Why is it 88.2% re IP speed vs sync speed?

[#1]

Hi - just wondering if someone can explain why it's 88.2% rather than 90% or whatever - it's a very precise percentage, so clearly it's deliberately that value for a reason!
e.g. currently synced at 54026Kbps - plusnet shows me as having 52.2 connection speed under Connection Settings > Highspeed Broadband. 88.2% of that is 46040 Kbps (which is roughly what I get on speedtest.net).
By my reckoning someone syncing at 79999Kbps (the absolute top whack in terms of the 80/20 package) can "only" get 70Mbps downstream, so why do BT et al talk about the sync rate rather than the actual throughput speed?  It should be marketed as a 70Mbps product...
If anyone can give some detail as to how the 88.2% figure is derived (and why it can't be higher), I'd love to hear.

[#2]

The 88.2% is for ADSL2+ services, fibre is 96.7% if memory serves correctly.
So for your sync of 54026 you should have a profile of around 53800.

[#3]

Thanks Chris - so basically I should be getting speeds closer to the figure in "high speed broadband" - that's the number *after* the IP overheads have been taken in to account.
From here:

Quote

21st Century Network (21CN) Available in a growing number of UK exchanges, 'Wholesale Broadband Connect' (WBC) technology is used to provide: Speeds up to a theoretical maximum of 8Mb via ADSL1 Speeds up to a theoretical maximum of 24Mb via ADSL2+ Speeds up to a theoretical maximum of 80Mb via Fibre to the Cabinet (FTTC)

...then...

Quote

The way an IP Profile is calculated depends on the broadband product: 21CN products: the IP profile will always be 88.2% of the sync rate

Hence my misunderstanding (I appreciate there's an overhead for getting packets from plusnet to me, but it sounds like that's covered off in the 96.7% you've mentioned).

[#4]

The overheads are to do with Internet Protocols and not Plusnet in case you are wondering.

[#5]

Quote from: Anotherone

The overheads are to do with Internet Protocols and not Plusnet in case you are wondering.

My understanding is that most of the overheads are covered off in the 96.69% [G.INP]/96.79% [non-G.INP] IP Profile.
From all of the various speed tests (to speedtest.net, thinkbroadband and BT) the best I ever seem to achieve is about 88% of the connection speed noted in Connection Settings > High Speed Broadband.
54026 * 0.967 = 52243 (52.2 - as shown by plusnet)
52200 * 0.882 = 46040 - essentially the maximum speed I'll see with a speedtest
The only time I've approached the sync speed was during the 10 day training period (was nearer 15 days from memory), when the profile was shown as 76Mbps.
I don't know if there's something else at play here, but I don't believe that 8Mbps (on my connection) is required for TCP/IP, PPPoE etc overheads.

[#6]

Hmmm... so MTU is still "a thing" it seems!
On my router I'd set it to 1492 for PPPoE as part of setting it up initially (got it last weekend) - this gives me 45.5Mbps.
The router has a default of 1480 (and a label saying "do not change unless necessary") - switching it back gives me 48.9Mbps and a lower ping (12-16ms to 8.8.8.8, rather than the 20ms I had before) - this is more inline with what I was expecting!
So, moral of the story, don't mess about with your routers MTU and try not to ask daft questions on the plusnet forum... 

[#7]

Did you change the MTU on your devices to match the 1492 MTU on the CPE?
The MTU on my CPE cannot be changed, but it does set the MTU to 1492 when PPPoE is selected and 1500 when PPPoA is selected. I then changed the MTU on my PC to 1492.
When I was on ADSL, I had a different CPE that did allow me to change the MTU, I found that lowing the MTU decreased down-speed, but increased up-speed.

[#8]

@lf2k
I think you might have been confusing IP Profile with achieved Throughput speed. The IP Profile is a fixed value as previously stated and you should be able to get close to that with Throughput if everything is set up correctly and no congestion - always best to check at off peak times to confirm that.

[#9]

@elfish - I've got a TP Link Archer C2 connected to a HG612...  I changed a setting on the TP Link (bit hard to go around changing MTU on phones/tablets/chromecast, and it really shouldn't be necessary)
@AnotherOne - no real confusion tbh, just some conflicting information in the docs - obviously I was expecting my throughput to be similar my line rate, and playing with the MTU seems to have bought the throughput in line with what I'd expect for my sync rate - e.g. 50Mbps on a 52.2Mbps connection....

[#10]

One thing I don't understand and I wouldn't expect anyone to have an answer for is on plusnet I get sync of 79999 with a profile that's been set as 77.3 (according to BT wholesale test) which would match up with the 96.7%) and we see speedtests up to about 73 meg.
Friend of ours on same exchange and even a relative in a different property but same exchange see 79999 sync on sky fibre, yet realworld speedtest of over 75meg. INow the exchange and cabs are g.inp enabled, but how is it sky can give a higher throughput ?
Im only going based on sync speed the routers report here, but 79999 sync speed, all 3 lines lose 5 meg throughput (ie sky gives 75 meg speedtest so rounding up a loss of 5 meg) yet plusnet rounds the profile down to 77.3 (say 78) and speedtest are ~ 73 (again 5 meg loss throughput) is it because plusnet don't offer an 80/20 product as such ? only 78/20 ?
Unfortunately the sky lines in question don't give an ip profile as the bt wholesale speedtest doesn't work on a sky line.

[#11]

The Plusnet profile reduces the speed test result and as far as I know Sky don't have the BT IP profile either

[#12]

Just to clarify:-
Empirical data since 2011 confirms that on non-G.INP active VDSL2 (FTTC) connections, BT's IP Profile should be approximately 96.79% of sync speed.
Occasionally a ROUTER (not MODEM) disconnect/reconnect is required to initiate a new PPPoE session that will force an update to BT's IP Profile.
Therefore, a sync speed of 79999 Kbps should have an IP Profile of around 77.43 Mbps.
In ideal conditions, actual throughput speed tends to be 'up to' approximately 97% of BT's IP Profile.

From what we have seen to date for G.INP active connections, BT's IP Profile seems to be a shade lower at approximately 96.69% of sync speed.
Therefore BT's IP Profile is likely to be around 77.35 Mbps.

Plusnet's own Current Line Speed profile is usually around 100 Kbps or so lower than BT's IP Profile (whenever an automated BT delta report is 'eventually' received by PlusNet).


The delta report system does seem rather hit & miss at times & thus PlusNet's Current Line Speed profile isn't always updated as quickly as it could/should be.
That's not a problem if BT's IP Profile (based upon actual sync speed) lowers as users can only achieve what the connection is able to deliver at the time it syncs.
However, it can be a problem when sync speed & BT's IP Profile increases.
e.g:-
If a non-G.INP active connection was in sync at say 60 Mbps, BT's IP Profile would be around 58.07 Mbps.
PlusNet's Current Line Speed Profile would be around 57.97 Mbps.
Let's say the connection resynced at 65 Mbps.
BT's IP Profile should then be around 62.91 Mbps & Plusnet's Current Line Speed Profile should be around 62.81 Mbps.
However, until PlusNet's profile is increased in line with BT's IP Profile, actual throughput speed would still be restricted to something below their previous profile of 57.97 Mbps.

[#13]

Quote from: Bald_Eagle1

Therefore, a sync speed of 79999 Kbps should have an IP Profile of around 74.43 Mbps.

77.43 Mbps I think you meant.

[#14]

Oops!
Typo now corrected.
Thanks for mentioning it.

[#15]

@Bald_Eagle1
Thanks for that detailed synopsis, I wasn't looking forward to writing something along the same lines 
@Oldjim
The effect of the Plusnet Current Line speed really is/should be quite marginal at Fibre speeds. The BT IP Profile is "built-in" to the transfer of traffic (for want of a simple explanation) and as Sky have to use the BT Network until the Traffic gets to an "OHP" they would seem to be lumbered with it.
@ericgripp
Sorry if I've missed it, but I couldn't see it anywhere - Have you checked that your Current Line speed (Login required) matches the BT IP Profile?
And to be clear, the difference between the sync speed and the download speed cannot be regarded as a loss primarily because of the overheads previously mentioned, but the difference between the IP Profile (which you can calculate if you know the sync speed but can't get a result from the BTw Tester) and the download speed could be regarded as a loss. On the assumption the the Current Line Speed is correct, then there may be other reasons for any loss such as Congestion (test at off peak times and compare to busy times), parts of any network en-route, modem and router at your end as well as any non-ideal settings of your own equipment (see lf2k's posts above for one such example).