3.1.5 Data Transmission

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3.1.5 Data transmission

a. What are the characteristics of a LAN (local area network) and a WAN (wide areanetwork)?

http://www.differencebetween.net/technology/difference-between-lan-and-wan/http://www.computer-realm.net/lan-wan/http://www.helium.com/items/1066784-what-are-the-differences-between-lan-and-wanhttp://www.diffen.com/difference/LAN_vs_WANgood table with comparisons.Text book: p44

Characteristics of a LAN are as follows:LANs are small to medium-sized networks and generally connect networkdevices that are no more than a few miles of one another, which Instituteof Electrical and Electronics Engineers, Inc. (IEEE) defines as being 4 km orless in diameter.LANs include networks that have been set up in homes, offices, the floor ofa building, an entire building, a campus or group of nearby buildings, orfacilities that are relatively close to one another.

Typically, a LAN is owned by a single person or organization and is managedby a single person or group of people.

WHAT IS A WAN?A wide area network (WAN) is a computer network covering a wide geographicalarea, including more than one remote location. The geographically dispersedlocations are interconnected, thus forming a WAN.

Characteristics of a WAN are as follows:WANs can span great geographical distances and connect different LANstogether using high-speed solutions or telephone lines.A WAN may connect LANs in different cities, regions, states/provinces, oreven countries.With WANs, ownership isnt a defining factor. WANs are often owned and managed by more than one organization.Each LAN that is part of the WAN may be managed by individuals orIT departments, and either the former or the latter maintains its connectionto the rest of the LAN or hires outside parties to perform thatfunction.

SWITCHING METHODSWANs are based on one of two types of switching methods: circuit switchingandpacket switching.

Circuit switching Circuit-switched networks are networks that are dialedon demand. The connection must be initiated before transmission can takeplace. Example: Integrated Services Digital Network (ISDN).Packet switching Packet-switched networks are always on. When youset the carriers link up, it stays up. Examples: Frame Relay, asynchronoustransfer mode (ATM), switched multimegabit data services (SMDSes),and X.25. Additional characteristics of packet-switched networks are asfollows:They divide the transmitting data into packets in which each is sentindividually from the source to the destination.All packets are given sequence numbers so that they can all be put backtogether again in the right order at the destination.Each packet can take a different route to get to its destination.

An effective way of understanding how a local area networkis related to a WAN is to look at how they are
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connected and how data is sent. This may differ fromorganization to organization, as there are several differentways of getting data from a LAN to a WAN, includingthe following:Modem is a device that allows you to connect toother computers and devices using telephone lines.Generally, when a modem is mentioned, it refers to

a dial-up modem (as opposed to the digital modemsused for other methods mentioned below). Thistype of connection is slow and allows connectionsat a maximum of 56 Kbps (meaning that 56,000bits of data can be sent or received per second)Integrated Services Digital Network (ISDN) sendsdata over telephone lines but at higher speeds upto 128 Kbps but averaging at 64 Kbps using anISDN modem or router.Digital subscriber line (DSL) sends data acrosstelephone lines at speeds ranging from 1.5 millionbits per second (Mbps) using a router or digitalmodem and configured phone lines.Cable transmits the data across cable lines usingthe same lines used for cable television at speedsof up to 1.5 Mbps.Satellite transmits data to a satellite at speeds ofup to 400 Kbps.T1 and T3 are dedicated connections that provideextremely high speeds. A T1 line provides speedsof 1.544 Mbps, while a T3 line provides speedsranging from 3 Mbps to 44.736 Mbps

b. What hardware and software do you need for a LAN and for accessing a WAN, egthe internet?

c. What are the different types of data transmission?

SIMPLEX, HALF-DUPLEX, AND FULL DUPLEXWhen data travels across the medium, it travels in a certain direction. To describethe movement of data across communication channels, certain terms are used,including the following:

d. Describe the characteristics of each data transmissions (serial and parallel; and

simplex, half-duplex and duplex modes)

Communications between devices occur two ways:

Manner in which signals are transferred:Serial single wire, one small bit of a byte at a time.Parallel multiple wires, one whole bit e.g computers internal bus where multiple wires areconnected. Most computers have at least one parallel port.


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Simplex It refers to data moving in a single direction.Half-duplex It means data travels in both ways, but in only one directionat a time.Full duplex It means data travels simultaneously in both directions.

e. Explain the relationship between bit rates and the time sensitivity of the information;

f. What are the errors that can occur in data transmission?

g. How can you detect and correct these errors? (parity checks, the use of parity in datablocks to become self-correcting, check sums and echoes);

h. What is packet switching and circuit switching?

i. Explain the difference in use of packet switching and circuit switching;

j. What is a protocol?

k. Why is protocol important to the transmission of data?

l. Describe the need for communication between devices and between computers, andexplain the need for protocols to establish communication links;


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m. Why are there a need for both physical and logical protocols and the need forlayering in an interface?

Bandwidth is a measurement of the amount of data that can be passed over a cablein a given amount of time. The bandwidth capacity of a network cable is usually

measured in the number of bits or bytes that can be transferred in a second.

Security IssuesThe security of cabling should be considered before installing a particular kindof cabling. You will need to be aware of security issues that are inherent to certaintypes of cabling, such as

Wiretapping This involves gaining physical access to a network cable andcutting or piercing the cable so that the wires inside the cable can be accessedand then spliced or tapped.Eavesdropping This involves listening to data being sent over the wirewithout actually piercing the cable.Fiber-optic cabling is not susceptible to either of these vulnerabilities.

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3.1.5 Data Transmission