ISTP was first presented as a technical paper:

``Design of the Interactive Sharing Transfer Protocol'',Waters R.C., Anderson D.B., & Schwenke D.L.,Postproc. WET ICE '97 --IEEE Sixth Workshops on Enabling Technologies: Infrastructure for Collaborative Enterprises, (MIT, June 1997),IEEE Computer Society Press, Los Alamitos CA, 1997

Download a full Postscript zipped copy of the ISTP Technical Report

What is ISTP?

The Interactive Sharing Transfer Protocol (ISTP) supports the sharing of information about a virtual world among a group of user processes. ISTP allows the interoperation of diverse systems running on diverse hardware. The key advantages of ISTP are that it supports :

(1) real-time interaction between users,
(2) the communication of every kind of information required in a virtual world, and
(3) scalability to large numbers of simultaneous users and large virtual worlds.

ISTP is used for communication by the Scalable Platform for Large Interactive Networked Environments (Spline) and its derivative open standards initiative, which we call Open Community (OC). Spline and Open Community make it easy to build Distributed Virtual Environments (DVEs)---virtual worlds where multiple people interact with each other and computer simulations in a 3D visual and audio environment. Using ISTP, Spline and OC perform all the processing necessary to maintain a distributed, modifiable, and extendable model of a virtual world that is shared between the participants.

It is important to realize that while ISTP and Spline have evolved together, they are completely separate. The Spline or Open Community API could be supported by other communication protocols and ISTP could be used to support other APIs.

Brief Description

Just as all the web servers in existence are implicitly combined into a single world wide web, all the ISTP processes that are running at any given moment are capable of interacting with each other. Running a web browser and knowing a Uniform Resource Locator (URL) (or running a web server and advertising a URL) are the only things that are needed to participate in the world wide web. Similarly, running an ISTP process and knowing or advertising a beacon tag (like a URL) are the only things that are necessary to enter the ISTP world.

ISTP achieves fundamentally lower bandwidth operation than DIS by using reliable communication of object update messages. This allows the use of compact differential messages and eliminates the need for keep-alive messages.

ISTP is a hybrid protocol that builds on top of four underlying protocols: TCP, UDP, RTP, and HTTP.
 

• TCP is used for the reliable communication of control information.
• UDP and RTP are used for the communication of time critical information. (UDP and RTP messages are both sent via multicast whenever possible.)
• HTTP is used for the distribution of large pieces of data.

By this hybrid approach, ISTP addresses the communications needed for different sizes and types of objects in a fairly efficient manner, and provides the reliablility and error correction necessary for operations across various types of network configurations.

Serverless Applications

While ISTP does allow the implementation of a centralized server, depending on the application, a centralized server may not be needed at all, and a truly distibuted, and therefore highly scaleable system configuration can be implemented.

Download a full Postscript zipped copy of the ISTP Technical Report