Socket Addresses

Domains Internet domains –familiar with these Unix domains –for processes communicating on the same hosts –not sure of widespread use –used to debug internally

Protocol families SNA - IBM Systems Network Architecture UUCP - Unix to Unix copy XNS - Xerox Network System NETBIOS - IBM Basic I/O system TCP/IP ( PF_INET ) UNIX ( PF_UNIX )

Constants for addresses PF_UNIX1 PF_INET2 PF_NS6 (xns) PF_SNA11 PF_DECnet12 PF_APPLETALK16 PF_X2520 …...

Address Formation All Protocols do not agree Socket Abstraction TCP/IP IP Address Protocol Port Unix socket Other Protocols Address format may be different Built to support multiple protocols

Address Families Socket abstraction has a series of address families so that each family can have it’s own format for endpoint addresses. TCP/IP has address family named AF_INET TCP/IP also has a protocol family : PF_INET Both have numeric value 2 which leads to further confusion.. They can be switched at will with no apparent consequence.

Generic Address (address family, endpoint address in family) socket API defines one to use as a general address, but it won’t work for everything Works for TCP/IP not Unix struct sockaddr { u_short sa_family; char sa_data[14]; }; E.g. Unix sockets (internal) use a named pipe for the endpoint and the length of it is comparable to a path/file name (much longer)

What TCP/IP uses for an address 2 byte address family (AF_INET) 2 byte port number 4 byte IP address 8 bytes unused struct sock_addr_in{ u_short sin_family; u_short sin_port; struct in_addr sin_addr; char sin_zero[8] } TCP/IP apps need not use sockaddr Use sockaddr_in

Procedures in API

socket () Purpose: create a socket for communications Returns: descriptor for a new socket Arguments: –protocol family PF_INET –type of service stream (TCP) datagram (UDP)

connect() Purpose: establish the connection Returns: success/failure Arguments: –remote endpoint

send() Purpose: send data through to other end Returns: success/failure Arguments: –socket descriptor –address –length of data –control directives

recv() Purpose: get response Returns: message received Arguments: –socket descriptor –address of buffer –length of buffer –control bits NOTE - recv is limited to buffer space and will cut off if necessary. Must go back

recv() (UDP) Works similarly If too much data: – truncated at the size of the receive buffer –discard remainder –return error condition

closesocket() Purpose: give socket resource back to OS if shared with other processes, reference count decremented (until 0). Returns: message received Arguments: –socket descriptor –address of buffer –length of buffer –control bits

bind() Purpose: specify local endpoint address Returns: message received Arguments: –socket descriptor –endpoint address ( sockaddr_in for TCP/IP) IP address port

listen() Purpose: put socket in passive mode and specify size of queue for incoming requests Returns: success/fail Arguments: –socket descriptor –size of queue

accept() Purpose: wait for next incoming request Returns: new socket for interaction Arguments: –socket descriptor

Windows client-server usage CLIENT WSAStartup socket connect send recv closesocket WSACleanUP SERVER WSAStartup socket bind listen accept recv send closesocket WSACleanup