I've added a photo of my self so you can associate a face to DIS. The city where I live and work is Marseille which is in Provence (south of France). View it with Google maps.
Below you can see the calanque of Sugiton, just next to Marseille, that you can reach after a 30 minute walk through a pine wood from Luminy.
A modern communication protocol must be secure. And to do it right, security must have been integrated in the design from the very start. Here is a short list of security requirements for DITP:
- authenticate peers
- support exchanged data authentication and encryption
- provide access control on accessible services, objects and methods
- support single and multi-signed information of any kind
- signed information supporting polymorphism and aggregates
- allow anyone to verify any signature with minimal knowledge
Multi-signed information is when more than one people sign a given information, (i.e. a contract).
With a stream oriented encoding this all imply that we are able to apply a hash function (i.e. SHA) on transmitted data while it is encoded or decoded.
This is what I am currently implementing. Unfortunately, a server crash, monopolized all my time this week. Murphy's law revenge...
IDR is the data encoding used with DITP. It is to DITP what XML is to SOAP. IDR uses bleams that combines the benefits of block and stream encoding:
- no need to specify total size in front of it
- no upper size limit
- may be encapsulated without depth limit
- no constrain on data and doesn't rely on markers or tags
- no need to parse and search payload data to locate the end of bleam
A bleam is encoded as a sequence of byte blocks of at most 16KB. Each block is preceded by an unsigned short value whose 14 less significant bits encodes the number of bytes of data that follow. Its most significant bit is set to one if the block is not first, and its second most significant bit is set to one if the block is not last.
When encapsulating a bleam, its sequence of blocks is simply inserted in the sequence of blocks of the encapsulating bleam. The encapsulated bleam can be stored in the data of the the encapsulating bleam block if it fully fits in one of its block.
The maximum payload size is 16382 so that the biggest block will be 2^14 byte long. The invalid size value 16383 (0x3FFF) is then used as a signal. A signal block has no payload data.
The signal is used in IDR to inform the receiver that the expected sequence of data is interrupted because an exception or an error occured. If the signal block is flagged as end of bleam, the interruption is anonymous. Otherwise subsequent bleam data provides information on the reason of the interruption. In IDR it is the serialized exception object and the objects it may be referencing. Such interruption will eventually propagate to encloding bleams and be encoded as anonymous interruptions.
Encoding and decoding bleams require some care, but the effort is worth it because of its multiple benefits. With small messages DITP is as performant as common inter-object communication protocols. With bigger message, DITP benefits from the stream oriented encoding and reduced latency and memory usage requirements. DITP can thus be used to send huge files, streamed films, etc.
Most inter-object communication protocols encode message into blocks with its size encoded in front. This requires that the message is fully encoded to compute the size of blocks before it is sent.
A stream oriented protocol doesn't need this. The communication process can be pipelined. As shown in the figure below, this reduces the communication latency. Note that in a two way transaction the saving is doubled.
In absence of the block size, one needs a marker to signal the end of the block. For instance SOAP uses xml tags as markers. There are two drawbacks with such encoding: the marker can't show up in regular data and the marker must be searched to locate the end of a block. When the block size is available, locating the end of the block is trivial and very fast.
IDR and DITP combines the benefits of blocks and streams encoding by introducing a new encoding called BLEAM. Here is a short list of the their properties:
- bleams have no size limits
- bleams may be encapsulated with unlimited depth
- bleams impose no constrain on contained data
- no need to search and parse contained data to locate the end of bleam
The last property is what makes the difference with SOAP and its xml encoding.
See next blog note for a description of the bleam encoding.
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.
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