B8ZS
B8ZS (Binary 8-Zero Substitution) is a line code used in telecommunications to ensure long streams of zeros do not cause synchronization issues. It replaces a sequence of eight zeros with a specific pattern to maintain a balance of zeroes and ones for transmission. This technique helps prevent loss of synchronization and data errors in digital communication systems.
There are a number of different encoding methods used on T1 lines. Alternate Mark Inversion (AMI), Bipolar With 8-Bit Substitution (B8ZS), and High Density Bipolar Three Code (HDB3).
AMI and B8ZS
A device optioned for B8ZS (Bipolar 8-Zero Substitution) inserts a bipolar violation into any frame containing 8 zeroes in a specific sequence during transmission of that frame. The device at the receiving end simply looks for that specific sequence and changes the bit sequence in that frame back to 8 zeros. For a more complete understanding, it's important to also understand Alternate Mark Inversion (AMI) Line Coding and what a Bipolar Violation means. AMI Line Coding means that each digital '1' bit (also referred to as a 'Mark') uses alternating positive and negative voltage pulses to represent those bits, even if those '1' bits are separated by '0' bits. A Bipolar Violation is when two consecutive '1' bits voilate that AMI rule. Since a DS1 signal depends on a certain level of 1's density to maintain receive synchronization, long strings of '0's can cause timing slips. To prevent this, when a frame containing 8 zero's is transmitted, B8ZS changes bits 4, 5, 7 and 8 into 1's, but bits 5 and 7 will either both be positive or both negative, causing the specific bipolar violation that a receiving device optioned for B8ZS is looking for, and it will change those four bits back to 0's. One other point - B8ZS only comes into play when an 8-bit frame containing all 0's occurs. So, B8ZS isn't really different from AMI, it's more like an enhancement to AMI, with a special condition that only occurs when an all-0's frame is encountered.
No, E1's use HDB3 instead. HDB3 stands for High Density Bipolar of order 3. In principle, it works in a similar way to B8ZS coding, but substitutes specific bipolar violation patterns to replace any instance of 4 consecutive zero bits (whereas B8ZS uses a specific BPV pattern in place of a frame containing 8 zeros).
A device optioned for B8ZS (Bipolar 8-Zero Substitution) inserts a bipolar violation into any frame containing 8 zeroes in a specific sequence during transmission of that frame. The device at the receiving end simply looks for that specific sequence and changes the bit sequence in that frame back to 8 zeros. For a more complete understanding, it's important to also understand Alternate Mark Inversion (AMI) Line Coding and what a Bipolar Violation means. AMI Line Coding means that each digital '1' bit (also referred to as a 'Mark') uses alternating positive and negative voltage pulses to represent those bits, even if those '1' bits are separated by '0' bits. A Bipolar Violation is when two consecutive '1' bits voilate that AMI rule. Since a DS1 signal depends on a certain level of 1's density to maintain receive synchronization, long strings of '0's can cause timing slips. To prevent this, when a frame containing 8 zero's is transmitted, B8ZS changes bits 4, 5, 7 and 8 into 1's, but bits 5 and 7 will either both be positive or both negative, causing the specific bipolar violation that a receiving device optioned for B8ZS is looking for, and it will change those four bits back to 0's. One other point - B8ZS only comes into play when an 8-bit frame containing all 0's occurs. So, B8ZS isn't really different from AMI, it's more like an enhancement to AMI, with a special condition that only occurs when an all-0's frame is encountered.
+-000+-0-+00+00
HDB3HDB3 (High Density Bipolar of order 3 code) is a telecommunications line code mainly used in Japan, Europe and Australia (for example, in E-1 lines) and is based on AMI. It is also very similar to the B8ZS encoding used in T-1 lines.For the source and more detailed information concerning this subject, click on the related links section (Answers.com) indicated below.
They are AMI (Alternate Mark Inversion) and B8ZS (Bi-polar with 8-Zero Substitution)
uni-polar, bi-polar, rz, nrz, ami, b8zs, b3zs, 2b/1q, manchester, differential manchester, 4b/5b
the line coding can be either AMI or B8ZS according to how the equipment is set up along the path and at either end.