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Originally Posted by Kushan

Have we? Everything was pretty clear until you came along and started nitpicking.

It's not nitpicking when you've seem to got the whole idea wrong.

I've highlighted the bit that's most obviously wrong here, from a simple maths point of view.

2.5 out of 4 leaves 1.5
2.5 out of 8 leaves 5.5

The network has 8, 2.5 out of 4 leaves 1.5 + 4 = still 5.5 Once again, simply because one modem has 4 channels doesn't reduce the entire network to 4 channels.

Not "exactly the same" at all. IF two Ambit users have 120mbit and happen to be on the same 4 channels, then it's impossible for them both to achieve 120Mbit down at the same time (2.5 + 2.5 = 5).

IF two Ambit users have 120mbit and happen to be on the same 4 channels trying to achieve 120Mbit down at the same time then load balancing is broken.

Can the CMTS switch one of those two users "on-the-fly"?

Yes. The CMTS can switch any users and any individual channels of any users at any time (well, any time the modem is actually connected).

Can it do that as soon as channels 1 and 2 become maxed out?

Yes.

(or rather, once channels 1-4 go above 50% capacity).

Yes. It can switch at any capacity level, modem count, or SID count specified by the network administrator (though IIRC some Cisco IOS versions won't allow you to set a threshold below 25%)

Right, someone who's a bit more qualified than me will have to come along and answer this, but how dynamic IS that load balancing on the CMTS?

As dynamic as the network administrator is competent enough to set it up to be.

What I mean is, how quickly can the CMTS tell the modem that it needs to jump channels?

Several times a second.

So yes, the CMTS load balances but can it load balance usage down to the minute, such as when one user starts downloading a large file versus overall usage in the area?

Yes

There's another scenario as well. Assume the CMTS is load balancing effectively, but the area has heavy use.

Then you should still notice no difference.

If load balancing is working as it should, it's reasonable to assume that all available channels have roughly the same amount of utilisation. Say all channels are regularly on 75% utilisation - quite high but quite a lot of capacity to spare. You've got 4 channels, what does that leave you with? On 4 channels, that leaves you with approximately 2 channels worth of bandwidth - not enough for your 120Mbit.

Load balancing isn't static. If all channels were at 75% and you load up your 4 to 100% while trying to pull 125%, then it'll get rebalanced so all 8 channels end up at 100%.

In many places this is already part of normal operation - 16 or more downstream channels across which many 1, 4, and 8 channel modems are distributed.