3GPP TSG-SA WG 2		TDoc S2-99344 
25-28 May 1999
Sophia Antipolis, France

Source:     	NEC Corporation
Subject: 	Proposed working assumption on SMS for UMTS
Purpose: 	for decision (UMTS 23.20)

Abstract
 This contribution proposes to move the statement of Short Message Service for UMTS in section 7 of UMTS23.20(i.e. UMTS 23.121) from section 9 of UMTS 23.20 as the working assumption.

Introduction
At the last S2 meeting in Yokohama in April 1999 the new sub-section of section 9 regarding the support of SMS in UMTS was proposed and agreed as one of the key issues for discussion. It was also discussed that if there are no major opposition at the May meeting, it can be moved to section 7 as the working assumption.

Discussion

The transport of SMS for UMTS Release99 is considered as the same manner as GSM/GPRS according to the working assumption in TSG-T2. Following text is quoted from the LS(SP-99120) from TSG-T2 at the TSG-SA plenary in April.

“TSG-T2 therefore requests TSGs RAN and CN to confirm that they are in the process of elaborating the necessary 3GPP specifications for the transport of SMS in an equivalent manner to GSM using both packet protocols (equivalent of GPRS) and signalling protocols (equivalent of GSM signalling) in accordance with the architecture design for SMS.

TSG-T2 believes that the best approach would be for the packet based transfer mechanism to be used where this is available, and for the signalling method to be used where the packet based mechanism is not available. ”

TSG-S1 agreed to change UMTS 22.100 to reflect the view of TSG-T WG2 which is that for Release 99 SMS specifications are based on the current GSM SMS specifications at the Hampton Court meeting in 10-12 May.

TSG-S2 should decide the architecture to support SMS for UMTS Release 99. Following solution is described in current section 9 of UMTS 23.20.
“When assuming that there is no LLC for the PS Domain Layer2 protocol, there is a need to reconsider the functionality which had been done at LLC in GPRS. There are two alternatives described below.
1.	Use U-plane as the alternative of LLC functionality.
2.	Use C-plane as the alternative of LLC functionality.
It is too much to establish U-plane connection to transfer small amount of data when focusing on the resource of the entire system.
If C-plane was used for data transfer, it can save resource compared with establishing U-plane connection (by using common channel, efficient use of radio resource is possible). It also possesses the advantage of making it possible to use same SMS transfer procedure for CS domain and PS domain. Therefore, it comes to a conclusion that the C-plane should be used for SMS transfer in UMTS system.”

Proposal
It is proposed to move the statement of SMS for UMTS to section 7 of UMTS23.20(i.e. UMTS 23.121) from section 9 of UMTS 23.20 as the working assumption in S2. Proposed material that is editorially modified from the current text in section 9 is shown in Annex.

Annex

7.x Short Message Service for UMTS
UMTS will continuously support Short Message Service which already exists for GSM/GPRS system.

7.x.x Protocols and architecture
When assuming that there is no LLC for the PS Domain Layer2 protocol, there is a need to reconsider the functionality which had been done at LLC in GPRS. There are two alternatives described below.
1.	Use U-plane as the alternative of LLC functionality.
2.	Use C-plane as the alternative of LLC functionality.
It is too much to establish U-plane connection to transfer small amount of data when focusing on the resource of the entire system.
If C-plane was used for data transfer, it can save resource compared with establishing U-plane connection(by using common channel, efficient use of radio resource is possible). It also possess the advantage of making it possible to use same SMS transfer procedure for CS domain and PS domain. Therefore, it comes to a conclusion that the C-plane should be used for SMS transfer in UMTS system.

Figure x : Protocol architecture for 3G SMS for both a CS service domain and a PS service   domain