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Enterprise Computing - Protocols





An enterprise application developer should know about various protocols. Here we can see some of the following:
  • HTTP
  • IIOP
  • JRMP

The HTTP protocol is based on a request/response paradigm. A client establishes a connection with a server and sends a request to the server in the form of a request method, URI, and protocol version, followed by a MIME-like message containing request modifiers, client information, and possible body content. The server responds with a status line, including the message's protocol version and a success or error code, followed by a MIME-like message containing server information, entity metainformation, and possible body content. On the
Internet, HTTP communication generally takes place over TCP/IP connections. The default port is TCP 80, but other ports can be used.
Proxy, an intermediary program which acts as both a server and a client for the purpose of making requests on behalf of other clients. Requests are serviced internally or by passing them, with possible translation, on to other servers. A proxy must interpret and, if necessary, rewrite a request message before forwarding it. Proxies are often used as client-side portals through network firewalls and as helper applications for handling requests via protocols not implemented by the user agent.
During the lifetime of a CORBA applications clients and servers can create multiple connections. Each of these connections usually involves a different port number - clients typically create a new connection for each server. Firewalls are an inherent part of the Internet environment and prevent such indiscriminate port management. Instead they maintain a well-defined set of ports for HTTP, mail, etc. So CORBA applications must become more well-behaved to live on the Internet. The ideal solution is to open an IIOP port through which all such traffic was directed. An IIOP proxy behind the firewall would then examine each IIOP message and redirect it to the appropriate server. However IIOP is currently viewed with some suspicion by the firewall community who are unwilling to open IIOP ports in their firewalls. All this leaves IIOP applications with having to reuse one of the existing ports - and associated protocols - available in firewalls. HTTP is tried and tested, which gives rise to 'HTTP Tunnelling'. HTTP tunnelling is a means of embedding IIOP messages inside a HTTP message which can be directed through the HTTP port every firewall supports. Behind the firewall an IIOP proxy is still required, but it now includes an extra step of examining each HTTP request to see if it contains an IIOP message, which it then redirects to the appropriate server. Each of these servers can be running on different machines behind the firewall - the proxy is capable of tracking them. It is even possible to 'federate' IIOP proxies to redirect requests across firewall boundaries.

HTTP protocol over SSL(Secure Socket Layer) is HTTPS. The default TCP port for HTTPS protocol is 443. SSL is a standard protocol for implementing cryptography and enabling secure transmission on the web. The request and response are encrypted before transmission.

  • Defines inter ORB communication
  • Runs on top of TCP/IP
  • Defines CORBA messages

The JRMP (Java's Remote Method Protocol) is a specialized protocol designed for RMI. Default port for RMI(Java Remote Method Invocation) is 1099. JRMP is a closest equivalent to IIOP. Unlike CORBA, which is programming language neutral, RMI is for Java. RMI has other advantages too, it supports remote garbage collection, preserves the Java security features.

RMI and CORBA have developed independently as distributed-objects programming models. RMI, a foundation of the EJB and Jini technologies, was introduced as a Java-based, easy-to-use programming model for distributed objects. CORBA (the Common Object Request Broker Architecture), defined by the OMG (Object Management Group), is a well-known distributed-object programming model that supports a number of languages. The IIOP protocol connects CORBA products from different vendors, ensuring interoperability among them. RMI-IIOP is, in a sense, a combination of RMI and CORBA.
more to come.....

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