TECHNICAL
switching process then a typical circuit switched network could be represented by Figure 2 below.
The use of a network model allows engineering discussions about performance, etc 7 . More importantly, perhaps in that modelling has been introduced to highlight that the Internet is nothing more than a “network of networks.” A simple fact, I would suggest, but very rarely understood. The Telco and Bitco Models There are two models in switching/ routing, namely the Telco model and the Bitco models. The Telco model is “loosely” associated with circuit switching and the Bitco model could be the “underpin” of today’s Internet. A Telco Model (Circuit Switching or “Beads on a String”) As mentioned within the introduction, when I started my career with Post Office Telecommunications, the telephone exchange and circuit switching was the norm. Over time, and looking back, the digitisation of both the signal and
Figure 2: An example of a circuit switched telephone network
One definition of circuit switching could be “the creation of a physical path (in real time) between two end points enabling, primarily, speech communications.” This path, as an example, could have been created by an operator i.e. manual switching but for the purposes of this article “circuit switching” will focus on automatic switching. From the analogue
The article examines several themes particularly with my degree of confusion surrounding the term “Telco” and whether we are closer to the Isenberg model, or further away? Modelling To aid any ongoing discussion, I have introduced the concept of “models 5 ” within this paper and would suggest that the circuit switched network model is now obsolescent and hence my focus is on packet networks only. A signal delivery model could be illustrated as in Figure 1 opposite, which has several components and note that the underlying transport network could be leased analogue circuits, a wavelength within a DWDM network, or a radio link, etc. This model in Figure 1 may represent either a packet or circuit switching network (or a combination of both 6 ) and illustrates a logical (and physical) separation between the routing/switching and transport networks. Note that this representation includes a mechanism for managing the “elements” of both the switch/routing network and transport network.
Figure 1: Switching Network Model, etc
Volume 48 No.23 SEPTEMBER 2026
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