Siemens Mux_guide_v06 Length indicator, Information field, Frame checking sequence field FCS, Bit

Multiplexer User's Guide

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4.2.4 Length indicator

The length indicator specifies the length of the following information field. As the maximum frame size N1 is 98 bytes and cannot be changed the E/A bit is always 1. The setting E/A = 0 defined in GSM 07.10 for a frame size greater than 127 bytes is not supported. See also Chapter 3.1.2 for details on the maximum frame size.

1st octet:

Bit 1	Bit 2	Bit 3	Bit 4	Bit 5	Bit 6	Bit 7	Bit 8
E/A	L1	L2	L3	L4	L5	L6	L7
2nd octet (not supported by Siemens wireless modules):
Bit 1	Bit 2	Bit 3	Bit 4	Bit 5	Bit 6	Bit 7	Bit 8
L8	L9	L10	L11	L12	L13	L14	L15

E/A = 1: only one octet for the Length Indicator

E/A = 0: two octets for the Length Indicator

4.2.5 Information field

The information field contains the data and has an octet structure. The field only exists for UIH frames (unnumbered information with header check).

To transfer information fields, the P/F bit is set to 0; a response is not necessarily expected.

4.2.6 Frame checking sequence field (FCS)

The Frame Checking Sequence (FCS) is computed with the address, control and length fields. It is a field added to the end of a frame that contains transmission error-checking information. This field contains a value which is calculated by the source computer. The receiving computer performs the same calculation. If the receiving computer’s calculation does not match the result sent by the source computer, the packet is judged corrupt and discarded. An FCS calculation is made for each packet.

Mux_guide_v06 Page 20 of 36 30.06.2004