6. Basic Signaling Procedures 6.1 Overview

6.1.1  Types of Signaling Procedures

There are various signaling procedures in the WCDMA system. In the protocol stack plane, there are signaling procedures in the access stratum and the non-access stratum; and in the network architecture plane, there are signaling procedures in the CS domain and the PS domain.

The signaling procedures in the access stratum and the non-access stratum are classified from the angle of the protocol stack. In the protocol stack, the RRC and RANAP layers and the protocol layers below them are called the access stratum, and the protocol layers MM, SM, CC and SMS above them are called the non-access stratum. Simply speaking, the access stratum signaling procedures refer to the procedures in which the radio access stratum equipment such as RNC and Node B shall participate. The non-access stratum signaling procedures refer to the procedures in which only UE and CN participate. The RNC and Node B in the radio access network do not participate in these procedures. That is, the access stratum signaling makes preparation for the signaling exchange of the non-access stratum. Through the signaling exchange of the access stratum, signaling paths are set up between UE and CN, so that the UE and the CN can enter the non-access stratum signaling procedures.

The access stratum procedures comprise PLMN selection, cell selection and radio resource management procedures. The radio resource management procedures are the procedures in the RRC layer. They consist of RRC connection setup procedure, UE-CN signaling setup procedure, RAB setup procedure, call release procedure, handover procedure and SRNS relocation procedure. Among them, the handover procedure and the SRNS relocation procedure involve two cases: Inter-RNC, and inter-SGSN/MSC. In that case, the SGSN/MSC needs to participate in the procedures. Therefore, in the protocol stack plane, the access stratum procedures are bottom layer procedures that provide bottom layer bearer for the upper layer signaling procedures.

The non-access stratum procedures consist of CS mobility management, CS call control, PS mobility management, and PS session management.

6.1.2  General Introduction

The following gives a simple description of the basic signaling procedures.

First is the service procedure from the UE switch-on, service proceeding to UE switch-off in the case the subscriber does not move.

1)      The UE is switched on and first enters the signaling exchange of the access stratum. First the UE selects a PLMN (the network of a certain operator) and a cell, and camps on an appropriate cell. Then it sets up the RRC connection, and the signaling connection of the Iu interface. By now, a signaling path has been set up between the UE and the CN for the non-access stratum signaling procedures through these access stratum signaling procedures.

2)      Then the non-access stratum mobility management procedure starts between the UE and the CN. The subscriber attach procedure will be executed, which includes minor procedures such as authentication, ciphering. The location update procedure will be executed when the subscriber in idle state change the location.

3)      After passing the procedures such as authentication, the UE enters the service-related procedures of the non-access stratum, which includes the CS call connection procedure and the PS session management procedure. These procedures establish the service bearer for service proceeding. After that, the subscriber can start to make a call or access the Internet.

4)      When the subscriber ends the service, the CS call connection procedure or the PS session management procedure will be executed to release the service bearer..

5)      If the subscriber powers off the UE at this time, the UE and the CN will use the non-access stratum mobility management procedure to detach from the CS domain or the PS domain.

6)      When the non-access stratum signaling exchange ends, the system will use the access stratum signaling procedures to clear the previously setup lu signaling connection and the RRC signaling connection.

By now, the service procedure from UE switch-on, service proceeding to UE switch-off ends in the case that the subscriber does not move. As shown in the above, the service procedure is completed through the coordination of the signaling procedures of both the access stratum and the non-access stratum. The access stratum signaling procedures provide signaling bearers for the non-access stratum signaling procedures.

The following is a called service procedure.

1)      The UE of the subscriber is in the idle state. Now it is paged from the network side.

2)      If there is no available signaling connection between UE and CN, the UE, the RNC and the CN will enter the access stratum signaling procedures, and set up the RRC connection and the Iu interface signaling connection.

3)      The authentication and ciphering procedures of mobility management may be executed.

4)      The service bearer is established through the CS call connection procedure and the PS session management procedure for service proceeding.

5)      After the service ends, the related service bearer is cleared.

6)      The signaling connections of the access stratum, including the Iu interface signaling connection and the RRC connection are released.

The above two procedures describe the service proceeding in the case that the subscriber does not move. The description is simple. Detailed descriptions of the procedures are given in the subsequent chapters.

Due to the mobility feature of mobile communications, there are a number of procedures related to mobility processing. For example, if a subscriber changes his/her location when he/she does not handle any service, mobility management procedures such as location update will be executed. And if the subscriber changes his/her location while handling the service, procedures such as handover and SRNS relocation will be executed.