Re: [nvrg-bof] What is Network Virtualization?

[Joe Touch <touch at ISI.EDU>]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1



Jennifer Rexford wrote:
| Joe,
|>
|> I agree in the sense that NV is a means to create a VM. I disagree
|> about the "shared substrate" part - it's the tunnels that define
|> the virtualization in my definition; how devices are shared is not
|> directly relevant (that's mechanism; see the end of this post).
|
| Well, terms like "overlay" and "virtual network" are admittedly used
| by many people with different meanings.

It would be useful to clarify; they are the same to me.

| In my mind, a tunnel itself is also a sort of mechanism, and the
| notion of a tunnel alone doesn't help draw a meaningful distinction
| for me between (say) a virtual network and an overlay network

As above, that isn't necessarily needed. Tunnels are the distinction
between the stacks used by conventional networks and those used by
virtual nets. Granted, they are just a mechanism, so maybe it's cleaner
to say:

VNs add a layer of indirection in the handling of messages.

There are various ways to do that; some encapsulate explicitly, some add
a "shim" header (as with 802 VLANs), etc.

|> The analogy to VM is useful here. There are many ways to achieve
|> VM, but they do not all involve sharing physical memory
|
| Yup, agreed.  That gets at the distinction I would make between
| "memory virtualization" and "virtual memory".  Memory virtualization
| would, to me, refer to the sharing of the physical memory (i.e., on a
| platform that supports virtualizing the physical memory so multiple
| virtual memories can share it), whereas virtual memory is the concept
| or abstraction or architecture as seen by a single process.

VM is the result; MV is the process by which VM is supported. I don't
see how either requires sharing of physical memory, as per the example I
gave previously. The key aspect is the additional layer of indirection
of the address space.

|> Asking what it means for "a substrate to support NV" is a different
|>  question than asking what VN or NV is, IMO.
|
| Yup, I understood your viewpoint, and was intending to offer a
| different view that draws a distinction between the abstraction (of a
| virtual network) and an underlying system that can support or host
| multiple instances of that abstraction (i.e., network
| virtualization).

Mechanisms that support network virtualization can be interesting, but I
wouldn't either explain or motivate VNs by their supporting mechanisms;
they change. Some old versions of VM mechanisms that (nearly always) no
longer apply:
	- swapping to disk
	- segmentation
	- overlays

Joe



-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.3 (MingW32)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFIWSV9E5f5cImnZrsRAuZwAKCYLPkXAFWBpLoNjlF9TNRH9wrVsgCgvIID
Occ+TrQjE+tdyWAjFol/280=
=//Jk
-----END PGP SIGNATURE-----