ECT 250: Survey of e-commerce technology

Networking

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In a network, communications equipment is usedto connect two or more computers allowing thesharing of various hardware, software, and dataresources.

The basic components of a data communicationssystems used to transmit information are:• A sending device• A communications link, consisting of both

communications hardware and software.• A receiving device

Networking

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Binary information is represented by the presenceor absence of an electronic pulse. This is referredto as digital signaling.

Some communications devices in place today weredesigned for voice data which uses analog signals.Data communications systems may use theseexisting lines.

Data transmission

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If the wires in place for communication use analogsignals, digital data must be converted to an analogsignal in order to be transmitted.

•The digital signal is transformed into an analogwave in a process called modulation.

•The analog wave is transmitted.•The analog signal is converted back into a digital

signal during a process called demodulation.

Piggybacking technology

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A modem is the hardware device that does theseconversions. (Short for modulate/demodulate).

Modem speeds are referred to by the number ofbits per second (bps) at which they can transmitand receive data.• The earliest modems has speeds around 300 bps.• Later modems had speeds ranging from 9600

to 33,600 bps. • Today modems have speeds of 56,000 bps (or

56 Kbps).

Modems

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A communications link is the physical mediumused for transmission of data.

There are several kinds:• Wire pairs/twisted pairs• Coaxial cables• Fiber optics• Microwave transmission• Satellite transmission

Communication links

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Sometimes called twisted pair, this media useswire pairs twisted together to form a cable. Thecable is then insulated.

Wire pairs are popular since this form of cablingis already installed and available in most places(telephone cabling).

It is, however, susceptible to electrical interference,called noise.

Wire pairs

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A coaxial cable is a single conductor wire that isthickly shielded.

• It sends a very powerful signal.• It is used for cable television.• These cables can transmit data at a very fast

rate.

Bundles of these cables can be laid undergroundor under the sea.

Coaxial cables

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Fiber optic cables use light instead of electricityto transmit data.

• The cables are made of ultra thin glass wires.Light beams can be transmitted for miles withlittle attenuation (reduction in signal strength).

• This media can handle many different typesof information including voice and data at thesame time.

Fiber optic cables

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In microwave transmission the signals are wirelessand can travel through the atmosphere.

Signals can, however, be blocked by the curvatureof the earth. (Line of sight transmission)

To prevent this, relay stations are located in highareas and are used to retransmit data to other relaystations.

Microwave transmission

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The basic components of satellite transmission:• Earth stations: Send and receive signals.• Transponder: Receives a transmission from

an earth station, amplifies the signal, changes the frequency, and retransmits the data to the receiving earth station.

The entire process takes only a few seconds.

Communications satellites are positioned in ageosynchronous orbit.

Satellite transmission

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• Internet access providers or Internet serviceproviders offer individuals and companiesaccess to the Internet.

• There are typically several connection options.• The primary difference between various ISPs

is the connection bandwidth (the amount ofdata that can travel through a communicationline in a given unit of time) available.

Internet service providers

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• The traffic on the Internet and the ISP can affectthe net bandwidth (the actual speed at whichinformation travels taking traffic into account).

• Upstream, also called upload, occurs wheninformation is sent from you to the ISP.

• Downstream, called download or downlink, occurswhen information flows to your computer fromthe ISP. Example: Web page download.

• Upstream bandwidth differs from downstreambandwidth for satellite and cable connections.

Connection terminology

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• POTS uses existing telephone lines and an analogmodem to provide a bandwidth of about 56Kbps.

• Higher grades of service use the Digital SubscriberLoop (DSL) protocol.These include:

– Integrated Services Digital Network (ISDN), available since 1984.

– Asymmetric Digital Subscriber Line (ADSL)– Symmetric Digital Subscriber Line (SDSL)

Upstream: 16 to 640 KbpsDownstream: 1.5 to 9 Mbps (million bps)

Telephone service

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• Cable modems connect to the same coaxial cablethat serves television.

• It is connected via twisted pair wire to a PC andprovides a cost-effective and high bandwidthconnection to an ISP.

• Upstream: 768 Kbps• Downstream: 10 Mbps• Cable bandwidths vary with the number of users.

Cable connections

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• Large firms with high traffic connect to an ISPusing higher bandwidth telephone connections.– T1: Operates at 1.544 Mbps– T3: Operates at 44.7 MbpsThese connections are more expensive than theprevious options.

• Network access providers use T1 and T3 lines aswell as Asynchronous Transfer Mode (ATM)connections with bandwidths up to 622 Gbps.

Higher bandwidth options

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• When making decisions about Internet connectionsyou must consider:– Bandwidth needed– Cost of startup– Monthly fees– Traffic issues

• There is a chart comparing features between variousoptions on page 72 of the text.

• Depending on where you live, you may have otheroptions, such as satellite connections.See the e-commerce links and sites.

Price and speed comparisons

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Networks can be classified according to theirgeographical reach.

• Local area network• Metropolitan area network• Wide area network

Types of networks

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A wide area network (WAN) is a network ofcomputers, terminals, and peripheral devicesthat is located over a very large area.

• It can span a state, country, or the world.• The central hubs or servers are usually

powerful minicomputers or mainframes.(The server is usually referred to as thehost computer).

• A single WAN may use a variety of transmission methods.

Wide-area network

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A local area network is a collection of computersthat share hardware, software, and data over ashorter geographical area than a WAN.(Usually limited to a single building or compound).

A LAN can also be very small.Example: LAN in my apartment contains one PC,one printer, and two laptops.

Local-area network

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Networks can also be classified according totheir purpose:

1. Internet2. Intranet3. Extranet

Purposes for networks

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• Only selected individuals can use an intranet.Example: CTI Intranet

• Intranets are a popular and inexpensive way to distribute information.

• Intranets typically use existing infrastructure.• Benefits include timely and current information

delivery, cheaper internal communication, lowmaintenance costs, and easy on-line training.

Intranets

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• Extranets provide the private infrastructure for companies to coordinate their purchases, exchange business documents, and communicate with each other.

• Some start out as intranets and become available topeople outside the institution in an effort to reducethe workload for employees. Example: FedEx

• There are three types of extranets:– A public network– A secure (private) network– A virtual private network (VPN)

Extranets

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• A public network extranet is one which can be accessed by the public or one in which two ormore companies agree to link their intranetsusing a public network.

• Security is an issue in this configuration.• This type of extranet is uncommon because of

the risk.

Public network

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• Uses a private, leased-line connection to connecttwo companies.

• A leased line is a permanent, dedicated telephoneconnection between two points. The line isalways active.

• This arrangement is significantly more secure.• The big drawback is the cost.• This type of arrangement does not scale well since

each new company requires another leased line.

Private network

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• A VPN uses public networks but through a systemcalled tunneling or encapsulation.

• Tunnels are private passageways through the publicInternet that provide secure transmission from onepartner to another.

• Separate security shells are used with the most sensitive data under the tightest controls.

• VPNs establish short-term connections in real timethat are broken once the session ends.

• This arrangement is inexpensive and scales well.

Virtual private network

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A protocol is a set of rules for the exchange ofdata across communication lines.

Because telecommunications systems use a widevariety of hardware and software, protocols areneeded to coordinate communication.

What kinds of issues do protocols need to handle?

Protocols

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Protocols need to handle the following tasks:• Identify the different devices in the communications path.• Establish the speed and method for transmission of data.• Alert the receiving device to the incoming data.• Define the method for the receiving device to confirm the

receipt of the data.• Determine the methods of error checking and correction.

Common Internet protocols include TCP/IP, SMTP,POP, IMAP, FTP, and HTTP. We will discuss eachof these in more detail later.

Tasks for protocols