| Prefix | Block | Addresses | First registered | Organization |
|---|---|---|---|---|
| 20:5F:3D | MA-L | 16.8 million | 11 May 2019 | Adtran Inc |
| 28:D0:CB | MA-L | 16.8 million | 25 Apr 2018 | Adtran Inc |
| AC:51:EE | MA-L | 16.8 million | 2 Feb 2012 | Adtran Inc |
Former Cambridge Communication Systems Ltd MAC address blocks
The IEEE registry once carried 3 blocks registered to Cambridge Communication Systems Ltd. All 3 blocks are now registered to Adtran Inc. Adtran Inc took over all of them.
Complete as of the current IEEE registry deploy. Dates are when each registration was first observed in public data, not legal assignment dates.