Nera Inmarsat-c, Service Manual

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AP1.3 Channel types and Signal processing
AP1-18
1. NCS CC/LES TDM Channel
The NCS common channel and LES TDM channels share a common overall structure.
The TDM channels are based on fixed-length frames of 10368 symbols tarnsmitted at
1200 symbols/s giving a frame time of 8.64S. 10,000 frames are transmitted every day
(8.64s x 10000= 24 hours).
Each frame carries a 639 byte information field, followed by a flush byte (all 0s).
The first packet in the information field is always the Bulletin Board (BB) packet.
The bulletin board contains information on the network configuration and the correct
frame number.
TDM Frame
8.64sec (10368 TDM symbols)
TDM Frame TDM Frame
Fig. AP1.3.1 TDM frame configuration
Frame Format
8 7 6 5 4 3 2 1
1
14
640
Bulltin Board Packet
Signalling Channel
Descriptor Packet
Message
or Signlling Packet
8 7 6 5 4 3 2 1
Type Length
0
Network Version
Frame Number
Sig Channel
2-F
Count
E Spare
Channel Local
Spare
Origin ID
Status
Services
Rnd Interval
Check sum
1
14
8 7 6 5 4 3 2 1
Type Length
0
28 x 2bit
Slot State
Markers
Check sum
1
13
A C D S L A
Spare
E
Satellite Freq. Code
Packet descriptor
0 (gero) when in
CES TDM
Frame descriptor
TDM descriptor
Service descriptor
Randomizing Interval
Packet descriptor
Indicating the channel of the
signalling channel