Cisco Systems UBR7225VXR specifications Testing the Upstream Configuration

Chapter 4 Connecting the Cisco uBR7225VXR Router to the Cable Headend

Connecting and Configuring the Upstream

Figure 4-22 Connecting and Configuring the Upstream

Cisco

uBR7225VXR

Upstream

2-way splitter (combiner)

40 dB

attenuator

X-level test point signal level

must be the same for all

optical receivers (+/- 0.5 dB), See Fig. 4-36 and Fig 4-37

10 dB		Optional attenuator
	X	to adjust X-level point
attenuator
		measurement

Diplex filter

LH To downstream forward

test point on laser transmitter

C

Cable modem

Optical

receiver

271676

Testing the Upstream Configuration

To test the upstream configuration, insert a test signal of known amplitude (+17 dBmV is shown in this example) into the fiber node and measure the amplitude output level at the output of the headend’s optical receiver. This measurement depends on return laser performance and optical distance. This procedure is known as establishing the “X-level” test point. (See Figure 4-23.)

Figure 4-23 The “X-level” Test Point

Spectrum analyzer

Optical

receiver

+17 dBmV 10 km

Fiber node 0.5 milliwatt

Insert +17 dBmV signal

Spectrum analyzer

+11 dBmV

1dB attenuator

Optical
receiver				Insert +17 dBmV signal
	30 km		Fiber node
			1.0 milliwatt
		Measure +10 dBmV at this point
	X
			14045
	(in this example)
X-level test point = +10 dBmV

	Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
OL-17309-02		4-19