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[licquorice]

May be a silly question, but how does DLM actually monitor downstream circuit performance? Does the DSLAM interrogate the modem for the information or is it somehow extrapolated from TCP/Phy re-transmision requests?

[burakkucat]

I have always assumed that there is a constant two-way dialogue taking place between the CO and CPE. 

Hopefully somebody who has made a study of the process will be able to enlighten us.

[NewtronStar]

I have always assumed that there is a constant two-way dialogue taking place between the CO and CPE. 

Constant no it's more like every 15 minutes  so four dialogues per hour and what you do in those 15 minutes it' some how still records your modem changes to the DLM

[licquorice]

Hopefully somebody who has made a study of the process will be able to enlighten us.

I was rather hoping so!

[burakkucat]

I wonder if the kitteh friendly WWWombat has an opinion?

[NewtronStar]

Kitz did a very good thread on how the DLM works
http://www.kitz.co.uk/adsl/DLM_system.htm
or is there something missing in that tutorial you need

 

[licquorice]

Yes I did read that, but it doesn't really describe the interaction between DSLAM and CPE in any detail.

It doesn't actually specifically state that CPE gathered information is passed to the DSLAM

Our own modem/router also has a data collector and some models allow the user to access this data to obtain a count of errors recorded on the line.  Home routers also usually record using 15 min bins, although it may only retain data for 2 or 3 x 15 min bins before pushing this information on a cumulative stack.

[NewtronStar]

So I guess your trying to find the protocol which stops the modem sending out end-user line data to the DLM is that correct 

[licquorice]

Mainly from an academic point of view, but probably the opposite actually. Wondering if there are there circumstances where the DSLAM doesn't recieve information from the CPE and what the outcome of that is.

[gt94sss2]

See pages 65 and 66 of http://www.sinet.bt.com/sinet/SINs/pdf/498v7p1.pdf

It describes what information Openreach expect CPEs to report in line with G.997.1 and G.993.2. Also worth looking at R.VDSL2.16 and 17 on pages 26-28

[Black Sheep]

A system called Yukon collates the real-time data from the CPE, I believe ??

[NewtronStar]

Mainly from an academic point of view, but probably the opposite actually. Wondering if there are there circumstances where the DSLAM doesn't recieve information from the CPE and what the outcome of that is.

No communication from DSLAM to modem = no connection and No communication from modem to DSLAM = no connection

[licquorice]

See pages 65 and 66 of http://www.sinet.bt.com/sinet/SINs/pdf/498v7p1.pdf

It describes what information Openreach expect CPEs to report in line with G.997.1 and G.993.2. Also worth looking at R.VDSL2.16 and 17 on pages 26-28

Thanks for that.

@NewtronStar  I meant stats information specifically, not general communication.

[NewtronStar]

Thanks for that.

@NewtronStar  I meant stats information specifically, not general communication.

If I see you on BT Forums i'll send you a rating the BT customers over there need as much help given buy educated Kitz members   

[WWWombat]

I was rather hoping so!

Here goes with the parts I understand...

Part 1: Getting counters from modem to DSLAM
The VDSL2 specification includes a lot of stuff on "operation and management", which both controls the setup of the connection and extracts information from it. (Section 11 of the VDSL2 specification).

Part of the protocol overhead of VDSL2 is to allow the two sides to send messages back and forth as part of this protocol: there are time -critical "indicator bits" and a non-time-critical "EOC channel" (embedded operations channel). I've attached a picture that shows the model
- VTU-O is the modem in the DSLAM
- VTU-R is the modem in the subscriber endpoint

One of the commands that can be sent on the EOC channel is one to query the management counters at the far end; the response includes the current counters for
- FEC
- CRC
- FEC errored seconds (a counter we never see normally!)
- Errored seconds
- Severely errored seconds
- LOS errored seconds
- Unavailable errored seconds

So the DSLAM can query your modem's counters at any time, as can your modem. Undoubtedly your modem does this in order to collect the upstream statistics that it keeps in 15 minute and 24 hour buckets.

Part 2: Getting counters out of DSLAM

You'll note, from that model, there is mention of "MIBs" and a "Q-interface". This is the mechanism by which a centralised "DLM process" can extract data for each line from the DSLAM. The Q-interface is achieved using SNMP, and the MIB's are standard SNMP data structures that hold a variety of data. In this case, one of the MIBs will be designed to hold the counters.

DLM just needs to use an SNMP query at regular intervals (presumable every 15 minutes) to extract the data.