egradation of the timing signal. For this reason, some vendors refer to these distributed PRTC+T-GM as Edge Grandmas- ters because they are located toward the (outer) edge of the back-haul network. Figure 11-8 shows a typical deployment topology for the PTS use case in combination with a T-GM deployed toward the network edge. The key to success is to ensure that there are very few hops between the "Edge GM" and the slave clock. If there are any significant forms of asymmetry in the network, then this rapidly becomes a problem. Aggregation / core network Access network High PDV network T-TSC-P PTP-unaware G.8275.2 No sync slave clock network element Edge GM carried Central mobile core PTP-aware PTP-aware network network T-TSC G.8275.1 G.8275.1 slave clock Figure 11-8 Grandmaster Deployment at Network Edge For a successful deployment in unaware networks, the design must address the following points: Reduce PDV to the absolute minimum. Exactly how much PDV can be tolerated is very hard to quantify. Reduce asymmetry to the absolute minimum. How much is too much depends on the overall timing budget, but every microsecond of asymmetry introduces 0.5 us of phase offset. Reducing PDV for PTP messages passing through an unaware node is not easy. One obvious an- swer to limit the effects of PDV is to configure the transit node as a PTP-aware clock (TC or BC), if possible. Note that PDV accumulates for every step along the unaware timing chain, and the most effective way to control it is to use a T-BC. That is because it terminates the old PTP stream from the master and regenerates a new stream toward the next slave, effectively resetting the PDV to zero. Consider the following points about PDV in an unaware transit node: Any queuing within the node contributes to PDV. This can be partially avoided by designing a set of QoS policies that ensure the PTP traffic is treated with the highest priority. The type of traffic and mix of frame lengths can contribute to PDV. In a converged network, the small PTP messages can be multip