How to track a cliff on the last mile?

Question

Computer networks

I had a network break at home. The guys from the provider came and they can’t understand anything, because. There is a link, but there is no signal. They called the office - they were told there "a break at 35 meters." Well, they quickly found this section of the wire by marking, immediately cut out a piece (one and a half meters) and connected it through the connector. After that everything worked.
Actually, the question is brewing - how do they monitor the last mile, and how do they track the cliff, and even with such accuracy?
PySy: what kind of pieces of iron are in the entrance - I have no idea. Provider Dom.Ru

Answer 1

1) if they were told from the office, then the TP on the switch in your house launched a command to check the cable length, and then it’s a matter of technology. In terminology of a tsiska it is called Time-Domain Reflectometr (TDR), you can google.
2) it is possible without a switch, installers use a special device for dialing, for example fluke. Only it costs horse money and it turns out expensive to carry it with each brigade.
At the expense of the link in the apartment - 3 or 6 cores were damaged in the wire, a reverse transmission is going through them. the signal from the node in the house comes to the router, but not back.
And this is not monitoring, but a one-time check, since at the time of its launch, the port is disabled. Yes, and really the wire should be disconnected from the other side. For real monitoring, BFD/OAM technologies are used.

Answer 2

There is a link diagnostic function on many managed switches. It works differently in different conditions, it greatly depends on the manufacturer and model of the device, but in general it can help in identifying the problem.
For example:

DES-1210-10:5# cable diagnostic port 9
Command: cable diagnostic port 9


 Perform Cable Diagnostics ...

 Port  Type   Link Status  Test Result   Fault Distance (meters)  Length(M)
 ----  -----  -----------  ------------  -----------------------  ---------
 9     GE     Link Down    Pair1:OPEN    Pair1:10                 N/A
                           Pair2:OPEN    Pair2:10
                           Pair3:OPEN    Pair3:10
                           Pair4:OPEN    Pair4:10

[email protected]_TEST> request diagnostics tdr start interface ge-0/0/1

Interface TDR detail:
Test status                     : Test successfully executed  ge-0/0/1

{master:0}
[email protected]_TEST> show diagnostics tdr interface ge-0/0/1

Interface TDR detail:
Interface name                  : ge-0/0/1
Test status                     : Passed
Link status                     : Down
MDI pair                        : 1-2
  Cable status                  : Normal
  Distance fault                : 0 Meters
  Polartiy swap                 : N/A
  Skew time                     : N/A
MDI pair                        : 3-6
  Cable status                  : Normal
  Distance fault                : 0 Meters
  Polartiy swap                 : N/A
  Skew time                     : N/A
MDI pair                        : 4-5
  Cable status                  : Impedance Mismatch
  Distance fault                : 19 Meters
  Polartiy swap                 : N/A
  Skew time                     : N/A
MDI pair                        : 7-8
  Cable status                  : Impedance Mismatch
  Distance fault                : 20 Meters
  Polartiy swap                 : N/A
  Skew time                     : N/A
Channel pair                    : 1
  Pair swap                     : N/A
Channel pair                    : 2
  Pair swap                     : N/A
Downshift                       : N/A

{master:0}

Answer 3

You can measure both the capacitance of the cable and the reflected signal. In general, physics and the cost of solutions varies greatly :)
MikroTik-and they can do this, they even show it quite accurately