The MPLS WG Archive

[Kireeti Kompella <kireeti@juniper.net>]

> The key point is that routing adjacency in circuit switched network data plane
> has nothing to do with control channels (the control plane). At least there
> shouldn't be any assumption about their co-existence.

Actually, there is a one-to-one correspondence (for GMPLS, anyway):
one routing adjacency for each control channel.

There is the issue of OSPF-incapable OXCs.  In this case, there may
be a proxy intelligent device that handles OSPF/signalling/LMP;
however, that device still needs to have an OSPF adjacency, so the
problem doesn't go away, it just moves to this device.  However, here
what you say may apply: the OXC may just need a simple TCP session to
the proxy device, depending on their (private) API.

> For each routing adjacency (in data plane), you only need a TCP session as Frank
> hinted. Not necessary a physical control channel.

You don't need a physical control channel, but you do need more than
a TCP session.  You need a routing adjacency (OSPF doesn't run over
TCP, and certainly ISIS doesn't), a path for signalling messages and
(probably) a path for LMP control messages.  Fortunately, a GRE tunnel
will do exactly this.

> BTW, I had a feeling that LMP suggest control channel for each bundle. (I read
> it long time ago, can't remember exactly). If this is the case, it's simply not
> right. For example, a OXC has 10 neighbors, between each neighbor there are 2
> bundles, then do you need 20 control channels? NO!

The next rev of LMP will address this issue.  We basically realized
that this is an issue for fast Hellos, failover and OSPF, but this
applies to signalling as well.  So, we'll try to bring this down to
one control channel per pair of neighboring GLSRs.

Kireeti.