15 June 2008

IT_Chapter_9B

Modem Communications

Plain Old Telephone System (POTS)

Standard phone line

Two-way voice communication

Uses analog transmission techniques

Data communication is slow

Modems

Modulator/Demodulator

Modulator converts digital to analog

Speed measured in bits per second (bps)

Current fastest speed is 56 Kbps

Quality of phone lines dictates speed

V.92 is the current modem standard

Several modem types

Internal

External

Voice

Fax

Modem uses

Connection to the Internet

File transfer

Uploading

Downloading

Digital Data Connections

Digital phone lines

Local telephone companies are upgrading

Service will faster and more reliable

New phones will be needed

Modems will need to be upgraded

Broadband connection

Any data connection faster than 56 Kbps

Common in business

Becoming popular in home installations

ISDN lines

Integrated Services Digital Network

Basic rate uses three channels

Two data channels each support 64 Kbps

Error correction channel

Primary rate uses 24 data channels

T lines

High-capacity voice/data lines

Used to control phone and data

Several variants

T1 transmits at 1.544 Mbps

T3 transmits at 44.736 Mbps

DSL technologies

Digital Subscriber Line

Popular with home users

Speeds range from 100 Kbps to 30 Mbps

Asymmetrical DSL (ADSL)

Upload speed slower than download speed

Symmetrical DSL (SDSL)

Requires a DSL modem

Cable modem connections

Popular with home and office users

Speeds between 1 and 3 Mbps

Requires a cable modem

ATM

Asynchronous Transfer Mode

Efficient transfer of video and sound

Requires a special NIC and hardware

Wireless Networks

Benefits

No cable to pull

Mobile devices access network resources

Mobility and flexibility for office workers

Wireless 802.11

Also called Wi-Fi

IEEE standard

Institute of Electronic and Electrical Engineers

Several versions

802.11b connects up to 11Mbps

802.11g connects up to 56Mbps

Use the same type of devices

Wireless Access Point

Center of a wireless network

WAPS combined cover a larger area

Distance to WAP determines bandwidth

Range is 50 to 150 meters

Extension points can extend range

Wireless Adapters

Used by devices to connect

Includes signal strength software

1 comment:

  1. In a world in which computer networks are involved in nearly every facet of business and personal life, it is paramount that each of us understand the basic features, operations and limitations of different types of computer networks.

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