ADTRAN T200 IDSL Manual de usuario descargar pdf (Pagina 6)

6 Issue 1, May 2004 61292023L5-5A

Signal Meter

The Total Reach OCU-R contains an LED indication

signal meter that approximates the amount of dB loss on

the Total Reach DDS loop at 13.3 kHz (135 ohms termi-

nation), the Nyquist frequency of Total Reach DDS.

The signal meter on the Total Reach OCU-R may be

used to verify that the loop loss is actually within Total

Reach DDS deployment guidelines without the

requirement of peripheral test equipment. The signal

meter is activated automatically upon power up during

the Total Reach DDS training sequence and remains

activated until synchronization occurs (usually 30 to 90

seconds after power-up). If the signal meter only illumi-

nates the 2.4 LED, then the loop loss is too great for

Total Reach DDS deployment. If the signal meter

illuminates 2.4 and 4.8 (only two LEDs), then the Total

Reach DDS loop loss is between 50 dB and 56 dB and

the loop is considered marginal for Total Reach DDS

deployment. If three or more rate LEDs are illuminated

during Total Reach DDS train-up, then the circuit is

considered to be within Total Reach DDS deployment

guidelines.

A translation of the signal meter loss ranges in dB is

shown in Figure 6. If the loop loss indicates a marginal

loop for Total Reach DDS deployment, then a more

precise loop loss measurement can be made with the

appropriate test equipment.

Figure 6. Signal Loss Indication

3. TESTING

Loopback Testing

Loopback tests can be performed from the Central

Office (CO) to verify proper loop and Total Reach

OCU-R operation. The Total Reach OCU-R provides a

network loopback in response to a network initiated

alternating or latching OCU loopback, or NIE loopback,

dependent upon the installed Total Reach DDS CO unit.

The Total Reach OCU-R also provides a sealing current

reversal when the CSU loopback command is detected.

Alternating loopbacks may be performed at all rates,

except 64 kbps Clear Channel. Table 6 details the alter-

nating loopback sequences.

X = Don’t care bit.

Tab le 7 details latching loopback sequences. The Total

Reach OCU-R supports testing of the two-wire loop

from the remote end when the Total Reach DDS CO

unit is performing a bidirectional DS0 or OCU

loopback.

Minimum of 35 TIP bytes required to disable established

latching loopback.

x = Don't care bit

19.2

9.6

4.8

2.4

0-10

10-20

20-30

30-40

40-50

50-56

>56

LED SIGNAL LOSS

(dB)

Signal level

Signal level indicated during synchronization

Table 6. Alternating Loopback Sequences

Sequence Function Received Bytes

Active Loopback Four consecutive bytes of

specified loopback code

X0101010 - OCU

X0101000-CSU

X0101100-DSU

Maintain loopback and test

bit errors

Data byte alternating with

loopback code example:

XDDDDDD1/X0101010

Clear loopback Four consecutive data

bytes without specified

loopback code

Table 7. Latching Loopback Sequences

Sequence

Function

Byte Code Number of

Received

Bytes

Clear existing

loopbacks

Transition in

progress (TIP)

X0111010

Minimum of 35

TIP bytes

Identify device

to be looped

Loopback select

code (LSC)

X0000101 - DS0

X1010101 - OCU

X0110001 - CSU

X1000001 - NIE

Minimum of 35

LSC bytes

Prepare to loop;

send MAP code

after 30 bytes

Loopback

enabled (LBE)

X1010110

Minimum of

100 LBE bytes

Activate

loopback

Far-End voice

(FEV)

X1011010

Minimum of 32

FEV bytes

1 2 3 4 5 6 7 8 9 10 11 ... 21 22

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