Introduction to Unix Network ProgrammingHow do we Communicate?What does Alice do?What does Bob do?What about sending a TCP/IP packet?Direction and PrinciplesSocketsNetwork Programming with SocketsClient-Server ModelClient-Server Communication ModelPowerPoint PresentationSlide 12TCP ConnectionsTCP ServiceUDP ServicesSlide 16AddressesAddresses and DataAddress Access/Conversion FunctionsStructure: hostentChoose portByte OrderingByte Ordering FunctionsSocket addressSocket Address StructureConnecting the socketServerAddress specificationbindListenAcceptTCP Connection ExampleUDP Connection ExampleFunctions: sendtoFunctions: recvfromTCP and UDP PortsReviewConcurrent Server FlowchartFork Concurrent ServerFork callThreaded serverPosix Threads (pthreads)pthreads AttributesSlide 44pthread Error Handlingpthread Creationpthread CleanupSlide 48pthreads vs. forkMultithreading-Safe FunctionsExample: getpwuidgetpwuid_rAnnouncementsIntroduction to Unix Network ProgrammingReference: Stevens Unix Network Programming8/29/07 UIUC - CS/ECE 438, Fall 2007 2How do we Communicate?Send a mail from Alice to BobAlice in Champaign, Bob in HollywoodExample:US Postal ServiceBobChampaign, IllinoisHollywood, CaliforniaAlice8/29/07 UIUC - CS/ECE 438, Fall 2007 3What does Alice do?Bob’s address (to a mailbox)Bob’s name – in case people share mailboxPostage – have to pay!Alice’s own name and address – in case Bob wants to return a messageBob100 Santa Monica Blvd.Hollywood, CA 90028Alice200 Cornfield Rd.Champaign, IL 618208/29/07 UIUC - CS/ECE 438, Fall 2007 4What does Bob do?Install a mailboxReceive the mailGet rid of envelopeRead the messageBob100 Santa Monica Blvd.Hollywood, CA 90028Alice200 Cornfield Rd.Champaign, IL 618208/29/07 UIUC - CS/ECE 438, Fall 2007 5What about sending a TCP/IP packet?Very similar to Alice-mailing-to-BobDifferent terminologies – very confusingWe have to rememberDifferent technologiesSuppose to be better (faster, more reliable, cheaper, …)8/29/07 UIUC - CS/ECE 438, Fall 2007 6Direction and PrinciplesPhysicalTransportData LinkNetworkProgramminglearn to use Internet for communication (with focus on implementation of networking concepts)Principles and Conceptslearn to build network from ground up8/29/07 UIUC - CS/ECE 438, Fall 2007 7SocketsprocessTCP withbuffers,variablessockethost orserverprocessTCP withbuffers,variablessockethost orserverInternetcontrolled byapp developerprocess sends/receives messages to/from its socketsocket analogous to mailboxsending process relies on transport infrastructure which brings message to socket at receiving process8/29/07 UIUC - CS/ECE 438, Fall 2007 8Network Programming with SocketsReading: Stevens 2nd or 3rd ed., Ch. 1-6 or 1st ed., Ch. 1-3, 6Sockets API: A transport layer service interfaceIntroduced in 1981 by BSD 4.1Implemented as library and/or system callsSimilar interfaces to TCP and UDPCan also serve as interface to IP (for super-user); known as “raw sockets”8/29/07 UIUC - CS/ECE 438, Fall 2007 9Client-Server ModelAsymmetric CommunicationClient sends requestsServer sends repliesServer/DaemonWell-known name (e.g., IP address + port)Waits for contactProcesses requests, sends repliesClientInitiates contactWaits for responseClientServerClientClientClient8/29/07 UIUC - CS/ECE 438, Fall 2007 10Client-Server Communication ModelService ModelConcurrent:Server processes multiple clients’ requests simultaneouslySequential:Server processes only one client’s requests at a timeHybrid:Server maintains multiple connections, but processes responses sequentiallyClient and server categories are not disjointA server can be a client of another serverA server can be a client of its own client8/29/07 UIUC - CS/ECE 438, Fall 2007 11int main(int argc, char **argv) { int sockfd = socket(PF_INET, SOCK_STREAM, 0); struct hostent * he = gethostbyname(argv[1]); struct sockaddr_in their_addr; their_addr.sin_addr = *((struct in_addr *)he->h_addr); their_addr.sin_port = htons(atoi(argv[2])); their_addr.sin_family = AF_INET; memset(their_addr.sin_zero, ‘\0’, sizeof their_addr.sin_zero); connect(sockfd, (struct sockaddr *) their_addr, sizeof their_addr); write(sockfd, “GET /\r\n”, strlen(“GET /\r\n”)); while (1) { char buf[100]; int len = read(sockfd, buf, 100); if (len <= 0) { close(sockfd);return 0; } else { write(1, buf, len); } }}8/29/07 UIUC - CS/ECE 438, Fall 2007 12Sockets int sockfd = socket(PF_INET, SOCK_STREAM, 0);Creates a new socketSOCK_STREAM = TCPSOCK_DGRAM = UDP8/29/07 UIUC - CS/ECE 438, Fall 2007 13TCP ConnectionsTransmission Control Protocol (TCP) ServiceOSI Transport LayerService ModelReliable byte stream (interpreted by application)16-bit port space allows multiple connections on a single hostConnection-orientedSet up connection before communicatingTear down connection when done8/29/07 UIUC - CS/ECE 438, Fall 2007 14TCP ServiceReliable Data TransferGuarantees delivery of all dataExactly once if no catastrophic failures Sequenced Data TransferGuarantees in-order delivery of dataIf A sends M1 followed by M2 to B, B never receives M2 before M1Regulated Data FlowMonitors network and adjusts transmission appropriatelyPrevents senders from wasting bandwidthReduces global congestion problemsData TransmissionFull-Duplex byte stream8/29/07 UIUC - CS/ECE 438, Fall 2007 15UDP ServicesUser Datagram Protocol ServiceOSI Transport LayerProvides a thin layer over IP16-bit port space (distinct from TCP ports) allows multiple recipients on a single host8/29/07 UIUC - CS/ECE 438, Fall 2007 16UDP ServicesUnit of TransferDatagram (variable length packet)UnreliableNo guaranteed deliveryDrops packets silentlyUnorderedNo guarantee of maintained order of deliveryUnlimited TransmissionNo flow control8/29/07 UIUC - CS/ECE 438, Fall 2007 17Addressesstruct hostent * he = gethostbyname(argv[1]);struct sockaddr_in their_addr; their_addr.sin_addr = *((struct in_addr *)he->h_addr);Look up destination host name8/29/07 UIUC - CS/ECE 438, Fall 2007 18Addresses and DataInternet domain namesHuman readableVariable lengthEx: sal.cs.uiuc.eduIP addressesEasily handled by routers/computersFixed lengthSomewhat geographicalEx: 128.174.252.2178/29/07 UIUC - CS/ECE 438, Fall
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