The MPLS-OPS Archive

[Spice Sylvia <falsesylvia@yahoo.co.uk>]

Hi Adrian,


 --- Adrian Farrel <adrian@olddog.co.uk> wrote: 
> Sylvia,
> 
> One "detail" you hide is switching resources.
> Labels may be sparse resources and switching a fat
> pipe only takes one label (or one slot in your
> matrix).
> 

I agree, but that too amounts to stitching, I "switch
equal capacity on port A to port B"

Now how is that different from "simply hanging a wire
between end points connected to A and B"

> This get more important (but this is not the only
> reason for the function) when you change granularity
> of switching commodity. For example, if I want to
> send some small packet LSPs down a WDM fiber I
> could:
> - map each LSP to a lambda, but I would quickly run
> out of lambdas 
> - wrap all of the packet LSPs in a lambda and demux
> the packets at
>    each router, but this is inefficient at the
> router (which might not even
>    be able to handle that number of packets). Note
> that in this case
>    you are sort of building a single hop hierarchy.
> 

So if I draw out what I understand:

N1-----N2======N3--N4
        |       |
N5------        -----N6

N3 and N2 will still allocate individual "lamdas" to
some entity "which has TE properties" i.e N5 and N6?

In other words, do I:
a. "switch" lambdas across? As you yourself mentioned,
that does not make sense.
b. switch components/fractions out of those lambdas,
then I anyways cannot do that as N2 and N3 just have
switching but not TE properties.

In other words, there is no problem here between
"manually provisioning" the lambdas permanently is
there? 
What could be the purpose of "signalling" needed in
this case?

I understand that this could be classified as a node
with switching but no TE properties, but in a
simplistic view, it is as good as having a set of
permanent toggle switches which once provisioned, will
be left as they are.

Is my understanding correct?

> Now, in your figure, the topology is linear and here
> your main saving is in the detailed switching and
> processing at transit routers. But even then,
> several parallel, tiny LSPs (maybe only 1 kbit) are
> hard to dynamically fit into an OC-48 switching
> network without some form of hierarchy or huge
> bandwidth wastage.
> 

Is that mainly a limitation due to the fact that the
Oc-48 switch is seperate from the "access" switch?

In other words, there is node further down which has
the capability to switch at kbps level, but can send
out a max of say 1/4th Oc-48? these sub OCs can be
bundled on node -B in an Oc-48. But as far as I can
tell, the quantum is still sub-OCs which are of
interest, if the single node in the middle cannot
switch "subs" of oc-48, it really is nothing but an
extended cross connect? 
Just like the analogy above. It does not have an TE
properties.

> This may become clearer looking at a topology such
> as:
> 
> I1          E1
>   \        / 
> I2-T1-T2-T3-E2
>   /        \
> I3          E3
> 
> and you wish to operate three LSPs I1-E1, I2-E2,
> I3-E3 then you can save switching resources (labels)
> on transit routers by building a tunnel from T1 to
> T3 and placing the three LSPs inside. 
> 
> Another detail that can be saved by the use of
> hierarchical LSPs is complexity in the traffic
> engineering database. Consider a packet network
> where the routers are connected over a TDM network.
> The packet network wishes to believe that its
> routers are adjacent even though they are connected
> by many hops through the TDM network. To do this,
> you operate the TDM network on its own and establish
> LSPs between its edges - these LSPs are presented as
> TE links (FAs) to the packet network (think of
> virtual connections).
> 

Yes, but we are making the assumption here that the
TDM network at the base does not participate in
signalling, hence has no switching/TE capabilities.
So from the view point of the routers, 2 links over
different TDM paths, as long as they terminate on the
same node, still form a bundled FA between the 2
nodes.

Can I understand the case where a "node may have
switching but not TE properties", but would *ever need
to pariticipate in signalling* ?

> Cheers,
> Adrian
-brgds
Sylvia


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