Chapter 4

نمط حلزونى منتظم

غير محمية – معزولة رقائق المعدن او ضفيرة مغلف ظاهرة تداخل الاشارات محمية – غير معزولة

حساس المشاكل البسيطة AgsqgCdV5QSPftVaCIkzb0Jzt0KhN0HXA0gSTdVA0sdBnCoLTM9DesBVl6WLE0cQialAgw

الكابل المحورى معدن على شكل قضيب

مناعة اقل عرضة محمى

ضخم – كبير الحجم

كابل الألياف البصرية كسوة الحقن بالليزر الحقن بانبعاث الضوء

ضعف

احادى الاتجاه AgsqgCdV5QSPftVaCIkzb0Jzt0KhN0HXA0gSTdVA0sdBnCoLTM9DesBVl6WLE0cQialAgw

Unguided Media It does not contain the signal in some physical conductor or metal. Rather, it transports electromagnetic signal through air. It is also known as wireless media. It includes: -  Infrared waves  Radio waves  Micro waves  Laser Transmission  Satellite Transmission

The Computer Continuum7-24 Infrared Waves الاشعة تحت الحمراء – Commonly used in TV and remote controls. – Use infrared frequencies of electromagnetic radiation that behave much like visible light. – Often used to connect keyboards, mousses, and printers. Wireless connections

Infrared Waves Electromagnetic waves having frequencies from 300 GHz to 400 THz are called IR waves or Infrared waves. IR waves are used for short range communication and use line of sight propagation. Infrared waves cannot pass through solid objects, like walls and be easily contained in a room. They are cheap, easy to build and do not require any government license to use. Wireless connections

The Computer Continuum7-26 Radio Waves – Uses radio frequencies. Function even though line of sight is interrupted. تعمل على الرغم من توقف خط الافق – The Radio waves have frequencies between 3khz and1Ghz Wireless connections

Radio waves Transmission Radio waves are omnidirection. Radio waves can penetrate buildings easily, so that are widely use for communication both indoors outdoors. At high frequency, radio wave tends to travel in straight line. Omni direction

The Computer Continuum7-29 Micro wave – Often used to communicate with distant locations. المواقع البعيدة – Must be line of sight. – Satellite communications use microwaves. Wireless connections

Microwaves Transmission Micro waves electromagnetic waves having frequency between 1 GHZ and 300 GHZ. There are two types of micro waves data communication system : terrestrial and satellite أرضى وفضائى Micro waves are widely used for one to one communication between sender and receiver, cellular phone, satellite networks and in wireless LANs. Vnu8&list=PL2D6507E06F9A7FB2

Laser Transmission This type of transmission use thin laser to transfer data up to few kilometers. Laser beams are unidirectional, therefore this type of transmission system use line of sight propagation. Such a system offer very high bandwidth at a very low cost. on hot sunny days these waves are affected by hot turbulent air and miss the detector. The major problem in this transmission system is that laser beams cannot penetrate rain or thick fog. المطر او الضباب الكثيف

Transmission Modes Simplex البسيط – One direction e.g. Television Half duplex أحادى الاتجاه – Either direction, but only one way at a time e.g. police radio Full duplex – Both directions at the same time e.g. telephone

The Computer Continuum7-37 Type of signals – Analog: Those signals that vary with smooth continuous changes. A continuously changing signal similar to that found on the speaker wires of a high-fidelity stereo system. – Digital: Those signals that vary in steps or jumps from value to value. They are usually in the form of pulses of electrical energy (represent 0s or 1s).