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Computer to Computer: Transmission Media

With such complex communications channels, we need to be aware of the capabilities and limitations of the various media in use.

Transmission media just means the physical materials that are used to transmit data between computers.

For communications between computers that are linked by cable, there are three choices.

Twisted wire

(phone line)

Advantage:	Easy to string Cheap
Disadvantage:	Subject to interference = static and garble

Coaxial cable

(round insulated wire)

Advantage:	Not susceptible to interference Transmits faster
Disadvantage:	Heavy & bulky Needs booster over distance

Fiber optic line

(glass fibers)

Advantage:	Smaller, Lighter, Faster, No interference
isadvantage:	Expensive Harder to install and modify

For longer distances or when cables are not practical, other transmission media come into play. We're getting really high tech here!

It may seem odd to call microwaves, radio waves, or light a "physical" medium. All are electromagnetic in nature. Sometimes they are treated by scientists like streams of teeny, tiny particles and other times like waves on the beach. In their "particle" life, they do behave like a bunch of physical particles. So it's not quite as odd as it first appears. (But all those electromagnetic things are plenty odd!)

Wireless

(infrared, light, radio) Wi-Fi uses radio waves.

Advantage:	Flexible Portable
Disadvantage:	Slower data transfer than hard-wired methods Subject to interference Infrared only for short distances - in the same room. Infrared and visible light easily blocked by objects Wi-Fi normally requires a passcode. Finding a public Wi-Fi hot spot can be difficult.

Wi-Fi signal logo

Microwave

Uses cell towers. 3G and 4G wireless connections are now common for smartphones but also laptops and tablets.

Advantage:	Works where your cell phone works and maybe on the same data plan
Disadvantage:	Can be blocked by buildings, metal, etc. Must be in an area with signal.

Satellite

Advantage:	Satellite is always in same spot in the sky. Excellent signal strength
Disadvantage:	Expensive uplink and downlink facilities Not easily portable yet Must be able to 'see' the satellite (line-of-sight)

Дата добавления: 2014-12-23