Performance of Direct-Cable Connection

by Johannes Helmig [Published on 1 Feb. 1998 / Last Updated on 1 Feb. 1998]

You have installed this network and expect now: Speed !

You can get fast data transfer rates and throughput near what a typical
Ethernet 10 Mbit connection can do by using Parallel Technologies'
DirectParallel®Universal Fast Cables with your Parallel Port configured to ECP.

For those of you who want to make a Serial DCC connection : Sorry to disappoint you,
but when using Serial-connection, you do not get very fast data transfer rates :
(however: they are usually, especially on the parallel cables, fast enough to share an Internet Connection )

I have setup on the "Host" the Windows95 "System Monitor":

You are getting a "through-put" of approx. 2 Kbytes per second (which is equivalent to 19.200 Bit/Second "Bandwidth" on the Serial cable.

If your systems have BOTH COM-ports with FIFO
(the 16550A chip) and you made the change in the
configuration (Configuration Direct-Cable Connection),
you are getting up to 9-10 Kbytes/sec ( note 1 )
Using the Parallel Printer port for the DCC-connection
allows a much higher transfer rate:
with a Basic 4 bit "LapLink type" cable you
should be now getting 60-80 Kbytes/sec ( note 1 ) .
(example: more than sufficient to share an Internet Connection )

With a DirectParallel®Universal Fast Cable
you should get 300-600 Kbytes/sec ( note 1 ) .

If you do not get this throughput, I suggest that
you check your Parallel- DCC connection
(using any type of parallel cable) with the great
utility from Parallel Technologies called
"DirectParallel® Connection Monitor" .

Lets compare this to an Ethernet 10 MBit connection between the same 2 systems, transferring
exactly the same data:

"Through-put" is approx. 300 Kbytes per second ( equivalent to 3.000.000 Bit/Second on the Ethernet cable), approx. 30-150 times faster than the Serial-Cable .
(and yes, that is a lot slower than you are used on your DOS "InterLnk/InterSvr" if you "forget" to configure the speed, but that is history !)

Note 1 : Effective data transfer rates are depending upon PC type, CPU speed, parallel port type, data compressibility
and protocol overhead.
The system has less overhead transfering few large files than more small files.
Since on Windows95/8/ME , Direct-Cable-Connection is very closely related to Dialup-networking, the system will
(as on connections via modems) invoke data compression, therefore highly compressible files will tansfer the fastest.

See Also

The Author — Johannes Helmig

Dr.Johannes Helmig is working as Director, Technical Knowledge Management in the Belgium office of Gerber Technology where he is involved in Customer Service and internal training, with special interest in Networking.


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