Re: [vnrg] Some more Acid tests & VN principles

[Roland Bless <roland.bless at kit.edu>]

Hi Sunay,

On 09.11.2010 20:07, Sunay Tripathi wrote:
> So looking at the Acid tests so far and VN principles, it seems like
> we need to tighten the isolation case a bit more. Specifically, just
> putting a Virtual Output Queue (VoQ) per VN on each link to provide
> isolation is not cutting it. The isolation (which translates
> into per packet latency and B/W) needs to be on a VN fabric level
> rather than on individual link level. Basically the VN should
> mirror the non virtualized physical network of same capacity i.e.
> a VN for 1Gbps on a 10Gbps network should see same or better
> behavior than if it was on a physical 1Gbps switch fabric by
> itself. This does need the network elements like switches and
> routers to do more work.

I don't agree on this, because it's too restrictive IMHO.
A chance for VNets is that they permit to use a different
virtual link QoS, too, even if it is not  exactly the same
QoS as a real physical substrate provides. For instance,
consider that an infrastructure provider can exploit some
statistical multiplexing gain by multiplexing several virtual
links over the same physical link, offering lower QoS
(maybe only a statistical guarantee) at lower costs.

In my view, a virtual network consists of virtual
nodes and virtual links that connect the virtual nodes.
So a VNet at "network layer" provides logical/direct
point-to-point connections between the virtual nodes.
Which underlying substrate network technology is used
to provide the virtual link between to virtual nodes
(which are hosted on substrate nodes) may vary widely,
for example it could be a TCP connection,
an IP-based tunnel (e.g., L2TP),
an MPLS LSP, a dedicated L2 connection, a VLAN,
some wave length on a WDM connection, or even shared
memory if the virtual nodes are hosted on the same physical
host. Similarly, what is running inside the virtual node
is completely independent of the substrate technology,
e.g., it could be the same technology or some future
networking layer.

Coming back to your proposal: I find it valuable to
realize a virtual 100 Mbit/s link using an IP-tunnel
within an EF-PHB over a 1 Gbit/s physical network.
The DiffServ-based QoS may not be comparable to a
dedicated 100 Mbit/s physical link, but may be good
enough for most uses and may span a much larger
distance and may be less expensive to realize.

> The other thing is related to management. A VN administrator
> needs to be able to administer his resources and name space
> independently.

Independently of what? Independently of what is running as
substrate technology, yes.

> But the issue that is bogging us down is what is the non virtualized
> part that ties entities to VN and allows the H/W to enforce the
> virtualization - is it the MAC address? Is it the VLAN? The problem
> with VLAN is that most hosts don't support Q-in-Q. Do people
> have thoughts on this?

As I said: substrate technologies to realize virtual links may vary
widely, this also implies different isolation properties.

Regards,
 Roland