| Describe the three most common types of
cabling media used in LANs. |
The
three most common types of cabling media used in LANs are:
- Coaxial Cable. Coaxial cable comes in two
versions: Thinnet and Thicknet.Thinnet looks like regular TV cable.* It
is about 1/4 inch in diameter and is very flexible and easy to work with. In
contrast,Thicknet is about 1/2 inch in diameter and not very flexible.
Thicknet is older and not very common anymore except as a backbone within and
between buildings. Coax transmits at 10 Mbps..
- Twisted Pair. Twisted pair looks like
telephone wire and consists of insulated strands of copper wire twisted
together. There are two versions of twisted pair cable: Shielded Twisted Pair
(STP) and Unshielded Twisted Pair (UTP).STP is commonly used in Token
Ring networks andUTP in Ethernet networks where it is referred to as
"10baseT." Transmission rates vary between 10-100 Mbps..
- Fiber-Optic Cable. Fiber-optic cable
consists of a thin cylinder of glass surrounded by glass cladding, encased in
protective outer sheath. Fiber-optic cable is very fast (100
Mbps). It can transmit over long distances (2 km +) but is expensive.
*Don’t confuse Thinnet cable (RG 58) with cable TV
cable (RG 59). They look alike but they are not interchangeable.
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|
| What are the recommended maximum segment
lengths for each type of cable?
|
What are the recommended
maximum segment lengths for each type of cable?
The type of cable plays a role in how fast a signal
will degrade as it is transmitted. The following are the recommended maximum
cable lengths:
- Thinnet
- maximum length of segment
(terminator to terminator) is 185 meters (607 feet)
- Thicknet
-maximum length of segment
(single run) is 500 meters (1,640 feet)
- Unshielded Twisted Pair (UTP)
-
maximum length of cable between hub and computer is 100 meters (328 feet)
- Fiber-Optic - maximum length of cable
is 2 kilometers. (6,562 feet)
|
| What is a backbone?
|
Backbone is a generic term used to
describe media that interconnects a number of computers, segments or subnets.
In its most common form, a backbone is used to connect
hubs. Each hub represents a segment on which individual workstations are
connected via UTP cable. The hubs from different segments are then connected to
each other with thinnet cable. In this case, the thinnet cable functions as the
backbone that links the hubs.
In another example, a backbone may be a length of
cable that serves as a trunk. Drop cables are attached from the backbone to
connect individual workstations.
A backbone is often used to connect networks in
separate buildings. Organizations typically use fiber-optic cable for this type
of backbone. Thicknet is also used as a backbone.<
|
| What are the characteristics of coaxial
cable?
|
Coaxial cable (coax)has the following
characteristics:
-
Transmission rate of about 10 Mbps
-
Maximum cable length of 185 meters for Thinnet, 500
meters for Thicknet
-
Good resistance to electrical interference
-
Less expensive than fiber-optics but more expensive
than twisted pair.
-
Flexible and easy to work with (Thinnet)
-
Wire type is 20 AWG for Thinnet (R-58) and 12 AWG for
Thicknet.
-
Ethernet designation is 10base2 (Thinnet)
or 10base5 (Thicknet, also referred to as 'standard Ethernet').
|
| What are the different types of coaxial
cable?
|
The following designations are used to distinguish the
different types of coaxial cable:
-
RG-58 A/U – Thinnet, stranded wire
core, 50 ohms
-
RG-58 /U – Thinnet, solid wire core,
50 ohms
-
RG-59 – Thicknet, cable television,
broadband
-
RG-62 – ArcNet, 75 ohms
A cable's designation is typically printed on the its
outer sheathing. As a general rule, you cannot mix coax cable types on
the network.
|
| What connection hardware is used with
thinnet coaxial cable?
|
Thinnet utilizes the following
connection hardware referred to as ‘BNC’ components:
-
Terminator – a resister used to
absorb the signal once it reaches the end of the bus; connects to a T- or
barrel connector; RG-58 requires a 50-ohm terminator; RG-62 requires a
75-ohm terminator.
-
Cable Connector – the interface at
the end of the cable that is used to connect to a barrel or T-connector
-
T-Connector – used to connect to a
NIC and another cable connector or a terminator (you cannot connect directly to
a NIC with a cable connector; you must use a T-connector)
-
Barrel Connector – used to splice to
segments of cable together or attach a terminator at the end of the cable
|
| What connection hardware is used with
thicknet coaxial cable?
|
|
Thicknet utilizes an AUI (Attachment Unit Interface)
connector to attach to a Network Interface Card (NIC). The AUI connector has 15
pins and is alternatively referred to as a DB-15 or DIX connector.
One of the unique characteristics of Thicknet is the
use of an external transceiver. (The transceiver is used to
convert signals from parallel to serial for transmission on the network.) The
Thicknet cable attaches to the transceiver via a clamp or vampire tap. The NIC
connects to the transceiver using a drop cable with AUI connectors.
|
| What is Plenum cable?
|
|
Plenum refers to the space in
buildings between the ceiling and the next floor above it. Because of the
potential fire hazard, building codes are very specific about what type of
wiring can be placed in this area. refers to the space in buildings between the
ceiling and the next floor above it. Because of the potential fire hazard,
building codes are very specific about what type of wiring can be placed in
this area.
Plenum cable refers to coaxial cabling
that meets the minimum standards to allow it to be strung in the plenum area
without having to use special conduit. The insulation and jacket on plenum
cabling must be fire resistant and not give off toxic fumes when burned. refers
to coaxial cabling that meets the minimum standards to allow it to be strung in
the plenum area without having to use special conduit. The insulation and
jacket on plenum cabling must be fire resistant and not give off toxic fumes
when burned.
Not all coaxial cable is plenum cable. The most common
type of coaxial cable is PVC (polyvinyl chloride) which is more
flexible and easier to work with than plenum but does not have the same fire
resistance features. PVC cable can give off toxic fumes when burned
|
| What are the key characteristics of UTP?
|
Unshielded Twisted Pair (UTP) has the
following key characteristics:
-
Transmission rate of 10-100 Mbps
-
Maximum cable segment of 100 meters
-
Most susceptible to electrical interference or
‘crosstalk’ (although shielding may lessen the impact)
-
Less expensive than coax or fiber-optic. In some
cases, preinstalled telephone wire may be used in the network (if it is of
sufficient grade).
-
Very flexible and easy to work with
-
Wire type is 22-26AWG
-
Uses an RJ-45 connector
-
Ethernet designation is 10baseT
|
| What are the characteristics of shielded
twisted pair (STP)?
|
Shielded twisted pair (STP) is similar
to UTP except it contains a copper braid jacket to ‘shield’ the wires from
electrical interference. It can support transmissions over greater distances
than UTP.
|
| What are the 5 categories of UTP and what
is the minimum acceptable category for 10baseT?
|
he following categories of unshielded twisted pair
(UTP) cable were established by the EIA/TIA* to support the
networks indicated:
-
Category 1 - Traditional telephone
cable; supports voice only, not data
-
Category 2 - Data transmissions up to
4 Mbps (but not token ring)
-
Category 3 - 10 Mbps Ethernet
-
Category 4 - 16 Mbps token-ring
-
Category 5 - 100 Mbps; supports ATM
The minimum acceptable cable for 10baseT Ethernet is
Category 3.
*EIA/TIA 568 is the standard developed
by the Electronic Industries Association/Telecommunications Industry
Association applies to all UTP that works with networks.
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| Are there other cable
specifications?
|
|
Yes. There are several different specifications used
to classify cable. One of the oldest is the AWG (American Wire Gauge)
rating. This rating measures the thickness or gauge of the wire with the size
being inverse to the rating. For example, a 22 AWG cable is thicker than a 24
AWG cable. 22 AWG wire is typically used in telephone wire and UTP.
IBM uses its own system of cable classification
whereby cables are categorized as ‘types.’ For example, Type 3 wire is
basically equivalent to the Category 3 wire discussed earlier. However, not all
of the types used by IBM coincide exactly with a particular category. In the
non-IBM world, UTP cable is typically referred to by its category
classification and coax by its RG designation.
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