Setup guide

OSx Migration Cookbook August 30, 2006

5 – Networking

AUI versus

Twisted Pair

Network isolation

and security

OSx systems have primarily used AUI (“Fat” coaxial Ethernet) for

their network cabling. This is an older technology. The newer

technology is twisted pair (TP) cables. Most business networks

have switched from AUI to TP. Sites where the network changed

from AUI to TP have had to install converters that allow AUI PCs

to connect to a TP network. It is possible to make OSx 4.1.1 and

4.1.2/4.1.2A connect directly to a TP network. The 3C900 network

cards in those OSx stations have both AUI and TP connectors. Even

so, the CP1434TF modules in the SIMATIC TI505 PLCs only have

AUI connectors.

When migrating OSx to PCS 7, network cabling must be

considered. An existing Tiway network must be replaced with a

new TP network and converters at each PLC CP module. Although

the CP1613 supports both AUI and TP Siemens recommends that

you convert to all TP cabling due to sporadic communications

drops using a CP1613 with AUI.

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Note: If AUI is used, breaks of 2 to 3 seconds can occur

sporadically in PLC communications. The PCS 7 monitoring time

for timeouts must not, therefore, be set to less than 5 seconds!

A converter that connects a TP network to an AUI device does not

need separate power. It gets its power from the network. Converters

for TP devices on AUI networks do exist, but these require separate

power supplies since TP connections require higher power than

AUI networks provide. This is another reason AUI cabling is not

recommended.

Siemens has always recommended that you should isolate an OSx

system from the rest of a site’s network by means of a router or a

gateway. This keeps OSx from competing with site traffic for

network bandwidth, makes access to OSx more secure, and still

gives OSx access to other computers on the site network. This

recommendation is also applicable to PCS 7.