Lecture Series in Mobile Telecommunications and Networks (1583KB)

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From wireless networks to sensor networks and onward to networked embedded contrtol This architecture, along with what is called peer-to-peer protocols – I claim that the architecture has been more important for the proliferation of networking, in comparison Application Layer Application Layer to the algorithms, even though the algorithms are very Presentation Layer Presentation Layer Source Channel Session Layer Session Layer Hardware Software Coding Coding important. Why do I say that? By the segregation of tasks, Transport Layer Transport Layer Network Layer Network Layer we guaranteed that each of us can work on our little Data Link Layer Data Link Layer Pshyical Layer Pshyical Layer specialty and, when we put them all together and compose them, the interfaces have been worked out so that the whole thing works. Not only that, but this layering also gives this technology longevity. Over the course of time, therefore, you may have a different and better idea on one of the layers – let us say TCP. Then, you do not need to replace the whole stack but you just replace that little sliver of it and the rest of it can work. That longevity allows this technology to evolve and the longevity also facilitates proliferation. Proliferation drives down the cost per implementation. The point I want to make is that there is always a tension between architecture and performance people, because performance people always want to bust architecture. They want to take short cuts – they say, ‘Gee, if I could just expose parameters of this layer to this layer, then I could improve this by 10 per cent.’ However, at the back of the room there could be another person saying, ‘Wait a second! If I expose these parameters to this one, I could do 15 per cent.’ If you start implementing all of these short cuts, however, in the end you will have a spaghetti architecture – which will mean no architecture at all, and it will be hard to maintain and to upgrade and so on. You may have a faster system, but you will not get a million of them. So, even though there is an apparent tension between architecture and performance, I contend that architecture is also performance oriented, while keeping in mind the long time horizon. Another example that I like very much is due to Les Valiant at Harvard. He claims that the success of serial computation is due to the von Neumann Bridge. The way to think about it is that you have Microsoft and Intel and they do not need to talk to each other but, as long as they conform to a vague abstractional on the other side, their products by and large will inter-operate. That has been the reason why serial computation has been phenomenally successful. In contrast, parallel computation has no von Neumann Bridge. It is very hard to separate architecture from algorithms and that is the reason why there has not been proliferation. Similarly, in communication, there is the separation between source coding and channel coding – source coding can be done in your JPEG, or you may do it in software, whereas channel coding may be done in your network interface card, and so on. This is Shannon’s result, and so on. The point is that we are now getting into very complicated systems where we have communication control, serial, parallel, everything. What are the appropriate abstractions and what is the architecture? What is the goal here? The critical resource is not the cost of the equipment but the critical resource is the designer’s time – your time and my time. When projects go into over-runs, it is not because something is a little too expensive but it is usually because there is something wrong in the whole design. Our goal therefore is to make it very easy to enable rapid design and deployment. Standardised abstractions and architecture help, so we can just build these things like levels and therefore enable proliferation. Information technology convergence lab: the systems Let me show you some efforts that we have in our lab. We have these model cars running around on this plywood sheet, with these cameras up in the sky. There is image processing going on here. There are all the levels of decision making – set points, tracking, scheduling, planning, re-planning, re-scheduling and so on. You may not be able to see it on the slide, but there is a wireless ad hoc network The Royal Academy of Engineering 13
here of laptops, and all these laptops are controlling the cars. This is a completely closed-loop system - it is closed over vision and it is closed over wireless networking, but what I want to focus on is the fact that it is closed over middleware. I will explain what I mean. IT convergence lab Let me first show you what we can do in this lab. [Video shown – model vehicles in lab] That is the interaction between logical dynamics and differential dynamics. This is a pursuit evasion scenario, OJ Simpson style. There is a car being driven by my student and these other two cars have to follow automatically in formation, and he is trying to confuse those two. [Video continues] http://decision.esl.uiuc.edu/~testbed/videos/Overall_Long Abstraction of virtual collocation The first abstraction I want to propose is what I call ‘virtual collocation’. What do I mean by that? Here, we have the car and the actuator, which could be the gas pedal, steering wheel or whatever. Then we have all the layers of decisionmaking. Then there are the sensors, and you have more than one sensor, so you have a server and data fusion because you have lots of cars. Then, of course, you need to supervise all of these and so on. If you ask a control designer to design directly for this very complicated view of the system, it is a difficult task because the notion of time is different at different nodes, and the notion of IP addresses is different. There is a great deal of detail which someone needs keep track of. What I want to do is to reduce this complicated system to an input/output view. If you go back and ask an electrical engineer what architecture is, they will probably say block diagrams - interconnecting by lines and block diagrams and that is architecture. It is the whole notion of signal flow graphs. What we want to do therefore is to reduce these complicated software systems to such input/output loops. The abstraction layers How do we do that? We do that through middleware – let me explain. Here, we have the system and the first abstraction that we have is that of a node – everything we call a node. Then the link layer creates the illusion of links. The networking layer clears the illusion of a graph – the notion of connectivity, enter and connectivity. The transport layer, for those of you who know communication, creates the illusion of pipes, so if you drop a file here, it shows up there and you do not need to worry about the graph any more. 14 The Royal Academy of Engineering We are moving from nodes to graphs to pipes and so on, and then next natural thing I contend is just to think of the whole system in its entirety, as a collocated system, not variable to the complexities of interconnection and the way
Page 1 and 2: Lecture Series in Mobile Telecommun
Page 3 and 4: Foreword This compilation brings to
Page 5 and 6: From wireless networks to sensor ne
Page 7 and 8: From wireless networks to sensor ne
Page 9 and 10: As far as the routing of packets is
Page 11 and 12: easons. In the internet, one never
Page 13: Implementation with laser pointers,
Page 17 and 18: adds a great deal of discrete compl
Page 19 and 20: Questions & Answers Mike Walker: Th
Page 21 and 22: Human beings will also evolve and w
Page 23 and 24: Welcome and introduction Professor
Page 25 and 26: ComReg Collection - Start 16/Apr/20
Page 27 and 28: evidence that people give in favour
Page 29 and 30: chunks of spectrum where you are in
Page 31 and 32: As an aside, I was reading a few of
Page 33 and 34: Of course, it is not just one mask,
Page 35 and 36: I apologise for hopping between top
Page 37 and 38: Questions & Answers Michael Walker:
Page 39 and 40: Nobody - believe you me, it came ou
Page 41 and 42: The second aspect of my comment is
Page 43 and 44: want to call it - that sits there a
Page 45 and 46: From plain old Telephony to flawles
Page 47 and 48: From plain old Telephony to flawles
Page 49 and 50: You can see that there is much room
Page 51 and 52: 1024, we transmit 10 bits, so to sp
Page 53 and 54: Bandwidth extension with hidden sid
Page 55 and 56: 4 Vision: ambience audio communicat
Page 57 and 58: Questions & Answers Michael Walker:
Page 59 and 60: I said five years ago and what I he
Page 61 and 62: them and perhaps leave out some of

Lecture Series in Mobile Telecommunications and Networks (1583KB)

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