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intro(3n) intro(3n)

Name
intro - introduction to network library functions

Description
This section describes functions that are available for interprocess communication (IPC). IPC takes place using sockets. The system call
creates a communications channel based on domain, type, and protocol.

Sockets are created without names. The system call is used to connect a name to a socket.

A connection with another process must be made before data can be transferred on a bound socket. The system call is used to rendezvous
with another process. This process must be listening on a bound socket using the system call. This listening process can accept a connec-
tion request using the system call.

Once two processes have connected and accepted an IPC, data can be transferred with the following system calls: and

Connectionless sockets are also possible (a socket is bound and data can be transferred). They use the following system calls to transfer
data: and

IPC operates in three domains:

UNIX Local node

INTERNET Local area network (LAN)

DECNET DECnet network

These types of sockets are available for IPC:

stream Sequenced, reliable, unduplicated data
CONNECTED socket
record boundaries not preserved
all domains

datagram Not guaranteed to be sequenced, reliable, or
unduplicated
user protocol needed to give guarantees
UNCONNECTED socket
record boundaries preserved
UNIX and INTERNET domains

sequenced packet Like stream socket, except record boundaries preserved
DECNET domain only

raw Access to communications protocols

Internet Addresses Routines
The inet routines manipulate Internet addresses.

Network Data Base File Routines
Standard mapping routines are used to retrieve entries in network data base files. Several routines operating on each data base file are
identified by a group name:

Retrieves entries from

Specific routines perform particular operations on each data base file:

Reads the next line of the file; opens
the file, if necessary.

Opens and rewinds the file.

Closes the file.

Searches the file sequentially from the beginning
until a matching name is found, or EOF is encountered.

Searches the file sequentially from the beginning
until a matching address is found, or EOF is encountered.

Searches the file sequentially from the beginning
until a matching port number is found, or EOF is encountered.

Searches the file sequentially from the beginning
until a matching protocol number is found, or EOF is encountered.

Each network library routine returns a pointer to a structure reflecting individual fields of a line in one of the network data base files.
The structure for each data base file contains some of the fields in the following list, with the prefix x replaced by a different letter
in each file:

pointer to a network address,
returned in network-byte order

address family of the address being returned

alternate names

length of an address, in bytes

official name

network number, returned in machine-byte order

resident port

protocol number

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UDP(4)							   BSD Kernel Interfaces Manual 						    UDP(4)

NAME

     udp -- Internet User Datagram Protocol

SYNOPSIS

     #include <sys/socket.h>
     #include <netinet/in.h>

     int
     socket(AF_INET, SOCK_DGRAM, 0);

DESCRIPTION

     UDP is a simple, unreliable datagram protocol which is used to support the SOCK_DGRAM abstraction for the Internet protocol family.  UDP
     sockets are connectionless, and are normally used with the sendto and recvfrom calls, though the connect(2) or connectx(2) call may also be
     used to fix the destination for future packets (in which case the recv(2) or read(2) and send(2) or write(2) system calls may be used).

     UDP address formats are identical to those used by TCP.  In particular UDP provides a port identifier in addition to the normal Internet
     address format.  Note that the UDP port space is separate from the TCP port space (i.e. a UDP port may not be ``connected'' to a TCP port).
     In addition broadcast packets may be sent (assuming the underlying network supports this) by using a reserved ``broadcast address''; this
     address is network interface dependent.

     Options at the IP transport level may be used with UDP; see ip(4).

DIAGNOSTICS

     A socket operation may fail with one of the following errors returned:

     [EISCONN]	      when trying to establish a connection on a socket which already has one, or when trying to send a datagram with the destina-
		      tion address specified and the socket is already connected;

     [ENOTCONN]       when trying to send a datagram, but no destination address is specified, and the socket hasn't been connected;

     [ENOBUFS]	      when the system runs out of memory for an internal data structure;

     [EADDRINUSE]     when an attempt is made to create a socket with a port which has already been allocated;

     [EADDRNOTAVAIL]  when an attempt is made to create a socket with a network address for which no network interface exists.

SEE ALSO

     connect(2), connectx(2), getsockopt(2), recv(2), send(2), socket(2), inet(4), intro(4), ip(4)

HISTORY

     The udp protocol appeared in 4.2BSD.

4.2 Berkeley Distribution					  March 18, 2015					 4.2 Berkeley Distribution

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