Category: Datacomm Tables

Attenuation / Next Loss

100-OHM UTP CABLE

Each four-pair cable shall be terminated in an eight-position modular jack in the work area. The 100-ohm UTP telecommunications outlet shall meet the requirements described in EIA/TIA-570.

150 OHM STP-CABLE

The telecommunications connector used for terminating the 150-ohm STP cable shall be that specified by ANSI/IEEE 802.5 for the media interface connector. This connector shall be designed so that like units will mate when oriented 180 degrees with respect to each other.

Four-pair 100 ohm UTP cables

The cable consists of 24 AWG thermoplastic insulated conductors formed into
four individually twisted pairs and enclosed by a thermoplastic jacket.
Four-pair, 22 AWG cables which meet the transmission requirements may also
be used. Four-pair, shielded twisted pair cables which meet the
transmission requirements may also be used.

The diameter over the insulation shall be 1.22mm (0.048 in) max.

The pair twists of any pair shall not be exactly the same as any other
pair. The pair twist lengths shall be selected by the manufacturer to
assure compliance with the crosstalk requirements of this standard.

Cable Specifications:

• The diameter of the completed cable shall be less than 6.35mm (0.25in)
• The ultimate breaking strength of the completed cable is 90 lb minimum.
  Maximum pulling tension should not exceed 25 lb to avoid stretching.
• The cable tested shall withstand a bend radius of 25.4mm (1in) at a
  temperature of -20C without jacket or insulation cracking.
• The resistance of any conductor shall not exceed 28.6 ohms per 305m
  (1000ft.) at or corrected to a temperature of 20C.
• The resistance unbalance between the two conductors of any pair shall
  not exceed 5% when measured at or corrected to a temperature of 20C in…
• The mutual capacitance of any pair at 1kHz shall not exceed 20 nF per
  305 M (1000ft.)
• The mutual capacitance of any pair at 1 kHz and measured at or
  corrected at a temperature of 20C, shall not exceed 17 nF per 305 m
  (1000ft) for category 4 and category 5 cables.
• the capacitance unbalance to ground at 1 kHz of any pair shall not
  exceed 1000 pF per 305m (1000ft.).

Unshielded data cables should not be installed near sources of
electromagnetism. There is a standard that specifies these distances for
structured data cabling systems. EIA/TIA-569, the cabling pathways
standard, specifies the following Minimum Separation Distance from Power
Source at 480V or less:

• Up to 50,000 users
• Facilities up to 10 million square feet
• 90 meter horizontal distance limit between closet and desktop
• 4 pairs of conductors to each outletâ??all must be terminated
• 25-pair cables may not be used (crosstalk problems)
• May not use old wiring already in place
• Bridge taps and standard telephone wiring schemes may not be used
• Requires careful installation procedures
• Requires extensive testing procedures

1. 1. Do not exceed a pulling tension of 20% of the ultimate breaking
   strength of the cable (these figures are available from the cable maker.)
2. 2. Lubricate the raceway generously with a suitable pulling compound.
   (Check with the manufacturer for types of lubricants that are best suited
   to the type of cable.)
3. 3. Use pulling eyes for manhole installations.
4. 4. For long underground runs, pull the cable both ways from a centrally
   located manhole to avoid splicing. Use pulling eyes on each end.
5. 5. Do not bend, install, or rack any cable in an arc of less than 12 times
   the cable diameter.

This cable is used to cascade hubs, or for connecting two Ethernet stations
back-to-back without a hub. Note pin numbering of straight-thru patch cord.

Due to the electrical properties of copper wiring, data signals
will undergo some corruption during their travels. Signal
corruption within certain limits is acceptable, but if the electrical
properties of the cable will cause serious distortion of the signal, that
cable must be replaced or repaired.

As a signal propagates down a length of cable, it loses some of its
energy. So, a signal that starts out with a certain input voltage,
will arrive at the load with a reduced voltage level. The amount of signal
loss is known as attenuation, which is measured in decibels, or dB. If the
voltage drops too much, the signal may no longer be useful.

Attenuation has a direct relationship with frequency and cable
length. The high frequency used by the network, the greater the
attenuation. Also, the longer the cable, the more energy a signal loses by
the time it reaches the load.

A signal losses energy during its travel because of electrical
properties at work in the cable. For example, every conductor
offers some dc resistance to a current (sometimes called copper losses).
The longer the cable, the more resistance it offers.

Resistance reduces the amount of signal passing through the wires –
it does not alter the signal. Reactance, inductive or capacitive,
distorts the signal.

The two concerns of signal transmission are:

1. That enough signal gets through. (Quantity)
2. That the signal is not distorted. (Quality)

A network is a collection of electrical signaling
circuits, each carrying digital signals between pieces of equipment. There
are power sources, conductors, and loads involved in the process. The
power source is a network device that transmits an
electrical signal. The conductors are the wires that the
signal travels over to reach its destination (another network device). The
receiver is the load. These items, connected together,
make up a complete circuit.

In the computer world, the electric signal transmitted by an energy source
is a digital signal known as a pulse. Pulses are simply
the presence of voltage and a lack of the presence of voltage, generated in
a sequence. These pulses are used to represent a series of ones and zeroes
and ones (the presence of voltage being a 1, and the absence of voltage
being a 0). These zeros or ones are called bits. Many years ago, computer
engineers began using groupings of eight bits to represent digital “words,
” and to this day, a series of 8 bits is called a byte. These terms are
used everywhere in the computer fields.

The key to successful signal transmission is that when a
load receives an electrical signal, the signal must have a voltage level
and configuration consistent with what had been originally transmitted by
the energy source. If the signal has undergone too much corruption, the
load won’t be able to interpret it accurately.

A good cable will transfer a signal without too much
distortion of the signal while a bad cable will render a signal useless.

Unshielded twisted pair cables, 22-24 gauge (UTP)

Advantages Inexpensive, may be in place
in some places; familiar and simple to install.

Disadvantages Subject to
interference, both internal and external; limited bandwidth, which
translates into slower transmissions. Somewhat vulnerable to security
breaches; may become obsolete quickly because of new technologies.

Shielded twisted pair cables, 22-24 (STP)

Advantages Easy installation; reasonable
cost; resistance to interference; better electrical characteristics than
unshielded cables; better data security; easily terminated with modular
connector.

Disadvantages May become obsolete due
to technical advances; can be tapped, breaching security.

Coaxial cables

Advantages Familiar and fairly easy to
install; better electrical characteristics (lower attenuation and great
bandwidth than shielded or unshielded cables; highly resistant to
interference; generally good data security; easy to connect.

Disadvantages May become obsolete due
to technological advances; can be tapped, breaching security.

Optical fiber cables

Advantages Top performance; excellent
bandwidth ( high in the gigabit range, and theoretically higher); very long
life span; excellent security; allows for very high rates of data
transmission; causes no interference and is not subject to electromagnetic
interference; smaller and lighter than other cable types.

Disadvantages Slightly higher
installed cost than twisted -pair cables.

10BASE-5 or (Thick Ethernet)

10BASE-5 is the original Ethernet system. It employs a quarter of an inch
diameter, 50 ohm coax cable ( with minimum bend radius of 10 inches).
10BASE-5 segments can run in length up to 500 meters with as many as 100
transceiver connections spaced at lease 2.75 yards apart.

10BASE-5 transceivers access the media by piercing the thick coaxial cable.
These transceiver taps are known as vampire taps. Since they don’t actually
require breaking the physical cable, the electrical signals over the cable
are typically fairly clean.

10BASE-5 systems were originally envisioned to be cheap and fairly easey to
build. The large cable needed simply to be run by rooms where computing
equipment would be located. Taps would be made into the cable by using
external transceivers. As it turned out, the requirement of an external
transceiver and the thick cable, which was expensive and difficult to work
with, limited the use of 10BASE-5.

10BASE-2 (Thin Ethernet)

Thin Ethernet was a fairly popular specification and is still used in many
environments today. With a maximum segment length of 203.5 yards, it
requires that the 50 ohm cable be only .2 inches thick ( a bend radius of
two inches). It also uses standard BNC connectors and “T’s” to provide
access to the media. Typically, T’s are connected directly to the back of
network interface cards, thus eliminating the need for an external
transceiver.

A maximum of 30 transceivers may be inserted onto a Thin Ethernet segment
and must be spaced at least 20 inches apart. 3Com hardware is able to
handle slightly longer segments, up to 220 yards in length. Unfortunately,
mixing other vedor’s equipment into an environment where cable runs exceed
203.5 yards can cause problems. For this reason, keeping total lengths to
203.5 yards is recommended.

Protectors are surge arresters designed for the specific requirements of
communications circuits. They are required for all aerial circuits not
confined with a block. (Block here means city block.) They must be
installed on all circuits with a block that could accidentally contact
power circuits over 300 volts to ground. They must also be listed for the
type of installation. Other requirements are the following:

Metal Sheaths of any communications cables must be grounded or interrupted
with an insulating joint as close as practicable to the point where they
enter any building (such point of entrance being the place where the
communications cable emerges through an exterior wall or concrete floor
slab, or from a grounded rigid or intermediate metal conduit).

Grounding conductors for communications circuits must be copper or some
other corrosion-resistant material, and have insulation suitable for the
area in which it is installed.

Communications grounding conductors may be no smaller than No. 14.

The grounding conductor must be run as directly as possible to the
grounding electrode, and be protected if necessary.

If the grounding conductor is protected by metal raceway, it must be bonded
to the grounding conductor on both ends.

Grounding electrodes for communications ground may be any of the following:

• The grounding electrode of an electrical power system.
• A grounded interior metal piping system. (Avoid gas piping systems for
  obvious reasons.)
• Metal power service raceway.
• Power service equipment enclosures.
• A separate grounding electrode.

If the building being served has no grounding electrode system, the
following can be used as a grounding electrode:

• Any acceptable power system grounding electrode.
• A grounded metal structure.
• A ground rod or pipe at least 5 feet long and 1/2 inch in diameter.
  This rod should be driven into damp (if possible) earth, and kept separate
  from any lightning protection system grounds or conductors.

Connections to grounding electrodes must be made with approved means. If
the power and communications systems use separate grounding electrodes,
they must be bonded together with a No. 6 copper conductor. Other
electrodes may be bonded also. This is not required for mobile homes.

For mobile homes, if there is no service equipment or disconnect within 30
feet of the mobile home wall, the communications circuit must have its own
grounding electrode. In this case, or if the mobile home is connected with
cord and plug, the communications circuit protector must be bonded to the
mobile home frame or grounding terminal with a copper conductor no smaller
than No. 12.

The Category Rating System was developed by TIA as a response to the
industry’s request for higher data rate specifications on applications over
unshielded (UTP) and shielded (STP) twisted pair.

This rating systems has been integrated into the body of the EIA/TIA-568A
standard document. The category rating system only applies to 100 ohm UTP
and STP wiring systems. EIA/TIA-568A also allows 150 ohm STP (also called
type I) and 62.5/125 um multi-mode optical fiber.

Category 3 Cable

Category 3 is characterized to 16 MHz and supports applications up to 10
Mbps. Applications may range from voice to 10BaseT.

Category 5 Cable

Category 5 is characterized to 100 Mhz and supports applications up to 100
Mbps. Applications may range from voice to TP-PMD.

Enhanced Category 5

Enhanced Category 5 is still characterized to 100 Mhz and supports
applications up to 100 Mbps. However, Enhanced Category 5 provides
additional NEXT margin (sometimes referred to as headroom) over the
specified frequency band from 1 MHz to 100 MHz. The total noise power with
all pairs energized (usually specified as Power Sum NEXT) meets or exceeds
the Category 5 specification for worst pair-to-pair NEXT. It also provides
improved ELFEXT (Equal Level Far-End Crosstalk) and Return Loss
Performance.

Category Safety Requirements

These Safety Requirements are valid for both Category 3 and 5 applications:

Safety Requirements:

1. UL 1459 (Telephone)
2. UL 1863 (Wire and Jacks)
3. NEC 1996, Article 800-4