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 engineering. 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 engineering. 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. -alan [1] - convergence - second only to the term 'carrier class' in silliness. [2] - pun unintentional Thus spake Yu Ning (yuning@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@mindless.com or yuning@263.net _____________________________________________