2 Replies Latest reply on Oct 30, 2017 10:09 AM by ajr3v

    ISDN PRI Loopback Plug

    ajr3v New Member

      I'm trying to bring up a SIP to PRI setup in the lab


      I've setup my PRI and SIP trunks.



      However, I am unable to bring up the D-Channel using a loopback plug. I am just receiving continues SABME messages


      PIN 1 -> PIN 4

      PIN 2 -> PIN 5


      01:59:21.346 ISDN.L2_FMT PRI  1  ==============================================

      01:59:21.346 ISDN.L2_FMT PRI  1  Sent  Sapi:00 C/R:C Tei:00 Ctl:SABME   P:1

      01:59:21.351 ISDN.L2_FMT PRI  1  ==============================================

      01:59:21.351 ISDN.L2_FMT PRI  1  Recd  Sapi:00 C/R:C Tei:00 Ctl:SABME   n 

      01:59:22.345 ISDN.L2_FMT PRI  1  ==============================================

      01:59:22.346 ISDN.L2_FMT PRI  1  Sent  Sapi:00 C/R:C Tei:00 Ctl:SABME   P:1

      01:59:22.351 ISDN.L2_FMT PRI  1  ==============================================

      01:59:22.351 ISDN.L2_FMT PRI  1  Recd  Sapi:00 C/R:C Tei:00 Ctl:SABME   P:

      01:59:23.345 ISDN.L2_FMT PRI  1  ==============================================

      01:59:23.346 ISDN.L2_FMT PRI  1  Sent  Sapi:00 C/R:C Tei:00 Ctl:SABME   P:1

      01:59:23.350 ISDN.L2_FMT PRI  1  ==============================================


      TA904#sho int t1 0/2

      t1 0/2 is UP

        Receiver has no alarms

        T1 coding is B8ZS, framing is ESF

        FDL type is ANSI

        Line build-out is 0dB

        No remote loopbacks, No network loopbacks

        Acceptance of remote loopback requests enabled

        Tx Alarm Enable: rai

        Last clearing of counters 02:13:34

          loss of frame  : 9, last occurred 00:27:33

          loss of signal : 8, last occurred 00:27:32

          AIS alarm      : 1, last occurred 01:43:48

          Remote alarm   : 0



        DS0 Status: 123456789012345678901234


        Status Legend: '-' = DS0 is not allocated

                       'X' = DS0 is allocated (nailed)



        Signaling Bit Status: 123456789012345678901234

                         RxA: 100100001001000000000000

                         RxB: 010000000100010000000000



                         TxA: 010001000000100100001001

                         TxB: 010001000000010000000100




        Line Status: -- No Alarms --



        5 minute input rate 0 bits/sec, 0 packets/sec

        5 minute output rate 0 bits/sec, 0 packets/sec

        Current Performance Statistics:

          0 Errored Seconds, 0 Bursty Errored Seconds

          0 Severely Errored Seconds, 0 Severely Errored Frame Seconds

          0 Unavailable Seconds, 0 Path Code Violations

          0 Line Code Violations, 0 Controlled Slip Seconds

          0 Line Errored Seconds, 0 Degraded Minutes



        TDM group 1, line protocol is not set

          Encapsulation is not set

      TA904#show interfaces pri 1

      pri 1 is DOWN

        Switch protocol:  National ISDN 2

        Signaling role:  network (NT) b-channel-restarts enabled

        Ringing signal:  calling TE provides audible ringing

        Calling-party override:  disabled

        Calling-party presentation:  allowed

        Calling-party number:  (no number configured)

        digits transferred all

        ISDN name-delivery:  via Facility msg following Proceeding msg

        progress indicator #8 in alerting message:  enabled

        progress indicator #2 in connect message:  disabled

        progress indicator #1 in setup message:  disabled

        progress indicator #3 in setup message:  disabled

        progress indicator location:  public

        resource-selection: circular descending

        TBCT:  disabled

        area code: 

        Transmission of redirecting numbers is enabled

        Redirecting numbers: sent as received

        Connected interface: t1 0/2 tdm-group 1

        Channel status 123456789012345678901234


          Legend: - = Unallocated        . = Inactive

                  A = Active B channel   B = Backup D channel

                  D = Active D channel   M = Maintenance

                  R = Restart

          2206 packets input, 6618 bytes, 0 no buffer

          0 runts, 6 giants, 0 throttles

          21 input errors, 9 CRC, 1 frame

          11 abort, 0 discards, 0 overruns

          2536 packets output, 7608 bytes, 0 underruns








      interface t1 0/2

        tdm-group 1 timeslots 1-24 speed 64

        no shutdown



      interface pri 1

        isdn name-delivery proceeding

        connect t1 0/2 tdm-group 1

        role network b-channel-restarts enable

        no shutdown



      isdn-group 1

        connect pri 1





      timing-source t1 0/2


      timing-source internal secondary





      voice feature-mode network

      voice forward-mode network






      voice trunk T01 type sip



        sip-server primary **HIDDEN**

        registrar primary **HIDDEN**

        registrar expire-time 0


      voice trunk T02 type isdn

        description "PRI"

        resource-selection circular descending

        connect isdn-group 1

        rtp delay-mode adaptive



      voice grouped-trunk SIP

        trunk T01

        accept $ cost 0



      voice grouped-trunk PRI

        trunk T02

        accept $ cost 0



      Am I missing something?


      T1 and PRI's are new to me, bringing it into the lab to understand them better.



        • Re: ISDN PRI Loopback Plug
          jayh Hall_of_Fame

          You will not be able to bring up a PRI with a loopback plug. The underlying T1 will come up but not the PRI.


          PRI connections have one end configured for role network and the other for role user. The loopback plug will echo back the configuration applied to the interface. so if your TA900 is set to role user it will reflect two user devices communicating with each other or if it is set to network, two network devices connected together. This is not a valid combination and the PRI will not come up.


          If you have two TA900 devices you can configure one of them as network and the other as user and they'll work fine.


          It may be possible to configure two PRIs on the same box for testing with one as role user and one as network just to see the PRI go active. I haven't tried this but it should be possible to at least get the D-channel up.


          As with any T1 connection, pay attention to clocking. One T1 needs to source the clock and the other sync to the received clock on the T1.