Rtcp
RTP Control Protocol RTCP packets are transmitted periodically to all participants in a session. There are four RTCP functions To provide feedback on the QoS of real-time data distribution. To carry a persistent identifier of the RTP source called a CNAME . To permit an adjustable RTCP packet distribution interval the report interval . To convey session control information. 11.2.1 RTCP packet types There are five types of RTCP packets SR a sender report, providing transmission and reception...
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 Hss
of it. 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 1
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...
I 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...
Info Ern
Figure 1.2 The IMS and its relationship with existing communication systems. Figure 1.1 The key ingredient to new, enriching user experiences is peer-to-peer IP connections of applications. Figure 1.2 The IMS and its relationship with existing communication systems. Figure 1.2 shows a consolidated network where the IMS introduces multimedia session control in the packet-switched domain and at the same time brings circuit-switched functionality in the packet-switched domain. The IMS is a key...
Uicc
Figure 3.4 IP Multimedia Services Identity Module. for request communication with other users see Section 3.4.1.2 for further information . The home network domain name consists of the name of the entry point of the home network. It is used in a registration request to route the request to the user's home network. Administrative data include various data, which could be used, say, by IMS subscribers for IMS operations or by manufacturers to execute proprietary auto-tests. Access Rule Reference...
Info Tmb
8.13.7 The SIP REFER method 293 8.13.8 The message sipfrag MIME type 294 8.13.9 SIP extension header for registering non-adjacent 8.13.10 Private SIP extensions for asserted identity within 8.13.11 Security mechanism agreement for SIP 296 8.13.12 Private SIP extensions for media authorization 298 8.13.13 SIP extension header for service route discovery 8.13.14 Private header extensions to SIP for 3GPP 299 8.13.15 Compressing SIP 300 9.1 SDP message contents 301 9.1.1 Session description 302...
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...
Info Mdd
Figure 25.4 Subscribing to a conference state. Figure 25.4 Subscribing to a conference state. More notifications can then follow depending on the change of state of the conference. 25.3.4 Conference creation using CPCP Using the Ut interface a CPCP message can be sent to the conference server to set up a conference. Figure 25.5 shows an example of a conference being created and participants added. User A creates the conference using the following procedure Start time 28-November-2003-7 00GMT....
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...
Acknowledgements
The authors of this book would like to extend their thanks to colleagues working in the 3GPP and the IETF for their great efforts in creating the IMS specifications and related protocols. The authors would also like to give special thanks to the following who helped in the writing of this book by providing excellent review comments and suggestions Erkki Koivusalo Hannu Hietalahti Tao Haukka Risto Mononen Kalle Tammi Risto Kauppinen Marco Stura Ralitsa Gateva Juha-Pekka Koskinen Markku Tuohino...