fact, the mechanics of the postal service are quite relevant when analysing network economics and the end-to-end economics of delivering voice and data over wireless, fibre, cable and copper networks. Part of the efficiency gain in telecommunications has traditionally been achieved by mul- tiplexing users over either single or multiple delivery channels to achieve what is commonly known as 'trunking gain'. Telephone lines for example started using frequency multiplexing experimentally in the 1920s and time division multiplexing became increasingly prevalent from the 1960s onwards. Trunked radio systems and first-generation cellular radio in the 1980s and 1990s were frequency multiplexed, second-generation cellular radio systems were frequency and time multiplexed, third-generation cellular systems can also be spatially multiplexed over the radio part of the end-to-end channel. Optical systems today can also be frequency and/or time multiplexed. Simplistically, trunking gain is achieved because most users only need resources for a rela- tively short time and therefore have no need for a dedicated channel. However, conversational voice is sensitive to delay and delay variability. Historically these end-to-end channels have therefore been deterministic with known and closely controlled end-to-end delay and delay variability characteristics. The transition from voice-dominant communication to a mix of voice and data, some of which is not time sensitive has allowed for additional multiplexing in which traffic is segregated into typically four traffic classes, conversational (voice and video calling), streaming, interactive and best effort. In theory at least, this allows for a significant increase in radio and network bandwidth utilisation that should translate into lower cost per bit delivered. This is the basis on which IP network efficiency gain assumptions are traditionally based. However, reference to our post-office analogy suggests the cost/efficiency equation is more complex. A letter or packet posted first cl