Subject: RE: Fast Reroute Interoperability

From: "Don Fedyk" <[email-masked]>
Date: Fri, 5 Oct 2001 21:31:01 -0400

Jim

> 
> This is true, and in the last meeting it was noted by the authors that
> they think they can bring together a common draft.  That 
> would be a good
> thing as it would seem to meet one of the requirements in
> draft-ietf-tewg-restore-hierarchy-00.txt.  This is the only 
> approach to
> restoration times in the 10s to 100s of ms.

You mean this is the only layer 3 based approach that allows this.
Optical systems have done this for years and they don't compromise
QoS like some layer 3. I would hope that your draft on hierarchy would 
point out that hardware based mechanisms at lower layers can be coordinated 
with layer 3 and it might not be such a good idea to have higher 
layers doing fast recovery before lower layers. It would also seem
to be beneficial to move protection to the lowest layer you could 
afford it to get the maximum scaling from protection. Applying this 
to a GMPLS network I would think these control mechanisms rerouting 
light paths in mesh networks and layer 3 mechanisms not being so 
time sensitive.

Don

> 
> Another approach that both do support is that of 1:1 Path 
> LSPs where when
> traffic is on a primary, and if that has problems, the traffic shifted
> onto another pre-signalled LSPs (assuming that one is still 
> ok).  This can
> bring restoration times down significantly (maybe shave 5-10 
> seconds off
> not having this), but there still are impacts at the head end 
> routers as
> they shift the traffic.  This approach satisfies another
> restoration requirement in the above mentioned tewg document.
> 
> Jim
> 
>

---

From: Jim Boyle <[email-masked]>
Date: Sat, 6 Oct 2001 11:08:54 -0400 (EDT)

> You mean this is the only layer 3 based approach that allows this.

yes, as we were talking about mpls.  To be fair, there are ATM
implementations that can do restoration on the order of 1-200 ms on a
national network, but that's not relevant to this discussion either.

> QoS like some layer 3. I would hope that your draft on hierarchy would

except in that latency of the layer 3 service can be much higher (e.g.
+60 ms rtt) than if restoration was done at layer 3.

> layers doing fast recovery before lower layers. It would also seem

it is mentioned that some like layer 1 restoration (you as an example),
some like layer 3 to do the restoration (me, for instance), and
most routers today have some tuning flexibility to be very responsive to
AIS, or to hold off for 1-200 ms, which allows for either architecture.

> afford it to get the maximum scaling from protection. Applying this

I'm not sure who it would benefit to do as much at Layer 1 as one can
"afford".  There are still situations you will have to protect against at
Layer 3, which means you'll have extra capacity at both layers - sounds
expensive.  Even if you do all sorts of APS into the routers, there are
still service issues (e.g. ability to deal with unplanned bandwith
loads, latency during protection, etc..)

> light paths in mesh networks and layer 3 mechanisms not being so

That is one valid approach.  Another is linear capacity at layer 1 and
restoration being done at layer 3.  Another, at some point, may be some
sort of more intertwined communication between the layers, but no-one
on the design team nor in the TEWG thought that was the pressing need at
this time.

Jim