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Regarding MPLS.

What is the reason for the N^2 ( N * N) connectivity in IP - Atm networks? And how this is resolved in MPLS?
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abhishek_p
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abhishek_p
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The--CaptainCommented:
Good question - I presume the reason that such things are said about ATM is due to the fact that all host-host connections need their own circuit (switched, or permanent) configured on the ATM fabric.

I have very little clue wrt MPLS - maybe check out the NANOG archives at merit.edu, or start lurking on the list itself (North American Network Operators Group).  My best advice - post a question there, saying it is off-topic, and request others to respond privately, off-list.  Most NANOGers seem to resent a post like 'Hello.  I heard you guys knew something about networks and so I have a question", rather seeming to prefer a "I don't know much about this subject and am sorry to waste your time - if you feel like helping and know something about this topic, please reply privately so we don't bother anyone who doens't want to hear it".  A bit self-deprecating, I must admit, but the list is populated by some serious networking heavyweights, and if you are nice enough some of them will probably try to help answer.  Technical overlords from all the big carriers seem to hang out there, as well as some rather knowledgeable folks from cisco, as well as one of the principle authors of BIND, etc.  I know they will know the answer - the trick is getting them to help you.

Cheers,
-Jon
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abhishek_pAuthor Commented:
Hi,
  Nice to hear this from you but to whom should I contact or somebody will contact me? By the way, according to this persons will, my email ID is alone18@rediffmail.com.  You can contact me here.
regards,
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The--CaptainCommented:
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The--CaptainCommented:
Be sure to search the list archives before posting.

Cheers,
-Jon

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MarkusAureliusCommented:
Firstly, it's not n^2, it's (n-1) + (n-2) + (n-3)... + 1.  So a network with 6 nodes would require 15 connections to be fully meshed.

This only applies to connection-oriented protocols such as frame relay and ATM.  This is because for one node to communicate to another, a permanent virtual circuit (PVC) or switched virtual circuit (SVC) has to be constructed between each one.

One of the strengths of a connectionless protocol such as IP is that it doesn't reuire these; data is routed via the addressing only.  Otherwise the Internet obviously wouldn't work, if every user had to have a permanent connection mapped out to every website server.

However, the trade-off is that with the lack of flexibility with FR or ATM, you can have quality of service (QoS) guarantees and class of service traffic since you've got a chunk of the bandwidth reserved for each PVC or SVC, whether it's being used or not.  That's inefficient from a bandwidth standpoint, but is traded off for the assurance that your priority traffic will always get through no matter how congested the network gets.

MPLS, though not created to directly address this trade-off, partly tries to have some of both the conection-oriented and connectionless worlds.  It's name, Multi-Protocol Label Switching, indicates the main purpose is to be able to feed different types of networks (FR, IP, ATM, SAN, X.25, etc.) onto one backbone.  One resulting benefit is that while it remains many-to-many (connectionless) like pure IP, you can have QoS guarantees as well.
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lrmooreCommented:
G'day, abhishek_p
No comment has been added lately (261 days), so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area for this question:

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The--CaptainCommented:
Sounds fine to me

As far as I've ever heard, MPLS is not nearly the sinecure Markus suggests (mainly due to vendor interoperability issues) and that networks built on MPLS tend to have problems...

Cheers,
-Jon
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