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Networks

Networks. Modem. Modem. Phone. Phone. Switched Telephone Network. Computer-Computer Comm. CPU. CPU. Memory. Comm Device. Comm Device. Memory. Data Networks. CPU. CPU. Memory. Network Device. Network Device. Memory. Specialized Data Network. WANs, MANs, and LANs

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Networks

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  1. Networks

  2. Modem Modem Phone Phone Switched Telephone Network Computer-Computer Comm CPU CPU Memory Comm Device Comm Device Memory

  3. Data Networks CPU CPU Memory Network Device Network Device Memory Specialized Data Network • WANs, MANs, and LANs • Specialized communication protocols • Multidrop • Packet oriented • Looks like other devices… make it look like a file ...

  4. Multidrop Network S S Network R R • Multiple senders • Can address multiple receivers

  5. Packet Network S S Telephone Circuit Based R R S S Data Packet Based R R

  6. Multidrop Packet Network • To transmit/receive: • Sender marshals data into a packet • Network interface hardware transforms data for physical transmission • Network deliver packets to variable destination • Receiver converts physical signal back into a data packet • Receiver unmarshals packet into data • Need a widely-agreed upon set of protocols

  7. Protocol Tasks • Control information delivery rates • Pass data across networks • Provide fast/reliable IPC-like communication • Support logical byte streams • Create other models for communication • File transfer • Procedure call paradigm • Shared memory paradigm • Translate machine-dependent data representations • … and more …

  8. Standardizing Protocols • ANSI X.25 • ARPAnet • ISO Open Systems Interconnect (OSI) model • Now widely used as a reference architecture • 7-layer model • Provides framework for specific protocols (such as IP, TCP, FTP, RPC, RSVP, …)

  9. ISO OSI Model Application Application Presentation Presentation Session Session Transport Transport Network Network Data Link Data Link Physical Physical

  10. ISO OSI Model Data Link Data Link Physical Physical Examples • Physical/Data Link layer networks: Ethernet, Wireless, ATM

  11. Low Level Protocols • Physical layer: Signaling technology • Data link layer: Frame management • All done in hardware • Examples • Ethernet • Token ring • X.25 • ATM • Read pages 490-496

  12. Ethernet (CSMA/CD) • Asynchronous • Carrier Sense • Multiple Access • Collision Detection • Backoff

  13. Wireless Backbone

  14. ISO OSI Model Network Network Data Link Data Link Physical Physical Examples • Physical/Data Link layer networks: Ethernet, Token Ring, ATM • Network layer net: The Internet

  15. Network Layer • Primary purpose is to combine networks • Internet protocol (IP) is dominant protocol • Creates an internet address space • Implements packet routing across networks Host X Network A Network B Network C Host R Host S Host Y

  16. Addressing & Routing Host X 3b4e87 3b6209 Network A Network C 3b4e62 3b4e55 3b621a Host R Host Y • Host X does not know how to send to Host Y • Can send a frame to Host R for forwarding • What should it tell Host R?

  17. Addressing & Routing 128.123.234.033 128.229.244.109 Host X To: 128.229.244.006 From: 128.123.234.033 Network Layer data 3b4e87 3b6209 Network A Network C 3b4e62 3b4e55 3b621a Host R Host Y 128.123.234.063 128.123.234.188 128.229.244.006 • Host X does not know how to send to Host Y • Can send a frame to Host R for forwarding • What should it tell Host R? • Internet address spans all machines

  18. Addressing & Routing 128.123.234.033 To: 3b4e55 From: 3b4e87 128.229.244.109 Host X To: 128.229.244.006 From: 128.123.234.033 Network Layer data 3b4e87 3b6209 Network A Network C 3b4e62 3b4e55 3b621a Host R Host Y 128.123.234.063 128.123.234.188 128.229.244.006 • Host X does not know how to send to Host Y • Can send a frame to Host R for forwarding • What should it tell Host R? • Internet address spans all machines • Send encapsulated packet to Host R with Host Y

  19. Addressing & Routing 128.123.234.033 128.229.244.109 Host X 3b4e87 3b6209 Network A Network B Network C 3b4e62 3b4e55 3b621a Host R Host S Host Y 128.123.234.063 128.123.234.188 128.229.244.006 • Host X does not know how to send to Host Y • Can send a frame to Host R for forwarding • What should it tell Host R? • Internet address spans all machines • Send encapsulated packet to Host R with Host Y

  20. Addressing & Routing 128.123.234.033 128.229.244.109 Host X 3b4e87 3b6209 Network A Network B Network C To: 3b621a From: ... 3b4e62 3b4e55 3b621a Host R Host Y To: 128.229.244.006 From: 128.123.234.033 Network Layer data 128.123.234.063 128.123.234.188 128.229.244.006 • Host X does not know how to send to Host Y • Can send a frame to Host R for forwarding • What should it tell Host R? • Internet address spans all machines • Send encapsulated packet to Host R with Host Y • Data Link frame is received by Host Y

  21. More on the Network Layer • Implements internet addressing & routing • ARPAnet IP protocol is dominant -- underlies the Internet • Intermediate hosts are called gateways • Connected to two or more networks • Runs IP routing software • nag is a gateway for the teaching lab • Read pages 471-477

  22. ISO OSI Model Transport Transport Network Network Data Link Data Link Physical Physical Examples • Physical/Data Link layer networks: Ethernet, Token Ring, ATM • Network layer net: The Internet • Transport layer net: TCP-based network

  23. Transport Layer • Provides yet another address extension • IP references only networks and hosts • Transport layer adds ports -- logical endpoints • Address form is <net, host, port> • Two primary protocols (both from ARPAnet) • User Datagram Protocol (UDP) • User-space interface to IP packets • No guarantee that packet will be delivered • Transmission Control Protocol (TCP) • Provides a stream-oriented interface to the network • Reliable delivery

  24. ISO OSI & TCP/IP ISO OSI Session ISO OSI packet ISO OSI TLI ISO OSI frame ISO OSI Network X.25 packet X.25

  25. ISO OSI & TCP/IP ISO OSI Session ISO OSI Session ISO OSI packet ISO OSI packet ISO OSI TLI ARPAnet TCP ISO OSI frame IP frame ISO OSI Network ARPAnet IP X.25 packet Ethernet packet X.25 Ethernet

  26. Domain Name Server (DNS) • IP uses 32-bit addresses • 128.138.241.1 • “anchor.cs.colorado.edu” • DNS: anchor.cs.colorado.edu128.138.241.1 • Huge table • Distributed/managed according to domain • .edu, .com, .net, .gov, … .us, .ca, are domains • .colorado is a sub domain managed by CU • .cs is a sub domain managed by Computer Sci • anchor is a computer in .cs (in .colorado, in .edu) • anchoris on net 128.138.241, and is host number 1

  27. DNS .edu First-Level Domain • Supports TCP • Uses UDP .colorado .edu Domain .cs .colorado Domain anchor neon pawnee .cs Domain

  28. The DNS Protocol Stack UDP packet ISO OSI Session DNS Resolver ISO OSI packet UDP packet ISO OSI TLI ARPAnet UDP ISO OSI frame IP frame ISO OSI Network ARPAnet IP X.25 packet Ethernet packet X.25 Ethernet

  29. P P P P Communication Ports • Global name for a “mailbox” • Will be many ports at one <net, host> Transport Layer Network Layer Low Layers <net, host> Machine X

  30. P P P P Communication Ports • Global name for a “mailbox” • Will be many ports at one <net, host> • Each port can be bound to an address Transport Layer Network Layer Low Layers <net, host> Machine X

  31. BSD Sockets • Sockets are comm ports in BSD UNIX • Semantics resemble pipes (files) • Bidirectional

  32. BSD Sockets • Sockets are comm ports in BSD UNIX • Semantics resemble pipes (files) • Bidirectional int socket(int addressFamily, int socketType, int protocolNo) s = socket(…) s

  33. P BSD Sockets (cont) • Once a socket has been created, it can be bound to an internet port s

  34. P BSD Sockets (cont) • Once a socket has been created, it can be bound to an internet port int bind(int skt, struct sockadrr *addr, int addrLength) s • Example code available on the web page

  35. UDP • Datagram (“connectionless”) service • Similar to disk I/O level of service • Logically associated with an IP packet & Data Link frame (but not physically) • Best-effort delivery of datagrams, but: • Datagram may be dropped (lost) • Datagrams may be delivered out of order • Efficient, relative to TCP

  36. Using UDP /* Set up a socket to talk to the server */ skt = socket(AF_INET, SOCK_DGRAM, 0); host = gethostbyname(remoteHostName); bzero(&remote, sizeof(remote)); remote.sin_family = host->h_addrtype; remote.sin_port = htons(remotePort); bcopy(host->h_addr, &remote.sin_addr, host->h_length); /* Export the socket to a port (and IP address) */ host = gethostbyname(localHostName); bzero(&local, sizeof(local)); local.sin_family = host->h_addrtype; local.sin_port = htons(localPort); bcopy(host->h_addr, &local.sin_addr, host->h_length); if(bind(skt, &local, sizeof(local))) { printf("Bind error ... restart\n"); exit(1); } . . . sendto(s, outBuf, strlen(outBuf), 0, remote, sizeof(remote)); if((len = recv(s, inBuf, BUFLEN, 0)) > 0) {. . .}

  37. TCP • Connected (or virtual circuit) protocol • Interface allows programmer to read/write a byte stream over the network • Byte stream is mapped into a series of packets • Reliable delivery • Each packet must be acknowledged • Effectively 2 packets per transmission • Must open/close a connection before use

  38. Using TCP -- Client skt = socket(AF_INET, SOCK_STREAM, 0); host = gethostbyname(serverHostName); bzero(&listener, sizeof(listener)); listener.sin_family = host->h_addrtype; listener.sin_port = htons(port); bcopy(host->h_addr, &listener.sin_addr, host->h_length); if(connect(skt, &listener, sizeof(listener))) { printf("Connect error ... restart\n"); printf("(Must start Server end first)\n"); exit(1); }; . . . write(s, outBuf, BUFLEN); if((len = read(s, inBuf, BUFLEN)) > 0) {. . .}

  39. Using TCP -- Server skt = socket(AF_INET, SOCK_STREAM, 0); /* Produce an inet address */ host = gethostbyname(serverHostName); bzero(&listener, sizeof(listener)); listener.sin_family = host->h_addrtype; listener.sin_port = htons(port); bcopy(host->h_addr, &listener.sin_addr, host->h_length); if(bind(skt, &listener, sizeof(listener))) { printf("Bind error ... restart\n"); exit(1); } listen(skt, BACKLOG); /* Listen for a request */ newSkt = accept(skt, &client, &clientLen); if (fork() == 0) { close(skt); /* Child doesn't need listener socket */ . . . } close(newSkt); /* Parent doesn't need the new socket */ if((len = read(s, inBuf, BUFLEN)) > 0) { . . .} write(s, outBuf, BUFLEN);

  40. ISO OSI Model Presentation Presentation Session Session Transport Transport Network Network Data Link Data Link Physical Physical Examples • Physical/Data Link layer networks: Ethernet, Token Ring, ATM • Network layer net: The Internet • Transport layer net: TCP-based network • Presentation/Session layer net: http/html, RPC, PVM, MPI

  41. ISO OSI Model Application Application Presentation Presentation Session Session Transport Transport Network Network Data Link Data Link Physical Physical Examples • Physical/Data Link layer networks: Ethernet, Token Ring, ATM • Network layer net: The Internet • Transport layer net: TCP-based network • Presentation/Session layer net: http/html, RPC, PVM, MPI • Applications, e.g., WWW, window system, numerical algorithm

  42. Client-Server Paradigm • Making a connection in TCP is an example of the client-server paradigm for distributed computing • Active component is the client • Runs autonomously • Decides when it wants to use server • Passive component is the server • Persistent • Always waiting for a client to request service • Not a machine -- just software

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