Ticketing
The Overground Network pilot was a branding exercise and did not include any new ticketing policies. When London Overground was launched, it was fully integrated into TfL's ticketing network from its launch, including full acceptance of the Oyster card electronic smartcard system. This ticketing policy was not extended to the former Overground Network, and for a number of years Oyster card pay-as-you-go tickets were not valid at stations bearing the "ON" brand, despite the similarity of the two network brand names. In January 2010, Oyster card was fully rolled out across National Rail services in London, and Oyster pay-as-you-go is now valid across the whole rail network, including the former "ON" system.
Read more about this topic: Overground Network