23.1213GPPArchitectural requirements for Release 1999Release 1999TS
UMTS will continuously support Short Message Service which already exists for GSM/GPRS system.
4.9.1 Protocols and architecture
The LLC layer is only applicable for GPRS and not for UMTS. Due to that, there is a need to reconsider the functionality which is done at LLC in GPRS. There are two alternative described below.
– Use U-plane as the alternative of LLC functionality.
– 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 shall be used for SMS transfer in UMTS system.
The C-plane is a signalling connection between UE and MSC or SGSN, respectively. Establishment of a secure signalling connection is offered by the GMM in the PS domain and by the MM in the CS domain. SMS is a user of that secure signalling connection.
Figure 4.45: Protocol architecture for 3G SMS for both a CS service domain and a PS service domain