Siemens Mux_guide_v06 Multiplexer control and signaling lines, Flow control, Logical flow control

Multiplexer User's Guide

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3.2 Multiplexer control and signaling lines

The following chapter covers all information you need to develop and set up a virtual driver. Differences and restrictions in comparison to the unframed module are pointed out.

3.2.1 Flow control

Logical flow control

The internal logical flow control (FC-BIT in MSC message, see Chapter 4.3.9) represents the existing flow control to the module. For example, if a data call is initiated and the customer application transmits data to the module on this channel, the module will stop the data transmission from time to time. This happens because the module operates with a bandwidth of 9k6 on air, but the customer application uses a larger width. In this case the module sends a MSC message with FC-BIT set. After all data stored in the internal buffer have been sent, the module will send a second MSC message with FC-BIT reset. As already pointed out, the logical flow control operates like RTS/CTS but with FC-BIT on every channel. The RTS/CTS are not used for flow control because the traffic on the logical channels may cause a temporary loss of bandwidth on another channel. This behavior has no impact on the handshake V.24 lines.

RTS/CTS on the physical channels

Hardware flow control (AT\Q3) is recommended for use with multiplexer. For power saving it is indispensable. The setting AT\Q3 needs to be made before switching on the multiplexer.

The customer application decodes and encodes the data. To prevent loss of data, the application must be able process the information about internal flow control (MSC) regulated by the module. Flow control information is transmitted within the data flow and contains messages whether or not the channel is allowed to send. See chapter 4.3.9 for MSC.

As of Multiplexer Protocol version 2, the customer application must set RTS (in the direction to the module) on channel 1. RTS shall not be switched off to prevent loss of data (control data cannot be sent in this case). If flow control is needed, it is recommended to use logical flow control on every channel.

Mux_guide_v06 Page 14 of 36 30.06.2004