The following figure shows the kernel components of the Distributed Information System, the road map and how far I am today. The items in black are implemented and operational and the items in gray still needs to be implemented. Progress is going clockwise :).

OID An OID is to DIS what the URL is to the web. It is a unique, binary encoded and non reusable reference to an information published in the distributed information system. It was the first tile I designed and implemented. Its simplicity is inversely proportional to the time and effort required to invent it because I had to explore and compare many different possible and existing solutions.

IDR It is to DIS what HTML or XML is to the web. IDR is the Information Data Representation used in DIS. It is a stream oriented encoding with support of object serialization and exceptions. The prototype implementation is currently being fully rewritten. It still miss the ability to specify the encoding version or a formalization of data description. The later is required to be able to display data in a human readable format or to automatically generate data manipulation functions or containers mapped to different programming languages.

DITP It is to DIS what HTTP is to the web. It is the protocol used to exchange information or invoke remote actions in DIS. It is very simple, modular and extensible through the use of dynamically configurable data processing tasks. Support of compression, authentication or encryption is then provided by some kinds of plugins. The protocol use the object oriented model with remote method invocation. The current prototype does not yet support concurrent asynchronous method invocation.

DIS DIS stands here for Distributed Information Service and is not to be confused with Distributed Information System. It is fundamental to DIS, so a confusion is not really a problem. This service combines the properties of DNS and LDAP and would be a new kind of service on the Internet. I can't disclose more  on it because it is still in development. A first prototype has been implemented unfortunately proving the need to support data description.

SEC This part covers authentication and access control in DIS. It requires a functional DIS service. An interesting feature is that it is designed to scale up so that a service could cope with millions of different users without having to keep track of million accounts and passwords.

IDX It is a service simply mapping human readable UTF8 strings to OID references. It is equivalent to the list of named entries in a directory. Like any other services, its access is controlled by ACL and can thus be modified remotely with appropriate privileges. An index may be huge with multiple alternate entry point, exactly like the DNS but exclusively as a flat name space. The OID associated to the UTF8 string is stored in an object so that polymorphism allow to associate images (icons) and other informations to entries by extension.

DIR It is a graph of IDX services with one root entry. Services or information published in DIS can then be referenced by a humanly readable path in the IDX graph relative to the root.



It is an ambitious project but, I am convinced, its added value is worth the effort. I wish I could work full time on this project with the help of some other developers, but this would require funding I don't have access to for now.

An application would help demonstrating the added value of the system. I'm still looking for one with an optimal balance in development effort and success potential.

While developing a prototype of DIS to check and validate it, I'm frequently confronted to bugs.

One reason is that the complexity of the program is comparable to a compiler. Individual encoding rules are simple, but they can be used in an infinite set of combinations.

After testing many different debuggers on Linux, my conclusion is that none of them is as good as the one of Visual C++ on Windows. So when I have to develop new code which may require debugging, I always develop it with Visual C++. Once it is validated, I move it on Linux.

The biggest difference is in the capability to explore data structures, STL containers, and other application specific data. If there wasn't Visual C++, I would have completely dropped Windows. It was thus a very smart marketing move of Microsoft to make Visual C++ available for free.

But Visual C++ is not yet perfect. So when not debugging, I prefer working on Linux. On feature I'm really missing in Visual C++ is one provided in Eclipse.

With object oriented programming, one usually store one class per file. I guess it is to simplify locating the class definition information. Simply look for a file with the same name as the class. The back side of this is that we end up with the code spread in many files. But when browsing the code, I often met a method call and would like to see its implementation.

To do this I have to switch to, or open, the corresponding file, locate the method definition in the file. Once examined, I may want to go back to where I was before.

Eclipse has this smart and powerful ability to change an identifier into a hyper text link. One simply move the pointer over the identifier and press the control key at the same time. The identifier changes into a hyper text link (underlined blue text) and a click moves you directly on the method implementation.

In visual, you get a context menu when clicking on an identifier and then you have to locate and click the "go to definition" menu command. Two clicks.

DITP is flexible, versatile and simple because it uses the inter-object communication model. Not only for the user needs to communicate with its service, but also to setup and configure the connection data processing (i.e. authentication, encryption, compression, logging, tunneling,...).

Inter-object communication

By adopting the inter-object communication model users can create any type of service (remote object) they want. They can also extend or refine their capabilities by using inheritance with the polymorphism property and preserve backward compatibility at the same time.

This makes DITP versatile and flexible, but any other inter-object communication protocol could claim the same.

Configuring and setting up the connection

What makes DITP different is that the connection configuration and setup are also performed by using the object oriented model. The different algorithms used are controlled by specific services and the client controls them by invoking the appropriate methods.

This makes the protocol very flexible and versatile since the algorithm can be combined and configured in any way. It is easy to add support for new algorithms and there is no constrain on the transaction polka required to configure them.

This design choice basically factorizes and parameterizes the protocol. What is left for DITP to define is how to open a connection, how to exchange messages between client and services and how to setup a new client-service binding.

Opening the DITP connection

Opening a DITP connection implies a very simple transaction where the client and the service side exchange a four byte message. If both message contain the expected value, the connection is considered opened. It can hardly be made simpler.

When the connection is opened the client and service implicitly attach a channel control service to the connection. This service has very few methods. One is used to close the connection and the other to request the attachment of another service whose type and identity are given as argument.

That is all it takes to have an operational DITP server. The exchanged messages have also a very simple structure, but will be described in another note because they have another original feature allowing to minimize latency.

Once the connection is opened, if the client wants to secure the connection by adding authentication or encryption, he request the attachment of the corresponding services and configure them by calling their methods.


This is why I claim that DITP is versatile, flexible and simple.

The DITP protocol has been designed to minimize the time required to setup an operational connection. This is achieved by a simple method which is made explicit in the following figure.

In common protocols, like HTTP and SMTP, the server is expected to send a greeting before the client can respond and proceed by sending its first request.

The time the client has to wait for this greeting message is usually dominated by the round trip time. In a LAN the round trip time is less than a millisecond, but on Internet it will take many tens of milliseconds and sometime hundreds of millisecond if the server is on another continent.

By simply swapping the DITP open transaction orientation, we save one round trip time delay before the client can sent its first transaction request. Another advantage of this method is that the server can use a very narrow timeout window for the arrival of the DITP connection setup request. This protects against some type of DOS attacks.

There are two additional things we can observe from the previous figure.

1.- The HTTP or SMTP protocol could be optimized by allowing the client to send its first data without having to wait for the server greeting.

2.- The round trip time due to TCP could be avoided if we could combine it with the DITP connection set up and the two first requests. There is clearly room for improvement on this layer, but this is out of scope regarding this project.

One fundamental question is the encoding of a time value. A time value has two types of use. One is as time stamp and the other is just as a general time reference.

Requirements

On one hand, a time stamp has the requirement to have a well defined and controlled precision, while the covered time span can be limited (i.e. +/- 200 years).  On the other hand, a general time reference needs to be applicable to a very large time span, with less constrains on the precision limit.

Options

For the time reference value one could use a double precision float representation with seconds as units. All arithmetic operations are provided right out of the box and generally hardwired in the processor. Conversion to calendar time is trivial since one simply has to extract the integer part of the value and convert it to a time_t value. From there one can use the common calendar time conversion and formatting functions.

For time stamps, using integers seems preferable. But we still have a choice between a split encoding like the timeval structure, a 64bit fixed point encoding, or an integer with very small time unit (i.e. nanoseconds).

Discussion

There is not much to discuss about the absolute time. Using a double precision float is an optimal solution. For time stamps however we have three different solutions.

From my experience, I've seen that split time encoding like the timeval structure is not convenient to use when dealing with time arithmetics. It is even error prone if the user has to program the operations himself.

I also tried to implement a fixed point time encoding class with the decimal point between bit 29 and 30. But this is tricky to get right and some operations are not trivial to implement correctly. This is because fractional computation requires normalization and optimal rounding errors handling.

A 64bit  integer using  nanoseconds as time units is apparently the most simple and straightforward time stamp encoding. Converting to seconds is done with a simple 64bit integer division which is also hardwired in most recent processors. Conversion to other time units like microseconds, milliseconds, days or week is as accurate and simple. Multiplication or division with decimal scalar values is also trivial.

Another advantage of the 64bit integer nanosecond values is that there is no need of special functions to do the conversions or operations. A programmer can easily figure out what to do and use conventional arithmetic operations.

With a 64 bit signed integers with nanosecond units, the covered time span is over +/- 292 years range. One can thus afford keep the current time_t January 1970 epoch and push back the wrapping limit far away. 

Conclusion

In DIS, we'll thus use a double precision float for general time reference value and a 64bit integer with nanosecond units for time stamps and delays encoding.

Note: I've seen the use of a double precision float for time encoding in some Windows operating system API. I still have to see the use of a 64bit signed integer with nanosecond units. It would make sense as an upgrade of time_t which is required since we are getting close to the wrapping limit.Update : It has been brought to my attention that Java stores time values in a signed 64bit integer with milliseconds as time units relative to January 1, 1970. The covered time span is thus +/- 290 million years. I'll stay with the nanosecond units for time stamps.

DIS has finally its logo. It was clear at the beginning of the design process that it should put forward the world wide networking feature of DIS which is key to its working principle. I looked for various networking grids but couldn't find anything original and explicit enough.

It is fortuitous that I saw an instance of the UVG120 grid which was first discribed in the article "The Planetary grid: a New Synthesis" written by William Becker and Dr. Bethe Hagens in 1984. I adopted this grid for the logo with the written permission of Dr Bethe Hagens.

I find this grid beautiful because of its apparent randomness and its subliminal regularity resulting from combining the vertices's of a dodecahedron and an icosahedron mapped on a sphere. The fact that these volumes integrate the divine proportion may contribute to the impression of beauty.

The logo was designed by the graphic designer Johan VINET. He runs the company grafxtory but is better known as lordyoyo with his blog offering copious tutorials and enlightening information on graphic design. He has a creative and yet a professional approach, with a pleasant benevolent patience I challenged with my exigencies and care of the details.