On Thu, 2003-05-29 at 15:46, Steven Critchfield wrote: > On Thu, 2003-05-29 at 15:06, Charles E. Youse wrote: > > On 29 May 2003, Steven Critchfield wrote: > > > > > On Thu, 2003-05-29 at 10:44, Charles E. Youse wrote: > > > > B8ZS is required for PRI. It's a digital service and can not handle the > > > > loss of data required for AMI. > > > > > > I wasn't aware that AMI lost data. AMI just inverts polarity on the line > > > for every other 1. B8ZS does the same thing but intentionally introduces > > > errors on the line to maintain 1's density. Neither one is lossy. > > > > > > > AMI is lossy. When the ones density in the signal is too low, AMI > > will insert ones to ensure that the far end does not lose sync. > > As I understand it, AMI is not lossy but will may cause problems due to > not maintaining 1's density. 1's density is used to make sure both sides > are synced up properly. B8ZS is AMI except that it introduces bipolar > violoations to make sure the line doesn't stay in an off state for too > long. > > So B8ZS intentionally throws errors on the line in a known manner so as > to make sure each side is in sync, but AMI does not care if the line > goes all 0's for a while. > > I still haven't been able to dig up any documentation to back up that > AMI is lossy, just maybe prone to errors via slips.
I still can't find any reference to AMI being lossy, and can't find any comments that show where a AMI circuit would introduce 1's to maintain 1's density. After reading a page describing test patterns and why they use certain test patterns, it makes sense why AMI might not be usable for a PRI though. http://www.electrodata.com/testpat.htm In a PRI, since the signalling is in the D channel, and the consecutive B channels could be completely clear, you could run into times with more than 15 consecutive zeros. Although I need to do more looking at how D4 or ESF lays on top of a T1 signal. Anyways, with more than 15 consectuives zeros you no longer are within ANSI spec. On a RBS circuit it would be less likely to fall too far out of spec using AMI. -- Steven Critchfield <[EMAIL PROTECTED]> _______________________________________________ Asterisk-Users mailing list [EMAIL PROTECTED] http://lists.digium.com/mailman/listinfo/asterisk-users
