99
CHAPTER 8: Testing Twisted-Pair Cable
2. If any of the tests you perform using the SCAN-LAN VI fail, use the
information from the troubleshooting tables provided earlier in this
chapter to determine the cause of the failure.
3. If the SCAN-LAN VI displays results you did not expect, make sure you
document the result or save the test for later printout. Then, if you are
unable to resolve your problem, contact Black Box.
8.4 Power Sum NEXT
Power Sum NEXT is a critical test for certifying the performance of
installed twisted-pair links. It is the sum of the pair-to-pair NEXT coupled
from all adjacent pairs in a cable.
Power Sum NEXT is an important measurement for emerging high-speed
local area networks such as 622-Mbps ATM and Gigabit Ethernet. These
networks transmit over multiple pairs at once to achieve their high data
rates. Because they transmit over several pairs simultaneously, the normal
pair-to-pair NEXT is not indicative of the coupled noise signal into the
receive pair. Rather, the coupled signal is larger because of the multiple
transmitters.
Crosstalk from multiple pairs is illustrated below.
Figure 8-13. Power Sum NEXT Measurement.
M
Signal measurement
Signal generators
7
8
4
5
3
6
1
2
Crosstalk
Summary of Contents for SCAN-LAN VI
Page 2: ......
