cancel
Showing results for 
Search instead for 
Did you mean: 

DLM question

jafreer
Rising Star
Posts: 830
Thanks: 49
Registered: 13-10-2012

DLM question

I know that when switching off the modem, it is recommended to disconnect the PPP session via the router first.
Whilst I think this is good practice, does DLM know whether a PPP session is established or not when the connection drops? And if DLM does know, does it care?
I am not advising using any different practice, and disconnecting the PPP session is good practice, but the question is, does DLM know or care?
I have a feeling that DLM does not take any account of whether a PPP session is established or not when it sees modem disconnects. But that is just a hunch.
Just curious.
38 REPLIES
Community Veteran
Posts: 2,285
Thanks: 109
Fixes: 4
Registered: 18-02-2013

Re: DLM question

No, It will only care if you mess about with the dsl connection more than once in a 30 minute period.
I can drop my PPP session 30 times in  a row, I find it better to drop the session just for ease!
Community Veteran
Posts: 1,841
Thanks: 103
Fixes: 6
Registered: 21-01-2013

Re: DLM question

Quote from: jafreer

I have a feeling that DLM does not take any account of whether a PPP session is established or not when it sees modem disconnects. But that is just a hunch.

I'm sure that's correct.
The reason people suggest dropping the ppp session first is so it has a graceful disconnect. This reduces the chance of having a stale ppp session which would prevent reconnecting the ppp.
Community Veteran
Posts: 6,824
Thanks: 1
Registered: 27-10-2012

Re: DLM question

This is correct (I did double check).
Openreach recommend also leaving your modem powered off for at least 30 secs if you ever need to disconnect/reconnect to the fibre DSLAM.
jafreer
Rising Star
Posts: 830
Thanks: 49
Registered: 13-10-2012

Re: DLM question

Thanks for the replies. Confirms what I suspected.
Community Veteran
Posts: 6,313
Thanks: 86
Fixes: 3
Registered: 08-01-2008

Re: DLM question

Quote from: AndyH
Openreach recommend also leaving your modem powered off for at least 30 secs

Are you sure that's 30 secs?  Only reason for asking is I've seen people quoting 30 minutes (which seems excessive to me but what do I know?).
Call me 'w23'
At any given moment in the universe many things happen. Coincidence is a matter of how close these events are in space, time and relationship.
Opinions expressed in forum posts are those of the poster, others may have different views.
Community Veteran
Posts: 6,824
Thanks: 1
Registered: 27-10-2012

Re: DLM question

Quote from: w23
Are you sure that's 30 secs

Yep, see here:
Community Veteran
Posts: 6,313
Thanks: 86
Fixes: 3
Registered: 08-01-2008

Re: DLM question

Thanks AndyH, always useful to know this kind of thing.
Call me 'w23'
At any given moment in the universe many things happen. Coincidence is a matter of how close these events are in space, time and relationship.
Opinions expressed in forum posts are those of the poster, others may have different views.
Community Veteran
Posts: 1,841
Thanks: 103
Fixes: 6
Registered: 21-01-2013

Re: DLM question

You're talking about two different issues.
The 30 second interval is as AndyH says, too ensure the modem has exhausted any residual current.
The 30 minute interval between resyncs or reboots is because the DLM monitors things in 15 minute intervals.
Apparently it's safest to have a clear 15 minute interval between resync to keep the DLM happy. Actually that's may not be the best advice, IIRC the original wisdom was to leave it disconnected for 30 minutes before reconnecting.
Community Veteran
Posts: 6,824
Thanks: 1
Registered: 27-10-2012

Re: DLM question

The two are connected though. The DSLAM can distinguish between a user initiated power cycle and a retrain due to some line problem. I assume this is time based.
In terms of retrains, there are two thresholds ( for the profile Plusnet provision fibre users on):
1) 24 hour retrain threshold - which is 20. Exceed this and you get a red flag on your line.
2) The Mean Time Between Retrains Threshold (MTBR = Uptime / Retrain Count). As long as your MTBR is less than 8400 seconds (approx. 12.3 retrains per day), then your line gets a green flag.
Community Veteran
Posts: 5,109
Thanks: 465
Fixes: 17
Registered: 10-06-2010

Re: DLM question

A higher MTBR is better, an MTBR less than the threshold would get a red flag.
Community Veteran
Posts: 6,824
Thanks: 1
Registered: 27-10-2012

Re: DLM question

Sorry, you're right:
- If the 24hr retrains is greater than the 24hr retrain threshold, you get a red flag.
- If the MTBR is less than the MTBR threshold, you get an amber flag.
- If the MTBR is greater than the MTBR threshold, you get a green flag.
There is also B flag (blue?), where the uptime is less than 900 seconds and not enough data is available.
kitz
Rising Star
Posts: 817
Thanks: 46
Registered: 08-06-2007

Re: DLM question

Quote from: jafreer
I have a feeling that DLM does not take any account of whether a PPP session is established or not when it sees modem disconnects. But that is just a hunch.

Correct - DLM monitors at the DSLAM so as long as you remain in sync it doesnt care.

Quote from: AndyH
Quote from: w23
Are you sure that's 30 secs

Yep, see here:

That is a red herring!
That's only so that the RAS see's the disconnect and can pick up a new IPprofile
If you do a really quick d/c then it doesnt always show on any diagnostics.  Ive had instances of quick resyncs where they weren't recorded purely down to the fact that the HG612 can perform a resync in less than 20 secs.
Although RAMBO is responsible for both IPprofile and DLM, these are two different subsets of the system, each with their own job to do: - 
- IP profile is part of the RAP function.  Profiles are set at the bRAS
- DLM profile is - guess what - part of the DLM function and is set at the DSLAM/MSAN.  Events are monitored by the DSLAMs element manager.   
As far as the DLM is concerned then a resync in the same 15min period counts as a retrain and strike one for the forced event counter.
30 mins ensures at least one complete 15 min period and the sync to be classed as an unforced event so discounted by the DLM
kitz
Rising Star
Posts: 817
Thanks: 46
Registered: 08-06-2007

Re: DLM question

Quote from: AndyH
The DSLAM can distinguish between a user initiated power cycle and a retrain due to some line problem. I assume this is time based.

Purely time based and monitoring for Wide Area Events.
If a line drops due to a fault/LoS/Errors  OR due to an EU simply deciding to Power cycle the modem - The DLM has absolutely no way of knowing if it was a fault or initiated by the EU.
Quote
In terms of retrains, there are two thresholds ( for the profile Plusnet provision fibre users on):
1) 24 hour retrain threshold - which is 20. Exceed this and you get a red flag on your line.

Red is MTBR = 16800.  So hit 20 per day and you get red.  Also if your up time is less than the full 86400 per day then the 20 will reduce accordingly in proportion.
Quote
2) The Mean Time Between Retrains Threshold (MTBR = Uptime / Retrain Count). As long as your MTBR is less than 8400 seconds (approx. 12.3 retrains per day), then your line gets a green flag.

Careful with green.   MTBR needs to be <8400 and also MTBE  <30
Theres also some additional monitoring that can go on here too before DLM may decide to make a reduction.
Quote
There is also B flag

Its Black - There are several other flags
Black - Insufficient days worth of data - ie the data collector hasnt got a full & continuous 15 mins worth of data.
Grey - for when theres either no data at all or corrupt data.
Crimson - MTBE  >300
Amber - All OK within defined parameters.  

------
ETA
Figures on the PN site are old - I contacted one of the reps ages ago about it.  
The figures quoted above are FTTC Stable -  Other ISPs may use FTTC Standard
Im also not sure if things may have changed with g.inp  MTBR will likely be the same.  Re MTBE  and Im not sure if DLM still uses the old figures or if there is some new g.inp monitoring that goes on too, rather than just watching for SES/ES,  weve not seen any evidence that it has changed, but it doesnt mean that it may not have.

---
Edited to fix typo - MTBR transposition of chars.
goldenfibre
Aspiring Pro
Posts: 2,605
Thanks: 48
Fixes: 2
Registered: 01-06-2010

Re: DLM question

It's always best to power down your openreach modem or fibre router with in-built modem for at least 30 minutes. (I always wait 31 minutes to be on safe side) as for PPP session soft disconnection (DLM don't care) I use PPP session soft disconnection to different gateway sometimes if the speed get slower in evening.