Q:Why router with ATM interface comes out earlier than pure SONET interface?
alan at globalcenter.net
Mon Aug 3 07:00:36 UTC 1998
This issue is precipitously close to a
religious issue, but hopefully we can
forego the fall.
One of the nifty things about ATM is that
cells are of the same size, so building
physical interfaces is a bit easier, as
the timing is deterministic.
One of the drawbacks of ATM is that to run
IP/ATM we have to do SAR [Segmentation
and Reassembly]. Another drawback is
the overhead of ATM, arguably somewhere
between 5-30%, but inarguably greater than
So, these two variables interact over time
to paint a climate in which we live. Of
course there are many more issues at stake,
which others can invariably describe in
better detail than I could attempt.
Notwithstanding these two significant
technical issues, market maturity and
interest also impacts this significantly.
Many people previous to '98 believed
'convergence'  would occur in a network
composed of ATM. So, the market grew
to accept anything related to ATM as the
future, and worthy of time and funding.
Recently the market seems to be growing
more towards 'convergence' at the IP
layer, with the predominant audience of
applications using native IP, be that over
VPN or the greater Internet.
In addition to that, we should consider
traffic engineering and the motivations
of a 'large' NSP/ISP to build a scalable
ATM (and frame) provides native
source-routing traffic engineering using
PVCs. Traditionally non-ATM networks
(remember, limited to DS3 until recently)
suffered from a lack of this traffic
Recently, due to good theoretical
work, and practical demonstrations by
vendors, MPLS has emerged as a viable
competitor for ATM in the field of traffic
I believe these variables contribute
to the history of ATM as a fore-runner
, and the emergence of Packet over
Sonet as the leading ubiquitous transport
platform for the communications network
of the world.
It will be quite interesting to see who
is first-to-production with OC-48.
My money's on Packet/Sonet.
 - convergence - second only
to the term 'carrier class' in silliness.
 - pun unintentional
Thus spake Yu Ning (yuning at mindless.com)
on or about Mon, Aug 03, 1998 at 11:02:33AM +0900:
> Hi friends,
> I find in an article, and it says: in 1995,1996 most nationalwide ISP face the demand
> of higher bandwidth than T3, and at that time the only avalible high bandwidth interface
> in router in ATM port(say 155M), then this makes many of them choose ATM as their
> backbone tech. Later, Giga router with POS(Packet over SONET/SDH) 155M(or higher)
> interface comes out, then the situation is changed.
> Then my question is: why 155M ATM interface is easier to make than 155M POS interface?
> Although the net capacity of 155M ATM is less than 155m POS, their capacity for IP packet
> is really close. I think its nearly the same challenge to pump up a 155M ATM pipe as a
> 155M POS pipe with IP packet for a router.
> Thanks for any comments.
> Yu Ning.
> Yu Ning
> ATM R&D Center of
> BUPT (Beijing U. of Posts&Telecom)
> Beijing (ZIP:100876, MBox:147#), P.R.China
> mailto:yuning at mindless.com or yuning at 263.net
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