A challenge that must be faced when considering backbone network enhancement, is that there is more than one motivation driving the demand and investment in main transmission facilities; these are basically network reliability/redundancy and capacity. Policy makers and regulators cannot act in isolation from these or imagine that even an expensive new investment in a third party network operator would be fully utilised or beneficial unless the present and future needs and economic motivations of the existing operators are fully understood and taken into account.
Links that are closer to the centre of a network carry more traffic. Failure of these links is therefore more serious than failures further out from the centre. The links nearest the centre are therefore typically made redundant, so that if one link fails then an alternative route between its end points can be used instead.
The following distinctions between backbone and access networks should be made:
- The core backbone network (often called the core or backbone network) comprises a mesh of links with at least two routes between any two major nodes. Many incumbent operators’ networks incorporate alternative routes, sometimes showing a Figure 8 structure (i.e., two separate national ring routes) linking the key switching and traffic points. In a mobile network also, the redundant links or rings are those between the key mobile switching centres (MSCs) or linking the network’s base station controllers (BSCs) to the main MSC. The investment decisions related to these links are very commercial in nature and rarely, if ever, are influenced by universal access (UA) policy or funding; and
- The access backbone networks (often called the aggregation of distribution network), which include the connections to small communities and retail customers, typically comprise a large number of branch links. Typically, access backbone networks connect to a single base station or small fixed network switch (e.g., in a small town or rural area). Many mobile base stations may be connected to a BSC by a non-redundant link. Since the economics of these links may be less certain or marginal, investment decision may be influenced by the availability of UA funding.
The distinction between core and access backbone networks is illustrated in principle in the figure below, although there may be many exceptions and nuances to this simple representation in individual network cases.
Figure: Schematic physical network connectivity
Incumbent fixed network operators often have fibre in their backbones, or at least between main cities and switching centres. Amongst mobile operators, a stronger business case can be made for choosing microwave links rather than for optical fibre links, especially where towers are already installed and can be utilised for base stations. For this reason, some policy makers consider the backbones of mobile operators to be less relevant to broadband traffic. However, chances are that bandwidths are sufficient for current demand and can be economically enhanced when justified by sufficient external demand. Also, many mobile operators are bound to upgrade their backbone networks for expected 2G and 3G service large-scale up-take by consumers.
Typically, investment decisions relating to the core backbone network may well relate to introducing redundancy rather than increasing capacity. However, a motivation based on universal access and service (UAS) requirements might focus on increased bandwidth capacity, so that other operators and Internet service providers can be more readily accommodated. Large increases in capacity may be commercially justified only after data services are very well established.
In summary, because the motivations for UAS and broadband build-out do not usually coincide with operators’ motivations, the availability of subsidy may not necessarily influence the timing of core backbone network investments. However, access network extensions, which are more often easily identified with UAS targets, will always have some limited backbone extension associated with them, and the availability of subsidy for them is more influential on the operators’ decisions.
It is normal for UAS tenders to include open access requirements on access backbone links so that service providers, other than the initial subsidy recipient, have use of the facilities. This has been for example the case in Nigeria, Uganda and Mongolia. Such forms of mobile infrastructure sharing are increasingly becoming an accepted norm, as noted in Section 3.4.6.