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Configuring Networks

3-5

SIMATIC NET Twisted-Pair and Fiber-Optic Networks

C79000-G8976-C125-02

3.1.3 AUI Links

According to the “Ethernet” standard IEEE 802.3 /1/ , a maximum length of 50 m is

permitted for AUI links.

Note

When using a CP 1511, the maximum cable length of the AUI link is restricted to

40 m!

3.1.4 Configuring the Entire Network (Collision Domains)

The network span of an Industrial Ethernet network is restricted by the limited

signal propagation time required for the CSMA/CD collision mechanism and by the

need to maintain a minimum gap between two data packets.

Delay Equivalent

The CSMA/CD collision mechanism of a local area network complying with IEEE

802.3 requires a limited signal propagation time. This means that the physical span

of a network (collision domain) is also restricted. Due to the signal propagation

time, a maximum of 4520 m is possible between any two DTEs. Each network

component has a delay equivalent which means a reduction in the maximum value.

The delay equivalent describes the signal delay caused by a component in the

signal path. The value of the signal delay is specified in meters instead of seconds.

The value in meters corresponds to the distance that a signal could travel in this

time if the signal propagated along a cable instead of through the component. The

total of all delay equivalents must be deducted from the overall budget (4520 m).

The remainder of the budget is available for cabling of the individual components.

In this case, it does not matter whether the cabling is optical fiber, Industrial

Twisted Pair, triaxial cable, drop cable etc.

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Siemens SIMATIC NET Instrucciones de operaciones Pagina 31