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

[Greg Mirsky <[e-mail]>]

Hi Jeff,
I do agree with Eric's characterization of 1+1, m:n, and 1:n (1:1 being the
special case of the former). G.808.1 (attached) gives a good overview of
protection architectures and I think that we can use that as the foundation
and the dictionary when talking about protection in the network slicing.
For example, section 7.1 explains 1+1 protection as follows:

In the 1+1 architecture type, a protection transport entity is dedicated as
a backup facility to the
working transport entity with the normal traffic signal bridged onto the
protection transport entity at
the source endpoint of the protected domain. The normal traffic on working
and protection transport
entities is transmitted simultaneously to the sink endpoint of the
protected domain where a selection
between the working and protection transport entity is made,

The next section explains the architecture of 1:n protection scheme:

In the 1:n architecture type, a dedicated protection transport entity is a
shared backup facility for n
working transport entities. The bandwidth of the protection transport
entity should be allocated in
such a way that it may be possible to protect any of the n working
transport entities in case the
protection transport entity is available.

One of the differences between 1+1 and 1:n/1:1 is that in the latter the
protection path may be used to carry extra traffic given that it will be
affected when the working path fails or deemed degraded below a
pre-determined level.
On the second point, regarding differences in the protection and switchover
of unidirectional vs. bi-directional line, I believe that it is better to
address the bi-directional (viewed as a single object) and consider the
unidirectional protection as the special case of the former.

On Tue, Feb 18, 2020 at 1:08 PM Jeff Tantsura <[e-mail]>
wrote:

> 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
> <https://protect2.fireeye.com/v1/url?k=4896fa91-141f5558-4896ba0a-0cc47ad93e1c-a95572c8cb9519ed&q=1&e=138ed022-c29c-4668-bda7-71975eb05cd5&u=https%3A%2F%2Furldefense.com%2Fv3%2F__https%3A%2F%2Fetherpad.ietf.org%2Fp%2Fns-dt-notes-feb10__%3B%21%21NEt6yMaO-gk%21R9MKmiaYXBuhuTZBYpZvNsiVYjnzH2xbzR2wZ5WPPMspWRsv7tVCr1efC9sXFr8%24>
> .
>
>
>
> 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
> <https://protect2.fireeye.com/v1/url?k=060f429c-5a86ed55-060f0207-0cc47ad93e1c-2d4397becaf63c66&q=1&e=138ed022-c29c-4668-bda7-71975eb05cd5&u=https%3A%2F%2Fgithub.com%2Fteas-wg%2Fteas-ns-dt%2Ftree%2Fmaster%2Fnotes>
> (in md format, I guess)?
>
>
>
> --
>
> Eric
>
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