On Fri, Feb 23, 2001 at 12:02:05PM +1300, Stephen Donnelly wrote:
dean(a)flatnet.gen.nz wrote:
Yeah Joe's right.
Given the fact that there is no way of sar-ing over oc48, most major players are now moving to POS. Even if you don't need oc48 or oc192 now, it makes little sense to embrace ATM for a new network and then have to throw it in the bin next year anyway. Also the higher the speed the more the celltax costs you. Eg if you pay for an oc12 on southern cross then you loose the equiv of an oc3 in overhead. Thats a heckload of cash. Loosing an oc12 on an oc48 link is even worse.
The 'cell tax' is 5 bytes of overhead for every 48 bytes of data, or about 1/10. So for OC12 (around 622Mbps), it's about 60Mbps, not 155, and for oc48 it's around 250Mbps. That is over an OC3, but much less than an OC12.
See Joes reply for a full description, but needless to say that the 5 byte header is not the only overhead that atm imposes.
In case you're interested, we have built a PCI card for passive monitoring OC48 POS. (no one wanted ATM, for some reason ;)
fairly old page: http://atm.cs.waikato.ac.nz/wand/docs/dag4/
Research group pages (also old): http://wand.cs.waikato.ac.nz/
Cool - We use agilent, ixia and smart bits for testing (although the smart bits imo are a bit light.) If you ever want to give me a sample to play with I'll see how it works with our gear. Dean --------- To unsubscribe from nznog, send email to majordomo(a)list.waikato.ac.nz where the body of your message reads: unsubscribe nznog