UMTS system and main interface protocols

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I. Basic concepts of UMTS

UMTS is short for Universal Mobile Telecommunication System. It is an important part of ITU IMT-2000 Third Generation Mobile Communication System (3G.

The UMTS system divides the entire network into two parts: the core control part and the wireless access part.

The core control part adopts the ATM technology and corresponding interface technology to support both circuit switching and packet switching methods.

In the wireless access section, utra (UMTS Terrestrial Radio Access) is used as the standard for global ground wireless access. The foundation of utra interface is W-CDMA technology, which has all the advantages of CDMA technology. At the same time, it can also adopt different modulation and demodulation methods in wireless access based on different traffic distribution: for urban areas with high traffic density, TDD and FDD can be used in suburban areas, it provides great convenience for flexible networking.

In addition to the existing voice and data services, the UMTS system can also provide new interactive multimedia services for mobile users. Its high-capacity system provides 2 Mbit/s data transmission rate. Currently, UMTS commercial networks will be available in some European countries, such as the UK and Germany. UMTS technology has attracted worldwide attention.

Ii. UMTS network structure and interfaces

1. The overall network structure is divided into utra network and core network.
There are few network elements in utra networks, including BTS and RNC. Similar to the base station in the GSM system, BTS is the basic unit for transmitting and receiving wireless signals. It supports the WCDMA encoding method. The RNC (Wireless Network Controller) function is equivalent to the combination of BSC and gprs pcu In the GSM system. It undertakes wireless resource management, BTS control, and switch management. RNC is connected through ATM.

The main functions of the entire Wireless Access Network include:
(1) wireless resource management (RRM function );
(2) mobile management of wireless connection (such as switching management );
(3) wireless access bearer (RAB function), which can provide different interface types according to different requirements of core networks;
(4) security function management (such as encryption );
(5) location service (LCS) management to determine the location information of user devices.

Core networks are divided into two layers: Circuit Switching and packet switching. In the circuit switching part, trau is the encoding conversion unit and provides a connection between utra and MSC. It converts the ATM Transmission Mode on the RNC side to TDM, and connects from the circuit necessary to provide MSC. MSC, HLR, and vlr functions are consistent with those of the corresponding network elements in the GSM network. The structure of the packet switching part is similar to that of GPRS: sgsn provides services such as mobility management and Route Selection for UE; ggsn mainly provides interfaces with external data networks; DNS is the Domain Name Server, translate the domain name into the corresponding IP address. From the network structure, we can see that the core network of the UMTS system is based on the evolution of the GSM/GPRS network, which maintains compatibility with the GSM/GPRS system and provides services related to the existing GSM system. Core networks can connect users to various external networks and business platforms, such as circuit switched voice networks and packet switched voice networks (IP voice networks), data network, Internet, Intranet, e-commerce, SMS center, etc.

2. UMTS systems mainly include the following interface types:

(1) B interface: MSC (vlr;
(2) D Interface: MSC (HLR;
(3) E interface: MSC (MSC;
(4) GC interface: ggsn (HLR;
(5) GJ interface: ggsn (external data network
(6) Gn interface: sgsn (ggsn;
(7) GR interface: sgsn (HLR;
(8) GS interface: sgsn (MSC/vlr;
(9) Uu interface: UE (User device) (BTS;
(10) lub interface: BTS (RNC;
(11) Lur interface: RNC (RNC;
(12) Lu interface: interfaces between RNC and core network. Lu interfaces include Lu CS (Circuit Switching Lu Interface) and Lu PS (packet switching Lu interface.

Among them, the Uu interface, lub interface, Lur interface, and Lu interface are the special interface types of UMTS system. The transmission protocols of Lub, Lur, and Lu interfaces are all ATM protocols, and different layers of the ATM Protocol are used for transmission based on the information type.

Iii. Main UMTS system protocols

1. utra System Protocol Platform

The universal protocol of utra system is divided into two planes: control plane protocol and user plane protocol. The control plane protocol is used to control the connection between wireless access and bearer services and between user devices and networks (including service requests, control of different transmission sources, and switch among others). The control plane protocol is used to implement wireless access and bearer services, for example, data is carried through the access layer. Four new Application Part signaling protocols are adopted in the utra system: ranap, rnsap, NBAP, and alcap.

Ranap (Wireless Access Network Application Protocol) is used to connect rnc to the core network. It includes the bssmap protocol of the GSM system. The main functions of this Protocol include Rab management, transparent transmission of NAS message flows, paging, security mode control, and location information reporting.

Rnsap (Wireless Network Subsystem Application Protocol) is used for the connection between RNC. The main functions of the Protocol include wireless link management, physical channel reconfiguration, and location update implementation.

NBAP (Node B Application Protocol) is used for the connection between BTS and RNC. The main functions of this Protocol include slice configuration management, monitoring and management of wireless links, measurement of common channels and dedicated channels, and system information management.

Alcap (access Link Control Application Protocol) defines how to establish and release the transmission bearer with the user. On the lub, Lur, and Lu CS interfaces, user data is transmitted through AAL 2 in the ATM structure. In this case, a control mechanism needs to be established. On the Lu PS interface, data is transmitted through AAL5, you do not need to establish a control mechanism.

2. core network signaling protocol

Multiple protocols are used in the core network. The basic transmission mechanism of the core network adopts the ATM/AAL5 protocol. The upper layer of the ATM includes two Protocols: MTPs and IP address, the nodes of the entire network can be addressed either through the signaling points in mtp3 or through IP addresses. The SCCP layer provides support for connection-oriented businesses in the upper ranap protocol.

The functions of the ranap Protocol are the same as those of the utra system. It is applicable to two interfaces: Lu CS and Lu ps. The protocols of TCAP, CAP/INAP, map, and user (including Tup and ISUP) are the same as those in the GSM system.

UDP is used to control non-connection-oriented data transmission) set up, release, and control IP channels. UDP and GTPs protocols are used for services related to data functions in UMTS systems. They are all based on the IP protocol.

The protocol system of the core network ensures the high-quality voice services and high-speed data services of the UMTS system.

From <China Telecom website>