TCP/IP Configuration and Management Manual

NonStop TCP/IP Processes and Protocols
TCP/IP Configuration and Management Manual—427132-004
B-21
User Datagram Protocol (UDP)
TCP and UDP allow IP to run several simultaneous sessions with a given host. Multiple
sessions are accommodated by specifying a port number, which identifies the
communication path, along with the Internet address. Each end of the communications
path is assigned a port number for that session.
Applications using TCP and UDP perform addressing by specifying a unique
combination of a destination Internet address, destination port number, source Internet
address, and source port number. In TCP, this combination uniquely identifies a
connection and is part of every TCP packet that goes over the Internet.
Generally, at least one end of the conversation asks for a port number that is
guaranteed to be unique. The client program normally requests a port number,
because the server typically uses a well-known port.
User Datagram Protocol (UDP)
The User Datagram Protocol (UDP) provides unreliable datagram service. The integrity
of the packets sent is maintained; when a packet is received, it is guaranteed to exactly
match what was sent. However, the delivery of packets is not guaranteed, and there is
no guarantee of the order in which datagrams are received.
A datagram is designed for connectionless protocols such as IP. A connection is not
established before the message is sent; thus, each datagram includes the address of
the destination host, as well as the source.
As for TCP, (described in Transmission Control Protocol (TCP)
on page B-20),
application processes call a socket routine to request the NonStop TCP/IP software to
create a UDP socket when needed; the application specifies the type of service
desired. The TCP and UDP protocols assume that the Internet Protocol (IP) is used for
network layer services. Like IP, UDP is a connectionless protocol; it uses datagrams.
TCP, on the other hand, is a connection-oriented protocol, requiring a connection to be
established before messages are sent.
TCP messages specify the connection with which they are associated. For UDP, the
same combination of addresses and numbers described for TCP identifies a temporary
source and destination, rather than a connection. This combination is a part of every
UDP packet that goes over the Internet.
For a detailed description of the socket library routines available, refer to the
TCP/IP
Programming Manual. For more detailed technical information on the UDP, refer to
RFC 768 (
DDN Protocol Handbook, Volume 2, DDN Network Information Center,
December, 1985, pp. 2-175 through 2-178). Also, refer to the book
TCP/IP Illustrated
by W. Richard Stevens, Prentice Hall, 1994.
Internet Protocol (IP)
The Internet Protocol (IP) accommodates the connectionless delivery of Internet
datagrams between heterogeneous networks. The IP also services various host-to-
host protocols. The IP provides many capabilities at the network level, and forms the
foundation of the NonStop TCP/IP product. The TCP and UDP protocols use the IP