I've one customer connected through one 2048Mb E1 leased line with csu/dsu with V35 interface. Circuit is always getting errors. Downs never occured. I've already replaced the cisco and the cisco cable @ customer site and I've already used a new port on another router at my node, without fixing. But, I couldn't say for sure it was a link trouble as Ptt run more than one end-2-end test with the instruments, without getting errorr or clock slips.
Anyway, I found that by running an extended ping with data pattern 0x0000, after a size of 160bytes I start to lose packets. While with the default data pattern or with data pattern 0xffff the ping run perfectly. I'd like to know if data pattern 0x0000 is showing me a clock issue or linecode problems. By looking at the clock the router is detecting it seem to be stable.
Today we enable the parameter V38-Scrambler on both the csu/dsu and now the ping with data pattern 0x0000 can work fine and the circuit is currently empty of errors