Without reference, identify principles relating to Computer Networks with at least 70

percent accuracy.

COMPUTER NETWORKS

Network A group of computers connected by cable, or other means, so

they can share information Common network terms • Server - Usually the most powerful computer on the network that

provides the services for the network • Client - A computer on the network that uses the services

provided by the server • Peer - A computer that acts as both a client and a server • Media - The physical connection between devices on a network • Resources - Anything connected to the network that is available to

a client • User - A person that uses a client to access the network • Protocol - any predetermined set of rules that define how two

devices or pieces of software should communicate with each other

COMPUTER NETWORKS

Networking Models Describe how information is processed by the computers on the network There are three basic models we need to discuss:

Centralized Networks

» The first computers were large mainframes that were very large and very expensive

» Large, intensive tasks were input into these systems and the results were later printed out

» These early centralized networks gave users the ability to access the network from remote locations

» Today's centralized networks keep shared information in one location, assuring everyone is working on the same information

» Costs less overall to operate and maintain » Because the mainframe/server handles all of the processing, this type of

network is generally slow » Additionally, if users have a variety of application needs, the users must

have these applications set up separately » Connectivity can become a large problem since users must connect to a

central site

COMPUTER NETWORKS

Distributed Networks » The popularity of PC's enable the processing power of

individual systems to be distributed to all computers on the network

» Data processing and storage is done on the local workstati

» Server do not need to be as powerful or as expensive » This type of network accommodates a variety of needs,

yet allows the sharing of data, resources and services » A drawback to this type of network is the susceptibility of

viruses » Developing an effective back up plan can be more

difficult if users store shared files on their own systems » The disadvantages of a centralized network become the

advantages of a distributed network, and vice-versa

COMPUTER NETWORKS

• Collaborative Networks » Collaborative computing allows computers to share processing power

across a network » Applications can be written to take advantage of this power to

accomplish tasks much faster than a single system » In addition to this capability, this type of network is similar to a

distributed network in its ability to share data and resources » This type of network also shares the advantages and disadvantages

of a distributed network

Networking Types Peer-to-Peer • The simplest form of networking • Each workstation acts as a client and a server • There is no central repository for data and no dedicated server to maintain • Data and resources are distributed throughout the network with each user

responsible for sharing these items connected to their systems • Small, inexpensive networks can easily be set up using peer-to-peer

COMPUTER NETWORKS

This type of network is ideal for small offices or home offices that require sharing of resources

All that is needed for a peer-to-peer network are the network adapter cards, cable (transmission media) and a networking operating system

A large disadvantage of this type of network is the number of users connected Once the number reaches 10, degradation of performance becomes

apparent depending upon how much the network resources are used Additionally, shared files can have several different revisions based upon

who is accessing them Different resources are usually attached to different systems Each user is responsible for maintaining administrative control of their

systems, though they may be improperly trained Security of the network is difficult to maintain Very dependent on user training

COMPUTER NETWORKS

Client/Server or Server-Based • A dedicated computer acts as a central repository for files and/or

applications The server controls the data, printers and other resources that clients need to

access Usually a very fast system with large amounts of memory and hard drive space Having a powerful server allows the clients to be less powerful since they only

request resources – The server will not normally act as a workstation as it's only purpose is to

provide resources and services to clients • Multiple servers can be utilized within the same network, each having

unique task handling capabilities File and print servers are optimized to hand out files to clients and handle

printing requests Application servers actually handle all the processing requirements of an

application being run on a client Mail servers are specifically set up to handle client e-mail needs Communications servers are set up to allow users remote access to the network

COMPUTER NETWORKS

• If your network has over 10 users, a server-based network should be considered • With a dedicated server, a synchronized file set can be maintained that

everyone works from • Security of the network is easier to manage since only the server needs to

maintain the accounts, rather than each workstation Specific users can be granted access to resources using their server account A peer-to-peer network uses a single password that is used by everyone to access a

resource • A server based network is also more cost efficient than a peer-to-peer network

The server stores most of the files and applications that are shared on the network, so workstations do not need large hard drives or large amounts of memory

This helps offset the cost of the server since workstations do not need to be as powerful

• One of the biggest disadvantages of having a server based network is the requirement of having a network administrator

Networking Services • File Services • Print Services • Message Services • Directory Services • Database Services

COMPUTER NETWORKS

• LANs, MANs and WANs Local Area Network (LAN)

» The smallest network size is referred to as a LAN » Normally contained within one building or in a small group of buildings » A LAN is typically a high speed, inexpensive network with very few or no errors

generated on the network Metropolitan Area Network (MAN)

» This is a group of LANs located within a city or metropolitan area » Since the LANs are geographically separated, specialized equipment is required for

connecting them to create a MAN » Typically, MANs are slower than LANs and carry a higher price » A MAN will have few errors, but more than a LAN

• Wide Area Network (WAN) This is the largest network size

» WANs can interconnect both LANs and MANs across a city, state, country or even the world

» The term Enterprise WAN refers to a network that contains all the LANs and MANs within an organization

» WANs use connections world-wide and are prone to errors » WANs are much slower than LANs or MANs » Highly specialized equipment that is very expensive

COMPUTER NETWORKS

Topologies Description of how computers are connected without regard to

how they communicate Bus • Simplest to install • All devices on the network are connected to one primary trunk cable • Each end of the trunk cable needs to be properly terminated • Bus topologies normally use coaxial cable • Advantages

Easy to install and configure Inexpensive Easily extended

• Disadvantages Performance degradation Weakened signal Difficult troubleshooting

COMPUTER NETWORKS

COMPUTER NETWORKS

Ring • Looks like a bus topology with connected ends • Provide high performance for a large number of users • Data flowing on the ring travels from computer to computer in one

direction • The signal is retransmitted by each system when passed on to its

neighbor • Token passing is frequently used on the ring topology • Advantages

provides an orderly network in which every device has access to the token and can transmit

performs well under a heavy load • Disadvantages

Malfunctioning workstations and cables create problems for the entire network

Changes made when adding or removing a device affect the entire network

COMPUTER NETWORKS

COMPUTER NETWORKS

Star • Uses a separate cable for each workstation • The cable connects the workstation to a central device, typically a

hub • Provides a more reliable network that is easily expanded • There is no central point of failure in the cable • To add more workstations, just add another hub • Hubs

Can be used as more than a central connection point. Passive hub » Used to connect computers in a broadcast network » The signal sent to a passive hub is sent to all workstations with no

regeneration or amplification Active hub » Uses an external power source » It regenerates the signal before sending it out to all workstations in a

broadcast network » Greater cable distances are allowed

COMPUTER NETWORKS

COMPUTER NETWORKS

Switched hub » Directs the signal directly to the recipient » Can greatly reduce network traffic

• Advantages (STAR) Easily expanded Easier to troubleshoot Multiple cable types supported by hubs

• Disadvantages (STAR) Hub failure Requires more cable May require a device to rebroadcast signals across the network

Mesh • Provides the highest level of fault tolerance • A true mesh network uses separate cables to connect each device to every

other device on the network, providing a straight communications path • Requires a large amount of cable and can quickly become confusing • Advantages

Enhanced fault tolerance provided by redundant links Easy to troubleshoot

COMPUTER NETWORKS

COMPUTER NETWORKS

• Disadvantages • Difficult to install • Costly to provide redundant links

Ethernet Standard The Ethernet standard was originally developed by Xerox in

the 1970's In the 1980's, Xerox let the Institute of Electrical and

Electronics Engineers (IEEE) take over control of the standard IEEE 802.3 is actually called the CSMA/CD committee although

the term Ethernet is what is commonly used in the industry today

Although technically there is a difference between the two, the terms are used interchangeably

COMPUTER NETWORKS

COMPUTER NETWORKS