re is a large tower with a good view of the sky and space to support a straight- forward installation. Unless the tower is owned by the MSP, however, the cost of renting a spot on the tower to accommodate the antenna can be significant. This approach is less popular with current 5G rollouts, because 5G needs a lot more radios to be deployed (referred to as densification). These new radios are increasingly sited indoors or in urban canyons where a sky view is impossible or severely limited (see the earlier section "Small Cells Versus Macro Cells"). In these urban environments, besides not having a good sky view, obtaining permission for cable access to a rooftop antenna can be a problem (and an expensive one). So, a solution is needed for those environments. One solution is to put one or two GNSS receivers somewhere in the facility and run PTP and SyncE locally around the site (such as around the building, sta- dium, or campus). There are also GNSS antenna-like devices that combine the antenna with a GNSS receiver and a PTP T-GM. These are located at the roof site and are connected to copper Ethernet cables SO that they can use Power over Ethernet as a power source. This device allows the timing signal to be carried as PTP and SyncE over Ethernet twisted pair to the radio equipment. This can be much easier to deploy than having to carry GNSS RF signals over unwieldy and expensive coaxial cable from the antenna to the receiver inside the building. Resilience in the case of local (or system) GNSS outage: Multi-constellation devices can help survive a systemic issue with one of the systems but may not help with a local outage, such as jamming (discussed in the following bullet point). Note also that there is a (small) possibility that space weather events could disrupt all space-based signals. One answer to these vulnerabilities is to deploy the GNSS receiver with an atomic clock hold- over-which is very expensive. The other approach is to have multiple backup PRTC and T- GM sites located outside the area potentially