e, the more difficult it will be to get accurate clock out to the cell site. There is substantial variation in the performance characteristics between the G.8275.1 and G.8275.2 models of PTP transport. This results from the major difference in the two profiles: one being at layer 2 and hop-by-hop, and the other being at layer 3 (IP) that can transit network nodes that will not process PTP. Table 11-1 describes the main trade-offs between the two approaches. Table 11-1 Fully Aware Network Versus Partially Aware Network Feature Fully Aware Network Partially Aware Network Network G.8271.1 G.8271.2 model Telecom G.8275.1 PTPoE G.8275.2 PTPoIP profile IP routing Not applicable Problems with rings, asymmetry Transit Not allowed Problems with PDV, asymmetry traffic Perform- Variable, nondeterministic, and dependent on traffic load and type Configur- ation On the physical port Attached to an L3 device model PTP over Solutions available for T-BC connected to another T-BC; No issue bundles otherwise a problem Asym- Reduced Can have high dynamic asymmetry metry Timestamping on wire and the lack Uncontrolled amounts of PDV/jitter introduced at unaware PDV/jitter of transit nodes limits its buildup nodes, which accumulates the further along the chain These differences will be explained in the following sections of this chapter. 11.3.1 GNSS Everywhere At the first glance, the simplest solution is to place a GNSS receiver at every location that needs fre- quency, phase, and time. This is a good solution and has been deployed in some parts of the world starting from several decades ago (such as North America CDMA networks that needed phase alignment). There are many vendors supplying products for this purpose. There are even pluggable SFP devices that can provide PTP and SyncE to an Ethernet port for a local source of PTP and SyncE on the router. However, this solution has some considerations that need to be addressed: GNSS solution only suitable for some sites: GNSS is a good solution for sites, typically macro sites, where the