TECHNICAL
Figure 3: The Bitco Model
perspective Strowger and Crossbar are good examples of circuit switching and from the electronic perspective TXE4. Rather surprisingly, the best definition of circuit switching found by this author is Davies 9 , et al within the UK National Physics Laboratory i.e. “A switching network must share its capacity among all its users who, in general do not want to use and pay for transmission circuit at all times. Therefore, it establishes circuits when they are requested and disconnects upon demand. This circuit, held for a period, is known as a call.” The development of circuit switching in the UK is summarised at numerous sources and this author’s instincts are that circuit switching is “loosely” associated with those Service Providers (SPs) who are sometimes described as providing a nationwide telephone service such as the PSTN. More loosely the term “Telco” is often used. 10 Circuit switching has been around for a long time, as has the standardisation efforts of the ITU-T - CCITT. The Bitco Model 11 Using Isenberg’s model as a starting point, a bit delivery network could be termed/modelled as a network whose sole function is to deliver bits between end points and see Figure 3 above. 12 The model suggests that the Bitco has one function i.e. delivering bits between nodes on its network and onwards to another network. I will argue that the Bitco concept was the model for the original ARPANET, 13 with the Bitco term originally introduced within Isenberg’s paper. Note that there is no intelligence in the Bitco model and hence can be compared against the Telco model in that additional functionality (if any) is introduced at end points only. The Bitco model is “underpinned” by the TCP/IP protocol
Figure 4: The Bitco Model expanded
Figure 5: An Internet Model
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SEPTEMBER 2026 Volume 48 No.3
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