CHAPTER 2
BASIC NETWORK MEDIA
Lesson 1: Network
Cabling . . . . . . . . . . . . . . . 50
Lesson 2: The
Network Interface Card . . . . . 73
Lesson 3: Wireless
Networking . . . . . . . . . . . 89
NETWORK CABLING
Building on our understanding of the different network topologies that connect computer, we focus
next on the cables that connect them. The type of construction, features, and operation of each type of
cable, and the advantages, and disadvantages.
PRIMARY CABLE TYPES
There are three types of cable used in the industry, and they are Coaxial Cable, Twisted Pair, and
fiber-optic cable.
Coaxial Cable
At one time coaxial cable was very popular, and widely used and relatively inexpensive. It was light
and easy to work with for installations. The core of the coaxial cable carries the electronic signals that
make up the data. This wire core can be either solid or stranded. If the core is solid, it is usually copper.
Coaxial cable is more resistant to interference and attenuation than twisted-pair cabling.
Coaxial cable is a good choice for longer distances and for reliably supporting higher data ranges with
less sophisticated equipment.
Types of Coaxial Cable
There are two types of coaxial cable, Thinnet and Thicknet. Thinnet can carry a data signal for 185m
before suffering from attenuation. Thicknet cable is relatively rigid coaxial cable, and it can carry a data
signal for 500M before loosing its signal.
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A tranceiver connects the thinnet coaxial cable to the larger thicknet coaxial cable. A tranceiver was
designed for thicknet Ethernet includes a connector known as a vampire trap, or a piercing tap, to make
the actual physical connection to the thicknet core. Connecton from the tranceiver to the NIC is made
using a tranceiver cable (drop cable) to connect to the attachment unit interface (AUI) port connector
on the card.
Thinnet vs Thicknet Card
As a general rule, the thicker the cable, the more difficult it is to work with. Thin cable is flexible and
easy to work with, and easy to install, and relatively inexpensive. Thicknet cable is more expensive,
harder to install because of its inability to bend, but Thicknet will carry a signal farther than thinnet.
Coaxial-Cable Connection Hardware
Both thinnet and thicknet cable use a connection component, known as BNC connector, to make the
connections between the cable and the computers.
The BNC T Connector joins the NIC care in the computer to the network cable.
It gets its name from the British Army from WWII.
The BNC Barrel Connector joins two lengths of thinnet cable to make one longer length.
The BNC Terminator closes each end of the bus cable to absorb stray signals.
Coaxial-Cable Grades and Fire Codes
Coaxial cable comes in two types of grades, PVC and Plenum grade which is fireproof. PVC or
polyvinyl chloride is a type of plastic used to construct the insulation and cable jacket for most types
of coaxial cable. PVC coaxial cable is flexible and can be easily routed through the exposed areas
of an office. However, when it burns it can give off poisonous gases. A plenum is the shallow space in
many building between the false ceiling and the floor above, it is used to circulate warm and cold air
through the building. Fire codes give very specific instructions about the type of wiring that can be routed
through this area, because any smoke or as in the plenum will eventually blend with the air breathed by
everyone in the building.
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Plenum-grade cabling contains special materials in its insulation and cable jacket. These materials are
certified to be fire resistant and produce a minimum amount of smoke, this reduces poisonous
chemical fumes. Plenum cable can be used in plenum area and in vertical runs, without conduit.
However, plenum cabling is more expensive and less flexible than PVC cable.
When to use Coaxial Cable
a) Transmit voice, video and data
b) Transmit data for greater distances than is possible with less expensive cabling
c) Offer a familiar technology with reasonable data security
Twisted-Pair Cable
Twisted-pair cable consists of two insulated strands of copper wire twisted around each other. There
are two types of twisted pair cable, UTP Unshielded twisted-pair, and STP Shielded twisted-pair.
A number of twisted-pair wires are often grouped together and enclosed in a protective sheath to
form a cable. The total number of pairs in a cable varies. The twisting cancels out electrical noise
from adjacent pairs and from other sources such as motors, relays, and transformers.
Unshielded Twisted-Pair (UTP) Cable
UTP, using the 10BaseT specification is the most popular type of twisted-pair cable and fast
becoming the more popular LAN cabling. The maximum cable length is 100 meters.
UTP consists of two insulated copper wires. In North America, UTP cable is the most commonly used
cable for existing telephone systems and is already installed in many office buildings.
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|
Category Number |
Type of
Transmission |
Comments |
|
1 |
Out-of date |
|
|
2 |
Replaced cat 1 is telephone grade 4 Mbps |
Used by ArcNet |
|
3 |
Worked well for Networking, 16 Mbps |
Token Ring Network |
|
4 |
Disappeared as soon as became available, 20 Mbps |
Used on Token Ring |
|
5 |
Most commonly used 100 Mbps. Uses RJ-45 connectors. |
Most technicians know how to make up Cat 5 |
Most telephone systems use a type of UTP. That is why UTP is so popular because many buildings
are already pre-wired for twisted-pair telephone systems. As part of the prewiring process, extra
UTP is often installed to meet future cabling needs. If the preinstalled UTP is of sufficient grade to
support data transmissions, it can be used in a computer network. But telephone wire may not have
sufficient twisting required, you can have fuzzy data transmission. If the wire is placed near any
lighting, you can have crosstalk. Therefore the greater number of twists in the wire, the less the
opportunity for crosstalk to occur.
Shielded Twisted-Pair (STP) Cable
STP cable uses a woven copper-braid jacket that is more protective and of a higher quality than the
jacket used by UTP. This gives STP an excellent shielding to protect the transmitted data from
outside interference, which in turn allows it to support higher transmission rates over longer
distances than UTP.
Connection Hardware Needed
The RJ-45 connector houses eight cable connections, while the RJ-11 houses only 4.
When to use Twisted-Pair Cabling
a) Your LAN is under budget constraints
b) You want a simple and easy installation
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When not to use Twisted-Pair Cabling
a) Your LAN requires a high level of security and you must be absolutely sure of data integrity.
b) You must transmit data over long distances at high speeds.
FIBER-OPTIC CABLE
In fiber-optic cable the data is carried by digital signals, in the form of pulses of light. Fiber-optic
cable cannot be tapped, and is therefore a very secure form of data transmission. It is very good
for very high-speed data transmission because of the purity
of the signal and lack of signal
attenuation.
Fiber-optic cable consists of an extremely thin cylinder of glass, called the core, surrounded by a
concentric layer of glass, known as the cladding. The fibers are sometimes made of plastic. Plastic
is easier to install, but cannot carry the light pulses for a long a distance as glass.
Because the glass strand passes signals in only one direction, a cable includes two strands in separate
jackets. One strand transmits and on receives.
The only problem with fiber-optic is it requires a very skilled technician for installing, and it is very
expensive, and is priced/foot. Fiber-optic cable transmissions are not subject to electrical
interference and are extremely fast, currently transmitting about 100Mbps, and can sometimes
reach 1 Gbps.
When to Use Fiber-Optic Cabling
If you need to transmit data at very high speeds over long distances and be secure.
When Not to use Fiber-Optic
Cabling
Are under a tight budget, and you do not have the expertise to install the cable
SIGNAL
TRANSMISSION
There are two types of signal transmission, baseband and broadband.
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Baseband Transmission
Baseband transmissions use digital signaling over a single channel. The digital signal uses the complete
bandwidth of the cable, which constitutes a single channel. The term bandwidth refers to the data
transfer capacity, or speed of transmission, of a digital communication system as measured in bits per
second (bps).
To reduce the occurrence of attenuation, baseband sytems sometimes use repeaters to receive incoming
signals and retransmit them at their original strength and definition. This increases the practical length of
a cable.
Broadband Transmission
Broadband transmissions uses analog signaling and it uses a range of frequencies.
With analog transmission, the signals are continuous and nondiscrete. With broadband transmissions,
the signal
flow is unidirectional.
Broadband also uses amplifiers to regenerate the analog signals to their original strength.
Increasing Bandwidth Performance
Simplex: the signal is sent in one direction only, from sender to the receiver.
Half-duplex transmission: means the data is sent in both directions, but only one at a time.
Full-duplex transmission: means the data can be sent and received at the same time,
eg. Telephone, TV and Internet.
Selecting Cabling
a) How heavy will the network traffic be
b) Is Security and issue
c) Are there any restriction on cabling locations, cement walls, historic etc.
d) What is the cabling Budget?
e) What is the distance the cable must cover?
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Cabling Considerations
As with most network components, there are trade-offs with the type of cable you purchase. If you
work for a large organization and choose the least expensive cable, the accountants might initially be
pleased, but you might soon notice that the LAN is inadequate in both transmission speed and data
security.
Ask yourself how easy is this cable to install, and work with, are there any small areas to put the
cable. Is it in an electrical area, is shielding required on the cable. Will the data suffer from attenuation
and crosstalk, think about that.
Is speed an issue? What about cost, and security.
NETWORK INTERFACE
CARD
Network Interface Cards (NICs) or NAC’s (network adapter cards) provide the interface between
cables and the computers. A NIC is the actual physical interface or connection between the computer
and the network cable. If a computer is on a Network it must have a NIC to be able to communicate
with the other computers. It is also important to get a good quality NIC, there are some cheap ones
on the market, and you will get what you pay for.
What is the Role of Network Interface Card
Network Interface Cards, usually referred to as NIC’s act as the physical interface or connection
between the computer and network cable. The cards are installed in an expansion slot in each
computer and server on the network. After the NIC has been installed, the network cable is attached
to the card’s port to make the actual physical connection between the computer and the rest of
the network.
a) prepares data from the computer for the network cable
b) sends the data to another computer
c) controls the flow of data between the computer and the cabling system
d) receive incoming data from the cable and translate it into bytes that can be understood by the
computer’s CPU.
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Preparing the Data
Before data can be sent over the network, the NIC must change it from a form the computer can
understand to a form that can travel over a network cable. The data moves through the computer
along paths called buses. These are actually several data paths placed side by side. Because the
paths are side by side (parallel), data can move along them in lateral groups instead of in a single
(serial) data stream.
Think of a 32-bit bus as a 32-lane highway with 32 cars moving side by side (moving in parallel),
each carrying one bit of data. When data travels on a network cable it is said to be traveling as a
serial transmission because one bit follows another.
The NIC takes data that is traveling in parallel as a group and restructures it so that it will flow
through the 1-bit-serial path of the network cable. This is accomplished through the translation of
the computer’s digital signals into electrical or optical signals that can travel on the network’s cables.
The component responsible for this is the transceiver (transmitter/receiver).
Network Address
In addition to transforming data, the NIC also has to advertise its own location or address, to the
rest of the network to distinguish it from all the other cards on the network. The NIC address is
permanently burned onto the card, it is also called the MAC address.
Because data can often more faster on the bus or the cable than the NIC can handle, the data is
sent to the card’s buffer, a reserved portion of RAM. Here it is held temporarily during both
the transmission and reception of data.
Sending and Controlling Data
Before the sending NIC actually sends data over the network, it carries on an electronic dialog
with the receiving NIC so that both cards agree on the following:
a) The maximum size of the groups of data to be sent
b) The amount of data to be sent before confirmation of receipt is given
c) The time intervals between sending data chunks (or packets)
d) The amount of time to wait before confirmation is sent
e) How much data each card can hold before it overflows (buffer size)
f) The speed of the data transmission
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CONFIGURATION
OPTIONS AND SETTINGS
Network interface cards often have configurable options that must be set in order for the card to
function properly.
a) IRQ Settings
b) Base I/O address
c) Base Memory Address (BMA)
d) Tranceiver
NOTE: Settings on older NIC’s are made by means of software, jumpers, or a combination of both.
Interrupt Request (IRQ) Lines
Interrupt request lines (IRQs) are hardware lines over which devices such as I/O ports, the keyboard,
disk drives and NIC’s can send interrupts or requests for service to the computer’s microprocessor.
IRQ’s are built into the computers internal hardware and are assigned different levels of priority.
When the NIC sends a request to the computer, it uses an interrupt, an electronic
signal sent to the computer’s CPU. Each device on the computer must have its own unique IRQ line.
NIC cards usually use the IRQ of 5 as a default, but it can also use a 3 too.
The base I/O port specifies a channel through which information flows between the computer’s
hardware and its CPU. Each hardware device on the system must have a separate I/O port
number.
Base Memory Address
The base memory address identifies a location in a computer’s memory (RAM). The NIC uses
this location as a buffer area to store the incoming and outgoing data frames.
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Selecting the Tranceiver
The NIC can have other settings that need to be defined during configuration. Some NIC’s
have internal and external transceivers.
NIC, Bus, and Cable Compatibility
To ensure compatibility between the computer and the network, the NIC must:
a) Fit with the computer’s internal structure (data bus architecture)
b) Have the right type of cable connector for the cabling
NIC cards must have a connection on them to attach to thinnet, thicknet and fiber-optic cabling.
Networking Cards
|
CARD NAME |
DESCRIPTION |
|
NIC card or NAC |
Common, translates parallel data from the computer to serial data |
|
ISA |
8-bit 4.77 mhtz, wait states, slows down the sytem |
|
EISA |
ISA cards fit in it, 16/32 bit |
|
PCI |
Slots white on the mother board (33 mhtz) MacIntosh adapted this standard |
|
AGP |
Video port |
Network Performance
Because of the effect it has on data transmission, the NIC has a significant effect on the performance
of the entire network. If the card is slow, data will not pass to and from the network quickly. This
is why it is important to use a good quality NIC. On a bus topology, where you have to take your
turn to transmit data, a slow card can increase the wait times for all the users.
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You can speed up the performance of your NIC card with the following enhancements:
a) Direct Memory Access (DMA) The computer moves the data directly from the NIC’s
buffer to the computer’s memory, without using the computer’s Microprocessor.
b)
Shared Adapter Memory The NIC contains RAM that it shares with the
computer. The
computer
identifies this RAM as if it is actually installed in the computer.
c)
Shared system memory The NIC’s processor
selects a section of the computer’s memory
and uses
it to process data.
d)
Bus Mastering The NIC takes temporary
control of the computer’s but, bypasses the computer’s
CPU, and moves data directly to the computer’s system memory. This will speed up the operation.
Bus
mastering can be expensive, but it can speed up memory by 20 – 70 %.
e) RAM Buffering Network traffic often travels too fast for most NIC’s to
Handle.
RAM chips on the NIC serve as a buffer.
Similar to cashing.
f) On-board microprocessor The NIC does not need the computer to help
Process the data.
Wireless NIC’s
Wireless NICs are available that support the major network operating systems. These NIC’s can be used
to create an all-wireless LAN or to add wireless stations to a cabled LAN (antenna at the back)
Remote-Boot PROM’s
These are workstations like at GM, in the plant all the dumb terminals. They were attached to the
Mainframe in
secure, there are no floppy drives and CD-ROMS. This way the users cannot take any of the data
from the site.
However, because computers normally start from either a floppy or a hard disk there has to be another
source for the software that initially starts (boots) the computer and connects it to a network. The NIC
can be equipped with a special chip called a remote-boot PROM (programmable read-only memory)
that contains the hardwired code that starts the computer and connects the user to the network.
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NIC Summary
The Network interface cards (NICs) are computer expansion cards that provide the interface between
the network cabling and the computer.
The function of the NIC is to prepare, send and receive, and in a Ring topology retransmit data
on the network.
A NIC is installed just like any other expansion card. You must properly set the IRQ, the base I/O
port address, and the base memory address.
In order for a NIC to be physically installed in a computer and connected to the network, it must both
match the computer’s expansion bus type and have the proper connector fittings for the network cabling.
WIRELESS
NETWORKING
The phrase “wireless environment” is misleading because it implies a network completely free of cabling.
Types of Wireless Networks
a) LAN’s
b) Extended LAN’s
c) Mobile computing
LANS
LANS that are wireless have a NIC with a tranceiver installed in each computer. The users communicate
with the network just as if they were using cabled computers.
Access Points is another name for a tranceiver, and it broadcasts and receives signals to and from the
surrounding computers and passes data back and forth between the wireless computers and the cables
network.
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Wireless Networks use 4 transmission techniques:
a) Infrared Transmission operates by a infrared light beam to carry the data between devices.
You cannot be near a window or a light source for this type of transmission to work. There are
4 kinds of infrared, line-of-sight networks, scatter infrared networks, reflective networks, and
broadband optical telepoint.
b) Laser Transmission is similar to infrared technology in that it requires a direct line of sight,
and any person or thing that breaks the laser beam will block the transmission.
c) Narrowband (Single-Frequency) Radio Transmission is similar to broadcasting from a radio
station.
d) Spread-Spectrum Radio Transmission, uses radio broadcast signals over a range of freq-
uencies. It picks random frequencies to send data, therefore can be a more secure way to
transmit data. Uses encrypting, outdoors can go up to 2 miles, and indoors can go up to
800 feet.
NOTE: Point-to-Point transmission uses wireless serial data transfer
Extended LANs
A wireless
A wireless bridge is a component that offers an easy way to link buildings without using cable.
Mobile Computing
Wireless mobile networks use telephone carriers and public services to transmit and receive signals
using:
a) Packet-radio communication
b) Cellular networks
c) Satellite stations
Mobile computing incorporates wireless adapters that use cellular-telephone technology to connect
portable computers with the cabled network. Portable computers use small antennas to communicate
with radio towers in the surrounding area. Satellites in near-earth orbit pick up lot-powered signals from
portable and mobile networked devices.
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Satellite Stations
Microwave systems are a good choice for interconnecting buildings in small, short-distance systems such
as those on a campus or in an industrial park. Microwave transmission is currently the most widely used
long-distance transmission method in the United States.