Process Process Process Layer CSCE 515: Computer Network TCP UDP Transport Layer Programming ------ Sockets ICMP, ARP & IP Network Layer Wenyuan Xu RARP Department of Computer Science and Engineering University of South Carolina 802.3 Data-Link Layer 9/8/2008 CSCE515 – Computer Network Programming Network API Network API API - Application Programming Interface API is a set of functionality/services delivered by a Internet OSI model Application programming system. protocol suite details Application User processor Presentation Application Network API Session The services ( often provided by the operating system) Transport TCP UDP that provide the interface between application and Network IPv4, IPv6 protocol software. Data link Data link kernel Physical Physical Communications details 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Network API wish list TCP/IP Generic Programming Interface. TCP/IP does not include an API definition. Support multiple communication protocol suites (families). Address (endpoint) representation independence. There are a variety of APIs for use with Provide special services for Client and Server? TCP/IP: Sockets by Berkeley Support for message oriented and connection XTI (X/Open Transport Interface) by AT&T oriented communication. Winsock - Windows Sockets API by Microsoft Work with existing I/O services (when this MacTCP / Open Transport by Apple makes sense). Operating System independence 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Client-Server Model Functions needed: Client 1 Specify local and remote communication Server Client 2 endpoints Initiate a connection Client 3 Wait for incoming connection One side of communication is client, and the other side Send and receive data is server Terminate a connection gracefully Server waits for a client request to arrive Server processes the client request and sends the Error handling response back to the client Iterative or concurrent 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Berkeley Sockets Elements of a Socket A socket is an abstract representation of a Each socket can be uniquely identified by communication endpoint. Source IP address Generic: Source port number support for multiple protocol families. address representation independence Destination IP address Destination port number Sockets (obviously) have special needs: An end-to-end protocol (TCP or UDP) establishing a connection specifying communication endpoint addresses Sockets work with Unix I/O services just like files, pipes & FIFOs 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Types of Sockets Stream Sockets Two different types of sockets Also known as connection-oriented socket Stream sockets Use TCP Datagram sockets Provide reliable, connected networking service Error free; no out-of-order packets Applications: telnet, ssh, http 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Datagram Sockets Unix Descriptor Table Also known as connectionless socket Descriptor Table Use UDP Data structure for file 0 Provide unreliable, best-effort networking 0 service 1 Data structure for file 1 Packets may be lost; may arrive out of 2 order 3 Data structure for file 2 Applications: streaming audio/video 4 int fd; int cc, nbytes; char *buf; fd = open (my_filename, O_RDONLY ); cc = write (fd, buf, nbytes); cc = read (fd, buf, nbytes); 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Socket Descriptor Data Structure Client-Server Model Server Descriptor Table Create a socket with the socket() system call Family: PF_INET 0 Family: PF_INET Bind the socket to an address using the bind() system Service:Service: SOCK_STREAMSOCK_STREAM call. For a server socket on the Internet, an address 1 LocalLocal IP:IP: 111.22.3.4111.22.3.4 consists of a port number on the host machine. RemoteRemote IP:IP: 123.45.6.78123.45.6.78 2 Listen for connections with the listen() system call LocalLocal Port:Port: 22492249 3 RemoteRemote Port:Port: 37263726 Accept a connection with the accept() system call. This call typically blocks until a client connects with 4 the server. int s, family, type, protocol; Send and receive data s = socket(family, type, protocol); etc... cc = read(s, buf, nbytes); 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Client-Server Model Creating a Socket Client int socket(int family,int type,int proto); Create a socket with the socket() system call specifies the protocol family Connect the socket to the address of the family AF_INET: IPv4 protocols server using the connect() system call AF_INET6: IPv6 protocols AF_ROUTE: Routing sockets Send and receive data. There are a number type specifies the type of service SOCK_STREAM of ways to do this, but the simplest is to use SOCK_DGRAM the read() and write() system calls. SOCK_RAW protocol specifies the specific protocol (usually 0, which means the default). IPPROTO_TCP: TCP transport protocol IPPROTO_UDP: UDP transport protocol 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming socket() Specifying an Endpoint Address The socket() system call returns a Remember that the sockets API is generic socket descriptor (small integer) or -1 on error. There must be a generic way to specify endpoint addresses. socket() allocates resources needed for TCP/IP requires an IP address and a port a communication endpoint - but it does not number for each endpoint address. deal with endpoint addressing. 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Necessary Background Information: bind() POSIX data types calling bind() assigns the address specified by the sockaddr structure to the int8_t signed 8bit int socket descriptor. uint8_t unsigned 8 bit int int16_t signed 16 bit int bind( mysock, (struct sockaddr*) &myaddr, uint16_t unsigned 16 bit int sizeof(myaddr) ); int32_t signed 32 bit int uint32_t unsigned 32 bit int 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming More POSIX data types Generic socket addresses el rn ke y sa_family_t address family struct sockaddr { b ed s socklen_t length of struct uint8_t sa_len; U in_addr_t IPv4 address sa_family_t sa_family; char sa_data[14]; in_port_t IP port number }; sa_family specifies the address type. sa_data specifies the address value. 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming sockaddr AF_CSCE515 An address that will allow me to use sockets Initializing a sockaddr structure to point to communicate with you. to Henry : address type AF_CSCE515 address values: struct sockaddr henry; Dean 1 Sayan 6 Devon 2 Yuliya 7 henry.sa_family = AF_CSCE515; Samuel 3 Razvan 8 henry.sa_data[0] = 5; Shamik 4 Mythri 9 Henry 5 Femitolu 10 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming AF_INET struct sockaddr_in (IPv4) For AF_CSCE515 we only needed 1 byte struct sockaddr_in { to specify the address. uint8_t sin_len; sa_family_t sin_family; in_port_t sin_port; For AF_INET we need: ly! on struct in_addr sin_addr; 16 bit port number v4 IP char sin_zero[8]; 32 bit IP address }; A special kind of sockaddr structure 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming struct in_addr Byte Ordering struct in_addr { Different computer architectures use in_addr_t s_addr; different byte ordering to represent }; multibyte values. 16 bit integer: in_addr just provides a name for the ‘C’ type associated with IP addresses. Low Byte Address A High Byte High Byte Address A+1 Low Byte 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Byte Ordering Byte Order and Networking Little-Endian Big-Endian Suppose a Big Endian machine sends a Low Byte High Byte High Byte Low Byte 16 bit integer with the value 2: Addr A Addr A+1 Addr A Addr A+1 0000000000000010 IBM 80x86 IBM 370 A Little Endian machine will think it got DEC VAX Motorola 68000 the number 512: DEC PDP-11 Sun 0000001000000000 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Network Byte Order Network Byte Order All values stored in a sockaddr_in must Conversion of application-level data is be in network byte order. left up to the presentation layer. sin_port a TCP/IP port number. But hold on !!! How do lower level layers sin_addr an IP address. communicate if they all represent values differently ? (data length fields in headers) A fixed byte order is used (called network byte order) for all control data. 9/8/2008 CSCE515 – Computer Network Programming 9/8/2008 CSCE515 – Computer Network Programming Network Byte Order Functions TCP/IP Addresses We don’t need to deal with sockaddr ‘h’ : host byte order ‘n’ : network byte order structures since we will only deal with a real protocol family. ‘s’ : short (16bit) ‘l’ : long (32bit) We can use structures. uint16_t htons(uint16_t); sockaddr_in uint16_t ntohs(uint_16_t); BUT: The C functions that make up the sockets uint32_t htonl(uint32_t); API expect structures of type sockaddr. uint32_t ntohl(uint32_t); int bind(int sockfd, struct sockaddr *my_addr, int addrlen); int connect(int sockfd,