FIG. 1 illustrates the known data protocol stacks that are applied in a packet-switched communication connection where one end is a Mobile Station (MS) and the communication takes place over a GPRS network (General Packet Radio Service) through a Base Station Subsystem (BSS), a Serving GPRS Support Node (SGSN) and a Gateway GPRS Support Node (GGSN). The protocol layers where the peer entities are in the MS and the BSS are the physical layer 101 that employs the GSM cellular radio system (Global System for Mobile telecommunications), the Media Access Control (MAC) layer 102 and the Radio Link Control layer 103 which sometimes is regarded as only a part of the MAC layer 102—hence the dashed line between them. The protocol layers where the peer entities are in the BSS and the SGSN are the L1bis layer 104, the Network Service layer 105 and the BSS GPRS Protocol (BSSGP) layer 106.
The layers for which the peer entities are in the MS and the SGSN are the Logical Link Control (LLC) layer 107 and the SubNetwork Dependent Convergence Protocol (SNDCP) layer 108. It should be noted that only data or user plane protocols are shown in FIG. 1; a complete illustration of protocols would include the Layer 3 Mobility Management (L3MM) and Short Message Services (SMS) blocks on top of the LLC layer 107 in parallel with the SNDCP layer 108. Additionally there are the known Session Management (SM) and Radio Resource management (RR) entities that are not located on top of the LLC layer. At the interface between the SGSN and the GGSN there are the Layer 1 (L1) layer 109, the Layer 2 (L2) layer 110, a first Internet Protocol (IP) layer 111, the User Datagram Protocol/Transport Control Protocol (UDP/TCP) layer 112 and the GPRS Tunneling Protocol (GTP) layer 113. Between the MS and the GGSN there are the X.25 layer 114 and a second Internet Protocol layer 115. An application layer 116 in the MS will communicate with a peer entity that is located for example in another MS or some other terminal.
Proposals for the future UMTS (Universal Mobile Telecommunication System) have suggested similar protocol structures for the communication between mobile stations, Radio Network Controllers (RNCs) and service nodes of packet-switched networks, with small changes or modifications in the designations of the devices, layers and protocols. It is typical to protocol structures like that in FIG. 1 that each layer has an exactly determined set of tasks to perform and an exactly determined interface with the next upper layer and the next lower layer. A certain amount of memory and processing power must be allocated in the devices taking part in the communication to maintain the layered structure and accomplish the tasks of each layer. It is therefore easily understood that the more complicated the structure of layered protocols, the more complicated the required software and hardware implementation. Complexity is disadvantageous in terms of costs incurred in design and manufacture and it increases the possibility of design errors. Additionally, in battery-driven mobile terminals it is a continual aim to reduce power consumption and diminish physical size, whereby a more simplified structure of protocol layers would create advantage.