Buck Rogers K4ABT Manual del operador descargar pdf (Pagina 30)

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.

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Buck Rogers K4ABT Manual del operador Pagina 30