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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