects
  non-unique write attempts with suggestions)
• Client offers a membercode, the server validates,
  possibly rejecting with suggested codes on
  failure while reserving suggested membercodes
  briefly
• Do we enumerate across embedded list members?
• Tentative direction modify the schema to permit
  the addition of attributes. Progress this draft
  separately.