Microbit RRC-1258 MkII(s) Manual do Utilizador descarregar pdf (Página 26)

120

Computers in Amateur Radio

receive end can request retransmission if a packet is received with

errors, whereas D-Star is a one-way protocol, so no response is re-

quired from the receiver to acknowledge that a packet has been

received. The reason D-Star does not require acknowledgements is

because, as previously stated, it has error detection and correction

built into the datastream.

The structure of the DV and DD modes are illustrated in Fig 10.1.

Each consists of a header and data segment.

D-Star utilises a common method of using one protocol to send

data formatted according to another protocol. In the DV packet, voice

data is contained in short segments (frames) which are formatted

according to the AMBE protocol. In the DD packet, the data is format-

ted using the Ethernet protocol. This process of putting data from one

protocol ‘inside’ another is called encapsulation.

The illustration of the packet structure is broken down in Fig 10.2

as follows:

Sync frame

Bit Sync is a standard pattern for GMSK 1010 modulation used by D-Star.

Frame Sync is ‘111011001010000’ - a unique bit pattern in D-Star packets.

Control flags

Control flags are used to direct the processing of the packet.

Flag 1 Indicates whether the data is control data or user data,

whether communication is simplex, repeater, set priority, etc.

Flag 2 Reserved for future use as identification data

Flag 3 Used to identify the version of D-Star protocol being used, so

that as new functions are added the receiver can apply them

Fig 10.1: (a)

Structure of DV

mode, and (b)

structure of DD

mode.

(a)

(b)

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Microbit RRC-1258 MkII(s) Manual do Utilizador Página 26