Re: Think Broadband Ping Monitor Results (POST YOURS)
 

one user with 10 or 12 meg upload could easily kill 1 upstream channel

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

How do you work that one out? Each upstream has about 30mbit of bandwidth. Sure, one person on 10meg upload could saturate over 1/3 of it, but hardly kill it.

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

20

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

30

http://en.wikipedia.org/wiki/DOCSIS#...onal_standards

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

Data rate = #_Bits_per_symbol * Symbol_Rate

Bits per symbol = 4
Symbol Rate = 5120000

= 20,480,000

or 20.48Mb/s

---------- Post added at 13:30 ---------- Previous post was at 13:30 ----------

http://volpefirm.com/blog/docsis-101...1_upstream-rf/

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

So it's because Virgin uses QAM16, then? Today I learned.

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

I guess it's the poor state of the field plant and the number of modems per channel that doesn't let them get to QAM64.

I see a lot of cut cables outside old VM customer houses in my area. I bet they haven't been disconnected at the cab.

My upstream power is all over the place from 41 to 44dBmV

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

Exactly!!

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

Whoops, missed this earlier (haven't been on much lately)

TCP overhead is typically 1.5-3% of the downstream usage. Then add on top DOCSIS overheads, and the fact an upstream channel has really about 1/3rd the capacity of a downstream channel, that means 4.5-9% of the upstream channel I just rounded that to 5-10%.

---------- Post added at 17:22 ---------- Previous post was at 17:16 ----------

Heh, well... On 50Meg they had 2 upstreams for every area (theoretically), but at half the bandwidth, so one upstream per 4 channels. What they have now, I don't know, but if it is 1-between-8, then that is not a good thing given general utilization in both directions will be higher now than it was when 50 came out.

50 didn't run particularly smoothly in areas with high utilization - engineers in my area quoted 90% capacity in use 90% of the time (!) - and getting more than 300Kbps upload was a chore some days.

The problem isn't him using his connection, both upstream and downstream channels are shared between hundreds of users. Other people using it to capacity will cause problems for him whether he uses it himself or not.

Bandwidth over the whole channel (8x55Mbit on the downstream, 1x20Mbit on the upstream).

Remember upstream is inherently inefficient on cable, because of the requirement for CSMA and guard intervals, etc. and you will rarely be able to use entirety of a channel's upstream capacity. The practical maximum is closer to 16-18Mbit available for actual use.

55Mbps dowstream with 2% used for ACKs is around 1.1Mbps if everything behaves efficiently, depending on RWIN, MTU, OS, etc. this can vary both up and down. Don't forget also a single 100/10 user could eat up over half the upstream capacity on such a channel.

(An ACK takes around 54 bytes 'on the wire', which with a pessimistic minimum MTU of 576 bytes, and no ack suppresion, etc., means 8 downstream channels could actually require ~40Mbps of upstream capacity in an almost-worst-case-scenario, without anybody doing any actual data uploads)

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

So on a channels with (in best case) 18Mbit useable bandwidth, on 8 downstreams, 8.8Mbit could be used just on acknowledgements, then there are users expecting to get 10 or 12Mbit upload speeds :erm:

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

The obsessive speedtester need not necessarily be you - remember, all capacity is shared. Some other person obsessively speedtesting (and using up over 50% of the network capacity at such a time) could well be the cause.

---------- Post added at 17:35 ---------- Previous post was at 17:34 ----------

Derp:
https://www.cableforum.co.uk/images/local/2014/10/8.png

---------- Post added at 17:37 ---------- Previous post was at 17:35 ----------

Best-case involves ACK suppression (VM don't bother with this) SACK's, zero packet loss and large RWINs that reduce ACK overhead to well under 1%.

The 1.5% - 3.0% overhead I quote is for typical real-world scenarios.

[Edit]
Never mind, you meant at best 18Mbps useable upload bandwidth, yes, right.

That said I'm only speculating on the number of upstream channels. Some people supposedly report their area only has one, but in the past common practice was to have at least two (at that time they were half the capacity per channel though)


---------- Post added at 17:40 ---------- Previous post was at 17:37 ----------

Yes they do.

A "one guy" with 10Mbps upload speed on a 20Mbps channel can easily cause congestion - congestion can become visible at as low as 60-70% utilization on the upstream. All other users need only be using 30% of available capacity between them before one 100/10 user can "congest the entire network"

---------- Post added at 17:41 ---------- Previous post was at 17:40 ----------

Way to advertise... "Press here to cripple our network".

---------- Post added at 17:42 ---------- Previous post was at 17:41 ----------

Up until a few months ago some areas still used BPSK. The BPSK => 16QAM upgrade only started in 2011.

That said till recently the Superhub also clearly displayed 20Mbps next to the upstream channels on its normal status pages.

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

AFAIK, VM used TAS (Ack Suppression) in the form of Turbodox. I don't know the poosition now, but I imagine it could still be in use. Here is a supporting quote from Mark Wilkin in September 2010:

We've just released the new 12.01 firmware update for VM300 Cable Modems across our network.

The new firmware was tested over the past 8 weeks with 2000 customers including volunteers from this forum and we've seen no significant issues in testing.

The new firmware enables 100Mbps throughput for our forthcoming 100Mbps service and is also designed to improve upstream stability and throughput. It also turns back on the TDOX feature that was switched off in July with the 10.12 firmware, due to a bug affecting performance.

BTW, note VM saying that the VMNG300 was fit for 100 meg.

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

it could be if eg. the normal utilisation is say 60% and then a top tier user with 10 or 12 upload goes full throttle. On a 18mbit US channel one user can use more than half of the bandwidth, a 12mbit customer can use 2/3 of a US channel by them self. Your comment is right if the normal utilisation is 0% which isnt the case. I have been surprised to hear reports VM have been activating 120/12 in areas with no US bonding, seems nuts.

---------- Post added at 18:12 ---------- Previous post was at 18:09 ----------

Ultimately thats the problem, in particular too many modems per service group, but also that isnt fat enough pipes at the docsis level as well. Any setup that has a customer able to use more than half of a shared pipe is going to be fragile even at 2:1 contention.

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

As far as I know 12Mbit upload is never implemented before 2-channel bonded upstream is implemented. In other words, 40Mbps upload channels are a prerequisite before anybody gets 12Mb

Re: Think Broadband Ping Monitor Results (POST YOURS)
 

Qas are you sure large rwins reduce ack overhead? The only thing I have found that affects ack overhead is delayed acks, nagle algorithm and adjusting mtu(mss) size. Whilst boosting rwin allows higher throughput the ack throughput goes up with it. Also supressing acks isnt without consequence, its good for certian bulk downloads but bad for small packets. sacks also sends the same amount of acks, the difference sacks offers is just how recovery works if packets are dropped.

---------- Post added at 18:19 ---------- Previous post was at 18:19 ----------

Thats what I thought until my neighbour was put on 12mbit without bonding and I seen reports on tbb with the same.