The Packet Radio
“
2 N 1
”
Handbook
by
Buck Rogers
K4ABT
Section 1
;
Packet Radio “The Basics
”
Section 2
;
The X1J4 System Node Operator’s (SNO) Handbook
Section II
;
TheNET X1J4 System Node Operators Handbook
__ Page 30
Configuring a multi-frequency TheNET
X1
node for three or more frequencys is almost as easy as dual-frequency
operation. A TNC2 with TheNET
X1
installed is used for each frequency. Once again, the TNCs are interconnected via
their RS232 ports. Interconnecting three or more TNCs requires nothing more elaborate than some isolation diodes
between the RS-232 ports.
DIGIPEATERS VS. NODES:
The AX.25 protocol was originally designed for point-to-point (non digipeated) connections. AX.25 was subsequently
extended to accommodate one digipeater, and later extended again to allow up to eight digipeaters. As all experienced
packet radio users know, however, AX.25 is practically unusable for digipeat paths exceeding two or three "hops". The
reason for this is that AX.25 digipeaters do not fully provide error control. For an AX.25 packet to traverse a multi-hop
path, it must not fall victim to a collision or other error during any of the hops; otherwise, it must be retransmitted by the
originating station and start its journey all over again.
The probability that a data packet can complete its journey through several
digipeaters
deteriorates rapidly as the number of
hops increases. Since the usual time for a five-hops of digipeating is 35 seconds, the average elapsed time to get the packet
through will average about 75 seconds.
Using TheNET
X1
nodes
instead of ordinary
digipeaters
changes this situation dramatically for the better. When the
Wadesboro, North Carolina user transmits a packet destined for Macon, Georgia, it is received by the local TheNET
X1
node serving Wadesboro, North Carolina. That node immediately passes the packet to its neighboring node to the south,
and sends an acknowledgment back to the user. This process is repeated five times in all. As a result, the average elapsed
time to get a packet through decreases to less than 15 seconds, about 700% improvement in throughput. For longer paths,
the payoff is even more dramatic.
