CMPE 150- Introduction to Computer Networks 1 CMPE 150 Fall 2005 Lecture 6 Introduction to Networks and the Internet

CMPE 150- Introduction to Computer Networks 2 Announcements Labs: –1 slot either M or W 4-6pm. –Other slot? T or Th 6-8pm? –First lab is next week. TA office hours: T 6-7pm and Th 1-2pm in BME 314.

CMPE 150- Introduction to Computer Networks 3 Last Class PHY. –Analog and digital technology/communication. –Digitization. –Sampling period and sampling rate. –Bit rate. –Signal and systems. Periodic signals. Fourier series. Bandwidth limitation. Channel capacity.

CMPE 150- Introduction to Computer Networks 4 Today PHY (contd). T1 demo.

CMPE 150- Introduction to Computer Networks 5 Guided Transmission Data Magnetic Media Twisted Pair Coaxial Cable Fiber Optics

CMPE 150- Introduction to Computer Networks 6 Magnetic Media Examples? Advantages? Disadvantages?

CMPE 150- Introduction to Computer Networks 7 Twisted Pair Oldest but still very common. Telephone system. Cheap and effective for long ranges. Bundles of twisted pairs. Can transmit both analog and digital signals. Bandwidth depends on thickness of wire and distance traveled. –Mb/s for few kilometers.

CMPE 150- Introduction to Computer Networks 8 Twisted Pair (a) Category 3 UTP. (b) Category 5 UTP.

CMPE 150- Introduction to Computer Networks 9 Twisted Pair

CMPE 150- Introduction to Computer Networks 10 Coaxial Cable Better performance than twisted pair, i.e., higher bandwidth and longer distances. –Good noise immunity. But… Bandwidths close to 1GHz. Used widely in telephone networks for longer distances; but gradually being replaced by fiber. Used for CATV!

CMPE 150- Introduction to Computer Networks 11 Coaxial Cable

CMPE 150- Introduction to Computer Networks 12 Fiber Optics Optical transmission. Optical transmission system: light source, medium, and detector. Pulse of light = 1. No light = 0. Transmission medium: ultra thin fiber of glass. Detector: generates electrical pulse when perceives light.

CMPE 150- Introduction to Computer Networks 13 Transmitting Light (a) Three examples of a light ray from inside a silica fiber impinging on the air/silica boundary at different angles. (b) Light trapped by total internal reflection.

CMPE 150- Introduction to Computer Networks 14 Fiber Cables (a) Side view of a single fiber. (b) End view of a sheath with three fibers.

CMPE 150- Introduction to Computer Networks 15 Fiber Optic Networks A fiber optic ring.

CMPE 150- Introduction to Computer Networks 16 Fiber Optic Networks (2) A passive star connection in a fiber optics network.

CMPE 150- Introduction to Computer Networks 17 Fiber versus Copper Wire Fiber can handle much higher bandwidths. Low attenuation: 50km without repeater. Unaffected by power surges/outages, and interference. Fiber is thin and lightweight: easy to deploy and add new capacity. Difficult to tap. But…

CMPE 150- Introduction to Computer Networks 18 Fiber versus Copper (contd) Fiber can be damaged easily. Optical transmission is unidirectional, so need 2 fibers or 2 frequencies for 2-way communication. Fiber and fiber interfaces is more expensive.

CMPE 150- Introduction to Computer Networks 19 Public Switched Telephone System Structure of the Telephone System The Politics of Telephones The Local Loop: Modems, ADSL and Wireless Trunks and Multiplexing Switching

CMPE 150- Introduction to Computer Networks 20 Structure of the Telephone System (a) Fully-interconnected network. (b) Centralized switch. (c) Two-level hierarchy.

CMPE 150- Introduction to Computer Networks 21 Structure of the Telephone System (2) A typical circuit route for a medium-distance call.

CMPE 150- Introduction to Computer Networks 22 Major Components of the Telephone System Local loops: Connection from subscriber to end office. Trunks Outgoing lines connecting offices. Toll office: Connects end offices. Switching offices Where calls are moved from one trunk to another.