Re: [Teas-ns-dt] Notes for today's NS-DT meeting

[Jeff Tantsura <[e-mail]>]

Eric,

I disagree with you, also reference to DetNet is not applicable here, they replicate because they follow TSN logic.
In general 1+1 (1:1) protection means that the secondary (protecting) path available is equal in its characteristics to the primary, whether they share fate is an additional property and could have many different semantics (from shared line-card to shared fiber duct).
It is very uncommon to send traffic on both, protected and protecting paths, often protecting path carries other traffic that would be pushed out based on priorities.
As a separate note - we need to discuss unidirectional vs bidirectional protection,  since they have different times to repair, in bidirectional case as long as return path has not been recovered forward path is considered down.

Cheers,
Jeff
On Feb 17, 2020, 12:29 PM -0800, Eric Gray <eric.gray=[e-mail]>, wrote:
> John,
>
>               With 1+1 protection, the sender sends traffic on both the working and protection path, so quite often – while there is a “switchover time” – it is basically a “name-changing” event (the protection path becomes the working path, but nothing else changes without operator intervention) and it is quite often the case that no traffic is impacted.  In other words, the switchover time is irrelevant, as long as it is not so long that a second failure may occur before the switchover is reported to the operator.
>
>               Note that the technology being defined in DetNet, uses packet replication and elimination, which is analogous to 1+1 protection in that sense.  In addition, 1+1 protection is defined for label switching as well.  In fact, 1+1 protection can be applied in any technology that allows for establishing diverse alternative paths.
>
>               Hence, a choice to use packet-switching should be orthogonal to a choice to use 1+1 protection.  And none of these choices has very much to do with “isolation.”
>
>               What you are probably referring to is a distinction between either 1+1 or 1:1, and 1:N or M:N protection – primarily because there is no dedicated protection path in either of the latter two cases.  Either there is 1 protection path for N working paths, or there are M protection paths for N working paths (where M is assumed to be less than N) in those cases, so a switchover may be non-trivial and (possibly) performance impacting.
>
>               For example, not having a dedicated alternative path in the 1:N case means that – if two working path connections fail both will see performance degradation.  Similarly, for the M:N case, if M+1 out of the N working paths fail, the users for at least two of the failed paths will see some performance loss.
>
>               But I fail to see how any of these are inherently cases involving “isolation.”
>
>               One thing I have heard of is using the term “protection isolation” to mean isolation of alternative paths, ensuring that a single failure does not take more than one working or protection path down.  But this is (possibly) more commonly referred to as “shared risk avoidance.”
>
> --
> Eric
>
> From: John E Drake <jdrake=[e-mail]>
> Sent: Monday, February 10, 2020 12:25 PM
> To: Eric Gray <[e-mail]>
> Cc: [e-mail]; Jari Arkko <[e-mail]>
> Subject: Re: [Teas-ns-dt] Notes for today's NS-DT meeting
> Importance: High
>
> Hi,
>
> Wrt protection isolation, if you have dedicated 1+1 protection you still have the switchover time, so this is the minimum service interruption with hard isolation.  If you have packet switching (soft isolation) there are a range of technologies that provide a range of service disruption times.
>
> Sent from my iPhone
>
>
> > On Feb 10, 2020, at 12:15 PM, Eric Gray <eric.gray=[e-mail]> wrote:
> > Are available at: https://etherpad.ietf.org/p/ns-dt-notes-feb10.
> >
> > Please review these notes and either add to them anything we discussed at the meeting, or send comments to me.
> >
> > Jari, later this week, could you push these to the GitHub repository at: https://github.com/teas-wg/teas-ns-dt/tree/master/notes (in md format, I guess)?
> >
> > --
> > Eric
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