7.6 Resilience in the BTS Access
In this section the access part of the backhaul is addressed – protocols and functionalities that allow building a resilient access tier.
7.6.1 BTS and BTS Site
As a network component, BTS itself is a single point of failure. Failure of a BTS, however, does not impact a large geographical area, and the failure of a single BTS is often at least partially compensated by radio coverage of the neighbouring BTSs – either by the same radio technology cells, or by another one (2G, 3G or LTE).
BTS sites are often shared between multiple BTSs. In these cases, transmission links may be wished to be shared as well. This is shown in Figure 7.20.
Sharing the physical link requires a cell site gateway for combining the traffic. Alternatively, the gateway function can be integrated into the BTS. For availability, the BTS integrated GW should be as independent as possible from the radio-related BTS functions.
When the backhaul service is common for multiple networks, such as 2G and LTE, the two systems become dependent on the same network components. The physical link, and the cell site GW, are shared. Synchronization is typically also obtained via the common gateway – via Synchronous Ethernet, or via packet based timing.
From availability point-of-view, the two radio networks should be independent, so that failure ...