\prefacesection{Abstract}

The motivation for this thesis is our desire to build faster routers and switches to accommodate for the traffic growth in the Internet. For the past few years, Internet traffic has been doubling every year, and nothing indicates that this growth rate will slow down in the near future. The Internet forwards information through packet switching, which has so far proven to scale from the early slow phone modems to the current fast link rates. However, it is unclear whether it will continue scaling to match future optical link rates.

Fiber optics and optical switching elements have demonstrated a capacity to forward information that today looks unattainable by electronic switching elements. As a consequence, one possible way of increasing network capacity is to build all-optical packet switches. However, these switches are not possible today because packet switching requires the buffering and processing of packets, and we do not (yet) know how to perform them in optics. On the other hand, optical circuit switches do not have these constraints, and thus they are already in use. The simplicity of the forwarding path in a circuit switch makes it faster than an equivalent router, even when implemented in electronics. In this thesis, I argue that we would greatly benefit from the use of circuit switching in the core of the network, in either electronic or optical form.

Circuit switching is already used in the Internet. Since the beginning of the Internet it is widely used in the core of the network; when early Internet service providers wanted to interconnect remote sites, the only option was to lease a circuit from the long-distance telephone carrier. Chapters \ref{chap:CSvsPS} and \ref{chap:ResponseTime} of this thesis analyze what type of network we would build were we to start with a clean slate. After analysis, modeling and simulation, I conclude that we would be better off with a hybrid network similar to the current one.

A problem with the current circuits in the core is that they are completely decoupled of packets in the edges. Rather than following traffic patterns in real time, circuits are usually provisioned manually, and thus they change very slowly. IP considers circuits to be static, point-to-point, layer-2 links between routers. Chapters \ref{chap:TCPSwitching} and \ref{chap:CoarseCircuits} propose two evolutionary ways of integrating circuit and packet switching, so that circuits are automatically controlled by the traffic carried by IP. The first approach uses lightweight, fine circuits to carry single user flows, whereas the second multiplexes several flows onto heavyweight, coarse circuits.

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%\section{old stuff}
%The work presented in this thesis is motivated by our desire to build faster routers and switches to accommodate the traffic growth in the Internet. Through the addition of new users and the increase in access-link speeds, Internet traffic currently doubles every year. One way of increasing the network capacity is to adapt the current switching method in the Internet to use optics, since optical information forwarding is improving at a much faster rate than electronic information processing and buffering.  However, optical packet switching is unfeasible today, because it requires the buffering and processing of packets, and we do not know how to do them in optics. On the other hand, optical circuit switches do not have these constraints, and, therefore, they are already a reality. The simplicity of the forwarding path in a circuit switch makes it faster than an equivalent router, even when implemented in electronics. In this thesis, I argue that we would greatly benefit from the use of circuit switching, with either electronic or optical data paths. 

%By observing in detail the current Internet, one can see that it is not just based on the switching of packets, but it already uses circuits extensively, both in the core and the edges. We have reached this network architecture almost by accident, as a result of the history of telecommunications; the only option that the early Internet Service Providers had to interconnect remote sites were leased circuits from long-distance telephone carriers. This thesis analyzes what type of network we would build, would we start with a clean slate. Would we use packets or circuits? Not surprisingly, the conclusion is that we would design a network very similar to the current one, with circuits in the core and packets in the edges. 

%One of the main contributions of the thesis is a network architecture that allows the adoption of circuit switching in the Internet in an evolutionary way. It exposes circuits to IP by mapping user flows to lightweight, fine circuits, so that circuits follow the current load of the network.




%\section{MINI ABSTRACT}
%This thesis is motivated by our desire for the Internet to be faster. The current Internet is based on electronic packet switching. One way of speeding the Internet is by replacing electronic packet switches by optical packet switches. However, this is not possible today, because packet switches require buffering and per-packet processing, and we do not know how to do it today with optics. On the other hand, optical circuit switches are a reality already, because they require no buffering and no per-packet processing. In this thesis, I argue that we would greatly benefit from the use of circuit switching, with either electronic or optical data paths. The main contribution of the thesis is a network architecture that allows the adoption of circuit switching in the Internet in an evolutionary way.
