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Unit 3 Elements of Computer Networks

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					Theme 3 Computer Networks                     Unit 3 Elements of Computer Networks (Rev 1.0)


                    Unit 3         Elements of Computer Networks


3.1 Elements of a small LAN

A small LAN is shown in Figure 3.1.1. It consists of the following components:
• Stations;
• Servers; and
• Network hardware including network hub and network cables.




                                          Figure 3.1.1

Stations are Personal Computers (PCs) running operating systems such as Microsoft
Windows 98 or ME. Servers, however, are more powerful PCs having shared resources such
as disk files or printers (see Figure 3.1.2). These servers usually run operating systems that are
specifically designed for servers. Examples of these operating systems are Windows NT
Servers and Linux.




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Theme 3 Computer Networks                  Unit 3 Elements of Computer Networks (Rev 1.0)




                                       Figure 3.1.2


The stations and servers are connected together to form a small LAN by using network cables
and a network hub. Unshielded Twisted Pair (UTP) cables are commonly used as network
cables, with both ends of a cable connected to standard network connectors called RJ-45
connectors (see Figure 3.1.3).




                                       Figure 3.1.3




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Theme 3 Computer Networks                  Unit 3 Elements of Computer Networks (Rev 1.0)




                                        Figure 3.1.4

Network hubs are used to provide communication between stations and servers (see Figure
3.1.4). Today, most network hubs operate based on a network standard called "Ethernet";
consequently, network hubs are also called Ethernet hubs.


3.2 Components of a Networked PC

Besides the basic components of a PC, a "networked" PC (no matter whether it is a station or
a server) has three network components as shown in Figure 3.2.1. They are, namely, network
applications, network protocols, and network hardware. These network components work
together to allow data communication between the PC and other networked PCs possible.




                                        Figure 3.2.1




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Theme 3 Computer Networks                  Unit 3 Elements of Computer Networks (Rev 1.0)




3.3 Network Applications

Network applications are computer software running on multiple networked PCs to perform
specific network functions. Examples of network applications are printing over the network,
file sharing, database management, and electronic mailing. Usually, PC operating systems
already provide some network functions such as file sharing and network printing. However,
many other network applications are provided as stand-alone software packages that are sold
separately to the users. Examples of this kind of software packages are Electronic Mailing
systems and Network Operating Systems (NOS).

Note that to use a network application, installation of software on all the PCs involved is
required. Each PC involved runs its own piece of network software to communicate with
other PCs. To facilitate such data communications, network protocols are required to
standardize the messages passed between two communicating PCs.


3.4 Network Protocols

A network protocol is a set of rules that governs the exchange of messages between
computers. Two communicating computers must use the same protocol to communicate with
each other. Examples of network protocols include:
• Transmission Control Protocol/Internetworking Protocol (TCP/IP);
• HyperText Transfer Protocol (HTTP);
• Simple Mail Transfer Protocol (SMTP); and
• Post Office Protocol (POP).

Network protocols are usually implemented as software components of OSs and software
applications. For example, the HTTP is implemented in all web browsers and web servers. A
web browser uses HTTP to send messages to a web server. A web server also uses HTTP to
send response messages to web browsers.


3.5 Network Hardware

Network hardware is the physical component that actually carries out data transmission.
Network hardware includes the network hubs and the network cables that have been discussed
above. These network hardware are installed outside a PC. Network hardware inside a PC,
however, is a Network Interface Card (NIC). A PC uses its NIC to send out messages to the
network. The network (which includes all the network cables and the network hub) will then
pass the messages to the NIC of the receiving PC.

Today, most of the NICs are Ethernet based. The common data rates for these NICs are
10Mbps and 100Mbps. When a NIC has the rate of 100Mbps, it is also called a "Fast Ethernet
Card". With the recent advances of technologies, NICs with a 1000Mbps (or Gbps) rate are
found commercially. These NICs are called "Gigabit Ethernet Cards".




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Theme 3 Computer Networks                  Unit 3 Elements of Computer Networks (Rev 1.0)


Figure 3.5.1 shows a photo of a NIC. You can see that the NIC has a socket that is for
plugging in an RJ-45 connecter of a network cable. This NIC can be installed in a card slot
inside a PC. In Figure 3.5.2, we see another type of NIC. This is called a "PCMCIA Network
Card". This kind of network cards is for plugging into the PCMCIA slots of notebook
computers.




                                       Figure 3.5.1




                                       Figure 3.5.2




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Theme 3 Computer Networks                   Unit 3 Elements of Computer Networks (Rev 1.0)


3.6 Summary

In summary, a networked PC has three key components: network application, network
protocol, and network hardware. The network application of a PC relies on its network
protocol to communicate with another PC. The network protocol of a PC, in turn, relies on its
network hardware to transmit data to another PC. Figure 3.6.1 shows how these three
corresponding components of two computers work together to achieve the web browsing
function.




   Web Browser                                                          Web Server




        TCP/IP                                                              TCP/IP




                                        Figure 3.6.1


Key terms:

UTP: A type of cable commonly used in LANs and telephone systems.
RJ45: A type of connector used in network cables.
Network hub: A device for connecting PCs together to form a small LAN.
Operating system: A set of computer programs that is used by a computer for managing its
        own resources.
Linux: An operating system with an open source code.
Network Operating Systems: A set of computer programs that is used by the computers of a
        network for managing the network resources.
Database management systems: A software system designed to manage and maintain a
        collection of data records.

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Theme 3 Computer Networks                Unit 3 Elements of Computer Networks (Rev 1.0)


Network Interface Card (NIC): An interface card that provides connectivity to a computer
        network.
Fast Ethernet: An Ethernet system that provides a data rate of 100Mbps.
Gigabit Ethernet: An Ethernet system that provides a data rate of 1000Mbps.
PCMCIA (Personal Computer Memory Card International Association): A special interest
        group to develop a standard for memory cards. These memory cards are called
        PCMCIA cards.




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