Information Technology Reference
In-Depth Information
TABLE 15.5
Field Tester Accuracy Levels
Performance
Accuracy
Accuracy
Accuracy
parameter
Level I
Level II
Level II-e
NEXT accuracy:
Permanent Link
3.8 dB
1.6 dB
2.4 dB
Channel
3.4 dB
1.5 dB
4.4 dB
ELFEXT accuracy
Permanent Link
3.0 dB
Channel
5.0 dB
Attenuation accuracy:
Permanent Link
1.3 dB
1.0 dB
1.7 dB
Channel
1.3 dB
1.0 dB
2.5 dB
Dynamic accuracy
1.0 dB
0.75 dB
Length accuracy
4%
4%
5% (5 m)
Propagation delay
25 ns
Delay skew
10 ns
Return loss
15 dB
15 dB
25 dB
Accuracy
2.1 dB Permanent Link
4.6 dB Channel
Random noise floor 50 - k * dB 65 - k * dB
Residual NEXT 40 - k * dB 55 - k * dB
Output signal balance 27 - k * dB 37 - k * dB
Common mode rejection 27 - k * dB 37 - k * dB
NOTE: The constant k * is equal to 15 log ( f /100) and thus varies with frequency. Performance and measurements
are not required below 75 dB for residual NEXT and for random noise floor, and are not required below 60 dB for
output signal balance, dynamic accuracy, and common mode rejection.
Testing Costs
Proper testing costs money over and above the basic cost of installing and verifying
the cable. As we will see in the next section, there are many tools that may be used
to test LAN wiring. Some of these tools are fairly simple testers that check continu-
ity and wire map (the proper pin connections). Use of such tools should be consid-
ered a normal part of cable installation and included in the price. These simple tests
verify the DC electrical integrity of the link and find gross failures that would pre-
vent the cable from functioning even in simple uses. This verification catches wiring
errors and can find cases where the cable has been severely damaged after installa-
tion. Verification, by visual inspection and continuity check, once was considered
sufficient testing for telecommunications cables. This is no longer the case.
 
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