07.103GPPTerminal Equipment to Mobile Station (TE-MS) multiplexer protocolTS
The multiplexer provides mechanisms for conveying streams of data between TE and MS over a single start-stop framed, serial link. Figure 1 shows the arrangement of the various protocol levels and functions. The multiplexer layer provides multiplexing of data arranged in octet streams with no other framing; if the structure of the data has to be conveyed, a convergence layer may be necessary. The present document defines some convergence layers, others may be added later.
Figure 1: Protocol Stacks
The multiplexer provides a virtual connection between a process in the TE and a similar process in the MS. For example, a PC application supporting SMS functions could be connected to the SMS handler in the MS via a multiplexer channel.
The present document uses start-stop transmission with eight-bit characters. Communication between the two multiplexing entities takes place using frames constructed as defined below.
Each channel between TE and MS is called a Data Link Connection (DLC) and is established separately and sequentially.
Each DLC may have individual flow control procedures for buffer management purposes and the aggregate link also has overall flow control mechanisms.
DLCs have two modes of operation; Error-Recovery Mode (ERM) and non-error-recovery mode (non-ERM), the choice of mode is made when a DLC is established. DLCs using error recovery mode may exist on the same link as DLCs using non-error recovery mode. If the error-recovery mode (ERM) is to be used at least on one DLC, then the multiplexer must be configured with the ISO HDLC transparency mechanism. The use of error recovery mode is optional. Non-error recovery mode uses the UI frame or UIH frame to carry user data; error recovery mode uses the I frame.
The multiplexer has three operating options, basic, advanced without error recovery and advanced with error recovery. The characteristics of the options are:
– Length indicator used instead of the HDLC transparency mechanism.
– Different flag octet from that used by HDLC.
– Can not be used on links which use XON/XOFF flow control.
– May have longer recovery procedure from loss of synchronisation.
Advanced without error recovery:
– Asynchronous HDLC procedures in accordance with ISO/IEC 13239.
– Can be used on links which use XON/XOFF flow control.
– Recovers quickly from loss of synchronisation.
Advanced with error recovery:
– Uses HDLC error-recovery procedures.