IMHO, this is a little vague and definitely out of date. > "Although both ATM and IP held the promise of building > converged > networks in principle, neither actually delivered in > practice. ATM > networks were unsuccessful because they could not > scale to the levels > required for pure data applications.
What is "pure data?" The term is meaningless. Does this mean circuit emulation? Or ..... ? And what is "impure data?" ;-) >Traditional IP > networks failed > because they used legacy routers that implemented > forwarding and > features in software. These routers were not able to > achieve anywhere > near the performance needed for delivering services at > speed. The 75xx series are probably the ultimate in "software based" routers .... and they certainly are no longer adequate in the core of a medium to large ISP network. IMHO, the problem is not just that much of the functionality is implemented in software, but also that all the traffic must cross one or two busses. However, newer routers like Cisco's GSR, Junipers, and others have been deployed for years now. With crossbar style backbones and plenty of ASICs, they are now faster than most ATM switches. OC-48 is no problem wit packet over sonet, and OC-192 interfaces are shipping. > So > providers had to choose between providing simple > connectivity with no > services or providing poor performance with services enabled." Does "no services" mean Sonet? Services don't have be provided from the backbone ... indeed, a backbone router should switch packets as fast as possible, meaning they should do as little other work as possible. Services should be provided at the access layer (check out the Cisco 10000 series - its a service provider access router marketed as a platform for providing services). This is what's done in practice, and its what Cisco has been preaching for years with their three layer model for network design. ATM's selling point was for implementing a single infrastructure for both voice and data. But its simply not economic at the very highest speeds (switches aren't fast enough, and the segmentation and re-assembly hardware in routers is too expensive and isn't fast enough). IMHO, this isn't because of any failure of ATM so much as it is because the load on a big ISP's backbone has grown so fast. At moderate to slower speeds, though, its useful as a very flexible layer 2 for carrying all kinds of traffic. Most of this is opinion, so YMMV. the "other" jason Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=26276&t=26245 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
