Yaskawa SmartTrac AC1 - Manual (Page 50)

SMART TRAC AC1
5-4
••
Networking the Smart Trac AC1 Technical Manual TM 3554-000
Ethernet Network Architecture
BNC, or "T"-shaped connectors are used to connect network devices to a coaxial
trunk cable in a linear bus topology. The bus is tied to ground, often at a wall
plate. The other end of the trunk cable (bus) must be terminated with a 50-ohm
resistor. Without termination, broadcast signals bounce back across the network,
causing contention. This, combined with the fact that each device on a linear bus
must wait its turn to broadcast information across the network, results in
decreased performance compared with a star topology, for example. Also, a
linear bus network is more difficult to troubleshoot because all devices are on a
single trunk cable.
A linear bus network is easy to install. All devices on the network connect to a
trunk cable. It does not require the use of equipment to amplify or regenerate the
signal, but can use devices to amplfy the signal. They are generally inexpensive
and can be expanded easily.
10BASE-T wall plate
Ethernet (RG-58 Coaxial Cable)
Laptop computer
SMART
TRAC
AC 1
SMART
TRAC
AC 1
IBM Compatible
Laser printer
50 ohm
terminating
resistor
Figure 7. A Linear Bus topology using 10Base-T
A star network topology connects two or more device clusters, or stars, together
using hubs. Either 10Base-2 or 10Base-T may be used in a star topology. A
separate cable connects each device to a "hub." A hub can be active (connects to
an external power source, amplifies the signal, and extends the length of the
network) or passive (requires no external power source).
A star network allows one part of the network to be down without experiencing
total system downtime. If a cable fails in a star configuartion, it usually affects
only one device or those in one star. If a hub fails, it takes down the devices in a
star but not usually the entire network.
It is easier to troubleshoot a star network than a linear bus network. A problem
can be quickly isolated to a device in one star, then a particular address or cable
within that star. While it can be more expensive to implement because more
cable may be needed, a star network is easily expanded.
Linear Bus using
10Base-T
Star network using
10Base-2 or 10Base-T