[c-nsp] crs-1 ISSU?

[Marlon Duksa]

Hi,Can anyone point me to the documentation where it says that Cisco IOS-XR
on CRS-1 supports a true  in-service-software-upgrades (ISSU)?

I've been looking on CCO but all they talk in IOS XR is ISSU where they
patch a code and things like that.

What I'm looking is to upgrade a CRS-1 to a new software image with a
subsecond outage. This means upgrading the control plane and line cards with
the new software images with subsecond outage. Not just a specific software
module or a line card but the whole system to upgrade between two major
releases.

I assume that non stop routing (not forwarding) would be a prerequisite for
this, but it seams that they support NSR only for ISIS. NSR implies
statefull failover where all protocol states/transactions are mirrored and
synched between two routing engines. For example, BGP TCP sessions stays the
same during the routing engine failover.

Thanks,
Marlon