Physical Transmission 1 Computer Network Components Components of a computer network: Computer with NIC (PCs, laptops, handhelds) routers & switches (IP router, Ethernet switch) Links Transmission media (wired, wireless) protocols (IP,TCP,CSMA/CD,CSMA/CA) applications (network services) i.e. Network Operating System (NOS) humans and service agents
Transmission 4 Transmission Media Anything that can carry information from a source to a destination. 5 Transmission Media LANs can be connected together using a variety of transmission media types.
Each type has its own advantages and disadvantages which will be examined in this section 6 Transmission Media Computers and telecommunication devices use signals to represent data.
These signals are transmitted from a device to another in the form of electromagnetic energy. Electromagnetic energy is a form of energy that is reflected from objects in the form of electrical and magnetic waves that can travel through space Examples of Electromagnetic energy: power, radio waves, infrared light, visible light, ultraviolet light, and X and gamma rays. 7 Transmission Media
Each of the previous examples constitutes a portion of the electromagnetic spectrum. Not all portion of the spectrum are currently usable for telecommunications. Each portion of the spectrum requires a particular transmission medium. 8 Transmission Media
There are two categories of Transmission media: 1. Wired (Guided) media A signal traveling along guided media is directed and contained by the physical limits of the medium 2. Wireless (Unguided) media Unguided media transport signals without using a physical conductor. 9 Overview For Guided Medium
The medium is more important For Unguided The bandwidth produced by the antenna is more important 10 Design Factors for Transmission Media Bandwidth: Communication capacity of a transmission media All other factors remaining constant, the greater the bandwidth of a signal, the higher the data rate that can be achieved.
Transmission impairments: Limit the distance a signal can travel. Interference: Competing signals in overlapping frequency bands can distort or wipe out a signal. Number of receivers: Each attachment introduces some attenuation and distortion, limiting distance and/or data rate. 11
1. Wired (Guided) media 12 I. Wired (Guided) media: There are three categories of guided media: 1. Twisted Pair : 1. Unshielded twisted pair (UTP) 2. Shielded twisted pair (STP) 2. 3. Coaxial Cable
Fiber Optic Cable 13 Twisted Pair Wires Consists of two insulated copper wires, each with its own plastic insulation, twisted together arranged in a regular spiral pattern to minimize the electromagnetic interference between adjacent pairs Often used at over distances to carry voice as well as data communications
Low frequency transmission medium 14 Types of Twisted Pair STP (shielded twisted pair) the pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic interference
UTP (unshielded twisted pair) each wire is insulated with plastic wrap, but the pair is encased in an outer covering 15 16 Advantages of UTP & STP The characteristics of UTP are: Cheap Ease of use flexible easy to install.
The characteristics of STP: less susceptible to noise materials and manufacturing requirements make STP more expensive than UTP 17 Twisted Pair Advantages & Disadvantages Advantages
Inexpensive and available Flexible and light weight Easy to work with and install Disadvantages Sensitivity to interference and noise Relatively low bandwidth (3000Hz)
18 Coaxial Cable (or Coax) Carries signals of higher frequency ranges than twisted pair cable. Has an inner conductor enclosed in an insulator, which is in turn encased in an outer conductor of metal braided mesh.
Both conductors share a common center axial, hence the term co-axial Used for cable television, LANs, telephony 19 20 Coaxial Cable (or Coax) Coaxial types: Thicker used with large networks. Thinner used with small networks.
21 Coax Advantages & Disadvantages Disadvantages Advantages Higher bandwidth High attenuation rate makes it expensive over long distance
Its not used anymore due to high cost and other technical factors. 400 to 600Mhz Much less susceptible to interference than twisted pair It will not cause a toxic gas when its burned. Thats why they use it in some buildings. 22
Fiber Optic Cable Relatively new transmission medium used by telephone companies in place of longdistance trunk lines Fiber Optic works on the properties of light. When light ray hits at critical angle it tends to refracts at 90 degree. This property has been used in fiber optic. The core of fiber optic cable is made of high quality glass or plastic. From one end of it light is emitted, it travels through it and at the other end light detector detects light stream and converts it to electric data form. Fiber Optic provides the highest mode of speed.
Also used by private companies in implementing local data communications networks Require a light source with injection laser diode (ILD) or light-emitting diodes (LED) 23 Fiber Optic Cable
Optical fiber is made of glass or plastic and transmits signals in the form of light. The cable consists of a strand of glass (core) surrounded by a glass tube (cladding). Its surrounded by a plastic isolation layer for protection . 24 Fiber Optic Types Digital data is converted to light Single mode - one light source flashes a light down the cable. can carries single ray of light Multimode - supports many simultaneous light
transmissions. capable of carrying multiple beams of light. 25 fiber optic multimode step-index fiber optic multimode graded-index fiber optic single mode 26 Fiber Optic Advantages & Disadvantages Advantages
greater capacity (bandwidth of up to 2 Gbps) Disadvantages expensive over short distance requires highly skilled installers
adding additional nodes is difficult Speed (100 - 500 mbps) smaller size and lighter weight lower attenuation immunity to environmental
interference highly secure 27 Type of Cable depends on: 1. 2. 3. 4. Transmission speed. Maximum cable length. Shielded requirements.
Price. 28 Comparison of Physical Media 29 Comparison of Physical Media 30
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