15 213 Course Theme Abstraction is good but don t forget reality Earlier courses to date emphasize abstraction Network technology Abstract data types Asymptotic analysis April 11 2000 These abstractions have limits Especially in the presence of bugs Need to understand underlying implementations Topics Useful outcomes Fundamental concepts protocols layering encapsulation network types Wide area networks phone lines and modems Internet backbones Local area networks Ethernet Become more effective programmers Able to find and eliminate bugs efficiently Able to tune program performance Prepare for later systems classes Compilers Operating Systems Networks Computer Architecture class23 ppt class23 ppt Harsh Realities of Computer Science 2 Typical computer system Int s are not integers float s are not reals Must understand characteristics of finite numeric representations You ve got to know assembly Basis for understanding what really happens when execute program Memory matters Memory referencing bugs especially difficult Violates programming language abstraction Significant performance issues E g cache effects There s more to performance than asymptotic complexity Constant factors also matter Computers do more than execute programs Get data in and out Communicate with each other via networks Keyboard Processor Interrupt controller 3 Mouse Keyboard controller Modem Serial port controller Printer Parallel port controller Local IO Bus Memory IDE disk controller SCSI controller Video adapter Network adapter Display Network SCSI bus disk disk class23 ppt CS 213 S 00 class23 ppt CS 213 S 00 Page 1 cdrom 4 CS 213 S 00 Questions about simple example Simple example What if more than 2 computers want to communicate Need an interconnect Need computer address field in packet What if the machines are far away WAN vs LAN Starting Point Want to send bits between 2 computers How do multiple machines share the interconnect FIFO First in First out queue buffer on each end Can send both ways full duplex Name for standard group of bits sent packet Packet format and rules for communicating them protocol multiple paths arbitration congestion control What if a packet is garbled in transit Add error detection field in packet What if a packet is lost Simple request response protocol and packet format header payload 0 1 data address More elaborate protocols to detect loss What if multiple processes per machine one queue per process separate field in packet to identify process 0 please send the data word at address 1 here is the data word you asked for class23 ppt 5 Warning You are entering a buzzword rich environment class23 ppt CS 213 S 00 host A protocol defines the format of packets and the rules for communicating them across the network Different protocols provide different levels of service host OS code network adapter interface card CS 213 S 00 Protocols Generic network protocol stack 6 software software software hardware hardware hardware link link link simple error correction ethernet uniform name space unreliable best effort datagrams host host IP reliable byte streams TCP unreliable best effort datagrams process process UDP multimedia data retrieval HTTP Interconnect wires repeaters bridges etc Crucial idea protocols leverage off of the capabilities of other protocols class23 ppt 7 class23 ppt CS 213 S 00 Page 2 8 CS 213 S 00 Protocol layering interface between user code and OS code Application program interface API Encapsulation Application program Protocols provide specialized services by relying on services provided by lowerlevel protocols i e they leverage lowerlevel services User code data User Interface API OS code TCP segment header data IP datagram TCP segment header header data Ethernet frame IP datagram TCP segment header header header data User application program FTP Telnet WWW email Unreliable best effort datagram delivery processprocess User datagram protocol UDP Transmission control protocol TCP Internet Protocol IP Reliable byte stream delivery processprocess IP Network interface ethernet Unreliable best effort datagram delivery host host TCP Adapter Physical connection hardware Adapter Network interface Network class23 ppt 9 class23 ppt CS 213 S 00 Transmission media twisted pair OS adapter interface exception mechanism fiber 10 Mb s at 5 km System area network SAN 100 200 Gb s at 1 km Metropolitan area network MAN same room meters 300 MB s Cray T3E light source Local area network LAN silica 1 2 Gb s at 1 km 15 Gb s at 1 hour insulator 7 GBytes tape 1000 tapes station wagon 50x50x50cm 7 000 GBytes total 7 000 GBytes 3600 seconds 15 Gb s stiff copper wire braided outer conductor same city 10 s of kilometers 800 Mb s Gigabit Nectar Wide area network WAN same bldg or campus kilometers 10 Mb sEthernet 100 Mb s Fast Ethernet 100 Mb s FDDI 150 Mb s OC 3 ATM 622 Mb s OC 12 ATM station wagon full of mag tapes hurtling down the highway every hour plastic cover CS 213 S 00 Basic network types 2 insulated copper wires coaxial cable 10 nationwide or worldwide 1000 s of kilometers telephone system 1 544 Mb s T1 carrier 44 736 Mb s T3 carrier We ll look at WANs and LANs 5 tape reused 10 times 500 tape cost 200 for shipping 10 cents GByte class23 ppt 11 class23 ppt CS 213 S 00 Page 3 12 CS 213 S 00 AT T Telephone Hierarchy 2 3 4 1 10 regional offices fully interconnected 10 6 7 Connecting distant computers with modems 5 8 28 8 Kb s analog local loop 9 V 34 modem 1 2 3 65 66 67 sectional offices 67 1 2 3 228 229 230 230 primary offices 1 2 3 1298 1299 1300 1 300 toll offices digital short cable or bus 33 MB s 1 544 Mb s T1 carrier digital codec local office 28 8 Kb s analog local loop digital codec toll office V 34 modem digital short cable or bus 33 MB s local office ISP computer home computer 19 000 end local offices local loops class23 ppt local loops 200 million telephones 13 class23 ppt CS 213 S 00 Modulating digital signals 0 1 0 1 1 0 0 1 0 0 1 14 CS 213 S 00 Quadrature amplitude modulation QAM 0 Modern modems use a combination of of amplitude and phase modulation to encode multiple bits per symbol i e amplitude phase pair binary signaling sine wave carrier 1kHz 2kHz phase angle is 1 4 amplitude modulation 1 8 phase modulation 00 no shift 01 1 4 shift left 10 1 2 shift left 11 3 4 shift left shifts are relative to previous wave class23 ppt 15 3 bits symbol QAM modulation 8 symbols class23 ppt CS 213 S 00 Page 4 4 bits symbol QAM modulation 16 symbols 16 CS 213 S 00 Conventional Modems T1
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