User:Graham.Fountain

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Work: Senior Engineer 3 - Technical Specialist in the Networks Group of the Research and Technology Dept., of a large multinational aerospace co.

Other: Chairman BSI committee ACE 6/-/9: Aerospace - Digital data buses, 1992 to Aug 2013.

Interests:

Avionic data networks and data buses:
Integrated Modular Avionics
ASAAC
Guaranteed reliable and secure (i.e. tolerant of faults, and malicious actions), real-time data transfers over packet switched networks, for safety-critical and mission critical applications. Moreover, allowing these guaranteed real-time transfers between the standard Ethernet network interface units that are integrated into almost all the likely equipments, i.e. done properly, not like AFDX or TTEthernet do it:
Network congestion prevention - the ultimate level of congestion control: for real-time data that must be proved to be transported safely, an ounce of prevention is worth a pound of management and a ton of avoidance.
In regard to hard real-time and soft real-time: “Hard real-time is hard, soft real-time is even harder.” (E. Douglas Jensen)
The difference between hard and firm real-time, at least in terms of data transport over imperfectly reliable media, merely represents the difference between theory and practise - “In theory, theory and practice are the same. In practice, they are not.” (Attributed to Albert Einstein) So, while distributed real-time systems like IMA may, in theory, be hard real-time, in practise they must allow for some level of loss, and are, necessarily, firm real-time.
However, what does not appear to be well understood, or is at least not well discussed, in regard to real-time data transport (unlike in real-time computing), is that delivering hard or firm real-time data after its deadline is the same as failing to deliver it at all. It may even be argued that late delivery is worse, because the data is valueless, but still consumes resources - see Time-utility function. Hence, sufficiently delaying a real-time data transfer has at least as great an impact as preventing or corrupting it. So, in the context of secure, real-time, safety/mission critical data transport, a real-time transport protocol has to provide a means of proving timely delivery, as well as providing proof of reliable delivery.
And the only way to actually prove that (either or) both reliability and timeliness requirements for delivery will be met (even firm real-time ones) is to guarantee that the real-time traffic is fully protected from congestion, which may not be easy, but has to be done. It may also go against the grain of IP, in requiring complex functionality in the network. But where provably reliable and secure, real-time performance is required, there is no choice.
The leaky bucket and the token bucket algorithms - they're the same thing really.
The generic cell rate algorithm (GCRA).
OpenFlow (versions 1.3.0 and later).
Legacy buses and networks:
MIL-STD-1553B
EN 3910 and EFABus - formerly STANAG 3910
The Asynchronous Transfer Mode
Liner Token Passing Bus - AS 4074.
Related issues
TEMPEST testing
The Triumph TR7 Sprint
59-61 cars built in 1977 as homologation specials for the Group-4, 16-valve TR7 rally car for the 1978 season: The 16-valve rally car had been homologated for group-4 in October 1975 as a modification of the Group-3, 8-valve that was homologated earlier in 1975. This used the "100-off" rule in the FIA's appendix J rules. That rule allowed certain modifications, like multi-valve heads, gearboxes, overdrives, and clutches, etc., on production of 100 of the part. It did not require 100 cars to be modified. However the rule was deleted in 1976, with homologated parts and cars allowed to continue to be rallied until the end of 1977. This meant that the 16-valve head had to be re-homologated on production. While the FIA's requirement for homologating a modification on production doesn't seem to be published, several other modified cars are reported to have been homologated on production of 50 - Vauxhall HSR and Porsche 924, and possibly 1978 spec Escort RS1800, homologated into group 4 as the 1975 cc Escort RS (FIA number 650). The 16-valve head was given approval for use on the TR7 in group 4 once again in February 1978, and a set of 6 photos in the archives of the British Motor Museum identify the TR7 Sprint in this process.
The Triumph Slant-4 engine#Sprint version
The Triumph TR7
The Triumph Dolomite Sprint


This user's motto is:

Why put off till tomorrow what you can put off till next week?

This user lives too close to Blackpool for comfort.

This user lives too far from York to be happy.

"It's a great place to live, but I wouldn't want to visit there."
Of the one-way system - "Well, if I was driving there (York central library), I wouldn't have started from here (Parliament St)."
From a bemused American tourist "Why the hell do they call the streets 'gates', the gates 'bars', and the bars 'pubs'?"