The Internet Phenomenon - Secure Java: For Web Application Development - page 7

Unlike the client/server environment, distributed architectures were designed to accommodate a
large number of systems in the network. he OS on these systems provided basic services such as
resource sharing, printing, terminal, and ile transfer. System network architecture (SNA) from
IBM, distributed network architecture (DNA) from DEC, and so on, are some examples of dis-
tributed architectures.
Although the architecture proposed by individual vendors worked ine in isolation, it had
serious issues when the enterprises needed to integrate two or more such networks. It was very
important for the enterprises that these networks communicate properly as most of the enterprises
had deployed applications on systems from multiple vendors. his led to the movement toward
open systems and saw the emergence of communication protocols such as transport communica-
tion protocol (TCP)/Internet protocol (IP) TCP/IP.
he growth of distributed architecture entailed four important aspects with respect to applica-
tions and services:

1. Remote procedure calls

2. Remote database access

3. Distributed transaction processing

4. Messaging

Remote procedure call (RPC) is a programming model for the distributed environment, and
this model facilitates services development on the distributed network. Likewise, remote data-
base access enables database access on remote systems. Distributed transaction processing enables
applications to execute in a transaction environment so that the services are delivered in a reliable
manner. Messaging is the asynchronous mode of communication, which is very helpful in imple-
menting a powerful integration among distributed networks.
Because RPC and messaging represent powerful mechanisms with the help of which integra-
tion among diferent vendor network can be brought about, it would be worthwhile to look into
a few more aspects of these two mechanisms. he next two sections discuss in some detail how
the RPC as well as messaging help in the development of services on the distributed architecture.

1.1.3.1 Remote Procedure Call

RPC was proposed by Birrel and Nelson sometime in the mid-1980s and standardized by Schroeder
and Burrows in the late 1980s. RPC enabled systems to communicate in a distributed architecture
environment. Figure 1.3 provides a graphical description of how the RPC model works in the
distributed environment. Diferent vendors have implemented RPC in diferent fashions.
For example, Microsoft, OMG, and Sun Microsystems have implemented RPC in diferent
ways. he following subsection presents concise information on these three implementations.

◾ Microsoft introduced Component Object Model (COM) sometime in the mid-1990s. COM

is a technology with the help of which software components could be developed for integrat-
ing applications on the network. To build these components, one must adhere to the speci-
ication so that the components can operate interoperably. Distributed COM (DCOM),
introduced sometime in the late 1990s, enabled interaction among network-based compo-
nents. DCOM is built on object RPC layer, which in turn is on top of DEC RPC to sup-
port remote object communication. Object Linking and Embedding (OLE), ActiveX, and