Re: [CCAMP] MELGs - Q&A

[Vishnu Pavan Beeram <[e-mail]>]

Fatai, Hi!

Good to see that you understand the construct now.

This is not a corner case. The utility of the construct becomes quite
significant if you have an application that does concurrent path
computations on an abstract topology.

Regards,
-Pavan


On Fri, Mar 22, 2013 at 4:24 AM, Fatai Zhang <[e-mail]> wrote:

>  Hi Pavan and Igor,****
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> I understand more after I read your draft and your explanation again.****
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> I now understand that MELGs are used to solve the competition of “the same
> resource” in the server layer shared by two or more VLs, so I agree what
> Igor said that MELGs are important only when you compute concurrently two
> or more paths.****
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>
> Do you think is this a corner case?****
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> Best Regards****
>
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>
> Fatai****
>
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> *From:* [e-mail] [mailto:[e-mail]] *On Behalf
> Of *Fatai Zhang
> *Sent:* Friday, March 22, 2013 9:15 AM
> *To:* Igor Bryskin; Vishnu Pavan Beeram; [e-mail]
>
> *Subject:* Re: [CCAMP] MELGs - Q&A****
>
>  ** **
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> Hi Pavan and Igor,****
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>
> Thanks for your clarification.****
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> I have seen the Question 1& 2 provided by Pavan. ****
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> When I asked “Why is there “mutual exclusivity”?  What is the essence of
> “mutual exclusivity”?,  I just want to know if “mutual exclusivity” exists
> because of “fate-sharing” in the server layer?****
>
> ** **
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> If the answer is “yes”, then SRLG  100%  fits the valide use-case (ie., no
> need to introduce a new concept). ****
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> Please correct me if I missed something on the essence of MELG.****
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> Best Regards****
>
> ** **
>
> Fatai****
>
> ** **
>
> *From:* Igor Bryskin [mailto:[e-mail]]
> *Sent:* Thursday, March 21, 2013 10:43 PM
> *To:* Fatai Zhang; Vishnu Pavan Beeram; [e-mail]
> *Subject:* RE: [CCAMP] MELGs - Q&A****
>
> ** **
>
> Fatai,****
>
> [Fatai] I don’t understand your definition of MELG(ie., MELGs are used to
> advertise “mutual exclusivity” information).  If we name it as XXLG, we can
> define XXLG similarly in your style: XXLGs are used to advertise “XX”
> informaiton.  My real question is: Why is there “mutual exclusivity”?
>   What is the essence of “mutual exclusivity”?****
>
> ** **
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> Let me try to answer that. With Virtual Links it is possible to advertise
> two or more VLs with only one of them from the group to be operational at
> any given time. Recall that VLs could be advertised without having
> underlying server layer connection (e.g. H-LSP) in place. Therefore, the
> group of VLs may depend in a mutually exclusive way on a single network
> resource (e.g. WDM transponder). In order to make TE domain aware of such
> mutual exclusive dependency, it is suggested to use the concept of MELG.
> The path computer will understand that two or more VLs are mutually
> exclusive if they have an MELG in common. ****
>
> ** **
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> Note, that MELGs are important only when you compute concurrently two or
> more paths, so that path computer wouldn’t select paths with two or more
> VLs that mutually exclude each other. When you compute one path at a time,
> MELGs are not important and could be ignored.****
>
> ** **
>
> Note also that MELGs make only sense for VLs, why otherwise you will
> advertise two links if only one of them at a time could be used, right?
> Normally you would advertise only one of them. However, with VLs it does
> make sense to advertise both as network topology potentiality. Hope this
> makes sense.****
>
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>
> Cheers,****
>
> Igor ****
>
> ** **
>
> *From:* [e-mail] [mailto:[e-mail]] *On Behalf
> Of *Fatai Zhang
> *Sent:* Wednesday, March 20, 2013 11:38 PM
> *To:* Vishnu Pavan Beeram; [e-mail]
> *Subject:* Re: [CCAMP] MELGs - Q&A****
>
> ** **
>
> Hi Pavan,****
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> 4. How is MELG different from SRLG?
>
> Each construct addresses a separate problem. SRLGs are used to advertise
> “fate-sharing” information. MELGs are used to advertise “mutual
> exclusivity” information. ****
>
> ** **
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> It is possible for TE-links that have a common SRLG to be
> instantiated/used at the same time. It is not possible for TE-links that
> have a common MELG to be instantiated/used at the same time - only one of
> them can be used at any given point of time****
>
> ** **
>
> [Fatai] I don’t understand your definition of MELG(ie., MELGs are used to
> advertise “mutual exclusivity” information).  If we name it as XXLG, we can
> define XXLG similarly in your style: XXLGs are used to advertise “XX”
> informaiton.  My real question is: Why is there “mutual exclusivity”?
>   What is the essence of “mutual exclusivity”?****
>
> ** **
>
> In additon, what you said in the second sentence about “possible” vs “not
> possible” is a kind of policy, there is nothing different between SRLG and
> MELG here. ****
>
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> ** **
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> Best Regards****
>
> ** **
>
> Fatai****
>
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