FT1 Device Loopback Select Code Name Code Byte

3.LOOPBACK ACTIVATION/DEACTIVATION

This section describes loopback activation and deactivation methods for the ADTRAN Fractional T1 system. Loopback activation and deactivation is controlled with the push-button located on the front panel, through craft interface, or latching loopback codes.

Both the FNID and the FT1 DP have a push-button located on the front panel labeled REM LBK or RLB which controls the activation of remote loopback. Pressing REM LBK or RLBon the FNID activates FT1 DP CPE loopback. Pressing REM LBK or RLB on the FT1 DP activates FNID network loopback or repeater loopback when a repeater is present. Remote loopback is deactivated by pressing the REM LBK or RLB or waiting for the 20-minute loopback timeout, if enabled.

The FNID and FT1 DP (when available) have a craft interface located on the front panel of the device. The craft interface allows access to the FT1 device through an RS-232-type interface. All loopbacks for the FNID and FT1 DP can be controlled from the craft interface. The craft interface on the FNID can activate and deactivate the FNID network loopback and the FNID CPE loopback. The FNID craft interface can also remotely activate and deactivate the FT1 DP network loopback, FT1 DP CPE loopback, and the repeater network loopback. The craft interface on the FT1 DP can activate and deactivate the FT1 DP network loopback and the FT1 DP CPE loopback. The FT1 DP craft interface can also remotely activate and deactivate the FNID network loopback and the FNID CPE loopback and the repeater network loopback.

FT1 DP, FT1 Repeater, and FNID network loopbacks can be activated by the DDS latching loopback sequence. The latching loopback sequence is detected in the primary DS0 of the FT1 system. When the loopback is activated on the device, the

whole FT1 bandwidth is looped. The FT1 DP, FT1 Repeater, and FNID each

Latching loopbacks for the FT1 system are activated by transmitting the following latching loopback sequence in the primary DS0 of the FT1 system:

A.Minimum of 35 transition in progress (TIP) bytes (N0111010).

B. Minimum of 35 loopback select code (LSC) bytes as defined in Table I.

C. Minimum of 100 loopback enable (LBE) bytes (N1010110).

D.Minimum of 35 all 1s bytes (S1111111), plus a minimum of 100 LBE bytes. (N-1) iterations, where N is the number of channel units of the same type (i.e., same LSC) that lie between the test center and the loopback to be operated. This step is only used when there are identical channel units in tandem.

E. Minimum of 32 far end voice (FEV) bytes (N1011010).

A25-second watchdog timer is activated between the 35 TIP bytes and 35 LSC bytes, between the 35 LSC bytes and 100 LBE bytes, and between the 100 LBE bytes and 32 FEV bytes. The timer requires the correct receipt of the latter sequences less than 25 seconds after receipt of the prior sequence. This prevents inadvertent setting of the latching loopbacks.

Latching loopbacks for the FT1 system are deactivated by transmitting the following latching loopback sequence in the primary DS0 of the FT1 system:

Minimum of 35 TIP bytes (N0111010).

4. LOOPUP STATE

In the loopup state, the active FT1 loopback will provide a continuous loop for the FT1 bandwidth. The data flow is continuously monitored for the loop deactivation commands to deactivate the loopbacks. Also, a 20-minute loopback timeout is checked. If the loopback timeout is enabled, any loopback that is in the loopup state for 20 minutes will be deactivated.

Table A-1. FT1 Loopback Select Codes

respond to a different loopback select code allowing for sectionalization of the network during testing. Table A-1 is a list of FT1 devices and their loopback select codes.

FT1 Device	Loopback Select	Loopback Select
	Code Name	Code Byte

FT1 DP	OCU loopback	N1010101
FT1 Repeater #1	NEI Position 1 loopback	N1000001
FT1 Repeater #2	NEI Position 2 loopback	N1000001
FNID without repeater	NEI Position 1 loopback	N1000001
FNID with one repeater	NEI Position 2 loopback	N1000001
FNID with two repeaters	NEI Position 3 loopback	N1000001

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Section 61245201L1-5, Issue 3

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