Modems 9.2 Transmission Media Communication

Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Chapter Contents

9.1 Modems 9.2 Transmission Media

9.3 Network Architecture: Local Area Networks 9.4 Communication Errors and Error Correcting Codes 9.5 Network Architecture: The Internet 9.6 Case Study: Asynchronous Transfer Mode Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Modem Communication • Communication over a telephone line with modems. Modem Modem Telephone Line Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Modulation Schemes • Three common forms of modulation. Digital Signal AM FM PM 1 1 1 Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Pulse Code Modulation • Conversion of an analog signal into a PCM binary sequence. Amplitude 000 001 010 011 100 101 110 111 Time PCM sequence = 011 110 011 001 100 111 101 Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Ideal vs. Transmitted Waves 1 1 1 1 Sampling instants at receiver Transmitted wave Ideal wave Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Transmission Media • Transmisson media. a Two- wire open lines; b twisted-pair lines; c coaxial cable; d optical fiber; esatellites. Signal GND a b c Signal GND Insulation d Optical core Plastic coating Optical cladding Uplink Downlink e Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring The Seven Layers of the OSI Model 1. Physical 2. Data Link 3. Network 4. Transport 5. Session 6. Presentation 7. Application Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring A Few Network Topologies • a Bus; b ring; and c star network topologies. b c a Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Parity • Even parity bits are assigned to a few ASCII characters. P 1 1 1 6 1 1 1 1 1 5 1 1 1 1 4 1 3 1 2 1 1 1 1 1 1 1 Even parity bit Bit position 7-bit ASCII character code a b c z A Character Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Check Bits • Check bits for a single error correcting ASCII code. C8 1 1 1 1 C4 1 1 1 1 C2 1 1 1 1 1 1 C1 1 1 1 1 1 1 1 2 3 4 5 6 7 8 9 10 11 Check bits Bit position checked Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring SEC coded ‘a’ • Format for a single error correcting ASCII code. Bit position 1 1 1 1 11 10 9 8 7 6 5 4 3 2 1 Check bits C2 C1 C8 C4 ASCII ‘a’ = 1100001 Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring SEC Coded ‘d’ • Parity computation for an ASCII character in an SEC code. Bit position 1 1 1 1 1 1 11 10 9 8 7 6 5 4 3 2 1 Check bits C2 C1 C8 C4 Location of error C1 checks: 1, 3, 5, 7, 9, 11 odd C2 checks: 2, 3, 6, 7, 10, 11 even C4 checks: 4, 5, 6, 7 odd C8 checks: 8, 9, 10, 11 even Parity Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring 3-Bit SEC Hypercube • Hamming distance relationships among three-bit codewords. Valid codewords are 000 and 111. The remaining codewords repre- sent errors. 000 001 010 011 100 101 110 111 Valid codeword Valid codeword Three changed bits between valid codewords results in a Hamming distance of 3. Error codewords Error codewords Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring LRC and VRC Checking • Combined LRC and VRC checking. Checksum bits form even par- ity for each column. 1 1 1 1 1 1 1 1 Code 1 1 1 1 P Character A B C D E F G H Checksum 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Cyclic Redundancy Checking 1 1 0 1 0 1 1 0 1 1 0 0 0 0 1 0 0 1 1 1 1 0 0 0 0 1 0 1 0 1 0 0 1 1 ⊕ 1 0 0 1 1 1 0 0 1 1 ⊕ 1 1 0 0 1 1 ⊕ 0 1 0 1 0 1 0 0 1 1 ⊕ 1 1 1 0 0 1 1 0 Gx , of degree n = 4 Mx n = 4 zeros Bitwise exclusive OR XOR, is the same as modulo-2 addition and modulo-2 subtraction. Quotient is discarded for the calculation of the original CRC. Rx is the CRC for Mx Transmitted frame Tx = 1 1 0 1 0 1 1 0 1 1 1 1 1 0 Mx Rx Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Internet Protocol Stack Application Transport Network MAC PHY Link Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring IPv4 Address Classes Class A 7 bits 24 bits netid host id Class B 14 bits 16 bits netid host id 1 Class C 21 bits 8 bits netid host id 1 Class D 28 bits multicast group id 1 Class E 27 bits reserved for future use 1 1 0 1 1 0 1 1 1 0 Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Encapsulation • Encapsulation in the TCPIP protocol suite. User data User data User data User data Application layer Transport layer Network layer Link layer TCP header TCP header TCP header IP header IP header Ethernet header Ethernet trailer Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Hub vs. Router vs. Switch • Configurations shown for a a hub; b a router; and c a switch. Hub a Hub Hub Router b c Switch Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Self-Routing Switch • A 4 × 4 self-routing switch based on the bubblesort algorithm. 4 1 2 3 1 2 3 4 1 4 1 2 2 4 3 4 2 3 Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring TDM vs. ATM • a Time division multiplexing vs. b asynchronous transfer mode. 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 Station time slots = Station data = Nothing to send 1 Cells, shown by source = Station data = Nothing to send 1 3 1 2 4 1 3 1 2 a b Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Format of an ATM Packet • Format of an ATM packet. a User-to-network interface UNI for- mat; and b network-to-network interface NNI format. GFC VPI VPI VCI PTI C L P HEC 48-byte information field 8 7 6 5 4 3 2 1 1 2 3 4 5 6 53 Bits Bytes a VPI VCI PTI C L P HEC 48-byte information field 8 7 6 5 4 3 2 1 b Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Simple ATM Network ATM Switch 1 ATM Switch 2 ATM Switch 3 VPI OUT VPI IN 7 9 5 7 VPI OUT VPI IN 5 7 VPI OUT VPI IN 7 3 VPI = 9 VCI = 3, 4 VPI = 3 VCI = 3, 4 VPI = 7 VCI = 3, 4 VPI = 7 VCI = 1, 2, 3 VPI = 5 VCI 1, 2, 3 VPI = 7 VCI = 1, 2, 3 Principles of Computer Architecture by M. Murdocca and V. Heuring © 1999 M. Murdocca and V. Heuring Principles of Computer Architecture Miles Murdocca and Vincent Heuring

Chapter 10: Trends in Computer