Toshiba V Series User Manual page 109

(b) TCP socket interface (See Figure 6-3 and Figure 6-4.)
Client
Active open
6F8C0904
Source node
UDP socket
(only if implemented by the user
Figure 6-2 UDP Sockets
• In TCP communication, a pipe-like virtual communications line (connection)
is established between sockets on two nodes that are communicating (send-
ing and receiving), and since the protocol handles control of reception verifi-
cation and retransmission processing, it provides a highly reliable
communication.
• There are two methods for establishing a connection: passive open and
active open.
• In passive open, the local socket is put into a state in which it is waiting for a
request to establish a connection from another node. In active open, a
request is issued for the establishment of a connection with a socket in the
passive open state.
• When establishing a connection between two nodes, one node must first
open a socket in passive open mode, and the other node must perform an
active open on a local socket with respect to a remote socket that is in the
passive open state.
• Since the passive open socket node "provides" data transmission and other
services, it is called the "server."
• Since the active open socket node "requests" services, it is called the "client."
• A socket for which a connection has been established is unable to transfer
data with any other sockets unless that connection is first released.
• Since sockets are connected by connections, there is no need to specify the
transmission source or transmission destination with every data item trans-
mitted.
Source node
TCP socket
Figure 6-3 TCP Socket (Connection)
Data transmission
Reception verification
program)
Connection
Data transmission
Reception verification
6.1 Overview
Destination node
UDP socket
Destination node
TCP socket Server
Passive open
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