TSG-SA Working Group 2 (Architecture) meeting #4	     TSGS2#3(99)237
19 - 22 April 1999 Yokohama

Source:    NTT COMMUNICATIONWARE
Subject: 	Proposed add to Draft UMTS 23.20, 
Combined Network initiated RA/LA Update Procedure
Purpose: 	for discussion

1. Introduction

In UMTS, as in GSM, CS/PS MM combined procedures (e.g. Attach, Detach and LA/RA Update) should be adopted for radio resource optimisation. It is clearly described in current 23.20 that such combined mechanism (similar to the GSM/GPRS combined mechanism) should be used in UMTS (see 23.20 v1.6.1 7.3.1.1).

On the other hand, the procedure regarding SRNS relocation and location registration is illustrated to clarify the possibility of the Network initiated RA Update procedure as an example for the separated CN case.

This contribution intends to include another example for integrated UMSC case in 23.20 for optimising radio resources usage as illustrated in e.g. Attach case.

2. Discussion

In the case of SRNS relocation (UE connected to a single CN node, 3G_SGSN) followed by location registration in new location area, two location registration messages would be used for Routing Area and Location Area separately because the example shows the separate CN architecture case (see 23.20 v1.6.1 7.3.11.2.2).
These location registration messages can be and should be combined into one message for the integrated CN (UMSC) architecture case in order to optimize the radio resources.
The example procedure of SRNS relocation (UE connected to a single service domain in the integrated CN node, UMSC (PS service domain)) is shown in the following.

3. Proposed Signalling Procedure
SRNS relocation (UE connected to a single service domain in the integrated CN node, UMSC(PS service domain)) followed by Location Registration in new Location Area
This example shows SRNS relocation when source RNC and target RNC are connected to different UMSC. Figure 1 and Figure 2 illustrate the situation before respective after the SRNS relocation and location registration. Figure 3 illustrates the signaling sequence where each step is explained in the following list.

Figure 1 Before the SRNS relocation and location registration
Before the SRNS relocation and location registration the UE is registered in UMSC1. The UE is in state MM connected towards PS service domain and in state MM idle towards CS service domain. The RNC1 is acting as SRNC and the RNC2 is acting as DRNC.

Figure 2 After the SRNS relocation and location registration
After the SRNS relocation and location registration the UE is registered in UMSC2. The UE is in state MM connected towards PS service domain and in state MM idle towards CS service domain. The RNC2 is acting as SRNC.

Figure 3 Interface information transfer for SRNS relocation update when changing UMSC area resulting in a change of registered location and followed by location registration in new Location Area.
1)	UTRAN makes the decision to perform the Serving RNC relocation procedure. This includes decision on into which RNC (Target RNC) the Serving RNC functionality is to be relocated. The source SRNC sends SRNC Relocation required messages to the UMSC1 (3G-SGSN). This message includes parameters such as target RNC identifier and an information field that shall be passed transparently to the target RNC.
2)	Upon reception of SRNC Relocation required message the UMSC1 determines from the received information that the SRNC relocation will (in this case) result in change of UMSC.
The UMSC will then send a Forward SRNC relocation request to the applicable UMSC, UMSC2, including the information received from the Source RNC and necessary information for the change of UMSC(e.g. MM context, PDP context).
3)	The UMSC2 will send a SRNC Relocation Request message to the target RNC. This message includes information for building up the SRNC context, transparently sent from Source RNC (e.g. UE id., no of connected CN nodes, UE capability information), and directives for setting up Iu user plane transport bearers.  
When the Iu user plane transport bearers have been established, and target RNC completed its preparation phase, SRNC Relocation Proceeding 1 message is sent to the UMSC2. 
4)	When the traffic resources between target RNC and UMSC2 has been allocated and the UMSC2 is ready for the SRNC move, then the Forward SRNC Relocation Response is sent from UMSC2 to UMSC1. This message indicates that necessary resources have been allocated for the SRNC relocation.
5)	When the Forward SRNC Relocation Response has been received in the UMSC1, the UMSC1 indicates the completion of preparation phase at the CN side for the SRNC relocation by sending the SRNC Relocation Proceeding 2 message to the Source RNC.
6)	When the source RNC has received the SRNC Relocation Proceeding 2 message, the source RNC sends a SRNC Relocation Commit message to the target RNC. The target RNC executes switch for all bearers at the earliest suitable time instance. 
7)	Immediately after a successful switch at RNC, target RNC (=SRNC) sends SRNC Relocation Complete message to the UMSC2. Upon reception of this message, the UMSC2 updates the GGSN with a Update PDP Context Request including the new UMSC address. The GGSN will then update the PDP context and return Update PDP Context Response. The UMSC will also send a Complete SRNC Relocation towards the UMSC1.
8)	At reception of the Complete SRNC Relocation, UMSC1 will send a release indication towards the Source RNC. This will imply release of all UTRAN resources that were related to this UE. 
9)	When the target RNC is acting as SRNC, it will send New MM System Information to the UE indicating e.g. relevant Routing Area and Location Area and operator mode. Additional RRC information may then also be sent to the UE, e.g. new RNTI identity.
10)	The UMSC2 informs the HLR of the change of UMSC by sending Combined Update location (IMSI, new UMSC address, new UMSC Number) to the HLR. The HLR cancels the context in the old UMSC, UMSC1, by sending Cancel Location (IMSI, Cancellation Type). The UMSC1 removes the context and acknowledges with Cancel Location Ack. The HLR sends Insert subscriber data (IMSI, PS and CS subscription data .etc) to the UMSC2. The UMSC2 acknowledges with Insert Subscriber Data Ack. The HLR acknowledges the Update location by sending Combined Update Location Ack to the UMSC2.
11)	At reception of Insert subscriber data from HLR, the UMSC2 will initiate the update of MM information stored in the UE. This is done by sending Network Initiated Combined Routing Area / Location Area Update Command to the UE. This message will include new RAI and new LAI , and possible also new P-TMSI and new TMSI. When the UE has made necessary updates it answers with Network Initiated Combined Routing Area / Location Area Update Complete. 
Before point (a), in Figure 3, the connection is established between UE and GGSN via Source RNC and UMSC1 (PS service domain).
After point (b), in Figure 3, the connection is established between UE and GGSN via Target RNC and UMSC2 (PS service domain).

4. Conclusion

It is proposed that chapter3 is included in 23.20 as 7.3.11.2.3.