As

The CCF also has timers for closing partial session CDRs. All the elements apart from the I-CSCF send session ACRs and all the elements apart from the MRFC send event ACRs. It is the operator's choice which SIP method or ISDN User Part (ISUP) message triggers the ACR. However, two mandatory items have been defined Whenever SIP 200 OK, acknowledging an initial SIP INVITE, is received or MGCF receives an ISUP answer, ACR start will be sent to the CCF. Whenever SIP BYE is...

Info

Figure 6.1 IMS session establishment call flow. The INVITE request that Tobias's UE sends toward Theresa includes the following headers that are related to either his or her identity INVITE sip theresa home2 . hu SIP 2.0 From Your Brother < sip tobiSbrother. con tag veli To My beloved Sister < sip Theresa sister ,com> P-Preferred-Identity < sip tobias homel.fr> Privacy None Obviously, the From and To headers can be set to any value the sender likes. We chose the wording in this...

Authentication and Key Agreement

Security in the IMS is based on a long-term secret key, shared between the ISIM and the home network's Authentication Centre (AUC). The most important building block in IMS security is the ISIM module, which acts as storage for the shared secret (K) and accompanying AKA algorithms, and is usually embedded on a smartcard-based device called the Universal Integrated Circuit Card (UICC). Access to the shared secret is limited. The module takes AKA parameters as input and outputs the resulting AKA...

Cx reference point

Subscriber and service data are permanently stored in the HSS. These centralized data need to be utilized by the I-CSCF and the S-CSCF when the user registers or receives sessions. Therefore, there has to be a reference point between the HSS and the CSCF. This reference point is called the Cx reference point and the selected protocol is Diameter. The procedures can be divided into three main categories location management, user data handling and user authentication. Generally, descriptions only...

Dh reference point

When multiple and separately addressable HSSs have been deployed in the network, the AS cannot know which HSS it needs to contact. However, the AS needs to contact the SLF first. For this purpose the Dh reference point was introduced in Release 6. In Release 5 the correct HSS is discovered by using proprietary means. The Dh reference point is always used in conjunction with the Sh reference point. The protocol used in this reference point is based on DIAMETER. Its functionality is implemented...

Session dialog transactions and branch

During session establishment and while the session is active as well, different types of signalling messages are exchanged and different kinds of relations between the two items of UE are established. The term session describes the media connections between the two users. Tobias wants to exchange audio and video media streams with his sister. This exchange of media is done on the so-called bearer level this means that Realtime Transport Protocol (RTP) packets are sent from the two items of UE...

Support of roaming

From a user point of view it is important to get access to her services regardless of her geographical location. The roaming feature makes it possible to use services even though the user is not geographically located in the service area of the home network. Section 2.1.1 has already described two instances of roaming namely, GPRS roaming and IMS roaming. In addition to these two there exists an IMS circuit-switched CS roaming case. GPRS roaming means the capability to access the IMS when the...

XCAP usage for resource presentity lists

Section 23.3 discussed resource presentity lists and how to gain state information about these lists. This section discusses how these lists are created and maintained. The list creation solution takes advantage of the XML Configuration Access Protocol XCAP see Chapter 21 as an application usage. Draft-ietf-simple-xcap-list-usage defines the XML schema along with its semantics. It also defines the following Application usage ID Additional constraints none. Resource interdependencies the list is...

Error handling

Diameter errors fall into two categories protocol errors and application errors. Protocol errors occur at the base protocol level and are treated on a per-hop basis e.g., errors in message routing may direct a downstream agent to take special action . Application errors are generated due to problems with specific Diameter applications. When a request message generates a protocol error an answer message is sent back with the E bit set in the Diameter header, indicating a protocol error. The...

GPRS entities

The Serving GPRS Support Node SGSN links the RAN to the packet core network. It is responsible for performing both control and traffic-handling functions for the PS domain. The control part contains two main functions mobility management and session management. Mobility management deals with the location and state of the UE and authenticates both the subscriber and the UE. The control part of session management deals with connection admission control and any changes in the existing data...

Mechanism to register multiple user identities at once

SIP allows one public user identity to be registered at a time so, if a user has more than one public user identity, then she has to register every public user identity individually. This may be frustrating and time-consuming from the end user perspective. Obviously, registering four public user identities would consume four times Figure 3.24 Example of implicit registration sets. Figure 3.24 Example of implicit registration sets. as much radio resource in the case of the UMTS than registering...

Scscf

If the I-CSCF does not know the address of the HSS, then it contains the destination realm. Number of Authentication Items information about how many authentication vectors the S-CSCF wants to download at once. Multiple authentication vectors can be downloaded e.g., if an operator wants to re-authenticate all re-registrations . Authentication Data includes authentication scheme e.g., Digest-AKAvl-MD5 and authentication information in case of synchronization failure. The HSS responds with...

Icscf

Figure 5.2 Routing during registration. Figure 5.2 Routing during registration. 6 Binds Contact to user's SIP URI 8 Sends Service-Route in 200 OK During the registration procedures the UE will learn the direct route to the S-CSCF from the Service-Route header. After that the I-CSCF will no longer need to be contacted when Tobias's UE sends out an initial request. The S-CSCF will become aware of the address of Tobias's P-CSCF from the Path header. This is necessary as all initial requests that...

PCSCFs subscription to registrationstate information

The P-CSCF also needs to subscribe to Tobias's registration-state information and, therefore, creates a SUBSCRIBE request, which looks similar to the one that the terminal generates SUBSCRIBE sip tobias homel. fr SIP 2 . 0 Via SIP 2 . 0 UDP pcscfl .visitedl.fi From lt s ip pc se f 1. vi s itedl.fi gt tag reti is i To Tobias lt sip tobias homel.fr gt P-Asserted-Identity lt sip pcscfl.visitedl.fi gt Accept application reginfo xml Contact lt sip pcscfl.visitedl.fi gt

Sharing a single user identity between multiple terminals

Traditionally, in the CS every single user has her own Mobile Subscriber International ISDN Number MSISDN number that is used to reach the user. It is not possible for a single user to use multiple terminals with the same MSISDN number simultaneously. Having two mobile stations with identical MSISDN numbers would cause significant conflicts in the network. Nowadays, users may have more than one item of UE with totally different capabilities big small screen, camera no camera, full keyboard and...

Compression negotiation

The ability to compress SIP messages over the air interface is essential for the IMS. How signalling compression SigComp works is described in Section 3.16. This section shows how the UE and the P-CSCF indicate that they support SigComp and are both willing to use it. P-CSCF and IMS UE must support SIP signalling compression SigComp , but they are not mandated to use it. Therefore, they need a mechanism to express whether they are willing to apply signalling compression. RFC3486 defines a new...

1

Figure 3.17 Distribution of charging information. Public Identification comprises those user public identities that are associated with a service profile. Identities can be either SIP URIs or tel URIs. Each public user identity contains an associated barring indication. If the barring indication is set, then the S-CSCF will prevent that public identity e.g., a temporary public user identity from being used in any IMS communication other than registrations and re-registrations. Figure 3.18...

Home Subscriber Server

The Home Subscriber Server HSS is the main data storage for all subscriber and service-related data of the IMS. The main data stored in the HSS include user identities, registration information, access parameters and service-triggering information 3GPP TS 23.002 . User identities consist of two types private and public user identities. The private user identity is a user identity that is assigned by the home network operator and is used for such purposes as registration and authorization, while...

Service provision

The IMS is not a service in itself on the contrary it is a SIP-based architecture for enabling an advanced IP service and application on top of the PS network. IMS provides the necessary means for invoking services this functionality is called service provision. IMS service provisioning contains three fundamental steps 1. Define possible service or service sets. 2. Create user-specific service data in the format of Initial Filter Criteria when a user orders modifies a subscription. 3. Pass an...

SIP Security Mechanism Agreement

5.8.1 Why the SIP Security Mechanism Agreement is needed The IMS in 3GPP Releases 5 and 6 makes use of IPsec as the security mechanism between the P-CSCF and the UE. IPsec is only one of several possible security mechanisms. The IMS was designed to allow alternative security mechanisms over the Gm interface as well. Allowing such an openness usually creates backward compatibility problems because, for example, a Release 6-compliant UE would not be able to understand any alternative security...

Mw reference point

The Gm reference point links the UE to the IMS namely, to P-CSCF . Next, a SIP-based reference point between different CSCFs is needed. This reference point is called Mw. The procedures in the Mw reference point can be divided into three main categories registration, session control and transaction In the registration procedure the P-CSCF uses the Mw reference point to forward a registration request from the UE to the I-CSCF. The I-CSCF then uses the Mw reference point to pass the request to...

Routing of PSIs

The concept of a public service identity PSI i.e., a URI that is not related to a user but to a service is explained in Section 3.4.2. This chapter is a basic introduction to the routing principles of PSIs, as they are quite different from those that are applied between two Internet Protocol Multimedia Subsystem IMS users. As PSIs are not registered, requests to and from them do not need to traverse any Serving-Call Session Control Function S-CSCF . There are three scenarios for PSI routing....

Figures

1.1 The key ingredient to new, enriching user experiences is peer-to-peer IP connections of applications 4 1.2 The IMS and its relationship with existing communication systems 4 1.3 Main 3GPP working groups doing IMS work 8 2.1 IMS connectivity options when a user is roaming 12 2.2 IMS CS roaming alternatives 16 2.3 IMS and layering architecture 18 2.5 Relationship between different AS types 26 2.6 Signalling conversion in the SGW 28 2.8 HSS resolution using the SLF 39 3.1 A high-level IMS...

Invite

Via ue, pcscf, scscfl, as, scscfl Route icscf Record-Route pcscf, scscf, as, scscfl of Theresa. To achieve this, the S-CSCF adds a set of routing-related headers by putting Its own address on top of the Route headers, in order to receive the INVITE request back from the AS. The address of the AS on top of the Route headers, in order to route the INVITE request to the AS as the next hop. Its own address on top of the Record-Route headers, so that it stays on the route for subsequent requests as...

Signalling PDP context establishment

Before Tobias's UE can start the IMS registration procedures, it needs to establish an IP connection with the network. In the case of GPRS such an IP connection is provided by either a dedicated signalling PDP context or a general purpose PDP context. The concepts and procedures for PDP context establishment and usage are described in Section 3.7 and Chapter 13. In this example it is assumed that Tobias's UE establishes a dedicated signalling PDP context with the GGSN in Finland. After the UE...

Gm reference point

The Gm reference point connects the UE to the IMS. It is used to transport all SIP signalling messages between the UE and the IMS. The IMS counterpart is P-CSCF. Procedures in the Gm reference point can be divided into three main categories registration, session control and transactions In the registration procedure the UE uses the Gm reference point to send a registration request with an indication of supported security mechanisms to the P-CSCF. During the registration process the UE exchanges...