North American Network Operators Group Date Prev  Date Next  Date Index  Thread Index  Author Index  Historical Re: value of colocation
> > What's the average packet size now? I think the overhead on DS3 ATM/SMDS > > is worse than on OC3, if I recall correctly, because the DS3 PLCP is so > > wasteful as well. Someone should redo these calculations more accurately. > > With PLCP, maximum bit rate available for ATM cells = > > 53 cells * 12 rows * 8bits / 125us = 40.704 mpbs. > > So, 40.704 * 48/53 = 36.864 mpbs = data rate. > > Now if you use AAL5, then it's another 2 bytes for SAR, and 2 bytes for > CS, so, 40.704 * (484)/53 = 33.792 mpbs. You are correct up til you get to the efficiency at the AAL level. AAL5 does not have any SAR overhead but it does have 8 bytes of CS overhead. Now, this overhead is on a per PDU basis and NOT a per cell basis. Thus, you maximum efficiency will be 36.864 * [(x8) / x] where x = PDU size in bytes. Thus, if you just send 64byte packets, your min throughput will be 36.8 * (56 / 64) = 32.3 Mbps. Of course, larger PDUs are more efficient. Shikhar
