CHAPTER 3 Physical Layer

Outline Recap Application Layer Hardware Application Architecture (Software) Web Email Outline Physical Layer Circuits Media Digital Transmission (Digital Data) Analog Transmission (Digital Data) Digital Transmission (Analog Data) 2

Sender PDU Receiver HTTP Request HTTP Request TCP HTTP Request TCP Application Packet Transport Segment Network Data Link Frame Physical HTTP Request HTTP Request TCP HTTP Request TCP HTTP Request IP TCP HTTP Request IP IP TCP HTTP Request Ethernet Ethernet IP TCP HTTP Request Ethernet IP TCP HTTP Request

3 Physical Layer - Overview Network Layer Includes network hardware and circuits Types of Circuits Physical circuits connect devices & include actual wires Logical circuits refer to the transmission characteristics of the circuit Physical and logical circuits may be the same or different. For example, in multiplexing, one physical wire may carry several logical circuits. Data Link Layer Physical Layer

Circuit Configurations Basic physical layout of the circuit Configuration types: Point-to-Point Configuration Multipoint Configuration 5

Point-to-Point/Multipoint Configuration 6

Data Flow (Transmission) How does data flow through the circuit Configuration types: Simplex Half-Duplex Full-Duplex 7

Data Flow (Transmission) SERVER CLIENT Simplex Half-Duplex Full-Duplex 8

Data Flow (Transmission) – Multiplexing Combines many low speed circuits into one high speed transmission Categories of multiplexing 9

Frequency Division Multiplexing Makes a number of smaller channels from a larger frequency band by dividing the circuit “horizontally” FDM FDM Host computer circuit Four terminals 10

Time Division Multiplexing Dividing the circuit “vertically” TDM allows terminals to send data by taking turns 11

Multiplexing Wavelength Division Multiplexing (WDM) A variant of FDM used in fiber optic circuits Makes use of multiple light wavelengths (colors) to divide circuit into channels Dense WDM can divide circuit into more than 100 channels per fiber each transmitting at 10 Gbps

Inverse Multiplexing Combines a number of low speed circuits to create a single high speed circuit on the opposite ends Why would companies choose to do this? 13

Inverse Multiplexing (IMUX) Shares the load by sending data over two or more lines 14

Media Physical matter that carries the transmission Types: Guided Media Radiated (Unguided) Media 15

Guided: Twisted Pair (TP) Wires Commonly used for telephones and LANs Reduced electromagnetic interference TP cables have a number of pairs of wires Price: Speed: Distance: Common Use: 16

Guided: Twisted Pair (TP) Wires (CAT5e) Interference reduced b/c wires twisted together Telephone wires: usually has 2 pair (4 wires) with only 2 being used at one time Ethernet: 4 pairs (8 wires) 17

Guided: Comparison of Cables Interference reduced b/c wires twisted together Telephone wires: usually has 2 pair (4 wires) with only 2 being used at one time Ethernet: 4 pairs (8 wires) 18

Guided: Coaxial Cable Less prone to interference than TP due to shield More expensive than TP, thus quickly disappearing Price: Speed: Distance: Common Use: 19

3.2.1.2 Guided: Problems with Copper 20

Guided: Fiber Optic Cable Light created by an LED (light-emitting diode) or laser is sent down a thin glass or plastic fiber Has extremely high capacity, ideal for broadband Works well under harsh environments Price: Speed: Distance: Common Use: 21

Guided: Fiber Optic Cable Fiber optic cable structure (from center): Core (v. small, 5-50 microns, ~ the size of a single hair) Cladding, which reflects the signal Protective outer jacket How they are made: http://www.youtube.com/watch?v=llI8Mf_faVo Communication: http://www.ehow.com/video_4951202_optical-fiber-work_.html 22

Types of Optical Fiber Multimode (about 50 micron core) Earliest fiber-optic systems Signal spreads out over short distances (up to ~500m) Inexpensive Graded index multimode Reduces the spreading problem by changing the refractive properties of the fiber to refocus the signal Can be used over distances of up to about 1000 meters Single mode (about 5 micron core) Transmits a single direct beam through the cable Signal can be sent over many miles without spreading Expensive (requires lasers; difficult to manufacture) 23

Optical Fiber 24

Guided: Which is faster – Fiber or Copper? Fiber transmits via light – does that mean it is faster than copper b/c it travels at the speed of light? Data Carrying Capacity What should companies use?

Wireless (Unguided) – WLAN (Radio) Wireless transmission of electrical waves through air Each device has a radio transceiver with a specific frequency Includes Speed: Distance 26

Wireless Media – Microwave/ Satellite Microwave: High frequency form of radio communications Performs same functions as cables Speed: Distance: Satellite: Signals travel at speed of light, yet long propagation delay due to great distance between ground station and satellite 27

Factors Used in Media Selection Type of network Cost Transmission distance Security Error rates Transmission speeds 28