+1-323-909-4740 [email protected]




Telstra Exit Date

The final exit date for ISDN in all areas nationwide is 31 May 2022.


  • U
  • S/T
  • S
  • T
  • R
  • NT1
  • NT2
  • TA
  • TE

B/D Channels

  • 2 x 64kbps (B) channels
  • 1 x 16kbps (D) channel


  • Q.921 describes data-link LAPD
  • Q.931 describes network layer

TE startup sequence

  • Line inactive
  • TE becomes active and signals a  7E  HDLC flag   (7E = “01111110”)
  • Network switch send frame with the A-bit set to 0  (A=0   = no activated)
  • TE then synchronises on three successive pairs of line code voilations
  • TE then starts sending physical frames
  • NT synchronises using line code violations
  • NT starts sending frames with A-bit set to 1   (A=1   = activated)


OSI Layers

Layer 1


NIST Testing Procedures

User Mode (TE) States

L1 StateL1 State NameL1 State Description
F1InactiveIn this inactive (powered-off) state, the terminal equipment (TE)1 is not transmitting and can not detect the presence of any input signals.
F2SensingThis state is entered after the TE has been powered on but has not determined the type of signal (if any) that the TE is receiving. When in this state, a TE may go into a low power consumption mode.
F3DeactivatedThis is the deactivated state of the physical protocol. Neither the network termination (NT)2 nor the TE is transmitting. When in this state, a TE may go to a low power consumption mode.
F4Awaiting SignalWhen the TE wishes to initiate activation, it sends an Activation signal to the NT and awaits a response.
F5Identifying InputAt first receipt of any signal from the NT, the TE stops sending Activation signals and awaits the activation signal or synchronized frame from the NT.
F6SynchronizedWhen the TE has received an activation signal from the NT, it responds with a synchronized frame and is awaiting a synchronized frame from the NT.
F7ActivatedThis is the normal active state, with the protocol activated in both directions. Both the NT and the TE are transmitting normal frames. State F7 is the only state where B-channel and D-channel contain operational data.
F8Lost FramingThis is the condition when the TE has lost frame synchronization and is awaiting re-synchronization.

Network Mode (NT1) States

L1 StateL1 State NameL1 State Description
G2Pending Activation
G3Activated and Working
G4Deactivated Request Received


Physical Interface

BRI S/T Interface (RJ-45) Pinout

RJ-45 PinTENTPolarity
3Transmit +Receive ++
4Receive +Transmit ++
5Receive –Transmit –
6Transmit –Receive –

BRI U Interface (RJ-45) Pinouts

WireNT (RJ-45)LT(RJ-45)

 Terminal Endpoint Identifier (TEI) 


Layer 2 (Q.921)


Layer 3 (Q.931)

Q.931 ISDN Cause Codes

0x11Unallocated or unassigned number
0x22No route to specified transit network (Transit Network Identity)
0x33No route to destination
0x44Send special information tone
0x55Misdialled trunk prefix
0x66Channel unacceptable
0x77Call awarded and being delivered in an established channel
0x88Prefix 0 dialed but not allowed
0x99Prefix 1 dialed but not allowed
0xA10Prefix 1 not dialed but required
0xB11More digits received than allowed, call is proceeding
0x1016Normal call clearing
0x1117User busy
0x1218No user responding
0x1319T.301 expired: – User Alerted, No answer from user
0x1521Call rejected
0x1622Number changed to number in diagnostic field.
0x1723Reverse charging rejected
0x1824Call suspended
0x1925Call resumed
0x1A26Non-selected user clearing
0x1B27Destination out of order
0x1C28Invalid number format or incomplete address
0x1D29EKTS facility rejected by network
0x1E30Response to STATUS ENQUIRY
0x1F31Normal, unspecified
0x2133Circuit out of order
0x2234No circuit/channel available
0x2335Destination unattainable
0x2436Out of order
0x2537Degraded service
0x2638Network out of order
0x2739Transit delay range cannot be achieved
0x2840Throughput range cannot be achieved
0x2941Temporary failure
0x2A42Switching equipment congestion
0x2B43Access information discarded
0x2C44Requested circuit channel not available
0x2E46Precedence call blocked
0x2F47Resource unavailable, unspecified
0x3149Quality of service unavailable
0x3250Requested facility not subscribed
0x3351Reverse charging not allowed
0x3452Outgoing calls barred
0x3553Outgoing calls barred within CUG
0x3654Incoming calls barred
0x3755Incoming calls barred within CUG
0x3856Call waiting not subscribed
0x3957Bearer capability not authorized
0x3A58Bearer capability not presently available
0x3F63Service or option not available, unspecified
0x4165Bearer service not implemented
0x4266Channel type not implemented
0x4367Transit network selection not implemented
0x4468Message not implemented
0x4569Requested facility not implemented
0x4670Only restricted digital information bearer capability is available
0x4F79Service or option not implemented, unspecified
0x5181Invalid call reference value
0x5282Identified channel does not exist
0x5383A suspended call exists, but this call identity does not
0x5484Call identity in use
0x5585No call suspended
0x5686Call having the requested call identity has been cleared
0x5787Called user not member of CUG
0x5888Incompatible destination
0x5989Non-existent abbreviated address entry
0x5A90Destination address missing, and direct call not subscribed
0x5B91Invalid transit network selection (national use)
0x5C92Invalid facility parameter 93 Mandatory information element is missing
0x5D93Message type non-existent or not implemented
0x5F95Invalid message, unspecified
0x6096Mandatory information element is missing
0x6197Message type non-existent or not implemented
0x6298Message not compatible with call state or message type non-existent or not implemented
0x6399Information element nonexistent or not implemented
0x64100Invalid information element contents
0x65101Message not compatible with call state
0x66102Recovery on timer expiry
0x67103Parameter non-existent or not implemented – passed on
0x6F111Protocol error, unspecified
0x7F127Internetworking, unspecified
0x80+128 orhigherProprietary diagnostic code (not necessarily bad). Typically used to pass proprietary control or maintenance messages between multiplexers.