DIAMETER

:''For the geometric term, see Diameter
'DIAMETER' is a computer networking protocol for AAA (Authentication, Authorization and Accounting). It is a successor to RADIUS.

Contents

Upgrade from RADIUS

Protocol description

Packet format

Commands

Attribute-Value Pairs (AVP)

State machines

Message flows

Applications

External links

Upgrade from RADIUS

The name is a pun on 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 :

★ it uses reliable transport protocols (TCP or SCTP, not UDP)

★ it can use network or transport level security (IPsec or TLS)

★ it has transition support for RADIUS

★ it has larger address space for AVPs (Attribute Value Pairs) and identifiers (32-bit instead of 8-bit)

★ it is a client-server protocol, with exception of supporting some server-initiated messages as well

★ both stateful and stateless models can be used

★ it has dynamic discovery of peers (using DNS SRV and NAPTR)

★ it has capability negotiation

★ it supports application layer acknowledgements, defines failover methods and state machines (RFC 3539)

★ it has error notification

★ it has better roaming support

★ it is more easily extended; new commands and attributes can be defined

★ it is aligned on 32 bit boundaries

★ it has basic support for user-sessions and accounting

Protocol description

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 and/or attributes. An application is not a program, but a protocol based on Diameter. Diameter security is provided by IPSEC or TLS, both well-regarded protocols.

Packet format

Commands

Each command is assigned a command code, which is used for both requests and answers.

Command-Name	Abbr.	Code
Abort-Session-Request	ASR	274
Abort-Session-Answer	ASA	274
Accounting-Request	ACR	271
Accounting-Answer	ACA	271
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

Attribute-Value Pairs (AVP)

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

Message flows

Applications

A ''Diameter Application'' is not a software application, but 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

★ 3GPP GBA (Generic Bootstrapping Architecture): Bootstrapping Server Function

External links

★ http://www.cisco.com/en/US/products/ps6638/products_data_sheet09186a00804fe332.html Cisco page outlining differences between RADIUS and DIAMETER

★ http://sourceforge.net/projects/openblox/ Open Source Java IMS optimised Full Diameter solution