Siemens Mux_guide_v06 - Manual (Page 20)

Multiplexer User's Guide
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Mux_guide_v06 Page 20 of 36 30.06.2004
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.
1
st 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
2
nd 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.