Method for detection of a shielding fault in a multiwire cable

1. Method for detection of a shielding fault in a multiwire cable forming part of a communication network, during functional operation of the said network, the said cable ( 10 ) transferring a multiframe signal S(t), characterized in that it comprises the following steps:

a disturbing signal I(t) is injected into the said cable through an injection clamp ( 14 ) for a determined time T;

when an item of equipment ( 12 ) receives the signal S(t), the number N of frames in fault during the injection period of the disturbing signal I(t) is counted; and

it is decided that there is a shielding fault in this cable if N/T≦TEP max , where TEP max is the maximum packet error rate to be guaranteed.

2. Method according to claim 1 , in which TEP max is equal to 0.

3. Method according to claim 1 , in which the communication network is an Ethernet network.

4. Method according to claim 1 , in which N is the number of error frames, that in particular includes CRC errors, frames that are too short, and missing frames.

5. Method according to claim 1 , in which the number N is included in the MIB part for different network equipment ( 11 , 12 ).

6. Method according to claim 1 , in which the following relation is true:

I1

ATT

min

<

I

<

I1

ATT

max

,

where:

I 1 : the level of the disturbing signal I(t) that disturbs the signal S(t) if there is no shielding protection;

ATT min : the minimum attenuation of the shielding necessary for the disturbance induced under the shielding to be less than I 1 , taking account of the expected maximum external aggression; and

ATT max : normal attenuation of the shielding.

7. Method according to claim 1 , in which the disturbing signal I(t) is similar to the signal S(t) transferred on the cable.

8. Method according to claim 1 , in which the disturbing signal I(t) has at least one frequency previously identified as particularly disturbing the signal S(t).