[CCAMP] Comments on FlexE draft "draft-izh-ccamp-flexe-fwk-04"

[Dieter Beller <[e-mail]>]

Hi Loa,

please find as promised during the CCAMP session the two FlexE data 
plane issues I raised regarding draft-izh-ccamp-flexe-fwk-04:

It is unclear what the intend for the semantics of the administrative 
locking function is. Is the intention that the group can be carrying 
live traffic when the group
is locked? The draft indicates that it is possible to add or remove PHYs 
from a group while the group is administratively locked. The FlexE IA 
says that PHYs cannot
be added or removed while the group is in service. Maybe the intent is 
that this would allow to temporarily ignore errors where the two ends 
temporarily think the
group is composed of a different set of PHYs and not bring the group 
down. But there is more to it than that: you need to deskew across a 
different set of PHYs,
which may mean adjusting the center point of the skew buffers to a 
different spot, which can’t be assured to be hitless bringing up a new 
group with a different
set of PHYs.

The biggest issue is with Figure 3 which illustrates FlexE client 
switching, which is not envisioned at all in the way FlexE is designed. 
What you can do is to have a
FlexE group at the transport network ingress and another FlexE group at 
the transport network egress, mapping the FlexE client into an ODUflex 
which is
switched as an LSP from one end to the other. But what they are 
illustrating is a set of network nodes that are interconnected by FlexE 
groups and daisy-chaining
this together to create a path through the network. The difficulty is 
that a FlexE client has been designed to have the semantics of an 
Ethernet PHY, which is a link
rather than a layer network. The nodes they are illustrating would have 
the semantics of a kind of crossbar switch interconnecting Ethernet PHYs 
in cut-through
mode. This has a bunch of issues: you are carrying the 66B flow over 
multiple link segments without going through any Ethernet bridge that 
would discard MAC
frames with bad MAC FCS and the MTTFPA can’t be maintained, and you also 
have no kind of OAM that will allow you to find where faults or errors 
occurred in the
network.

The draft must not add any FlexE data plane functionality and the FlexE 
draft should strictly be scoped to GMPLS control plane aspects for a 
given data plane.


Thanks,
Dieter