an canyons, indoors, or under cover. Therefore, either there is no option to deploy GNSS or it is available only at considerable cost (to buy ac- cess to a good sky view, rent space for the GNSS antennas, and gain permission to run the an- tenna cables back to the indoor radios). Deployed mainly in areas of high population density and sheltered locations with poor coverage (so, not in rural areas). Small cells tend to have lower output, have shorter range, and be de- ployed in very large numbers in high-traffic areas. They are designed more for coverage inside buildings or increased bandwidth than to support high mobility. They could also use higher fre- quency bands and even mm Wave. Frequently newer deployments in shared locations and in areas that cannot be well secured by the operator. It could be easy for unauthorized personnel to gain access to the equipment, or at least access the cables connecting it to the back-haul network. Good connection options to the back-haul network. The site would normally be well served by fiber or Carrier Ethernet (CE) solutions, allowing for simple deployment of a timing over transport solution. Poor oscillators with almost no satisfactory holdover performance. Their timing performance is normally poor when deprived of a reference signal. For example, they might have no support for SyncE at all, and once they lose their PTP timing signal, they just switch off their transmit- ters rather than attempt holdover. Coordinate their radio signals with macro cells that could be providing overlapping coverage. Imagine a large macro cell situated beside a major highway rest stop, but the restaurant, re- strooms, and surrounding rest areas are covered by small cells. Lacking substantial environmental control and supporting infrastructure (being indoors). Altern- atively, they can be deployed in outdoor cabinets or in limited spaces (such as street poles). This means that they can suffer from conditions such as extreme temperature variations. Figure 11-2 shows the difference between a mac