Ericsson CDMA2000 User's Manual
Contents
1. Ericsson Instant Talk Niclas Medman Krister Svanbro and Per Synnergren Push to talk is a quick and informal way of communicating person to person and with groups With a simple push of a button users can activate voice communication with friends and family much the same way as using walkie talkies or private mobile radios But because it is a mobile commu nication service push to talk also enjoys the range and wide area cover age of traditional mobile services Ericsson Instant Talk is a voice over IP VoIP service set up using the session initiation protocol SIP The technical realization is based ona total business approach that gives operators a complete solution con sisting of the Instant Talk Application Server the IP Multimedia IPMM system terminal clients and professional services Ericsson s practice of basing products on open standards to ensure interoperability and rapid uptake of service also applies to Instant Talk The solution is fully compliant with the push to talk over cellular PoC specification It has also been built with service evolution in mind giving operators the ability to add new features and services to enrich the ser vice and the IPMM BOX A TERMS AND ABBREVIATIONS 3GPP AMR ASCII AUC BSS CDMA CS CSCF DNS EDGE EVRC FTP GLMS GPRS HLR HSS HTTP 16 Third generation Partnership Project Adaptive multirate American Standard Code for Infor mation Interchange2. Authentication center Base station subsystem Code division multiple access Circuit switched Call session control function Domain name service Enhanced data rates for GSM evolu tion Enhanced variable rate codec File transfer protocol Group list management server General packet radio service Home location register Home subscriber server Hypertext transfer protocol Introduction Push to talk is the common name for half duplex voice services activated by pressing a button PoC is the name of the open spec ifications for this service In the consumer segment push to talk allows users to stay in touch with friends and coordinate leisure activities such as visits to the cinema or simultaneous communication with a group of family members In the enterprise seg ment it can be used to share information in IETF Internet Engineering Task Force IMS IP multimedia subsystem IP Internet protocol IPMM IP Multimedia IS IT Information system information technology MRF Media resource function OMA Open Mobile Alliance PoC Push to talk over cellular QoS Quality of service RTCP RTP control protocol RTP Real time transport protocol SDP Session description protocol SIP Session initiation protocol UDP User datagram protocol UDVM Universal decompression virtual machine URI Uniform resource indicator WCDMA Wideband CDMA a group for instance a field technician can use it to ask colleagues for help or advice Er
3. standard that avoids lock in and creates interoperability between operators and between terminals from different ven dors Ericsson and the other members of the consortium have submitted the Phase 1 specification to OMA The OMA process is moving forward and the PoC Phase 1 spec ification has formed a basis for the OMA PoC standard Further development will in clude new features in the PoC specifications such as a standardized presence solution Figure 3 an enhanced authentication REFERENCES Roger Panroce Lajtaward Boom A Richard Feyeman i Danis Dennett A Poa Erdos Srimivaca Ramanujan Freeman Cys Murray Gell Mann i Richard Gavekins Figure 3 Mobile presence makes everyday communication easier method and a network to network inter face to enable charging between operators and to make the PoC solution compatible with additional radio access networks WCDMA and CDMA2000 As the OMA PoC standard evolves the Ericsson Instant talk product will be updated Conclusion Ericsson Instant Talk is the first of many IP based applications that will be available over IPMM which is based on the 3GPP IMS standard The applications running on IPMM ate controlled using SIP and SigComp to make SIP efficient in mobile communications Instant Talk consists of three parts the IPMM system which can be reused in fu ture applications the Instant Talk Applica tion Server and the handset client Inst
4. ant Talk is fully compliant with PoC specifica tions which ensures interoperability and fa cilitates rapid uptake of service 1 Heino Hameleers and Christer Johansson IP Technology in WCDMA GSM core net works Ericsson Review Vol 79 2002 1 14 27 2002 2 Peter Granstr m Sean Olson and Marc Peck The future of communication using SIP Ericsson Review Vol 79 2002 1 28 35 2002 Ericsson Review No 1 2004 3 Gonzalo Camarillo SIP demystified McGraw Hill 2002 4 Mats Nordberg Hans Hannu Jan Christof fersson and Lajos Zaccomer Improving SigComp performance through extended operations Proceedings of VTC Fall 2003 Vehicular Technology Conference Orlando October 2003 5 Jan Christoffersson Hans Hannu Stefan Forsgren Stefan Wanstedt and Krister Svanbro Reducing call setup delays using SIP SDP compression Proceedings of RVK 02 Radiovetenskap och Kommunikation 02 Stockholm June 2002 19
5. by query ing domain name service DNS servers to map SIP uniform resource identifiers URI or E 164 numbers to network addresses In an IPMM based service media is di rected to replicated in and distributed from 17 Figure 2 The IPMM system is built with service evolution in mind 18 the media resource function Because Instant Talk is a half duplex service the media resource function must prevent two or more users from sending media at the same time This is called talk burst control The MRF employs a request response mech anism to control transmission rights Users who want to transmit must wait until their requests have been granted The MRF can also revoke transmission rights when a user abuses the service The HSS maintains the Instant Talk subscriber profile by keeping track of the core network node tasked with handling the subscriber An evolution of the home loca tion register HLR and the authentication center AUC used by all IMS services the HSS also handles Instant Talk subscriber authentication and authorization functions Instant Talk application server The Instant Talk application server is basi cally a database tool that handles subscriber data during call set up e to ensure that the called party is a sub scriber e to determine who is to be included in the group during the call e to determine whether or not users have activated Do not disturb mode and e to check whether
6. e receiving terminal without being decoded in the base station subsystem BSS Thanks to SIP end to end negotiation new media coders de coders codec may be introduced in termi nals as they become available Signaling compression When designing SIP the Internet Engi neering Task Force IETF had the large bandwidth and low latencies of the public Internet in mind which is to say the size of SIP messages was not a priority But in the context of mobile environments the size of SIP messages can be a drawback In mobile systems radio spectrum is an expensive re source that must be used wisely Operators must always try to maximize data transport Ericsson Review No 1 2004 efficiency over the air interface This prob lem has been addressed through signaling compression SigComp another IETF stan dard initiated by Ericsson SigComp is a ver satile compression framework that can use any compression algorithm to compress ASCII based protocols such as SIP toa frac tion of their original size reducing both bit rate requirements and transport latency SigComp sessions are initialized during the registration phase of the Instant Talk service The SigComp compressor generates a decompression byte code that contains a preferred compression algorithm and trans mits it to the decompressor The decom pressor called the universal decompression virtual machine UDVM decodes the byte code and adopts the decompression algo r
7. ge headers in the IP UDP RTP layers This means that several voice codec frames are sent in one RTP packet As dictated by IETF the Ericsson Review No 1 2004 frame bundling feature is supported in the AMR and EVRC payload format Built in functionality in the MRF makes it possible to order clients to change the number of frames in an RTP packet to adapt to current network conditions The MRF employs the RTP control protocol RTCP to monitor the network Standardization The Ericsson Instant Talk solution is based on the PoC industry standard initially de veloped by an industry consortium made up of Ericsson Motorola Nokia and Siemens mobile and supported by AT amp T Wireless Services Cingular Sonim Tech nologies and Sony Ericsson It is an open published and demonstrated interoperable multi vendor specification PoC Phase I in cludes detailed specifications that mandate the requirements and architecture of the solution In additon to the Stage 1 and 2 specifications the consortium also devel oped a complete Stage 3 suite of PoC spec ifications that stipulate signaling flows user plane flows including talk burst con trol mechanisms and group and list man agement methods One of the specifica tions applies specifically to the radio access network describing the recommended QoS attributes of the radio link and the op eration of the voice codec To avoid mar ket segmentation Ericsson has striven for an open
8. icsson s Instant Talk solution complies with the PoC specifications Its users can make person to person calls or create an ad hoc group call At present it is available for implementation in GPRS EDGE and CDMA2000 networks WCDMA solutions will follow PoC and Instant Talk are based on the IP Multimedia System IMS evi dence that Ericsson is taking concrete steps toward realizing IP services on IMS in mo bile networks SIP based service Ericsson Instant Talk is an important step toward making IP based services an integral part of the mobile service offering and of making the Internet protocol a dominant transport technology for mobile applica tions The solution is controlled by SIP whose philosophy of client to client control over multimedia session establishment while drawing on support from servers in the network distinguishes it from other common application layer protocols FTP HTTP Because SIP can establish modify and terminate multimedia sessions between two or more clients it facilitates one to many communication which is a key feature of Instant Talk Clients use the session de scription protocol SDP contained in the body of SIP messages to describe what kinds of media they can use and how the media should be transported End to end negotia tion of media types and transport permits tandem free operation that is the coded bit stream that contains the talk burst is sent directly to the encoder in th
9. ithm making it ready to receive com pressed SIP messages Extended operations an important feature enable SigComp to learn from SIP messages Therefore SigComp becomes increasingly efficient as compression and SIP signaling proceed SigComp is a critical component of Ericsson Instant Talk because it can signif icantly reduce the number of bits sent over the wireless link compression ratios of 8 1 are not unusual It greatly reduces the transmission delay of SIP messages and con sequently the time it takes to establish an Instant Talk session Technical realization Ericsson has taken a total business approach in its technical realization of Intant Talk providing the infrastructure terminal clients and professional services and ensur ing availability of terminals Guided by this approach Ericsson will continue to opti mize performance by implementing en hancements in the radio access network mo bile core network application servers and clients Ericsson s ability and willingness to influence the nodes in the end to end path of telecommunications systems set it apart from other vendors of push to talk solutions The commercial launch of Ericsson Instant Talk will include vertical service assurance One more important factor is that Ericsson bases its products on open stan dards Therefore handset interoperability will not be an issue Operators and end users will be able to choose terminals and termi nal ve
10. ndors freely Instant Talk consists of three main parts the IPMM the Instant Talk application server and the handset client Ericsson Review No 1 2004 Instant Talk client Access network GPRS CDMA2000 WCDMA Call session control function CSCF Home subscriber server HSS Media resource function MRF Figure 1 Ericsson Instant Talk high level architecture IP multimedia system Figure 1 shows a schematic drawing of the nodes involved in the Instant Talk service At the heart of the solution is the Ericsson IPMM system Figure 2 which complies with the principles of the IMS standard 3GPP that was drafted to bring SIP based communications to the wireless market The IMS can be deemed a new domain that has been added to the mobile core network to support a wide range of SIP based appli cations such as Instant Talk instant mes saging and presence services The IPMM architecture includes the call session control function CSCF the media resource function MRF and the home subscriber server HSS The CSCF is the teminal s first point of contact in the IPMM domain All SIP signaling is routed through the CSCF which also performs SigComp The role of the CSCF is to handle subscriber registration and to support the establishment modification and release of Instant Talk sessions The CSCF ensures interoperability with telephone systems and network addressing mechanisms
11. the user has activated manual or auto answer mode The application server also stores and pass es down rules and regulations to the MRF Local policies stored in the application server typically include timer values such as remaining talk time in a user s account The Instant Talk application server also supports group list management server GLMS functionality which enables users with list management operations to create modify retrieve and delete the groups and contact lists needed for the Instant Talk ser vice The GMLS also provides storage space for groups and lists Client Ericsson works with third parties to inte grate clients into terminals from different vendors Pre integrated clients can be opti mized for the hardware platform on which they run For instance to set its clients apart from downloadable clients Ericsson can make use of the native voice codec imple mented for circuit switched calls to in crease performance and battery life To ensure maximum voice quality even in environments with limited bandwidth Ericsson employs the adaptive multirate AMR codec and the enhanced variable rate codec EVRC The AMR codec is used in EDGE GPRS and WCDMA terminals EVRC is used for CDMA2000 clients Besides SIP Ericsson Instant Talk clients use the real time transport protocol RTP to carry real time data generated by the voice codec Frame bundling is used to reduce the effect of relatively lar
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