Cell Relay Archive

[Gaurish R Dalvi <gaurishr@wipinfo.soft.net>]

The fundamental purpose of MPOA is to provide end-to-end network-layer
connectivity across an ATM fabric, whether hosts are attached directly to
the ATM fabric, or to legacy LANs or those using LANE. 

A) The router presents a potential scalability and performance limitation.

MPOA overcomes this problem by supporting connections between nodes on
different subnets, as opposed to LANE. Or put simply, this means that
inter-subnet connections need not pass through a router.

Interestingly, while MPOA might seem to supersede LANE, MPOA works in
cooperation with LANE to support ELAN. However, MPOA uses NHRP for
establishing shortcut connections, using the indirect approach. And this
helps it overcome one of the major scalability limitations of LANE.

However, these architectures raise technical issues of their own.

Having shortcut connections across LIS boundaries implies the need for
proper coordination of routing and addressing between the ATM and network
layers. The ATM forum chose the overlay model over the peer, conventional,
classical models (again none of these is without its own problems and none
can be said to be a clear cut best fit solution).

One problem of course is the possiblity of routing loops => limitations on
network topologies that can be supported. 

Also interoperability will be a major bottleneck.

Actually, I was trying to search out some practical problems with MPOA
scalability, but did not turn up anything very useful. You might also try
searching for problems with the technologies that MPOA uses like overlay
addressing to help answer your question. 

In addition you might want to take a look at the following articles :

http://www.atmforum.com/atmforum/library/53bytes/backissues/v4-3/article-04.html

http://www.itweb.co.za/office/di/9803121121.htm

Here is an old paper I found. Might be useful :
http://solar.chonbuk.ac.kr/~bjlee/mirror/Tutorials/switch.html


Gaurish


> 
> Does anyone have any material or know of any web sites with
> information regarding to the scalability of MPOA. I deliver ATM
> training courses and look at both MPOA and the use of MPLS over ATM.
> More than once I have been asked about the scalability of both models.
> I think that I understand the way in which an MPLS network may scale
> based on following a traditional routing model, however I am not so
> sure about MPOA.
>