CWW.NET.CN December 2, 2003 14:33 Communication World Network 1. Overview Currently, the third generation of mobile communication systems have become more and more focus, as one of the two mainstream systems will be Future Global Communications Market plays an important role. For wireless communication systems, a call can be established is a very important issue. Calling builds involving many network elements in wireless networks, is the basic function of the communication system. Analysis of call processes for WCDMA systems will help test and maintenance of the entire system. This article mainly introduces the call flow of circuit exchange (CS) and packet exchange (PS), and performs comparative analysis.
Second, WCDMA System Structure This section we will introduce the system structure and protocol stack structure of WCDMA. We will focus on the network elements and protocol layers involved in the calling process. From the function, the WCDMA system consists of three parts: CN (core network), UTRAN (UMTS ground access network) and UE (user equipment). The CN is responsible for processing exchanges and routing selection between calls and data connections between external networks. UTRAN processes all features related to wireless access. The UE is an interface with the user. The interface between the CN and the UTRAN is called the Iu interface, and the interface between UTRAN and the UE is called the UU interface. The system structure of WCDMA, where UTRAN is composed of one or more wireless network subsystems (RNs). An RN is composed of a wireless network controller (RNC) and one or more Node B. The RNC can be connected to another RNC via the IUR interface. The RNC is connected to the Node B through the IUB interface. The call flow we described here is the call flow from the end-to-end between the UE and the CN, including the UE actively initiates a call (we usually referred to as UE to express) and the UE accept the call (the UE is called). Since the other end of the call may be different network system terminals such as PSTN, PLMN, ISDN, which will involve a message interaction between wired or wireless networks, we will not introduce. The protocol stack of the WCDMA system is given below, and we will briefly describe the protocol modules that may be involved in the call flow. High-level protocol modules unrelated to the wireless access We are generally known as non-access layer (NAS), NAS homogens in UE and CN, mainly processing and service-related functions. Physical layer we call L1 layer. On the UU interface, the physical layer is an important part in the WCDMA system, mainly processing transmission of wireless data. IUB, IU, and IUR interfaces are wired, and physical layers typically refer to physical connection entities such as fiber optic, cables. The Media Access Control (MAC) and Wireless Link Control (RLC) protocol belong to the second layer (L2), mainly providing data transmission and exchange. The Wireless Resource Control (RRC) protocol mainly completes the management and assignment of wireless resources. Where Node B's RRC, RLC, the MAC module completes only system broadcast function, and most of the wireless resource management functions are implemented in RNC. The Node B Application section (NBAP) primarily handles signaling of the IUB interface, and FP processes data transfer of each interface. The wireless access network application section (RANAP) and network service access point (RNSAP) protocol processes signaling transmission of IU and IUR interface, respectively. In the calling process, it is mainly related to UU, IUB, and IU interfaces and related protocol modules. We mainly introduce some parts related to WCDMA wireless access, other, such as RNC and Node B, RNC and CN, wireless transmission (ATM in the Release99 protocol Transfer) is a general transmission mode, we will no longer be introduced. Third, the call processing process is before introducing the call processing process, we must first understand several concepts: RRC connection. The RRC connection is a two-way point-to-point connection between the UE and the RRC protocol layer of the UTRAN. For a UE, there is a RRC connection. The RRC is connected to the UE and UTRAN to transmit wireless network signaling, such as allocation of radio resources, and the like. The RRC connection is established at the beginning of the call, released after the call is completed and maintained during the period. Iu signaling connection. If the RRC connection establishes a signaling path between the UE and UTRAN, the Iu signaling connection is a signaling path between the UE and CN. Iu signaling connection The main transmission of non-access layer signaling between UE and CN. In UTRAN, the non-access layer signaling is transparent through the direct transmission of signaling through the downstream. IV.
For network security performance, when the call is set up, the network must authenticate the UE. Wireless access bearer (RAB). The RAB can be seen as a service provided by the UE and the CN to the non-access layer, mainly for the transmission of user data. The RAB is directly related to the UE business, which relates to each protocol module of the access layer. On the air interface, the RAB is reflected in the wireless bearer (RB). Wireless bearer (RB). RB is a service provided by the UE and the UTRAN L2 to the upper layer. The RRC connection we mentioned above can also be seen as a RB that carries the signaling. Wireless link (RL). The wireless link refers to a logical connection between a UE and a UTRAN access point, which is usually composed of one to a plurality of wireless bearer transports on a physical implementation. There is a wireless link between the UE and a UTRAN access point (usually referred to). 1. The CS rescue process circuit switching service The following basic procedures: the first step, establish an RRC connection. When it is called, the RRC of the UE is first received to send the RRC connection establishment request message to the UTRAN, in which the name of the called UE number, the service type, and the like are included. After the UTRAN receives the message, the radio resource is allocated according to the network, and is sent to the UE in the RRC Connection Setup message, the UE will configure each protocol layer parameter according to the message while returning a confirmation message. There are two cases of RRC connection establishment: RRC connection establishment and RRC connection on the public channel is established. The difference between the two is different from the transport channel used by the RRC connection, so the process of connecting is different. The RRC connection on the public channel establishes the RRC connection on a private channel establishes the second step, the establishment of Iu signaling connection. After the RRC connection is established, the UE will send a service request to the CN. At this point, the RRC of the UE transmits the INITIAL DIRECT TRANSFER message containing information of the non-access layer (CM Service Request) in this message. After the RNC receives the message, the RNC's RANAP transmits the INITIAL UE Message to transparently forward the non-access layer message of the UE to the CN, and an Iu signaling connection is created while the message is transmitted. After IU signaling connection is established, non-access layer messaging between UEs and CNs is performed using DownLink Direct Transfer and Uplink Direct Transfer messages. The specific process is shown below: The third step, authentication. After IU signaling is established, CN needs to be authenticated to the UE. Authentication is a non-access layer function, transparently transmitted in UTRAN. See the process of 3-6 messages in the process of seeing the second step. The fourth step, the establishment of RAB. After the UE business request is received by the network, the CN will allocate a wireless access bearer (RAB) based on the service situation. At the same time, the corresponding wireless bearer (RB) will be established in the air interface. It should be noted that 4-8 messages If a wireless link is established in the RRC connection, you need to perform the reconfiguration process of the above-mentioned wireless link. If no wireless link is established in the RRC connection, a public channel is established. When the RRC connection is connected, the process of wireless link should be performed here. The fifth step, waiting for a response. At this point, the UE will wait for the caller to answer and enter the call status. Below is a holistic flowchart for the entire circuit switching service UE. 2, the CS Call Process CS Call Process is basically similar to the starting process, just before the RRC connection is created, the UE first receives the Paging Type 1 message on the paging channel, and then performs the establishment of the RRC connection. After each part is the same as the converging process.
