15 213 Network technology November 12 1998 Topics class24 ppt Overview Telephone system Ethernet ATM 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 class24 ppt 2 CS 213 F 98 Harsh Realities of Computer Int s are not integers float s are not reals Science 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 class24 ppt 3 CS 213 F 98 Computer system Keyboard Keyboard Processor Processor and andL1 L1cache cache 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 SCSI SCSI controller controller SCSI SCSIbus bus disk Disk disk Disk class24 ppt 4 Video Video adaptor adaptor Network Network adaptor adaptor Display Display Network Network disk cdrom CS 213 F 98 Simple example Starting Point Want to send bits between 2 computers FIFO queue 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 0 1 payload data address 0 please send the data word at address 1 here is the data word you asked for class24 ppt 5 CS 213 F 98 Questions about simple example What if more than 2 computers want to communicate Need computer address field in packet 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 machine one queue per process separate field in packet to identify process Warning You are entering a buzzword rich environment class24 ppt 6 CS 213 F 98 Generic network host host protocol stack s w s w interface interface h w h winterface interface adaptor interface card s w s w interface interface h w h winterface interface link host kernel code s w s w interface interface h w h winterface interface link link Interconnect Interconnect class24 ppt 7 CS 213 F 98 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 class24 ppt 8 CS 213 F 98 Protocol layering Protocols provide specialized services by building on services provided by other protocols Application Application 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 class24 ppt Transmission Transmissioncontrol controlprotocol protocol TCP TCP Internet InternetProtocol Protocol IP IP Reliable byte stream delivery processprocess Network Networkinterface interface ethernet ethernet ATM ATM hardware hardware 9 Physical connection CS 213 F 98 Encapsulation data data Application TCP TCPsegment segment header header data data TCP IP IPdatagram datagram TCP TCPsegment segment header header header header data data IP Ethernet Ethernetframe frame IP IPdatagram datagram TCP TCPsegment segment header header header header header header data data Network interface class24 ppt 10 CS 213 F 98 Protocol stacks Telnet FTP HTTP email TCP UDP application application transport transport Repeaters Bridges Routers Reliable efficient end user service Routing Flow control Congestion IP network network network network CSMA CD data link data link data link data link Framing Error recovery media access 10Base T physical physical physical physical Xmit raw bits Host A class24 ppt Host B 11 CS 213 F 98 Transmission media twisted twistedpair pair fiber fiber 1 2 Mb s at 1 km 100 200 Gb s at 1 km 2 insulated copper wires light source coaxial coaxialcable cable silica station stationwagon wagonfull fullofofmag magtapes tapes hurtling hurtlingdown downthe thehighway highway 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 minutes 15 Gb s 5 tape reused 10 times 500 tape cost 200 for shipping 10 cents GByte class24 ppt 12 CS 213 F 98 Shared vs switched media Shared media e g Ethernet aa bb cc Switched media e g ATM aa dd cc input ports aa bb cc dd aa bb cc dd aa bb cc dd class24 ppt bb output ports switch aa bb 13 dd cc switch CS 213 F 98 dd Network performance measures class24 ppt 14 CS 213 F 98 Example performance measures Interconnect Example Bisection BW Int Link BW Latency HW Overhead to from SAN CM 5 N x 5MB s 20 MB s 5 sec 0 5 0 5 s LAN Ethernet 1 125 MB s 1 125 MB s 15 sec 6 6 s SW Overhead to from 1 6 12 4 s 200 241 s 207 360 s TCP IP on LAN WAN class24 ppt 15 WAN ATM N x 10 MB s 10 MB s 50 to 10 000 s 6 6 s CS 213 F 98 Importance of Overhead Latency Ethernet SS10 9 Mb s BW 900 secs ovhd ATM Synoptics 78 Mb s BW 1 250 secs ovhd NFS trace over 1 week 95 msgs 200 bytes 10 000 9325 secs 7129 secs 8 000 6 000 Transmission Overhead 4 000 Time sec 2 000 0 Ethernet ATM Link bandwidth is as misleading as MIPS class24 ppt 16 CS 213 F 98 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
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