Networking BASICS
Wide Area
Networks
Unit 3
Lesson 9
Lesson 9—Networking BASICS
1
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.
Lesson 9—Networking BASICS
2
Wide Area Network
• It connects computers and
LANs over a larger
geographical area.
• It crosses public thoroughfares such as roads,
railroads, and water.
Lesson 9—Networking BASICS
3
WAN vs. LAN
• Geography
• Ownership
• Management
• Speed
• Cost
Lesson 9—Networking BASICS
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.
Lesson 9—Networking BASICS
5
Wired Analog Service
Lesson 9—Networking BASICS
6
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.
Lesson 9—Networking BASICS
7
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.
Lesson 9—Networking BASICS
8
Trunk-Based Leased Lines
Lesson 9—Networking BASICS
9
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
Lesson 9—Networking BASICS
10
Digital Subscriber Lines (DSL)
Lesson 9—Networking BASICS
11
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
Lesson 9—Networking BASICS
12
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.
Lesson 9—Networking BASICS
13
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.
Lesson 9—Networking BASICS
14
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.
Lesson 9—Networking BASICS
15
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.
Lesson 9—Networking BASICS
16
Low Earth Orbiting (LEO)
Lesson 9—Networking BASICS
17
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.
Lesson 9—Networking BASICS
18
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.
Lesson 9—Networking BASICS
19
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.
Lesson 9—Networking BASICS
20
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.
Lesson 9—Networking BASICS
21
Virtual Private Network (VPN)
Lesson 9—Networking BASICS
22
Public Switched Data Networks
(PSDN)
• Actual network itself
• X.25
• Frame Relay
• Asynchronous Transfer
Mode (ATM)
Lesson 9—Networking BASICS
23
Public Switched Data Networks
(PSDN)
• Integrated Services Digital
Network (ISDN)
• Synchronous Optical
Network (SONET)
• Metro Ethernet Network
(MEN)
Lesson 9—Networking BASICS
24
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.
Lesson 9—Networking BASICS
25
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.
Lesson 9—Networking BASICS
26
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.
Lesson 9—Networking BASICS
27
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 telecommunications 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.
Lesson 9—Networking BASICS
28
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.
Lesson 9—Networking BASICS
29
Summary (continued)
• Leased data connections are permanent and dedicated lines
between two sites. These connections can be leased from public 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.
Lesson 9—Networking BASICS
30
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 lowfrequency 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.
Lesson 9—Networking BASICS
31
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 altitudes 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.
Lesson 9—Networking BASICS
32
Summary (continued)
• A remote wireless bridge is designed to connect two or more
LANs that are located in different buildings. The distance between 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 transmit 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 individuals 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.
Lesson 9—Networking BASICS
33
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 connect it to the PSDN. X.25 was the first public switched data network (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-checking system helps Frame Relay run faster, with speeds starting at
56 Kbps and running to a top speed of 40 Mbps.
Lesson 9—Networking BASICS
34
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. Synchronous 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.
Lesson 9—Networking BASICS
35
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 networks 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.
Lesson 9—Networking BASICS
36
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 BASICS
37