In August 2009 the BBC wrote to Ofcom after third-party content owners asked the BBC to undertake measures to ensure that all Freeview HD boxes would include copy protection systems as required by the Digital TV Group's D-Book, which sets technical standards for digital terrestrial television in the UK. The BBC proposed to ensure compliance with copy-protection standards on the upgraded Freeview HD multiplex by compressing the service information (SI) data, which receivers need to understand the TV services in the data stream. To encourage boxes to adopt copy protection, the BBC made its own look-up tables and decompression algorithm, necessary for decoding the EPG data on high-definition channels, available without charge only to manufacturers who implement the copy-protection technology. This technology would control the way HD films and TV shows are copied onto, for example Blu-ray discs, and shared with others over the internet. No restrictions will be placed on standard-definition services. In a formal written response, Ofcom principal advisor Greg Bensberg said that wording of the licence would probably need to be changed to reflect the fact that this new arrangement is permitted. The BBC had suggested that as an alternative to the SI compression scheme, the Freeview HD multiplex may have to adopt encryption. Bensberg said that it would appear "inappropriate to encrypt public service broadcast content on DTT".