[e2e] TCP "experiments"

Marco Mellia mellia at tlc.polito.it
Thu Aug 1 10:37:54 PDT 2013

> Two observations.
> 1) YouTube usage needs the same data rate, whether its content is spread over multiple TCP connections or not.  It's hardly obvious that there is a significant problem here.  Van Jacobson and I talk about the rate-of-convergence to a

False, since YouTube uses adaptive streaming… So being more aggressive allows you to get more capacity => switch to higher quality etc.

> "fair sharing" of whatever bottleneck resource there is.  Rate-of-convergence is orthogonal to fairness and ideally the faster the rate of convergence the less impact congestion has.  So I wish that others would model/measure/explore this behavior.  Though obviously, the real goal of a network is to rarely have any bottleneck in the network that interferes with user traffic, assuming the users are paying for service.

Good point. When YouTube will switch by default to HD video, more than doubling the bandwidth, who is going to pay for the additional capacity? End-users are really not likely to give a dime more to the ISP...

> 2) Anarchy is the wrong name.  In an anarchy, *individuals* act independently in their own interest.  In a network, communication requires cooperation.   Cooperation is at least pairwise, and generally is much higher-dimensional (or "groupy").  That is, large subsets need to agree on a protocol strategy among themselves to succeed in communicating. This *cannot* be anarchy.   Maybe it is "multi-archy" rather than hierarchy.  However, it is the case that if you choose your own personal congestion management protocol, you are likely not to be able to communicate, and certainly will have difficulty sharing the network with others.

Ok, you don't like anarchy… But I don't get the "if you choose a different congestion management protocol, you are likely not to be able to communicate". It seems to me that congestion control, and parameter setting (e.g., initial window, initial timeout, back off factor, etc) can be changed almost freely without breaking the communication...

> The forcing function of cooperation (call it Metcalfe's Law or Reed's Law or whatever the heck you want to call it) drives all participants in the Internet, and all of their suppliers, to develop common approaches.  The ones that work well, win.   Evolution of the Internet (either by design or by accident) generally drives toward effective sharing.

100% agree if you are saying that when A changes something so it get a better service, than B and C and D will sooner of later implement the same change.
The problem is when A has already a predominant role in the market, and keep rolling out modifications that improves its service (at the expense of someone else eventually). This could lead to monopoly. Not sure I'd like this.

> This is ignored by most professors of communications networks, and I doubt is mentioned in most textbooks.  Yet it is staring us in the face.

Economic principles are not part of the OSI model :)

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