Hi Neil,
I think there is a difference between a "data
plane label" which is a Layer Information (LI) used by a given server
layer and a "control plane label", which is a piece of information
signaled between adjacent controllers for the purpose of connection
provisioning. IMO the former is always a superset of the latter. Let's
take, for instance, connection oriented Ethernet. MAC SA is a very
important part of the data plane label because it identifies the source of
the connection. However, the connection frames are forwarded according to
MAC DA/VID, and hence connection ingress node, for example, needs only be
signaled with this tuple by the downstream neighbor, hence the control
plane label is MAC DA/VID (or just VID, for those who like the idea of the
VID cross-connects architecture).
So, IMO IEEE should be responsible for the
definition of data plane labels, while CCAMP for control plane
labels.
Cheers,
Igor
neil.2.harrison@bt.com wrote:
Dimitri
wrote 07 September 2007 16:36 in response to Adrian
> >
> > This is also something we would
expect to describe within
> > CCAMP although
> >
"what is a label" would come to us from the data plane
>
specification.
>
> do i interpreet correctly your statement
that if the
> specification that CCAMP is going to receive from
IEEE does
> not speak about "label" and its encoding there will
be no
> place to discuss any "label processing" and "label
> distribution" protocol in IETF - being domain-wide or
link-local
> -
>
> in that case, isn't the .1Q
specification outside scope of
> this effort since not referring
- as of today at least - to
> any "label" semantic as part of the
Ethernet frame header
> information field ?
>
>
thanks,
> -d.
What do you think a MAC DA, MAC SA and VID
are? These are all 'labels'.
You also have to remember that the
nature of the labels required in a
traffic unit are determined by the
type of the network mode one is
dealing with.
In the co-cs and
co-ps modes we have a construction known as a
'connection'. This
implies specific architectural requirements....but
the most
significant, for this discussion at least, is that a connection
must
have a single source. What this means is that one does not have
to
incorporate a SA label in a co mode traffic unit....under
defect-free
conditions it is redundant information as the connection
itself provides
the source information. {Compare this to the cl-ps
mode which does not
have connections...here having a SA in the
traffic unit is essential}
Ergo why co-cs and co-ps mode
technologies to date that respect the
requirements of a connection
have only focussed on incorporating a DA
(forwarding) label. Further,
these forwarding labels only need to be
distinct in resolving some
number (N say) of different client layer
(link-connection) instances
within a server layer (network connection)
resource partition.
However, there are advantages from having both a SA
and DA label in a
co-ps traffic unit that are network unique and not
just
link-connection unique (ie not swapped)....the inherent
robustness
under misconnectivity defects (without any adjunct OAM
flow) is one of
these. And of course, these are the nature of the
native labels one
already gets in Ethernet due to its cl-ps mode
origins. So why would
one even contemplate not using these since they
are already there?
The VID label is slightly different in that
one can consider it as a
'route discriminator label' and a local
extension to the SA or DA, ie it
provides the ability to identify
disjoint paths between nodal end
points.
The mere fact IEEE
may not refer to the above quantities as 'labels'
does not change the
fact that this is what they are. So I'm not clear
what your real
point is here.
regards, Neil
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