T1 Line Code

Parameter group

Trunk Interface

Access level


Possible values





Specifies which T1 line coding scheme Blueworx Voice Response uses to ensure a ones density that is enough for proper timing recovery of the T1 digital signal.

When alternate mark inversion (AMI) is selected, the Blueworx Voice Response line coding scheme is AMI with zero code suppression (ZCS). With AMI, binary one bits are represented by alternate positive and negative pulses (marks) and binary zero bits are represented by spaces. AMI with ZCS changes the second least significant bit (bit 7) from a zero bit (space) to a one bit (pulse) whenever 8 successive zeros occur. The bit is not restored to a 0 at the receiving end.

Note: Some equipment manufacturers refer to AMI with ZCS as bit 7 stuffing. (AMI without ZCS is often referred to as transparent.)

When Bipolar Eight Zero Substitution (B8ZS) is selected, the Blueworx Voice Response line coding scheme is AMI with B8ZS. B8ZS uses bipolar violations to ensure a good enough ones density. Each block of eight successive zeros is replaced by the B8ZS code 000VB0VB, where “B” represents an inserted pulse that conforms to the AMI rule and “V” represents an AMI violation (also known as a bipolar violation (BPV)). At the receiving end, the B8ZS code is replaced by 8 zeros.

B8ZS is required to provide clear channel capability, which allows data rates to 64 Kbits per second. Clear channel operation is possible only with common channel signaling such as ISDN.

Note: Both the switch and Blueworx Voice Response must be using the same T1 line coding scheme or errors occur.

See Setting parameters for hangup tone detection for guidance on which value to select.