Specifications

DocSTAR Level 2 Service Training Workbook Page 29
If termination is not in place, much like SCSI, there will be signal bounce and loss of
network communication integrity. A break in the line at any point will bring the network
down. One of the most common methods of transmitting data in a bus network is
Ethernet. Ethernet is called a contention method of communication because it employs
CSMA/CD technology. CSMA/CD stands for Carrier-Sense Multiple Access with Collision
Detection. This method of communication means that multiple computers on a network
will listen for or sense an opportunity to send data when the network is not busy. Once
the network is clear the sending computer will send its data. If, however, another
computer mistakenly sends data at the same time, a collision will occur and data will be
corrupted. In this case, the collision is detected and both computers will wait a random
amount of time to sense a new opportunity and re-transmit their data. The most common
cable type for a bus network is coaxial cable.
The RING topology connects computers in a single circle of cable forming a closed loop.
In the ring topology data is communicate from one computer to the next computer in the
loop until the intended computer receives the data. In this way the signal is regenerated
each time it passes through a computer. Once again, a break in the line will bring the
entire network down. One of the most common methods of transmitting data around a
ring is to use a ‘token.’ A token is passed from computer to computer until it gets to a
computer that needs to send data. The sending computer modifies the token, puts an
address on the data and sends it around the ring. The data travels around the ring until it
finds the computer with an address that matches the address on the data. Once the
receiving computer receives the data it sends a message back to the sending computer
confirming that the data was received. The sending computer then creates a new token
and releases it on the network. This type of network is called a Token Ring network. The
most common cable type for a ring network is coaxial cable.
Figure 3.2 Simple Token Ring Network