ZTE´s All-IP Based CDMA2000 Network Solution

ZTE provides various IMS test equipment, including CSCF, MRF, MGW, HSS, and multiple ASs supporting various service functions.

    ZTE´s IMS products (including the AGW/PDSN and the HA of the PS domain) adopt the industry-leading and unified hardware platform with superpower functions, making it a basis for carriers to implement flexible networking and uninterrupted transition simply by changing and upgrading the software part, thus protecting their investments efficiently. ZTE´s IMS products, help build the next generation IMS network with the advantages of large capacity, low-cost and easy management.

More information at:
http://www.zte.com.cn/English/03product/list3.jsp?CateID=118

    Along with the achievements of 3G mobile technologies and the convergence of mobile communication networks and IP-based Internet, the world is heading for the mobile information era at a extremely rapid pace. The global communication industry is deliberately promoting a step-by-step evolvement of the current networks into next generation networks. As one of the biggest vendors of communication equipment in China, ZTE Corporation, following the most advanced communication technologies of the world, develops communication products that meet the current market requirements and pays more attention to the development of the next generation networks. ZTE has the ability to provide total solutions to the evolution of the CDMA network to the next generation
all-IP network.

    The evolution target of the coming CDMA network will be an all-IP based Multimedia Domain (MMD). In the future, voice, data and new multimedia services will run over the all-IP network. As the multimedia services will be dominant in the future and the current network nodes are not able to implement the complex control on them, the IP Multimedia Subsystem (IMS) is added particularly to the current network structure to process the increasing IP multimedia services and control the integrated call flow. The evolution from traditional circuit domains in the current CDMA network to future multimedia domains needs to be carried out through multiple phases to protect the investment and support subscribers and terminals of the current and future networks. Every part (the core network, interface A and air interface) of the network is able to evolve separately and support the traditional network as well as the forward and backward compatibility at the same phase or between different phases. Therefore, the network provides carriers with a maximum flexibility in their network deployment. According to the description in relevant 3GPP2 protocols, the future CDMA 3G network is divided into three domains at the core network side: Legacy Mobile Staton Domain (LMSD) that supports traditional 2G and 2.5G terminals, Packet Switched (PS) domain that supports data services, and IMS for 3G services that supports  multimedia session calls.

    According to the evolutionary changes of the CDMA network structure, ZTE takes two major steps in the evolution from the current CDMA network to the all-IP network. The first one is to create the emulation function for the 3G network to support 2G and 2.5G equipment and services by adopting the IP bearer technology whereby to make the coming CDMA 3G network support the current terminal and services, that is to implement LMSD of the CDMA 3G network. The second step is, after addressing the emulation support of the 2G and 2.5G terminals by the 3G network, to implement overlay IMS, the multimedia domain support function of the 3G network and the all-IP network of the entire network, based on the current CDMA 1X packet domain and LMSD. ZTE has achieved smooth evolution from the current network whether to the LMSD or to MMD. This has been done without affecting the current services, thus considerably protecting the investment and interest of the carriers.

1 Traditional CDMA Network Evolving to 3G LMSD
The evolution to an all-IP network starts with the traditional circuit-switched network. The core network of the traditional CDMA network is based on IS41D protocol, its air interfaces on CDMA2000 Release0 and its Radio Access Network (RAN) interfaces (interface A) on IOS4.2. All these standards support circuit switching as well as the initial packet switching technology. The packet service is represented by the service type "33". The air interface protocol supports IS707 instead of data call handover between circuit domains to implement Radio Link Protocol (RLP). The structure of the packet data network (the core network packet domain) is defined by P.S0001, with a simple IP and a mobile IP serving as the access mode of packet data services. Also, with AAA (RA-DIUS server) it performs the authentication, authorization and accounting of the packet services, as shown in the Figure 1. The packet core network has Packet Control Function (PCF) and Packet Data Serving Node (PDSN) to support data services.
As to the traditional CDMA network, ZTE´s complete set of products, including Base Transceiver Station (BTS), Base Station Controller (BSC), Mobile Switching Center (MSC), Home Location Register (HLR), PDSN/Foreign Agent (FA), Home Agent (HA), Authentication Authorization and Accounting (AAA) and so on, has been running steadily and efficiently on carriers´ networks at home and abroad.

    The first step to evolve the traditional CDMA network to the CDMA 3G network is to make the 3G network support the traditional network functions or LMSD. LMSD, which is transparent to subscribers, provides the IP-based core network with the function of supporting traditional terminals (such as IS95A, IS95B and IS2000) and also supports the services and functions of the traditional network. The IP core network provides new services and functions for the subscribers using new terminals. Compared the traditional CDMA network with the LMSD network, as shown in Figure 2, the latter divides the MSC into MSCe, Media Gateway (MGW) and Multimedia Resource Function Processor (MRFP) to separate the signaling and bearer of the traditional switch in the circuit domain. Entities (such as the MSCe, HLRe and SCPe) supporting the traditional circuit constitute Legacy Mobile Station Domain Support (LMSDS), that takes the charge of the signaling processing, and the new MGW and MRFP are responsible for the media processing related to the bearer.

    At the LMSD phase of the CDMA 3G network, ZTE can provide such signaling control equipment as IP-based BSC, MSCe, HLRe and SCPe, as well as embedded signaling conversion function. Besides, it has rolled out its MGW that integrates Signaling Gateway (SGW), MGW and MRFP.

2 Integrated Network Evolving to All-IP IMS (MMD)
The evolution target of the CDMA network is to achieve the IMS (also referred to as MMD in this document). In the CDMA 3G network with IMS, the network entities include the service related logical nodes (such as Open Service Architecture (OSA) application server and Session Initiation Protocol (SIP) application server). Also includes the IP multimedia related logical nodes (such as Call Session Control Function (CSCF), Multimedia Resource Function Controller (MRFC), MRFP, MGW and PDF), the core network packet domains (such as Access Gateway (AGW) and FA), the core network circuit domain (LMSDS) and the radio access network (such as BTS and BSC/PCF), as shown in the Figure 3.

    The core network at this phase supports signaling, transmitted over IP and media stream interfaces. Also, the network supports the traditional IS41 network services and the interaction of the voice service with other data services (such as voice first, call waiting). Moreover, it allows roaming and handover with the traditional IS41 network. It separates signaling from bearer capability. Both signaling and media stream are borne over IP, and the MMD/IMS network supports open service architecture capable of delivering new IP-based services.

    In this network, CSCF, the core functional entity of IMS, controls the integrated call flow, and provides the upper layer service platform with standard interfaces to separate service from call control. As same as the CS domain and the PS domain subsystem, the IMS can initiate, hold and release a call. Besides, it controls the handover of the multimedia stream and supports multimedia services. Therefore, it includes more functional entities to implement various functions.ZTE provides various IMS test equipment, including CSCF, Multimedia Resource Function (MRF), MGW, Home Subscriber Server (HSS), and multiple Application Servers (ASs) supporting various service functions. The part below describes basic functions of ZTE´s IMS equipment.

(1) CSCF
    It integrates the P-CSCF, I-CSCF, S-CSCF and Breakout Gateway Control Function (BGCF) specified in 3GPP2. The P-CSCF is the first link node for the mobile terminal to get IMS services. The subscriber equipment gets the P-CSCF address through a "local CSCF discovery procedure". As an agent server, the P-CSCF processes or forwards the requests and services received, and as a subscriber agent, it can interrupt or create a SIP transaction independently under an abnormal condition. The I-CSCF serves as either a connection point of all the subscribers or a service access point of the roaming subscribers in the current service area. It is possible to set multiple I-CSCFs in a network. The S-CSCF maintains the session state information according to the requirements of the network carriers and implements the session control function. CSCF integrates BGCF and is able to select a network to connect with the PSTN (or CS domain) interface points.

(2) MRF
    It integrates the functions of the MRFC and the MRFP logical node specified in the 3GPP2. It provides the media stream resource and its control function, translates information from the AS and the S-CSCF (such as the session identifier), and controls the media resource correspondingly and creates billing records. Besides, it mixes the media stream input (for example, it mixes them for the multi-part conference), sends the multi-media stream (for example, it sends them for the multimedia broadcast), and processes the multimedia stream (for example, it converts the speech coders and analyzes the media).

(3) MGW
    It integrates the logical functions of the SGW, MGW and Multimedia Gateway Control Function (MGCF) specified in the 3GPP2. It controls the connection of media stream, communicates with the CSCF, selects a CSCF from the incoming call initiated by the traditional network according to the route number to hand over the Integrated Services Digital Network User Part (ISUP) protocol and the IMS call control protocol. In addition, terminates the bearer channel from the circuit switching network and the media stream from the packet network, and supports media handover, the bearer control and the load processing (such as the multimedia digital signal coder/decoder, the echo suppressor and the conference bridge). Morever, the MGW is able to implement the billing function correspondingly.

(4) HSS
    In IMS, HSS is the upgrade product of AAA and HLR. It combines the highly efficient and stable business database system and the memory database system with high-parallel processing ability developed by ZTE. It adopts Diameter protocol to implement various functions such as authentication, authorization, accounting and storage of IMS subscribers, distribution of the subscriber service filter, as well as S-CSCF location.

(5) AS
    It communicates with the S-CSCF through the OSA API or the IP Multimedia Service Control (ISC) interface. It implements such specified service functions as the voice mailbox, multiparty service, and call forwarding.

(6) AGW
    It is the gateway between the radio network and the core network. ZTE´s AGW supports the CDMA2000
1X/EV-DO access technology and is also expected to support other access technologies, such as WiMAX, WLAN, the cable modem, and xDsl. ZTE´s AGW also acts as the Broadcast Serving Node (BSN) to support the
Broadcast-Multicast Service (BCMCS).

3 Conclusions
At present, ZTE has ability to put its LMSD product series into commercial use, and is making great efforts to improve its products at the IMS phase. ZTE has always been committed to provide carriers with sophisticated products. Along with the development of relevant standards, some changes may be pertinent to IMS products, but the basic principle remains unchanged. So the relationship of the products and the current network would be prudent to achieve desirable compatibility and uninterrupted transitioo. ZTE´s IMS products (including the AGW/PDSN and the HA of the PS domain) adopt the industry-leading and unified hardware platform with superpower functions, making it a basis for carriers to implement flexible networking and uninterrupted transition simply by changing and upgrading the software part, thus protecting their investments efficiently. ZTE´s IMS products help build the next generation IMS network with the advantages of large capacity, low-cost and easy management.

Manuscript received: 2005-02-26