Chapter 12
Introduction to Networking
and Local-Area Networks
12-1: Network Fundamentals
12-2: LAN Hardware
12-3: Ethernet LANs
12-4: Token-Ring LAN
12-1: Network Fundamentals
12-2: LAN Hardware
12-3: Ethernet LANs
12-4: Token-Ring LAN
A network is a communication system with two or
more stations that can communicate with one
another.
Figure 12-1: A network of four PCs.
The number of links L
required between N PCs
(nodes) is determined by
using the formula
L = N(N−1) / 2
There are four basic Types of Networks
Wide-area networks (WANs),
Metropolitan-area networks (MANs)
Local-area networks (LANs)
Personal-area networks (PANs)
Wide-Area Networks (WANs)
 A WAN covers a significant geographical area.
 Public telephone systems are WANs.
 There are also WANs that are not part of the
public telephone networks, e.g., military.
 The nationwide and worldwide fiber-optic
networks to carry Internet traffic are also
WANs.
 Each telephone set is a node in a network that
links local offices and central offices.
Metropolitan-Area Networks (MANs)
 MANs are smaller than WANs and generally
cover a city, town, or village.
 MANs are usually fiber-optic rings
encircling a city that provide local access to
users. Businesses, governments, schools,
hospitals, and others connect their internal
LANs to them.
 MANs also connect to local and longdistance telephone companies. The MANs
provide fast and convenient connections to
WANs for global Internet connectivity.
Local-Area Networks (LANs)
 A LAN is the smallest type of network in
general use.
 A LAN consists primarily of personal
computers interconnected within an office or
building.
 LANs can have as few as three to five users,
although most systems connect to several
thousand users.
 Home networks of two or more PCs are also
LANs and today most home LANs are fully
wireless or incorporate wireless segments.
Network Topologies
 The topology of a network describes the
basic communication paths between, and
methods used to connect, the nodes on a
network.
 The three most common topologies used in
LANs are star, ring, and bus.
Star Topology
 A basic star configuration consists of a
central controller node and multiple
individual stations connected to it.
 The resulting system resembles a
multipointed star.
 The central or controlling PC, often referred
to as the server, is typically larger and faster
than the other PCs and contains a large
hard drive where shared data and programs
are stored.
Figure 12-3: A star LAN configuration with a server as the controlling computer.
Star Topology Characteristics
 A star-type LAN is extremely simple and
straightforward.
 New nodes can be quickly and easily
added to the system, and the failure of one
node does not disable the entire system.
 If the server node goes down, the network
is disabled but individual PCs will continue
to operate independently.
Ring Topology
 In a ring configuration, the server or main control
computer and all the computers are simply linked
together in a single closed loop.
 Usually, data is transferred around the ring in only
one direction, passing through each node.
Figure 12-4: A ring LAN configuration.
Ring Topology Characteristics
 The ring topology is easily implemented and
low in cost.
 The downside of a ring network is that a failure
in a single node generally causes the entire
network to go down.
 It is also difficult to diagnose problems on a
ring.
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Bus Topology
A bus is a common cable to which all of the
nodes are attached.
The bus is bidirectional in that signals can be
transmitted in either directions between any
two nodes.
Only one node can transmit at a given time.
A signal to be transmitted can be destined
for a single node, or transmitted or broadcast
to all nodes simultaneously.
The bus is faster than other topologies,
wiring is simple, and the bus can be easily
expanded.
Figure 12-5: A bus LAN configuration.
Mesh Topology
 A mesh network is one in which each node
is connected to all other nodes.
 In a full mesh, every node can talk directly
to any other node.
 There are major costs and complications as
the number of nodes increases, but the use
of wireless interconnections between nodes
helps to alleviate this problem.
Mesh Topology Characteristics
 A variation of the full mesh is the partial
mesh, in which all nodes can communicate
with two or more other nodes.
 The primary value of the mesh network is
that there are multiple paths for data to take
from one node to another.
 This offers redundancy that can provide a
continuous connection when one or more of
the links are broken, thus providing
increased network reliability.
12-1: Network Fundamentals
12-2: LAN Hardware
12-3: Ethernet LANs
12-4: Token-Ring LAN
All LANs are a combination of hardware and
software.
The primary hardware devices are the
computers, cables, and connectors.
Additional hardware includes:
– Network interface cards (NICs)
– Repeaters
– Hubs and concentrators
– Bridges
– Routers
– Gateways
Cables
 Most LANs use some type of copper wire
cable to carry data from one computer to
another via baseband transmission.
 The three basic cable types are:
1. Coaxial cable
2. Twisted pair
3. Fiber-optic cable
Figure 12-6: Coaxial cable
Coaxial Cable Characteristics
Its extremely wide bandwidth permits very highspeed bit rates.
Loss is generally high, but is usually offset by
using repeaters that boost signal level.
The major benefit of coaxial cable is that it is
completely shielded, so that external noise has
little or no effect on it.
Figure 12-7 (a) Twisted-pair unshielded (UTP) cable. (b)
Multiple shielded twisted-pair (STP) cable
Twisted Pair Characteristics
Twisted pair cable is two insulated copper wires
twisted together loosely to form a cable.
Telephone companies use twisted pair to connect
individual telephones to the central office.
The wire is solid copper, 22, 24, or 26 gauge.
The insulation is usually PVC.
 Cheaper, lighter, and easier to work with than
coaxial cables.
Figure 12-9: Fiber-optic cable
Fiber-Optic Cable Characteristics
Fiber-optic cable is a nonconducting cable consisting
of a glass or plastic center cable surrounded by a
plastic cladding encased in a plastic outer sheath.
Most fiber-optic cables are extremely thin glass, and
many are usually bundled together.
Special fiber-optic connectors are required to attach
them to the network equipment.
Speeds of up to 1 Tbps (terabits per second) are
achievable by using fiber optics.
Figure 12-10: Common coaxial connectors
Figure 12-11: (a) T connector. (b) Barrel connector.
Figure 12-12 Modular (telephone) connectors used
with twisted-pair cable. (a) RJ-11. (b) RJ-45
Optical Fiber Connectors
http://www.tradevv.com/chinasuppliers/topfiber_p_62ed4/china-optical-fiberconnector.html
Figure 12-13: A network interface card
Network Interface Cards and Chips
A network interface card (NIC) provides the I/O
interface between each node on a network and
the network wiring.
NICs usually plug into the PC bus or are built into
the PC motherboard and provide connectors at
the rear of the computer for attaching the cable
connectors.
The NIC is the key hardware component in any
LAN.
The NIC completely defines the protocols and
performance characteristics of the LAN.
Repeater
A repeater is an electronic circuit that takes a partially
degraded signal, boosts its level, shapes it up, and
sends it on its way.
Repeaters are small, inexpensive devices that can be
inserted into a line with appropriate connectors or
built into other LAN equipment.
Most repeaters are really transceivers, bidirectional
circuits that can both send and receive data.
Figure 12-14: Concept of a repeater
Hub
 A hub is a central connecting box designed to receive the
cable inputs from the various PC nodes and to connect
them to the server.
 In most cases, hub wiring physically resembles a star
because all cabling comes into a central point, or hub.
 Hubs are usually active devices containing repeaters.
They amplify and reshape the signal and transmit it to all
connection parts.
Switch
A switch is a hublike device that is used to
connect individual PC nodes to the network
wiring.
 A hub shares the total bandwidth among all
users, while a switch provides a dedicated line at
full bandwidth between every two devices
transmitting to each other.
Switches have largely replaced hubs in most
large LANs because they greatly expand the
number of possible nodes and improve
performance.
Bridge
 A bridge is a network device that is connected as a node
on a network and performs bidirectional communication
between two LANs.
 A bridge is generally designed to interconnect two LANs
with the same protocol, for example, two Ethernet
networks, although some perform protocol conversion.
 Remote bridges are special bridges used to connect two
LANs that are separated by a long distance.
Router
Routers are designed to connect two networks.
The main difference between bridges and routers
is that routers are intelligent devices that have
decision-making and switching capabilities.
The basic function of a router is to expedite traffic
flow on both networks and maintain maximum
performance.
Some routers are a combination of a bridge and
a router.
Gateway
A gateway is another internetwork device that
acts as an interface between two LANs or
between a LAN and a larger computer system.
The primary benefit of a gateway is that it can
connect networks with incompatible protocols
and configurations.
The gateway acts as a two-way translator that
allows systems of different types to
communicate.
Most gateways are computers and are
sometimes referred to as gateway servers.
Figure 12-17: A gateway commonly connects a LAN to a larger host computer
Internet
Service
Provider
12-1: Network Fundamentals
12-2: LAN Hardware
12-3: Ethernet LANs
12-4: Token-Ring LAN
Ethernet
One of the oldest and by far the most widely
used of all LANs is Ethernet.
The original versions of Ethernet used a bus
topology. Today, most use a physical star
configuration.
Ethernet uses baseband data-transmission
methods.
The serial data to be transmitted is placed
directly on the bus media.
Before transmission, the binary data is encoded
into a unique variation of binary code known as
the Manchester code.
Ethernet Speed
The standard transmission speed for Ethernet
LANs is 10 Mbps.
The most widely used version of Ethernet is
called Fast Ethernet. It has a speed of 100
Mbps.
Other versions of Ethernet run at speeds of 1
Gbps or 100 Gbps, typically over fiber-optic cable
but also on shorter lengths of coaxial or twistedpair cable.
Transmission Medium: Coaxial Cable
 The original transmission medium for Ethernet was
coaxial cable. However, today twisted-pair versions
of Ethernet are more popular.
 Ethernet systems using thick coaxial cable are
generally referred to as 10Base-5 systems:
10 means a 10-Mbps speed
Base means baseband operation
5 designates a 500-m maximum distance
between nodes, transceivers, or repeaters.
 Ethernet LANs using thick cable are also referred
to as Thicknet.
Transmission Medium: Coaxial Cable
Ethernet systems implemented with thinner
coaxial cable are known as 10Base-2, or
Thinnet systems.
The 2 indicates the maximum 200-m (actually,
185-m) run between nodes or repeaters.
The most widely used thin cable is RG-58/U.
It is much more flexible and easier to work with
than RG-8/U cable.
Transmission Medium: Twisted-Pair Cable
More recent versions of Ethernet use twisted-pair
cable.
The twisted-pair version of Ethernet is referred to
as a 10Base-T network, where the T stands for
twisted-pair.
Transmission Medium:100-Mbps Ethernet
By far the most popular version of 100-Mbps
Ethernet is 100Base-TX, or Fast Ethernet.
It uses two unshielded twisted pairs instead of
the single pair used in standard 10Base-T.
One pair is used for transmitting, and the other is
used for receiving, permitting full duplex
operation, which is not possible with standard
Ethernet.
Transmission Medium: Gigabit Ethernet
Gigabit Ethernet (1 GE) is capable of achieving
1000 Mbps or 1 Gbps over fiber-optic cable.
Transmission Medium: 10-Gbit Ethernet
The newest version of Ethernet is 10-Gbit
Ethernet (10 GE), which permits data speeds up
to 10 Gbps over fiber-optic cable.
Three of the five variations of 10-Gbit Ethernet
use serial data transmission.
The other two use what is called widewavelength division multiplexing (WWDM).
Also known as coarse wavelength division
multiplexing (CWDM), these versions divide the
data into four channels and transmit it
simultaneously over four different wavelengths of
infrared light near 1310 nm.
WWDM is similar to frequency-division
multiplexing.
Access Method
Access method refers to the protocol used for
transmitting and receiving information on a bus.
Ethernet uses an access method known as
carrier sense multiple access with collision
detection (CSMA/CD)
Occasionally, two or more nodes may attempt to
transmit at the same time. When this happens, a
collision occurs and both transmitting stations
will terminate transmission.
The CSMA/CD algorithm calls for the sending
stations to transmit again after a brief pause.
Packet Protocols
 The packet in the 802.3 protocol is made up of
two basic parts:
1. The frame, containing the data plus addressing and
error detection codes
2. An additional 8 bytes (64 bits) at the beginning, which
contains the preamble and the start frame delimiter
(SFD).
 The destination address is a 6-byte, 48-bit code
that designates the receiving node.
 Next is a 6-byte source address that identifies the
sending node.
Packet Protocols (cont.)
Next is a 2-byte field that specifies how many
bytes will be sent in the data field.
The data itself is transmitted.
The packet and frame end in a 4-byte frame
check sequence generated by putting the entire
transmitted data block through a cyclical
redundancy check (CRC).