RFC 4740
Diameter Session Initiation Protocol (SIP) Application
Network Working Group M. Garcia-Martin, Ed. Request for Comments: 4740 Nokia Category: Standards Track M. Belinchon M. Pallares-Lopez C. Canales-Valenzuela Ericsson K. Tammi Nokia November 2006 Diameter Session Initiation Protocol (SIP) Application Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The IETF Trust (2006).Abstract
This document specifies the Diameter Session Initiation Protocol (SIP) application. This is a Diameter application that allows a Diameter client to request authentication and authorization information. This application is designed to be used in conjunction with SIP and provides a Diameter client co-located with a SIP server, with the ability to request the authentication of users and authorization of SIP resources usage from a Diameter server.
Table of Contents
1. Introduction ....................................................4 2. Terminology .....................................................5 3. Definitions .....................................................5 4. Acronyms ........................................................6 5. Applicability Statement .........................................6 6. Overview of Operation ...........................................7 6.1. General Architecture .......................................7 6.2. Diameter Server Authenticates the User .....................9 6.3. Delegating Final Authentication Check to the SIP Server ...12 6.4. SIP Server Requests Authentication and Authorization ......15 6.5. Locating the Recipient of the SIP Request .................16 6.6. Update of the User Profile ................................17 6.7. SIP Soft State Termination ................................18 6.8. Diameter Server Discovery .................................19 7. Advertising Application Support ................................21 8. Diameter SIP Application Command Codes .........................22 8.1. User-Authorization-Request (UAR) Command ..................22 8.2. User-Authorization-Answer (UAA) Command ...................23 8.3. Server-Assignment-Request (SAR) Command ...................27 8.4. Server-Assignment-Answer (SAA) Command ....................29 8.5. Location-Info-Request (LIR) Command .......................33 8.6. Location-Info-Answer (LIA) Command ........................33 8.7. Multimedia-Auth-Request (MAR) Command .....................35 8.8. Multimedia-Auth-Answer (MAA) Command ......................36 8.9. Registration-Termination-Request (RTR) Command ............39 8.10. Registration-Termination-Answer (RTA) Command ............39 8.11. Push-Profile-Request (PPR) Command .......................41 8.12. Push-Profile-Answer (PPA) Command ........................42 9. Diameter SIP Application AVPs ..................................44 9.1. SIP-Accounting-Information AVP ............................46 9.1.1. SIP-Accounting-Server-URI AVP ......................47 9.1.2. SIP-Credit-Control-Server-URI AVP ..................47 9.2. SIP-Server-URI AVP ........................................47 9.3. SIP-Server-Capabilities AVP ...............................47 9.3.1. SIP-Mandatory-Capability AVP .......................48 9.3.2. SIP-Optional-Capability AVP ........................48 9.4. SIP-Server-Assignment-Type AVP ............................48 9.5. SIP-Auth-Data-Item AVP ....................................50 9.5.1. SIP-Authentication-Scheme AVP ......................50 9.5.2. SIP-Item-Number AVP ................................51 9.5.3. SIP-Authenticate AVP ...............................51 9.5.4. SIP-Authorization AVP ..............................52 9.5.5. SIP-Authentication-Info AVP ........................52 9.5.6. Digest AVPs ........................................53 9.6. SIP-Number-Auth-Items AVP .................................55
9.7. SIP-Deregistration-Reason AVP .............................55
9.7.1. SIP-Reason-Code AVP ................................55
9.7.2. SIP-Reason-Info AVP ................................56
9.8. SIP-AOR AVP ...............................................56
9.9. SIP-Visited-Network-Id AVP ................................56
9.10. SIP-User-Authorization-Type AVP ..........................56
9.11. SIP-Supported-User-Data-Type AVP .........................57
9.12. SIP-User-Data AVP ........................................57
9.12.1. SIP-User-Data-Type AVP ............................58
9.12.2. SIP-User-Data-Contents AVP ........................58
9.13. SIP-User-Data-Already-Available AVP ......................58
9.14. SIP-Method AVP ...........................................59
10. New Values for Existing AVPs ..................................59
10.1. Extension to the Result-Code AVP Values ..................59
10.1.1. Success Result-Code AVP Values ....................59
10.1.2. Transient Failures Result-Code AVP Values .........60
10.1.3. Permanent Failures Result-Code AVP Values .........60
11. Authentication Details ........................................61
12. Migration from RADIUS .........................................63
12.1. Gateway from RADIUS Client to Diameter Server ............63
12.2. Gateway from Diameter Client to RADIUS Server ............63
12.3. Known Limitations ........................................64
13. IANA Considerations ...........................................64
13.1. Application Identifier ...................................64
13.2. Command Codes ............................................65
13.3. AVP Codes ................................................65
13.4. Additional Values for the Result-Code AVP Value ..........65
13.5. Creation of the SIP-Server-Assignment-Type
Section in the AAA .......................................66
13.6. Creation of the SIP-Authentication-Scheme Section
in the AAA ...............................................66
13.7. Creation of the SIP-Reason-Code Section in the
AAA Registry .............................................66
13.8. Creation of the SIP-User-Authorization-Type
Section in the AAA .......................................66
13.9. Creation of the SIP-User-Data-Already-Available
Section in the ...........................................66
14. Security Considerations .......................................67
14.1. Final Authentication Check in the Diameter
Client/SIP Server ........................................67
15. Contributors ..................................................68
16. Acknowledgements ..............................................68
17. References ....................................................68
17.1. Normative References .....................................68
17.2. Informative References ...................................69
1. Introduction
This document specifies the Diameter Session Initiation Protocol (SIP) application. This is a Diameter application that allows a Diameter client to request authentication and authorization information to a Diameter server for SIP-based IP multimedia services (see [RFC3261] about SIP). Furthermore, this Diameter SIP application provides the Diameter client with functions that go beyond the typical authorization and authentication, such as the ability to download or receive updated user profiles, or rudimentary routing functions that can assist a SIP server in finding another SIP server allocated to the user. We assume that the SIP server (such as SIP proxy server, registrar, redirect server, or alike) and the Diameter client are co-located in the same node, so that the SIP server is able to receive and process SIP requests and responses. In turn, the SIP server relies on the Authentication, Authorization, and Accounting (AAA) infrastructure for authenticating the SIP request and authorizing the usage of particular SIP services. This document provides Diameter procedures to implement certain required functionality when SIP is the protocol chosen to initiate and tear down multimedia sessions or when SIP is used for other non-session-related applications. However, this document does not mandate any particular mapping of SIP procedures to Diameter SIP application procedures, nor does it mandate any particular sequence of events between SIP and Diameter. This document provides useful examples to show the interaction between SIP and the Diameter SIP application in order to achieve the desired functionality. This application does not require and is not related to other authentication services provided by the Diameter Mobile IPv4 [RFC4004] or the Diameter Network Access Server [RFC4005] applications. This Diameter SIP application is loosely related to the Diameter credit-control application [RFC4006]. Although both applications are independent, the Diameter SIP application is able to supply the addresses of credit-control servers that will be implementing the Diameter credit-control application [RFC4006]. Section 5 discusses assumptions and configurations assumed by this document. Section 6 provides the reader with informative descriptions of the Diameter SIP application commands and responses and with some guidance about their linkage with SIP procedures.
Advertisement of this application is specified in Section 7. Section 8 provides a normative description of all the new Diameter commands defined by this specification. This application extends the Result-Code Attribute-Value-Pair (AVP) with some new values. Further information is described in Section 10. This application defines some new AVPs. All these AVPs are described in Section 9. Some extra information about authentication is provided in Section 11.2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [RFC2119] and indicate requirement levels for compliant implementations.3. Definitions
For the purpose of this document, the following terms and definitions apply: Node: an addressable device attached to a computer network that implements SIP functionality, Diameter functionality, or a combination of both. For the purpose of this document, the following terms and definitions given in RFC 3261 [RFC3261] Section 6, apply: o Address-of-Record (AOR) o Outbound proxy o Proxy o Registrar o Server (SIP server) o User Agent (UA) o User Agent Client (UAC) o User Agent Server (UAS) For the purpose of this document, the following terms and definitions given in RFC 3588 [RFC3588] Section 1.3, apply:
o Authorization o Authentication o Attribute-Value Pair (AVP) o Diameter Client o Diameter Server o Home Realm o Redirect Agent o User4. Acronyms
AKA: Authentication and Key Agreement LIR: Location-Info-Request LIA: Location-Info-Answer MAR: Multimedia-Auth-Request MAA: Multimedia-Auth-Answer PPR: Push-Profile-Request PPA: Push-Profile-Answer RTR: Registration-Termination-Request RTA: Registration-Termination-Answer SAR: Server-Assignment-Request SAA: Server-Assignment-Answer SL: Subscriber Locator UAR: User-Authorization-Request UAA: User-Authorization-Answer5. Applicability Statement
This document assumes a general architecture where a Home Realm is composed of one or more nodes implementing Diameter or SIP functions. Users are issuing SIP requests to access SIP resources. For each particular user, the Home Realm needs to authenticate and authorize the usage of those resources and/or the route to the appropriate node. We assume that the database containing the user-related data is located outside the SIP node that requires authorization. Data belonging to different users may be stored in different nodes in the Home Realm, but we assume that all the data related to a particular user is stored in a single node. Note: Central to the architecture is the fact that the user data is stored in a single point in the network. This restriction does not mandate a particular implementation, e.g., it is possible to implement clusters of databases operating in mirror mode to provide redundancy. The property required by this specification is that the user data the Diameter server has access to is stored safely in what is seen, from the external point of view, as a single user database.
This document allows several configurations of the Home Realm. In one configuration, a SIP server (proxy, registrar, etc.) is allocated to a user for the purpose of triggering and executing services. The allocation of the SIP server may be done dynamically, e.g., at the time the user registers in the network. This configuration requires a SIP server, typically located at the edge of the network, that is able to allocate another SIP server for the user and that also supports routing of SIP requests and responses towards that allocated SIP server. Both SIP server nodes implement a Diameter client. In another configuration, the address of a SIP outbound proxy is configured (by means outside the scope of this specification) into the SIP User Agent. The outbound Diameter client in the SIP outbound proxy node authenticates the user, requests authorization for SIP requests, and performs accounting activities.6. Overview of Operation
This section provides an informative description of how the Diameter SIP application can be used together with SIP. This section is not intended to mandate any specific usage of the Diameter SIP application nor does it mandate a specific mapping between SIP and Diameter messages. We provide a collection of examples that show how the required AAA functionality can be achieved in conjunction with SIP.6.1. General Architecture
The Diameter SIP application can be used in a SIP environment where an interface to a AAA infrastructure is required to authenticate and authorize the usage of SIP resources. This application provides support for SIP User Agents and proxies that implement and use HTTP Digest authentication [RFC2617], which is the authentication mechanism mandated by SIP [RFC3261]. The application is extensible and, if need arises, it can be extended to provide support for other authentication mechanisms or extensions to HTTP Digest authentication when they occur. This application provides limited support for accounting services as follows: the Diameter server is able to provide the addresses of accounting severs to the Diameter client. Figure 1, below, shows a general overview of the integration of the SIP architecture with the AAA architecture. According to Figure 1, there are one or more SIP User Agents (UAs) that initiate or terminate SIP traffic through one or more SIP servers. Both SIP servers implement a Diameter client that supports the Diameter application described in this specification.
+--------+ UAR/UAA +--->|Diameter|<----+ PPR/PPA LIR/LIA | | server | | MAR/MAA | +--------+ | SAR/SAA | | RTR/RTA | | v v +------+ SIP +--------+ SIP +--------+ SIP +------+ | SIP |<--------->| SIP |<-------->| SIP |<--------->| SIP | | UA | |server 1| |server 2| | UA | +------+ +--------+ +--------+ +------+ ^ ^ UAR/UAA | | LIR/LIA | | MAR/MAA | +--------+ | SAR/SAA +--->|Diameter|<----+ | SL | +--------+ Figure 1: Architecture of the Diameter application for SIP In Figure 1, it can be seen that SIP server 1 sends different Diameter commands and receives different responses than those sent and received by SIP server 2. This is because SIP server 1 in Figure 1 is located at the edge of a network, and its main task is to locate SIP server 2. SIP server 2 is requesting and receiving authentication and authorization data from the Diameter server and is not located at the edge of the network. This Diameter application assumes that all the data pertaining to a given user is stored in a single Diameter server. For redundancy purposes, several Diameter servers can be configured in a redundancy fashion, in which case all of them keep the data synchronized and operate externally as a single Diameter server. With respect to SIP server 1 in Figure 1, the Diameter SIP application provides support for the existence of a farm of these servers, typically configured through one or more DNS records that point to several hosts (this is a typical configuration in common SIP deployments). There is no requirement for these types of servers to keep state related to the Diameter SIP application. The Diameter SIP application provides support for a feature that allows an administrative domain to provide a collection of SIP servers 2 (as per Figure 1). Once the user registers for the first time, one of these SIP servers is selected and all the SIP requests related to the user are processed by the same SIP server.
The Diameter Subscriber Locator (SL) serves the purpose of locating the Diameter server that contains the user-related data. Its functionality is based on the Diameter redirect mechanism and is further described in Section 6.8. It should be noted that this document does not mandate any particular SIP/AAA architecture. However, the Diameter SIP application provides the functionality needed to accommodate all the different architectures where SIP and Diameter are used. The following subsections provide an informative overview of the Diameter SIP application, its commands, and a possible interaction with SIP signaling.6.2. Diameter Server Authenticates the User
This is the generic mechanism to authenticate users. In this approach, we show an example of an administrative network where the Diameter server is authenticating SIP user requests. This could be the case of a medium-size network where the Diameter server is keeping user records and authenticating SIP requests to perform a certain transaction. We have chosen to show a SIP REGISTER request in the example, but the SIP server could request authentication of any other SIP request.
+--------+ +--------+ +--------+ | SIP | |Diameter| | SIP | |server 1| | server | |server 2| +--------+ +--------+ +--------+ | | | 1. SIP REGISTER | | | -------------------->| 2. UAR | | |------------------>| | | 3. UAA | | |<------------------| | | 4. SIP REGISTER | |-------------------------------------->| | | 5. MAR | | |<------------------| | | 6. MAA | | |------------------>| | 7. SIP 401 (Unauthorized) | 8. SIP 401 (Unauth.) |<--------------------------------------| <--------------------| | | 9. SIP REGISTER | | | -------------------->| 10. UAR | | |------------------>| | | 11. UAA | | |<------------------| | | 12. SIP REGISTER | |-------------------------------------->| | | 13. MAR | | |<------------------| | | 14. MAA | | |------------------>| | 15. SIP 200 (OK) | 16. SIP 200 (OK) |<--------------------------------------| <--------------------| | | | | 17. SAR | | |<------------------| | | 18. SAA | | |------------------>| | | | Figure 2: Authentication performed in the Diameter server According to Figure 2, a SIP User Agent Client (UAC) sends a SIP REGISTER request (step 1) to SIP server 1, which receives the SIP request. In Figure 2, we assume that this SIP server is located at the edge of the administrative home domain. The Diameter client in SIP server 1 contacts its Diameter server by sending a Diameter User-Authorization-Request (UAR) message (step 2) to determine if this user is allowed to receive service, and if so, request the
address of a local SIP server capable of handling this user. The Diameter server answers with a Diameter User-Authorization-Answer (UAA) message (step 3), which indicates a list of capabilities that SIP server 1 may use to select an appropriate SIP server (SIP server 2) and/or a SIP or SIPS URI pointing to SIP server 2. SIP server 1 forwards the SIP REGISTER request (step 4) to an appropriate SIP server (SIP server 2). Then the Diameter client in SIP server 2 requests user authentication from the Diameter server by sending a Diameter Multimedia-Auth-Request (MAR) message (step 5). This request also serves to make the Diameter server aware of the SIP or SIPS URI of SIP server 2, so as to return subsequent requests for the same user to the same SIP server 2. The Diameter server responds with a Diameter Multimedia-Auth-Answer (MAA) message (step 6) with Result-Code AVP set to the value DIAMETER_MULTI_ROUND_AUTH. The Diameter server also generates a nonce and includes a challenge in the MAA message. SIP server 2 uses that challenge to map into the WWW-Authenticate header in the SIP 401 (Unauthorized) response (step 7), which is sent back to SIP server 1 and then to the SIP UAC (step 8). SIP server 1 receives a next SIP REGISTER request containing the user credentials (step 9). Note that SIP server 1 does not need to keep a state, and even more, there is no guarantee that the SIP request arrives at the same SIP server 1; there could be a farm of SIP servers 1 operating in redundant configuration. The Diameter client in SIP server 1 contacts the Diameter server by sending a Diameter UAR message (step 10) to determine the SIP server allocated to the user. The Diameter server sends the SIP or SIPS URI of SIP server 2 in a Diameter UAA message (step 11). Then SIP server 1 forwards the SIP REGISTER request to SIP server 2 (step 12). SIP server 2 extracts the credentials from the SIP REGISTER request. The Diameter client in SIP server 2 sends those credentials in a Diameter MAR message (step 13) to the Diameter server. At this point, the Diameter server is able to authenticate the user, and upon success, returns a Diameter MAA message (step 14) with the AVP Result-Code set to the value DIAMETER_SUCCESS. Then SIP server 2 generates a SIP 200 (OK) response (step 15), which is forwarded to SIP server 1 and eventually to the SIP UAC (step 16). If the Diameter client in SIP server 2 is interested in downloading the user profile information or is required to store the address of the SIP server in the Diameter server, then the Diameter client sends a Diameter SAR message (step 17) to the Diameter server. The Diameter server replies with a Diameter SAA message (step 18) that contains the requested user profile information and the
acknowledgement of the SIP server address storage. These actions are needed when the SIP server has to retrieve a user profile used to provide services to the served user, or when the SIP server keeps a state for the user, so the Diameter server needs to store the SIP server's address.6.3. Delegating Final Authentication Check to the SIP Server
An operator with a large base of installed SIP servers may wish to minimize the number of round-trips between the Diameter client and the Diameter server. We provide support for a mechanism where the Diameter server delegates the final authentication check to the SIP server, thereby saving a round-trip. Section 14.1 discusses the security considerations of this scenario. It must noted that this scenario is not applicable when the Diameter server is configured to use a session MD5 (MD5-sess) algorithm, because the Diameter server requires the client nonce to compute the H(A1) before sending it to the Diameter client. However, the client nonce might not be available at that time.
+--------+ +--------+ +--------+ | SIP | |Diameter| | SIP | |server 1| | server | |server 2| +--------+ +--------+ +--------+ | | | 1. SIP REGISTER | | | -------------------->| 2. UAR | | |------------------>| | | 3. UAA | | |<------------------| | | 4. SIP REGISTER | |-------------------------------------->| | | 5. MAR | | |<------------------| | | 6. MAA | | |------------------>| | 7. SIP 401 (Unauthorized) | 8. SIP 401 (Unauth.) |<--------------------------------------| <--------------------| | | 9. SIP REGISTER | | | -------------------->| 10. UAR | | |------------------>| | | 11. UAA | | |<------------------| | | 12. SIP REGISTER | |-------------------------------------->| | | 13. SAR | | |<------------------| | | 14. SAA | | |------------------>| | 15. SIP 200 (OK) | 16. SIP 200 (OK) |<--------------------------------------| <--------------------| | | | | | Figure 3: Delegation of authentication to the SIP server Figure 3 shows an example where a SIP server is dynamically allocated to serve a SIP User Agent with the support of the Diameter server. This may be the case of certain architectures, such as that of the 3rd Generation Partnership Project (3GPP) IP Multimedia Core Network Subsystem. A first SIP server receives a SIP REGISTER request (step 1) whose target is the home network domain. In Figure 3, we assume that this SIP server is located at the edge of the administrative home domain. The Diameter client in this SIP server requests authorization from the Diameter server to proceed with the registration, by sending a
Diameter User-Authorization-Request (UAR) message (step 2). The message includes, among other Attribute-Value-Pairs (AVPs), the SIP Address-Of-Record (AOR) that is included in the SIP REGISTER request. The Diameter server verifies the SIP AOR and, if it is a valid defined user in the home network, authorizes the registration to proceed. The Diameter server responds with a Diameter User-Authorization-Answer (UAA) message (step 3), which informs the Diameter client/SIP server about the result of the user authorization. In case of a successful authorization, the Diameter UAA message indicates the address of a local SIP server (SIP server 2 in Figure 3) and/or a list of capabilities that SIP server 1 may use to select an appropriate SIP server 2. When the authorization is successful, SIP server 1 forwards the SIP REGISTER request (step 4) to the appropriate SIP server (SIP server 2). The Diameter client in SIP server 2 requests authentication parameters by sending a Diameter Multimedia-Auth-Request (MAR) message (step 5) to the Diameter server. This request also makes the Diameter server aware of the SIP or SIPS URI of SIP server 2, so as to return subsequent requests of the same user to the same SIP server 2. The Diameter server responds with a Diameter Multimedia-Auth-Answer (MAA) message (step 6), which includes a nonce and all the rest of the parameters necessary for the designated authentication algorithm associated with the user. Among others, the MAA message includes a Digest-HA1 AVP that contains H(A1) (as defined in RFC 2617 [RFC2617]), and that allows the Diameter client to calculate the expected response. Then the Diameter client can compare this expected response with the response to the challenge sent from the SIP UA. The absence of the Digest-HA1 AVP in MAA indicates that authentication and authorization take place in the Diameter server, as per the scenario described in Section 6.2. SIP server 2 creates a SIP 401 (Unauthorized) SIP response (step 7) based on the challenge included in the MAA message, including the authentication material needed by the SIP User Agent Client (UAC) to include the appropriate credentials. SIP server 1 forwards the SIP response to the SIP UAC (step 8). The SIP server 1 receives the next SIP REGISTER request containing the user credentials (step 9). Because SIP server 1 does not need to keep a state (and there is no guarantee that the SIP request arrives to the same SIP server 1), the Diameter client in SIP server 1 contacts the Diameter server again by sending a Diameter UAR message (step 10) to determine the SIP server allocated to the user. The Diameter server sends the SIP or SIPS URI of SIP server 2 in a Diameter UAA message (step 11).
SIP server 1 forwards the SIP REGISTER request to SIP server 2 (step 12). SIP server 2 validates the credentials by comparing the response supplied by the SIP UA with the expected response calculated by the SIP server 2 (based on the H(A1) received from the Diameter server). If the credentials are valid, SIP server 2 sends a Diameter Server-Assignment-Request (SAR) message (step 13) requesting the Diameter server to confirm the completion of the authentication procedure and to confirm the SIP or SIPS URI of the SIP server that is currently serving the user. The Diameter SAR message also serves the purpose of requesting that the Diameter server send the user profile to the SIP server. The Diameter server responds with a Diameter Server-Assignment-Answer (SAA) message (step 14). If the Result-Code AVP value does not inform SIP Server 2 of an error, the SAA message can include zero or more SIP-User-Data AVPs containing the information that SIP server 2 needs in order to provide a service to the user. SIP server 2 generates a SIP 200 (OK) response (step 15), which is forwarded to SIP server 1 and eventually to the SIP UAC (step 16).6.4. SIP Server Requests Authentication and Authorization
Figure 4 depicts a typical scenario where a stateless SIP proxy requests authentication information and authorization to a Diameter server, for the purpose of providing SIP routing services to a SIP User Agent. The SIP proxy server may be configured as an outbound SIP proxy, so that all the requests initiated by the SIP UA traverse the SIP proxy. According to Figure 4, a SIP User Agent sends a SIP request to its outbound SIP proxy server. In this case, the message is a SIP INVITE request (see step 1), but it could be any other SIP request. We assume that this SIP request does not contain any credentials at this time. The outbound SIP proxy server needs to authenticate and authorize the proxy services offered to the user. The Diameter client in the SIP server sends a Multimedia-Auth-Request (MAR) message (step 2). The Diameter server generates a nonce and sends a Multimedia-Auth-Answer (MAA) message (step 3) that includes the nonce and the rest of the data necessary for the SIP server to challenge the user, typically with HTTP Digest Authentication indicated in the MAA message. This data enables the SIP server to create a SIP 407 (Proxy Authentication Required) response (step 4) that contains a challenge. The SIP UA creates a new INVITE request (step 5) that contains the credentials. The Diameter client in the SIP server sends the credentials to the Diameter server in a new Diameter MAR message (step 6). The Diameter server validates the credentials and
authorize the SIP transaction in a Diameter MAA message (step 7). The SIP server forwards the SIP INVITE request to its destination (step 8) as per regular SIP procedures. Eventually, the session setup is confirmed with a SIP 200 (OK) response (step 9) that is forwarded to the SIP UA (step 10). The session setup is complete. +--------+ +--------+ |Diameter| | SIP | | server | | server | +--------+ +--------+ | | | | 1. SIP INVITE | ----------------------------------->| | 2. MAR | |<------------------| | 3. MAA | |------------------>| | | 4. SIP 407 (Proxy | Authentication Required) | <-----------------------------------| | | 5. SIP INVITE | ----------------------------------->| | 6. MAR | |<------------------| | 7. MAA | |------------------>| 8. SIP INVITE | |----------------> | | 9. SIP 200 (OK) 10. SIP 200 (OK) |<---------------- <-----------------------------------| | | Figure 4: SIP server requests authorization6.5. Locating the Recipient of the SIP Request
Figure 5 shows the scenario where SIP server 1 may be configured as a SIP edge proxy server, processing SIP traffic at the edge of a network. SIP server 1 receives a SIP INVITE request (step 1). SIP server 1 needs to find the address of SIP server 2, which is serving the recipient of the SIP request. The Diameter client in SIP server 1 sends a Diameter Location-Info-Request (LIR) message (step 2) to the Diameter server. The Diameter server responds with a Diameter Location-Info-Answer (LIA) message (step 3) that contains the SIP or
SIPS URI of SIP server 2. SIP server 1 then forwards the SIP INVITE to SIP server 2 (step 4). SIP server 2 eventually forwards the SIP INVITE to the appropriate UAS (step 5). +--------+ +--------+ +--------+ | SIP | |Diameter| | SIP | |server 1| | server | |server 2| +--------+ +--------+ +--------+ | | | 1. SIP INVITE | | | -------------->| 2. LIR | | |---------------->| | | 3. LIA | | |<----------------| | | 4. SIP INVITE | |--------------------------------->| | | | 5. SIP INVITE | | |--------------> | | | | | | Figure 5: Locating the SIP server of the recipient Although the example shows the connection between a SIP INVITE request and the Diameter LIR message, any SIP request other than REGISTER (such as SUBSCRIBE, OPTIONS, etc.) would trigger the same Diameter message. (A SIP REGISTER request will trigger a Diameter UAR message, as indicated in Figure 2 and Figure 3.) The scenario described in this section is also applicable in case an outbound SIP server is not interested in authenticating the user, but is required to locate a further SIP server to route the outbound SIP requests. In this case, the outbound SIP server is mapped to SIP server 1 as shown in Figure 5.6.6. Update of the User Profile
The Diameter SIP application provides a mechanism for a Diameter server to asynchronously download a user profile to a SIP server whenever there is an update of such user profile. It must be noted that the Diameter server also attaches the user profile to the Diameter Server-Assignment-Answer (SAA) message. This is valid for most of the daily situations; however, the administrator may decide to update or modify the user profile for a particular user, due to, e.g., new services made available to the user. This may involve mechanisms outside the scope of this specification, such as human
intervention, in the Diameter server. In this situation, the Diameter server is able to push the new user profile into the SIP server allocated to the user. The scenario is illustrated in Figure 6. When the user profile changes, the Diameter server sends a Diameter Push-Profile-Request (PPR) message (step 1) to the Diameter client in the SIP server allocated to that user (SIP server 2 in the examples). The Diameter PPR message contains one or more SIP-User-Data AVPs, a User-Name AVP and zero or more SIP-AOR AVPs. The Diameter client in SIP server 2 acknowledges the Diameter PPR message by sending a Diameter Push-Profile-Answer (PPA) message (step 2) to the Diameter server. +--------+ +--------+ |Diameter| | SIP | | server | |server 2| +--------+ +--------+ | | | 1. PPR | |------------------>| | | | 2. PPA | |<------------------| | | Figure 6: Diameter server pushes an update of the user profile6.7. SIP Soft State Termination
SIP can create soft states in SIP nodes based on events such as SIP registrations or SIP event subscriptions. These states are periodically refreshed, and cease to exist if they are not refreshed. Additionally, an administrative action can be taken to terminate a SIP soft state, or the SIP UA can explicitly terminate a SIP soft state. The Diameter base protocol offers a mechanism to create and delete states in Diameter nodes. These states are called Diameter user sessions. The Diameter server decides whether to use a Diameter user session as a mechanism to map to a SIP soft state. If the Diameter server decides to use Diameter user sessions, the termination of a Diameter user session implies the termination of the corresponding SIP soft state (e.g., registration, event subscription), and vice versa. If the Diameter server does not use Diameter user sessions, this Diameter SIP application offers specific commands to manage the SIP soft states. Implementations compliant with this specification MUST support both mechanisms of session management.
We provide support for both Diameter client- and Diameter
server-initiated session termination. Depending on whether Diameter
sessions are used, termination of a SIP soft state can be achieved by
one of the following methods:
o When the Diameter client (SIP proxy) wants to terminate the SIP
soft state and Diameter user sessions are not maintained (i.e.,
the Auth-Session-State AVP has been previously set to
NO_STATE_MAINTAINED), the Diameter client MUST send a
Server-Assignment-Request (SAR) message with the
SIP-Server-Assignment-Type AVP (Section 9.4) set to any of the
deregistration values: TIMEOUT_DEREGISTRATION,
USER_DEREGISTRATION, TIMEOUT_DEREGISTRATION_STORE_SERVER_NAME,
USER_DEREGISTRATION_STORE_SERVER_NAME,
ADMINISTRATIVE_DEREGISTRATION, DEREGISTRATION_TOO_MUCH_DATA.
o When the Diameter client (SIP proxy) wants to terminate the SIP
soft state and Diameter user sessions are maintained (i.e., the
Auth-Session-State AVP has been previously set to
STATE_MAINTAINED), the Diameter client MUST send a Session-
Termination-Request (STR) message as per regular procedures
according to RFC 3588 [RFC3588].
o When the Diameter server wants to terminate the SIP soft state and
Diameter user sessions are not maintained (i.e., the
Auth-Session-State AVP has been previously set to
NO_STATE_MAINTAINED), the Diameter server MUST send a
Registration-Termination-Request (RTR) message (see Section 8.9).
o When the Diameter server wants to terminate the SIP soft state and
Diameter user sessions are maintained (i.e., the
Auth-Session-State AVP has been previously set to
STATE_MAINTAINED), the Diameter server MUST send an
Abort-Session-Request (ASR) message as per regular procedures
according to RFC 3588 [RFC3588].
6.8. Diameter Server Discovery
The basic architecture assumption of this document is that all the
data related to a user is stored in a unique Diameter server.
Contrary to general opinion, this does not create a single point of
failure. It is assumed that Diameter servers are configured in a
redundant fashion in an attempt to mitigate the
single-point-of-failure problem.
In large networks, where the number of users may be significantly
high, there might be a need to scale the number of Diameter servers.
All the data associated with a user is still stored in one Diameter
server (typically, operating in a redundant configuration), but the data associated with different users may reside in different Diameter servers. Although this configuration scales well, it introduces a new problem, namely: given the user's SIP AOR as an input, how to determine which of various Diameter servers is storing the data for that particular SIP AOR. We solve this problem with inspiration from the Diameter redirection mechanism specified in RFC 3588 [RFC3588]. We include in the architecture a new Diameter node that, for the purpose of this document, is known as Diameter Subscriber Locator (SL). The Diameter SL contains a database or routing tables that map SIP AORs to Diameter server URIs. A particular Diameter server URI points to the actual Diameter server that stores all the data related to a particular SIP AOR, and in consequence, to the user who owns the SIP AOR. The Diameter SL acts in a similar way to a Diameter Redirect Agent, dispatching Diameter requests (e.g., providing the redirection URI in the answer). The Diameter SL can redirect all the request pertaining to a user by setting the Redirect-Host-Usage AVP with a value ALL_USER, as specified in RFC 3588 [RFC3588]. The Diameter SL can be replicated in different nodes along the network, for the purpose of building scalability and redundancy. The database or routing tables have to be consistent across all these different Diameter SLs, so that equal Diameter requests will produce equal Diameter answers, no matter which Diameter SL processes the request. +--------+ +--------+ +--------+ +--------+ | SIP | |Diameter| |Diameter| | SIP | |server 1| |SL red. | |server 1| |server 2| +--------+ +--------+ +--------+ +--------+ | | | | 1. SIP INVITE| | | | ------------>| 2. LIR | | | |---------->| | | | 3. LIA | | | |<----------| | | | 4. LIR | | |---------------------->| | | 5. LIA | | |<----------------------| | | 6. SIP INVITE | | |----------------------------------->| 7. SIP INVITE | | | | -------------> | | | | Figure 7: Locating a Diameter server. SL redirecting requests
Figure 7 shows an example of operation of a Diameter SL acting in redirect mode. SIP server 1 receives an INVITE request (step 1) addressed (in the SIP Request-URI) to a user for which the Diameter client in SIP server 1 does not possess routing information. In other words, the Diameter client in SIP server 1 does not know the URI of the Diameter server 1. The Diameter client sends a Diameter LIR message (step 2) to any of the Diameter SLs configured in the network. The address of those SLs is assumed to be pre-provisioned in the Diameter client. The Diameter SL, based on the contents of the SIP-AOR AVP and its own routing tables, determines the Diameter server that stores the information allocated to such user. Then it builds a Diameter LIA message (step 3) that includes a Result-Code AVP set to DIAMETER_REDIRECT_INDICATION and one Redirect-Host AVP, whose value is set to the URI of the Diameter server that stores the information related to such user. Then the Diameter client in SIP server 1 builds a new LIR message (step 4) addressed to the Diameter server received in the Redirect-Host AVP. The rest of the procedure is completed as described in previous sections.
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