18 August 1998
a. Wirelines are twisted pairs that consist of two solid copper insulated conductors twisted and
shielded together to minimize interference by unwanted signals.
b. Twisted shielded pairs carry information over a wide range of speeds depending on line
characteristics. To maintain a particular data transmission rate, the line bandwidth, time delay, or the
signal to noise ratio may require adjustment by conditioning the line. Twisted pairs are permanently
hardwired lines between the equipment sending and receiving data. The nominal bandwidth of
unconditioned twisted pairs is between 300 and 3000 Hz. For each Hz of available bandwidth, 2 bps may
be transmitted. Data transmission in unconditioned twisted pairs, in most cases, is limited to a speed of
9600 bps or less. Hardwired twisted pairs must be conditioned by the supplier in order to obtain
operating speeds up to 19.2 Kbps. Data transmission between field equipment panels is by means of
twisted pairs connecting line drivers operating at a speed selected by the system.
c. To implement a wireline data transmission system, it is necessary to encode the data for
transmission over the media using modems or line drivers.
d. The modem is a device which performs encoding and decoding of digital data by modulation and
demodulation. The most commonly used format is frequency shift keying (FSK) of digital data into a
series of "marks" and "spaces" represented by two audio tones. Modems are provided with sharply
tuned filters which eliminate interference outside the normal pass band of the "marks" and "spaces"
audio tones. Modems for UMCS operate at a speed up to 9600 bps using V.42 error correction and V.42
bis data compression.
e. A line driver is a hardware device which supplies sufficient output power to transmit digital
signals over miles with balanced lines, such as between field equipment panels. The line driver output is
a low power output transistor. Optical isolators are used as protection devices in the line driver output.
Line drivers for UMCS operate at 9600 bps.
4. 10 BASE-T. 10 Base-T is an ethernet physical star topology with a data transmission speed of 10
Mb/s, utilizing wirelines with a maximum segment length of 100 meters. The segment length can be
extended to 150 meters when 10 Base-T transceivers are used. 10 Base-T hubs typically have up to 12
ports. They are stackable to provide expansion of the number of ports. 10 Base-T hubs are selected
with ports for attachment to fiber optic or coaxial cable LANs, and connect to UMCS workstations or
other computers through network interface cards.
a. Coaxial cable is used as a communication media in some central station or island station LANs.
Its use is typically limited to within a single building because of its susceptibility to electromagnetic
b. Thick coaxial cable (10 Base-5 ethernet cable) is a 0.4 inch diameter cable that requires
transceivers at nodes and has a distance limitation of 500 meters. The ends of a thick coaxial cable LAN
are terminated using N-series terminators. Thick coaxial cable ethernet LANs will support a maximum of
100 nodes per segment.
c. Thin coaxial cable (10 Base-2 ethernet cable) is a 0.2 inch diameter cable that does not require
transceivers at nodes and has a distance limitation of 186 meters between nodes. The ends of a thin
coaxial cable LAN are terminated using BNC terminators. Thin coaxial cable LANs support a maximum
of 30 nodes per segment.
d. Coaxial cable shieldings are grounded at one end.