High Density Bipolar Three A line interface standard for E1 which is similar to B8ZS, which eliminates data streams with 8 or more consecutive zeros. Allows for 64Kbps clear channel capacity and still assures a minimum ones density required by E1 lines.
HDB3 (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 B8 ZS encoding used in T-1 lines.