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