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CDMA2000
User Manual
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Ericsson CDMA2000 User Manual

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Introduction
Push to talk is the common name for half­duplex voice services activated by pressing a button. PoC is the name of the open spec­ifications 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 seg­ment, it can be used to share information in
a group—for instance, a field technician can use it to ask colleagues for help or advice.
Ericsson’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)—evi­dence that Ericsson is taking concrete steps toward realizing IP services on IMS in mo­bile networks.
1,2
SIP-based service
3
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 de­scription 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 negotia­tion 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 the receiving terminal without being decoded in the base station subsystem (BSS). Thanks to SIP end­to-end negotiation, new media coders/de­coders (codec) may be introduced in termi­nals as they become available.
Signaling compression
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Ericsson Review No. 1, 2004
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 commu­nication service, push to talk also enjoys the range and wide area cover­age 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 on a total business approach that gives operators a complete solution con­sisting 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 ser­vice and the IPMM.
3GPP Third-generation Partnership Project AMR Adaptive multirate ASCII American Standard Code for Infor-
mation Interchange AUC Authentication center BSS Base station subsystem CDMA Code-division multiple access CS Circuit-switched CSCF Call/session control function DNS Domain name service EDGE Enhanced data rates for GSM evolu-
tion EVRC Enhanced variable rate codec FTP File transfer protocol GLMS Group list management server GPRS General packet radio service HLR Home location register HSS Home subscriber server HTTP Hypertext transfer protocol
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
BOX A, TERMS AND ABBREVIATIONS
Ericsson Review No. 1, 2004
17
efficiency over the air interface. This prob­lem has been addressed through signaling compression (SigComp), another IETF stan­dard initiated by Ericsson. SigComp is a ver­satile compression framework that can use any compression algorithm to compress ASCII-based protocols, such as SIP, to a frac­tion 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 trans­mits it to the decompressor. The decom­pressor, called the universal decompression virtual machine (UDVM), decodes the byte code and adopts the decompression algo­rithm, making it ready to receive com­pressed SIP messages. Extended operations (an important feature) enable SigComp to learn from SIP messages.4Therefore, SigComp becomes increasingly efficient as compression and SIP signaling proceed.
SigComp is a critical component of Ericsson Instant Talk because it can signif­icantly reduce the number of bits sent over the wireless link (compression ratios of 8:1 are not unusual).5It greatly reduces the transmission delay of SIP messages, and con­sequently, 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 ensur­ing availability of terminals. Guided by this approach, Ericsson will continue to opti­mize performance by implementing en­hancements in the radio access network, mo­bile 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 stan­dards. Therefore, handset interoperability will not be an issue. Operators and end-users will be able to choose terminals and termi­nal vendors freely.
Instant Talk consists of three main parts: the IPMM, the Instant Talk application server, and the handset client.
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.
2
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 appli­cations, such as Instant Talk, instant mes­saging, 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 by query­ing 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 di­rected to, replicated in, and distributed from
Access network
(GPRS,
CDMA2000
WCDMA)
Instant Talk client
Instant Talk application
server
Core
network
SIP
Signaling
RTP
Media
Call/session control function (CSCF)
Home subscriber server (HSS)
Media resource  function (MRF)
Figure 1
Ericsson Instant Talk high-level architecture.
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 mech­anism 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 loca­tion 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 basi­cally a database tool that handles subscriber data during call set-up
• to ensure that the called party is a sub­scriber;
• to determine who is to be included in the group during the call;
• to determine whether or not users have activated Do-not-disturb mode; and
• to check whether the user has activated manual or auto-answer mode.
The application server also stores and pass­es 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 ser­vice. The GMLS also provides storage space for groups and lists.
Client
Ericsson works with third parties to inte­grate clients into terminals from different vendors. Pre-integrated clients can be opti­mized 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 imple­mented for circuit-switched calls, to in­crease performance and battery life.
To ensure maximum voice quality, even
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 large 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
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Ericsson Review No. 1, 2004
Ericsson Instant Talk Application
server
New service
#1
Application
server
IPMM
CSCF
HSS
MRF
New service
#2
Application
server
Figure 2 The IPMM system is built with service evolution in mind.
Ericsson Review No. 1, 2004
19
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 de­veloped by an industry consortium made up of Ericsson, Motorola, Nokia, and Siemens mobile, and supported by AT&T Wireless Services, Cingular, Sonim Tech­nologies, and Sony Ericsson. It is an open, published and demonstrated interoperable multi-vendor specification. PoC Phase I in­cludes detailed specifications that mandate the requirements and architecture of the solution. In additon to the Stage 1 and 2 specifications, the consortium also devel­oped a complete Stage 3 suite of PoC spec­ifications that stipulate signaling flows, user-plane flows (including talk burst con­trol mechanisms), and group and list man­agement methods. One of the specifica­tions applies specifically to the radio access network, describing the recommended QoS attributes of the radio link and the op­eration of the voice codec. To avoid mar­ket segmentation, Ericsson has striven for an open standard that avoids lock-in and creates interoperability between operators and between terminals from different ven­dors.
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 spec­ification has formed a basis for the OMA PoC standard. Further development will in­clude new features in the PoC specifications, such as a standardized presence solution (Figure 3), an enhanced authentication
method, and a network-to-network inter­face 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
Instant Talk consists of three parts: the IPMM system, which can be reused in fu­ture applications, the Instant Talk Applica­tion Server, and the handset client. Instant Talk is fully compliant with PoC specifica­tions, which ensures interoperability and fa­cilitates rapid uptake of service.
1 Heino Hameleers and Christer Johansson,
“IP Technology in WCDMA/GSM core net­works," Ericsson Review, Vol. 79(2002):1, 14-27, 2002.
2 Peter Granström, Sean Olson and Marc
Peck, "The future of communication using SIP," Ericsson Review, Vol. 79(2002):1, 28­35, 2002.
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 Wänstedt and Krister Svanbro, "Reducing call setup delays using SIP/SDP compression," Proceedings of RVK 02 - Radiovetenskap och Kommunikation 02, Stockholm, June 2002.
REFERENCES
Figure 3 Mobile presence makes everyday communication easier.
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