[Nml-wg] Ports with multiple connections?

[Jeroen van der Ham]

Hello,

I have been examing some of the topologies of the IDC network at 
Internet2 and others more closely and I have encountered some things 
that we may want to look at.

One of the things that I would not know how to describe exactly in NML 
is the following example:
A domain has a port on one of its devices. This port has an inter-domain 
connection. Through this port there are two possible connections to 
other domains, by means of separate VLAN labels. For example VLANs 
1000-2000 go to one domain and 3000-4000 go to another.


There are different ways of solving this at the moment.
You do have to describe this somewhere as a single port, because of the 
limitations on the capacity of this port. I came up with three possible 
solutions, all with their own disadvantages:

- Describe a single port with two links attached to it.
This means breaks the assumption that a port can have at most one 
bi-directional link attached to it.

- Describe a single port with two virtual ports each with its separate link.
This breaks the assumption that a port is always connected by a Link 
(either a cross-connect or an external link), and we introduce a new 
concept of a virtual port. Are there other cases that would warrant this 
introduction?

- Describe a single port that is connected to a "virtual" node where the 
connection is split into two.
This makes the description more complex, and also seems to allow a 
direct connection between the two inter-domain connections without using 
the original port.

Any other ideas?

Jeroen.