Upstream Frequency and Channel

[chris26engwales]

I noticed today that my dads upstream and frequency has changed in his modem settings. The only reason i looked was because his connection seems a little sluggish it was...

Upstream Lock : Locked
Upstream Channel ID : 2
Upstream Frequency : 29200000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 2560 Ksym/sec
Upstream transmit Power Level : 48.0 dBmV
Upstream Mini-Slot Size : 2

and now its...

Upstream Lock : Locked
Upstream Channel ID : 1
Upstream Frequency : 25800000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 2560 Ksym/sec
Upstream transmit Power Level : 48.5 dBmV
Upstream Mini-Slot Size : 2


Would this be the answer to why its sluggish?

[Peter_]

I noticed today that my dads upstream and frequency has changed in his modem settings. The only reason i looked was because his connection seems a little sluggish it was...

Upstream Lock : Locked
Upstream Channel ID : 2
Upstream Frequency : 29200000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 2560 Ksym/sec
Upstream transmit Power Level : 48.0 dBmV
Upstream Mini-Slot Size : 2

and now its...

Upstream Lock : Locked
Upstream Channel ID : 1
Upstream Frequency : 25800000 Hz
Upstream Modulation : QPSK
Upstream Symbol Rate : 2560 Ksym/sec
Upstream transmit Power Level : 48.5 dBmV
Upstream Mini-Slot Size : 2


Would this be the answer to why its sluggish?
No the Upstream is meant to range up and down the frequency till it gets its best lock.

Post the Downstream power levels.

[Ignitionnet]

No the Upstream is meant to range up and down the frequency till it gets its best lock.

Post the Downstream power levels.

Not quite it takes the first 'offer it gets from the CMTS and locks to that, if it can't either the network is segmented so it can't or there's a problem.

Sat Apr 11 18:17:18 2009 Sat Apr 11 18:17:18 2009 Information (7) MAP w/initial maintenance region received

On a 4 upstream downstream these MAPs will sequentially contain information for different upstreams in order 0, 1, 2, 3 (or 1,2,3,4 depending how it's expressed!) so whichever MAP the modem sees first is the upstream it'll lock on to.

If nothing else changed it's possible there's an SNR issue on the new upstream and the modem lost lock and reacquired or was pushed onto it overnight.

Any visible packet loss on the service? This would usually be a symptom of upstream issues.

[Peter_]

Not quite it takes the first 'offer it gets from the CMTS and locks to that, if it can't either the network is segmented so it can't or there's a problem.

Its still classed as ranging as the is no specific frequency to lock on as with downstream.

[Ignitionnet]

Its still classed as ranging as the is no specific frequency to lock on as with downstream.

Yes there is, they are configured on the CMTS, it notifies the cable modems of the available upstreams via the MAP messages I mentioned. The upstreams are fixed on the VM network, the capability is there for upstreams to 'roam' on the spectrum searching for the cleanest frequencies where you are using line cards with spectrum analysers built in but this functionality is not used on the VM network.

The CMTS broadcasts messages with things like, emphasis on like you can get the full description of the upstream MAP messages from the standards ;)

Upstream ID 1 - Frequency 29.2MHz - Modulation QPSK - Channel Width 3.2MHz

Next MAP

Upstream ID 2 - Frequency 30.8MHz - Modulation 16QAM - Channel Width 3.2MHz
...
Upstream ID 3 - Frequency 32.4MHz - Modulation 16QAM - Channel Width 3.2MHz
...
Upstream ID 4 - Frequency 40.2MHz - Modulation 64QAM - Channel Width 6.4MHz (Though not on VM :( )
...
Upstream ID 1 - Frequency 29.2MHz - Modulation QPSK - Channel Width 3.2MHz
...
Upstream ID 2 - Frequency 30.8MHz - Modulation 16QAM - Channel Width 3.2MHz

etc

The modem ranges to find a usable downstream but it receives the frequency of upstreams from the CMTS, no frequency ranging involved. The only ranging is the power level ranging that the modem does to find the correct transmit level, where it interactively tunes its' transmit power with the guidance of the CMTS until it either reaches close enough to target receive power at the CMTS for it to be happy or cannot transit at a higher level, for example:

Modem Transmits @ 32dBmV - CMTS target receive power is 0dBmv, actual received power is too low to register.
Modem Increases Tx power 3dBmV as it received no unicast ranging response - CMTS receives @ -12dBmV - directs modem to increase Tx power by 12dBmV
Modem Increases Tx power 12dBmV, Tx power now 47dBmV - CMTS receives @ 0dBmV - CMTS informs modem ranging complete

[Peter_]

Yes there is, they are configured on the CMTS, it notifies the cable modems of the available upstreams via the MAP messages I mentioned. The upstreams are fixed on the VM network, the capability is there for upstreams to 'roam' on the spectrum searching for the cleanest frequencies where you are using line cards with spectrum analysers built in but this functionality is not used on the VM network.

The CMTS broadcasts messages with things like:

Upstream ID 1 - Frequency 29.2MHz - Modulation QPSK - Channel Width 3.2MHz

Next MAP

Upstream ID 2 - Frequency 30.8MHz - Modulation 16QAM - Channel Width 3.2MHz
...
Upstream ID 3 - Frequency 32.4MHz - Modulation 16QAM - Channel Width 3.2MHz
...
Upstream ID 4 - Frequency 40.2MHz - Modulation 64QAM - Channel Width 6.4MHz (Though not on VM :( )
So meant to range but as with many things on Virgin it has been disabled, what a surprise.

[Ignitionnet]

So meant to range but as with many things on Virgin it has been disabled, what a surprise.

No, it can be dynamic, it's not meant to be but the functionality is there. It's left as fixed on the VM network as the fear is that letting the cards manage the upstreams themselves will make noise busting and trouble shooting harder. Noise comes on the network the card will move the upstream to a different frequency and potentially VM are none the wiser.

[Peter_]

No, it can be dynamic, it's not meant to be but the functionality is there. It's left as fixed on the VM network as the fear is that letting the cards manage the upstreams themselves will make noise busting and trouble shooting harder. Noise comes on the network the card will move the upstream to a different frequency and potentially VM are none the wiser.
Much clearer now and can see why, thanks.