3GPP TSG-SA WG 2		TDoc S2-99217         
19-21 April 1999
Yokohama, Japan

Source:     NEC Corporation
Subject: 	Proposed add to Draft UMTS 23.20, 
Point-to-Point Short Message Service deliverly in UMTS
Purpose: 	for discussion

Abstract
 In this document, it is proposed a statement of Short Message Service for UMTS in UMTS23.20.

Discussion
 In the UMTS system, it is required to continuously support SMS, which is supported already in GSM/GPRS system. Discussion of this issue is not held yet and it must be discussed as soon as possible.
 Assumption for this discussion is described below.
•	Scope of this contribution, SMS, is a service which handles small amount of text based data that already exists in GSM/GPRS system. Multimedia Media Service, which can handle large amount of data such as data for E-mail and Graphic Image, is also proposed, but there still should be needs for a service which efficiently transports small amount of data, and therefore these two services could be considered two different services.
•	For the Layer2 protocol from the MT to the UMTS PS service domain, it is considered that there is no LLC. Therefore, is can be said that the Layer2 protocol stack at the Radio Network(between MT and RNC) is same as the one for the CS Domain.

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 alternative 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.

Proposal
It is proposed that the following statement to support SMS should be incorporated in chapter 9 of UMTS23.20.

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

9.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 alternative 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