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Welcome to COS 461

Welcome to COS 461. Vivek Pai. Mechanics. First time teaching 461 But have been doing some level of networking for a while… Same book as last year – Peterson/Davie Will also put others on reserve Syllabus on web site, but not updated General concepts the same Actual dates will differ.

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Welcome to COS 461

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  1. Welcome to COS 461 Vivek Pai CS 461

  2. Mechanics • First time teaching 461 • But have been doing some level of networking for a while… • Same book as last year – Peterson/Davie • Will also put others on reserve • Syllabus on web site, but not updated • General concepts the same • Actual dates will differ CS 461

  3. Assignment • Read Chapter 1 • Send me an e-mail • Name, year, phone #, preferred e-mail address • Jpeg image of yourself • Reason for taking the course • Go to newsgroup pu.cs.461 CS 461

  4. But First, A Word From Slammer Bank of America said 13,000 of its ATMs refused to dispense cash. In South Korea, the country's largest ISP, KT, said all almost all its customers lost their connections during the attack. Chinese computer users saw sites freeze and a dramatic slowdown in download speeds, as the worm's effects hit the Internet's nameservers--the computers that translate Web addresses into numerical Internet Protocol addresses. And all this in just 376 bytes of code, meaning the entire SQL Slammer worm code is about half the length of this paragraph. CS 461

  5. Introduction Outline Statistical Multiplexing Inter-Process Communication Network Architecture Performance Metrics Implementation Issues CS 461

  6. … Building Blocks • Nodes: PC, special-purpose hardware… • hosts • switches • Links: coax cable, optical fiber… • point-to-point • multiple access CS 461

  7. Switched Networks • A network can be defined recursively as... • two or more nodes connected by a link, or • two or more networks connected by a node CS 461

  8. Strategies • Circuit switching: carry bit streams • original telephone network • Packet switching: store-and-forward messages • Internet CS 461

  9. Addressing and Routing • Address: byte-string that identifies a node • usually unique • Routing: process of forwarding messages to the destination node based on its address • Types of addresses • unicast: node-specific • broadcast: all nodes on the network • multicast: some subset of nodes on the network CS 461

  10. L1 R1 L2 R2 Switch 1 Switch 2 L3 R3 Multiplexing • Time-Division Multiplexing (TDM) • Frequency-Division Multiplexing (FDM) CS 461

  11. Statistical Multiplexing • On-demand time-division • Schedule link on a per-packet basis • Packets from different sources interleaved on link • Buffer packets that are contending for the link • Buffer (queue) overflow is called congestion … CS 461

  12. Host Host Application Host Channel Application Host Host Inter-Process Communication • Turn host-to-host connectivity into process-to-process communication. • Fill gap between what applications expect and what the underlying technology provides. CS 461

  13. IPC Abstractions • Stream-Based • video: sequence of frames • 1/4 NTSC = 352x240 pixels • (352 x 240 x 24)/8=247.5KB • 30 fps = 7500KBps = 60Mbps • video applications • on-demand video • video conferencing • Request/Reply • distributed file systems • digital libraries (web) CS 461

  14. What Goes Wrong in the Network? • Bit-level errors (electrical interference) • Packet-level errors (congestion) • Link and node failures • Packets are delayed • Packets are deliver out-of-order • Third parties eavesdrop CS 461

  15. Layering • Use abstractions to hide complexity • Abstraction naturally lead to layering • Alternative abstractions at each layer Application programs Request/reply Message stream channel channel Host-to-host connectivity Hardware CS 461

  16. Protocols • Building blocks of a network architecture • Each protocol object has two different interfaces • service interface: operations on this protocol • peer-to-peer interface: messages exchanged with peer • Term “protocol” is overloaded • specification of peer-to-peer interface • module that implements this interface CS 461

  17. Interfaces Host1 Host2 Service High-level High-level interface object object Protocol Protocol Peer-to-peer interface CS 461

  18. Protocol Machinery • Protocol Graph • most peer-to-peer communication is indirect • peer-to-peer is direct only at hardware level Host 2 Host 1 Digital Digital Video Video File File library library application application application application application application RRP MSP RRP MSP HHP HHP CS 461

  19. Machinery (cont) • Multiplexing and Demultiplexing (demux key) • Encapsulation (header/body) Host 1 Host 2 Application Application program program Data Data RRP RRP RRP Data RRP Data HHP HHP HHP RRP Data CS 461

  20. FTP HTTP NV TFTP UDP TCP IP … NET NET NET 2 1 n Internet Architecture • Defined by Internet Engineering Task Force (IETF) • Hourglass Design • Application vs Application Protocol (FTP, HTTP) CS 461

  21. ISO Architecture End host End host Application Application Presentation Presentation Session Session Transport Transport Network Network Network Network Data link Data link Data link Data link Physical Physical Physical Physical One or more nodes within the network CS 461

  22. Performance Metrics • Bandwidth (throughput) • data transmitted per time unit • link versus end-to-end • notation • KB = 210 bytes • Mbps = 106 bits per second • Latency (delay) • time to send message from point A to point B • one-way versus round-trip time (RTT) • components Latency = Propagation + Transmit + Queue Propagation = Distance / c Transmit = Size / Bandwidth CS 461

  23. Bandwidth versus Latency • Relative importance • 1-byte: 1ms vs 100ms dominates 1Mbps vs 100Mbps • 25MB: 1Mbps vs 100Mbps dominates 1ms vs 100ms • Infinite bandwidth • RTT dominates • Throughput = TransferSize / TransferTime • TransferTime = RTT + 1/Bandwidth x TransferSize • 1-MB file to 1-Gbps link as 1-KB packet to 1-Mbps link CS 461

  24. Delay x Bandwidth Product • Amount of data “in flight” or “in the pipe” • Usually relative to RTT • Example: 100ms x 45Mbps = 560KB CS 461

  25. Socket API • Creating a socket int socket(int domain, int type, int protocol) • domain =PF_INET, PF_UNIX • type = SOCK_STREAM, SOCK_DGRAM, SOCK_RAW • Passive Open (on server) int bind(int socket, struct sockaddr *addr, int addr_len) int listen(int socket, int backlog) int accept(int socket, struct sockaddr *addr, int addr_len) CS 461

  26. Sockets (cont) • Active Open (on client) int connect(int socket, struct sockaddr *addr, int addr_len) • Sending/Receiving Messages int send(int socket, char *msg, int mlen, int flags) int recv(int socket, char *buf, int blen, int flags) CS 461

  27. Protocol-to-Protocol Interface • Configure multiple layers • static versus extensible • Process Model • avoid context switches • Buffer Model • avoid data copies CS 461

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