6 SWd Description

29.2733GPP3GPP EPS AAA interfacesEvolved Packet System (EPS)Release 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

6.1 Functionality

6.1.1 General

The SWd reference point connects the 3GPP AAA Proxy and the 3GPP AAA Server. The functionality of the SWd reference point is to transport authentication, authorization and related information in AAA messages including:

– Carrying data for authentication signalling between 3GPP AAA Proxy and 3GPP AAA Server;

– Carrying data for authorization signalling between 3GPP AAA Proxy and 3GPP AAA Server

– Carrying charging signalling per user;

– Carrying keying data for the purpose of radio interface integrity protection and encryption;

– Carrying authentication data for the purpose of tunnel establishment, tunnel data authentication and encryption, for the case in which the ePDG is in the VPLMN;

– Carrying mapping of a user identifier and a tunnel identifier sent from the ePDG to the 3GPP AAA Proxy through the 3GPP AAA Server;

– Used for purging a user from the access network for immediate service termination;

– Enabling the identification of the operator networks amongst which the roaming occurs;

– If QoS mechanisms are applied: carrying data for AN QoS capabilities/policies (e.g. the supported 3GPP QoS profiles) within authentication request from 3GPP AAA Proxy to 3GPP AAA Server.

– Carrying the IP Mobility Capabilities between 3GPP AAA Proxy and 3GPP AAA Server.

6.1.2 Procedures Description

6.1.2.1 Trusted non-3GPP Access / Access Gateway related procedures

6.1.2.1.1 Trusted Non-3GPP Access Authentication and Authorization

When used in connection with the STa interface, the SWd interface shall support the trusted non-3GPP access authentication and authorization procedure defined in clause 5.1.2.1. For this procedure, the 3GPP AAA Proxy shall forward the Diameter commands received from the 3GPP AAA Server and the trusted non-3GPP access network as a stateful Diameter proxy, with the following exceptions:

– The 3GPP AAA Proxy may reject an authentication and authorization request, if roaming is not allowed for the users of the given HPLMN.

– When forwarding an authentication and authorization request, the 3GPP AAA Proxy shall check the presence and value of the visited network identifier. If the AVP was missing, it shall insert it, if the AVP was present, it may overwrite the AVP value before forwarding the request.

– The 3GPP AAA Proxy may modify the service authorization information in the authentication and authorization answer that it forwards to the trusted non-3GPP access network, in order to enforce the QoS limitations according to the local policies and the roaming agreement with the home operator.

– The 3GPP AAA Proxy may decide about the trustworthiness of the non-3GPP access from the VPLMN point of view and insert a trust relationship indicator to the authentication and authorization request.

– If it supports the ER server functionality, the 3GPP AAA Proxy may decide about the use of ERP for re-authentication and indicate its willingness to act as the ER server for this session into the first authentication and authorization request forwarded to the 3GPP AAA server.

The 3GPP AAA Proxy shall decide about using the S2a-PMIP based S8 chaining and in case it has selected that option, it shall select the Serving GW to be invoked and it shall add the Serving GW address to the authentication and authorization answer that is sent upon successful completion of the authentication.

Table 6.1.2.1.1/1 describes the trusted non-3GPP access authentication and authorization request forwarded on the SWd interface.

Table 6.1.2.1.1-1: Trusted non-3GPP Access Authentication and Authorization Request on SWd

Information element name	Mapping to Diameter AVP	Cat.	Description
User Identity	User-Name	M	This information element shall contain the identity of the user. The identity shall be represented in NAI form as specified in IETF RFC 4282 [15] and shall be formatted as defined in clause 19 of 3GPP TS 23.003 [14]. This IE shall include the leading digit used to differentiate between authentication schemes.
EAP payload	EAP-payload	M	This IE shall contain the Encapsulated EAP payload used for the UE – 3GPP AAA Server mutual authentication
Authentication Request Type	Auth-Request-Type	M	This IE shall define whether the user is to be authenticated only, authorized only or both. AUTHORIZE_AUTHENTICATE shall be used in this case.
UE Layer-2 address	Calling-Station-ID	M	This IE shall contain the Layer-2 address of the UE.
Supported 3GPP QoS profile	QoS-Capability	O	If the trusted non-3GPP Access supports QoS mechanisms, this information element may be included to contain the access network’s QoS capabilities as defined in IETF RFC 5777 [9].
Mobility Capabilities	MIP6-Feature-Vector	C	This information element shall contain the mobility capabilities of the trusted non-3GPP access network, if dynamic mobility mode selection is done. This information may also be used to decide whether to authorize access to EPC to a user accessing a TWAN. The PMIP6_SUPPORTED flag and/or the GTPv2_SUPPORTED flag shall be set if the trusted non-3GPP access network supports PMIPv6 and/or GTPv2. PMIP6_SUPPORTED flag is defined in IETF RFC 5779 [2]. The flag MIP6_INTEGRATED shall be set if DHCPv6 based Home Agent address discovery is supported as defined in IETF RFC 5447 [6]. The MIP4_SUPPORTED flag shall be set if the trusted non-3GPP access supports MIPv4 FA-CoA mode.
Access Type	RAT-Type	M	This IE shall contain the trusted non-3GPP access network technology type that is serving the UE.
Access Network Identity	ANID	M	This IE shall contain the access network identifier used for key derivation at the HSS. (See 3GPP TS 24.302 [26] for all possible values)
Visited Network Identifier	Visited-Network-Identifier	M	This IE shall contain the Identifier that allows the home network to identify the Visited Network.
Full Name for Network	Full-Network-Name	O	This IE shall contain the full name for network as specified in 3GPP TS 24.302 [26]. This AVP may be inserted by the non-3GPP access network depending on its local policy and only when it is not connected to the UE’s Home Network. If the Visited Network Identifier is present, this AVP shall be set.
Short Name for Network	Short-Network-Name	O	This IE shall contain the short name for network as specified in 3GPP TS 24.302 [26]. This AVP may be inserted by the non-3GPP access network depending on its local policy and only when it is not connected to the UE’s Home Network. If the Visited Network Identifier is present, this AVP shall be set.
APN Id	Service-Selection	O	If present, this information element shall contain the Network Identifier part of the APN the user wants to connect to (if available).
Terminal Information	Terminal-Information	O	If present, this information element shall contain information about the user’s mobile equipment. The type of identity carried depends on the access technology type. For HRPD access network, the 3GPP2‑MEID AVP shall be included in this grouped AVP.
Trust Relationship Indicator	AN-Trusted	O	If present, This AVP shall express the trusted/untrusted decision about the non-3GPP IP access, from the VPLMN’s point of view. The value "TRUSTED" shall be used in this case.
Selected Trusted WLAN Identifier	WLAN-Identifier	O	If present, this IE shall contain the Trusted WLAN Identifier selected by the UE to access the Trusted WLAN Access Network (see clause 16 of 3GPP TS 23.402 [3]).
DER Flags	DER-Flags	O	This Information Element contains a bit mask. See 5.2.3.20 for the meaning of the bits.
Transport Access Type	Transport-Access-Type	C	For interworking with Fixed Broadband access networks (see 3GPP TS 23.139 [39]), if the access network needs to receive the IMSI of the UE in the authentication response, then this information element shall be present, and it shall contain the value "BBF" (see clause 5.2.3.19).
Supported TWAN Connection Modes	TWAN-Connection-Mode	O	The TWAN should include this IE. If present, this information element shall contain the TWAN connection modes supported by the TWAN, i.e.TSCM, SCM and/or MCM.
Provided Connectivity Parameters	TWAN-Connectivity-Parameters	C	This information element shall be present if the 3GPP AAA Server has previously authorized the SCM to be used for EPC access. TWAN-Connectivity-Parameters is a grouped AVP. If the requested connectivity has been granted, the following information elements shall be included: – selected APN – selected PDN type – UE IPv4 Address (for PDN type IPv4 or IPv4v6) – UE IPv6 Interface Identifier (for PDN type IPv6 or IPv4v6) – Protocol Configuration Options (if received from the PGW) – TWAG user plane MAC address The absence of both an IPv4 address and an IPv6 Interface Identifier indicates that the requested connectivity could not be granted. If the requested connectivity has not been granted, the following information elements may be included: – a cause indicating why the requested connectivity has not been granted
TWAG Control Plane IP Address	TWAG-CP-Address	C	The TWAN shall include this IE if it indicates support of the MCM in the Supported TWAN Connection Modes IE. When present, this IE shall contain the TWAG Control Plane IPv4 Address, or the TWAG Control Plane IPv6 link local address, or both (if the TWAG supports IPv4 and IPv6), to be used for WLCP by the UE if the MCM is used.
Domain-Specific Re-authentication Key Request	ERP-RK-Request	O	If present, this IE indicates the willingness of an ER server in the non-3GPP access network or the 3GPP AAA proxy to act as the ER server for this session. When present, this IE shall contain the name of the realm in which the ER server is located.

NOTE: For more details on the 3GPP AAA Proxy behaviour, refer to clause 5.1.2.1.3.

6.1.2.1.2 HSS/AAA Initiated Detach for Trusted non-3GPP Access

When used in connection with the STa interface, the SWd interface shall support the HSS initiated detach procedure defined in clause 5.1.2.2.

For this procedure, the 3GPP AAA Proxy shall forward the Diameter commands received from the 3GPP AAA Server and the access network GW as a stateful Diameter proxy.

6.1.2.1.3 Access and Service Authorization information update

When used in connection with the STa interface, the SWd interface shall support the trusted non-3GPP access and service authorization information update procedure defined in clause 5.1.2.3. For this procedure, the 3GPP AAA Proxy shall forward the Diameter commands received from the 3GPP AAA Server and the trusted non-3GPP access network as a stateful Diameter proxy, with the following exceptions:

Table 6.1.2.1.3/1 describes the trusted non-3GPP access authorization request forwarded on the SWd interface. As the content is very similar to that of the request received on the STa interface, only those AVPs are listed that are handled differently on the two interfaces.

Table 6.1.2.1.3/1: Trusted Non-3GPP Access Authorization Request on SWd interface

Information element name	Mapping to Diameter AVP	Cat.	Description
Permanent User Identity	User-Name	M	This information element shall contain the permanent identity of the user. The identity shall be represented in NAI form as specified in IETF RFC 4282 [15] and shall be formatted as defined in clause 19 of 3GPP TS 23.003 [14]; this IE shall not include the leading digit prepended in front of the IMSI used to differentiate between authentication schemes.
Request-Type	Auth-Req-Type	M	This IE shall contain the Authorization Request Type. The following values only shall be used: AUTHORIZE_ONLY This value shall indicate the initial request for authorization of the user to the APN.
Visited Network Identifier	Visited-Network-Identifier	M	This IE shall contain an identifier that allows the home network to identify the Visited Network.
Routing Information	Destination-Host	M	This IE shall contain the 3GPP AAA Server name that is obtained from the Origin-Host AVP of a previously received message.
Supported 3GPP QoS profile	QoS-Capability	O	If the trusted non-3GPP Access supports QoS mechanisms, this information element may be included to contain the access network’s QoS capabilities as defined in IETF RFC 5777 [9].
Access Type	RAT-Type	O	If present, this IE contain the trusted non-3GPP access network access technology type that is serving the UE.

NOTE: For more details on the 3GPP AAA Proxy behaviour, refer to clause 5.1.2.3.3.

6.1.2.1.4 Trusted non-3GPP Access Network Initiated Session Termination

When used in connection with the STa reference point, the SWd reference point shall support the access network initiated session termination procedures as defined in clause 5.1.2.4

For this procedure, the 3GPP AAA Proxy shall forward the Diameter commands received from the 3GPP AAA Server and the access network gateway as a stateful Diameter proxy.

6.1.2.2 Untrusted non-3GPP Access / ePDG related procedures

When used in connection with the SWm reference point, the SWd reference point shall support the following procedures:

– Authentication procedures as defined in clause 7.1.2.1

– Authorization procedures as defined in clause 7.1.2.2

– Access network/ePDG initiated session termination procedures as defined in clause 7.1.2.3

– HSS/AAA initiated detach procedures as defined in clause 7.1.2.4

– Service authorization information update procedures as defined in clause 7.1.2.5

For all these procedures, the 3GPP AAA Proxy shall forward the Diameter commands received from the 3GPP AAA Server and the ePDG as a stateful Diameter proxy, with the following exceptions:

– The 3GPP AAA Proxy may reject an authentication or an authorization request, if roaming is not allowed for the users of the given HPLMN.

– The 3GPP AAA Proxy may modify the service authorization information in the authorization answer that it forwards to the ePDG, in order to enforce the QoS limitations according to the local policies and the roaming agreement with the home operator.

– The 3GPP AAA Proxy shall decide about using the S8-S2b chaining and in case it has selected that option, it shall select the Serving GW to be invoked and it shall add the Serving GW address to the authentication answer that is sent upon successful completion of the authentication.

NOTE: For more detailed behavior of the 3GPP AAA Proxy, refer to clauses 7.1.2.1.3 and 7.1.2.2.3 respectively.

When used in connection with the SWa interface point, the SWd reference point shall support the following procedures:

– Authentication and authorization procedure as defined in clause 4.1.2.1

– HSS/AAA initiated detach procedures as defined in clause 4.1.2.2

– Untrusted non-3GPP access network initiated detach procedures as defined in clause 4.1.2.3

– Re-Authentication and Re-Authorization Procedure as defined in clause 4.1.2.4

For all these procedures, the 3GPP AAA Proxy shall forward the Diameter commands received from the 3GPP AAA Server and the untrusted non-3GPP access network as a stateful Diameter proxy, with the following exceptions:

– The 3GPP AAA Proxy may reject an authentication and authorization request, if roaming is not allowed for the users of the given HPLMN.

– When forwarding an authentication and authorization request, the 3GPP AAA Proxy shall insert the visited network identifier.

6.1.2.3 PDN GW related procedures

When used in connection with the S6b reference point, the SWd reference point shall support the following procedures:

– Authentication and authorization procedures when using DSMIP as defined in clause 9.1.2.1

– Authorization procedures when using NBM as defined in clause 9.1.2.2

– PDN GW initiated session termination procedures as defined in clause 9.1.2.3

– HSS/AAA initiated detach procedures as defined in clause 9.1.2.4

– Service authorization information update procedures as defined in clause 9.1.2.5

For all these procedures, the 3GPP AAA Proxy shall forward the Diameter commands received from the 3GPP AAA Server and the PDN GW as a stateful Diameter proxy, with the following exceptions:

– The 3GPP AAA Proxy may reject an authentication or authorization request, if roaming is not allowed for the users of the given HPLMN

– The 3GPP AAA Proxy may modify the service authorization information in the authorization answers that it forwards to the PDN GW, in order to enforce the QoS limitations according to the local policies and the roaming agreement with the home operator.

NOTE: For more detailed behavior of the 3GPP AAA Proxy, refer to clauses 9.1.2.1.4, 9.1.2.2.4, 9.1.2.3.4, and 9.1.2.4.4, respectively.

6.2 Protocol Specification

6.2.1 General

The SWd reference point shall be based on Diameter, as defined in IETF RFC 6733 [58] and contain the following additions and extensions:

– IETF RFC 4005 [4], which defines a Diameter protocol application used for Authentication, Authorization and Accounting (AAA) services in the Network Access Server (NAS) environment.

– IETF RFC 4072 [5], which provides a Diameter application to support the transport of EAP (IETF RFC 3748 [8]) frames over Diameter.

– IETF RFC 5779 [2], which defines Diameter extensions and application for PMIPv6 MAG to AAA and LMA to AAA interfaces.

– IETF RFC 5447 [6], which defines Diameter extensions for Mobile IPv6 NAS to AAA interface.

There is no separate application ID defined for the SWd interface. The application ID used by the 3GPP AAA Proxy depends on the command sent over SWd.

NOTE: Even though the 3GPP AAA Proxy may add new AVPs to the Diameter commands forwarded to/from the 3GPP AAA Server, there is no AVP present in the SWd reference point that would not be present in the interface that is used in connection with it. Therefore, the same Application ID can be used.

6.2.2 Commands

6.2.2.1 Commands used in connection with the STa interface

6.2.2.1.1 Commands for STa PMIPv6 or GTPv2 authentication and authorization procedures

6.2.2.1.1.1 Diameter-EAP-Request (DER) Command

The Diameter-EAP-Request (DER) command, indicated by the Command-Code field set to 268 and the "R" bit set in the Command Flags field, is sent from a trusted non-3GPP access network NAS to a 3GPP AAA server. The ABNF is re-used from the IETF RFC 5779 [2].

< Diameter-EAP-Request > ::= < Diameter Header: 268, REQ, PXY, 16777250 >

< Session-Id >

[ DRMP ]

{ Auth-Application-Id }

{ Origin-Host }

{ Origin-Realm }

{ Destination-Realm }

[ Destination-Host ]

{ Auth-Request-Type }

{ EAP-Payload }

[ User-Name ]

[ Calling-Station-Id ]

…

[ RAT-Type ]

[ ANID ]

[ QoS-Capability ]

[ MIP6-Feature-Vector ]

[ Visited-Network-Identifier ]

[ Service-Selection ]

[ Terminal-Information ]

[ AN-Trusted ]

[ Full-Network-Name ]

[ Short-Network-Name ]

*[ Supported-Features ]

[ WLAN-Identifier ]

[ DER-Flags ]

[ TWAN-Connection-Mode ]

[ TWAN-Connectivity-Parameters ]

* 2 [ TWAG-CP-Address ]

[TWAN-S2a-Failure-Cause]

[ ERP-RK-Request ]

…

*[ AVP ]

6.2.2.1.1.2 Diameter-EAP-Answer (DEA) Command

The Diameter-EAP-Answer (DEA) command, indicated by the Command-Code field set to 268 and the "R" bit cleared in the Command Flags field, is sent from a 3GPP AAA server to a 3GPP AAA Proxy. The ABNF is re-used from the IETF RFC 5779 [2]. The ABNF also contains AVPs that are reused from IETF RFC 4072 [5].

< Diameter-EAP-Answer > ::= < Diameter Header: 268, PXY, 16777250 >

< Session-Id >

[ DRMP ]

{ Auth-Application-Id }

{ Result-Code }

[ Experimental-Result ]

{ Origin-Host }

{ Origin-Realm }

{ Auth-Request-Type }

[ EAP-Payload ]

[ User-Name ]

[ Session-Timeout ]

[ Accounting-Interim-Interval ]

[ EAP-Master-Session-Key ]

[ Context-Identifier ]

[ APN-OI-Replacement ]

*[ APN-Configuration ]

[ MIP6-Feature-Vector ]

[ Mobile-Node-Identifier ]

*[ Redirect-Host ] ]

[ Trace-Info ]

[ Subscription-ID ]

*[ Supported-Features ]

[ DEA-Flags ]

[ TWAN-Connection-Mode ]

[ TWAN-Connectivity-Parameters ]

[ Terminal-Information ]

[ Key ]

[ ERP-Realm ]

…

*[ AVP ]

6.2.2.1.2 Commands for STa HSS/AAA Initiated Detach for Trusted non-3GPP Access

The ABNFs defined for the STa interface in clause 5.2.2.2 and in its clauses apply.

6.2.2.1.3 Commands for STa Access and Service Authorization Update Procedure

The ABNFs defined for the STa interface in clause 5.2.2.3 and in its clauses apply.

6.2.2.1.4 Commands for Trusted non-3GPP Access network Initiated Session Termination

The ABNFs defined for the STa interface in clause 5.2.2.4 and in its clauses apply.

6.2.2.2 Commands used in connection with the SWm interface

The ABNFs defined for the SWm interface in clause 7.2.2 and in its clauses apply.

6.2.2.3 Commands used in connection with the S6b interface

The ABNFs defined for the S6b interface in clause 9.2.2 and in its clauses apply.

6.2.3 Information Elements

6.2.3.1 General

The following table describes the Diameter AVPs defined for the SWd interface protocol in NBM mode, their AVP Code values, types, possible flag values and whether or not the AVP may be encrypted.

For all AVPs which contain bit masks and are of the type Unsigned32, bit 0 shall be the least significant bit. For example, to get the value of bit 0, a bit mask of 0x00000001 should be used.

Table 6.2.3.1/1: Diameter SWd AVPs

				AVP Flag rules
Attribute Name	AVP Code	Clause defined	Value Type	Must	May	Should not	Must not
MIP6-Feature-Vector	124	5.2.3.3	Unsigned64	M			V,P
QoS-Capability	578	5.2.3.4	Grouped	M			V,P
RAT-Type	1032	5.2.3.6	Enumerated	M,V			P
ANID	1504	5.2.3.7	UTF8String	M,V			P
Service-Selection	493	5.2.3.5	UTF8String	M			V,P
Mobile-Node-Identifier	506	5.2.3.2	UTF8String	M			V,P
AN-Trusted	1503	5.2.3.9	Enumerated	M,V			P
Full-Network-Name	1516	5.2.3.14	OctetString	V			M,P
Short-Network-Name	1517	5.2.3.15	OctetString	V			M,P
WLAN-Identifier	1509	5.2.3.18	Grouped	V			M,P
APN-Configuration	1430	8.2.3.7	Grouped	M,V			P
Visited-Network-Identifier	600	9.2.3.1.2	OctetString	M,V			P
DER-Flags	1520	5.2.3.20	Unsigned32	V			M,P
DEA-Flags	1521	5.2.3.21	Unsigned32	V			M,P
SSID	1524	5.2.3.22	UTF8String	V			M,P
HESSID	1525	5.2.3.23	UTF8String	V			M,P
TWAN-Connection-Mode	1527	5.2.3.25	Unsigned32	V			M,P
TWAN-Connectivity-Parameters	1528	5.2.3.26	Grouped	V			M,P
Connectivity-Flags	1529	5.2.3.27	Unsigned32	V			M,P
TWAN-PCO	1530	5.2.3.28	OctetString	V			M,P
TWAG-CP-Address	1531	5.2.3.29	Address	V			M,P
TWAG-UP-Address	1532	5.2.3.30	UTF8String	V			M,P
TWAN-S2a-Failure-Cause	1533	5.2.3.31	Unsigned32	V			M,P
NOTE 1: The AVP header bit denoted as "M", indicates whether support of the AVP is required. The AVP header bit denoted as "V", indicates whether the optional Vendor-ID field is present in the AVP header. For further details, see IETF RFC 6733 [58]. NOTE 2: If the M-bit is set for an AVP and the receiver does not understand the AVP, it shall return a rejection. If the M-bit is not set for an AVP, the receiver shall not return a rejection, whether or not it understands the AVP. If the receiver understands the AVP but the M-bit value does not match with the definition in this table, the receiver shall ignore the M-bit.

The following table describes the Diameter AVPs re-used by the SWd interface protocol from existing Diameter Applications, including a reference to their respective specifications and when needed, a short description of their use within SWd. Other AVPs from existing Diameter Applications, except for the AVPs from Diameter base protocol defined in IETF RFC 6733 [58], do not need to be supported.

Table 6.2.3.1/2: SWd re-used Diameter AVPs

Attribute Name	Reference	Comments	M-bit
Accounting-Interim-Interval	IETF RFC 6733 [58]
Auth-Request-Type	IETF RFC 6733 [58]
Calling-Station-Id	IETF RFC 4005 [6]
Subscription-ID	IETF RFC 4006 [20]		Must not set
EAP-Master-Session-Key	IETF RFC 4072 [5]
EAP-Payload	IETF RFC 4072 [5]
RAT-Type	3GPP TS 29.212 [23]
Re-Auth-Request-Type	IETF RFC 6733 [58]
Session-Timeout	IETF RFC 6733 [58]
User-Name	IETF RFC 6733 [58]
Terminal-Information	3GPP TS 29.272 [29]
APN-OI-Replacement	3GPP TS 29.272 [29]
Supported-Features	3GPP TS 29.229 [24]	See NOTE 1.
Feature-List-ID	3GPP TS 29.229 [24]	See NOTE 1.
Feature-List	3GPP TS 29.229 [24]	See NOTE 1.
PDN-Type	3GPP TS 29.272 [29]
Served-Party-IP-Address	3GPP TS 32.299 [30]
DRMP	IETF RFC 7944 [53]	See clause 8.2.3.25	Must not set
ERP-RK-Request	IETF RFC 6942 [57]		Must not set
ERP-Realm	IETF RFC 6942 [57]		Must not set
Key	IETF RFC 6734 [56]	This is a grouped AVP containing Key-Type, Keying-Material and, optionally, Key-Lifetime.	Must not set
NOTE 1: There is no separate Diameter application ID defined for the SWd interface so a separate supported feature list is not required. The supported features depend on the command being proxied over SWd. NOTE 2: The M-bit settings for re-used AVPs override those of the defining specifications that are referenced. Values include: "Must set", "Must not set". If the M-bit setting is blank, then the defining specification applies. NOTE 3: If the M-bit is set for an AVP and the receiver does not understand the AVP, it shall return a rejection. If the M-bit is not set for an AVP, the receiver shall not return a rejection, whether or not it understands the AVP. If the receiver understands the AVP but the M-bit value does not match with the definition in this table, the receiver shall ignore the M-bit.

Only those AVP initially defined in this reference point and for this procedure are described in the following clauses.