Hi, On Aug 18, 2005, at 11:25, Pekka Nikander wrote:
I am slowly trying to go forward with my thinking re/ tunnelling and virtualisation, and got a detail question of something that I don't understand. You referred to a pretty interesting tech report:J. Touch, Y. Wang, L. Eggert, G. Finn, "Virtual Internet Architecture,"ISI Technical Report ISI-TR-2003-570, March 2003. http://www.isi.edu/touch/pubs/isi-tr-2003-570/This paper talks quite a lot about revisiting virtual networks, and then later on you stated the following:[...] That doesn't allow you to support large programs in a small amount of memory - - akin to 'revisitation' in virutal nets.Could you please explain what you mean with revisitiation? I don't quite understand it, even after reading your paper the second time with this in mind. Especially, I don't understand how revisitation is kind of supporting large programs in a small amount of physical memory. The other thing that I don't understand is the benefits of revisitation, other than for research and early deployment purposes.
"Revisitation" means being able to support larger virtual topologies than you have physical resources for, e.g., deploying a 100-node ring on ten machines in a lab. This is done by hosting multiple virtual nodes on a single physical node. (You "revisit" a physical node multiple times for one overlay - the term may not be perfect.)
Many existing systems that deploy virtual networks can only deploy virtual nets that are at most as large as the underlying physical resources, i.e., they can arrange a subset of the physical nodes into arbitrary topologies by creating tunnels, but they cannot create virtual topologies that have more nodes than available physical machines.
Revisitation is similar to VM, in the sense that both enable the creation of virtual resources of apparently larger capacity than the underlying physical resource. This more completely decouples the two, increasing the power of the virtual abstraction. AFAIK the X-Bone is still the only virtual nets architecture that support this.
(A different aspect of this decoupling between physical and virtual resource would be replication of a single virtual node onto multiple physical machines for fault tolerance. This isn't in X-Bone yet, AFAIK.)
Lars -- Lars Eggert NEC Network Laboratories
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