Subject: Re:Some queries

From: Atsushi Iwata <[email-masked]>
Date: Sun, 17 Dec 2000 18:20:35 +0900

Ramanjaneyulu

>>WHY use MPLS?
>~~~~~~~~~~~~~
>  MPLS forwarding and LSP set up  is ATM like technology , but there r lot
>of differences between ATM and MPLS technologies. The following are the
>problem with ATM.
>
>  --- Scalability issue : In MPLS we can allow any number of Hierarchies,
>where as in ATM only 2 level hierarchy allowed. More over ATM VCI is 5 -
>bit , this becomes constraint in terms of scalability.

I think that this includes a wrong statement.

In MPLS, the number of hierarchies depends on the routing protocol that you
use. Normally you can have upto 4 level hierarchies, 2 level OSPF and 2
level BGP (if you use BGP confederation).

In ATM, you can use 104 level hierarhy in theory if you use PNNI in
bit-by-bit hierachy assignment. However, 4 or 5 level hierarhy would be
enough in the current ATM network, though.

Thanks

----------------------------------------------------------------
Atsushi Iwata
Assistant Manager
Network Architecture TG,
Computer and Communication Media Research Labs, NEC Corporation
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---

From: "Alexander Marhold" <[email-masked]>
Date: Sun, 17 Dec 2000 14:45:03 +0100

> level BGP (if you use BGP confederation).
I think that this includes a wrong statement

the MPLS hierarchy (if you want to call it this) DOES NOT depend on any
hierarchy in the IGP
ît also only partly relies on the BGP hierarchy ( see interprovider VPNs and
Carrier's Carrier hierarchies)
So by using Carrier's carrier architectures (not implemented now but
specified in drafts) you can create as many hierarchies as you like.

One of the big advantages of MPLS (MPLS/VPN) is that you get the outside and
its hierarchies to be decoupled from the inside transport.

with best regards
Alexander Marhold
Senior Consultant
PRO IN

---

From: Atsushi Iwata <[email-masked]>
Date: Mon, 18 Dec 2000 12:05:45 +0900

Alexander,

At 14:45 00/12/17 +0100, Alexander Marhold wrote:

>$B{U(B also only partly relies on the BGP hierarchy ( see interprovider VPNs and

I may be wrong. 

What's a difference between the current BGP hierarchical networks and the
BGP-VPN networks in terms of hierarchy perspective. If we apply an IP-in-IP
tunneling scheme to the current BGP networks, then we can do the same thing
as what BGP-VPN does. Is it wrong ? 

I'm not sure what's a main point that you want to discuss for MPLS specific
capability. I would appreciate if you could tell me about it.

Do you also assume that you have label stacking across the domains ?
If it is true, the penalty of having the label stacking (i.e. MPLS header
tax) has to be taken into account, too. Therefore the tradeoff between
multiple hierarchies and multiple label stacking exists.

Any comments?