SDP Offer Answer for Voice Only Sessions

Many factors determine how the SDP offers and answers will be constructed for voice-only sessions. Multimedia telephony clients are required to support the AMR codec for narrowband voice and the AMR-WB codec if the client supports wideband voice. The client is required to support all codec modes for these codecs but a media gateway may support only a subset of the codec modes. Even if the media gateway itself supports all codec modes, it typically needs to restrict the allowed codec modes to a...

General SDP Usage

For Multimedia Telephony, the media types that can be used for real-time communication are audio, video or text. The clients also need to define what UDP port to send the media type to. If several media types are used, then one should use one UDP port for each medium. The participants also need to agree on the transport protocol that will be used for the media. For real-time media in Multimedia Telephony, RTP will be used. The RTP profile to use is the RTP Profile for Audio and Video...

Delay Calculation

Ims Signaling Flow

The total time to send a SIP message between a Multimedia Telephony client and the IMS core or vice versa is given by the sum of the following the time for Multimedia Telephony client processing in the mobile terminal to do e.g. Figure 7.41 Signaling flow of the Multimedia Telephony session setup with delay components. the RAN transmission time of the SIP message from the mobile terminal to the P-CSCF the time for SIP SigComp processing in the IMS core and processing in the PCC policy control...

IMS Signaling Security

SIP signaling between the IMS terminal and the P-CSCF Gm reference point is protected by IPsec, as discussed in the following subsections. In the common roaming scenario described in Section 6.2.3, where the mobile terminal has its point of presence in the home GGSN, the SIP signaling is protected all the way from the mobile terminal in the visited network to the P-CSCF in the home IMS network. SIP signaling traffic between other IMS nodes is protected by NDS mechanisms on a hop-by-hop basis,...

Media and Session Adaptation

Media layer adaptation in IMS Multimedia Telephony has not been standardized at all, at least not yet. However, discussions are ongoing and, since rate adaptation is already in place for speech, it is fair to assume that there will be some kind of media layer adaptation in place in the final 3GPP IMS Multimedia Telephony standard for 3GPP release 7. Hence, in this section, we take the liberty to discuss one example of how media layer adaptation could be done for speech in IMS Multimedia...

Shyam Chakraborty Tomas Frankkila

The innovation of voice communication with electrical means by Alexander Graham Bell initiated the era of Public Switched Telephone Networks PSTN , and revolutionized the way people in modern civilization would communicate. The important elements of PSTN are full-duplex conversational service, narrowband speech and Circuit Switching CS . The success of PSTN provided a strong impetus for seeking improvements and modifications to the basic conversational service to provide a richer experience,...

Establishment of Multimedia Telephony Sessions

The SIP INVITE method is used to establish Multimedia Telephony sessions. The SIP method in its simplest form uses a three-way handshake to establish a SIP session. In that case a SIP INVITE message is sent from the originating client to the terminating client. When the user answers the call, the client responds with a SIP 200 OK message. When receiving the SIP 200 OK message the originating client acknowledges the message with a SIP ACK. However, to meet the requirements for establishing the...

OMA PoC Release

As the cellular networks evolve, they will be able to provide other more advanced IP-based real-time services than the plain voice services offered in the OMA PoC Release 1 specifications. Advanced services should, in this context, be seen as services that are more demanding in terms of bit rate and delay, and that offer improved possibilities of person-to-person communication and thus increase perceived user value compared to a plain voice call. OMA is trying to make use of the new...

The Tispan Next Generation Network

Ims With Ibcf

Figure 3.23 The TISPAN NGN architecture. Figure 3.23 The TISPAN NGN architecture. ETSI TISPAN has developed an architecture to provide multimedia services over fixed accesses. This architecture is called Next Generation Network NGN and is based on the IMS. NGN is an access agnostic architecture able to provide IMS services to users using any type of access. This way, users can enjoy the same set of services regardless of the access they use. Therefore, TISPAN NGN achieves the much expected...

The Home Subscriber Server and the Subscription Location Function

The Home Subscriber Server HSS is a database that stores the profile of all the users of a domain. A user's profile includes security-related information such as cryptographic keys, service-related information such as to which services the user is subscribed, and other information such as the S-CSCF that has been allocated to the user or the user's location. An HSS is supposed to be a central database for a domain. However, some networks have more users than a single HSS can handle. These...

CELP Speech Codecs

Most modern speech codecs are based on the Codebook Excited Linear Predictive CELP codec model 49 , where speech is synthesized according to a model of how the speech is produced by humans. The synthesis, in the decoder, follows the following steps 1. A fixed code book generates an innovation. This simulates the air flow created by the lungs. 2. The innovation is passed through a pitch predictor, which is also often called adaptive code book. This creates pitch pulses in a similar way as the...

Policy Control Signaling

Service Data Flow Pcc

Policy control is an important mechanism for a Multimedia Telephony service since it is the mechanism that is used to coordinate events such as Multimedia Telephony session initiation modification in the application layer and resource management events such as bearer establishment modification in the IP bearer layer. Policy control is the mechanism that enables IMS to enforce suitable QoS for a given service or media flow. In 3GPP release 6, two different architectures were used for policy...

Multimedia Telephony Service Scenario

A service scenario defines how an end-user may want to use a service to fulfill a particular communication need. The scenario tries to explain the context of use and the concept of the service from an end-user perspective. By developing scenarios for a service under development a good foundation for requirement derivation is laid. In this section a Multimedia Telephony communication service scenario is presented in order to highlight end-user and operator requirements and benefits of a...

OMA Instant Messaging

Oma Service Enabler

Instant Messaging IM allows users to exchange information with others in near real time. The interactive nature of an IM service encourages the IM users to engage in conversations. Typically, small text messages are exchanged in IM conversations but the OMA Instant Messaging communication service supports other content types than text like images, video clips, etc., making it a multimedia IM service enabler. The OMA Instant Messaging communication service enables a user to send messages to...

References

1 3GPP. 3G security Network Domain Security NDS IP network layer security. TS 33.210, 3rd Generation Partnership Project 3GPP , December 2005. 2 3GPP. 3GPP enablers for Open Mobile Alliance OMA Push-to-talk over Cellular PoC services Stage 2. TR 23.979, 3rd Generation Partnership Project 3GPP , June 2005. 3 3GPP. AMR speech codec Error concealment of lost frames. TS 26.091, 3rd Generation Partnership Project 3GPP , January 2005. 4 3GPP. AMR speech codec General description. TS 26.071, 3rd...

Video

Each of the video codecs used in the IMS Multimedia Telephony service has a payload format of its own. H.263 uses RFC 2429 52 , MPEG-4 Visual uses RFC 3016 130 and H.264 AVC uses the payload format defined in RFC 3984 186 . They have in common that each RTP packet consists of the fixed RTP header and possibly extra media-type specific headers followed by or interleaved with the video bitstream. With a few exceptions, RTP packets should not contain video data from different frames, i.e. the...

IMS Communication Services

IMS was already from the beginning seen as a service platform that should be able to support a multitude of different service types including telephony kind of services. The 3GPP provided the first set of IMS specifications in 3GPP release 5 in 2002. But the first set of IMS specifications lacked standardized services. In fact, the early view was that IP multimedia applications should not be standardized and existing legacy telephony and supplementary services should not be restandardized as IP...

IMS Security Overview

Access to IMS services requires authorization. The authorization is based on user authentication performed in conjunction with user registration in the systems. The user authentication scheme called IMS Authentication and Key Agreement AKA 15 uses the same principles as user access authentication in UMTS, and hence IMS AKA provides mutual authentication. It also provides keys shared between the user and the IMS domain. These keys will be used for the protection of the SIP signaling between the...

Error Resilient Speech Service

One of the most challenging aspects of creating a real-time service in any system is how to make the service resilient to the various types of impairments that may occur. In the literature, the most commonly discussed problem is handling of packet losses. The typical reason for packet losses is channel interference due to either poor coverage or high system load. For dedicated channels in UTRAN, the fast and precise power control typically manages to maintain a BLock Error Rate BLER that is...

OMA PoC Release 1 Architecture

Figure 8.6 shows the high-level architecture of an OMA PoC Release 1 compliant system. The system includes a number of nodes and logical functions. The CSCF implements the S-CSCF, I-CSCF and P-CSCF functionality that provides SIP signaling, routing and registration. Lis amp ntgroupManagement , XCAP Lis amp ntgroupManagement , XCAP Figure 8.6 The logical architecture of OMA PoC Release 1. The HSS implements functionality for authentication, location query updates and subscriber profile storage....

Radio Realization

In order to support efficient transport of conversational media over the air interface, it is often necessary or at least beneficial to optimize the network configuration. In this section we discuss the most important radio network parameters affecting the media, and show how they could be optimized for best performance. The actual performance is then evaluated in Chapter 7, for both optimized and unoptimized configurations. UMTS provides several options for realizing the Multimedia Telephony...

A2 MaxCQI Scheduler

Figure A.9 Maximum, average packet delays and 98 and 99 percentiles for 10 left and 20 right relative load with the max-CQI scheduler. Figure A.10 Maximum, average packet delays and 98 and 99 percentiles for 30 left and 35 right relative load with the max-CQI scheduler. Figure A.11 Maximum, average packet delays and 98 and 99 percentiles for 55 load with the max-CQI scheduler. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Burst length 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Burst length Figure A.12 Histogram...

CSICS Architecture

When using CSICS, the CSICS client implemented in the mobile terminal presents the CS call and the IMS session within one context to the user. To facilitate this, the following capabilities need to be supported exchange of information related to the current access exchange of terminal capability information addition of an IMS session to an ongoing CS call addition of a CS call to an ongoing IMS session. Figure 8.1 shows a high-level end-to-end architecture of a simultaneous IMS session and CS...

SDP Offers and SDP Answers

For 3GPP networks, the SDP offer-answer model defined in RFC 3264 170 is used to reach a common agreement on how the media should be encoded and how the media packets should be configured. One fundamental idea with the SDP offer-answer model is that the client that initiates a session should construct an SDP offer that includes all the media types that it wants to use in the session and all the capabilities that the initiating client can support for each media type. One RTP Payload Type is...

Mobile TerminalRansgsnggsn

Pdp Context Activation Create Pfc

Figure 4.4 GPRS session management flow for a mobile terminal originated establishment of PDP context. Figure 4.4 GPRS session management flow for a mobile terminal originated establishment of PDP context. 1. The mobile terminal generates an Active PDP Context Request message when activating a so-called primary PDP context or an Activate Secondary PDP Context Request message when activating a so-called secondary PDP context . The choice of activating a primary or secondary PDP context depends...

The Sip Update Method

Update Method Sip

A use case suitable for the SIP UPDATE method is the Multimedia Telephony client gets an indication from the radio layers of the mobile terminal that it needs to change one or more media related parameters. One such example is a sudden change of the radio access, which triggers the need to lower the maximum possible session bandwidth. The resulting SIP UPDATE flow is described in Figure 4.12 and below. 1. The Multimedia Telephony client A has received information that it needs to renegotiate...

WeShare a 3Gpp Csics Service Example

As mentioned earlier, 3GPP CSICS is an enabler, a communication service, which can be used to packetize useful multimedia services for the end-user. One effort to create such a service is the 'Video Share definition' specifications developed by GSM Association GSMA . In this section one service offering that complies with these specifications, the Ericsson IMS WeShare solution, is presented. The Ericsson WeShare solution is a multimedia person-to-person service that provides the end-users with...

OMA Instant Messaging Architecture

The IM architecture has similarities with the OMA PoC architecture, which is presented in Section 8.2.2. As in OMA PoC the IM server implements different roles. One reason is to be able to offer one-to-many chat sessions in a multi-operator environment. The roles used in that case are the controlling IM function and the participating IM function. Figure 8.12 show a high-level view of a multi-operator group IM communication. But there are differences compared to PoC, one main difference being...

Using Mobile Terminal Initiated QoS

When using mobile terminal initiated QoS, it is mandatory for the Multimedia Telephony client to be able to get knowledge about the status of the resource reservation. The basic idea is that when the Multimedia Telephony client knows that it does not have resources reserved for the media stream it indicates using the SDP attribute 'inactive' see RFC 3108 131 and using the SIP precondition method see RFC 3312 57 and RFC 4032 56 that it has no resources available. The SIP precondition method...

Communication Hold

The HOLD supplementary service enables a Multimedia Telephony user to suspend the media stream s of an established Multimedia Telephony session, and resume the media stream s at a later time. The HOLD service utilizes a set of procedures in accordance with RFC 3264 170 . Thus, these are the SDP parameters to use when putting media streams on hold 'inactive' if the media stream was previously set to 'recvonly' 'sendonly' if the media stream was previously set to 'sendrecv'. And the following...

Speech Transport Processing Jitter

In this section, several different aspects of jitter are discussed in the scope of the speech media component. Since the speech codecs standardized for IMS Multimedia Telephony are AMR and AMR-WB as described in Section 5.1.1.3, they are assumed to be the speech codecs used when applying the jitter management schemes discussed. However, the jitter management schemes are not uniquely tied to these codecs and they may be used in other circumstances equally well. In order to be able to handle...

Using Network Initiated QoS

Network initiated QoS, which enables the use of QoS even if the Multimedia Telephony clients have no QoS knowledge, is proposed as a possible enhancement in 3GPP release 7. This would enable the use of QoS in Multimedia Telephony also for instance for a PC client that has its PS connection via a switch connected to an HSPA modem. Since the Multimedia Telephony client needs no knowledge about QoS and resource reservations, the signaling flow for a Multimedia Telephony session establishment...

Daniel Enstrom Krister Svanbro Per Synnergren

Since the introduction of IMS in 3GPP release 5, VoIP over cellular access has been discussed in the mobile industry. However, the early 3GPP specifications did not specify any VoIP service in detail and thus there was an ambiguity in the industry regarding the technical realization of an interoperable VoIP service. To address this issue, Ericsson initiated an activity to define an IMS-based Multimedia Telephony communication service in 3GPP release 7. The aim was to create specifications...

Charging

The IMS provides two types of charging offline and online. Offline charging is typically used to charge users with permanent subscriptions while online charging is typically used for prepaid users. 3.5.10.1 Offline Charging Architecture Figure 3.20 shows the offline charging architecture. The SIP elements with information about the session being charged send that information to the Charging Data Function CDF over the Diameter-based Rf interface. The CDF generates the Charging Data Records CDRs...

Core Network and Service Layer Realization

Multimedia Telephony makes use of the IMS functionality in the service layer. In Figure 3.25 one possible realization of Multimedia Telephony is shown. The system presented includes the IMS as outlined in Section 3.5 and information about the functions and interfaces can be found there. The text below highlights some of the functions that are of special interest for Multimedia Telephony and are part of this particular realization of the Multimedia Telephony communication service. The functions...

Kmh 120 kmh

Number of speech frames lost per hand-over Figure 7.13 The complementary cumulative distribution function of the number of voice frames lost per hand-over when using HSDPA. The results are shown for three mobile speeds, 3 km h, 50 km h and 120 km h. The authors would like to thank Stefan Wager for providing data for this plot. In Figure 7.13 we show the Complementary Cumulative Distribution Function CCDF of the number of voice frames lost per hand-over for various mobile speeds. It can be seen...

Hybrid Video Coding

One of the paradigms of video coding is to take advantage of temporal redundancy between frames to make the coding as efficient as possible. This is particularly true for low bit rates and qualities characteristic for mobile applications where inter-frame prediction plays a crucial role in the coding process. All video coding standards mentioned in the following sections are so-called hybrid coding standards that utilize temporal motion compensation for inter-frame prediction in combination...

Authentication and Authorization

Ims Registration

In IMS, a user must register before being allowed to access services. At the initial registration, the mobile terminal and the S-CSCF perform mutual authentication by running the IMS AKA protocol 15 . The IMS AKA uses the long term key that is associated with the Private User Identity and that is shared between the ISIM and the HSS. Figure 6.6 shows the IMS authentication procedure. The message sequence is the same as in the IMS registration shown in Figure 4.1, but here the relevant message...

UMTS Authentication and Key Agreement

Umts Authentication Procedure

As mentioned, the authentication and key agreement scheme used by IMS is the same as in UMTS. Therefore, a short presentation of the UMTS authentication and key agreement mechanism is in order. Mobile terminals used in UMTS typically contain a UMTS Subscriber Identity Module USIM . The USIM contains, among other things, a key, K, which is also present in the HSS in the home operator's network. When a mobile terminal attaches to a UMTS network the user is authenticated by providing proof of...

Video Standards H263 and MPEG4

For video conversation in 3G mobile devices, H.263 120 and MPEG-4 Visual 93 are the most important video coding standards. They are used in 3G-324M, which is the mobile circuit switched video telephony standard defined by 3GPP in 6 and 7 based on the ITU-T Recommendation H.324 119 for video conferencing. The baseline version of H.263 was approved in 1995 and has been adopted by 3GPP as the common mandatory video codec that all video-enabled 3G mobile phones must support. There are two extended...

Identities

Every IMS user is assigned a Private User Identity. The Private User Identity uniquely identifies the user's subscription and is authenticated at user registration. Private User Identity takes the form of a Network Access Identifier NAI as defined in RFC 2486 48 and TS 23.003 34 . Associated with the Private User Identity, one or more Public User Identities are allocated to the IMS user. Each Public User Identity takes the form of a SIP URI or a TEL URI e.g. 'tel 1-123-456-7890' and is used for...

SDP Offer Answer for Video

A client may support several video codecs and may therefore include more than one codec and corresponding profiles and levels in its SDP offer. An example is shown in Table 5.14 where two options associated with the RTP Payload Type numbers 99 and 100 are offered. Table 5.14 Example SDP offer for H.263 and MPEG-4 Part 2 video. m video 49154 RTP AVP 99 100 a rtpmap 99 H263-2000 90000 a fmtp 99 profile 0 level 45 a rtpmap 100 HP4V-ES 90000 a fmtp 100 profile-level-id 9 The first offer includes...

OMA PoC and PDP Context Establishment

Ims Session Establishment

The set of OMA PoC specifications do not specify when resource reservations e.g. setting up a PDP context for the media should be done. The reason for this is that OMA develop services for general IP access. Instead it is the responsibility of the organizations developing the underlying access to specify if resources need to be reserved and in that case how and when resources are reserved for the service. The 3GPP developed a technical report see 3GPP TR23.979 2 that addresses the issue of how...

Communication Diversion Communication Forwarding on Mobile Subscriber Not Reachable

Call Forward Not Reachable

The CFNRc service is a new addition to the set of CDIV services that already includes CFB, CFNL and CFNR which enable the communication to be diverted when the user is busy, not logged in or there is no reply. The difference is that the CFNRc service targets a mobile terminal specific scenario, namely the case when the user is not reachable due to for instance being out of coverage. Thus, the CFNRc service was first discussed in 3GPP and later it was agreed to include CFNRc also in the TISPAN...

Communication Deflection

Ims Call Forwarding Flow

The second example presented in Figure 4.15 shows an example of call forwarding using the Communication Deflection method. In this case the Multimedia Telephony user B has also activated the call forwarding service. The difference from the Communication Forwarding Unconditional service is that in this case it is the Multimedia Telephony client B1 that has the knowledge that the user is now available at Multimedia Telephony client B2 rather than the network. It should be noted that the...

Header Compression

Multimedia telephony is the way to realize telephony in an all-IP cellular network. An all-IP cellular network assumes that voice payload is transported IP all the way, i.e. the IP protocols do not terminate before the air interface. IP all the way enables IP service flexibility, that is, there are fewer dependences between applications and the wireless access network and a base is created where it is easier to create new services including a voice component. This could be compared with today's...

QoS Attributes

GERAN and UTRAN use a common core network for packet transfer. This common core network provides the General Packet Radio Service GPRS , which is designed to support several QoS levels to allow efficient transfer of non-real-time traffic as well as real-time traffic. Table 3.1 Quality of Service attributes per traffic class. Table 3.1 Quality of Service attributes per traffic class. In order to send and receive packet data via GPRS, the mobile terminal must activate a PDP context. This...

Speech

Tandem Free Operation

Probably the most interesting interworking scenario is interworking between the voice media component in Multimedia Telephony and legacy circuit switched voice calls in GERAN and UTRAN. The reason why this is so important is simply because of the large amount of legacy phones and systems deployed over the whole world. It has been estimated by GSM Association 83 , that there are currently over 2 billion GSM subscribers in about 210 countries over all the world. Section 5.7.1.1 therefore...

Example Delay Budget for HSPA

The end-to-end delay is an important compromise in all real-time wireless communication systems. On the one hand, for CS bearers a certain amount of delay is required to give room for sufficient interleaving. Interleaving is needed to handle fading dips and distribute the bit errors over time so that the channel decoder has a fair chance of recovering the transmission block. For best possible channel coding performance, the interleaving should be as long as possible. On the other hand, long...

IMS Registration

As discussed in Section 4.1.1, registrations create a binding between an AoR and a contact URI. In the IMS, registrations create an extra state in the network, in addition to that type of binding. IMS users may have several AoRs, which in the IMS are referred to as public user identities. For example, a user may have a public user identity that consists of a SIP URI and another public user identity that consists of a tel URI e.g. lt tel 4681234567 gt . A single IMS registration may bind several...

Signaling Compression

Message Flow Control Ims

As an option, signaling compression can be applied to the SIP signaling for e.g. Multimedia Telephony. The use of SIP for IMS session establishment in cellular systems such as UMTS may lead to unnecessarily long setup times if the available bandwidth for SIP signaling is low. In order to reduce the setup times, the Signaling Compression scheme SigComp see RFC 3320 161 and RFC 3321 85 has been developed by the IETF to compress text-based protocols such as SIP. In an IMS system, SigComp is...

OMA PoC Talk Burst Control

PoC is a half-duplex, one-way communication method between participants and implies that one party speaks while the other parties listen this requires a talk burst control mechanism, also known as floor control. The talk burst control mechanism in OMA PoC is a confirmed request grant procedure within the PoC server performing the controlling PoC function, insuring that only one user is sending media at a given time. The talk burst control mechanism in OMA PoC forms a second control layer under...

Gonzalo Camarillo Per Synnergren

This chapter explains how the control plane of the Multimedia Telephony service works. The first part of the chapter explains the Session Initiation Protocol SIP that is used by the Multimedia Telephony clients and IMS to set up, modify and release the Multimedia Telephony sessions. SIP, together with the Session Description Protocol SDP , is also used to realize supplementary services like communication diversion, conferencing and communication barring that are present in ISDN PSTN. To...

Explicit Communication Transfer

The ECT service provides the possibility for a party involved in a Multimedia Telephony session to transfer the communication to a third party. Thus, there are three actors active in a transfer, acting in the following roles The transferor is the party that initiates the transfer of the active communication that it has with the transferee. The transferee is the party that stays in the communication which is transferred. The transfer target is the party to which the communication is transferred...

Daniel Enstrom Tomas Frankkila Per Frojdh Janne Peisa Krister Svanbro

Voice coding has been an essential feature in digital cellular networks since the introduction of the GSM system. Significant developments have been made during the last 20 years in order both to increase the perceived quality and to reduce the required bit rate. Video coding became an essential feature of mobile phones with the introduction of video telephony services in third generation systems. Video coding is also used in multimedia messaging and streaming services. Text coding was...

SDP Examples

Amr Octet Aligned

This section includes quite a few examples of SDP offers and SDP answers. They were derived by first defining the scenarios that are the most likely ones and then deriving the SDP offers and answers. The scenarios were defined based on the following parameters The media that will be used in the session. It is possible to choose one or several of the following media types narrowband speech, wideband speech, video and text. What codecs can be used for each respective media. Whether the session...

Tomas Frankkila

During my years within the company I have mainly worked with speech coding for Circuit Switched CS cellular systems. This work includes fixed-point and DSP implementation, research, verification of speech quality and standardization. I started working with Voice over IP VoIP issues during 2001 and have worked with VoIP ever since. During these years, I have had three 'Aha experiences' and I will try to describe these here. When I started with VoIP, most people working in this area were focusing...

Conference

The CONF simulation service enables a user to participate and control a simultaneous communication involving a number of users. The CONF simulation service provides means to create conferences to which users have to join by calling in to the conference bridge or the creation of ad-hoc multiparty calls to which users are invited. In this section the flow in Figure 4.16 demonstrates the creation of a conference and the invitation of a second user is shown. It should be noted that the conference...

IMS Session Establishment

The remaining sections of this chapter contain a few Multimedia Telephony signaling flows, including flows showing Multimedia Telephony session establishments. However, all those flows abstract out the IMS nodes and represent them by a black box called the IMS core. This section discusses what happens in that black box at session establishment time. Figure 4.2 shows the establishment of an IMS session. An IMS terminal generates a SIP INVITE request 1 and sends it to its P-CSCF, which forwards...