Kinds of Packets
As shown in the above diagram, the “control” field in an AX.25 packet includes a
code telling what kind of packet the current packet is. In addition to connected
information packets, the AX.25 protocol also defines two other kinds of packets,
each of which is nearly identical in structure to the connected information packet:
control packets (of which there are several kinds) and unnumbered packets. To
learn more about these, see the documentation for the KAM’98’s MCOM com
-
mand.
As noted at the beginning of this section, the organization of amateur radio pack
-
ets is defined by the AX.25 protocol. Now it is useful to give a brief discussion of
this protocol, and another that fits “within” it.
Packet Communication Introduction
KAM’98 v 8.3 31 User’s Guide
An AX.25 information packet (also called a "frame")
Flag
Flag
Address
Control
Data
Checksum
PID
Singlecharacter,for
"beginning of packet"
Singlecharacter,for
"end of pa cket"
Destina tion station,
Source station, and
up to 8 intermedia te sta tions
Kind of packet,
packetnumber,
andothercontrol
informa tion
Protocol ID: Code
forprotocol used
forthis packet
(e.g., AX.25 or
TC P / I P )
Code derived
from this packet,
used to check
forerrors in
transmission
(string of bits)
Data:
Information or message
being sent "inside" this
packet (1 to 256 bytes,
which may include
protocol-related data)
© Copyright1996 by Kantronics Co., Inc.
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