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CSS490 Message Passing Textbook Ch2 - 3

CSS490 Message Passing Textbook Ch2 - 3. Instructor: Munehiro Fukuda These slides were compiled from the course textbook, the reference books, and the instructor’s original materials. OSI 7 Layers. Site A. Site B. Application protocol. 7. Application. rsh, ftp, Telnet. Application.

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CSS490 Message Passing Textbook Ch2 - 3

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  1. CSS490 Message Passing Textbook Ch2 - 3 Instructor: Munehiro Fukuda These slides were compiled from the course textbook, the reference books, and the instructor’s original materials. CSS490 Message Passing

  2. OSI 7 Layers Site A Site B Application protocol 7 Application rsh, ftp, Telnet Application Presentation protocol Presentation 6 Dealing with heterogeneity And cryptography Presentation Session protocol 5 Session Dialog control (rarely supported) Session Transport protocol Transport 4 UDP, TCP Transport Network protocol Network Network 3 IP Data link protocol IEEE802.2 connection or connectionless Data link Data link 2 Ethernet Physical protocol Physical 1 Physical Network CSS490 Message Passing

  3. Physical/Data Link LayerExample: CSMA/CD and Token Ring • IEEE802.3: CSMA/CD (Carrier sense multiple access with collision detection) • Listening to the shared medium • Transmitting a data packet • Detecting collision on the medium • Deferring and retransmitting a packet in 2k–time base collision window • IEEE802.5: Token Ring • Receiving a free token from my (left) neighbor • Attaching a data packet to the token • Forwarding the token to my (right) neighbor • Detaching a packet from the token if it is addressed here 1 listen 3. detect 2 transmit Ⅹ 1. Free token 2. Attach 4. Detach 3. busy token CSS490 Message Passing

  4. Class A Octet 2 – 4 (1,677,716) Octet 1 0-127 0 Net # Host # Net # Host # 1 0 S S D D L L 1 1 0 Net # Host# Class B IP packet ID and size IP packet ID and size Destination IP address Destination IP address Octet 1 128-191 Octet 3 – 4 (65,536) Octet 2 Source IP address Source IP address Class C Octet 4 (256) Octet 1 128-191 Octet 2 – 3 Network LayerExample: IP Transportation layer Datagram fragmentation reassembly Data link layer Best-effort deliver semantics Class D: for broadcasting CSS490 Message Passing

  5. Transport Layer:Example1: UDP • User Datagram Protocol • Connectionless • May be lost • No FIFO order • Multicast feature • Unix datagram • Example: TFTP, rwho client server socket() socket() Create a sock descriptor bind() bind() Bind it to an IP address recvfrom() sendto() Blocks until data received sendto() recvfrom() CSS490 Message Passing

  6. Transport Layer:Example2: TCP client server • Transport Control Protocol • Connection-oriented • Reliable • FIFO order • No Multicast feature • Unix stream socket • Example: ftp, http, rsh all major applications socket() socket() Create a sock descriptor bind() Bind it to an IP address liseten() Declare this is connection-oriented accept() Wait for a connection Connection established connect() Blocks until connection established read() write() read() wrte() CSS490 Message Passing

  7. Application LayerExample: RSH Client Server inetd shell TCP connection request Command rsh ls- l rshd shell TCP connection Inherited all the way To a child Command ls -l CSS490 Message Passing

  8. Socket Programming: Socket.h #include <iostream> extern "C" { #include <sys/types.h> // for sockets #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <netdb.h> // for gethostbyname( ) #include <unistd.h> // for close( ) #include <string.h> // for bzero( ) } #define NULL_FD -1 #define MAXSIZE 20 class Socket { public: Socket( int ); ~Socket( ); int getClientSocket( char[] ); int getServerSocket( ); private: int port; int clientFd; int serverFd; }; CSS490 Message Passing

  9. Socket Programming: Socket.cpp (Client) // Fill in the structure "sendSockAddr" with the server address. sockaddr_in sendSockAddr; bzero( (char*)&sendSockAddr, sizeof( sendSockAddr ) ); sendSockAddr.sin_family = AF_INET; //Address Family Internet sendSockAddr.sin_addr.s_addr = inet_addr( inet_ntoa( *(struct in_addr*)*host->h_addr_list ) ); sendSockAddr.sin_port = htons( port ); // Open a TCP socket (an Internet strem socket). if( ( clientFd = socket( AF_INET, SOCK_STREAM, 0 ) ) < 0 ) { cerr << "Cannot open a client TCP socket." << endl; return NULL_FD; } // Connect to the server. while ( connect( clientFd, (sockaddr*)&sendSockAddr, sizeof( sendSockAddr ) ) < 0 ); // Connected return clientFd; } #include "Socket.h" Socket::Socket( int port ) : port( port ), clientFd( NULL_FD ), serverFd( NULL_FD ) { } Socket::~Socket( ) { if ( clientFd != NULL_FD ) close( clientFd ); if ( serverFd != NULL_FD ) close( serverFd ); } int Socket::getClientSocket( char ipName[] ) { // Get the host entry corresponding to ipName struct hostent* host = gethostbyname( ipName ); if( host == NULL ) { cerr << "Cannot find hostname." << endl; return NULL_FD; } CSS490 Message Passing

  10. Socket Programming: Socket.cpp (Server) int Socket::getServerSocket( ) { if ( serverFd == NULL_FD ) { // Server not ready sockaddr_in acceptSockAddr; // Open a TCP socket (an internet stream socket). if( ( serverFd = socket( AF_INET, SOCK_STREAM, 0 ) ) < 0 ) { cerr << "Cannot open a server TCP socket." << endl; return NULL_FD; } // Bind our local address so that the client can send to us bzero( (char*)&acceptSockAddr, sizeof( acceptSockAddr ) ); acceptSockAddr.sin_family = AF_INET; // Address Family Internet acceptSockAddr.sin_addr.s_addr = htonl( INADDR_ANY ); acceptSockAddr.sin_port = htons( port ); if( bind( serverFd, (sockaddr*)&acceptSockAddr, sizeof( acceptSockAddr ) ) < 0 ) { cerr << "Cannot bind the local address to the server socket." << endl; return NULL_FD; } listen( serverFd, 5 ); } // Read to accept new requests int newFd = NULL_FD; sockaddr_in newSockAddr; socklen_t newSockAddrSize = sizeof( newSockAddr ); if( ( newFd = accept( serverFd, (sockaddr*)&newSockAddr, &newSockAddrSize ) ) < 0 ) { cerr << "Cannot accept from another host." << endl; return NULL_FD; } return newFd; } CSS490 Message Passing

  11. Socket Programming: Main #include "Socket.h" #define PORT 10000 // You are given a specific pot from the instructor int main( int argc, char *argv[] ) { Socket sock( PORT ); int fd; if ( argc == 1 ) { // I'm a server while ( true ) { if ( ( fd = sock.getServerSocket( ) ) == NULL_FD ) return -1; char recvMessage[MAXSIZE]; read( fd, recvMessage, MAXSIZE ); cout << recvMessage << endl; close( fd ); } } if ( argc == 2 ) { // I'm a client if ( ( fd = sock.getClientSocket( argv[1] ) ) == NULL_FD ) return -1; char sendMessage[MAXSIZE]; cin >> sendMessage; write( fd, sendMessage, MAXSIZE ); } return 0; } CSS490 Message Passing

  12. Blocking/Non-Blocking Communication • Blocking communication • TCP, UDP, and other communication packages • Client: blocked only when the destination buffer is full • Server: blocked if no message has arrived from the client. • Rendezvous • Client: blocked for a server to receive a message • Server: blocked if no message has arrived from the client. • Non-blocking communication • Server does not want to be blocked when • It may receive a message from a different client. • It has another jobs to be done such as computation or message transmission. • Some synchronization is necessary later. CSS490 Message Passing

  13. Synchronization in Non-Blocking Communication • Polling • Periodically check if a socket is ready to read data: • Example: • sd = socket( AF_INET, SOCKET_STREAM, 0); • set_fl(sd, O_NONBLOCK); // set the socket as non-blocking • struct pollfd pfd; • pfd.fd = sd; • poll( &pfd, 1, timeout ) // poll the socket status • Interrupt • Notified from the system when a socket is ready to read data; • Example: • sd = socket(AF_INET, SOCKET_STREAM, 0); • signal(SIGIO, sigio_func); // set a future interrupt to call sigio_func( ) • fcntl(sd, F_SETOWN, getpid( )); // ask OS to deliver this fd interrupt to me • fcntl(sd, F_SETFL, FASYNC); // set this fd asynchronous • int sigio_func( ) { // invoked upon an interrupt } CSS490 Message Passing

  14. Buffering • No Buffering • A message remains on the sender until the receiver issues receive( ). • Rendezvous • Performance drawback • Single Message Buffer • The sender can send at most one message even if the receiver has not issued receive( ). • Stop-and-wait protocol • A message can be kept read in advance. • What if the sender has multiple messages? • Finite-Bound Buffer • Unsuccessful communication - Go-Back-N Technique • Flow-controlled communication - sliding window in TCP • Socket: capable of changing its buffer size with setsockopt( ) message message message message message message CSS490 Message Passing

  15. Process Addressing • Explicit address • machine id + local id • Example: TCP/IP and UDP/IP use IP + port • Demerit: No process migration allowed • machine id + local id + the last machine id • Process migration allowed • Messages forwarded along links to the final destination • Receiver informing sender of its last machine id • Sender using this info from the following messages • Implicit addressing • System-wide id (function name) • Example: RPC • Name server required CSS490 Message Passing

  16. server client client server request request request 2 ack timeout response timeout response response 2 request request ack ack response request 2 timeout Failure Handling • Loss of request message • Loss of response message • Unsuccessful execution of request • Do we really need acknowledgment messages? CSS490 Message Passing

  17. Idempotency server client server client • A pair of request and response is enough to handle faults • Idempotency assumed: • At-least one semantics • Last-one semantics request Timeout request request 2 Timeout response request 3 Timeout response request 4 reesponse 2 CSS490 Message Passing

  18. Exactly-One Semantics • What if errors in the banking system • New semantics required: • Exactly-one semantics • Server must keep track of the request sequence Withdraw $100 Withdraw995 $100 $1000-$100 = $900 $1000-$100 = $900 for Trans995 Not received Not received Withdraw $100 Withdraw995 $100 Trans995 completed No subtraction $900-$100 =$800! $100 received $100 received CSS490 Message Passing

  19. Exercises (No turn-in) • Why do we need layered network protocols? • When implementing TCP with datagram, what do we have to take care of? • Consider the pros and cons of polling and interrupt in non-blocking communication. • Consider an example inducing an accidental system hang-up (named a deadlock) in no-buffering communication. • Which of the following operations are idempotent? • cin >> data; • ifstream infile(“input.txt”); infile.seek( ); • cout << data; • int a = 1, b = 2, c; c = a + b; • int c = 1; c++; CSS490 Message Passing

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