Introduction to Computer Networks CMPE 150 Fall 2005 Lecture 8 CMPE 150 Introduction to Computer Networks 1 Announcements Labs start this week Tue 6 8pm Wed 4 6pm Write ups will be up on the Web page Homework 1 due today by midnight E mail to sudrang soe Only txt or pdf Homework 2 Katia s office hours Wed 3 15 4 15 CMPE 150 Introduction to Computer Networks 2 Reading Assignment Tanenbaum Chapter 2 CMPE 150 Introduction to Computer Networks 3 Last Class PHY Cont d PSTN CMPE 150 Introduction to Computer Networks 4 Today PHY cont d Finish PSTN Wireless Mobile telephony Wireless transmission CMPE 150 Introduction to Computer Networks 5 Public Switched Telephone System Structure of the Telephone System The Local Loop Modems ADSL and Wireless Trunks and Multiplexing Switching CMPE 150 Introduction to Computer Networks 6 Local Loop Cont d We covered Different modulation schemes E g QPSK QAM TCM Parity as error detection scheme CMPE 150 Introduction to Computer Networks 7 Full Duplex Half Duplex Simplex Full duplex traffic in both directions simultaneously Half duplex traffic in both directions but 1 direction at a time Simplex traffic allowed only one way Examples CMPE 150 Introduction to Computer Networks 8 What s next Modems were getting faster e g 56Kbps But demand for faster access was growing CATV and satellite as competitors Phone company s response DSL Broadband access ADSL asymmetric digital subscriber line When you subscribe to DSL service you are connected to the local office without the filter to frequencies below 300Hz and above 3400Hz Physical limitation still exists and depends on thickness length etc CMPE 150 Introduction to Computer Networks 9 Digital Subscriber Lines Bandwidth versus distanced over category 3 UTP for DSL CMPE 150 Introduction to Computer Networks 10 Digital Subscriber Lines 2 Operation of ADSL using discrete multitone modulation Available 1 1MHz local loop spectrum divided into 256 channels 4 3KHz each CMPE 150 Introduction to Computer Networks 11 ADSL Typically 32 channels for upstream and the rest for downstream traffic Usually 512 Kbps downstream and 64 Kbps upstream standard and 1 Mbps downstream and 256 Kbps upstream premium Within each channel modulation scheme is used sampling at 4000 baud CMPE 150 Introduction to Computer Networks 12 Typical ADSL Setup A typical ADSL equipment configuration CMPE 150 Introduction to Computer Networks 13 Wireless Local Loop Last mile is wireless Why Historically local telcos had monopoly for local telephone service In the mid 1990 s market open to competition e g long distance carriers Cheaper alternative to stringing cables to customers is using a wireless local loop Mobile telephony Fixed wireless CMPE 150 Introduction to Computer Networks 14 Wireless Local Loops Architecture of an LMDS system Tower with multiple highly directional antennae but small range 2 5Km CMPE 150 Introduction to Computer Networks 15 Trunking and Multiplexing CMPE 150 Introduction to Computer Networks 16 Trunking Deployment of high bandwidth pipes Current and future demand Switching offices higher in the PSTN hierarchy Multiplexing ability to send a number of conversations simultaneously over the same pipe Multiplexing schemes Frequency Division Multiplexing FDM Time Division Multiplexing TDM CMPE 150 Introduction to Computer Networks 17 The Multiplexing Problem frequency Shared channel how to divide resource among multiple recipients time Analogy a highway shared by many users CMPE 150 Introduction to Computer Networks 18 Frequency Division Multiplexing frequency user 1 user 2 user 3 user 4 guard band time Analogy a highway has multiple lanes CMPE 150 Introduction to Computer Networks 19 Time Division Multiplexing frequency user 1 user 2 user 3 user 4 user 1 user 2 guard band time Requirement precise time coordination CMPE 150 Introduction to Computer Networks 20 Frequency Time Division frequency time slot usually of the same size time CMPE 150 Introduction to Computer Networks 21 Frequency Division Multiplexing a The original bandwidths b The bandwidths raised in frequency c The multiplexed channel CMPE 150 Introduction to Computer Networks 22 FDM versus TDM FDM requires analog circuitry TDM can be done entirely using digital electronics But TDM can only be used for digital data Analog signals from local loops need to be digitized at the local office At end office all individual local loops arrived are digitzed and multiplexed CMPE 150 Introduction to Computer Networks 23 TDM Multiplexing CMPE 150 Introduction to Computer Networks 24 PCM Pulse Code CMPE 150 Introduction to Computer Networks 25 PCM Pulse Code Modulation Digitization of voice channels Sampling frequency If voice signal peaks at 4KHz what s the sampling frequency Nyquist 8000 samples sec or 125 microsec sample Each sample is 8 bits 7 for data and 1 for control Data rate 7 8000 56Kbps of data and 8Kbps of signaling per channel No world wide standard for PCM In the US and Japan T1 technically DS1 CMPE 150 Introduction to Computer Networks 26 T1 The T1 carrier 1 544 Mbps T1 24 multiplexed voice channels 1 544 Mbps CMPE 150 Introduction to Computer Networks 27 T2 and Beyond Multiplexing T1 streams into higher carriers CMPE 150 Introduction to Computer Networks 28 SONET SDH SONET and SDH multiplex rates SONET Synchronous Optical NETwork SDH Sync Digital Hierarchy CMPE 150 Introduction to Computer Networks Optical TDM for fiber transmission 29 Switching CMPE 150 Introduction to Computer Networks 30 Circuit and Packet Switching a Circuit switching b Packet switching CMPE 150 Introduction to Computer Networks 31 Switching Circuit Message CMPE 150 Introduction to Computer Networks Packet Switching 32 Packet Switching CMPE 150 Introduction to Computer Networks 33 Wireless Transmission CMPE 150 Introduction to Computer Networks 34 Wireless Transmission Electron movement electromagnetic waves that propagate through space T CMPE 150 Introduction to Computer Networks R 35 Propagation Maximum speed speed of light c 3 108 m s In vacuum all EM waves travel at the same speed c Otherwise propagation speed is function of frequency c f where f is frequency Hz and is wavelength m CMPE 150 Introduction to Computer Networks 36 The Electromagnetic Spectrum The electromagnetic spectrum and its uses for communication CMPE 150 Introduction to Computer Networks 37 Radio Transmission 1Km a In the VLF LF and MF bands radio waves follow the curvature of the earth E g AM radio uses MF b In the HF and
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