The FAA were also considering similar problems but were assuming that a new pair of frequencies would be required. Ullyatt showed that the existing 1030 MHz and 1090 MHz frequencies could be retained and the existing ground interrogators and airbornes transponders, with suitable modifications, could be used. The result was a Memorandum of Understanding between the US and the UK to develop a common system. In the US the programme was called DABS (Discrete Address Beacon System), and in the UK Adsel (Address selective).