Computer Network

Computer Tutorial

Introduction to Networking Elementary Terminology of Networks History (Development) of Computer Networks Advantages of Computer Networks Disadvantages of Computer Networks Applications & Uses of Networks ARPANET Internet

Data Communication Data Communication Component Data Transmission Modes Types of Connections Analog Transmission Digital Transmission

» Transmission Media » Twisted Pair Cable » Coaxial Cable » Optical Fiber » Wireless Communication » Radio waves » Microwave » Infrared

Types of Computer Networks Personal Area Network Local area networks Metropolitan Area Network Wide Area Network Type of Network on the term purpose

Computer Network topologies Bus Topology Ring Topology Star Topology Mesh Topology Tree Topology Hybrid Topology

Networking Devices Hubs Switches Bridges Routers Gateways Wireless Access Point Modems Media Converters Firewalls

Wireless or Mobile Computing Evolution of mobile communication systems Second Generation Networks Third Generation Networks Fourth & Fifth Generation Networks Wireless Transmission Protocols Multiple Access Techniques Frequency Division Multiple Access Time Division Multiple Access Code Division Multiple Access Space Division Multiple Access

Computer Network Model Layered Tasks The OSI Model Physical Layer Data Link Layer Network Layer Transport Layer Session Layer Presentation Layer Application Layer TCP/IP Reference Model

Medium Access Methods ALOHA Slotted ALOHA CSMA CSMA / CD Collision-Free Protocols

Error Detection and Correction Types of errors Error Detecting Codes Simple Parity check Two-dimension Parity Check Checksum Cyclic redundancy check Error Correcting Codes

Network Security Network Security Threats Network Security Threats Prevention Why Three Encryption Techniques? Firewall

Computer Networ MCQ

Unguided Media (Wireless Communication)

Unguided media, also called as wireless communication, transport electromagnetic waves without using a physical conductor. The signals propagate through air (or sometimes water). The communication band for unguided media. We shall concentrate on the radio communications.
Wireless signals travel or propagated in three ways:
1. Ground-wave propagation
2. Sky-wave propagation
3. Line-of-sight propagation

Ground-wave propagation

Ground Wave Propagation follows the curvature of the Earth. Ground Waves have carrier frequencies up to 2MHz. AM radio is an example of Ground Wave Propagation.

Sky-wave propagation

Ionospheric Propagation bounces off of the Earths Ionospheric Layer in the upper atmosphere. It is sometimes called Double Hop Propagation. It operates in the frequency range of 30 - 85MHz. Because it depends on the Earth's ionosphere, it changes with weather and time of day. The signal bounces off of the ionosphere and back to earth. Ham radios operate in this range. Characteristics of Sky Propagation are as follows: Signal reflected from ionized layer of atmosphere back down to earth; Signal can travel a number of hops, back and forth between ionosphere and earth’s surface; Reflection effect caused by refraction.

Line-of-sight propagation

Line of Sight Propagation transmits exactly in the line of sight. The receive station must be in the view of the transmit station. It is sometimes called Space Waves or Tropospheric Propagation. It is limited by the curvature of the Earth for ground based stations (100 km: horizon to horizon). Reflected waves can cause problems. Examples of Line of Sight Propagation are: FM Radio, Microwave and Satellite. Transmitting and receiving antennas must be within line of sight.

Computer Network

Unguided Media (Wireless Communication)