Danial Masood

Chapter

11

Wide Area Network

Wide Area Network

• It connects computers and LANs over a larger geographical area.

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

4

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.

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Wired Analog Service

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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.

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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 operates at 1.5 Mbps over

• twisted pair wires.

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Trunk-Based Leased Lines

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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

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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

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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.

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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.

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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.

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Low Earth Orbiting (LEO)

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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.

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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.

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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.

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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.

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Virtual Private Network (VPN)

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Public Switched Data Networks (PSDN)

• Actual network itself• X.25• Frame Relay• Asynchronous Transfer Mode

(ATM)

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Public Switched Data Networks (PSDN)

• Integrated Services Digital Network (ISDN)

• Synchronous Optical Network (SONET)

• Metro Ethernet Network (MEN)

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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.

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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.

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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.