AEA PK-232 Technical Reference Manual page 53

PK-232 TECHNICAL MANUAL
The above frame is the same as
(WB4JFI, SSID=1). The H bit is set, indicating this is from the output of the repeater.
A.2.13.3 Multiple Repeater Operation
The link-layer AX.25 protocol allows operation through more than one repeater, creating a primi-
tive frame routing mechanism. Up to eight repeaters may be used by extending the repeater-ad-
dress subfield. When there is more than one repeater address, the repeater address immediately
following the source address subfield will be considered the address of the first repeater of a multi-
ple-repeater chain. As a frame progresses through a chain of repeaters, each successive repeater
will set the H bit (has-been-repeated bit) in its SSID octet, indicating that the frame has been suc-
cessfully repeated through it. No other changes to the frame are made (except for the necessary
recalculation of the FCS). The destination station can determine the route the frame took to each
it by examining the address field.
The number of repeater addresses is variable. All but the last repeater address will have the ad-
dress extension bits of all octets set to zero, as will all but the last octet (SSID octet) of the last re-
peater address. The last octet of the last repeater address will have the address extension bit set
to one, indicating the end of the address field.
PK232TM Rev. A 5/87
Fig. 4A – AX.25 frame in repeater mode
Octet ASCII Bin. Data
01111110
Flag
A1 K 10010110
A2 8 01110000
A3 M 10011010
A4 M 10011010
A5 O 10011110
A6 space 01000000
11100000
A7 SSID
A8 W 10101110
10000100
A9 B
A10 4 01100100
A11 J 10010100
A12 F 10001100
A13 I 10010010
A14 SSID 01100000
A15 W 10101110
A16 B 10000100
A17 4 01101000
10010100
A18 J
A19 F 10001100
10010010
A20 I
A21 SSID 11100011
00111110
Control I
PID none 11110000
xxxxxxxx
FCS part 1
FCS part 2 xxxxxxxx
Flag 01111110
76543210
Bit position
Fig. 3A, except for the addition of a repeater-address subfield
A-8
APPENDIX A – AX.25 LEVEL 2 PROTOCOL
Hex Data
7E
96
70
9A
9A
9E
40
E0
AE
84
68
94
8C
92
60
AE
84
68
94
8C
92
E3
3E
F0
HH
HH
7E
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