Internet Engineering Task Force (IETF) M. Jones

Internet Engineering Task Force (IETF) M. Jones
Request for Comments: 9390 Individual
Category: Standards Track M. Liebsch
ISSN: 2070-1721 NEC
L. Morand
Orange
April 2023

Diameter Group Signaling

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 can result in many thousands
of command exchanges enforcing the same operation on each session in
the group. In order to reduce signaling, it is 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 is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9390.

Copyright Notice

Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.

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in the Revised BSD License.

Table of Contents

1. Introduction
2. Terminology
3. Protocol Overview
3.1. Building and Modifying Session Groups
3.2. Issuing Group Commands
3.3. Permission Considerations
4. Protocol Description
4.1. Session Grouping Capability Discovery
4.1.1. Capability Discovery Based on the Application Id
4.1.2. Capability Discovery Based on AVP Presence
4.2. Session Grouping
4.2.1. Group Assignment at Session Initiation
4.2.2. Removing a Session from a Session Group
4.2.3. Mid-session Group Assignment Modifications
4.3. Deleting a Session Group
4.4. Performing Group Operations
4.4.1. Sending Group Commands
4.4.2. Receiving Group Commands
4.4.3. Error Handling for Group Commands
4.4.4. Single-Session Fallback
5. Operation with Proxy Agents
6. Commands Formatting
6.1. Formatting Example: Group Re-Auth-Request
7. Attribute-Value Pairs (AVPs)
7.1. Session-Group-Info AVP
7.2. Session-Group-Control-Vector AVP
7.3. Session-Group-Id AVP
7.4. Group-Response-Action AVP
7.5. Session-Group-Capability-Vector AVP
8. Result-Code AVP Values
9. IANA Considerations
9.1. AVP Codes
9.2. New Registries
10. Security Considerations
11. Normative References
Appendix A. Session Management -- Exemplary Session State Machine
A.1. Use of Groups for the Authorization Session State Machine
Acknowledgments
Authors' Addresses

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 can result in
many thousands of command exchanges enforcing the same operation on
each session in the group. In order to reduce signaling, it is
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 Attribute-Value Pairs
(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:

* minimal impact to existing applications

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

* fallback to single-session operation

* 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
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.

The client and the 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 one or more such groups, 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. For example, the
server issues a single Session Termination Request (STR) command,
including the identifier of the group of sessions that are to be
terminated. The Diameter client treats the STR as a 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
Session Termination Answer (STA) command, which includes the
identifier of the group.

3.3. Permission Considerations

Permission considerations in the context of this document 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 server decides to create a new session group, e.g.,
to group all sessions that 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 not remove a session
from a group that 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 intrinsically support
Diameter session grouping and group operations. In these cases,
there is no need of a specific discovery mechanism for the support of
session grouping capability besides the discovery of the Application
Id assigned to the application advertised during the capability
exchange phase described in Section 5.3 of [RFC6733].

System-specific 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 Authentication,
Authorization, and Accounting (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
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, with 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., Network Access Server
Requirements (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 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
with 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
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 (one or
more) of the 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 one or more
newly identified groups to its local list of known session groups.
When sending the response to the client, e.g., a service-specific
authorization response, as per NASREQ AA-Answer [RFC7155], the server
MUST include all Session-Group-Info AVPs 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 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 AVPs 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 authorization response, as per NASREQ AA-Answer
[RFC7155], and MUST include all Session-Group-Info AVPs 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 a 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 a failure. In such case, the session is treated as a
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 that 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
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 AVPs,
the server MUST NOT assign the new session to any session group but
treat the request the same 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 with 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 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 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 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 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 a 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
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 that 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 that 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 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-Auth-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-Auth-Answer (RAA) or a service-
specific answer to respond to the server's request. The client
subsequently sends a 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 authorization
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 with the service-
specific authorization 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, the server includes in the service-specific authorization
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 AVPs 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 authorization 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-Auth-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-Auth-
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
authorization response and includes 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
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 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 with the SESSION_GROUP_STATUS flag cleared and
the Session-Group-Id AVP identifying the session group that 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 is 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 and 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 that
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-Auth-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 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 one or more corresponding answers, as the answers
will only be sent back when the request is processed for all the
sessions or all the sessions 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 for a single session, the sender does not append
any group identifier; it identifies only 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 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 include any group identifier but only the Session-Id identifying
the 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 operation capabilities towards the client and the server,
respectively. The Proxy Agent MUST update and maintain consistency
of its local session states as per the result of the group commands
that 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 the 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
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 states (only
transaction states are maintained). Consequently, the notion of a
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 an 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 of the session-group-related 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 and 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 apply the
command to all sessions associated with the identified group or
groups.

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 AVPs, as well as
appending a single instance of a Group-Response-Action AVP to the Re-
Auth-Request (RAR). One or multiple Session-Group-Id AVPs identify
one or more associated groups for which 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 or groups. 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.

<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 (AVPs)

+=================================+==========+====================+
| Attribute Name |AVP Code |AVP Flag rules |
+=================================+Value Type+====+===+======+====+
| | |MUST|MAY|SHOULD|MUST|
| | | | |NOT |NOT |
+=================================+==========+====+===+======+====+
| Session-Group-Info |671 | |P | |V |
| |Grouped | | | | |
+---------------------------------+----------+----+---+------+----+
| Session-Group-Control-Vector |672 | |P | |V |
| |Unsigned32| | | | |
+---------------------------------+----------+----+---+------+----+
| Session-Group-Id |673 | |P | |V |
| |UTF8String| | | | |
+---------------------------------+----------+----+---+------+----+
| Group-Response-Action |674 | |P | |V |
| |Unsigned32| | | | |
+---------------------------------+----------+----+---+------+----+
| Session-Group-Capability-Vector |675 | |P | |V |
| |Unsigned32| | | | |
+---------------------------------+----------+----+---+------+----+

Table 1: AVPs for the Diameter Group Signaling

7.1. Session-Group-Info AVP

The Session-Group-Info AVP (AVP Code 671) 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: 671 >
< Session-Group-Control-Vector >
[ Session-Group-Id ]
* [ AVP ]

7.2. Session-Group-Control-Vector AVP

The Session-Group-Control-Vector AVP (AVP Code 672) is of type
Unsigned32 and contains a 32-bit flag 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 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 673) 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
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 674) 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 that 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 675) is of type
Unsigned32 and contains a 32-bit flag 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 capability is 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.
Documents specifying 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

IANA has registered the following new AVPs from the "AVP Codes"
registry defined in [RFC6733]. The AVPs are defined in Section 7.

* Session-Group-Info

* Session-Group-Control-Vector

* Session-Group-Id

* Group-Response-Action

* Session-Group-Capability-Vector

9.2. New Registries

IANA has created the following two new registries.

* The "Session-Group-Control-Vector AVP Values (code 672)" registry
for control bits. Two initial assignments are described in
Section 7.2. The registration assignment policy is Specification
Required.

* The "Session-Group-Capability-Vector AVP Values (code 675)"
registry. One initial assignment is described in Section 7.5.
The registration assignment policy is Standards Action.

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 AVP in
the same manner as the Session-Id AVP in the Diameter base protocol
[RFC6733].

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 /
Stream Control Transmission Protocol (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 a 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 a server. In such case, the security requirements that normally
apply to a client (or a server) apply equally to the Proxy Agent.

11. 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>.

[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>.

[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>.

Appendix A. Session Management -- Exemplary Session State Machine

A.1. Use of Groups for the Authorization Session State Machine

Section 8.1 of [RFC6733] defines a set of finite state machines that
represent the life cycle of Diameter sessions, 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, for example, additional state transitions related to the
processing of the group commands that may impact multiple sessions.

The group membership is a 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 or NASREQ).

The following state machine is observed by a client when the state is
maintained on the server. State transitions that 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].

Additionally, the following acronyms are used in the tables below.

GASR: Group-Abort-Session-Request

GASA: Group-Abort-Session-Answer

GSTA: Group-Session-Termination-Answer

GSTR: Group-Session-Termination-Request

+=================================================================+
| CLIENT, STATEFUL |
+=========+==========================+==================+=========+
| State | Event | Action | New |
| | | | State |
+=========+==========================+==================+=========+
| Idle | Client or Device | Send service- | Pending |
| | Requests access | specific | |
| | | authorization | |
| | | req optionally | |
| | | including groups | |
+---------+--------------------------+------------------+---------+
| Open | GASR received with | Send GASA | Discon |
| | Group-Response-Action = | Result-Code = | |
| | ALL_GROUPS, session is | SUCCESS, Send | |
| | assigned to received | GSTR | |
| | group(s) and client will | | |
| | comply with request to | | |
| | end the session | | |
+---------+--------------------------+------------------+---------+
| Open | GASR received with | Send GASA with | Discon |
| | Group-Response-Action = | Result-Code = | |
| | PER_GROUPS, session is | SUCCESS, Send | |
| | assigned to received | GSTR per group | |
| | group(s) and client will | | |
| | comply with request to | | |
| | end the session | | |
+---------+--------------------------+------------------+---------+
| Open | GASR received with | Send GASA with | Discon |
| | Group-Response-Action = | Result-Code = | |
| | PER_SESSION, session is | SUCCESS, Send | |
| | assigned to received | STR per session | |
| | group(s) and client will | | |
| | comply with request to | | |
| | end the session | | |
+---------+--------------------------+------------------+---------+
| Open | GASR received, client | Send GASA with | Open |
| | will not comply with | Result-Code != | |
| | request to end all | SUCCESS | |
| | sessions in received | | |
| | group(s) | | |
+---------+--------------------------+------------------+---------+
| Discon | GSTA received | Discon. user/ | Idle |
| | | device | |
+---------+--------------------------+------------------+---------+
| Open | GRAR received with | Send GRAA, Send | Pending |
| | Group-Response-Action = | service-specific | |
| | ALL_GROUPS, session is | group re-auth | |
| | assigned to received | req | |
| | group(s) and client will | | |
| | perform subsequent re- | | |
| | auth | | |
+---------+--------------------------+------------------+---------+
| Open | GRAR received with | Send GRAA, Send | Pending |
| | Group-Response-Action = | service-specific | |
| | PER_GROUP, session is | group re-auth | |
| | assigned to received | req per group | |
| | group(s) and client will | | |
| | perform subsequent re- | | |
| | auth | | |
+---------+--------------------------+------------------+---------+
| Open | GRAR received with | Send GRAA, Send | Pending |
| | Group-Response-Action = | service-specific | |
| | PER_SESSION, session is | re-auth req per | |
| | assigned to received | session | |
| | group(s) and client will | | |
| | perform subsequent re- | | |
| | auth | | |
+---------+--------------------------+------------------+---------+
| Open | GRAR received and client | Send GRAA with | Idle |
| | will not perform | Result-Code != | |
| | subsequent re-auth | SUCCESS, Discon. | |
| | | user/device | |
+---------+--------------------------+------------------+---------+
| Pending | Successful service- | Provide service | Open |
| | specific group re- | | |
| | authorization answer | | |
| | received | | |
+---------+--------------------------+------------------+---------+
| Pending | Failed service-specific | Discon. user/ | Idle |
| | group re-authorization | device | |
| | answer received | | |
+---------+--------------------------+------------------+---------+

Table 2: Group Authorization Session State Machine for Stateful
Client

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

+================================================================+
| SERVER, STATEFUL |
+=========+========================+===================+=========+
| State | Event | Action | New |
| | | | State |
+=========+========================+===================+=========+
| Idle | Service-specific | Send successful | Open |
| | authorization request | service-specific | |
| | received, and user is | answer optionally | |
| | authorized | including groups | |
+---------+------------------------+-------------------+---------+
| Open | Server wants to | Send GASR | Discon |
| | terminate 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 | Update session(s) | Open |
| | Result-Code = SUCCESS | | |
+---------+------------------------+-------------------+---------+
| Pending | GRAA received with | Cleanup | Idle |
| | Result-Code != SUCCESS | session(s) | |
+---------+------------------------+-------------------+---------+
| Open | Service-specific group | Send successful | Open |
| | re-authorization | service-specific | |
| | request received and | group re-auth | |
| | user is authorized | answer | |
+---------+------------------------+-------------------+---------+
| Open | Service-specific group | Send failed | Idle |
| | re-authorization | service-specific | |
| | request received and | group re-auth | |
| | user is not authorized | answer, Cleanup | |
+---------+------------------------+-------------------+---------+

Table 3: Group Authorization Session State Machine for
Stateful Server

Acknowledgments

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

Authors' Addresses

Mark Jones
Individual
Email: [email protected]

Marco Liebsch
NEC Laboratories Europe GmbH
Kurfuersten-Anlage 36
D-69115 Heidelberg
Germany
Email: [email protected]

Lionel Morand
Orange Labs
38/40 rue du General Leclerc
92794 Issy-Les-Moulineaux Cedex 9
France
Email: [email protected]