Subject: RE: Last Call on RSVP Label Allocation for Backup Tunnels

From: Bora Akyol <[email-masked]>
Date: Tue, 3 Apr 2001 18:47:30 -0700

Ping

At least in one implementation of APS and FR that I am familiar with, the
timing to generate a switchover between the two is very close in terms of
failover and in this particular implementation, APS switchover timing meets
less than 50 ms.

So I would not immediately rule out FR timing in place of APS.

Bora
Who is quite "familiar" with one implementation

-----Original Message-----
From: Ping Pan [mailto:[email-masked]]
Sent: Tuesday, April 03, 2001 6:33 PM
To: Dave Cooper
Cc: [email-masked]
Subject: Re: Last Call on RSVP Label Allocation for Backup Tunnels

Dave Cooper wrote:
> 
> But on the topic of MPLS OAM, it has its
> merits -- especially when software failures (whereby the control plane
> does not detect failures in the data plane) seem to continue to be the
> bane of most MPLS implementations.  I've been preaching this directly
> to vendors for quite some time and despite what tweaks we put into the
> control plane for dealing with failure (whether its fast reroute, normal
> reroute, whatever), its still doesnt fix this constant problem.  Customers
> are tired of hearing the vendor bug excuse.
> 
> dave
> 

Dave,

Agree! Also it's hard to find much overlap between MPLS fast-reroute and
physical link failure detection (such as SONET APS). Although both try
to minimize packet loss, these are fundamentally different technologies.
One does not replace the other, and one does not preclude the use of
other. 

In particular, one big difference between the two is timing:
fast-reroute time is probably lower than typical ISIS/OSPF convergence
time in today's backbone. But fast-reroute time may still be higher than
SONET APS. In particular, I don't think that fast-reroute can offer
guarantees on the upper bound of fail-over time. There are simply too
many uncontrollable variables affecting the fail-over speed, no matter
what type of fast-reroute mechanism you choose.

Regards,

- Ping

---

From: Ping Pan <[email-masked]>
Date: Tue, 03 Apr 2001 19:26:56 -0700

> So I would not immediately rule out FR timing in place of APS.

Bora,

I was pointing out that the fail-over time can be *unpredictable* at
protocol level, where a link failure may trigger heavy processing among
many protocols (such as BGP and RSVP). I have no doubt that if you put a
link detection routine within link card's driver or something, the
failover time can be quite fast.

- Ping

---

From: Bora Akyol <[email-masked]>
Date: Tue, 3 Apr 2001 20:27:10 -0700

>failover time can be quite fast.

Agreed but what I was trying to say thatthe failover time despite 
being dependent on the number of LSPs that have fast reroute enabled 
is not terribly different than SONET APS switchover times. But yes if 
you have N LSPs where N is really large the failover may take longer 
than if you had only one. In practice you will probably not have more 
than 1000 LSPs so this processing delay is not huge.

Bora

---

From: Curtis Villamizar <[email-masked]>
Date: Wed, 04 Apr 2001 20:57:36 -0400

> failover time can be quite fast.

And since 10s of msec is a goal, why would you put it anywhere other
than right on the forwarding cards?

Curtis