Diameter Maintenance and                                        M. Jones Extensions (DIME)                      M. Liebsch Jones
Internet-Draft                                                 L. Morand
Intended status: Standards Track                       February 15, 2014                              M. Liebsch
Expires: August 19, January 5, 2015
                                                               L. Morand

                                                            July 4, 2014

                        Diameter Group Signaling
                 draft-ietf-dime-group-signaling-03.txt
                 draft-ietf-dime-group-signaling-04.txt

Abstract

   In large network deployments, a single Diameter peer can support over
   a million concurrent Diameter sessions.  Recent use cases have
   revealed the need for Diameter peers to apply the same operation to a
   large group of Diameter sessions concurrently.  The Diameter base
   protocol commands operate on a single session so these use cases
   could result in many thousands of command exchanges to enforce the
   same operation on each session in the group.  In order to reduce
   signaling, it would be desirable to enable bulk operations on all (or
   part of) the sessions managed by a Diameter peer using a single or a
   few command exchanges.  This document specifies the Diameter protocol
   extensions to achieve this signaling optimization.

Status of this This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 19, 2014. January 5, 2015.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  4   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .  5   3
   3.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .  6   4
     3.1.  Building and Modifying Session Groups . . . . . . . . . .  6   4
     3.2.  Issuing Group Commands  . . . . . . . . . . . . . . . . . .  6   4
     3.3.  Permission Model . . . . . Considerations . . . . . . . . . . . . . . . .  7   4
   4.  Protocol Description  . . . . . . . . . . . . . . . . . . . . .  8   6
     4.1.  Session Grouping  . . . . . . . . . . . . . . . . . . . . .  8   6
       4.1.1.  Group assignment at session initiation  . . . . . . . .  8   7
       4.1.2.  Removing a session from a session group . . . . . . . 10   8
       4.1.3.  Mid-session group assignment modifications  . . . . . . 11   9
     4.2.  Session Grouping Capability Discovery . . . . . . . . . . 12  10
       4.2.1.  Implicit  Explicit Capability Discovery . . . . . . . . . . . . 12  10
       4.2.2.  Explicit  Implicit Capability Discovery . . . . . . . . . . . . 12  11
     4.3.  Releasing  Deleting a Session Group Identifier  . . . . . . . . . . . 12 . . . . .  11
     4.4.  Performing Group Operations . . . . . . . . . . . . . . . 13  11
       4.4.1.  Sending Group Commands  . . . . . . . . . . . . . . . . 13  11
       4.4.2.  Receiving Group Commands  . . . . . . . . . . . . . . . 13  12
       4.4.3.  Error Handling for Group Commands . . . . . . . . . . 14  12
       4.4.4.  Single-Session Fallback . . . . . . . . . . . . . . . 14  13
   5.  Operation with Proxies Agents . . . . . . . . . . . . . . . . 15  13
   6.  Commands Formatting . . . . . . . . . . . . . . . . . . . . . 16  13
     6.1.  Formatting Example: Group Re-Auth-Request . . . . . . . . 16  14
   7.  Attribute-Value-Pairs (AVP) . . . . . . . . . . . . . . . . . 17  14
     7.1.  Session-Group-Info AVP  . . . . . . . . . . . . . . . . . . 17  15
     7.2.  Session-Group-Feature-Vector  Session-Group-Control-Vector AVP  . . . . . . . . . . . . . 17  15
     7.3.  Session-Group-Id AVP  . . . . . . . . . . . . . . . . . . . 18  16
     7.4.  Session-Group-Action  Group-Response-Action AVP . . . . . . . . . . . . . . . .  16
     7.5.  Session-Group-Capability-Vector AVP . 18 . . . . . . . . . .  17
   8.  Result-Code AVP Values  . . . . . . . . . . . . . . . . . . . . 19  17
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20  17
     9.1.  AVP Codes . . . . . . . . . . . . . . . . . . . . . . . . 20  17
   10. Security Considerations . . . . . . . . . . . . . . . . . . . 21  17
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 22  18
   12. Normative References  . . . . . . . . . . . . . . . . . . . . . 23  18
   Appendix A.  Session Management -- Exemplary Session State
                Machines . . . . . . . . . . . . . . . . . . . . . . 24  18
     A.1.  Authorization Session State Machine . . . . . . . . . . . 24  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 28  22

1.  Introduction

   In large network deployments, a single Diameter peer can support over
   a million concurrent Diameter sessions.  Recent use cases have
   revealed the need for Diameter peers to apply the same operation to a
   large group of Diameter sessions concurrently.  For example, a policy
   decision point may need to modify the authorized quality of service
   for all active users having the same type of subscription.  The
   Diameter base protocol commands operate on a single session so these
   use cases could result in many thousands of command exchanges to
   enforce the same operation on each session in the group.  In order to
   reduce signaling, it would be desirable to enable bulk operations on
   all (or part of) the sessions managed by a Diameter peer using a
   single or a few command exchanges.

   This document describes mechanisms for grouping Diameter sessions and
   applying Diameter commands, such as performing re-authentication, re-
   authorization, termination and abortion of sessions to a group of
   sessions.  This document does not define a new Diameter application.
   Instead it defines mechanisms, commands and AVPs that may be used by
   any Diameter application that requires management of groups of
   sessions.

   These mechanisms take the following design goals and features into
   account:

   o Minimal impact to existing applications

   o Extension of existing commands' CCF Command Code Format (CCF) with
   optional AVPs to enable grouping and group operations

   o Fallback to single session operation

   o Implicit discovery of capability to support grouping and group
   operations in case no external mechanism is available to discover a
   Diameter peer's capability to support session grouping and session
   group operations.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   This document uses terminology defined [RFC6733].

3.  Protocol Overview

3.1.  Building and Modifying Session Groups

   Client and Server can add assign a new Diameter session to a group, e.g.
   in case the subscription profile of the associated user has similar
   characteristics as the profile of other users whose Diameter session
   has been added assigned to one or multiple groups.  Such similarities  A single command can be
   for example maximum bandwidth bounds of each user in the a group.
   These users may share resources of, e.g., an access multiplexer,
   together
   issued and applied to all sessions associated with other users.  Runtime adjustments in the granted
   bandwidth bounds such group(s),
   e.g. to adjust common profile or other Quality policy settings.

   The assignment of Service related attributes can
   be accomplished for the whole group by identifying the group in the a Diameter session to a group command.

   In case can be changed mid-
   session.  For example, if a user's subscription profile changes during runtime, either
   node, mid-
   session, a Diameter Server or Diameter client, peer may decide to remove this
   user's Diameter the session from its current
   group and assign the session group.  The user's Diameter
   session can be assigned to a different group, whose adjusted profile
   matches group that is more
   appropriate for the one new subscription profile.

   In case of the different group.  Both groups, mobile users, the user's
   previous group and its new group, will be modified mid-session.

   In case of mobile users, a change in the node implementing the
   Diameter client can happen, which has impact to a group of sessions a
   particular pair of Diameter client and server has in common.  Due to
   mobility, the mobile user's session may get transferred to a
   new Diameter client during runtime without mandating from-scratch
   authorization.  Such scenario necessitates mid-session modification.

3.2.  Issuing Group Commands

   A policy decision point may decide handover and assigned to terminate a group of sessions, different
   group, which is maintained at the new Diameter client, mid-session.

   A session group, which has sessions assigned, can be deleted, e.g. based on previous agreement for temporary authorization
   due to
   access a system.  All Diameter change in multiple users' subscription profile so that the
   group's assigned sessions do not share certain characteristics
   anymore.  Deletion of associated users with such
   temporarily granted access will be added group requires subsequent individual
   treatment of each of the assigned sessions.  A peer may decide to a single Diameter session
   assign some of these sessions to any other existing or new group.  After the time limit for

3.2.  Issuing Group Commands

   Changes in the temporary authorization has been
   reached, network condition may result in the policy Diameter server's
   decision point can issue to close all sessions in a given group.  The server issues a
   single Session Termination Request (STR) to the policy enforcement point.  The STR command identifies , identifying the
   group of Diameter sessions which are to be terminated.  The policy enforcement point Diameter client
   treats the STR as group command and initiates termination of all
   sessions in associated with the identified group.  Subsequently, the policy enforcement point
   client confirms successful termination of these sessions to the policy decision point
   server by sending a single Session Termination Answer (STA) command command,
   which includes the identifier of the group.

3.3.  Permission Model

   A permission model Considerations

   Permission considerations in the context of this draft defines apply to the
   permission of Diameter nodes to build new session groups, to add/ assign/
   remove a session to/from a session group and to delete an existing
   session group.

   This specification follows the most flexible model where both, a
   Diameter client and a Diameter server can build create a new group and
   assign a new identifier to that session group.  When a Diameter node
   decides to issue create a new session group, e.g. to group all sessions
   which share certain characteristics, the node must identify itself in
   the DiameterIdentity element of the builds a session group
   identifier
   (Section according to the rules described in Section 7.3) as and
   becomes the owner of the group.  The permission model as per
   this  This specification solely constrains does not
   constrain the permission to close add or remove a session to/from a session
   group and release the associated identifier to the group
   owner.

   Irrespective of the group ownership, as per this specification any
   Diameter node has the permission owner, instead each peer can add a session to add/remove any
   known group or remove a session to/from an
   existing from a group.  A session group is
   deleted and its identifier released after the last session has been
   removed from the session group.  Also the modification of groups in
   terms of moving a session from one session group to a different
   session group is permitted to any Diameter node.  A Diameter peer can
   delete a session group and its group identifier mid-session,
   resulting in individual treatment of the sessions which have been
   previously assigned to the deleted group.

   The enforcement of a more constrained model permissions is left to the
   specification of a particular group signaling enabled Diameter
   application and implementation,
   which must then ensure that relevant Diameter nodes have the same
   view compliant implementations of such application must
   enforce the associated permission model, either through administrative
   configuration or protocol-based capability discovery. model.  Details about enforcing a
   more constraint permission model are out of scope of this
   specification.  For example, a more constrained model could require
   that a client MUST NOT remove client MUST NOT remove a session from a group which is owned
   by the server.

   The following table depicts the permission considerations as per the
   present specification:

   +-------------------------------------------------+--------+--------+
   |                 Operation                       | Server | Client |
   +-------------------------------------------------+--------+--------+
   | Create a new Session Group (peer becomes        |    X   |    X   |
   | the group owner)                                |        |        |
   +-------------------------------------------------+--------+--------+
   | Assign a Session to an owned Session Group      |    X   |    X   |
   +-------------------------------------------------+--------+--------+
   | Assign a Session to a non-owned Session Group   |    X   |    X   |
   +-------------------------------------------------+--------+--------+
   | Remove a Session from an owned Session Group    |    X   |    X   |
   +-------------------------------------------------+-----------------+
   | Remove a Session from a non-owned Session Group |    X   |    X   |
   +-------------------------------------------------+--------+--------+
   | Remove a Session from a Session Group where the |    X   |    X   |
   | peer created the assignment                     |        |        |
   +-------------------------------------------------+--------+--------+
   | Remove a Session from a Session Group where the |        |        |
   | peer did not create the assignment              |        |        |
   +-------------------------------------------------+--------+--------+
   | Overrule a peer's group assignment *)           |        |        |
   +-------------------------------------------------+--------+--------+
   | Delete a Session Group owned by the peer        |    X   |    X   |
   +-------------------------------------------------+--------+--------+
   | Delete a Session Group not owned by the peer    |        |        |
   +-------------------------------------------------+--------+--------+

               Default Permission as per this Specification

   *) Editors' note: The protocol specification in this document does
   not consider overruling a peer's assignment of a session from to a group which is owned
   by the server. session
   group.  Group signaling enabled applications may take such protocol
   support and associated protocol semantics into account in their
   specification.

4.  Protocol Description

4.1.  Session Grouping

   Either Diameter peer can initiate assigning the assignment of a session to a
   single or multiple session groups.  Modification of a group by
   removing or adding a single or multiple user sessions can be
   initiated and performed at runtime mid-session by either Diameter peer.
   Diameter AAA applications typically assign client and server roles to
   the Diameter peers, which are referred to as relevant Diameter peers
   to utilize session grouping and issue group commands.  Section 5
   describes particularities about session grouping and performing group
   commands when relay agents or proxies are deployed.

   Diameter peers, which are group-aware, must store and maintain an
   entry about the group assignment together with a session's state.  A
   list of all known session groups should be locally maintained on each
   peer, each group pointing to individual sessions being assigned to which at least one session, for which
   the group.  A peer holds a state, is assigned.  Along with the group's Session-Id, must also keep a list of Diameter record about sessions, which are have
   been assigned to the group, must be
   stored.  This specification assumes that a session group is built and
   handled between pairs of Diameter nodes.  Clients and servers MUST
   maintain Diameter state of individual sessions grouped in a session
   group. by that peer.

4.1.1.  Group assignment at session initiation

   To assign a session to a group at session initiation, a Diameter
   client sends a service specific request, e.g.  NASREQ AAR [RFC4005],
   containing one or more group identifiers.  A Diameter client as
   sender of a command for session initiation can determine one or
   multiple groups to which the new session should be assigned.  Each of these groups need
   to be identified by a unique Session-Group-Id contained in a separate
   Session-Group-Info AVP as specified in Section 7.

   The client may choose one or multiple sessions from a list of
   existing session groups, irrespective of the group ownership. groups.  Alternatively, the client may decide to
   create a new group and identify itself in the DiameterIdentity
   element of the Group-Session-Id AVP as per Section 7.3

   The client MUST set the SESSION_GROUP_ALLOCATION_ACTION of the
   Session-Group-Feature-Vector
   Session-Group-Control-Vector AVP in each appended Session-Group-Info
   AVP to indicate that the identified session should be added assigned to the
   identified session group.

   If the Diameter server receives a command request from a Diameter
   client and the command comprises at least one Session-Group-Info AVP
   having the SESSION_GROUP_ALLOCATION_ACTION flag of the Session-Group-
   Feature-Vector
   Control-Vector AVP set, the server must add assign the new session to
   each of the one or multiple identified session groups.  In case one
   or multiple identified session groups are not know to the server, the
   server must add the one or multiple new groups to its locally
   maintained local list of
   known session groups.  When sending the response to the client, e.g.
   a service-specific auth response as per NASREQ AAA [RFC4005], the
   server must include all Session-Group-Info AVPs as
   received in the client's request.

   In addition to the one or multiple session groups identified in the
   client's request, the server may decide to add the new session to one
   or multiple additional groups.  In such case, the server add to the
   response additional Session-Group-Info AVPs, each identifying a
   session group, to which the server has assigned the new session.
   Each of the Session-Group-Info AVP added by the server, the
   SESSION_GROUP_ALLOCATION_ACTION flag of the Session-Group-Feature-
   Vector AVP must be set.

   If the Diameter server receives a command for session initiation from
   a Diameter client and include all Session-Group-Info AVPs as received in the command comprises at least one Session-
   Group-Info AVP, but
   client's request.

   In addition to the one or multiple Session-Group-Info AVP do not
   identify any session group to which groups identified in the session should be assigned,
   client's request, the server may decide to assign the new session to
   one or multiple session additional groups.  Each  In such case, the server adds to
   the response additional Session-Group-Info AVPs, each identifying a
   session group, to which the server assigns has assigned the new
   session, must be identified in a separate session.
   Each of the Session-Group-Info AVP
   having added by the server must have the
   SESSION_GROUP_ALLOCATION_ACTION flag of the associated
   Session-Group-Vector Session-Group-Control-
   Vector AVP set.

   If the Diameter client receives a response to its previously issued
   request from the server and the response comprises at least one
   Session-Group-Info AVP having the SESSION_GROUP_ALLOCATION_ACTION
   flag of the associated Session-Group-Feature-Vector Session-Group-Control-Vector AVP set, the
   client must add the new session to all session groups as identified
   in the one or multiple Session-Group-Info AVPs.

   A Diameter server receiving a command for session initiation which
   includes at least one Session-Group-Info AVP but the server does not
   understand the semantics of this optional AVP because it does not
   support group operations according to the specification in this
   document, MUST ignore the optional group operations specific AVPs and
   proceed with processing the command for a single session.

   A Diameter client, which sent a request for session initiation to a
   Diameter server and appended a single or multiple Session-Group-Id
   AVPs but cannot find any Session-Group-Info AVP in the associated
   response from the Diameter server proceeds with processing the
   command for a single session.  Furthermore, the client keeps a log to
   remember that the server is not able to perform group operations.

4.1.2.  Removing a session from a session group

   When a Diameter client decides to remove a session from a particular
   session group, the client sends a service-specific re-authorization
   request to the server and adds one Session-Group-Info AVP to the
   request for each session group, from which the client wants to remove
   the session.  The session, which is to be removed from a group, is
   identified in the Session-Id AVP of the command request.  The
   SESSION_GROUP_ALLOCATION_ACTION flag of the Session-Group-Feature- Session-Group-Control-
   Vector AVP in each Session-Group-Info AVP must be cleared to indicate
   removal of the session from the session group identified in the
   associated Session-Group-id AVP.

   When a Diameter client decides to remove a session from all session
   groups, to which the session has been previously assigned, the client
   sends a service-specific re-authorization request to the server and
   adds a single Session-Group-Info AVP to the request which has the
   SESSION_GROUP_ALLOCATION_ACTION flag cleared and the Session-Group-Id
   AVP omitted.  The session, which is to be removed from all groups, to
   which the session has been previously assigned, is identified in the
   Session-Id AVP of the command request.

   If the Diameter server receives a request from the client which has
   at least one Session-Group-Info AVP appended with the
   SESSION_GROUP_ALLOCATION_ACTION flag cleared, the server must remove
   the session from the session group identified in the associated
   Session-Group-Id AVP.  If the request comprises at least one Session-
   Group-info AVP with the SESSION_GROUP_ALLOCATION_ACTION flag cleared
   and no Session-Id AVP present, the server must remove the session
   from all session groups to which the session has been previously
   assigned.  The server must include in its response to the requesting
   client all Session-Group-Id AVPs as received in the request.

   When the Diameter server decides to remove a session from one or
   multiple particular session groups or from all session groups to
   which the session has been assigned beforehand, the server sends a
   Re-Authorization Request (RAR) to the client, indicating the session
   in the requests Session-Id AVP.  The client sends a Re-Authorization
   Answer (RAA) to respond to the server's request.  The client
   subsequently sends service-specific re-authorization request
   containing one or multiple Session-Group-Info AVPs, each indicating a
   session group, to which the session had been previously assigned.  To
   indicate removal of the indicated session from one or multiple
   session groups, the server sends a service-specific auth response to
   the client, containing a list of Session-Group-Info AVPs with the
   SESSION_GROUP_ALLOCATION_ACTION flag cleared and the Session-Group-Id
   AVP identifying the session group, from which the session should be
   removed.  The server MAY include to the service-specific auth
   response a list of Session-Group-Info AVPs with the
   SESSION_GROUP_ALLOCATION_ACTION flag set and the Session-Group-Id AVP
   identifying session groups to which the session remains subscribed.
   In case the server decides to remove the identified session from all
   session groups, to which the session has been previously assigned,
   the server includes in the service-specific auth response at least
   one Session-Group-Info AVP with the SESSION_GROUP_ALLOCATION_ACTION
   flag cleared and Session-Group-Info Session-Group-Id AVP absent.

4.1.3.  Mid-session group assignment modifications

   Either Diameter peer can modify the group membership of an active
   Diameter session, irrespective of session according to the group ownership. specified permission
   considerations.

   To update an assigned group mid-session, a Diameter client sends a
   service-specific re-authorization request to the server, containing
   one or multiple Session-Group-Info AVPs with the
   SESSION_GROUP_ALLOCATION_ACTION flag set and the Session-Group-Id AVP
   present, identifying the session group to which the session should be
   added.
   assigned.  With the same message, the client may send one or multiple
   Session-Group-Info AVP with the SESSION_GROUP_ALLOCATION_ACTION flag
   cleared and the Session-Group-Id AVP identifying the session group
   from which the identified session is to be removed.  To remove the
   session from all previously assigned session groups, the client
   includes at least one Session-Group-Info AVP with the
   SESSION_GROUP_ALLOCATION_ACTION flag cleared and no Session-Group-Id
   AVP present.  When the server received the service-specific re-
   authorization request, it must update its locally maintained view of
   the session groups for the identified session according to the
   appended Session-Group-Info AVPs.  The server sends a service-
   specific auth response to the client containing one or multiple
   Session-Group-Info AVPs with the SESSION_GROUP_ALLOCATION_ACTION flag
   set and the Session-Group-Id AVP identifying the new session group to
   which the identified session has been added. assigned.

   When a Diameter server enforces an update to the assigned groups mid-
   session, it sends a Re-Authorization Request (RAR) message to the
   client identifying the session, for which the session group lists are
   to be updated.  The client responds with a Re-Authorization Answer
   (RAA) message.  The client subsequently sends service-specific re-
   authorization request containing one or multiple Session-Group-Info
   AVPs with the SESSION_GROUP_ALLOCATION_ACTION flag set and the
   Session-Group-Id AVP identifying the session group to which the
   session had been previously assigned.  The server responds with a
   service-specific auth response and includes one or multiple Session-
   Group-Info AVP with the SESSION_GROUP_ALLOCATION_ACTION flag set and
   the Session-Group-Id AVP identifying the session group, to which the
   identified session is to be added. assigned.  With the same response
   message, the server may send one or multiple Session-Group-Info AVPs
   with the SESSION_GROUP_ALLOCATION_ACTION flag cleared and the
   Session-Group-Id AVP identifying the session groups from which the
   identified session is to be removed.  When server wants to remove the
   session from all previously assigned session groups, it send at least
   on Session-
   Group-Info Session-Group-Info AVP with the response having the
   SESSION_GROUP_ALLOCATION_ACTION flag cleared and no Session-Group-Id
   AVP present.

4.2.  Session Grouping Capability Discovery

   Diameter nodes should assign a session to a session group and perform
   session group operations with a peer only after having ensured that
   the peer announced associated support beforehand.

4.2.1.  Implicit  Explicit Capability Discovery

   By appending at least one Session-Group-Info AVP, the

   New Diameter client
   announces its capability to applications may consider support for Diameter session
   grouping and for performing group operations according to the
   specification in this document to commands during the addressed Diameter server.  If standardization
   process.  Such applications provide intrinsic discovery for the Diameter client supports
   support of group operations, it MUST append at
   least one Session-Group-Info AVP to commands and announce its this capability to
   support group operations.

   A session-group aware Diameter server receiving a command for session
   initiation which includes at least one Session-Group-Info AVP learns
   about through the sender's
   assigned application ID.

   System- and deployment-specific means for capability exchange can be
   used to announce peers' support for session grouping and session
   group operations.

   By appending at least one Session-Group-Id AVP,  In such case, the optional Session-Group-
   Capability-Vector AVP, as described in Section 4.2.2 can be omitted
   in Diameter messages being exchanged between peers.

4.2.2.  Implicit Capability Discovery

   If no explicit mechanism for capability discovery is deployed to
   enable Diameter server
   announces its nodes to learn about peers' capability to support
   session grouping and group operations according to commands, Diameter peers SHOULD append the
   specification in this document
   Session-Group-Capability-Vector AVP to the addressed Diameter client.

4.2.2.  Explicit Capability Discovery

   New any Diameter applications may consider messages
   exchanged with its peers to announce its capability to support for Diameter
   session grouping and for performing session group commands during operations.  Implementations
   following this specification set the standardization
   process.  Such applications provide intrinsic support for BASE_SESSION_GROUP_CAPABILITY
   flag of the Session-Group-Capability-Vector AVP.

   When a Diameter node receives at least one Session-Group-Capability-
   Vector AVP from a peer with the BASE_SESSION_GROUP_CAPABILITY flag
   set, the Diameter node maintains a log to remember the peer's
   capability to support
   of group commands and announce this capability through the assigned
   application ID. commands.

4.3.  Releasing  Deleting a Session Group Identifier

   To close delete a session group and release the associated Session-Group-Id
   value, the owner of a session group appends a single Session-Group-
   Info AVP having the SESSION_GROUP_STATUS_IND flag cleared and the
   Session-Group-Id AVP identifying the session group, which is to be
   closed.
   deleted.  The SESSION_GROUP_ALLOCATION_ACTION flag of the associated
   Session-Group-Feature-Vector
   Session-Group-Control-Vector AVP MUST be cleared.

4.4.  Performing Group Operations

4.4.1.  Sending Group Commands

   Either Diameter peer can request the recipient of a request to
   process an associated command for all sessions being assigned to one
   or multiple groups by identifying these groups in the request.  The
   sender of the request appends for each group, to which the command
   applies, a Session-Group-Info AVP including the Session-Group-Id AVP
   to identify the associated session group.  Both, the
   SESSION_GROUP_ALLOCATION_ACTION flag as well as the
   SESSION_GROUP_STATUS_IND flag must be set.

   If the CCF of the request mandates a Session-Id AVP, the Session-Id
   AVP MUST identify a single session which is assigned to at least one
   of the groups being identified in the appended Session-Group-Id AVPs.

   The sender of the request can MUST indicate to the receiver how follow up
   message exchanges should be performed by appending a Session-Group-
   Action single instance
   of the Group-Response-Action AVP.  Even if the request includes
   multiple instances of a Session-Group-Info AVP, the request MUST NOT
   comprise more than a single instance of a Group-Response-Action AVP.
   If the sender wants the receiver to perform follow up exchanges with
   a single command for all impacted groups, the sender sets the value
   of the Session-Group-Action Group-Response-Action AVP to ALL_GROUPS (1).  If follow up
   message exchanges should be performed on a per-group basis in case
   multiple groups are identified in the group command, the value of the Session-Group-Action
   Group-Response-Action AVP is set to PER_GROUP (2).  A value set to
   PER_SESSION (3) indicates to the receiver that all follow up
   exchanges should be performed using a single message for each
   impacted session.

   If the sender wants the receiver of the request to process the
   associated command solely for a single session does not append any
   group identifier, but identifies the relevant session in the
   Session-Id Session-
   Id AVP.

4.4.2.  Receiving Group Commands

   A Diameter peer receiving a request to process a command for a group
   of sessions identifies the relevant groups according to the appended
   Session-Group-Id AVP in the Session-Group-Info AVP. AVP and processes the
   group command according to the appended Group-Response-Action AVP .
   If the received request identifies multiple groups in multiple
   appended Session-
   Group-Id Session-Group-Id AVPs, the receiver should process the
   associated command for each of these groups. if a session has been
   assigned to more than one of the identified groups, the receiver must
   process the associated command only once per session.

   The Diameter peer receiving a request which requests performing the
   command to at least on session group SHOULD perform follow up message
   exchanges according to the value identified in the Session-Group-Info
   AVP.

4.4.3.  Error Handling for Group Commands

   When a Diameter peer receives a request to process a command for one
   or more session groups and the result of processing the command is an
   error that applies to all sessions in the identified groups, an
   associated protocol error must be returned to the source of the
   request.  In such case, the sender of the request MUST fall back to
   single-session processing and the session groups, which have been
   identified in the group command, MUST be closed deleted according to the
   procedure described in Section 4.3.

   When a Diameter peer receives a request to process a command for one
   or more session groups and the result of processing the command
   succeeds for some sessions identified in one or multiple session
   groups, but fails for one or more sessions, the Result-Code AVP in
   the response message SHOULD indicate DIAMETER_LIMITED_SUCCESS as per
   Section 7.1.2 of [RFC6733].  In case of limited success, the
   sessions, for which the processing of the group command failed, MUST
   be identified using a Failed-AVP AVP as per Session 7.5 of [RFC6733].

4.4.4.  Single-Session Fallback

   Either Diameter peer, a Diameter client or a Diameter server, can
   fall back to single session operation by ignoring and omitting the
   optional group session-specific AVPs.  Fallback to single-session
   operation is performed by processing the Diameter command solely for
   the session identified in the mandatory Session-Id AVP.  The response
   to the group command must not identify any group but identify solely
   the single session for which the command has been processed.

5.  Operation with Proxies Agents

   This specification assumes in case of a present stateful Proxy Agent
   between a Diameter client and a Diameter server that the Proxy Agent
   is aware of session groups and session group handling.  The Proxy
   MUST reflect the state of each session associated with a session
   group according to the result of a group command operated between a
   Diameter client and a server.

   In case a Proxy Agent manipulates session groups, it MUST maintain
   consistency of session groups between a client and a server.  This
   applies to deployment where the Proxy Agent utilizes session grouping
   and performing group commands with, for example, a Diameter server,
   whereas the Diameter client is not group-aware.  The same applies to
   deployment where all nodes, the Diameter client and server, as well
   as the Proxy Agent are group-aware but the Proxy Agent manipulates
   groups, e.g. to adopt different administrative policies that apply to
   the client's domain and the server's domain.

6.  Commands Formatting

   This document does not specify new Diameter commands to enable group
   operations, but relies on command extensibility capability provided
   by the Diameter Base protocol.  This section provides the guidelines
   to extend the CCF of existing Diameter commands with optional AVPs to
   enable the recipient of the command to perform the command to all
   sessions associated with the identified group(s).

6.1.  Formatting Example: Group Re-Auth-Request

   A request that one or more groups of users are re-authentication is
   issued by appending one or multiple Session-Group-Id AVP(s) to the
   Re-Auth-Request (RAR). (RAR) and a single instance of a Group-Response-
   Action AVP.  The one or multiple Session-Group-Id AVP(s) identify the
   associated group(s) for which the group re-
   authentication re-authentication has been
   requested.  The Group-Response-Action AVP identifies the expected
   means to perform and respond to the group command.  The recipient of
   the group command initiates re-authentication for all users
   associated with the identified group(s).  Furthermore, the sender of
   the group re-
   authentication re-authentication request appends a Session-Group-Action Group-Response-Action
   AVP to provide more information to the receiver of the command about
   how to accomplish the group operation.

   The value of the mandatory Session-Id AVP MUST identify a session
   associated with a single user, which is assigned to at least one of
   the groups being identified in the appended Session-Group-Id AVPs.

         <RAR>  ::= < Diameter Header: 258, REQ, PXY >
                    < Session-Id >
                    { Origin-Host }
                    { Origin-Realm }
                    { Destination-Realm }
                    { Destination-Host }
                    { Auth-Application-Id }
                    { Re-Auth-Request-Type }
                    [ User-Name ]
                    [ Origin-State-Id ]
                  * [ Proxy-Info ]
                  * [ Route-Record ]
                    [ Session-Group-Capability-Vector ]
                  * [ Session-Group-Id Session-Group-Info ]
                    [ Session-Group-Action Group-Response-Action ]
                  * [ AVP ]

7.  Attribute-Value-Pairs (AVP)
                                                  +--------------------+
                                                  |   AVP Flag rules   |
                                                  +----+---+------+----+
                                 AVP              |    |   |SHOULD|MUST|
 Attribute Name                  Code Value Type  |MUST|MAY| NOT  | NOT|
+-------------------------------------------------+----+---+------+----+
|Session-Group-Info              TBD1 Grouped     |    | P |      | V  |
|Session-Group-Feature-Vector
|Session-Group-Control-Vector    TBD2 Unsigned32  |    | P |      | V  |
|Session-Group-Id                TBD3 OctetString |    | P |      | V  |
|Session-Group-Action
|Group-Response-Action           TBD4 Unsigned32  |    | P |      | V  |
|Session-Group-Capability-Vector TBD5 Unsigned32  |    | P |      | V  |
+-------------------------------------------------+----+---+------+----+

                   AVPs for the Diameter Group Signaling

7.1.  Session-Group-Info AVP

   The Session-Group-Info AVP (AVP Code TBD1) is of type Grouped.  It
   contains the identifier of the session group as well as an indication
   of the node responsible for session group identifier assignment.

      Session-Group-Info ::= < AVP Header: TBD1 >
                             < Session-Group-Feature-Vector Session-Group-Control-Vector >
                             [ Session-Group-Id ]
                           * [ AVP ]

7.2.  Session-Group-Feature-Vector  Session-Group-Control-Vector AVP

   The Session-Group-Feature-Vector Session-Group-Control-Vector AVP (AVP Code TBD2) is of type
   Unsigned32 and contains a 32-bit flags field of capabilities
   supported by to control the group
   assignment at session-group aware node. nodes.

   The following capabilities are defined in this document:

   SESSION_GROUP_ALLOCATION_ACTION (0x00000001)

      This flag indicates the action to be performed for the identified
      session.  When this flag is set, it indicates that the identified
      Diameter session is to be added assigned to the session group as
      identified by the Session-Group-Id AVP or the session's assignement assignment
      to the session group identified in the Session-Group-Id AVP is
      still valid.  When the flag is cleared, the identified Diameter
      session is to be removed from at least one session group.  When
      the flag is cleared and the Session-Group-Info AVP identifies a
      particular session group in the associated Session-Group-Id AVP,
      the session is to be removed solely from the identified session
      group.  When the flag is cleared and the Session-Group-Info AVP
      does not identify a particular session group (Session-Group-Id AVP
      is absent), the identified Diameter session is to be removed from
      all session groups, to which it has been previously assigned.

   SESSION_GROUP_STATUS_IND (0x00000010)

      This flag indicates the status of the session group identified in
      the associated Session-Group-Id AVP.  The flag is set when the
      identified session group has just been created or is still active.
      If the flag is cleared, the identified session group is closed deleted
      and the associated Session-Group-Id is released.  If the Session-
      Group-Info AVP does not comprise a Session-Group-Id AVP, this flag
      is meaningless and MUST be ignored by the receiver.

7.3.  Session-Group-Id AVP

   The Session-Group-Id AVP (AVP Code TBD3) is of type UTF8String and
   identifies a group of Diameter sessions.

   The Session-Group-Id MUST be globally and eternally unique, as it is
   meant to uniquely identify a group of Diameter sessions without
   reference to any other information.

   The default format of the Session-Group-id MUST comply to the format
   recommended for a Session-Id, as defined in the section 8.8 of the
   [RFC6733].  The DiameterIdentity element of the Session-Group-Id MUST
   identify the Diameter node, which owns the session group.

7.4.  Session-Group-Action  Group-Response-Action AVP

   The Session-Group-Action Group-Response-Action AVP (AVP Code TBD4) is of type Unsigned32
   and contains a 32-bit address space representing values indicating
   how the peer SHOULD issue follow up exchanges in response to a
   command which impacts mulitple multiple sessions.  The following values are
   defined by this application:

   ALL_GROUPS (1)
      Follow up exchanges should be performed with a single message
      exchange for all impacted groups.

   PER_GROUP (2)
      Follow up exchanges should be performed with a message exchange
      for each impacted group.

   PER_SESSION (3)
      Follow up exchanges should be performed with a message exchange
      for each impacted session.

7.5.  Session-Group-Capability-Vector AVP

   The Session-Group-Capability-Vector AVP (AVP Code TBD5) is of type
   Unsigned32 and contains a 32-bit flags field to indicate capabilities
   in the context of session-group assignment and group operations.

   The following capabilities are defined in this document:

   BASE_SESSION_GROUP_CAPABILITY (0x00000001)

      This flag indicates the capability to support session grouping and
      session group operations according to this specification.

8.  Result-Code AVP Values

   This document does not define new Result-Code [RFC6733] values for
   existing applications, which are extended to support group commands.
   Specification documents of new applications, which will have
   intrinsic support for group commands, may specify new Result-Codes.

9.  IANA Considerations

   This section contains the namespaces that have either been created in
   this specification or had their values assigned to existing
   namespaces managed by IANA.

9.1.  AVP Codes

   This specification requires IANA to register the following new AVPs
   from the AVP Code namespace defined in [RFC6733].

   o  Session-Group-Info

   o  Session-Group-Feature-Vector  Session-Group-Control-Vector

   o  Session-Group-Id

   o  Session-Group-Action  Group-Response-Action

   o  Session-Group-Capability-Vector

   The AVPs are defined in Section 7.

10.  Security Considerations

   TODO

11.  Acknowledgments

   The authors of this document want to thank Ben Campbell and Eric
   McMurry for their valuable comments to early versions of this draft.

12.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4005]  Calhoun, P., Zorn, G., Spence, D., and D. Mitton,
              "Diameter Network Access Server Application", RFC 4005,
              August 2005.

   [RFC6733]  Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
              "Diameter Base Protocol", RFC 6733, October 2012.

Appendix A.  Session Management -- Exemplary Session State Machines

A.1.  Authorization Session State Machine

   Section 8.1 in [RFC6733] defines a set of finite state machines,
   representing the life cycle of Diameter sessions, and which MUST be
   observed by all Diameter implementations that make use of the
   authentication and/or authorization portion of a Diameter
   application.  This section defines the additional state transitions
   related to the processing of the new commands which may impact
   multiple sessions.

   The group membership is session state and therefore only those state
   machines from [RFC6733] in which the server is maintaining session
   state are relevant in this document.  As in [RFC6733], the term
   Service-Specific below refers to a message defined in a Diameter
   application (e.g., Mobile IPv4, NASREQ).

   The following state machine is observed by a client when state is
   maintained on the server.  State transitions which are unmodified
   from [RFC6733] are not repeated here.

   A Diameter group command in the following tables is differentiated
   from a single-session related command by a preceding 'G'.  A Group
   Re-Auth Request, which applies to one or multiple session groups, has
   been exemplarily described in Section 6.1.  Such Group RAR command is
   denoted as 'GRAR' in the following table.  The same notation applies
   to other commands as per [RFC6733].

                              CLIENT, STATEFUL
      State     Event                          Action       New State
      ---------------------------------------------------------------
      Idle      Client or Device Requests      Send         Pending
                access                         service
                                               specific
                                               auth req
                                               optionally
                                               including
                                               groups

      Open      GASR received with             Send GASA    Discon
                Session-Group-Action
                Group-Response-Action          with
                = ALL_GROUPS,                  Result-Code
                session is assigned to         = SUCCESS,
                received group(s) and          Send GSTR.
                client will comply with
                request to end the session

      Open      GASR received with             Send GASA    Discon
                Session-Group-Action
                Group-Response-Action           with
                = PER_GROUPS,                  Result-Code
                session is assigned to         = SUCCESS,
                received group(s) and          Send GSTR
                client will comply with        per group
                request to end the session
      Open      GASR received with             Send GASA    Discon
                Session-Group-Action
                Group-Response-Action          with
                = PER_SESSION,                 Result-Code
                session is assigned to         = SUCCESS,
                received group(s) and          Send STR
                client will comply with        per session
                request to end the session

      Open      GASR received,                 Send GASA    Open
                client will not comply with    with
                request to end all session     Result-Code
                in received group(s)           != SUCCESS

      Discon    GSTA Received                  Discon.      Idle
                                               user/device

      Open      GRAR received with             Send GRAA,   Pending
                Session-Group-Action
                Group-Response-Action          Send
                = ALL_GROUPS,                  service
                session is assigned to         specific
                received group(s) and          group
                client will perform            re-auth req
                subsequent re-auth

      Open      GRAR received with             Send GRAA,   Pending
                Session-Group-Action
                Group-Response-Action          Send
                = PER_GROUP,                   service
                session is assigned to         specific
                received group(s) and          group
                client will perform            re-auth req
                subsequent re-auth             per group

      Open      GRAR received with             Send GRAA,   Pending
                Session-Group-Action
                Group-Response-Action          Send
                = PER_SESSION,                 service
                session is assigned to         specific
                received group(s) and          re-auth req
                client will perform            per session
                subsequent re-auth

      Open      GRAR received and client will  Send GRAA    Idle
                not perform subsequent         with
                re-auth                        Result-Code
                                               != SUCCESS,
                                               Discon.
                                               user/device

      Pending   Successful service-specific    Provide      Open
                group re-authorization answer  service
                received.

      Pending   Failed service-specific        Discon.      Idle
                group re-authorization answer  user/device
                received.

   The following state machine is observed by a server when it is
   maintaining state for the session.  State transitions which are
   unmodified from [RFC6733] are not repeated here.

                                SERVER, STATEFUL
      State     Event                          Action       New State
      ---------------------------------------------------------------

      Idle      Service-specific authorization Send         Open
                request received, and user     successful
                is authorized                  service
                                               specific
                                               answer
                                               optionally
                                               including
                                               groups

      Open      Server wants to terminate      Send GASR    Discon
                group(s)

      Discon    GASA received                  Cleanup      Idle

      Any       GSTR received                  Send GSTA,   Idle
                                               Cleanup

      Open      Server wants to reauth         Send GRAR    Pending
                group(s)

      Pending   GRAA received with Result-Code Update       Open
                = SUCCESS                      session(s)

      Pending   GRAA received with Result-Code Cleanup      Idle
                != SUCCESS                     session(s)

      Open      Service-specific group         Send         Open
                re-authoization request        successful
                received and user is           service
                authorized                     specific
                                               group
                                               re-auth
                                               answer

      Open      Service-specific group         Send         Idle
                re-authorization request       failed
                received and user is           service
                not authorized                 specific
                                               group
                                               re-auth
                                               answer,
                                               cleanup

Authors' Addresses

   Mark Jones

   Email: mark@azu.ca

   Marco Liebsch

   Email: marco.liebsch@neclab.eu

   Lionel Morand

   Email: lionel.morand@orange.com