SNR problem.. and strange modem parameters

[ccarmock]

I ave been suffering a problem with loss of sync on the 10 Mb/s business package - with an EPC2100 modem.

When sync is lost this is usually accompanied by SNR falling from the usual 40-41 dBmV to around 15 or 10 dBmV

Usually downstream channel number is 7, but today I am seeing strange parameters:-

Locked
Channel ID 228
Downstream Frequency 299000000 Hz
Modulation 256QAM
Bit Rate 55616000 bits/sec
Power Level 1.9 dBmV
Signal to Noise Ratio 38.4 dB


Upstream was stuck at:-

Upstream Status Ranging
Channel ID 2
Upstream Frequency 25800000 Hz
Modulation 16QAM
Symbol Rate 10240000 bits/sec
Power Level 40.5 dBmV


This then usually flips to QPSK on this channel and works for 5-10 mins and sync is lost again.

VMB say they will look into it. Is this usually noise on the network or an indication of a faulty modem?

[Ignitionnet]

You just got chucked onto the overlay DOCSIS 3 network.

[ccarmock]

really? that'll explain why it's having major problems I guess then as it's not a DOCSIS 3 modem!

Is it possible that excessive noise on the network could cause the modem to attempt to connect this way? Currently it's failing to sync at all. So using 3G dongle.

[Ignitionnet]

You don't need a DOCSIS 3 modem to connect to that network it's backwards compatible.

Noise is the cause of the disconnect probably though not the cause of the move to the DOCSIS 3 network, you were moved there by VM's own actions.

[ccarmock]

VMB faults called me back today they tell me that theer was a complete network 'break/outage' at around the time I experienced the problem in this area. However I didn't experience a total outage - just frequent periods of dropping SNR that caused loss of sync. All seems ok now though the modem logs show T3 timeouts still happenign up to 9am this morning, yet the fault was supposedly cleared in the early hours of the morning.

Since then all seems fine. What I do notice when I reboot the modem is that initially the downstream syncs at around 50 Mb/s on channle number 228, and then it will change to the correct sync speed usually on Ch 7

[Ignitionnet]

Originally Posted by ccarmock

What I do notice when I reboot the modem is that initially the downstream syncs at around 50 Mb/s on channle number 228, and then it will change to the correct sync speed usually on Ch 7

The modem is locking to the first DOCSIS downstream it can find, 228 at 299MHz. Once the DOCSIS 3 kit notices what kind of customer you are it punts you over to the correct frequency, 331MHz, as you shouldn't be on the DOCSIS 3 network.

This is entirely under VM's control, the configuration files are geared up in your area and as far as I know every other one to keep business customers on 10Mb away from the DOCSIS 3 kit due to that it will force IP addresses to change which would likely upset people using their reserved leases.

[ccarmock]

Thanks for that - it explains a lot to me. I suspect that is why VMB didn't offer fixed IP on the 20 Mb/s service due to the fact that that was typically moved to the DOCSIS 3 network and they had not implemented their 'fixed' IP address solution on that network.

Out of interest the DOCSIS 1 frequency it ended up on is 339 Mhz, channel 7 at 256QAM,
upstream at 22200000 Hz channel 2 at QPSK


of course the new Business services will improve the way the fixed IP services work, but last I heard is they aren't ready to take an upgrade order yet, just a new provide.

[Ignitionnet]

Understood - 331MHz is the primary DOCSIS 1.1 channel with 339MHz as a second channel if downstream load requires it.

They connect to the same line card, it has 2 downstream ports, you get to use both of them for your area rather than having them split between 2.