226 CHAPTER 3: D EVICE CONFIGURATION■ Payload Loopback — A loopback in which the signal returnedtoward the source of the loopback command comprises the payloadof the received signal (with bit sequence integrity retained) and newlygenerated ESF framing (not necessarily maintaining the integrity of thechannel timeslots, frames, or superframes of the received signal). Thenewly generated ESF data link contains a valid performance reportmessage with a value of one in every LB-labeled bit position for theduration of the loopback indicating the signal is the result of a payloadloopback.Enabling or DisablingLoopback TestsYou can use the NBX NetSet utility to enable or disable loopback testsupport in the 3C10116D T1 and 3C10165D E1 cards. By default,loopback test support is disabled. Once enabled, you can initiate theLocal and Framer tests. The Line and Payload tests must be initiated bythe Central Office or by test equipment emulating Central Officeequipment.CAUTION: Enabling one or more loopback tests will terminate any activecalls on all channels of the selected span and make that span unavailablefor calls until loopback testing is disabled.To enable or disable loopback support:1 Login to the NBX NetSet utility as administrator.2 Click Device Configuration > Digital Line Cards > T1 Span ListorDevice Configuration > Digital Line Cards > ISDN PRI Span List3 Choose a span from the list and the click Modify.4 Enable or clear the Enable Loopbacks check boxes are required and thenclick Apply.You can view the results of Local and Framer loopback testing in the SpanStatus dialog box. To view Span status:1 On the Digital Line Cards tab, select T1 Span List or ISDN PRI SPAN Listfrom the Select Device Type list, and then click Apply.2 Select the span and click Status.A red alarm indicates that the test failed. No alarm indicates that the testpassed.
