Transcript Principles of Electronic Communication Systems

1
Principles of Electronic
Communication Systems
Third Edition
Louis E. Frenzel, Jr.
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Chapter 12
Introduction to Networking
and Local-Area Networks
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Topics Covered in Chapter 12
 12-1: Network Fundamentals
 12-2: LAN Hardware
 12-3: Ethernet LANs
 12-4: Token-Ring LAN
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12-1: Network Fundamentals
 Most computers today are networked, that is,
connected to one another so that they can
communicate with one another and share resources.
 Virtually 100 percent of business and industrial
computers are networked.
 It is estimated that more than 70 percent of all home
and personal computers are also networked.
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12-1: Network Fundamentals
 A network is a communication system with two or
more stations that can communicate with one another.
 When it is desired to have each computer
communicate with two or more additional computers,
the interconnections can become complex.
 The number of links L required between N PCs
(nodes) is determined by using the formula
L = N(N−1) / 2
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12-1: Network Fundamentals
Figure 12-1: A network of four PCs.
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12-1: Network Fundamentals
Types of Networks
 Each computer or user in a network is referred to as a
node.
 The interconnection between the nodes is referred to as
the communication link.
 In most networks, each node is a personal computer,
but in some cases a peripheral device such as a printer
can be a node.
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12-1: Network Fundamentals
Types of Networks
 There are four basic types of networks:
 Wide-area networks (WANs),
 Metropolitan-area networks (MANs)
 Local-area networks (LANs)
 Personal-area networks (PANs)
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12-1: Network Fundamentals
Types of Networks: Wide-Area Networks (WANs)
 A WAN covers a significant geographical area.
 Local telephone systems are WANs, as are the many
long-distance telephone systems linked together across
the country and to WANs in other countries.
 Each telephone set is, in effect, a node in a network that
links local offices and central offices.
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12-1: Network Fundamentals
Types of Networks: Wide-Area Networks (WANs)
 There are also WANs that are not part of the public
telephone networks, e.g., corporate and military.
 The nationwide and worldwide fiber-optic networks set
up since the mid-1990s to carry Internet traffic are also
WANs.
 Known as the Internet core or backbone, these highspeed interconnections are configured as either direct
point-to-point links or large rings with multiple access
points.
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12-1: Network Fundamentals
Types of Networks: Metropolitan-Area Networks (MANs)
 MANs are smaller than WANs and generally cover a
city, town, or village.
 Cable TV systems are MANs.
 Other types of MANs, or metro networks as they are
typically called, carry computer data.
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12-1: Network Fundamentals
Types of Networks: Metropolitan-Area Networks (MANs)
 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 long-distance
telephone companies. The MANs provide fast and
convenient connections to WANs for global Internet
connectivity.
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12-1: Network Fundamentals
Types of Networks: 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.
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12-1: Network Fundamentals
Types of Networks: Personal-Area Networks (PANs).
 A PAN is a short-range wireless network that is set up
automatically between two or more devices such as
laptop computers, personal digital assistants (PDAs),
peripheral devices, or cell phones.
 The distance between the devices is very short, no
more than about 10 m and usually much less.
 PANs are referred to as ad hoc networks that are set up
for a specific single purpose, such as the transfer of
data between the devices as required by some
application.
 Most PANs just involve two nodes, but some have been
set up to handle up to eight nodes and sometimes
more.
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12-1: Network Fundamentals
Types of Networks: Storage-Area Networks (SANs)
 SANs are an outgrowth of the massive data storage
requirements developed over the years thanks to the
Internet.
 These networks usually attach to a LAN or Internet
server and store and protect huge data files.
 The SAN also provides network users access to
massive data files stored in mass memory units, called
redundant arrays of independent disks (RAIDs).
 RAIDs use many hard drives interconnected to the
network and may be located anywhere since access
can be via the Internet or a fiber-optic WAN or MAN.
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12-1: Network Fundamentals
Types of Networks: Network Hierarchy
 LANs inside a building are usually connected to a MAN
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that may be, for example, a local telephone central
office.
The MANs connect to the WANs, which may be a longdistance telephone network or one set up for data
transmissions.
Some WANs are hierarchies of rings and direct
connection points.
MANs and WANs are virtually all fiber-optic networks.
Interconnection points of the networks may be special
computers called servers or routers.
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12-1: Network Fundamentals
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.
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12-1: Network Fundamentals
Network Topologies: 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.
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12-1: Network Fundamentals
Network Topologies: Star Topology
 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.
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12-1: Network Fundamentals
Figure 12-3: A star LAN configuration with a server as the controlling computer.
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12-1: Network Fundamentals
Network Topologies: Ring Topology
 In a ring configuration, the server or main control
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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.
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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12-1: Network Fundamentals
Figure 12-4: A ring LAN configuration.
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12-1: Network Fundamentals
Network Topologies: Bus Topology
 A bus is a common cable to which all of the nodes are
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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.
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12-1: Network Fundamentals
Figure 12-5: A bus LAN configuration.
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12-1: Network Fundamentals
Network Topologies: 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.
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12-1: Network Fundamentals
Network Topologies: Mesh Topology
 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.
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12-1: Network Fundamentals
Network Topologies: Other Topologies.
 There are many variations and combinations of the
basic topologies.
 Two examples:
 The daisy chain topology is a ring that has been
broken.
 The tree topology is a bus design in which each node
has multiple interconnections to other nodes through
a star interconnection.
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12-1: Network Fundamentals
LAN Applications
 The common denominator of all LANs is the
communication of information.
 Networks are used for many applications other than
centralizing and sharing expensive peripherals and for
database applications:
 E-mail
 Internet access
 Groupware (e.g., Lotus Notes)
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12-1: Network Fundamentals
Client-Server and Peer-to-Peer LANs
 Most LANs conform to one of two general
configurations: client-server or peer-to-peer.
 In the client-server type, one of the computers in the
network, the server, essentially runs the LAN and
determines how the system operates.
 The server manages printing operations of a central
printer and controls access to a very large hard drive or
bank of hard drives containing databases, files, and
other information that the clients—the other computers
on the network—can access.
 The server also provides Internet access.
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12-1: Network Fundamentals
Client-Server and Peer-to-Peer LANs
 In a peer-to-peer system, any PC can serve as either
client or server; any PC can have access to any other
PC’s files and connected peripherals.
 Peer-to-peer LANs are smaller and less expensive than
the client-server variety, and provide a simple way to
provide network communication.
 Disadvantages include:
 Lower performance (lower-speed transmission capability).
 Manageability and security problems (any user may
access any other user’s files).
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12-2: LAN Hardware
 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
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12-2: LAN Hardware
Cables
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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
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12-2: LAN Hardware
Cables: Coaxial Cable
 Coaxial cable is far superior to twisted pair as a
communication medium.
 Its extremely wide bandwidth permits very high-speed
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.
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12-2: LAN Hardware
Figure 12-6: Coaxial cable.
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12-2: LAN Hardware
Cables: Twisted Pair
 Twisted pair cable is two insulated copper wires
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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.
Twisted pair has a characteristic impedance of about
100 Ω.
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12-2: LAN Hardware
Figure 12-7 Types of twisted-pair cable. (a) Twisted-pair unshielded (UTP) cable. (b)
Multiple shielded twisted-pair (STP) cable.
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12-2: LAN Hardware
Cables: Twisted-Pair Cable
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There are two basic types of twisted-pair cables in use
in LANs:
1. Unshielded (UTP): UTP cables are susceptible to
noise, particularly over long cable runs.
2. Shielded (STP): STP cables are more expensive
than UTP cables.
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They have a metal foil or braid shield around them, forming a
third conductor.
The shield is usually connected to ground and, therefore,
provides protection from external noise and crosstalk.
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12-2: LAN Hardware
Cables: Twisted-Pair Cable
 The most widely used UTP is category 5 (CAT5). It can
carry baseband data at rates up to 100 Mbps at a range
up to 100 m.
 Twisted-pair cable specifications also include
attenuation and near-end cross talk figures.
 Attenuation means the amount by which the cable
attenuates the signal. The longer the cable, the greater
the amount of loss in the cable and the smaller the
output.
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12-2: LAN Hardware
Cables: Twisted-Pair Cable
 Near-end cross talk (NEXT): Cross talk refers to the
signal transferred from one twisted pair in a cable to
another by way of capacitive and inductive coupling.
Near-end cross talk is the signal appearing at the input
to the receiving end of the cable.
 Many newer office buildings are constructed with
special vertical channels or chambers, called plenums,
through which cables are run between floors or across
ceilings.
 Cable used this way, called plenum cable, must be
made of fireproof material that will not emit toxic fumes
if it catches fire.
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12-2: LAN Hardware
Cables: Fiber-Optic Cable
 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.
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12-2: LAN Hardware
Figure 12-9: Fiber-optic cable.
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12-2: LAN Hardware
Connectors: Coaxial Cable Connectors
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All cables used in networks have special terminating
connectors that provide a fast and easy way to
connect and disconnect the equipment from the
cabling and maintain the characteristics of the cable.
 Coaxial cables in networks use two types of
connectors:
1. N connectors are widely used in RF applications
2. BNC connectors are commonly used for attaching
test leads to measuring instruments such as
oscilloscopes.
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12-2: LAN Hardware
Connectors: Coaxial Cable Connectors
 BNC T connectors are used to interconnect two cables
to the network hardware.
 The barrel connector provides a convenient way to
connect two coaxial cables.
 A terminator is a special connector containing a
resistor whose value is equal to the characteristic
impedance of the coaxial cable (typically 50Ω).
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12-2: LAN Hardware
Figure 12-10: Common coaxial connectors.
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12-2: LAN Hardware
Figure 12-11: BNC connector accessories and adapters. (a) T connector. (b) Barrel
connector.
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12-2: LAN Hardware
Connectors: Twisted-Pair and Fiber-Optic Connectors
 Most telephones attach to an outlet by way of an RJ-11
connector or modular plug.
 RJ-11 connectors are used to connect PC modems to
the phone line but are not used in LAN connections.
 A larger modular connector known as the RJ-45 is
widely used in terminating twisted pairs.
 A wide range of connectors are available to terminate
fiber-optic cables.
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12-2: LAN Hardware
Figure 12-12 Modular (telephone) connectors used with twisted-pair cable. (a) RJ-11.
(b) RJ-45.
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12-2: LAN Hardware
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.
 NICs are low in price and available from many
manufacturers.
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12-2: LAN Hardware
Figure 12-13: A network interface card.
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12-2: LAN Hardware
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.
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12-2: LAN Hardware
Figure 12-14: Concept of a repeater.
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12-2: LAN Hardware
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.
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12-2: LAN Hardware
Figure 12-15: A hub facilitates interconnections to the server.
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12-2: LAN Hardware
Bridges
 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.
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12-2: LAN Hardware
Figure 12-16: A bridge connects two LANs.
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12-2: LAN Hardware
Switch
 A switch is a hublike device that is used to connect
individual PC nodes to the network wiring.
 A switch provides a means to connect or disconnect a
PC from the network wiring.
 Switches have largely replaced hubs in most large
LANs because they greatly expand the number of
possible nodes and improve performance.
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12-2: LAN Hardware
Router
 Routers are designed to connect two networks.
 The main difference between bridges and routers is that
routers are intelligent devices that have decisionmaking 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.
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12-2: LAN Hardware
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.
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12-2: LAN Hardware
Figure 12-17: A gateway commonly connects a LAN to a larger host computer.
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12-2: LAN Hardware
Modem
 Modems are interfaces between PCs and standard
telephone systems.
 Modems convert the binary signals of the computer into
audio-frequency analog signals compatible with the
telephone system and, at the other end, convert the
analog signals back into digital signals.
 The most common application is one in which remote
PCs use modems to connect to an Internet service
provider (ISP) which provides services such as Internet
access and e-mail.
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12-2: LAN Hardware
Wireless LAN
 One way to avoid the expense and headache of running
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and maintaining LAN cabling is to use wireless LANs,
which communicate via radio.
Each PC in a wireless LAN must contain a wireless
modem or transceiver.
The radio modem transceiver converts the serial binary
data from the computer to radio signals for transmission
and converts the received radio signals back to binary
data.
Wireless LANs operate as cable-connected LANs in
that any node can communicate with any other node.
Most wireless LANs have a top speed of 11 to 54 Mbps.
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12-3: Ethernet LANs
Topology and Encoding
 One of the oldest and by far the most widely used of all
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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.
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12-3: Ethernet LANs
Figure 12-18: The Ethernet bus.
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12-3: Ethernet LANs
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
10 Gbps, typically over fiber-optic cable but also on
shorter lengths of coaxial or twisted-pair cable.
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12-3: Ethernet LANs
Transmission Medium: Coaxial Cable
 The original transmission medium for Ethernet was
coaxial cable. However, today twisted-pair versions of
Ethernet are more popular.
 The two main types of coaxial cable used in Ethernet
networks are RG-8/U and RG-58/U.
 RG-8/U cable is known as thick cable, and large typeN coaxial connectors are used to make the
interconnections.
 When thick network cable is used, it does not attach
directly to the NICs. The inputs and outputs from the
NIC terminate in an attachment user interface (AUI).
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12-3: Ethernet LANs
Transmission Medium: Coaxial Cable
 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.
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12-3: Ethernet LANs
Figure 12-20: The Ethernet (10Base-5) bus.
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12-3: Ethernet LANs
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.
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12-3: Ethernet LANs
Figure 12-21: 10Base-2 coaxial Ethernet bus.
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12-3: Ethernet LANs
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.
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12-3: Ethernet LANs
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.
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12-3: Ethernet LANs
Transmission Medium: Gigabit Ethernet
 Gigabit Ethernet (1 GE) is capable of achieving 1000
Mbps or 1 Gbps over category 5 UTP or fiber-optic
cable.
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12-3: Ethernet LANs
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 wide-wavelength
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.
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12-3: Ethernet LANs
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. The waiting
interval is determined randomly.
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12-3: Ethernet LANs
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.
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12-3: Ethernet LANs
Packet Protocols
 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).
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12-4: Token-Ring LAN
 In the Token-Ring configuration, all of the nodes or
PCs in the network are connected end to end in a
continuous circle or loop.
 Data in the network travels in only one direction on the
ring.
 The transmitted information passes through the NICs
of each PC in the loop.
 Token Ring uses baseband transmission; the binary
data is placed directly on the cable.
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12-4: Token-Ring LAN
 A modified version of the Manchester coding scheme
is used with Token-Ring.
 Token-Ring versions running at 4- and 16-Mbps are
still in use, but more recent versions run at 100Mbps
and 1 Gbps.
 Token-ring LANs use twisted pair cable and
connections are made by using RJ-45 modular
connectors.
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12-4: Token-Ring LAN
 The data transmitted around the ring passes through
the NIC of all PCs in the loop, so two twisted-pair
cables are needed for the connection at each node.
 One twisted pair, the ring in (RI), comes into the card;
another twisted pair, the ring out (RO), carries the
data out to the next node.
 To make wiring simpler, the two twisted pairs in a
single cable terminate at a wiring hub referred to as a
multistation access unit (MAU).
 The wiring inside the MAU connects the PCs in a
logical ring.
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12-4: Token-Ring LAN
Figure 12-28: Token-Ring wiring.
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12-4: Token-Ring LAN
Figure 12-29: Wiring of the Token Ring through the MAU.
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12-4: Token-Ring LAN
Access Method
 The access method used by Token-Ring systems is
token passing.
 A token is a unique binary word passed from one node
to another around the ring.
 Whenever a node desires to transmit information, it
captures the token. The NIC builds a packet or frame of
information and transmits the data on the ring.
 After the packet of information has been received, it
continues on around the ring until it comes back to the
transmitting node, which takes the data off the ring.
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12-4: Token-Ring LAN
Packet Protocol
 The token frame format consists of 3 bytes: a starting
delimiter (SD), an access control (AC) byte, and an
ending delimiter (ED).
 The actual token is 1 bit in the AC byte.
 It is followed by a frame control (FC) byte, a 6-byte
destination address, and then a 6-byte source address.
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12-4: Token-Ring LAN
Packet Protocol
 The data (message information) is transmitted next in a
synchronous format.
 The data is followed by a 4-byte (32-bit) CRC frame
check sequence that is generated to catch transmission
errors.
 The packet ends with the ending delimiter and frame
status (FS) bytes.
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12-4: Token-Ring LAN
Figure 12-30: Token-Ring packet format. (a) Token. (b) Data frame.
© 2008 The McGraw-Hill Companies