ETSI STC SMG2 Handover ad-Hoc		          Tdoc 26/00
6 – 8 March 2000		                                                Revised Tdoc SMG2 2- 00- 018
Copenhagen, Denmark
Source:	Ericsson,Siemens
Title:	Handover Command message for handover to UMTS

Purpose: 	Discussion

Introduction

This CR proposes a new Handover Command message to be used for handover to other Radio Access Technologies such as handover to UMTS. The proposal is based on what has been discussed in 3GPP concerning the contents in a new RRC message HANDOVER TO UMTS COMMAND. The expected overall figures for UMTS information to be transferred to the UE in GSM mode is 250 octets. The objective is to reduce this figure down to be contained in one GSM L2 segment (23 octets). This may be accomplished by use of pre-load UMTS data to the UE before the actual handover. Which UMTS handover data to be pre-configured is currently discussed within 3GPP. SMG2 should address this when defining how the pre-configuration should be signalled to the mobile. This CR only addresses the Handover Command message. 
Description

After target RNC having allocated the resources for handover from GSM to UMTS it generates the RRC message HANDOVER TO UMTS COMMAND. This message will be sent via the core network to the source BSS via BSSMAP signalling. The HANDOVER TO UMTS COMMAND is mapped by the core network into a container and transported transparently to the UE via GSM.
The MSC sends the HANDOVER TO UMTS COMMAND data in a new BSSMAP message, INTER SYSTEM HANDOVER COMMAND message. This new message is structured as Handover Command BSSMAP. 
By reception of INTER SYSTEM HANDOVER COMMAND the BSC will proceed in the same way as reception of a Handover Command BSSMAP message.The BSC will then send a new RR message, INTER SYSTEM HANDOVER COMMAND, containing the HANDOVER TO UMTS COMMAND data to the mobile. 
By reception INTER SYSTEM HANDOVER COMMAND the mobile will unpack the message and decode the L3 information and by reception of HANDOVER TO UMTS COMMAND proceed with the execution of handover as defined in relevant specification (for handover see TR 25.331)
The attached CR towards GSM 04.18 and GSM 08.08 describes in details the changes needed for Handover Command message for handover to UMTS.