Kitz ADSL Broadband Information
adsl spacer  
Support this site
Home Broadband ISPs Tech Routers Wiki Forum
 
     
   Compare ISP   Rate your ISP
 
Please login or register.

Login with username, password and session length
Advanced search  

News:

Author Topic: ADSL / PPP / ATM / Hawk Tester  (Read 509 times)

Gee

  • Just arrived
  • *
  • Posts: 5
ADSL / PPP / ATM / Hawk Tester
« on: August 21, 2017, 11:52:29 AM »

Good morning all,

I had a recently interaction with a BT Openreach engineer that was dispatched due to a line dropping it's PPP session constantly. All EU checks had been performed..test socket, replacement router and cabling and so on, but errors could still be seen on the line.

I am led to believe that errors on the line can cause the PPP session to drop, while sync still stays up. I spoke with the SFI engineer who stated that he should not of been sent out as it is the PPP session that was dropping, but no sync. His tester did not show any drops and he stated there was nothing he could do.

In regards to the tester that the engineer uses, how to they test for PPP drops? Obviously their tester doesn't authenticate with each ISP's network, so do they simply look for any errors while the tester is on the line?

I was advised their testers does not perform an ATM layer so wouldn't be able to mimic the issue?
Logged

Black Sheep

  • Helpful
  • Kitizen
  • *
  • Posts: 4456
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #1 on: August 21, 2017, 08:51:47 PM »

Hi

Firstly, I'd be very surprised to see an engineer using the more-or-less obsolete HAWK tester, for anything other than the TDR function. This function can 'see' a high-resistance fault better than the hand-held testers (EXFO or JDSU), that we currently use today .... especially a 'near-end' HR condition.  :)

Now then, the problem that is dropping PPP session.

Our mandate as Openreach engineers, is to perform various industry agreed tests including ......

A PQT (Pair Quality Test - IE: The pair of wires that feed your house from the Telephone Exchange).
A DSL Close-out test ( This is the broadband test that logs-on to the ISP's radius and passes data back and forth for a pre-determined amount of time - industry standard is 5 mins, but can be set for longer if required).
An Eclipse/Fast Test2 test (Depends on how the task has been built, or how the tests is performed, but basically only tests the low-frequency phone side. As mooted, the test can also incorporate a further high-frequency test that will ping the router at various frequencies across the bandwidth).
A QLT (Quiet Line Test - used to listen for audible noise on the landline).

You are right in your assumptions that PPP can be lost whilst the router remains in synch ...... I would say (generically) in order of probability the fault is likely ............ 1) Router 2) HR fault 3) IP addressing settings (Static or Dynamic) 4) REIN.

However, you mention the engineer could see errors during his testing ??? This really boils down to the severity of the errors and what kind of error it is ?? CRC or FEC ??
A further trick we use to magnify a potential issue is to ring the landline, or make an outgoing call on the landline (usually 17070) to see if the errors increment dramatically ... pointing towards a probable metallic fault somewhere.

I don't suppose you could post some router stats up so that the proper clever people on here can peruse, and hopefully identify an issue ??

 
Logged

burakkucat

  • Global Moderator
  • Senior Kitizen
  • *
  • Posts: 19559
  • Over the Rainbow
    • The ELRepo Project
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #2 on: August 21, 2017, 09:13:36 PM »

I was advised their testers does not perform an ATM layer so wouldn't be able to mimic the issue?

I think that really depends upon which SIM (module) is being used with a JDSU HST-3000. They certainly have the ability to emulate a combined modem plus simple web-browser.
Logged
:cat:  100% Linux and, previously, Unix. Co-founder of the ELRepo Project.

Please consider making a donation to support the running of this site.

NewtronStar

  • Kitizen
  • ****
  • Posts: 4638
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #3 on: August 21, 2017, 09:37:42 PM »


A DSL Close-out test ( This is the broadband test that logs-on to the ISP's radius and passes data back and forth for a pre-determined amount of time - industry standard is 5 mins, but can be set for longer if required).


This one is interesting when the OR engineer is doing the close-out test and you do a sneaky call from mobile to the landline/circuit this will confuse the engineers results is that true ?
Logged

Black Sheep

  • Helpful
  • Kitizen
  • *
  • Posts: 4456
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #4 on: August 21, 2017, 09:40:04 PM »

I suppose it could, NS.  ;) :)
Logged

kitz

  • Administrator
  • Senior Kitizen
  • *
  • Posts: 30133
  • Trinity: Most guys do.
    • http://www.kitz.co.uk
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #5 on: August 22, 2017, 12:19:46 PM »

Quote
I am led to believe that errors on the line can cause the PPP session to drop, while sync still stays up.

Highly unlikely if you are talking about a fault related to the physical side.
Any CRC type errors go through an escalation process which will eventually cause loss of sync way before the PPP session drops.

A PPP session can (& will) actually survive a resync.  A session is negotiated and only drops when told by either the ISP or modem.  It's why at one time stale sessions were problematic for many users because PPP remained up despite the line resyncing.   
To avoid this ISPs must now restart any PPP sessions upon a line retrain by ensuring L2TP/PPP timeout is set at a minimum of 20 seconds. PPP will either drop when forced by ISP or modem... or when PPP idle timeout has been detected by either side.

CRCs cause Errored seconds, get enough errored seconds and the modem enters into an alarm state.  The modem will go through a series of error alarm states eg  An LOS defect is triggered after just 20ms.. and 2 consecutive defects will cause an LOS event.  Most alarm state deactivation periods are 10 seconds..  so youre likely going to enter loss of link and a retrain of the line way before the PPP drops. - See the various error states for more info.

If it helps, think of the PPP session as like a cookie which doesn't expire until its told. Most of the recurring PPP session drops are usually down to a router misconfig issue.
The engineer who visited is correct, he can't do anything about PPP unless the line is also experiencing sufficient CRC & Err Sec type errors to cause the line to retrain. :/

What modem/router are you using?

Logged
Please do not PM me with queries for broadband help as I may not be able to respond.
-----
How to get your router line stats :: ADSL Exchange Checker

ejs

  • Kitizen
  • ****
  • Posts: 1356
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #6 on: August 22, 2017, 05:08:10 PM »

CRC errors can cause the PPP session to drop, without dropping the underlying DSL link, if the PPP / LCP messages are lost. This can and does happen. It's even possible to rack up CRC errors at the maximum possible rate without losing the DSL connection. It probably depends on the modem, some even have low-level configurable settings to control when it drops the DSL link.

LOS has nothing to do with CRC errors.
Logged

kitz

  • Administrator
  • Senior Kitizen
  • *
  • Posts: 30133
  • Trinity: Most guys do.
    • http://www.kitz.co.uk
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #7 on: August 22, 2017, 09:39:20 PM »

>> CRC errors can cause the PPP session to drop,

and the chances of it repeatedly 'just' being the LCP echo messages that drop without causing the modem to go into an alarm state or showing any of the other more serious error types and/or changes in SNRM if thats being recorded?
Yes perhaps it could happen on an odd occasion, but constantly without any of the other symptoms?

I still maintain that its far more common to see constant PPP drops through either the modem or ISP misconfiguration. Some can be resolved by changing settings in the router, but its not unknown to be a problem at the ISP end either for example it was happening a few years ago with one of Zens gateways.  I asked for the type of router because it tends to be own bought routers rather than ISP preconfig ones.

The other thing to bear in mind is that from some router logs the PPP down may be more obvious than loss of sync, Ive seen many people say loss of PPP when the line is also losing sync.

I just chose LOS because its one of the more common ones we see recorded in the line stats, indicating there is a problem with the physical link. There are plenty of others which is why I deliberately said eg and linked to the full list :/

As BS said, we need to see more info from line stats really.
Logged
Please do not PM me with queries for broadband help as I may not be able to respond.
-----
How to get your router line stats :: ADSL Exchange Checker

burakkucat

  • Global Moderator
  • Senior Kitizen
  • *
  • Posts: 19559
  • Over the Rainbow
    • The ELRepo Project
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #8 on: August 22, 2017, 10:23:49 PM »

I would definitely like to know the make/model of the CPE in question.
Logged
:cat:  100% Linux and, previously, Unix. Co-founder of the ELRepo Project.

Please consider making a donation to support the running of this site.

ejs

  • Kitizen
  • ****
  • Posts: 1356
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #9 on: August 23, 2017, 02:58:17 PM »

I'm not convinced the modem has an "alarm state" merely for lots of CRC errors. Obviously it wouldn't be just the LCP echo messages being lost, packet loss in general would be fairly high for anything else attempting to access the Internet over the connection.

In any case, if the CRC errors can be monitored and plotted on a graph, it should be simple to see if the PPP drops happen when there are large bursts of errors.
Logged

Gee

  • Just arrived
  • *
  • Posts: 5
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #10 on: August 23, 2017, 03:53:15 PM »

Hi

Firstly, I'd be very surprised to see an engineer using the more-or-less obsolete HAWK tester, for anything other than the TDR function. This function can 'see' a high-resistance fault better than the hand-held testers (EXFO or JDSU), that we currently use today .... especially a 'near-end' HR condition.  :)

Sorry, I couldn't remember what the new testers were called!

Now then, the problem that is dropping PPP session.

Our mandate as Openreach engineers, is to perform various industry agreed tests including ......

A PQT (Pair Quality Test - IE: The pair of wires that feed your house from the Telephone Exchange).
A DSL Close-out test ( This is the broadband test that logs-on to the ISP's radius and passes data back and forth for a pre-determined amount of time - industry standard is 5 mins, but can be set for longer if required).
An Eclipse/Fast Test2 test (Depends on how the task has been built, or how the tests is performed, but basically only tests the low-frequency phone side. As mooted, the test can also incorporate a further high-frequency test that will ping the router at various frequencies across the bandwidth).
A QLT (Quiet Line Test - used to listen for audible noise on the landline).

Ahh. Sounds like it was the close out test that was performed which did not replicate the issue.

You are right in your assumptions that PPP can be lost whilst the router remains in synch ...... I would say (generically) in order of probability the fault is likely ............ 1) Router 2) HR fault 3) IP addressing settings (Static or Dynamic) 4) REIN.

However, you mention the engineer could see errors during his testing ??? This really boils down to the severity of the errors and what kind of error it is ?? CRC or FEC ??
A further trick we use to magnify a potential issue is to ring the landline, or make an outgoing call on the landline (usually 17070) to see if the errors increment dramatically ... pointing towards a probable metallic fault somewhere.

Sorry, no the ISP could see errors on the line but the SFI engineer did not suggest there were any.

I don't suppose you could post some router stats up so that the proper clever people on here can peruse, and hopefully identify an issue ??

I'll try shortly :)


Thanks for the information.
Logged

Gee

  • Just arrived
  • *
  • Posts: 5
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #11 on: August 23, 2017, 03:54:50 PM »

This one is interesting when the OR engineer is doing the close-out test and you do a sneaky call from mobile to the landline/circuit this will confuse the engineers results is that true ?

Thank you. It seems I was either misinformed on things have changed from years ago :)
Logged

Gee

  • Just arrived
  • *
  • Posts: 5
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #12 on: August 23, 2017, 03:57:33 PM »

I would definitely like to know the make/model of the CPE in question.

Two routers were tested.

A Zyxel AMG 1302-T10B and a Draytek Vigor 2760.

Though both exhibit the problem, the Dratek is not as bad.
Logged

Black Sheep

  • Helpful
  • Kitizen
  • *
  • Posts: 4456
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #13 on: August 23, 2017, 05:12:45 PM »

I wonder if it is HEC's , regarding errors 'seen' ?? We don't see them on any of our tests with the HHT, but the ISP can see them. Just a thought.
Logged

Gee

  • Just arrived
  • *
  • Posts: 5
Re: ADSL / PPP / ATM / Hawk Tester
« Reply #14 on: August 25, 2017, 09:04:47 AM »

I wonder if it is HEC's , regarding errors 'seen' ?? We don't see them on any of our tests with the HHT, but the ISP can see them. Just a thought.

It's possible. The line has settled down a bit now, but still loses session here and there.
Logged