[Nml-wg] [Fwd: Re: [Nsi-wg] G.805/G.800 applied to NSI]

[Jeroen van der Ham]

Hello,

I agree that G.800 is a very valuable input towards describing computer
networks. However, reading through the document and the G.800 standard,
I'm somewhat confused about the difference between Points and Ports.
Also, I'm not entirely convinced that the authors of the G.800 are
really sure on this either.

Unfortunately, there is no real definition in the G.800 standard
describing the relation between the Point and Port. The only thing that
comes close is in the diagramatic conventions:
A Point is defined as two Ports connected by a Link, all within a
Subnetwork.

Then they make a distinction between Access Point, Forwarding Point,
Forwarding End Point and Link Point, wich are all conveniently denoted
by the same symbol.

What confuses me is Figure 8. According to their own diagramatic
conventions, they are showing Points within Subnetworks. I assume that
this is an error and that they meant to use open circles there, thus Ports.

However, later on in Table 1 on Page 19 the authors seem to define that
all relations are between Points, for example Adaptation is between
Forwarding Points, not Ports.

And to make it even more confusing there's this paragraph on page 13:
> An "access relationship" transport entity is created when a
> forwarding function is configured in a layer network. The ingress
> access ports and egress access ports of the forwarding relationship
> are identified together with any policy related to these ports. An
> access relationship cannot be partitioned. The access relationship
> may be established either before or after the termination is bound to
> an adaptation, i.e., it may be bounded by access ports or access
> points or a combination.

This seems to imply you can somehow mix Points and Ports.


The definition of a Link Point seems to be pretty clear, there are two
paragraphs describing that:

The definition of Access Group:
  > An access group is a group of co-located termination functions. It is
  > bounded by a link port that contains the individual FwEPts and the
  > set of individual access ports of each of the termination functions.
  > When the link port is bound to a subnetwork or link, it forms a link
  > point.

And the following page contains:
  > The internal structure of this [transport] plane can be further
  > described by partitioning the largest subnetwork into smaller
  > subnetworks (points of flexibility) and the links that interconnect
  > them. The binding between a link and a subnetwork results in a link
  > point.
(This is not directly between Port and Point, but Links are defined to
be between two Ports.)

Reading this, I believe that a Link Point consists of two Ports, i.e.
the connector on the cable and the physical port on the device.


However, I'm completely in the dark about the meanings of Forwarding
(End) Points and Access Points.

Jeroen.
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