Chapter 3: The Basics of Networking

Chapter 5: Locating information on the WWW

Chapter 6: Case Study in Online Research

Objectives - Provide basic components, features and functions associated with Computer Networks.  You will be exposed to many new areas that are not addressed in the text but you will be responsible for these items for the Tests.

The figure above shows the basic components of a network or data communications channel.

Networks contain computers, communication links (transport layer), data transfer components (e.g. modem), and the software that allows all of these hardware components to communicate and transfer data.  This is why this section is also called data communication, in order to better describe the components that allow data to be transferred or methods of data transmission.

Most computers produce data or information as digital signals and most transport layers (such as phone lines and cable) transfer analog signals.  Therefore, the data signals often must be converted in order to communicate between computers on a network.  The modem performs two functions, modulates the digital signal from the computer so the data can be transmitted over analog lines (e.g. phone) and demodulates the analog signal so it can be placed back into the computer.  This figure shows a terminal, but it is assumed that at both ends of this network there are computers to perform the processing of the data to and from the modem.

Note: In the figure below, analog signals are the wave like red lines, and digital signals look like little square hill tops.

Some uses of networks are:

1. E-mail

2. Facsimile (Fax)

3. Groupware

4. Teleconferencing and video conferencing

5. Electronic data interchange (EDI)

6. Electronic fund transfers (EFT)

7. Automatic Teller Machines (ATM)

8. Telecommuting

9. Online services

10. The Internet or World Wide Web (WWW)

Networks can be either internal to organization or building which is known as an intranet or Local Area Network (LAN). External which would include connecting to the World Wide Web (WWW) or more commonly called the internet. External networks are usually classified as Wide Area Networks (WAN).  Below there will be discussion on the network topologies that are used on WAN, which are Star, Ring and Bus topologies.

Depending on the connections that a user has to the internet and the transport layer being used, will depend on the transfer speed of the data.

The following chart shows the internet connections, download time (speed of data transfer) and advantages (pros) as well as disadvantages (cons) associated with each type of connection. 

As mentioned above most computers generate digital signals, and if there is a transport layer that handles these digital signals, then there is no need to convert the digital signal.  Therefore, digital transmission method sends pulses over digital lines.

Where as most transport layers uses the analog transmission method. 

Some of the devices available to access the internet are:

1. Modem

Most computers use a modem to convert digital signal to analog signals.  A modem modulates the digital signal to an analog signal, so the analog transmission method can be used over analog transport layer. This is called modulation.

A modem also demodulates the analog signal to a digital signal, after the analog signal has been already transferred over the analog transport layer. This is called demodulation.

Typical modem speed (according to the Chart above) is up to 56,000 bps (56k or thousand bits per second).  However, the transport layers, conventional phone lines usually don't allow this speed.

2. Integrated Services Digital Network (ISDN)

With ISDN, users can talk on the phone line and transmit data at the same time, up to 128,000 bps (128k or thousand bits per second).

This service requires an adapter and upgrade phone services (upgrades phone transport layer) in order to get the 128k bps.

The ISDN services usually have limited service area.

3. Digital Subscriber Line (DSL)

With DSL, users also uses conventional phone lines, signals are still converted from digital to analog, but DSL uses multiple frequencies to simulate many modems transmitting at once, thus there is less competition for connections.

These phone lines also share phone lines with voice, with speeds up to 10,000,000,000 bps (10M or million bits per second). Users can always be on line with this device.

DSL systems do not have an industry standard and usually require the user to be within 2 miles of the host stations, so service is also limited.  The closeness to the host along with the number of users on the network, are two items that makes the speed so fast.

4. Cable modems

Without the benefit of digital phone lines to each house or building, for personal users one of the growing options is cable modems. This device connects up to the television cable system and can have speeds up to 10,000,000,000 bps (10M or million bits per second).  The user can be always on line with this device.

Cable television companies are also installing digital cable and offering digital cable access to the internet, so the speed is much higher than regular phone lines or traditional cable.

5. Cellular modems

These devices are relatively slow and do not currently have many customer users, since using cell phones for internet access often depends on where the cell towers are.  If you are not in an area that has the capacity to handle internet access, your service will more than likely be unacceptable.

Return to Top

Bandwidth refers to the range of frequencies that a medium can carry and is a measure of the capacity of that link.  It is also dependant on transport layer media.

There are a variety of transport layers and some are dependent on the industry standard protocols (a set of rules set up for data communications) which allow the communication over these transport layers.  These protocols are important because no one manufacture in the industry builds all of the hardware or software in the communication channels.

The protocol that makes the internet universally possible is Transmission Control Protocol/Internet Protocol (TCP/IP). 

The IP packet, like the postcard, has space for the data, a destination IP address, and a sequence number. IP packets are sent over the Internet one at a time using whatever route is available.

The network protocol that accesses the network by first 'listening' to determine whether the cable is free is called Ethernet.  Depending on the technology, the physical setup for an Ethernet network is a wire, wire pair, or optical fiber, called the channel, that winds past a set of computers. 

Some of the media used as transport layers are:

1. Wire pair (wired) also known as twisted pair, which are inexpensive and these are already used in telephone systems.

2. Shielded twisted pair (wired) which use a protective sheath to reduce noise and increased speed.

3. Coaxial cable (wired) which have higher bandwidth than phone lines, they are less susceptible to noise, and are used in cable TV systems.

4. Fiber optics which transmit data using light, have a higher bandwidth, are less expensive than phone lines, are immune to electrical noise and are more secure than the previously mentioned media.

5. Microwave transmission (wireless) which is an easy and cost effective way of setting up a network, they are reserved for line-of-site transmissions and weather can cause interference.

6. Satellite transmission (wireless) which is a microwave transmission with a satellite acting as a relay for long distance communications.

7. A combination of transmission types can also be used to transmit information from one computer to another.

                                                      Return to Top

The above figures show network configurations which are also called network topologies (physical layout of a network) and can be set up for local as well as wide area networks.

There are three network topologies which we need to future address.  Each topology has key characteristics, advantages and disadvantages.

1. Star

1. Key characteristic - has a central hub (e.g. node in the middle)

2. Advantage - central hub prevents collisions and conflicts, plus if a node other then the hub fails it does not effect the overall network

3. Disadvantage - if the link to the hub goes down, there is no alternative path

2. Ring

1. Key characteristic - DOES NOT have a central hub (e.g. node in the middle)

2. Advantage - has an alternative path

3. Disadvantage - if a node fails then the whole network fails, and no central hub to handle conflicts

3. Bus

1. Key characteristic - has a single pathway where all nodes are attached

2. Advantage - if a collision results the data is re-sent or transmitted, and if a node fails there is no effect on the over all network.  Thus, most widely used in WWW communications.

3. Disadvantage - may have a limited number of nodes it can support

Return to Top

Since many of the networks today involve Local Area Networks (LANs) which are usually a network of personal computers that share hardware, software and data, there some important hardware devices that are used to assist with the LAN connections.

They are: 

1. Bridge which connects similar network protocols.

2. Router is a special computer which directs traffic to best available path within the network.

3. IP (internet protocol) switches are replacing routers since they are less expensive and faster.

4. Gateway which connects LANs with dissimilar hardware and software and varying protocols.