NetIPC 3000/XL Programmer's Reference Manual (5958-8600)

Table Of Contents

18 Chapter1

NetIPC Fundamentals

NetIPC Concepts

The following paragraphs describe the concept of sockets, and the

NetIPC terms used to describe a NetIPC connection.

Sockets

NetIPC uses a data structure called a socket to create a connection to a

NetIPC process on another system. Even though this process may

reside upon the same node, the process that receives the NetIPC call is

known as a remote system. The NetIPC calls are used to establish

connections and manipulate sockets so that data can be exchanged with

other processes. The Transmission Control Protocol (Transport Layer)

(TCP) regulates the transmission of data to and from these data

structures. When direct access to level 3 (X.25) is used, the X.25

protocol regulates the transmission of data between sockets. Although

data must pass through the control of lower-level protocols, these

details are transparent to NetIPC processes when they send and

receive data.

Connections

Before a connection can be established between two NetIPC processes,

each process must create a call socket. A call socket is a type of socket

that is roughly analogous to a telephone handset with multiple buttons

or extensions. NetIPC processes engage in a three-way handshake over

the connection formed by their respective call sockets in order to create

a virtual circuit (VC) socket at each process. A call socket can be

thought of as one of the steps needed to build a VC socket.The VC

sockets created by this dialogue are the endpoints of a new connection

called a virtual circuit or virtual circuit connection. A call socket

is analogous to a telephone with multiple extensions, and a VC socket is

analogous to one of the telephone extensions as shown in Figure 1-1.

Figure 1-1 Telephone Analogy

VC VC VC VCVC VC VC VC

SOCKETS

VIRTUAL CIRCUIT

CALL SOCKET