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Re: draft-otani-ccamp-interas-gmpls-te-00.txt
Hi Adrian,
Thank you for your comments.
Some of SPs including ourselves have a plan to introduce GMPLS control
plane
technologies for a NGN, and even NGNs should be interconnected with each
other,
as SONET/SDH networks are as well as IP/MPLS networks are.
Your supposed model is another example to reveal the necessity of Inter
AS TE.
I agree that a crankback mechanism is one of the ways to achieve this.
In terms of the amount of computation by the ASBR, we have to
investigate
the impact on the load to the ASBR, hearing from the routing (EGP: BGP4?)
expert.
That's why, in the draft, we described that the TE information may be
statically or
dynamically exchanged. Operators would like to know the route of a
GMPLS LSP
within an AS and the pair of ASBR in advance, if the LSP is established
across
the inter AS, especially multiple ISPs, resulting in the implementation
of TE extensions.
The network resiliency is getting significant more and more in a SP
environment.
There was a big discussion about SRLGs among us and so far, as you
pointed out,
we do not have any solutions for this. Altouhgh each SP believes
that these TE links
are not a SRLG because these are belonging to a different SP, fibers
accommodating
such TE links may be laid in the same duct otherwise the same tunnel
under the road.
Our conclusion is that the level of SRLG is another issue.....(one issue
is indeed how
to assign SRLG IDs to each SP)
Regards,
tomo
At 18:41 04/07/27, Adrian Farrel wrote:
Hi,
A nice short draft. Congratulations!
Also, it is very good to see SPs bringing
forward requirement drafts. Thank you.
I understand the point you are making in the
draft, but I am not sure it is specific to GMPLS and switching
capabilities.
For example, suppose we modify the bandwidth
in your MPLS example network to:
+----+
+----+ |
+----+ +----+
| A1 |----//----| A3 |---------| B1 |----//----| B3 |
+----+ 10G +----+
10G +----+ 2.5G +----+
|
|
|
|
|
=2.5G
=10G |
=2.5G =2.5G
|
|
|
|
|
+----+
+----+ |
+----+ +----+
| A2 |----//----| A4 |---------| B2 |----//----| B4 |
+----+ 2.5G +----+
10G +----+ 10G +----+
|
MPLS AS
1
| MPLS AS 2
Now, set up a 10G service from A1 to B4.
AS 1 is going to select the ASBR pair A3/B1 as the shortest path out of
AS 1.
But B1 will fail the setup.
We must rely on crankback or a wider view (PCE, TE aggregation, etc.) in
order to be successful.
I think what your draft points out, however, is that the complexity for
GMPLS is increased considerably (perhaps to a power of three). It is
further worth noting that if we added some speculative future routing
constraints (such as source-based lambda selection, optical impairments,
etc.) the problem would get even more complex.
Essentially, however, the problem is the
same: IP route aggregation is not sufficient to enable inter-domain TE
and some other solution is needed. Your proposal for EGP extensions to
general reachability information is certainly one option.
The concern that I have heard voiced is that
there may be significant churn in this information, and this would result
in a significant amount of aggregation computation by the ASBRs. My view
is that:
- in a non-PSC GMPLS network the rate of change is
not likely to be significant
- we should, in any case, specify damping of computation
and updates if we proceed with this approach.
But I would be interested to hear this debated further especially by the
EGP experts.
Your point about SRLGs is very valid.
Currently, however, (as I understand it) we don't have a satisfactory
encoding for SRLG IDs to allow an ID to be globally unique *and* to allow
an SRLG to span ASs.
Thanks,
Adrian