CSMA/CA (carrier sense multiple access with collision
avoidance) system, the media-access method uses RTS
(ready to send) and CTS (clear to send) signals before
sending a frame onto the network. A node transmits
only after the node has requested access to the line and
access has been granted. Other nodes will be aware of
the RTS/CTS transmission and will not try to transmit at
the same time.
RTS. A hardware signal sent from a potential
transmitter to a destination to indicate that the
transmitter wishes to begin a transmission. If the
receiver is ready, it sends a CTS signal in return.
CTS. A hardware signal sent from a receiver to a
transmitter to indicate that the transmitter can begin
sending. ACTS signal is generally sent in response to
an RTS signal from the transmitter.
NETWORK SYSTEM CONNECTIONS
The testing and evaluation of network connections
is accomplished with the same test equipment that is
used to test network components. This equipment
includes voltmeters, ammeters, volt-ohm-
milliammeters, and line scanners. All of this test
equipment checks the voltage, resistance, and current
that passes through the cable and the connectors
between the network nodes. Any increase or decrease in
voltage or current or an increase in the resistance will
cause communications problems for the users.
Whether the cable is pre-made or you make it, you
should always test the cable before it installed into the
network. This will alleviate the possibility of installing
a bad cable or connector to the system. Any time that
you can detect a bad connector will be to your
advantage, since each connector has a limited number
of connections before it has to be replaced.
COMMUNICATION LINE PROBLEMS
Communication line problems fall into three
general categories: excessive noise, cabling, and
backbone connections. With proper testing and
precautions, these problems can be taken care of before
Noise is the term for random electrical signals that
become part of a transmission, and that serve to make
the signal (information) component of the transmission
more difficult to identify. Noise can take various forms,
including the following:
Impulse noise: voltage increases that last for just
a short period, usually for only a few
White noise: random background noise.
Crosstalk: interference on one wire from
There are limits set on the allowable levels for each
of these types of noise. A noise filter can be used to
remove random noise from a signal.
In a transmission, signal-to-noise ratio (SNR) is the
ratio between the signal and noise levels at a given
point, usually at the receiving end of the transmission.
The SNR value is generally expressed in dB.
The SNR can be used to determine how long a cable
segment can be before the signal loss is unacceptably
high. The SNR also helps to determine whether a
particular type of cable will work for the intended use.
Cable testers can help determine whether a particular
type of cable is appropriate in a specific environment.
In general, digital signals have a much higher SNR
than analog signals. Because analog signals in a
broadband network must be confined to a portion of the
total bandwidth, filtering and other signal-cleaning
measures are necessary This confinement makes the
signal more delicate and subject to distortion.
Several types of filtering maybe used to help clean
a broadband transmission. The filters are distinguished
by the filtering technique they use as well as by where in
the transmission process they are applied.
For example, filters applied early in the
transmission, prior to modulation, are known as
baseband or premodulation filters. Those applied after
the modulation are known as passband or
Cables are good media for signals, but they are not
perfect. The signal at the end of the cable should be as
loud and clear as at the beginning, but this will not be
Any transmission consists of signal and noise
conponents. Even a digital signal degrades when
transmitted over a wire. This is because the binary
information must be converted to electrical form for
transmission, and because the shape of the electrical
signal changes over distance.