Microbit RRC-1258 MkII(s) Manual de usuario descargar pdf (Pagina 27)

121

D Star

Identification Data

Received Repeater Callsign Callsign of the repeater that is to receive

the packet

Send Repeater Callsign Callsign of the repeater sending the packet

Counterpart Callsign Callsign of station that is to receive the data

Own Callsign 1 Callsign of the station that created the data

Own Callsign 2 Callsign suffix information

P-FCS Checksum

A checksum is used to detect errors. The P-FCS checksum ID is com-

puted from the flag and ID data.

How D-Star corrects errors in digital voices

D-Star uses two methods of combating transmission errors:

1. Error Detection codes are used to detect errors. These codes

only tell the receiver that the data is damaged or corrupted, not

how corruption came about. D-Star checksums follow the CRC-

CCITT Standard.

2. Error correcting codes contain information about the data. Be-

cause the codes are sent with the data (to enable correction at the

receive end), they are called Forward Error Correcting or FEC

codes. FEC codes contain enough information for the receiver to

repair most damage.

Both the DV and DD data packets in Fig 10.1 use the P-FCS

checksum in the header, but the DD packet also contains the Ethernet

data packet checksum at the very end.

With the DV packet data segment, each AMBE digitised voice

frame contains its own FEC code to allow the receiver to repair errors.

DV Digital data frames are not protected, relying on the applications to

detect and correct errors.

Fig 10.2: D-Star

packet structure.

1 2 ... 22 23 24 25 26 27 28 29 30

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Microbit RRC-1258 MkII(s) Manual de usuario Pagina 27