Traditional telecommunications (telecoms) networks were developed to carry a single type of service, such as voice calls. In contrast, Next Generation Networks (NGNs) carry all types of services, including voice, video and e-mail, on a common platform. BT's planned roll-out of its £10bn '21st Century Network' (21CN) by 2012 will make the UK the first country to replace its incumbent telephone network with an NGN. NGNs offer significant cost savings to operators and new services to consumers, but there are also challenges in maintaining the quality, reliability and security of communications. Their introduction has been described as 'the most significant change to telecoms networks since competition was introduced two decades ago'.