Re: [mpls-tp] Comments on draft-fbb-mpls-tp-data-plane-00: ~ECMP =>~ETH aggregation?

[Maarten Vissers <[e-mail]>]

Curtis,

MPLS-TP and other packet transport technologies can be run over a compound
link. Such compound link can be provided by multiple section layer transport
paths or by multiple edge-to-edge LSPs. In both cases the nodes at the edge
of such compound link have to make sure that all traffic within a
service/transport path is transported via only one link within the compound
link. This to maintain e.g. the order of packets/frames within the
service/transport path.

To deploy the survivability provided by compound links, ITU-T Q.9/15 has
developed the Adaptive Compound Link SubNetwork Group protection with
Inherent monitoring (ACL-SNCG/I) mechanism. This ACL-SNCG/I protection
controls the distribution of 
1) PWs, service-LSPs and service path layer PST LSPs over a service path
layer component links (supported by edge-to-edge LSPs) within a compound
link,
2) edge-to-edge LSPs and transport path layer PST LSPs over a transport path
layer component links (supported by sections)within a compound link .

The initial work done assumed the presence of non-adaptive media, which
would cause a component link to be completely available or completely
unavailable (as in ethernet LAG). At the moment this work is being extended
to also support adaptive media, which are able to reduce their bandwidth to
a lower level; i.e. creating a partly available state in between the
original two states.

Input to the distribution process is the CIR(EIR) and relative priority of
each service path or transport path that is carried over the compound link
and the available bandwidth of each component link within the compound link.
The distribution process computes the distribution of the service paths, or
transport paths. If the bandwidth of the compound link becomes too small to
support all, then the lowest priority service/transport paths are blocked
and packets/frames of those paths are not longer forwarded over the compound
link.

A service path or transport path's bandwidth must always be smaller then the
bandwidth of the component links.

Regards,
Maarten

-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf
Of Curtis Villamizar
Sent: vrijdag 5 maart 2010 6:51
To: Adrian Farrel
Cc: [e-mail]; Rui Costa
Subject: Re: [mpls-tp] Comments on draft-fbb-mpls-tp-data-plane-00: ~ECMP
=>~ETH aggregation?


In message <21AFCCB59EFE4816B26E280DF3355CE2@your029b8cecfe>
"Adrian Farrel" writes:
>  
> Surely the formation of the server layer and the use of OAM within the 
> server layer is entirely an issue for the server layer.
>  
> It is a mistake for the MPLS-TP layer to be aware of the underlying 
> technology that provides the link connectivity between to adjacent 
> LSRs. The links provided by the server layer have certain resiliency 
> and recovery properties, as well as properties associated with 
> in-order (or not) packet delivery that are announced to the MPLS-TP 
> network (usually through
> configuration) and the MPLS-TP network can choose which links to use 
> accordingly.

The goal is to make OAM work by adding entropy.  If there is no underlying
LAG, then the entropy serves no purpose but does no harm.

If there is an underlying LAG then not having entropy allows the OAM traffic
to test only one member.  For example, if an MPLS LSP hop
(section) is a LAG, traffic within that MPLS LSP would take different LAG
members if the entire label stack was not the same for all traffic or if the
LSP carried IP traffic from more than one host pair.  If the OAM traffic had
a fixed label stack it would test only one LAG member.

> LAG at a server Ethernet layer is a way of providing a composite link 
> to the MPLS-TP layer. That link has specific properties, but the 
> MPLS-TP layer cannot be expected to take specific measures to operate 
> the link. That is the job of the server layer itself (noting that the 
> adaptation into the LAG is a function of the server layer, just as the
operation).

If CL is allowed for MPLS-TP, then OAM must work for CL.  We should not
knowingly just specify something that is broken.

> So, the MPLS-TP layer runs OAM across the link. It doesn't know how 
> the link is formed. It is the responsibility of adaptation function to 
> either distribute the MPLS-TP packets across the group members such 
> that link degradation will be noticed by the MPLS-TP layer (this could 
> be noted as a requirement that the MPLS-TP layer puts on the server 
> layer that link degradation should be detectable by any measure of 
> MPLS-TP packets); or the server layer must perform its own OAM to 
> detect link degradation and report it to the MPLS-TP layer at the link end
points.

For plain old MPLS, it doesn't know about any LAG either, but the 127.x
source addresses add the entropy needed to provide effective OAM.  That is
why IETF specified MPLS Ping and and rejected 1711 and why MPLS Ping works
and 1711 doesn't work.

> LAG is not the only "complex" way of forming links in the MPLS-TP 
> network from multiple links in the server network, and we really don't 
> want to embark on making MPLS-TP understand each and every server
technology.
>  
> Cheers,
> Adrian

However, any method which is capable of supporting an LSP that is greater in
capacity than any one component link needs to look below the top label to do
so.  I think that is trivailly provable given that the top level is always
the same for that LSP.

Therefore no matter what we define CL to be, if this CL supports LSP of
greater than a LAG member size, a capability we currently have with Ethernet
LAG or ECMP over parallel links (another form of link aggregation that
predates Ethernet LAG by over a decade), then OAM needs to provide entropy
to insure that any CL/LAG/ECMP along the path is exercised.

Curtis


> ----- Original Message -----
> From: "Stewart Bryant" <[e-mail]>
> To: <[e-mail]>
> Cc: "Rui Costa" <[e-mail]>; <[e-mail]>
> Sent: Wednesday, March 03, 2010 10:59 AM
> Subject: Re: [mpls-tp] Comments on draft-fbb-mpls-tp-data-plane-00: 
> ~ECMP => ~ETH aggregation?
>  
>  
> > Curtis Villamizar wrote:
> >> In message <[e-mail]> Stewart Bryant writes:
> >>
> >>>  I would think that if the operator wanted the bandwidth more than 
> >>> they wanted the fate sharing, they will deploy the technology.
> >>>  - Stewart
> >>>
> >>
> >>
> >> There is no reason not to put some entropy in the extension to MPLS 
> >> Ping so that there was fate sharing over LAG.
> >>
> >> Curtis
> >>
> >>
> > Curtis
> >
> > Do you have some text in mind?
> >
> > - Stewart
> > _______________________________________________
> > mpls-tp mailing list
> > [e-mail]
> > https://www.ietf.org/mailman/listinfo/mpls-tp

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