Diameter (protocol)
| Internet protocol suite |
|---|
| Application layer |
| Transport layer |
| Internet layer |
| Link layer |
Diameter is an authentication, authorization, and accounting protocol for computer networks and an alternative to RADIUS.
Diameter Applications extend the base protocol by adding new commands and/or attributes, such as those for use of the Extensible Authentication Protocol (EAP).
Contents |
Comparison with RADIUS [edit]
The name is a pun, derived from the RADIUS protocol, which is the predecessor (a diameter is twice the radius). Diameter is not directly backwards compatible but provides an upgrade path for RADIUS. The main differences are the following:
- Reliable transport protocols (TCP or SCTP, not UDP)
- The IETF is in the process of standardizing TCP Transport for RADIUS
- Network or transport layer security (IPsec or TLS)
- The IETF is in the process of standardizing Transport Layer Security for RADIUS
- Transition support for RADIUS, although Diameter is not fully compatible with RADIUS
- Larger address space for attribute-value pairs (AVPs) and identifiers (32 bits instead of 8 bits)
- Client–server protocol, with exception of supporting some server-initiated messages as well
- Both stateful and stateless models can be used
- Dynamic discovery of peers (using DNS SRV and NAPTR)
- Capability negotiation
- Supports application layer acknowledgements, defines failover methods and state machines (RFC 3539)
- Error notification
- Better roaming support
- More easily extended; new commands and attributes can be defined
- Aligned on 32-bit boundaries
- Basic support for user-sessions and accounting
Applications [edit]
A Diameter Application is not a software application but is a protocol based on the Diameter base protocol (defined in RFC 3588). Each application is defined by an application identifier and can add new command codes and/or new mandatory AVPs. Adding a new optional AVP does not require a new application.
Examples of Diameter applications:
- Diameter Mobile IPv4 Application (MobileIP, RFC 4004)
- Diameter Network Access Server Application (NASREQ, RFC 4005)
- Diameter Extensible Authentication Protocol Application (RFC 4072)
- Diameter Credit-Control Application (DCCA, RFC 4006)
- Diameter Session Initiation Protocol Application (RFC 4740)
- Various applications in the 3GPP IP Multimedia Subsystem
(Generic Bootstrapping Architecture): Bootstrapping Server Function
History [edit]
The Diameter protocol was initially developed by Pat R. Calhoun, Glen Zorn, and Ping Pan in 1998 to provide an Authentication, Authorization, and Accounting (AAA) framework that could overcome the limitations of RADIUS. RADIUS had issues with reliability, scalability, security and flexibility. RADIUS cannot effectively deal well with remote access, IP mobility, and policy control. The Diameter protocol defines a policy protocol used by clients to perform Policy, AAA, and Resource Control. This allows a single server to handle policies for many services.[1]
Like RADIUS, Diameter provides AAA functionality but in addition it is made more reliable by using TCP and SCTP instead of UDP. The Diameter protocol is further enhanced by the development of the 3rd Generation Partnership Project (3GPP) IP Multimedia Subsystem (IMS). The Cx, Dh, Dx, Rf, Ro, and Sh interfaces are supported by Diameter applications.[2] Through the use of extensions, the protocol was designed to be extensible to support Proxies, Brokers, Strong Security, Mobile-IP, Network Access Servers (NASREQ), Accounting, and Resource Management.
Protocol description [edit]
![[icon]](/wiki/File:Wiki_letter_w_cropped.svg){kind=small} |
This section requires expansion. (June 2008) |
The Diameter base protocol is defined by RFC 3588 and defines the minimum requirements for an AAA protocol. Diameter Applications can extend the base protocol by adding new commands, attributes, or both. Diameter security is provided by IPsec or TLS. The IANA has assigned TCP and SCTP port number 3868 to Diameter.
Packet format [edit]
The packet consists of a Diameter header and a variable number of Attribute-Value Pairs, or AVPs, for encapsulating information relevant to the Diameter message.
| Bit offset | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | version | message length | ||||||||||||||||||||||||||||||
| 32 | R | P | E | T | command code | |||||||||||||||||||||||||||
| 64 | application ID | |||||||||||||||||||||||||||||||
| 96 | hop-by-hop ID | |||||||||||||||||||||||||||||||
| 128 | end-to-end ID | |||||||||||||||||||||||||||||||
| 160 ... |
AVPs ... |
|||||||||||||||||||||||||||||||
The "R" (Request) bit – If set, the message is a request. If cleared, the message is an answer.
The "P" (Proxiable) bit – If set, the message MAY be proxied, relayed or redirected. If cleared, the message MUST be locally processed.
The "E" (Error) bit – If set, the message contains a protocol error, and the 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.
The "T" (Potentially re-transmitted message) bit – This flag is set after a link failover procedure, to aid the removal of duplicate requests. It is set when resending requests not yet acknowledged as an indication of a possible duplicate due to a link failure.
Commands [edit]
Each command is assigned a command code, which is used for both Requests and Answers.
The values 0-255 are reserved for RADIUS backward compatibility. The values 256-16777213 are for permanent, standard commands allocated by IANA. The values 16777214 and 16777215 (hex 0xFFFFFE and 0xFFFFFF) are reserved for experimental and testing purposes.
Some common Diameter commands are:
| 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 |
| Update-Location-Request | ULR | 316 |
| Update-Location-Answer | ULA | 316 |
| Authentication-Information-Request | AIR | 318 |
| Authentication-Information-Answer | AIA | 318 |
| Notify-Request | NR | 323 |
| Notify-Answer | NA | 323 |
|
This section requires expansion. (December 2009) |
Attribute-Value Pairs (AVP) [edit]
| Bit offset | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | AVP code | |||||||||||||||||||||||||||||||
| 32 | V | M | P | AVP length | ||||||||||||||||||||||||||||
| 64 | vendor ID (optional) | |||||||||||||||||||||||||||||||
| 96 ... |
data ... |
|||||||||||||||||||||||||||||||
For simplicity, "V" bit Means Vendor Specific; "M" bit means Mandatory; "P" bit means Protected.
The "V" bit, known as the Vendor-Specific bit, 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.
The "M" bit, known as the Mandatory bit, indicates whether support of the 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.
The "P" bit indicates the need for encryption for end-to-end security.
| Attribute-Name | Code | Data Type |
|---|---|---|
| Acct-Interim-Interval | 85 | Unsigned32 |
| Accounting-Realtime-Required | 483 | Enumerated |
| Acct-Multi-Session-Id | 50 | UTF8String |
| Accounting-Record-Number | 485 | Unsigned32 |
| Accounting-Record-Type | 480 | Enumerated |
| Accounting-Session-Id | 44 | OctetString |
| Accounting-Sub-Session-Id | 287 | Unsigned64 |
| Acct-Application-Id | 259 | Unsigned32 |
| Auth-Application-Id | 258 | Unsigned32 |
| Auth-Request-Type | 274 | Enumerated |
| Authorization-Lifetime | 291 | Unsigned32 |
| Auth-Grace-Period | 276 | Unsigned32 |
| Auth-Session-State | 277 | Enumerated |
| Re-Auth-Request-Type | 285 | Enumerated |
| Class | 25 | OctetString |
| Destination-Host | 293 | DiamIdent |
| Destination-Realm | 283 | DiamIdent |
| Disconnect-Cause | 273 | Enumerated |
| E2E-Sequence | 300 | Grouped |
| Error-Message | 281 | UTF8String |
| Error-Reporting-Host | 294 | DiamIdent |
| Event-Timestamp | 55 | Time |
| Experimental-Result | 297 | Grouped |
| Experimental-Result-Code | 298 | Unsigned32 |
| Failed-AVP | 279 | Grouped |
| Firmware-Revision | 267 | Unsigned32 |
| Host-IP-Address | 257 | Address |
| Inband-Security-Id | 299 | Unsigned32 |
| Multi-Round-Time-Out | 272 | Unsigned32 |
| Origin-Host | 264 | DiamIdent |
| Origin-Realm | 296 | DiamIdent |
| Origin-State-Id | 278 | Unsigned32 |
| Product-Name | 269 | UTF8String |
| Proxy-Host | 280 | DiamIdent |
| Proxy-Info | 284 | Grouped |
| Proxy-State | 33 | OctetString |
| Redirect-Host | 292 | DiamURI |
| Redirect-Host-Usage | 261 | Enumerated |
| Redirect-Max-Cache-Time | 262 | Unsigned32 |
| Result-Code | 268 | Unsigned32 |
| Route-Record | 282 | DiamIdent |
| Session-Id | 263 | UTF8String |
| Session-Timeout | 27 | Unsigned32 |
| Session-Binding | 270 | Unsigned32 |
| Session-Server-Failover | 271 | Enumerated |
| Supported-Vendor-Id | 265 | Unsigned32 |
| Termination-Cause | 295 | Enumerated |
| User-Name | 1 | UTF8String |
| Vendor-Id | 266 | Unsigned32 |
| Vendor-Specific-Application-Id | 260 | Grouped |
State machines [edit]
|
This section requires expansion. (December 2009) |
The RFC 3588 defines a core state machine for maintaining connections between peers and processing messages. This is part of the basic protocol functionality and all stacks should support it and as such abstract from the connectivity related operations.
-
Peer State Machine Part 1
-
Peer State Machine Part 2
Additionally, application specific state machines can be introduced either later or at a higher abstraction layer. The RFC 3588 defines an authorization and an accounting state machine.
-
Diameter Authorization State Machines (Client)
-
Diameter Authorization State Machines (Server)
-
Diameter Accounting State Machines (Client)
-
Diameter Accounting State Machines (Server)
Message flows [edit]
The communication between two diameter peers starts with the establishment of a transport connection (TCP or SCTP). The initiator then sends a Capabilities-Exchange-Request (CER) to the other peer, which responds with a Capabilities-Exchange-Answer (CEA). For RFC3588 complaint peers TLS (Transport Layer Security) may optionally be negotiated. For RFC6733 compliant peers TLS negotiation may optionally happen before the CER/CEA.
The connection is then ready for exchanging application messages.
If no messages have been exchanged for some time either side may send a Device-Watchdog-Request (DWR) and the other peer must respond with Device-Watchdog-Answer.
Either side may terminate the communication by sending a Disconnect-Peer-Request (DPR) which the other peer must respond to with Disconnect-Peer-Answer. After that the transport connection can be disconnected.
RFCs [edit]
The Diameter protocol is currently defined in the following IETF RFCs: Obsolete RFCs are indicated with strikethrough text.
| # | Title | Date published | Related article | Obsoleted by | Notes |
|---|---|---|---|---|---|
| RFC 6733 | |||||
| RFC 3589 | Diameter Command Codes for Third Generation Partnership Project (3GPP) Release 5. | September 2003 | |||
| RFC 4004 | Diameter Mobile IPv4 Application. | August 2005 | |||
| RFC 4005 | Diameter Network Access Server Application | August 2005 | |||
| RFC 4006 | Diameter Credit-Control Application. | August 2005 | Diameter Credit-Control Application | ||
| RFC 4072 | Diameter Extensible Authentication Protocol (EAP) Application. | August 2005 | |||
| RFC 4740 | Diameter Session Initiation Protocol (SIP) Application. M. | November 2006 | |||
| RFC 5224 | Diameter Policy Processing Application. | March 2008 | |||
| RFC 5431 | Diameter ITU-T Rw Policy Enforcement Interface Application. | March 2009 | |||
| RFC 5447 | Diameter Mobile IPv6: Support for Network Access Server to Diameter Server Interaction. | February 2009 | |||
| RFC 5516 | Diameter Command Code Registration for the Third Generation Partnership Project (3GPP) Evolved Packet System (EPS). | April 2009 | - | ||
| RFC 5624 | Quality of Service Parameters for Usage with Diameter. | August 2009 | |||
| RFC 6733 | Diameter Base Protocol. | October 2012 | |||
| RFC 6737 | The Diameter Capabilities Update Application. | October 2012 |
See also [edit]
References [edit]
- ^ Pat R. Calhoun, Glen Zorn and Ping Pan (2001-02). "DIAMETER Framework Document". IETF. Retrieved 2009-04-30.
- ^ Naman Mehta (2009-03-20). "Introduction to Diameter Protocol - What is Diameter Protocol?". Sun Microsystems. Retrieved 2009-04-30.
External links [edit]
- Introduction to Diameter - Get the next generation AAA protocol
- Cisco page outlining differences between RADIUS and DIAMETER
- Diameter: next generation’s AAA protocol Paper about Diameter by Håkan Ventura
- The Open IMS Core JavaDiameterPeer The Open IMS Core JavaDiameterPeer
- freeDiameter, open-source implementation of Diameter Base Protocol and Extensions
- Reference page listing vendors of Diameter Gateways, Diameter Signaling Controllers and Diameter Stacks
