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Diameter Group Signaling
draft-ietf-dime-group-signaling-14

Document Type Active Internet-Draft (dime WG)
Authors Mark Jones , Marco Liebsch , Lionel Morand
Last updated 2022-08-03
Replaces draft-jones-diameter-group-signaling
Stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
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OPSDIR Last Call Review Incomplete, due 2021-01-25
Stream WG state Submitted to IESG for Publication
Document shepherd Jouni Korhonen
Shepherd write-up Show Last changed 2018-12-28
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draft-ietf-dime-group-signaling-14
Diameter Maintenance and Extensions (DIME)                      M. Jones
Internet-Draft                                                Individual
Intended status: Standards Track                              M. Liebsch
Expires: February 4, 2023                                            NEC
                                                               L. Morand
                                                                  Orange
                                                          August 3, 2022

                        Diameter Group Signaling
                 draft-ietf-dime-group-signaling-14.txt

Abstract

   In large network deployments, a single Diameter node can support over
   a million concurrent Diameter sessions.  In some use cases, Diameter
   nodes need 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 node using a single or a few command exchanges.  This
   document specifies the Diameter protocol extensions to achieve this
   signaling optimization.

Status of 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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 4, 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Protocol Overview . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Building and Modifying Session Groups . . . . . . . . . .   4
     3.2.  Issuing Group Commands  . . . . . . . . . . . . . . . . .   4
     3.3.  Permission Considerations . . . . . . . . . . . . . . . .   5
   4.  Protocol Description  . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Session Grouping Capability Discovery . . . . . . . . . .   5
       4.1.1.  Capability Discovery based on the Application Id  . .   5
       4.1.2.  Capability Discovery based on AVP Presence  . . . . .   6
     4.2.  Session Grouping  . . . . . . . . . . . . . . . . . . . .   6
       4.2.1.  Group assignment at session initiation  . . . . . . .   7
       4.2.2.  Removing a session from a session group . . . . . . .   9
       4.2.3.  Mid-session group assignment modifications  . . . . .  11
     4.3.  Deleting a Session Group  . . . . . . . . . . . . . . . .  12
     4.4.  Performing Group Operations . . . . . . . . . . . . . . .  12
       4.4.1.  Sending Group Commands  . . . . . . . . . . . . . . .  12
       4.4.2.  Receiving Group Commands  . . . . . . . . . . . . . .  13
       4.4.3.  Error Handling for Group Commands . . . . . . . . . .  13
       4.4.4.  Single-Session Fallback . . . . . . . . . . . . . . .  14
   5.  Operation with Proxy Agents . . . . . . . . . . . . . . . . .  14
   6.  Commands Formatting . . . . . . . . . . . . . . . . . . . . .  15
     6.1.  Formatting Example: Group Re-Auth-Request . . . . . . . .  15
   7.  Attribute-Value-Pairs (AVP) . . . . . . . . . . . . . . . . .  16
     7.1.  Session-Group-Info AVP  . . . . . . . . . . . . . . . . .  16
     7.2.  Session-Group-Control-Vector AVP  . . . . . . . . . . . .  17
     7.3.  Session-Group-Id AVP  . . . . . . . . . . . . . . . . . .  17
     7.4.  Group-Response-Action AVP . . . . . . . . . . . . . . . .  18
     7.5.  Session-Group-Capability-Vector AVP . . . . . . . . . . .  18
   8.  Result-Code AVP Values  . . . . . . . . . . . . . . . . . . .  18
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  AVP Codes . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.2.  New Registries  . . . . . . . . . . . . . . . . . . . . .  19
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  19
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   12. Normative References  . . . . . . . . . . . . . . . . . . . .  20

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   Appendix A.  Session Management -- Exemplary Session State
                Machine  . . . . . . . . . . . . . . . . . . . . . .  21
     A.1.  Use of groups for the Authorization Session State Machine  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  25

1.  Introduction

   In large network deployments, a single Diameter node can support over
   a million concurrent Diameter sessions.  In some use cases, Diameter
   nodes need 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 node 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' 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", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP

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   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   This document uses terminology defined in [RFC6733].

3.  Protocol Overview

3.1.  Building and Modifying Session Groups

   In order to accommodate bulk operations on Diameter sessions, the
   concept of session groups is introduced.  Once sessions are added to
   a group, a command acting on the group will affect all the member
   sessions.

   Client and Server can 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 assigned to one or multiple groups.  A single command can be
   issued and applied to all sessions associated with such group(s),
   e.g., to adjust common profile or policy settings.

   The assignment of a Diameter session to a group can be changed during
   an ongoing session (mid-session).  For example, if a user's
   subscription profile changes mid-session, a Diameter server may
   remove a session from an existing group and assign this session to a
   different group that is more appropriate for the new subscription
   profile.

   In the case of mobile users, the user's session may get transferred
   mid-session to a new Diameter client during handover and assigned to
   a different group, which is maintained at the new Diameter client.

   It may be required to delete a session group, e.g. at the expiry of a
   promotional period that applied to multiple subscriber profiles.
   Deletion of such group requires subsequent individual treatment of
   each of the assigned sessions.  A node may decide to assign some of
   these sessions to any other existing or new group.

3.2.  Issuing Group Commands

   Changes in the network condition may result in the Diameter server's
   decision to close all sessions in a given group.  As example, the
   server issues a single Session Termination Request (STR) command,
   including the identifier of the group of sessions which are to be
   terminated.  The Diameter client treats the STR as group command and
   initiates the termination of all sessions associated with the
   identified group.  Subsequently, the client confirms the successful
   termination of these sessions to the server by sending a single

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   Session Termination Answer (STA) command, which includes the
   identifier of the group.

3.3.  Permission Considerations

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

   When a client or a server decides to create a new session group,
   e.g., to group all sessions which share certain characteristics, this
   node builds a session group identifier according to the rules
   described in Section 7.3 and becomes the owner of the group.

   After the creation of a session group, a session can be added to this
   session group by either the client or the server.  However, a session
   can only be removed from a session group by the Diameter node (client
   or server) that has assigned this session to the session group.

   A session group can only be deleted by the owner of the session
   group, resulting in individual treatment of the sessions that were
   assigned to this session group.

   Diameter applications with implicit support for session groups MAY
   define a more constrained permission model.  For example, a more
   constrained model could require that a client must not remove a
   session from a group which is owned by the server.  Details about
   enforcing a more constrained permission model are out of scope of
   this specification.

4.  Protocol Description

4.1.  Session Grouping Capability Discovery

   Diameter nodes SHOULD NOT perform group operations with peer nodes
   unless the node has advertised support for session grouping and group
   operations.

4.1.1.  Capability Discovery based on the Application Id

   Newly defined Diameter applications may natively support Diameter
   session grouping and group operations.  Such applications provide
   intrinsic discovery for the support of session grouping capability
   using the assigned Application Id advertised during the capability
   exchange phase described in Section 5.3 of [RFC6733].

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   System- and deployment-specific means, as well as out-of-band
   mechanisms for capability discovery can be used to announce nodes'
   support for session grouping and session group operations.  In such
   case, the optional Session-Group-Capability-Vector AVP, as described
   in Section 4.1.2 can be omitted in Diameter messages being exchanged
   between nodes.

4.1.2.  Capability Discovery based on AVP Presence

   If no other mechanism for capability discovery is deployed to enable
   Diameter nodes to learn about nodes' capability to support session
   grouping and group commands for a given application, a Diameter node
   SHOULD append the Session-Group-Capability-Vector AVP to any Diameter
   application messages exchanged with the other Diameter nodes to
   announce its capability to support session grouping and session group
   operations for the advertised application.  Implementations following
   the specification as per this document MUST set the
   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 node with the BASE_SESSION_GROUP_CAPABILITY flag
   set, the receiving Diameter node discovers the supported session
   grouping capability of the sending Diameter node for the advertised
   application and MUST cache this information for the lifetime of the
   routing table entry associated with the peer identity/Application Id
   pair (see Section 2.7 of [RFC6733]).

4.2.  Session Grouping

   This specification does not limit the number of session groups to
   which a single session is assigned.  It is left to the implementation
   of an application to determine such limitations.  If an application
   facilitates a session to belong to multiple session groups, the
   application MUST maintain consistency of associated application
   session states for these multiple session groups.

   Either Diameter node (client or server) can initiate 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 mid-session by either Diameter node
   responsible for the session assignment to this group.  Although
   Diameter is a peer-to-peer protocol, Diameter AAA applications
   typically assign the role of a "Diameter client" to the Diameter node
   initiating the Diameter session and the role of "Diameter server" to
   the node authorizing the Diameter session.  This specification does
   not restrict group creation, assignment or deletion actions to a
   specific role.  In the following sections, "Diameter node" is used to

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   refer to either role.  Section 5 describes particularities about
   session grouping and performing group commands when relay agents or
   proxies are deployed.

   Any Diameter node that has advertised support of session grouping and
   group operations MUST store and maintain the group assignment as part
   of the session's state.  A list of all known session groups is
   locally maintained on each node, each group pointing to individual
   sessions being assigned to the group.  Each Diameter node MUST also
   keep a record about sessions that it has assigned to a session group.

4.2.1.  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 AA-Request
   [RFC7155], containing one or more session group identifiers.  Each of
   these groups MUST 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 session groups from a list of
   existing session groups.  Alternatively, the client may decide to
   create a new group to which the session is assigned and identify
   itself in the <DiameterIdentity> portion of the Session-Group-Id AVP
   as per Section 7.3.  For all assignments of a session to an active
   session group made by the client or the server, the
   SESSION_GROUP_STATUS flag in the Session-Group-Info AVP, which
   identifies the session group, MUST be set.  A set
   SESSION_GROUP_STATUS flag indicates that the identified session group
   has just been created or is still active.

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

   The client may also indicate in the request that it supports
   assignment of the session to one or more groups by the server.  In
   such a case, the client MUST include the Session-Group-Info AVP in
   the request including the Session-Group-Control-Vector AVP with the
   SESSION_GROUP_ALLOCATION_ACTION flag set but no Session-Group-Id AVP.

   If the Diameter server receives a command request from a Diameter
   client and the command includes at least one Session-Group-Info AVP
   having the SESSION_GROUP_ALLOCATION_ACTION flag in the Session-Group-
   Control-Vector AVP set, the server can accept or reject the request
   for group assignment.  Reasons for rejection may be e.g., lack of

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   resources for managing additional groups.  When rejected, the session
   MUST NOT be assigned to any session group.

   If the Diameter server accepts the client's request for a group
   assignment, the server MUST assign the new session to each of the one
   or multiple identified session groups when present in the Session-
   Group-Info AVP.  If one or multiple identified session groups are not
   already stored by the server, the server MUST store the newly
   identified group(s) to its local list of known session groups.  When
   sending the response to the client, e.g., a service-specific auth
   response as per NASREQ AA-Answer [RFC7155], 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 assign the new session to
   one or multiple additional groups.  In such a case, the server MUST
   add to the response the additional Session-Group-Info AVPs, each
   identifying a session group to which the new session is assigned by
   the server.  Each of the Session-Group-Info AVP added by the server
   MUST have the SESSION_GROUP_ALLOCATION_ACTION flag set in the
   Session-Group-Control-Vector AVP.

   If the Diameter server rejects the client's request for a group
   assignment, the server sends the response to the client, e.g., a
   service-specific auth response as per NASREQ AA-Answer [RFC7155], and
   MUST include all Session-Group-Info AVPs as received in the client's
   request (if any) while clearing the SESSION_GROUP_ALLOCATION_ACTION
   flag of the Session-Group-Control-Vector AVP.  The server MAY still
   accept the client's request for the identified session to proceed
   despite rejecting the group assignment.  The response sent to the
   client will then indicate success in the result code.  In this case,
   the session is treated as single session without assignment to any
   session group by the Diameter nodes.

   If the assignment of the session to one or some of the multiple
   identified session groups fails, the session group assignment is
   treated as failure.  In such case the session is treated as single
   session without assignment to any session group by the Diameter
   nodes.  The server sends the response to the client and MAY include
   those Session-Group-Info AVPs for which the group assignment failed.
   The SESSION_GROUP_ALLOCATION_ACTION flag of included Session-Group-
   Info AVPs MUST be cleared.

   If the Diameter server receives a command request from a Diameter
   client and the command includes a Session-Group-Info AVP which does
   not include a Session-Group-Id AVP, the server MAY decide to assign
   the session to one or multiple session groups.  For each session
   group, to which the server assigns the new session, the server

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   includes a Session-Group-Info AVP with the Session-Group-Id AVP
   identifying a session group in the response sent to the client.  Each
   of the Session-Group-Info AVPs included by the server MUST have the
   SESSION_GROUP_ALLOCATION_ACTION flag of the Session-Group-Control-
   Vector AVP set.

   If the Diameter server receives a command request from a Diameter
   client and the command does not contain any Session-Group-Info AVP,
   the server MUST NOT assign the new session to any session group but
   treat the request as for a single session.  The server MUST NOT
   return any Session-Group-Info AVP in the command response.

   If the Diameter client receives a response to its previously issued
   request from the server and the response includes at least one
   Session-Group-Info AVP having the SESSION_GROUP_ALLOCATION_ACTION
   flag of the associated 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.  If the Diameter
   client fails to add the session to one or more session groups as
   identified in the one or multiple Session-Group-info AVPs, the client
   MUST terminate the session.  The client MAY send a subsequent request
   for session initiation to the server without requesting the
   assignment of the session to a session group.

   If the Diameter client receives a response to its previously issued
   request from the server and the one or more Session-Group-Info AVPs
   have the SESSION_GROUP_ALLOCATION_ACTION flag of the associated
   Session-Group-Control-Vector AVP cleared, the client MUST terminate
   the assignment of the session to the one or multiple groups.  If the
   response from the server indicates success in the result code but
   only the assignment of the session to a session group has been
   rejected by the server, the client treats the session as single
   session without group assignment.

   If a Diameter client sends a request for session initiation
   containing one or more Session-Group-Info AVPs but the response from
   the Diameter server does not contain a Session-Group-Info AVP, the
   Diameter client MUST proceed as if the request was processed without
   group assignments.  The Diameter client MUST NOT retry to request
   group assignment for this session, but MAY try to request group
   assignment for other new sessions.

4.2.2.  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

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   the session.  The session that 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-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-Id AVP in the re-authorization request
   identifies the session that is to be removed from all groups to which
   it had been previously assigned.

   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 includes 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) or a service-specific server-initiated
   request to the client, indicating the session in the Session-Id AVP
   of the request.  The client sends a Re-Authorization Answer (RAA) or
   a service-specific answer 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.
   If the server decides to remove the identified session from all
   session groups, to which the session has been previously assigned,

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   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-Id AVP absent.

4.2.3.  Mid-session group assignment modifications

   Either Diameter node (client or server) can modify the group
   membership of an active Diameter session according to the 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
   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 assigned.

   When a Diameter server decides to update assigned groups mid-session,
   it sends a Re-Authorization Request (RAR) message or a service-
   specific request 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 or a service-specific answer.
   The client subsequently sends a 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 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

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   is to be removed.  When a server wants to remove the session from all
   previously assigned session groups, it sends at least one Session-
   Group-Info AVP with the response having the
   SESSION_GROUP_ALLOCATION_ACTION flag cleared and no Session-Group-Id
   AVP present.

4.3.  Deleting a Session Group

   To explicitly 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 flag cleared
   and the Session-Group-Id AVP identifying the session group, which is
   to be deleted.  The SESSION_GROUP_ALLOCATION_ACTION flag of the
   associated Session-Group-Control-Vector AVP MUST be cleared.

   A session group is implicitly deleted and its identifier released
   after the last session has been removed from this session group.

4.4.  Performing Group Operations

4.4.1.  Sending Group Commands

   Either Diameter node (client or server) can request the recipient of
   a request to process an associated command for all sessions 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 flag MUST be set.

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

   The sender of the request MUST indicate to the receiver how multiple
   resulting transactions associated with a group command are to be
   treated by appending a single instance of a Group-Response-Action
   AVP.  For example, when a server sends a Re-Authorization Request
   (RAR) or a service-specific server-initiated request to the client,
   it indicates to the client to follow the request according to one of
   three possible procedures.  When the server sets the Group-Response-
   Action AVP to ALL_GROUPS (1), the client sends a single RAR message
   for all identified groups.  When the server sets the Group-Response-
   Action AVP to PER_GROUP (2), the client sends a single RAR message
   for each identified group individually.  When the server sets the
   Group-Response-Action AVP to PER_SESSION (3), the client follows-up

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   with a single RAR message per impacted session.  If a session is
   included in more than one of the identified session groups, the
   client sends only one RAR message for that session.

   If the sender sends a request including the Group-Response-Action AVP
   set to ALL_GROUPS (1) or PER_GROUP (2), it has to expect some delay
   before receiving the corresponding answer(s) as the answer(s) will
   only be sent back when the request is processed for all the sessions
   or all the session of a session group.  If the processing of the
   request is delay-sensitive, the sender SHOULD NOT set the Group-
   Response-Action AVP to ALL_GROUPS (1) or PER_GROUP (2).  If the
   answer can be sent before the complete process of the request for all
   the sessions or if the request timeout timer is high enough, the
   sender MAY set the Group-Response-Action AVP to ALL_GROUPS (1) or
   PER_GROUP (2).

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

4.4.2.  Receiving Group Commands

   A Diameter node receiving a request to process a command for a group
   of sessions, identifies the relevant groups according to the included
   Session-Group-Id AVP in the Session-Group-Info AVP and processes the
   group command according to the included Group-Response-Action AVP.
   If the received request identifies multiple groups in multiple
   included 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.

4.4.3.  Error Handling for Group Commands

   When a Diameter node 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 deleted according to the
   procedure described in Section 4.3.

   When a Diameter node 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

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   the response message SHOULD indicate DIAMETER_LIMITED_SUCCESS as per
   Section 7.1.2 of [RFC6733].

   In the case of limited success, the sessions, for which the
   processing of the group command failed, MUST be identified by
   including their Session-Id AVP in the Failed-AVP AVP as per
   Section 7.5 of [RFC6733].  The sender of the request MUST fall back
   to single-session operation for each of the identified sessions, for
   which the group command failed.  In addition, each of these sessions
   MUST be removed from all session groups to which the group command
   applied.  To remove sessions from a session group, the Diameter
   client performs the procedure described in Section 4.2.2.

4.4.4.  Single-Session Fallback

   Either Diameter node 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.  In such case, 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 Proxy Agents

   In the case of a present stateful Proxy Agent between a Diameter
   client and a Diameter server, the Proxy Agent MUST perform the same
   mechanisms per this specification to advertise session grouping and
   group operations capability towards the client and the server
   respectively.  The Proxy MUST update and maintain consistency of its
   local session states as per the result of the group commands which
   are operated between a Diameter client and a server.  In such case,
   the Proxy Agent MUST act as a Diameter server in front of the
   Diameter client and MUST act as a Diameter client in front of the
   Diameter server.  Therefore, the client and server behavior described
   in Section 4 applies respectively to the stateful Proxy Agent.

   If a stateful Proxy Agent manipulates session groups, it MUST
   maintain consistency of session groups between a client and a server.
   This applies to a deployment where the Proxy Agent utilizes session
   grouping and performs group operations with, for example, a Diameter
   server, whereas the Diameter client is not aware of session groups.
   In such case the Proxy Agent must reflect the states associated with
   the session groups as individual session operations towards the
   client and ensure the client has a consistent view of each session.
   The same applies to a deployment where all nodes, the Diameter client
   and server, as well as the Proxy Agent are group-aware but the Proxy

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   Agent manipulates groups, e.g., to adopt different administrative
   policies that apply to the client's domain and the server's domain.

   Stateless Proxy Agents do not maintain any session state (only
   transaction state are maintained).  Consequently, the notion of
   session group is transparent for any stateless Proxy Agent present
   between a Diameter client and a Diameter server handling session
   groups.  Session group related AVPs being defined as optional AVP are
   ignored by stateless Proxy Agents and should not be removed from the
   Diameter commands.  If they are removed by the Proxy Agent for any
   reason, the Diameter client and Diameter server will discover the
   absence the related session group AVPs and will fall back to single-
   session processing, as described in Section 4.

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 applying the command to all
   sessions associated with the identified group(s).

6.1.  Formatting Example: Group Re-Auth-Request

   A request for re-authentication of one or more groups of users is
   issued by appending one or multiple Session-Group-Id AVP(s), as well
   as a single instance of a Group-Response-Action AVP to the Re-Auth-
   Request (RAR).  The one or multiple Session-Group-Id AVP(s) identify
   the associated group(s) for which the group 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 request appends a 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.

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         <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-Info ]
                    [ 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-Control-Vector    TBD2 Unsigned32  |    | P |      | V  |
|Session-Group-Id                TBD3 UTF8String  |    | P |      | V  |
|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-Control-Vector >
                             [ Session-Group-Id ]
                           * [ AVP ]

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7.2.  Session-Group-Control-Vector AVP

   The Session-Group-Control-Vector AVP (AVP Code TBD2) is of type
   Unsigned32 and contains a 32-bit flags field to control the group
   assignment at session-group aware nodes.  For defined flags only
   numeric values that are 2^x (power of two, where 0<=x<32) are
   allowed.

   The following control flags 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 assigned to the session group as
      identified by the Session-Group-Id AVP or the session's 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 (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 deleted
      and the associated Session-Group-Id is released.  If the Session-
      Group-Info AVP does not include 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 unique.  The Session-Group-Id
   includes a mandatory portion and an implementation-defined portion
   delimited by the ";" character.  The Session-Group-Id MUST begin with
   the identity of the Diameter node that owns the session group.  The
   remainder of the Session-Group-Id is implementation-defined and MAY

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   follow the format recommended for the implementation-defined portion
   of the Session-Id AVP in section 8.8 of [RFC6733].

7.4.  Group-Response-Action AVP

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

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

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

   PER_SESSION (3)
      Follow up message exchanges associated with a group command should
      be performed with a separate 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.  For
   defined flags only numeric values that are 2^x (power of two, where
   0<=x<32) are allowed.  The value of (0) is reserved.

   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.

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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-Control-Vector

   o  Session-Group-Id

   o  Group-Response-Action

   o  Session-Group-Capability-Vector

   The AVPs are defined in Section 7.

9.2.  New Registries

   This specification requires IANA to create two registries:

   o  Session-Group-Control-Vector AVP registry for control bits with
      two initial assignments, which are described in Section 7.2.  The
      future registration assignment policy is proposed to be
      Specification Required.

   o  Session-Group-Capability-Vector AVP with one initial assignment,
      which is described in Section 7.5.  The future registration
      assignment policy is proposed to be Standards Action.

   The AVP names can be used as registry names.

10.  Security Considerations

   The security considerations of the Diameter protocol itself are
   discussed in [RFC6733].  Use of the AVPs defined in this document
   MUST take into consideration the security issues and requirements of
   the Diameter base protocol.  In particular, the Session-Group-Info
   AVP (including the Session-Group-Control-Vector and the Session-
   Group-Id AVPs) should be considered as a security-sensitive AVPs in
   the same manner than the Session-Id AVP in the Diameter base protocol
   [RFC6733].

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   The management of session groups relies upon the existing trust
   relationship between the Diameter client and the Diameter server
   managing the groups of sessions.  This document defines a mechanism
   that allows a client or a server to act on multiple sessions at the
   same time using only one command.  If the Diameter client or server
   is compromised, an attacker could launch DoS attacks by terminating
   or applying change operations to a large number of sessions with a
   limited set of commands using the session group management concept.

   According to the Diameter base protocol [RFC6733], transport
   connections between Diameter peers are protected by TLS/TCP, DTLS/
   SCTP or alternative security mechanisms that are independent of
   Diameter, such as IPsec.  However, the lack of end-to-end security
   features makes it difficult to establish trust in the session group
   related information received from non-adjacent nodes.  Any Diameter
   agent in the message path can potentially modify the content of the
   message and therefore the information sent by the Diameter client or
   the server.  There is ongoing work on the specification of end-to-end
   security features for Diameter.  Such features would enable the
   establishment of trust relationship between non-adjacent nodes and
   the security required for session group management would normally
   rely on this end-to-end security.  However, there is no assumption in
   this document that such end-to-end security mechanism will be
   available.  It is only assumed that the solution defined on this
   document relies on the security framework provided by the Diameter
   based protocol.

   In some cases, a Diameter Proxy agent can act on behalf of a client
   or server.  In such a case, the security requirements that normally
   apply to a client (or a server) apply equally to the Proxy agent.

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.
   Furthermore, authors thank Steve Donovan and Mark Bales for the
   thorough review and comments on advanced versions of the WG document,
   which helped a lot to improve this specification.

12.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC6733]  Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
              Ed., "Diameter Base Protocol", RFC 6733,
              DOI 10.17487/RFC6733, October 2012,
              <https://www.rfc-editor.org/info/rfc6733>.

   [RFC7155]  Zorn, G., Ed., "Diameter Network Access Server
              Application", RFC 7155, DOI 10.17487/RFC7155, April 2014,
              <https://www.rfc-editor.org/info/rfc7155>.

Appendix A.  Session Management -- Exemplary Session State Machine

A.1.  Use of groups for the 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, as example, additional state
   transitions related to the processing of the group 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.

   The Diameter group command in the following tables is differentiated
   from a single-session related command by a preceding 'G' (Group).  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

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                                               auth req
                                               optionally
                                               including
                                               groups

      Open      GASR received with             Send GASA    Discon
                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
                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
                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
                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
                Group-Response-Action          Send
                = PER_GROUP,                   service
                session is assigned to         specific

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                received group(s) and          group
                client will perform            re-auth req
                subsequent re-auth             per group

      Open      GRAR received with             Send GRAA,   Pending
                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.

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                                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

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Authors' Addresses

   Mark Jones
   Individual

   Email: mark@azu.ca

   Marco Liebsch
   NEC Laboratories Europe GmbH
   Kurfuersten-Anlage 36
   D-69115 Heidelberg
   Germany

   Email: marco.liebsch@neclab.eu

   Lionel Morand
   Orange Labs
   38/40 rue du General Leclerc
   Issy-Les-Moulineaux Cedex 9  92794
   France

   Email: lionel.morand@orange.com

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