copy of datacomm ch2
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CHAPTER 2CHAPTER 2DATA COMMUNICATIONS circuits,
topologies and models.
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DATA COMMUNICATIONS NETWORKSDATA COMMUNICATIONS NETWORKS
Any groups of computers connected together
can be called a data communications network,
and the process of sharing resources between
computers over a data communication networkis called networking
There are many factors involved when designing a
computer network, including the following:
Network goals as defined by organizational managementNetwork securityNetwork uptime requirements
Network response-time requirements
network and resource cost
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Computer networkComputer network
The concept of networking began when someone
determined that there was a need to share software and data
resources and that there was a better way to do it than storing
data on a disk and literally running from one computer to
another. By the way, this manual technique of moving data on
disk is sometimes referred as sneaker net
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Components of a networkComponents of a network
y Servers e.g. File Servers, print servers, mail servers,communications servers, database servers, directory/security
servers, fax servers, and Web servers
y Clients
y Transmission media
y Shared data
y Shared printers and other peripherals
y Network interface card
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Network interface cardNetwork interface card
1.The NIC constructs, transmits, receives, andprocess data to and from a PC and the connected
network.
2.Each device connected to a network must have a
NIC installed.
3. An NIC is generally installed in a computer as a
daughterboard, although some computer
manufacturers incorporate the NIC into the
motherboard during manufacturing
4.Each NIC has unique six-byte media access
control (MAC) address, which is typically
permanently burned into the NIC when it is
manufactured. The MAC address is sometimes
called the physical, hardware, node, Ethernet, or
LAN address.
5.The NIC must be compatible with the network
(i.e., Ethernet 10 baseT or token ring) to operate
properly.
6.NICs manufactured by different vendors vary in
speed, complexity, manageability and cost.
7.The NIC requires drivers to operate on the
network.
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Network ModelsNetwork Models
Computer network can be represented with
two basic network models: peer-to-peerclient/server and dedicated client/server
Peer-to-peer client/server network- A peer-to-peerclient/server network is one in which all computersshare their resources, such as hard drives,
printers, and so on, with all the other computers on
the network. Therefore, the peer-to-peer operating
system divides its time between servicing the
computer on which it is loaded and servicingrequest from other computers. In a peer-to-peernetwork (sometimes called workgroup), there are
no dedicated servers or hierarchy among thecomputers.
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PeerPeer--toto--peer client/server networkpeer client/server network
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Dedicated client/server network- In a dedicatedclient/server network, one computer is designed
the server, and the rest of the computers areclients. As the network grows, additionalcomputers can be designated servers. Generally,the designated servers function only as serversand not used as a client or workstation. The serversstore al the networks shared files and applications
programs, such as word processor documents,compilers, database applications, spreadsheet,and the network operating system. Clientcomputers can access the servers and haveshared files transferred to them over thetransmission medium
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Dedicated client/server networkDedicated client/server network
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Network TopologiesNetwork Topologies
Network topology describes the layout or
appearance of a network- that is, how the
computers, cables, and other components
within a data communications network are
interconnected, both physically and logically.The physical topology describes how the
network is actually laid out, and the logical
topology describes how data actually flow
through the network.
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Star topologyStar topologyA star topology is a multipoint
data communications networkwhere stations are connected
by cable segments directly to
a centrally located computer
called a hub, which act like a
multipoint connector. In
essence, a star topology issimply a multipoint circuit
comprised of many two-pointcircuits where each remote
station communicates directly
with a centrally located
computer. With a startopology, remote stations
cannot communicate directlywith one another, so they must
relay information through the
hub.
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Bus topologyBus topologyA bus topology is a multipoint
data communications circuit thatmakes it relatively simple to
control data flow between and
among the computers because
this configuration allows all
stations to receive every
transmission over the network.With a bus topology, all the
remote stations are physically or
logically connected to a single
transmission line called a bus.
The bus topology is the simplest
and most common method ofinterconnecting computers. The
two ends of the transmission linenever touch to form a complete
loop
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Ring topologyRing topologyA ring topology is a multipoint
data communications networkwhere all stations are
interconnected in tandem
(series) to form a closed loop or
circle. A ring topology is
sometimes called a loop. Each
station in the loop is joined bypoint-to-point links to two other
stations (the transmitter of one
and the receiver of the other)
(see figure 2-11). Transmissions
are unidirectional and must
propagate through all thestations in the loop. Each
computer acts like a repeater inthat it receives signals from
down-line computers and then
retransmits them to up-line
computers.
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Mesh topologyMesh topologyIn a mesh topology, every
station has a direct two-pointcommunications link to every
other station on the circuit as
shown in Figure 2-12. The mesh
topology is sometimes called
fully connected. A disadvantage
of a mesh topology is a fullyconnected circuit requires n(n-
1)/2 physical transmission
paths to interconnect n stations
and each station must have n-1
input/output ports. Advantages
of a mesh topology are reducedtraffic problems, increased
reliability, and enhancedsecurity.
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Hybrid topologyHybrid topology
A hybrid topology is simply combining two or more of
the traditional topologies to form a larger, morecomplex topology. Hybrid topologies are sometimes
called mixed topologies. An example of a hybrid
topology is the bus star topology shown in figure 2-13.
Other hybrid configurations include the star ring, bus
ring, and virtually every other combination you can
think of.
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Network ClassificationsNetwork Classifications
Network Classifications
Local Area Network
Local area networks (LANs) are typically privately owned
data communications networks in which 10 to 100computer users typically share data resources with one or
more file servers. LANs use a network operating system toprovide two-way communications at bit rates typically in the
range of 10 Mbps to 100 Mbps and higher between a largevariety of data communications equipment within a
relatively small geographical area, such as in the room,building, or building complex
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LANs were designed for
sharing resources between a
wide range of digital
equipment, including personalcomputers, workstations, and
printers. The resourcesshared can be software as
well as hardware. Most LANs
are owned by the company or
organization that uses it andhave a connection to a
building backbone for accessto other department LANs,
MANs, and GANs.
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Metropolitan area networkMetropolitan area network
A metropolitan area network (MAN) is a high-speed network
similar to a LAN except MANs are designed to encompasslarger areas, usually that of an entire city
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Wide area networkWide area network
Wide area networks (WANs) are the oldest type of data
communications network that provide relatively slow-speed,
long distance transmission of data, voice, and video
information over relatively large and widely dispersedgeographical areas, such as a country or an entire continent