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Author Topic: FTTC - IP Profiles / BRAS Rates vs Sync speed  (Read 9713 times)

Bald_Eagle1

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FTTC - IP Profiles / BRAS Rates vs Sync speed
« on: January 11, 2012, 09:23:49 AM »


There has been some general discussion regarding how a user's FTTC IP Profile / BRAS Rate is calculated.

Having studied a number of FTTC connection stats, it appears that the new(ish) 88.2% quantisation method for calculating ADSL IP Profiles does not apply to FTTC connections.

It would appear that FTTC IP Profiles are typically calculated to be approximately 96.79% of DS Sync speed.

Users with unlocked FTTC modems will be able to see their Sync speed & calculate their IP profile, double-checking it against the IP Profle as reported in BT's usual speed/performance tester.

However, users with locked modems have no real idea of their Sync speed.

e.g. a typical IP Profile / BRAS Rate for a user achieving the full 40Mb sync speed would be in the region of 38715K (96.79% of 39999K).

My own connection is currently Synced at 28839K, the reported IP Profile / BRAS Rate is 27914 K.
Again, the IP Profile is approximately 96.79% of sync speed.

Conversely, DS Sync speed can be calculated as approximately 103.3% of IP Profile.

As an aside, my DS throughput (when not affected by contention etc.), as reported by speedtest.net, is usually around 97% of my IP Profile / BRAS Rate:-



My connection wasn't initially affected by contention, regardless of the time of day or night, but I have recently noticed DS throughput speeds typically reducing by 3 or 4 Mb or so at peak evening periods:-




Paul.
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burakkucat

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Re: FTTC - IP Profiles / BRAS Rates vs Sync speed
« Reply #1 on: January 11, 2012, 09:47:14 AM »

Hmm.  :hmm:  Is it really meaningful to quote those percentages to two decimal places?

I think I would be far happier to see you use 88%, 97% and 103%, respectively.
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waltergmw

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Re: FTTC - IP Profiles / BRAS Rates vs Sync speed
« Reply #2 on: January 11, 2012, 02:38:28 PM »

@ BKK & Paul,

I can see BKK's point re the overall accuracy of attempting %age calculations which, in practice, will only bear a passing similarity to the data transfer speeds actually obtained.

However for the miserable ordinary FTTC population it might be useful to retain accurate calculations as it is those figure upon which all our discussions and observations are based.
This can be important when we are attempting to define what "improvements" are being applied to these services, especially when we have to do yet more empirical tests to discover precisely what and when the faster profiles are implemented commercially.

Kind regards,
Walter
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jeffbb

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Re: FTTC - IP Profiles / BRAS Rates vs Sync speed
« Reply #3 on: January 11, 2012, 03:35:01 PM »

Hi
quote My connection wasn't initially affected by contention, regardless of the time of day or night, but I have recently noticed DS throughput speeds typically reducing by 3 or 4 Mb or so at peak evening periods:-

This does mean that

Conversely, DS Sync speed can be calculated as approximately 103.3% of IP Profile.
 If there is contention then the backward calculation to derive the synch rate will not be very useful for those with locked modems because the contention is will not be known .However multiple checks during quiet periods may give some reasonable result.

Regards Jeff
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Bald_Eagle1

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Re: FTTC - IP Profiles / BRAS Rates vs Sync speed
« Reply #4 on: January 11, 2012, 08:59:53 PM »

Hi b*cat,

Hmm.  :hmm:  Is it really meaningful to quote those percentages to two decimal places?

I think I would be far happier to see you use 88%, 97% and 103%, respectively.

I used fairly precise figures as they are the typical (approximate) recurring values that I have observed for both my own, & other users' connections.

e.g. Sync 28839 k, IP Profile 27914 k.
96.79253788272825% is the actual value, but even I thought that may have been a little too precise :lol:.

In another forum, I have actually seen discussions regarding some users querying a difference of as little as 1 k following a switch from the 8c to the 17a profile.

It's easy enough to round fairly precise values up or down for general purposes, but impossible to glean a precise value from a rounded value.

I did try to be careful with my wording, such as "it appears that", "typically", "approximate" etc. ;)


Paul.
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Bald_Eagle1

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Re: FTTC - IP Profiles / BRAS Rates vs Sync speed
« Reply #5 on: January 11, 2012, 09:25:32 PM »

Hi jeffbb,

If there is contention then the backward calculation to derive the synch rate will not be very useful for those with locked modems because the contention is will not be known .However multiple checks during quiet periods may give some reasonable result.

I agree with you 100% (or could that be 99.95631248%)  that calculating sync speeds from speed tests such as speedtest.net when contention may be an issue would not be advisable :)

However, the BT speed/performance test does report the IP Profile.
For whatever reason, BT have decided NOT to report Sync speed for FTTC connections.

IF my observations are reasonably correct, a typically reported FTTC IP profile of say 38716 k at 103.3138754003513% would indeed produce the current maximum Sync speed of 39999.00000000001k.

If users believed the 88.2% method was also used for calculating/setting IP Profiles for FTTC connections, they could mistakenly think their sync speed would be around 43896 k (approximately).


Paul.
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jeffbb

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Re: FTTC - IP Profiles / BRAS Rates vs Sync speed
« Reply #6 on: January 11, 2012, 10:27:56 PM »

Good accuracy  ;D
Regards Jeff
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renluop

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Re: FTTC - IP Profiles / BRAS Rates vs Sync speed
« Reply #7 on: April 14, 2015, 08:30:41 PM »

Sorry, as usual late to a party! ::) But how is the US calculated? Just curious for useless data! :(
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