[Nml-wg] Path definition

[Aaron Brown]

On Aug 25, 2008, at 10:48 AM, medhioub wrote:

> Definition
>
> *PATH
> *
> A *Path* is an ordered list of links and interfaces to describe a
> node-to-node connection.
> A Path can contain physical and/or virtual Network Element.

Since the path is being brought up, the DICE folks have been  
discussing a path element that differs slightly from the above  
definition, I figured I'd send something to the list. The DICE folks  
want to be able to describe multipath and asymmetric paths (both very  
specific paths as well as more general paths). Not specifically  
discussed yet on DICE, but a point-to-multipoint path is doable using  
the basic approach that's been fleshed out.

Here's the list of path types that logically might need to be described:

point-to-point - specific paths (it goes out interface A over link B  
to interface C, out interface D over link E to interface F, etc).
point-to-point - generic paths (it goes from domain A to domain B to  
node C to domain D)
point-to-multipoint (both generic and specific) - for describing a  
multicast tree or similar
point-to-point via multipath - A goes via routes X and Y to node B
asymmetric variants of the above.

The actual specifics of the implementation DICE paths are given in  
examples below.

What do you guys think?

Cheers,
Aaron

Here are some examples of the DICE paths:

Bidirectional path. downstream same as upstream:

     <!-- Bidirectional path. Specifying only the downstream path. The  
empty path is implicitly the 'opposite' of the other path -->
     <bidirectionalPath id="Path1">
         <path direction="downstream">
             <hop id="i2">
                  
<domainIdRef>urn:ogf:network:domain=dcn.internet2.edu</domainIdRef>
                 <nextHop>esnet</nextHop>
             </hop>
             <hop id="esnet">
                 <domainIdRef>urn:ogf:network:domain=es.net</ 
domainIdRef>
             </hop>
         </path>
         <path direction="upstream" />
     </bidirectionalPath>

Asymmetric Paths:

     <!-- asymetric bidirectional path. Downstream goes internet2 ->  
esnet -> geant. Upstream goes geant -> uslhcnet -> internet2 -->
     <bidirectionalPath id="Path2">
         <path direction="downstream">
             <hop id="i2">
                  
<domainIdRef>urn:ogf:network:domain=dcn.internet2.edu</domainIdRef>
                 <nextHop>esnet</nextHop>
             </hop>
             <hop id="esnet">
                 <domainIdRef>urn:ogf:network:domain=es.net</ 
domainIdRef>
                 <nextHop>geant</nextHop>
             </hop>
             <hop id="geant">
                 <domainIdRef>urn:ogf:network:domain=geant.net</ 
domainIdRef>
             </hop>
         </path>
         <path direction="upstream">
             <hop id="geant">
                 <domainIdRef>urn:ogf:network:domain=geant.net</ 
domainIdRef>
                 <nextHop>uslhcnet</nextHop>
             </hop>
             <hop id="uslhcnet">
                  
<domainIdRef>urn:ogf:network:domain=lhcnet.caltech.edu</domainIdRef>
                 <nextHop>i2</nextHop>
             </hop>
             <hop id="i2">
                  
<domainIdRef>urn:ogf:network:domain=dcn.internet2.edu</domainIdRef>
             </hop>
         </path>
     </bidirectionalPath>