TCM345 Summary of Media Types Page 1

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					                                      Summary of Media Types                                                   -1–
                                          And Standards

MEDIA TYPES
The most basic level of communications is accomplished at the OS1 Layer 1, which includes cable media and
interfaces.
There are four basic media types: coaxial cable, twisted-pair cable, fiber-optic cable. and wireless technologies.
The characteristics of each media type make it suitable for particular types of networks. The most commonly used
cabling is twisted-pair.
Coaxial cable, though still common, is used mainly in older LANs.
Fiber-optic cable is usually used to connect computers that demand high-speed access and to connect networks
between different floors and buildings.
Wireless technologies are used in situations where it is difficult or too expensive to use cable.

When choosing the best medium for a LAN or WAN. it is important to consider the capabilities and limitations of
each type, including factors such as:
•      Data transfer speed
•      Use in specific network topologies
•      Distance requirements
•      Cable and cable component costs
•      Additional network equipment that might be required
•      Flexibility and ease of installation
•      Immunity to interference from outside sources a Upgrade options


COAXIAL CABLE
Coaxial cable (typically called coax) comes in two varieties, thick and thin.
Thick coax cable was used on early networks, mainly as a backbone to join different networks. It was the first
media type defined when Ethernet standards were established in the early 1980s. Thick coax is used infrequently
today because there are better alternatives, such as fiber-optic cable.
Thin coax cable has a much smaller diameter than thick coax cable and is used on networks to connect desktop
workstations to LANs.

Table 1 -Thick Coax Cable 10Base5 Properties for Ethernet Applications
Property                                          Ethernet Specification
Impedance                                         50 ohms
Maximum length                                    500 meters (approx. 169D 1)
Maximum number of taps into the cable             100 (including terminators)
Minimum distance between taps                     2.5 meters (approx. 8.25 ft)
Maximum AUI cable length                          50 meters (approx. 165 ft) for thick AUI cable and 125 meters
                                                  (approx. 41.25 ft) for office grade AUI cable
Maximum speed                                     10 Mbps
Band type                                         Baseband
Maximum number of connected segments              5
Maximum number of segments                        3
   containing nodes
Maximum number of repeaters                       4
   (times the signal is amplified and retimed)
Maximum total length via repeaters                2500 meters (approx. 1.5 miles)
                                        Summary of Media Types                                                       -2–
                                            And Standards

Table 2 Thin Coax Cable (10Base2) Properties for Ethernet Applications
Property                                         Ethernet Specification
Impedance                                        50 ohms
Maximum length                                   185 Meters (approx. 610.5 ft)
Maximum number of taps into the cable            30 (including terminators)
Minimum distance between taps                     0.5 meters (approx. 1.65 ft)
Maximum speed                                    10 Mbps
Band type                                        Baseband
Maximum number of connected segments             5
Maximum number of segments                       3
   containing nodes
Maximum number of repeaters (times               4
   the signal is amplified and retimed)
Maximum total length via repeaters               925 meters (approx. 3052.5 ft)

TWISTED-PAIR CABLE
Twisted-pair cable, which resembles telephone wire, was approved for networking by the IEEE in 1990. Twisted-
pair cable is a flexible communications cable that contains pairs of insulated copper wires, which are twisted
together for reduction of EMI and RFI and covered with an outer insulating jacket. Twisted-pair is more flexible
than coax cable and therefore better for running through walls and around corners. If it is attached to the right
network equipment, this cable can be adapted for high-speed communications of 100 Mbps or faster. For most
applications, the maximum run of twisted-pair cable is 100 meters.

Although twisted-pair can be extended up to 100 meters, common practice is to limit runs to 90 meters or less
to take into account extra wiring in network equipment and in wiring closets.

Twisted-pair cable is connected to network devices with RJ45 plug-in connectors, which resemble the RJ-11
connectors used on telephones (Figure 3-4). These connectors are less expensive than T-connectors, and less
susceptible to damage when moved. They are also easy to connect and allow more flexible cable configurations than
coax cable.
There are two kinds of twisted-pair cable, shielded and unshielded. Unshielded cable is preferred because of its
lower cost and high reliability .
Shielded twisted-pair (STP) cable consists of pairs of insulated old wire surrounded by a braided or corrugated
shielding. Braided shielding is used for indoor wiring, and corrugated shielding is used for outside or underground
wiring. Twisting the wire pairs also help reduce RFI and EMI but not to the same extent as the shield. For effective
RFI and EMI reduction, the interval of twists in each pair should be different. Connectors and wall outlets must be
shielded for the best results. If the main shielding is torn at any point within the jacket, signal distortion is likely to
be high. Another important factor in STP is to have proper grounding, in order to have a reliable transmission signal
reference point.
This type of cable is recommended in situations where heavy electrical equipment or other strong sources of
interference are nearby. Type 2A cable is used mainly indoors. Newer STP cabling is used in high-speed networks.
Shielded cable and connectors along with the compatible network equipment are more expensive than unshielded
cable.
Unshielded twisted-pair (UTP) cable is the most frequently used network cable because it is relatively inexpensive
and easy to install. UTP consists of wire pairs within an insulated outside covering; and has no shielding material
between the pairs of insulated wires twisted together and the cable's outside jacket. As with STP, each inside strand
is twisted with another strand to help reduce interference to the data-carrying signal. An electrical device called a
media filter is built into the network equipment, workstation, and file server connections to reduce EMI and RFI.
UTP is popularly called 10Base-T cable, which means it has a maximum transmission rate of 10 Mbps (although the
actual rate can be up to 16 Mbps for some data transmissions), uses baseband communications, and a twisted-pair.
UTP is generally preferred to STP because it has fewer points of failure, since there is no shield that can tear and
connectors and wall outlets do not need shielding. Although proper grounding is important for UTP, it is not as
critical to purity of the signal as for STP
Category 5 twisted-pair cable is a good choice for new cable installations because it has high-speed
networking capabilities at 100 Mbps.
                                   Summary of Media Types                                                    -3–
                                       And Standards

Table 3 Twisted-pair Cable Standards
Twisted-pair as Defined in the EIA/TIA-568 Specifications      Shielding      Maximum Transmission Rate
for Horizontal and Backbone Cable
IBM Type 1A                                                    Shielded       4 Mbps
IBM Type 2A                                                    Shielded       4 Mbps .
Category 3                                                     Unshielded     16 Mbps
Category 4                                                     Unshielded     20 Mbps
Category 5                                                     Unshielded     100 Mbps

Table 4 Token Ring Twisted-pair Cable Applications
Cable Type        Description
Type 1 and 1 A    Shielded twisted-pair cabling using two pairs of 22-gauge AWG wire surrounded by a
                  mesh shield and used in conduits, inside walls, and in wire troughs
Type 2 and 2A     The same: as Type 1 cable, but includes four additional pairs of 22-26-gauge AWG
                  conductors outside the shield for telephone use
Type 3            Unshielded four-pair wire, 22-24-gauge AWG, not quite as suitable for use as Types I and
                  2 because of susceptibility to EMI and RFI
Type 5            62.5/125 or 100/140 micron fiber-optic cable primarily used as a ring backbone
Type 6 and 6A     Shielded 26-gauge AWG wire pairs used as patch cables and for token ring network
                  adapter cables
Type 8            Shielded 26-gauge AWG twisted pair wire with a plastic protective ramp, designed for use
                  on the floor when cable cannot be run in walls
Type 9            Shielded single-pair 26-guage AWG wire with a plenum jacket

Table 5 10Base-T Unshielded Twisted-pair Ethernet Specification
Property                                   Ethernet Specification
Maximum length of one segment              100 meters (approx. 330 feet)
Maximum number of nodes per segment        2 nodes
Minimum distance between nodes             3 meters (approx. 9.9 feet)
Maximum number of segments                 1024
Maximum number of segments with nodes      1024
Maximum number of daisy-chained hubs       4
Impedance                                  100 ohms

Table 6 10Base- T Shielded Twisted-Pair Ethernet Specifications
Property                                    Ethernet Specification
Maximum length of me segment                100 meters (approx. 390 feet)
Maximum number of nodes per segment         2 nodes
Minimum distance between nodes              3 meters (approx. 9.9 feet)
Maximum number of segments                  1024
Maximum number of segments with nodes       1024
Maximum number of daisy-chained hubs        4
Impedance                                   150 ohm

Table 7 Token Ring Design Specifications
Property                                                            Token Ring Specification
Number of nodes per MAU                                             8
Maximum segment length for Type I cable when using only 1 MAU       300 meters (approx. 990 feet)
Maximum segment length for Type 1, 2, 3, and 9 cable                100 meters (approx. 330 feet)
Maximum number of MAUs per entire ring                              12
Maximum number of nodes per ring for cable Types 1, 2, and 9        260
Maximum number of nodes per ring for Type 3 cable                   72
                                      Summary of Media Types                                                    -4–
                                          And Standards

FIBER-OPTIC CABLE
Fiber-optic cable consists of one or more glass or plastic fiber cores encased in a glass tube, called cladding. The
fiber cores and cladding are surrounded by a PVC cover. Signal transmission along the inside fibers usually consists
of infrared light.
There are three commonly used fiber-optic cable sizes. The size is measured in microns and has two components,
the core diameter and the cladding diameter.
For example, 50/125-Micron (um) fiber cable has a core diameter of 50 microns and a cladding diameter of
125 microns.
The other two commonly used sizes are 62.5/125-micron fiber cable and 100/140-micron cable.
All three types of cable have multimode transmission capability, which means that multiple light waves can be
transmitted on the cable at once. The most commonly used for Multimode cable applications is 62.5/125.
The transmission of signals by light waves is related to the wavelength of the light. Some wavelengths travel
through optical fiber more efficiently than others.
Light wavelength is measured in nanometers (nm).
Visible light, in the range of 400-700 nm., does not travel through fiber-optic cable with enough efficiency for data
transfer.
Infrared light in the range of 700-1600 nm travels efficiently enough for data transmission.
Optical communications occur at three ideal wavelengths or windows. 850 nm, 1300 nm, and 1550 nm.
High-speed transmissions use the 1300-nm window.

Fiber-optic cable comes in two modes: single-mode and multimode
Single-mode cable is used mainly for long-distance communications and has a central core diameter of 8-10
microns and a 125-micron cladding diameter. The central core diameter is much smaller than that of multimode
cable. Only one light wave is transmitted on the cable at a given time.
Laser light is the communications signal for single-mode cable. The laser light source, contained in the sender's
transmitting interface, coupled with a relatively large bandwidth, enables long-distance transmissions at high speeds.
Multimode cable can support simultaneous transmission of multiple light waves for broadband communications.
The transmission distance potential is not as great as for single-mode cable, because the available bandwidth is
smaller and the light source is weaker.
The transmission source for multimode cable is an LED device that is in the sending node's network interface.

Table 3-8 Specifications for Single-mode Fiber-optic Cable
Property                                                          Value or Characteristic
Maximum length of one backbone segment                            3000 meters (approx. 1.2 miles)
Maximum length of one horizontal segment (to the desktop)         Not recommended for horizontal wiring
Maximum number of nodes per segment                               2
Maximum attenuation                                               Less than 0.5 dB/km
Cable type                                                        8.3/125 micron
Connector                                                         ST or SC connectors

Table 3-9 Specifications for Multimode Fiber-optic Cable
Property                                        Value or Characteristic
Maximum length of one backbone segment          2000 meters (approx. 1.2 mites)
Maximum length of one horizontal segment        100 meters (approx. 330 feet)
   (to the desktop)
Maximum number of nodes per segment             2
Maximum attenuation                             3.75 dB/km for transmissions with a wavelength of 850 nm;
                                                1.5 dB/km for transmissions at 1300 nm
Maximum number of segments                      1024
Maximum number of segments with nodes           1024
Maximum number of daisy-chained hubs            4
Cable type                                      62.5/125 micron
Connector                                       ST or SC connectors
                                        Summary of Media Types                                                      -5–
                                            And Standards
Hybrid Fiber/Coax (HFC) cable has a bright future for WAN communications because it uses the vast existing
cable 1V infrastructure. Using HFC, cable operators can provide telephone service, multiple channels of interactive
1V, and high-speed data services for PCs. A full HFC system can deliver:
•      Plain Old Telephone Service (POTS)
•      Up to 37 analog 1V channels
•      Up to 188 digital1V channels
•      Up to 464 digital point channels (customer-requested services)
•      High-speed two-way digital data link for PCs
Essentially, a hybrid cable consists of a single cable sheath that contains fibers and copper cables in different
combinations for different implementations, ranging from backbone cables to single-site cable installations.

Table 10 Review of Cable Types and Characteristics
Cable Type               Coax                     Twisted-pair              Fiber-optic             Hybrid
Specification            10BaseS                  10Base- T                10Base-F                 N/A
                         10Base2                  100Base-T                100Base-F
Topology                 Bus                      Star                     Star                     Bus
                                                  Ring                     Ring                     Star
                                                                           Ring
Speed                    10 Mbps                  10 Mbps                  10 Mbps to               10 Mbps and
                                                  100 Mbps                 multi-Gbps               above depending
                                                  (currently being                                  on the
                                                  proposed for                                      composition
                                                  1 Gbps)                                           arid network
                                                                                                    application
Flexibility              Not very                 Very flexible            Fragile                  Not very flexible
                         flexible                                                                   to fragile

Upgrade Options          Limited (but             Easily upgraded          Designed for             Designed for
to High-Speed            some versions            depending on the         high-speed               high-speed
Networking and           are available            version installed,       communications           communications
WANs                     for broadband            particularly             and WANs                 and WANs
                         transmissions)           Category 5 cable

WIRELESS COMMUNICATIONS
As alternatives to cable, there are several wireless media available for transmitting network packets: radio waves,
infrared signals, and microwave.
Radio Technologies: In radio network transmissions, a signal is transmitted in one or multiple directions depending
on the type of antenna that is used. The wave is very short in length with a low transmission strength, which means
it is best suited to short-range line-of-sight transmissions. A limitation of line-of-sight transmissions is that they are
interrupted by tall landmasses, such as hills and mountains. A low power (1-10 watts) single-frequency signal has
a data capacity in the range of 1-10 Mbps.
Most wireless network equipment employs spread Spectrum technology for packet transmissions. This technology
uses one or more adjoining frequencies to transmit the signal across greater bandwidth. Spread spectrum frequency
ranges are very high, in the 902-928 MHz range and higher. Spread spectrum transmissions typically send data at a
rate of 2-6 Mbps.
There are significant disadvantages to radio communications.
Infrared Technologies: Infrared light can also be used as a medium for network communications. This technology
is probably most familiar in the remote controls for your television and stereo. Infrared can be broadcast in a single
direction or in all directions, using an LED to transmit and a photodiode to receive. It transmits in light frequency
ranges of 100 GHz (gigahertz)-1,000 THz (terahertz).
Significant disadvantages to this communications medium include data transmission rates that only reach up to 16
Mbps for directional communication; and are less than 1 Mbps for omnidirectional communications.
                                      Summary of Media Types                                                   -6–
                                          And Standards
Microwave Technologies: Microwave systems work in one of two ways. One way, called terrestrial microwave is
to transmit the signal between two directional antennas, shaped like dishes. These transmissions are performed in the
frequency ranges of 4-6 GHz and 21-23 GHz, and require the operator to obtain an FCC license.
Satellite microwave transmits the signal between three directional antennas, one of which is on a satellite in space.
For an organization to use this technology, it is necessary to launch a satellite or lease service from a company
offering this technology. These transmissions are in the 11-14 GHz range.
Both types of microwave media transmit at speeds from 1 to 10 Mbps, which is a limitation where higher network
speeds are desired. Microwave has some other limitations, too. It is expensive and difficult to install and maintain.
Atmospheric conditions, bad weather, and EMI can also interrupt microwave transmissions.

Table 11 Advantages and Disadvantages of Wireless Communications
                            Radio                        Infrared                     Microwave
Advantages.                 • An inexpensive             • An inexpensive.            • An alternative where
                            alternative where            alternative where            communications
                            communications               communications               cabling cannot be
                            cabling cannot be            cabling cannot               installed easily,
                            installed easily             be installed easily          such as over long
                            • An option for              • Signal is difficult        distances
                            portable                     to secretly intercept
                            communications
                            • Usually no licensing
                            requirements
Disadvantages               • May not be feasible        • May not be feasible        • May not be feasible
                            when high-speed              when high-speed              when high-speed
                            communications are           communications are           communications are
                            needed                       needed                       needed
                            • Subject to                 • Subject to                 • Expensive to
                            interference from            interference from            install and maintain
                            the military , amateur       other light sources          • Subject to
                            radio, cell phones,          • Does not go                interference from
                            and other sources            through walls                bad weather, EMI,
                            • Subject to                                              and atmospheric
                            interference from                                         conditions
                            natural obstacles

				
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