2 Replies Latest reply on Mar 23, 2016 11:51 AM by mccvoip

    TA908e Random B-channel Restarts

    mccvoip New Member

      I am testing the TA908E connected to a Cisco UC540 PBX for SIP-PRI and I have noticed that occasionally when there are not active calls - the IAD is sending B-channel restarts for every channel in the PRI. I am trying to time it and see if it happens every hour as a "refresh" or "keepalive" or if there is actually an interoperability issue between the two devices. I'm not seeing slips, code violations etc.


      Show commands below and snippet of PRI config.



      TA908e#sh int pri 3

      pri 3 is UP

        Switch protocol:  National ISDN 2

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

        b-channel-restarts:  enabled

        Calling-party override:  disabled

        Calling-party presentation:  allowed

        Calling-party screening:  auto

        Calling-party number:  (no number configured)

        Digits transferred all

        Name-delivery:  via Setup msg / Facility IE

        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: linear descending

        TBCT:  enabled

        area code: 

        Transmission of redirecting numbers is enabled

        Redirecting numbers: sent as received

        Connected interface: t1 0/3 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

        Last clearing of "show interface" counters: never

          36235 packets input, 173906 bytes, 0 no buffer

          0 runts, 0 giants, 0 throttles

          1 input errors, 0 CRC, 0 frame

          1 abort, 0 discards, 0 overruns

          36215 packets output, 173885 bytes, 0 underruns



      TA908e#sh int t1 0/3

      t1 0/3 is UP

        Receiver has no alarms

        T1 coding is B8ZS, framing is ESF

        Clock source is system, FDL type is disabled

        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 3d 19:18:18

          loss of frame  : 1, last occurred 01:56:15

          loss of signal : 1, last occurred 01:56:15

          AIS alarm      : 0

          Remote alarm   : 0



        DS0 Status: 123456789012345678901234


        Status Legend: '-' = DS0 is not allocated

                       'X' = DS0 is allocated (nailed)



        Signaling Bit Status: 123456789012345678901234

                         RxA: 000000000000000000000000

                         RxB: 000000000000000000000000



                         TxA: 000000000000000000000000

                         TxB: 000000000000000000000000




        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




      ! ADTRAN, Inc. OS version R11.10.1.E

      ! Boot ROM version R10.9.3.B2

      ! Platform: Total Access 908e (3rd Gen), part number 4243908F2

      ! Serial number CFG1444961


      interface t1 0/3

        fdl none

        tdm-group 1 timeslots 1-24 speed 64

        no shutdown


      interface t1 0/4




      interface pri 3

        role network b-channel-restarts enable

        isdn name-delivery setup

        connect t1 0/3 tdm-group 1

        isdn supplementary-service tbct

        no shutdown



      isdn-group 1

        min-channels 1

        max-channels 12

        connect pri 3


      voice codec-list USERS


        codec g711ulaw



      voice trunk T02 type isdn

        description "PRI to PBX"

        resource-selection linear descending

        connect isdn-group 1

        no early-cut-through


        rtp delay-mode adaptive

        codec-list USERS



      voice grouped-trunk "PRI TRUNK GROUP"

        trunk T02

        accept $ cost 0


        • Re: TA908e Random B-channel Restarts
          jay Employee

          George, it appears you have b-channel restarts enabled:


          interface pri 3

            role network b-channel-restarts enable


          If you want them disabled, just change that command to "role network".





          • Re: TA908e Random B-channel Restarts
            mccvoip New Member

            I understand that the command is in place actually making it restart b-channels I was looking more for why b-channel-restarts would be needed at all every 60 minutes. I received the answer from support.


            B channel restarts is an ISDN spec. If it is enabled, we will send a restart message every hour for inactive B channels. It requires that the device receiving the restart , send an ACK to the restart. If it does not the ISDN spec calls for that B channel to be locked out.


            The advantage of restart messages is that it helps prevent B channel lock out conditions. Either side of the PRI can send them.


            The disadvantages of restarts are, that in a high call volume environment , you have a short period where calls can't be made or received. Also it is possible that a PBX does not support

            restart messaging because, either 1 it is not configured or 2 the firmware is out of date on the PBX.