The ESRO specification describes the service model, the notation and the protocol for Efficient Short Remote Operations (ESRO). The ESRO service is similar to and is consistent with other Remote Operation and Remote Procedure Call services. The emphasis of the ESRO service definition and the ESRO protocol is on efficiency. ESRO is designed specifically with wireless network (e.g. CDPD) usage in mind.
The ESRO protocol provides reliable connectionless remote operation services on top of UDP (or any other non-reliable connectionless transport service) with minimum overhead. ESRO supports segmentation and reassembly, concatenation and separation, as well as multiplexing for service users (applications).
ESRO allows for trade-offs between efficiency and reliability by specifying both 2-way handshake and 3-way handshake based protocols.
The ESRO specifications also define a notation and the services provided by an application-service element to support interactive applications in a distributed systems environment. A Remote Operation is invoked by one entity; the other entity attempts to perform the Remote Operation and then reports the outcome of the attempt.
Encoding mechanisms for presentation of the parameters of remote operations are outside the scope of ESRO. However, identification (tagging) of the encoding mechanism in use (e.g. XDR, BER, PER) is supported by ESRO.
A variety of applications can use the ESRO protocol. Some early applications which use ESRO include: efficient short message submission and delivery, credit card authorization, and white pages lookup.
The key requirement driving the design of ESRO is efficiency. Reliable transfer of a short message using TCP involves 5 transmissions at a minimum. Reliable transfer of a short message using ESRO involves only 3 or 2 transmissions.
For many applications in which optimization of efficency is desired, it is likely that elimination of the extra 2 transmissions which are inherent to TCP, justifies deviation from it and use of ESRO instead.
The efficiency premium realized by the use of ESRO rather than TCP can be very significant. For example, EMSD (a mail submission and delivery protocol that uses ESRO) can be upto 5 times more efficient than SMTP, while maintaining precisely the same level of reliability and security. The paper entitled ``Efficiency Study of EMSD vs. SMTP/POP3/IMAP'' [57] quantifies the efficiency of ESRO in comparison to traditional TCP based applications.
ESRO is a reliable connectionless transport mechanism.
A reasonable question is: Why did we design ESRO's service interface to be based on the Remote Operations model?
Many Internet protocols are "text-based" on top of TCP. And the ``here is some text'' followed by ``here is some more text'' followed by ``here is some text in response'' has become the tradition of simple Internet protocols. Protocols designed on the basis of this "text-based" approach have a good track record of acceptance throughout the Internet, primarily because they are simple to understand and simple to implement.
When efficiency matters, however, the traditional text exchange model can be better expressed by the client requesting a particular operation from the server, and the server responding with the results of that operation, thereby eliminating the traditional ``text-based'' chit-chat. With such an approach, the design of the protocol becomes a natural fit for the remote operations model.
For short interactions, a reliable connectionless transport mechanism and the Remote Operations model are simply the same thing. The formalism of Remote Operations is an asset that ESRO exploits.
ESRO provides a service which supports interaction of applications based on a remote operation model. A Remote Operation is invoked by one entity; the other entity attempts to perform the Remote Operation and then reports the outcome of the attempt. The ESRO protocol is designed to be able to support a large variety of applications.
The ESRO protocol is completely open. It has been published as RFC-2188.
For information on how to obtain the ESRO protocol, visit the "Base
Protocol Specifications" section of
http://www.esro.org/.
ESRO.org is a public organization which enables and facilitates the development, maintenance and enhancement of protocols and related technologies which address the efficiency requirements of generic Internet applications.
Anyone interested in participating in the development of the ESRO protocol can join ESRO.org by visiting the "Joining the ESRO.org and Related Mailing Lists" section of http://www.esro.org/.
Patent-free declarations have been made with respect to ESRO and RFC-2188 through the Free Protocols Foundation.