ADTRAN Loopback Activation and Deactivation, Table A-1. FT1 Loopback Select Codes

3.LOOPBACK ACTIVATION AND 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.

Apush-button labeled ÒLBK,Ó located on the front panel of the FNID, controls the activation of remote loopback. Pressing this button activates the FT1 DP CPE loopback. Two push-buttons, labeled ÒLCLÓ and ÒREM,Ó respectively, are located on the front panel of the FT1Ê DP. Press REM on the FT1 DP in order to activate FT1 Repeater loopback (when available) or FNID network loopback. To deactivate Remote loopback, either press REM or wait for the loopback timeout (if enabled).

Craft interfaces, located on the front panels of the FNID and FT1Ê DP, allow access to the FT1 device through an RS-232-type interface. All loopbacks for the FNID, FT1 Repeater, and FT1 DP can be controlled from the craft interface. The craft interface located on the FNID faceplate can activate and deactivate FNID network and FNID CPE loopbacks; and remotely activate and deactivate FT1 Repeater network loopback, FT1 DP network loopback, and FT1 DP CPE loopback. The craft interface located on the FT1Ê DP faceplate can activate and deactivate FT1 DP network loopback and FT1 DP CPE loopbacks; and remotely activate and deactivate the FT1 Repeater networkloopback, FNID network loopback, and FNID CPE loopback.

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 A-1.

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 receiving 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 25 TIP bytes (N0111010)

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 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 code.

Table A-1. FT1 Loopback Select Codes

	Loopback Select	Loopback Select
FT1 Device	Code Name	Code Byte
FT1 DP	OCU loopback	N1010101
FT1 Repeater	NEI Position 1 loopback	N1000001
FNID without repeater	NEI Position 1 loopback	N1000001
FNID with repeater	NEI Position 2 loopback	N1000001

61245211L1-5A Section 61245211L1-5, Issue 1 A-3