15 213 Network technology April 11 2000 Topics Fundamental concepts protocols layering encapsulation network types Wide area networks phone lines and modems Internet backbones Local area networks Ethernet class23 ppt Course Abstraction is good but don t forget reality Theme Earlier courses to date emphasize abstraction Abstract data types Asymptotic analysis These abstractions have limits Especially in the presence of bugs Need to understand underlying implementations Useful outcomes 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 2 CS 213 S 00 Harsh Realities of Computer Science 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 class23 ppt 3 CS 213 S 00 Typical computer system Keyboard Keyboard Processor Processor Interrupt Interrupt controller controller Mouse Mouse Keyboard Keyboard controller controller Modem Modem Serial Serialport port controller controller Printer Printer Parallel Parallelport port controller controller Local IO Local IOBus Bus Memory Memory IDE IDEdisk disk controller controller disk SCSI SCSI controller controller SCSI SCSIbus bus disk class23 ppt 4 Video Video adapter adapter Network Network adapter adapter Display Display Network Network cdrom CS 213 S 00 Simple example Starting Point Want to send bits between 2 computers 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 Simple request response protocol and packet format header payload 0 1 data address 0 please send the data word at address 1 here is the data word you asked for class23 ppt 5 CS 213 S 00 Questions about 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 How do multiple machines share the interconnect 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 More elaborate protocols to detect loss What if multiple processes per machine one queue per process separate field in packet to identify process Warning You are entering a buzzword rich environment class23 ppt 6 CS 213 S 00 Generic network host protocol stack network adapter interface card software software hardware hardware software software hardware hardware link host OS code software software hardware hardware link link Interconnect Interconnect wires wires repeaters repeaters bridges bridges etc etc class23 ppt 7 CS 213 S 00 Protocols A protocol defines the format of packets and the rules for communicating them across the network Different protocols provide different levels of service 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 Crucial idea protocols leverage off of the capabilities of other protocols class23 ppt 8 CS 213 S 00 interface between user code and OS code Application program interface API Protocol layering Protocols provide specialized services by relying on services provided by lowerlevel protocols i e they leverage lowerlevel services User Userapplication applicationprogram program FTP FTP Telnet Telnet WWW WWW email email Unreliable best effort datagram delivery processprocess User Userdatagram datagramprotocol protocol UDP UDP Unreliable best effort datagram delivery host host class23 ppt Transmission Transmissioncontrol control protocol TCP protocol TCP Internet InternetProtocol Protocol IP IP Reliable byte stream delivery processprocess Network Networkinterface interface ethernet ethernet hardware hardware 9 Physical connection CS 213 S 00 Encapsulation Application program User code OS code data data TCP TCPsegment segment header header data data IP IPdatagram datagram TCP TCPsegment segment header header header header data data Ethernet Ethernetframe frame IP IPdatagram datagram TCP TCPsegment segment header header header header header header data data IP TCP User Interface API OS adapter interface exception mechanism Adapter Adapter Network interface Network class23 ppt 10 CS 213 S 00 Transmission media twisted twistedpair pair 10 Mb s at 5 km fiber fiber 100 200 Gb s at 1 km 2 insulated copper wires light source silica station stationwagon wagonfull fullof ofmag magtapes tapes hurtling hurtlingdown downthe thehighway highwayevery every hour hour coaxial coaxialcable cable 1 2 Gb s at 1 km plastic cover 15 Gb s at 1 hour insulator stiff copper wire braided outer conductor 7 GBytes tape 1000 tapes station wagon 50x50x50cm 7 000 GBytes total 7 000 GBytes 3600 seconds 15 Gb s 5 tape reused 10 times 500 tape cost 200 for shipping 10 cents GByte class23 ppt 11 CS 213 S 00 Basic network types System area network SAN Metropolitan area network MAN Local area network LAN Wide area network WAN same city 10 s of kilometers 800 Mb s Gigabit Nectar same room meters 300 MB s Cray T3E nationwide or worldwide 1000 s of kilometers telephone system 1 544 Mb s T1 carrier 44 736 Mb s T3 carrier 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 We ll look at WANs and LANs class23 ppt 12 CS 213 S 00 AT T Telephone Hierarchy 2 3 4 5 1 10 regional offices fully interconnected 10 6 7 8 9 1 2 3 65 66 67 67 sectional offices 1 2 3 228 229 230 230 primary offices 1 2 3 1298 1299 1300 1 300 toll offices 19 000 end local offices local loops class23 ppt 200 million 13telephones local loops CS 213 S 00 Connecting distant computers with modems V 34 V 34 modem modem digital short cable or bus 33 MB s 28 8 Kb s analog local loop 1 544 Mb s T1 carrier digital digital codec codec local office codec codec toll office local office V 34 V 34
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