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Re: Q:Why router with ATM interface comes out earlier than pure SONET interface?

  • From: Alan Hannan
  • Date: Mon Aug 03 03:15:06 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
  native IP/sonet.

  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' [1] 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
  efficient architecture.

  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
  [2], 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.


  [1] - convergence - second only
  to the term 'carrier class' in silliness.
  [2] - pun unintentional

Thus spake Yu Ning (
 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
> or
> _____________________________________________

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