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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
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.
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.
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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.