In the PTP standard all nodes are able to act as both master and slaves. The Best Master Clock algorithm in a slave can select from a number of available masters in a network. If it finds no other it enters a master mode.
In the following application the M50-34 is locked into a master mode at startup. Its Pulse-per-Second (PPS) and Time-of-Day (ToD) inputs are connected to a reliable time source, in this case a GPS. As long as the M50 module has valid signals on these inputs it can act as a stratum 1 clock in the network (clock based on the UTC reference).
In the event of a signal loss the M50 enters into holdover mode for a certain period of time. The quality parameters are configurable. If there is an other active master in the network the unit goes into a passive mode, if not, the unit will be in a free-running state until it receives valid PPS/ToD inputs again.
The network configuration in a PTP system calls for setting the number synchronization per second the master is sending (sync rate) and the number of delay requests a slave is permitted to ask for per second as inputs to its delay measurements. The capacity of a grandmaster is often measured in the number of slaves it can handle. The M50-34 is designed to handle up to approximately 200 slaves simultaneously.
Qulsar claims the space of Edge GrandMasters which is the opposite of a centralized timeserver strategy. Many low-cost Grandmaster units can be placed close to the end user equipment – the Edge of the network. The times service becomes more redundant and overall performance potentially increases due to the lower number of hops between the grandmasters and the subscriber units.
Moving to level C of integration (see Integration Levels) a complete grandmaster unit can be built based on the M50 (figure 1). It essentially consists of five elements: a GPS module with an antenna, an M50, an external oscillator (pref. OCXO), the RJ 45 connector with magnetic and a power supply. Such a Edge GrandMaster has a bill of material (BoM) of less than 80 USD. Feeding power over Ethernet (PoE) is possible due to the low power consumption and doesn't change the BoM too much. Using PoE technology the unit can be fit together with an antenna in a very small box and be placed wherever an Ethernet cable can be routed. No other connections required. The self-configuring PTP network topology solves all configuration problems. The slave units just get another master “in the neighborhood”. The Edge GrandMaster constitutes an easy and straight forward way to deploy the PTP into an existing network without the need for installing new PTP enabled switches in the network.
Figure 1: An Edge GrandMaster Application