Re: [ippm] New Version Notification for draft-mhmcsfh-ippm-pam-03.txt

[Peter Thompson <[e-mail]>]

Dear Greg at el,

I think this a very interesting direction of work and I support the idea of creating metrics for service availability. I have some questions:

1) Definition of a ’service’

There is an implicit identification of a ’service’ with a particular flow of packets. However, if we think of, e.g., a bearer service, this is a *capability* to deliver packets regardless of whether any packets are currently flowing. It seems odd to record a service as ‘available’ only when it is being actively used! Also, a higher-level service may have units of information exchange that are not individual packets, and the notion of whether it is ‘available’ may go beyond whether packets are being exchanged with sufficient reliability.

2) Flow being measured

When we speak of a ‘violated packet’ are we thinking of measuring *all* packets in a flow or just a subset (e.g. a co-incident stream of test packets)? Using a test packet stream has advantages:
- Packets can include transmission times and sequence numbers, making measurement of delay and loss much easier
- measurements continue even when there is no active service flow

3) Service availability transition

A service is moved to the ‘unavailable’ state if ten consecutive SVIs are detected - shouldn’t this number be a configurable parameter? Could it be N of M in a rolling window? (If only every tenth interval was unviolated this ’10 consecutive’ test would fail but the service wouldn’t be very good!)

Peter Thompson, Chief Technical Officer Predictable Network Solutions Ltd., +44 (0)333.340.7713 • Twitter: @PNSolLtd

PS this is my first post to this list, so I apologise in advance for any infelicities of format or etiquette!