Upstream Channel Query

[craigj2k12]

Since changing to the VMNG300 from the superhub, I have noticed that I am only able to connect to upstream channel 6, it no longer gives me channel 5 as the superhub did. The superhub connects sometimes to channel 5 and sometimes to 6, however the VMNG300 only locks to channel 6. In my opinion channel 5 gave me a lower, more stable ping, and I would restart the superhub a couple of times so it locked to 5. Why isnt it getting channel 5 on the VMNG300?

[Chrysalis]

I think a caching system gets used. So when a modem recconects fast it just auto picks the last channel used. I noticed that numerous times when trying to hop channels, I often had to turn the modem off for 20 mins or so to get it to change. If you deliberatly weaken the signal by half removing the cable this can also force it to move. Thats how I got myself onto channel 7, (like yourself 2 channels one lower utilised then other).

[pip08456]

Don't know if it actually works like that Chrys, we need Igni to explain things here I think.

BTW I'll fire an email off to Neil at SamKnows in the morning for you.

[craigj2k12]

when i was on the superhub, it liked channel 5 more during p2p management times, it picked channel 6 during the day (or so it seemed)

the modem hasnt been an anything apart from 6, but the jitter is still lower on the modem, even on channel 6. ill try whats been mentioned, ill leave it off for 20 minutes during p2p management and see what happens when its hooked back up

[Ignitionnet]

I think a caching system gets used. So when a modem recconects fast it just auto picks the last channel used. I noticed that numerous times when trying to hop channels, I often had to turn the modem off for 20 mins or so to get it to change. If you deliberatly weaken the signal by half removing the cable this can also force it to move. Thats how I got myself onto channel 7, (like yourself 2 channels one lower utilised then other).

Nope the modem is offered all upstream channels connected to that downstream group in turn and will lock to the first usable channel. These are offered in order, so while a modem may only have 5 and 6 available it could be offered others, in theory a modem could see the information for 1,2,3,4 - which it will try to establish lock to and fail - then 5 which it will lock to, assuming it has finished trying to lock to the others.

Modems can and do remember downstream frequencies, that is all they remember though, they should not remember upstream.

[craigj2k12]

so does it try them in numerical order?

[Chrysalis]

whats the explanation tho for a highly utilised channel been used repeatedly?

channel 8 I get 9 times out of 10 easily, and its very clearly higher utilised.

when I was on 20mbit with docsis1 downstream the modem had a bad habit of picking highly utilised downstream channels as well.

The answer would appear to be based on what you said if they always offered in order then unless there is a fault on the first channel that will always be picked.

This may explain why when I weakened my signal it got me onto the better channel. Seems a poor system for load balancing.

[craigj2k12]

my downstream channels never change. i always get 125, 126, 127 and 128.

i have never had any other channels.

[Ignitionnet]

so does it try them in numerical order?

Depends, it tries whatever it sees the offer for, the offer usually runs in numerical order so it works out that way. The CMTS advertises the specifications of each upstream channel in turn, whatever the modem sees first when it gets downstream sync it will try to lock to, if that fails it will try the next channel it sees an advertisement for.

I guess a modem could remember the channels that were offered and try them in order, it's not mandated within the standards.

---------- Post added at 17:37 ---------- Previous post was at 17:33 ----------

whats the explanation tho for a highly utilised channel been used repeatedly?

channel 8 I get 9 times out of 10 easily, and its very clearly higher utilised.

when I was on 20mbit with docsis1 downstream the modem had a bad habit of picking highly utilised downstream channels as well.

The answer would appear to be based on what you said if they always offered in order then unless there is a fault on the first channel that will always be picked.

This may explain why when I weakened my signal it got me onto the better channel. Seems a poor system for load balancing.

Just as well really that this isn't how the operational load balancing is done, that's done with upstream channel changes.

Why modems get stuck on higher utilised channels depends entirely on how the channel load is being calculated, via number of devices or via loading, how the CMTS is configured and how well the software balances. Given that very few next gen CMTS operate multiple usable upstreams within the same MAC domain I wouldn't be surprised if load balancing isn't active on them at this time. That would probably be one to ask someone who knows how the BSRs are configured.

[craigj2k12]

how do you know this stuff?

[Ignitionnet]

I worked for ntl and did a bit on a consultancy basis with a North American cable company.

[craigj2k12]

your a genius!

---------- Post added at 19:29 ---------- Previous post was at 19:28 ----------

... but by the way, I still cant get onto channel 5, after multiple re-starts, last night i was leaving it off for 20 mins, plugging back in, and getting channel 6 over and over, I have up after two hours messing about

[Chrysalis]

the superhub works downwards, it tries higher frequencies first. So thats why I was stuck on channel 8 and why you stuck on channel 6. Try to weaken the snr by removing the cable a bit, then it will think there is a issue with the channel and try channel 5. When it does that quickly put the cable back in properly. Just remembered you on the vmng300 now but maybe that does the same and works downwards so still try the idea.

[craigj2k12]

I dont know how the modem is activated, I have both the VMNG300 and superhub activated at the same time, however the superhub uses one IP address and teh modem uses another. the superhub swaps and changes between channel 5 and 6 upstream, but the modem is refusing to use any channel besides 6. I have tried pulling the cable out, the downstream disconnects, but the upstream stays connected, even when just the last bit of copper is in, the snr doesnt even change! so it stays on channel 6!

[pip08456]

That's cos the VMNG300 is a more robust piece of kit!:D:D:D

[Chrysalis]

email CEO office, explain they can change your config to use channel 5 which you know for fact is physically connected and lower utilised or you end services.

VM seem to create some problems for themselves simply by bad configuration.

[Ignitionnet]

the superhub works downwards, it tries higher frequencies first. So thats why I was stuck on channel 8 and why you stuck on channel 6.

As I said above it doesn't try higher frequencies at all, it attempts to lock to whatever the CMTS is sending it there is no ranging on upstream sweeping the frequencies as there is on downstream.

CMTS all, as far as I know, offer them in forward order.

If the VMNG can't lock to the other channel there's a reason for it and it should be worked on appropriately as a fault.

[Ignitionnet]

the superhub works downwards, it tries higher frequencies first. So thats why I was stuck on channel 8 and why you stuck on channel 6.

As I said above it doesn't try higher frequencies at all, it attempts to lock to whatever the CMTS is sending it there is no ranging on upstream sweeping the frequencies as there is on downstream.

CMTS all, as far as I know, offer them in forward order.

If the VMNG can't lock to the other channel there's a reason for it and it should be worked on appropriately as a fault.

[Chrysalis]

yeah its downstream frequency that went downwards.

So what makes the superhub decide which upstream channel to use when sent 2 available?