Subject: [CCAMP] Comments on draft-sambo-ccamp-yang-fsm-transponder-reconf-00

From: Dieter Beller <[email-masked]>
Date: Wed, 21 Mar 2018 19:54:01 +0100

Hi Nicola,

as there was no time left for providing my comments at the end of the 
CCAMP session this morning, I am providing my comments by e-mail:

Are you assuming that the FSM is running autonomously on the optical 
transponder? What are the events that  trigger state transitions?
I understood that there are local events that the optical transponder 
creates and there can also be external events coming from an SDN 
controller for example.

Slide 6 only shows half of the picture: when the FSM of an OT decides to 
change its state, the remote transponder has to do exactly the same 
state transition.
If the two transponders terminating the optical signal are not 
configured consistently, no traffic can be carried across the optical 
path. This means that state
changes require coordination between the two optical transponders. How 
is this accomplished such that the service disruption time is minimized?

Slide 6 shows an example where the modulation scheme is changed from 
16-QAM to QPSK. This reduces the data rate of the traffic to 50% (from 
200Gbps
to 100Gbps for example). I suppose that the traffic that can be dropped 
must be best effort traffic.

These network operations issues need to be addressed in the draft for 
this specific optical transponder FSM use case. Otherwise, its 
applicability is doubtful.

Thanks,
Dieter

---

From: nicola sambo <[email-masked]>
Date: Thu, 22 Mar 2018 12:15:59 +0100

Hi Dieter,

answers inline:

> transponder? What are the events that  trigger state transitions?

the FSM is installed by the SDN controller in the agent of the transponder
and then runs there. We enabled this instruction with a NETCONF
<edit-config> message.

For the case of a transponder, the events can be a BER above the threshold
or the OSNR below a threshold or some other monitored parameter. We assumed
these parameters monitored at the DSP of coherent receiver.

> creates and there can also be external events coming from an SDN controller
> for example.
>

The events are detected (more than created) by the transponder at the
receiver end. The SDN controller only instructs the transponder about the
possible events and reactions by setting the thresholds and the
reconfiguration settings. So, the SDN controller only instructs the
transponder.

> change its state, the remote transponder has to do exactly the same state
> transition.
> If the two transponders terminating the optical signal are not configured
> consistently, no traffic can be carried across the optical path. This means
> that state
> changes require coordination between the two optical transponders. How is
> this accomplished such that the service disruption time is minimized?
>

One of the actions when the event is detected is this coordination. The
transponder at the receiver side sends a message to the  transmitter to
synchronize about the transmission parameters to be adopted. This message
can be sent over a control channel. This way both the tx and rx know the
format, FEC, and so on.

We mentioned this in the draft. We will add a more detailed paragraph in
the new version of the draft.

> must be best effort traffic.

Yes, right. We can also expand this in the new version, by referring to
service classes use cases from Telecom Italia and DT.

>
> These network operations issues need to be addressed in the draft for this
> specific optical transponder FSM use case. Otherwise, its applicability is
> doubtful.
>
>
Ok. We'll clarify these points in the version 01.

Thanks.

Best,
Nicola

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