TCP/IPv6 Configuration and Management Manual (G06.24+)

NonStop TCP/IPv6 Protocols and Configuration Files
HP NonStop TCP/IPv6 Configuration and Management Manual—524523-008
D-2
Transmission Control Protocol (TCP)
Transmission Control Protocol (TCP)
The Transmission Control Protocol (TCP) is used by applications that require reliable
end-to-end data transfer. It is a stream-oriented protocol that has no concept of packet
boundaries. TCP guarantees that all data sent will be received and will arrive in the
same order in which it was sent.
The NonStop TCP/IPv6 process provides a socket interface to the Transmission
Control Protocol (TCP, RFC 793), which uses Guardian file-system procedures for
interprocess communication. TCP is a stream-oriented protocol with no concept of
record boundaries.
Application processes call a socket routine to request that the NonStop TCP/IPv6
software create a socket when needed; the application specifies the type of service.
Port Numbers
Both TCP and UDP use a 16-bit port number to select a socket on the host. Client
programs normally use more-or-less random port numbers; however, specific port
numbers (called well-known ports) are assigned for use by server programs. Each
well-known port is associated with a specific service. A client requesting a particular
service specifies as the destination port the well-known port associated with that
service. The server program listens at that port for requests. The well-known port
numbers are listed in TCP6MAN.
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.