lesson 9—networking basics1 networking basics wide area networks unit 3 lesson 9

1Lesson 9—Networking BASICS

Networking BASICSWide Area

Networks

Unit 3

Lesson 9

Lesson 9—Networking BASICS 2

Objectives• Define a WAN and tell how it is

used.• List and describe different WAN

technologies.• Explain how to protect a WAN from

unauthorized users.• Define privacy.


Wide Area Network • It connects computers and

LANs over a larger geographical area.

• It crosses public thorough-fares such as roads, railroads, and water.


WAN vs. LAN • Geography• Ownership• Management• Speed • Cost


Wired Analog Service• It uses standard wired analog

telephone lines.• It requires a modem to convert

digital signals to analog signals.• Its top is speed 56 Kbps.• Asymmetric – Some modems are

faster downloading than uploading.


Wired Analog Service


Digital Cellular • It provides WAN data access to mobile

users.• Its coverage area is divided into smaller

cells.• Users “roam” into adjacent cells or

“handoff” into remote networks.• The current technology is 2.5G with a

maximum speed of 384 Kbps.


Trunk-Based Leased Lines

• The same type of lines are used to connect the telephone company’s switches.

• They provide “always-on” high-speed connections.

• The most common is T1, which oper-ates at 1.5 Mbps over twisted pair wires.


Trunk-Based Leased Lines


Digital Subscriber Lines (DSL)

• They transmit at 1.5 Mbps over regular telephone lines.

• They use the higher unused frequencies to send data.

• Different versions of DSL: ADSL, G.list, HDSL, HDSL2


Digital Subscriber Lines (DSL)


Cable Modem• It uses the same coaxial cable that

brings in cable TV signals.

• All cables for a neighborhood are connected to a neighborhood splitter.

• The connection is shared among all users in a neighborhood.

• Speed: 300 Kbps – 1.5 Mbps


Local Multipoint Distribution Service (LMDS)

• Transmits: Maximum 155 Mbps downstream and 1.54 upstream

• Range: 2 – 5 miles• It is a low-cost option to laying fiber

optic cables.• Its signals are susceptible to

interference from rain or fog.


Multichannel Multipoint Distribution Service (MMDS)

• It uses lower-frequency signals than LMDS.

• Range: up to 35 miles

• Its signals are less susceptible to interference from rain or fog.


Satellites • They have been used for

over 40 years.• They relay signals from one

point on earth to another.• They are classified according

to the type of orbit.


Low Earth Orbiting (LEO)

• They orbit at an altitude of 200 – 900 miles.

• They circle the earth in 90 minutes.

• They have a small “footprint.”

• More satellites are needed to cover the entire earth.


Low Earth Orbiting (LEO)


Medium Earth Orbiting (MEO)

• They orbit at altitudes between 1,500 – 10,000 miles.

• They circle the earth every 12 hours.

• They have a large “footprint.”• Fewer are needed to cover the

earth.


Remote Wireless Bridge

• It connects LANs located in different buildings.

• The distance between buildings can be up to 18 miles at 11 Mbps.

• It has similar characteristics to a wireless LAN.


Free Space Optics (FSO)

• It transmits up to 1.25 Gbps at a distance of 2.5 miles.

• It uses low-powered infrared beams.

• Its transmissions cannot be eavesdropped.


Virtual Private Network (VPN)

• It uses the public Internet to transmit private data.

• It encrypts data into a packet before sending.

• There is no cost for setting up or using a VPN.


Virtual Private Network (VPN)


Public Switched Data Networks (PSDN)

• Actual network itself

• X.25

• Frame Relay

• Asynchronous Transfer Mode (ATM)


Public Switched Data Networks (PSDN)

• Integrated Services Digital Network (ISDN)

• Synchronous Optical Network (SONET)

• Metro Ethernet Network (MEN)


Firewall• It inspects incoming traffic. • Packet-filter firewall – Inspects

header of each packet.• Stateful packet-filter firewall –

Examines a packet’s source IP.• Proxy firewall – Examines the

contents of a packet.


Network Address Translators (NAT)

• Disguises the internal IP by substituting a fake IP and port number.

• When a packet is returned, NAT replaces the fake numbers with the actual IP and port number.


Privacy• Privacy is the right to be left

alone to the degree that you choose.

• It is a difficult problem to keep personal data private.

• Identity theft is a major crime.


Summary• The definition of a wide area network (WAN) is a network that

connects computers and LANs over a large geographical area. Most industry experts consider a network to be a WAN if it crosses a public thoroughfare such as a road, highway, railroad, or body of water. There are several differences between WANs and LANs. WANs are a key component of the telecommunica-tions industry. This industry is made up of government agencies that regulate telecommunications and carriers, which provide the services consumers can purchase. WANs play a vital role in the world of business today. Businesses such as the airline and banking industries, investment services, and credit card services rely heavily on these networks to perform basic everyday operations.


Summary (continued)• There are four general categories of WAN technologies and

within each category are several different types of WANs. One of the original methods for connecting a computer to a WAN was using a standard wired analog telephone. In order for a computer to use a telephone dial-up line, a modem is needed. The top speed that data can be sent over a dial-up connection is about 56 Kbps. Digital cellular service transmits data in a digital format using cellular telephony. Digital cellular telephony today is called 2.5G and operates at a maximum speed of 384 Kbps. The future of digital cellular telephony is called Third Generation (3G). 3G is intended to be a uniform and global worldwide standard for cellular wireless communications.


Summary (continued)

• Leased data connections are permanent and dedicated lines between two sites. These connections can be leased from pub-lic telephone carriers or from private companies. Trunk-based leased lines provide “always-on” high-speed connections. A Digital Subscriber Line (DSL) transmits at 1.5 Mbps over regular telephone lines and has a low cost. Another carrier that can provide access to WANs is the local cable television operator. Multipoint distribution services refer to a technology that uses wireless high-frequency microwave radio signals to connect to a WAN.


Summary (continued)• Local Multipoint Distribution Service (LMDS) can transmit from

51–155 Mbps downstream and 1.54 Mbps upstream. Because it uses low-powered radio frequency waves, these have a limited range. The coverage area for LMDS is between 2–5 miles. Multichannel Multipoint Distribution Service (MMDS) uses low-frequency signals that can travel farther, are less susceptible to interference from rain and fog, and are better able to penetrate buildings than high-frequency LMDS signals. MMDS can send data signals at 1.5 Mbps downstream and 300 Kbps upstream at distances of up to 35 miles. Satellites have been used for worldwide communications for over 40 years. Satellites relay signals from one point on the earth to another point.


Summary (continued)• Satellite systems are classified according to the type of orbit

they use. Low earth orbiting (LEO) satellites orbit the earth at an altitude of just 200–900 miles. Because they are in such a low orbit, their area of earth coverage (called the footprint) is small. Medium earth orbiting (MEO) satellites orbit the earth at alti-tudes between 1,500–10,000 miles and have a bigger earth footprint; thus, fewer satellites are needed for total coverage.

• Leased data connections require that a certain amount be paid monthly or annually for the data connection. An alternative is to use private data connections. With a private data connection, a business purchases and owns the equipment, thus eliminating any leases for data connections.


Summary (continued)• A remote wireless bridge is designed to connect two or more

LANs that are located in different buildings. The distance be-tween buildings can be up to 18 miles when transmitting at 11 Mbps or up to 25 miles when transmitting at 2 Mbps. Free space optics (FSO) is an optical wireless point-to-point technology used to connect remote sites to create a WAN. FSO can trans-mit at speeds of up to 1.25 Gbps at a distance of 2.5 miles. A virtual private network (VPN) uses the public Internet to transmit sensitive data, but does it in such a way that unauthorized indi-viduals cannot read the data, thus acting like a private network. VPN works by encrypting the data and then storing it in a packet (called encapsulating) before it is sent out through the Internet. The receiving computer then decrypts and extracts the data.


Summary (continued)• A different solution than leasing or creating a free data

connection is to use a public switched data network (PSDN). A PSDN is an actual network itself, whereas leased or public data connections are only the connections between networks. With a PSDN, each site needs only a single leased line circuit to con-nect it to the PSDN. X.25 was the first public switched data net-work (1960s) and, by today’s standards, is considered to be very slow (9.6–64 Kbps). The most popular PSDN is Frame Relay. Unlike X.25, Frame Relay does not use an error-check-ing system; instead, the sending and receiving devices are responsible for checking for errors. This lack of an error-check-ing system helps Frame Relay run faster, with speeds starting at 56 Kbps and running to a top speed of 40 Mbps.


Summary (continued)• Asynchronous Transfer Mode (ATM) can support data, voice,

and video all on one network. ATM uses small, fixed-length packets of only 53 bytes, allowing the packets to be moved very quickly. ATM currently runs at speeds of 155 Mbps or 622 Mbps. Integrated Services Digital Network (ISDN) is a digital telephone line that can be used for either data or voice transmission. Syn-chronous Optical Network (SONET) uses fiber optic lines to transmit data, voice, or video at high speeds. SONET services are available at a variety of speeds. Metro Ethernet Network (MEN) transmits Ethernet LAN data across an Ethernet-based WAN. MEN eliminates the need to convert LAN data to another format before transmitting it over a PSDN WAN.


Summary (continued)• Any computer connected to a WAN or to the Internet faces a

serious security risk. Unauthorized users, sometimes called hackers, can use sophisticated tools and a knowledge of net-works to break into computer networks. A number of steps can be taken to reduce security risks. A firewall inspects incoming traffic and accepts or denies entrance to that traffic based on a set of predefined rules. A network address translator (NAT) disguises internal IP addresses by substituting fake IP numbers. On each packet going out to the WAN, the NAT removes the real source IP number and port number and replaces them with a fake IP address and fake port number.


Summary (continued)• Privacy has been defined as “the right to be left alone to the

degree that you choose.” Prior to WANs and the Internet, it was easy to limit the amount of information that another person could learn about you. However, today it is more difficult to keep information private. Industry experts recommend that consumers regularly review credit reports, use appropriate passwords on financial computer accounts, shred bills after they are paid, and use a firewall to protect personal computers.

lesson 9—networking basics1 networking basics wide area networks unit 3 lesson 9

Documents

networking basicstrunk

networking basicswan

networking basicssatellites

networking basicscable

analog signals

entire earth

milesits signals

digital signals