The MPLS WG Archive

[Alex Zinin <azinin@cisco.com>]

Yangguang,

One thing that seems interesting to me in the context of optical
networks is potential possibility to prune the topology of IGP
adjacencies to minimally necessary (e.g., redundant spanning tree),
while still announcing TE information about all optical links.
The state of the links would be defined with protocols like LMP
or mechanisms integrated into lower layers. This is possible
because in case of p2p links (valid for ONs), we do not use
IGP topology database for CSPF. However, we do use it in other
networks when calculate the paths through multi-access segments.

-- 
Alex Zinin


Wednesday, October 18, 2000, 10:57 AM, Yangguang Xu <xuyg@lucent.com> wrote:

> Kireeti,

> I guess I didn't address clearly about using TCP session.

> There are two ways to distribute transport network topology. Either way has pros
> and cons. 

> 1) Piggyback through standard OSPF Opaque LSA
>    If we want to apply OSPF/ISIS, CR-LDP/RSVP directly to circuit switched
> transport network, you are absolutely right. There should be a one-to-one
> correspondence of routing adjacency and control channel. 

>    However, there is a fundamental problem here, folks (including me) always try
> to apply existing protocols directly to other applications. Protocols are always
> designed for a certain problem with unique features, assumptions and
> requirement. For other "similar" problems which may have different assumptions
> and requirement, "Here it is and use it" isn't always a good solution. We should
> first understand the correct assumption and requirements of optical network and
> then tune routing and signaling protocols for them.

>    Using existing solutions, protocols to define problem, application and
> assumption seems to be not quite right. 

> 2) An independent application 
>    You don't need a dedicated control channel in this case. A TCP session is
> enough. 

> Thanks,

> Yangguang

> Kireeti Kompella wrote:
>> 
>> > 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.