Protocol OV: (3) Diameter Message Format (Header, AVP), Command Code, Appl-ID

Protocol OV - Diameter Overview (3)

4). Diameter Packet format Overview

§ The Diameter base protocol defines the protocol header and the necessary Attribute-Value Pairs (AVPs).

§ Diameter uses Attribute-Value pairs to send data or AAA specific information.

§ Diameter AVPs are defined in the base protocol or Diameter application documents.

§ The applications can extend the protocol by defining new messages and AVPs and append them to the Protocol Data Units (PDUs).

DIAMETER types of messages:

§ Two types of messages: Requests and Answers

§ Diameter is a request and answer protocol, xxR matches xxA; They always appear together.

§ Answer message contains Result-Code AVP

Request messages may be proxiable or non-proxiable (indicated by flag “P” in message header)

§ Non-proxiable: strictly intended for the next hop peer; never forwarded

§ Proxiable: routable and are routed by realm

4-1). Diameter Message format

§ The Diameter message consists of a Diameter header and one or more attribute-value pairs (AVPs) which carry authentication, authorization or accounting information or protocol specific data.

Figure: Diameter Message Format (N/A)

4-2). Diameter Message Header:

§ The Diameter header is 20 bytes, divided in fields

§ Each command request/answer pair is assigned a command code, and the sub-type (i.e., request or answer) is identified via the ‘R’ bit in the command Flag field of the Diameter header.

Figure: Diameter Message Header (N/A)

§ In the command Flag field the first four bits are defined, the other four are reserved for later use:

§ Request (R): If set, the message is a request. If cleared, the message is an answer.

§ Proxiable (P): If set, the message MAY be proxied, relayed or redirected. If cleared, the message MUST be locally processed.

§ Error (E): If set, the message contains a protocol error, and the error message will not conform to the ABNF described for this command. Messages with the 'E‘ bit set are commonly referred to as error messages. This bit MUST NOT be set in request messages.

§ Potentially re-transmitted message (T): This flag is set after a link failover procedure, when a retransmission is sent, to help the removal of duplicate requests. This flag can only be set in request messages. It is set when resending requests not yet acknowledged, as an indication of a possible duplicate due to a link failure.

§ The "r" bits are unused flags that are reserved for future use, and MUST be set to zero, and ignored by the receiver.

§ The Hop-by-Hop Identifier aids in matching requests and replies.

§ In requests, the Hop-by-Hop Identifier is replaced at each hop as the Diameter message is relayed to its final destination.

§ The sender of an Answer message returns the same value that was found in the corresponding request.

§ The End-to-End Identifier, together with the origin host's identity, is used to detect duplicate request messages.

§ The End-to-End Identifier is unmodified as a request is forwarded to its final destination.

§ The originator of an Answer message returns the same value that was found in the corresponding request.

4-3A). Diameter Command Code Values:

§ Based on the IETF RFC, the IANA has allocated a standard command code.

Command-Name	Abbr.	Code
AA-Request	AAR	265
AA-Answer	AAA	265
Diameter-EAP-Request	DER	268
Diameter-EAP-Answer	DEA	268
Abort-Session-Request	ASR	274
Abort-Session-Answer	ASA	274
Accounting-Request	ACR	271
Accounting-Answer	ACA	271
Credit-Control-Request	CCR	272
Credit-Control-Answer	CCA	272
Capabilities-Exchange-Request	CER	257
Capabilities-Exchange-Answer	CEA	257
Device-Watchdog-Request	DWR	280
Device-Watchdog-Answer	DWA	280
Disconnect-Peer-Request	DPR	282
Disconnect-Peer-Answer	DPA	282
Re-Auth-Request	RAR	258
Re-Auth-Answer	RAA	258
Session-Termination-Request	STR	275
Session-Termination-Answer	STA	275
User-Authorization-Request	UAR	300
User-Authorization-Answer	UAA	300
Server-Assignment-Request	SAR	301
Server-Assignment-Answer	SAA	301
Location-Info-Request	LIR	302
Location-Info-Answer	LIA	302
Multimedia-Auth-Request	MAR	303
Multimedia-Auth-Answer	MAA	303
Registration-Termination-Request	RTR	304
Registration-Termination-Answer	RTA	304
Push-Profile-Request	PPR	305
Push-Profile-Answer	PPA	305
User-Data-Request	UDR	306
User-Data-Answer	UDA	306
Profile-Update-Request	PUR	307
Profile-Update-Answer	PUA	307
Subscribe-Notifications-Request	SNR	308
Subscribe-Notifications-Answer	SNA	308
Push-Notification-Request	PNR	309
Push-Notification-Answer	PNA	309
Bootstrapping-Info-Request	BIR	310
Bootstrapping-Info-Answer	BIA	310
Message-Process-Request	MPR	311
Message-Process-Answer	MPA	311

4-3B). Diameter Command Code values for 3GPP:

§ Based on the IETF RFC 3589 [10] the IANA has allocated a standard command code range 300 ‑ 313 for 3GPP.

Command code	Command name	Abbreviation	Specified in 3GPP TS
300	User-Authorization-Request/-Answer	UAR/UAA	29.229 [2]
301	Server-Assignment-Request/-Answer	SAR/SAA
302	Location-Info-Request/-Answer	LIR/LIA
303	Multimedia-Auth-Request/-Answer	MAR/MAA
304	Registration-Termination-Request/-Answer	RTR/RTA
305	Push-Profile-Request/-Answer	PPR/PPA
306	User-Data-Request/-Answer	UDR/UDA	29.329 [4]
307	Profile-Update-Request/-Answer	PUR/PUA
308	Subscribe-Notifications-Request/-Answer	SNR/SNA
309	Push-Notification-Request/-Answer	PNR/PNA
310	Boostrapping-Info-Request/Answer	BIR/BIA	29.109 [7]
311	Message-Process-Request/Answer	MPR/MPA	29.140 [16]
312	GBAPush-Info-Request/Answer	GPR/GPI	29.109 [7]

4-3C). Diameter Command Code values in 3GPP:

3GPP Diameter Commands supported in different interfaces and functions: (matrix)

http://docs.google.com/View?id=ddh56dhg_287ds83gngs

§ IETF RFC 5516 [23]. IANA has allocated the following command code values for the S6a/S6d interface application and S13/S13’ interface application

Command code	Command name	Abbreviation	Specified in 3GPP TS
316	Update-Location-Request/Answer	ULR/ULA	29.272 [21]
317	Cancel-Location-Request/Answer	CLR/CLA
318	Authentication- Information -Request/Answer	AIR/AIA
319	Insert Subscriber Data-Request/Answer	IDR/IDA
320	Delete-Subscriber-Data-Request/Answer	DSR/DSA
321	Purge-UE-Request/Answer	PUR/PUA
322	Reset-Request/Answer	RSR/RSA
323	Notify-Request/Answer	NOR/NOA
324	ME-Identity-Check-Request/Answer	ECR/ECA

4-4). Diameter application identifiers:

§ Each Diameter application MUST have an IANA assigned Application Identifier.

§ The base protocol does not require an Application Identifier since its support is mandatory.

Some of the application identifiers in use are:

§ Diameter Common Messages 0

§ NASREQ 1 [NASREQ]

§ Mobile-IP 2 [DIAMMIP]

§ Diameter Base Accounting 3

§ Credit Control 4

§ Relay 0xffffffff

§ The 3GPP specific application identifiers allocated by IANA are listed in the following table

4-5). Diameter 3GPP application identifiers:

§ The 3GPP specific application identifiers allocated by IANA are listed in the following table

Application ID	Application	3GPP TS	Description
16777216	3GPP Cx/Dx	29.228 and 29.229	CSCF -- HSS
16777217	3GPP Sh/Dh	29.328 and 29.329	AS – SLF/HSS
16777218	3GPP Re	32.296	EBCF/SBCF – Rating Function
16777219	3GPP Wx	29.234	AAA Server --- HSS
16777220	3GPP Zn	29.109	NAF --- BSF (in GAA)
16777221	3GPP Zh	29.109	BSF --- HSS (in GAA)
16777222	3GPP Gq	29.209	PDF (PCRF) --- AF
16777223	3GPP Gmb	29.061	GGSN --- BM-SC
16777224	3GPP Gx	29.210	PCRF (Gx) --- PCEF (in PCC)
16777225	3GPP Gx over Gy	29.210	PCRF (Gx) --- PCEF (Gy) --- OCS
16777226	3GPP MM10	29.140	MMS Relay/Server --- MSCF
16777229	3GPP Rx/Gx	29.211	Rx: PCRF --- AF and Gx:PCRF --- PCEF
16777230	3GPP Pr	29.234	AAA Server --- Presence Network Agent
16777236	3GPP Rx	29.214	PCRF --- AF (in PCC)
16777238	3GPP Gx	29.212	PCRF --- PCEF (in PCC)
16777250	3GPP STa	29.273	WLAN AN --- AAA Proxy or Server
16777251	3GPP S6a/S6d	29.272	MME --- HSS and SGSN --- HSS
16777252	3GPP S13/S13’	29.272	MME --- EIR and SGSN -- EIR
16777264	3GPP SWm	29.273	AAA Proxy -- ePDG
16777265	3GPP SWx	29.273	AAA Server --- HSS
16777266	3GPP Gxx	29.212	PCRF --- BBERF (in PCC)
16777267	3GPP S9	29.215	V-PCRF --- H-PCRF (in PCC)
16777268	3GPP Zpn	29.109	NAF --- BSF (in GAA Push Function)
16777272	3GPP S6b	29.273	AAA Server or AAA Proxy --- PDN GW

4-6). Diameter Attribute-Value Pairs (AVP)

§ Diameter uses Attribute-Value Pairs (AVP) to send data or AAA specific information.

§ Diameter AVPs are defined in the base protocol or Diameter application documents.

Figure: Diameter AVP Format (N/A)

§ Every AVP must be padded to align on a 32-bit boundary.

§ A Grouped AVP is an AVP whose data is a sequence of AVPs. Grouped AVPs are used to nest more AVPs in an AVP. In this case the data field of the AVP contains more AVPs.

§ The AVP Code and AVP Length fields determine the format and length of the Data field.

§ AVP Code: 1~255 reserved for backward compatibility with RADIUS, without setting the Vendor-Id field. The AVP code combined with the vendor-ID gives a unique identification. AVP numbers 256 and above are used for Diameter, which are allocated by IANA.

§ AVP Flags: V(endor specific), M(andatory), P(EncryPtion), r(eserve).

§ AVP Length: all AVP length, include AVP code, flag vendor-id and AVP data.

§ Vendor-ID: optional, set if AVP flag is V.

§ AVP Data field is zero or more octets and contains information specific to the Attribute.

§ AVP Data:

§ Basic format: OctetString, Integer32/64, unsigned32/64, float32/64, Grouped.

§ Derived AVP Data Formats: Address, Time, UTF8String…

§ Basic AVP Data Formats. Commonly used AVP Derived Data Formats are: Address, Time, UTF8String, DiameterIdentity, DiameterURI, Enumerated, IPFilterRule, QoSFilterRule.

The first three AVP flags are defined as follows:

§ AVP Flags: V(endor specific), M(andatory), P(EncryPtion), r(eserve).

§ 'V' Bit Means Vendor Specific; 'M' Bit means Mandatory; 'P' Bit means Protected.

§ Vendor-specific (V): Indicates whether the vendor-id field is present in the header - indicates whether the optional Vendor-ID field is present in the AVP header. When set the AVP Code belongs to the specific vendor code address space.

§ Mandatory (M): Indicates whether the support of this AVP is required. If an AVP with the 'M' bit set is received by a Diameter client, server, proxy, or translation agent and either the AVP or its value is unrecognized, the message MUST be rejected. Diameter Relay and redirect agents MUST NOT reject messages with unrecognized AVPs.

§ End-to-end encryption (P): Indicates the need for encryption and end-to-end security.

§ "r" bits: are unused flags that are reserved for future use.

4-7). Diameter 3GPP vendor identifier value:

§ The IANA has allocated a vendor identifier value 10415 for 3GPP

4-8). Diameter 3GPP specific AVP codes:

§ The 3GPP specific AVP codes refers to TS 29.230