Review Step 2c: Characteristics & Trade-offs
A range of different technologies that are commonly used in access networks are also used for longer distances in middle-mile/backhaul links. While the majority of data traffic for terrestrial links in backhaul networks transits through microwave links, other technologies such as fibre, satellite, cellular links and even copper wire continue to be used today. Copper continues to be phased out, however, and other wireless and emerging technologies (such as WiMax and HAPS) are also currently used in limited situations. The technology with the largest share of terrestrial backhaul traffic, microwave technology utilizes ultra-high or higher frequencies in high-capacity, high-power wireless radio network links between towers that connect last-mile access networks to the national backbone network. These links, which usually take the form of point-to-point relays that require topology and/or towers to provide direct line of sight between radios, can cost less per distance than optical fibre deployment, especially in geographies and terrain where topography or other physical challenges (such as bodies of water) hamstring fibre deployment. High-power microwave links can cover Between tens and several hundred kilometers in a single hop, and multiple hops are utilized in backhaul transmissions. Note however, that LEO and MEO satellite systems (as well as HAPS) are being deployed that may offer compelling alternatives to point-to-point microwave backhaul, owing to their ability to cover all geographies cost-effectively and to the ease of deployment. And satellite technologies have recently been used to expand and upgrade terrestrial mobile networks from 2G to 3G and 4G, often in combination with terrestrial fixed links.
Figure 28. Backhaul for mobile voice and data by method, global and sub-Saharan Africa (2017)