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Chapter 4 Highlights – Computer Networks
Why network or connect computers?
 Share Data/Files
 Share Hardware
e.g. Printers, Scanners
 Access Company
Information Systems
 Share Internet Connection
 Communicate
e.g. Telephone (VOIP), Chat, E-mail, Video Conference)
 In the home, you can share entertainment devices
LAN = Local Area Network
In the 1980’s companies began
networking their computers.
Various topologies and LAN
protocols were used.
The star topology using Ethernet
has become the standard today.
Star Topology
Typical of
10BaseT Ethernet
100BaseT Ethernet
Gigabit Ethernet
Categories of Networks

Local area network (LAN): covers a relatively small geographical area, such as a home,
office building, or school.
Most popular LAN protocol is Ethernet running in a star configuration.

Wide area network (WAN): covers a large geographical area. A WAN is often used to
connect two or more LANS.
Popular WAN protocols are T1 and T3 lines, ATM, and frame relay

Metropolitan area network (MAN): Some cities offer public networks for police, fire, or
WiFi for all residents.

Personal area network (PAN): A term that is sometimes used for an individual's network
of personal devices such their PC, phone, headset, and printer.

Intranet: A private network for a company that is set up like the Internet. This term often
refers to web sites that are only accessible internally at a company.

VPN: A private secure network that uses the Internet for data communication. Branch
offices for a large company may set up an VPN over the Internet to communicate to the
parent office. This is cheaper than purchasing expensive private data lines. Security and
encryption is essential since the Internet is a public network.
Data Transmission

Analog versus Digital – In analog transmission, information is in
the form of waves. In digital transmission, information is sent as
binary 1’s and 0’s. Television broadcasts are currently converting
from analog to digital (HDTV). Vinyl records stored music as analog
sound waves. CD’s store music digitally.

Bandwidth – Is the speed of data communication.
It is usually measured in bits/second.
Q: If your Internet connection is 2 Mbps, how long
would it take to download a 2 MB file?
A:
We need to convert bytes to bits:
2 Million Bytes = 16 Million Bits.
At 2 Million bits/second, it would take 8 seconds to xfer 16 Million bits.
Q: If your Internet connection is 256 Kbps, how long would it take to download a 1 MB file?
Circuit-Switched vs. Packet-Switched
The telephone network is a circuit-switched network – you have a dedicated
path between you and the person you are talking to. The Internet is packetswitched. Everything sent over the Internet is broken up into small packets of
data and sent on their way.
Protocols
A protocol is the set of rules that defines
how devices communicate in a network.
For Internet communication, TCP/IP is used. This
protocol is how you open web sites, send e-mail, etc.
Other protocols define how data travels around a LAN
(e.g. Ethernet), WAN, or a wireless network (e.g. WiFi).
Ethernet - LANs
Ethernet is most popular LAN protocol. It is used to connect
computers at businesses as well as at your home. In the
1980’s, Ethernet LANs used coax cable in a bus configuration,
but now they use twisted pair wire in a star configuration.
Each network adapter has a hard-coded
MAC address. To see this address on the
Ethernet adapter on a PC, open a
command prompt and type ipconfig /all
Windows lists this as the “physical address”.
Cell Phone Transmission
1G – The original cell
phones (1980’s) were
analog transmission
2G – Cell phones
switched to digital
transmission (1990’s).
This added data
support such as txt
messages.
3G – We are now
switching to 3G cell
phone service which
offers high-speed
Internet.
WiFi – (802.11)
WiFi can be used to create an entirely wireless
network, or to add wireless capabilities to an
existing wired Ethernet network.
WiFi Hotspots refer to public places that users
can connect their laptops. For example
Starbucks, or at Eastfield.
Limitations: A WiFi network is designed for
no more than 300 feet in distance and no
roaming (like cell phones).
WiFi Standards:
802.11b = original WiFi standard at 11 Mbps
802.11g = current WiFi standard at 54 Mbps
802.11n = newest WiFi standard at 300 Mbps
Wireless
Access
Point
Wireless - BlueTooth
Bluetooth was designed for wirelessly
connecting personal consumer devices and
peripherals. Bluetooth works over short
distances, typically less than 30 feet.
Communication speed is less than 1 Mbps.
Pairs of devices establish a trusted
relationship by the user entering a shared
passkey or PIN. Trusted devices may
encrypt the data that they exchange over
the air so that no one can listen in.
Growing in popularity is using bluetooth equipped phones
to make payments.
Summary of Wireless Protocols
Typical Company Network Diagram
To Branch Office
Internet
router
firewall
router
Database Server
Corporate
Info System
DMZ
hub
switch
E-mail server
Wireless
Access Point
Web server