intro(6) TCP/IP 5.4R3.00 intro(6)
NAME
intro - Communications Protocols introduction to networking
facilities
SYNOPSIS
#include <netinet/tcp.h>
#include <netinet/udp.h>
#include <netinet/ip.h.
#include <netinet/ipicmp.h>
#include <net/if.h>
DESCRIPTION
This section briefly describes the DG/UX system networking
facilities. Documentation in this section covers three areas: the
Internet protocol family, the available protocols, and the network
interfaces. The Internet protocol family is described on the
inet(6F) manual page, whereas entries describing the protocols are on
manual pages marked 6P. Network interfaces are described on manual
pages marked 7.
The Internet family includes the Transmission Control Protocol (TCP),
User Datagram Protocol (UDP), Internet Protocol (IP), and Internet
Control Message Protocol (ICMP). These protocols are communications
facilities implemented in the DG/UX system kernel that transfer
information from user programs to the network and back. Programmers
writing user-level programs can access TCP, IP, and UDP with the
socket(2) family of system calls and the Transport Layer Interface
(TLI) library routines.
The Transmission Control Protocol (TCP) fits into the layered
networking architecture just above IP. Application programs, such as
remote terminal agents and file transfer agents, usually run on top
of TCP, using its services.
TCP assures reliable end-to-end delivery of a data byte stream. TCP
deals with user data copied to the protocol's buffers. It packages
the data into segments and passes this information to IP, which then
breaks the information into packets that can be easily transmitted
across the network. IP then determines the next hop on a path
through the network for the packet being transmitted and transfers
the packet to the first host on the path. A gateway host would
receive the packet and route it to the destination host. When
packets arrive at the destination host, TCP reconstructs the entire
message, checking to ensure that the data is complete and correctly
ordered before sending it to application programs. If there is a
problem, TCP requests that the message be retransmitted.
Like TCP, the User Datagram Protocol (UDP) fits into the layered
networking architecture just above IP. It provides procedures for
application programs to send messages to other programs with a
minimum of protocol mechanism. UDP is a simple datagram protocol.
Unlike TCP, it neither guarantees reliable delivery nor does it
provide protection from duplicate messages.
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intro(6) TCP/IP 5.4R3.00 intro(6)
The Internet Protocol (IP) is primarily concerned with getting a
datagram to the next host on the route to the datagram's final
destination. A datagram is a self contained package of data carrying
sufficient information for hosts to deliver it to its destination.
Since host availability changes, the packets that make up a complete
message may have different routes and may end up at the destination
out of their original order. The TCP layer is responsible for re-
ordering the packets correctly. Some packets may be lost or garbled
in transmission. IP frequently notifies higher level protocols when
packets are lost or damaged, but sometimes does not.
The Internet Control Message Protocol (ICMP) is used to report errors
in datagram processing. ICMP is an integral part of IP and must be
implemented by every IP module. ICMP messages are sent to report
problems in the communication environment, not to make IP a reliable
protocol.
Addressing
Associated with each protocol family is an address format. The
following address formats are used by the system:
#define AFUNIX 1 /* local to host (pipes) */
#define AFINET 2 /* internetwork: UDP, TCP, etc. */
Interfaces
Each network interface in a system corresponds to a path through
which messages may be sent and received. A network interface usually
has a hardware device associated with it, though certain interfaces
such as the loopback interface, loop(7), do not.
The following ioctl calls may be used to manipulate network
interfaces. See Programming with TCP/IP on the DG/UX (Trademark)
System for details.
SIOCSIFADDR
Set interface address. Following the address assignment, the
"initialization" routine for the interface is called.
SIOCGIFADDR
Get interface address.
SIOCSIFBRDADDR
Set interface broadcast address. This address is used to send
IP broadcast packets on broadcast capable interfaces.
SIOCGIFBRDADDR
Get interface broadcast address.
SIOCSIFDSTADDR
Set the destination address for point-to-point network
interfaces.
SIOCGIFDSTADDR
Get interface destination address.
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intro(6) TCP/IP 5.4R3.00 intro(6)
SIOCSIFMETRIC
Set the interface routing metric. This information is used by
routing applications.
SIOCGIFMETRIC
Get the interface routing metric.
SIOCSIFNETMASK
Set the interface subnetwork mask.
SIOCGIFNETMASK
Get the interface subnetwork mask.
SIOCSIFFLAGS
Set interface flags field. If the interface is marked as
down, any processes currently routing packets through the
interface are notified.
SIOCGIFFLAGS
Get interface flags.
SIOCGIFCONF
Get interface configuration list.
SEE ALSO
ioctl(2), socket(2), Programming with TCP/IP on the DG/UX System.
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