Copy of Datacomm Ch2

8/6/2019 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

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Copy of Datacomm Ch2