I'm hoping someone can tell me if there is an issue with my broadband. Until June this year I had a fairly standard 1Mbps / 256K ADSL connection with fairly good line statistics (32dB attenuation / 30dB noise margin on the downstream). In June I upgraded to my ISPs "upto 20Mbps" ADSL2+ connection. I knew I was never going to get the full 20Mbps but from the research I had done with various online checkers, it looked like I was good for about 13Mpbs, and my ISP agreed when they tested my line prior to the upgrade.
Shortly after the upgrade was done I noticed a lot of disconnections and packet loss. Turns out my router (Cisco 877W) is not 100% happy on 21CN lines (even with the latest firmware patch). After speaking with a colleague, I purchased a Draytek Vigor 120ADSL modem to sit between the phone line and the Cisco. They has certainly stabilised the line.
Since installing the Draytek modem I've noticed that it racks up a lot of RX CRC errors (at one point > 60,000 in a week). I raised a case with my ISP to have the line checked and to ask if this was normal. I was advised to test the connection via the BT Test Socket (located behind the master socket faceplate - this eliminates all customer wiring and extensions). I plugged everything in and informed my ISP that it was connected. They ran some tests on the line whilst I left everything connected for the day ( > 8 hrs). The modem continued to see RX CRC errors but my ISP told me there was nothing wrong with the line (in fact the tech support guy told me it was normal).
I also asked my ISP why my profile was struggling to get above 9Mbps and was told BT had "banded" my profile due to frequent disconnections. My ISP agreed to contact BT and get this removed and to restart the 10-day training period. This was done and the line stayed stable for in excess of 15 days at which point it had to reconnect (possibly due to maintenance by BT forcing a disconnection). Following the reconnect the line came back at a slower rate (9Mbps) and then dropped the next day (12th Nov) to come back at 8Mbps. I then contacted my ISP and they advised that BT have banded my profile (again). They contacted BT to get this removed and a day later my modem re-synced at a 10Mbps profile (where it stayed for all of 7 days before dropping and coming back at an 8Mbps profile).
I've noticed (and will confirm tomorrow) that the Draytek router appears to rack up RX CRC errors even when the Cisco 877W is turned off (which means I'm not logged into the ISP network and no traffic should be on my line).
So, some questions:
- Is it "normal" to see so many CRC errors? My understanding is that CRC errors are generated when data becomes corrupt and has to be retransmitted.
- What can be causing these CRC errors? I don't remember seeing them on the 1Mbps service (but then again I wasn't really looking for them - and the service just worked).
- Could "the problem" that is causing these CRC errors also be responsible for the low(ish) sync speed?
- If not, any ideas what could be causing the low(ish) sync speed.
I have posted a PDF document here
showing my current network layout along with a screenshot showing the current Draytek status page
Many thanks for taking the time to read this (longish) post.