Subject: [AAA-WG]: [issue] Handling of Accounting-Multi-Session-Id AVP (draft-mobileip-08)

From: "Bob Kopacz" <[email-masked]>
Date: Wed, 27 Feb 2002 11:03:26 -0500

Issue :         Handling of Accounting-Multi-Session-Id AVP 
Submitter name: Bob Kopacz 
Submitter email address: [email-masked] 
Date first submitted: 02-27-2002 
Reference: 
Document:       draft-mobileip-08 
Comment type:   Technical 
Priority:       1 
Section: 

Rationale/Explanation of issue: 

  Changes to generation & handling of the Accounting-Multi-Session-Id AVP.

  The following lines prefixed with "*" are extracted from
  draft-mobileip-08.  The lines are numbered to make them referencable
  in the discussion.

   *01 1.2  Inter-Realm Mobile IP
   *02
   *03 [...]
   *04
   *05 For new sessions, the AAAH MUST create an accounting session
   *06 identifier, which is added to the Accounting-Multi-Session-Id AVP in
   *07 the HAR message sent to the home agent.
   *08
   *09 During the creation of the HAR, the AAAH MUST use a different session
   *10 identifier than the one used in the AMR/AMA (see figure 2). Of
   *11 course, an AAAH MUST use the same session identifier for all HARs
   *12 initiated on behalf of a given mobile node's session. [...]
   *13

  (1) According to the Introduction, an AAAH may be session-stateless. I
  don't think a session-stateless AAAH can differentiate a new session
  from a handoff of an existing session.  Therefore a session-stateless
  AAAH couldn't send the same session-id for handoffs, as stated in 
  line *11.

   *14 [...]
   *15
   *16 Upon receipt of the HAR, the Home Agent first processes the Diameter
   *17 message. [...]  The Accounting-Multi-Session-Id AVP in
   *18 the HAR MUST be included in the HAA, which is then forwarded to the
   *19 AAAH.
   *20

  (2) The last sentence is not quite right.  While the HA does send an
  Accounting-Multi-Session-Id AVP in the HAA, it may be a different one
  than was received in the HAR. (see lines *44-*46).

   *25 1.3  Support for Mobile IP Handoffs
   *26
   *27 [...]
   *28
   *29 Since the new AAAH in the home network MAY not have access to the
   *30 session identifier that was used by the old AAAH, it is necessary for
   *31 the resulting HAR received by the HA to be identified as a
   *32 continuation of an existing session. If the HA receives an HAR for a
   *33 mobile node, with a new session identifier, and the HA can guarantee
   *34 that this request is to extend service for an existing service, then
   *35 the HA MUST be able to modify its internal session state information
   *36 to reflect the new AAAH and session identifier.  The HA MUST also
   *37 issue an STR message with the old session identifier to the AAAH it
   *38 was communicating with when using the old session identifier.
   *39
   *40 It is necessary for accounting records to have some commonality
   *41 across handoffs in order for correlation to occur. Therefore, in the
   *42 event that a home agent receives an HAR with a different Accounting-
   *43 Multi-Session-id AVP (and obviously a different Session-Id AVP), the
   *44 home agent MUST send an HAA with the Accounting-Multi-Session-Id AVP
   *45 that was received by the AAAH in the first HAR for the mobile's
   *46 session. This modified Accounting-Multi-Session-Id AVP will be
   *47 returned to the foreign agent by the AAAH in the AMA. Both the
   *48 foreign and home agents MUST include the Accounting-Multi-Session-Id
   *49 in the accounting messages.
   *50

  (3) Since the AAAH must be prepared to have the AAAH-generated
  Accounting-Multi-Session-Id overridden by the HA, the protocol should
  change to just have the HA always specify the
  Accounting-Multi-Session-Id.

  The thinking is that the HA is constant over the MN's session, while the
  AAAHs and AAAFs and FAs change.  So the HA is in a position to specify a
  constant Accounting-Multi-Session-Id, eliminating the extra
  complications of a switcheroo.

  The proposal is that the AAAH will not send a
  Accounting-Multi-Session-Id in the HAR.  The HA MUST send a
  Accounting-Multi-Session-Id in the HAA.  All of the messages for a
  MN's session will have the same value for the
  Accounting-Multi-Session-Id AVP.

  (4) Since the AAAH may be session-stateless, the HA would send the STR
  to the AAAH, as indicated in lines *36-*38, if and only if the AAAH
  has changed.

Requested change: 

  In Section 1.2  Inter-Realm Mobile IP

  Replace:

    "For new sessions, the AAAH MUST create an accounting session
    identifier, which is added to the Accounting-Multi-Session-Id AVP in
    the HAR message sent to the home agent.

    "During the creation of the HAR, the AAAH MUST use a different session
    identifier than the one used in the AMR/AMA (see figure 2). Of
    course, an AAAH MUST use the same session identifier for all HARs
    initiated on behalf of a given mobile node's session. [...]

  With:

    "During the creation of the HAR, the AAAH MUST use a different session
    identifier than the one used in the AMR/AMA.  

    "If the AAAH is session-stateful, it should send the same session
    identifier for all HARs initiated on behalf of a given mobile node's
    session.  

    "If the AAAH is not session-stateful, it will manufacture a unique
    session-id for every HAR.  (Note--This will not cause a problem for
    the HA, who must be able to recognize a handoff even if the AAAH
    thinks the session is new; an AAAH may incorrectly view a session as
    new when the handoff AMR goes to a different AAAH than the previous
    AMR).

  - - - - 

  In Section 1.2  Inter-Realm Mobile IP

  Replace the last sentence of the following paragraph:

    Upon receipt of the HAR, the Home Agent first processes the Diameter
    message. [...]  The Accounting-Multi-Session-Id AVP in
    the HAR MUST be included in the HAA, which is then forwarded to the
    AAAH.

  With:

    The HA MUST include an Accounting-Multi-Session-Id AVP in the HAA
    returned to the AAAH.

  - - - - 

  In section 1.3  Support for Mobile IP Handoffs

  Replace:

    Since the new AAAH in the home network MAY not have access to the
    session identifier that was used by the old AAAH, it is necessary for
    the resulting HAR received by the HA to be identified as a
    continuation of an existing session. If the HA receives an HAR for a
    mobile node, with a new session identifier, and the HA can guarantee
    that this request is to extend service for an existing service, then
    the HA MUST be able to modify its internal session state information
    to reflect the new AAAH and session identifier.  The HA MUST also
    issue an STR message with the old session identifier to the AAAH it
    was communicating with when using the old session identifier.

    It is necessary for accounting records to have some commonality
    across handoffs in order for correlation to occur. Therefore, in the
    event that a home agent receives an HAR with a different Accounting-
    Multi-Session-id AVP (and obviously a different Session-Id AVP), the
    home agent MUST send an HAA with the Accounting-Multi-Session-Id AVP
    that was received by the AAAH in the first HAR for the mobile's
    session. This modified Accounting-Multi-Session-Id AVP will be
    returned to the foreign agent by the AAAH in the AMA. Both the
    foreign and home agents MUST include the Accounting-Multi-Session-Id
    in the accounting messages.

  With:

    "Since the new AAAH in the home network MAY not have access to the
    session identifier that was used by the old AAAH, or since the AAAH
    may be session-stateless, it is necessary for the resulting HAR
    received by the HA to be identified as a continuation of an existing
    session. 

    "If the HA receives an HAR for a mobile node, with a new session
    identifier, and the HA can guarantee that this request is to extend
    service for an existing service, then the HA MUST be able to modify
    its internal session state information to reflect the (possibly) new
    AAAH and new session identifier.  

    "If the AAAH is new, the HA MUST also issue an STR message with the old
    session identifier to the AAAH it was communicating with when using
    the old session identifier.

    "It is necessary for accounting records to have some commonality across
    handoffs in order for correlation to occur.  Therefore, the home agent
    MUST send the same Accounting-Multi-Session-Id AVP value in all HAAs for
    the mobile's session.  That is, the HA generates a unique
    Accounting-Multi-Session-Id when receiving an HAR for a new session, and
    returns this same value in every HAA for the session.

    "This Accounting-Multi-Session-Id AVP will be returned to the foreign
    agent by the AAAH in the AMA. Both the foreign and home agents MUST
    include the Accounting-Multi-Session-Id in the accounting messages."

  - - - - 

  In Section 1.5 "Co-located Mobile Node"

  Add the following sentence:

    "The HA includes the Accounting-Multi-Session-Id AVP in the AMR sent to
    the AAAH, as the AAAH may find this a useful piece of session-state or
    log entry information."

  - - - - 

  In section 2.3  Home-Agent-MIP-Request

  Remove { Accounting-Multi-Session-Id } from the message ABNF.

  - - - - 

  In section 2.4  Home-Agent-MIP-Answer

  Change [ Accounting-Multi-Session-Id ] to { Accounting-Multi-Session-Id }
  in the message ABNF.

  - - - - 

  In section 8.1  Mobile IP Command AVP Table,

  Add an entry for the Accounting-Multi-Session-Id AVP.

    Attribute Name                | AMR | AMA | HAR | HAA |
    ------------------------------|-----+-----+-----+-----+
    Accounting-Multi-Session-Id   | 0-1 | 1   | 0   | 1   |

  - - - - 

  In section 8.2  Accounting AVP Table
  Add an entry for the Accounting-Multi-Session-Id AVP.

    Attribute Name                | ACR | ACA |
    ------------------------------|-----+-----+
    Accounting-Multi-Session-Id   | 1   | 0-1 |

---

From: Tony Johansson <[email-masked]>
Date: Wed, 27 Feb 2002 20:10:39 -0800

All,

I agree on this change and would like to adopt it.

Any comments / objections.

Regards,

/Tony