GE Reason RT430 Technical Manual page 90

GPS Grandmaster Clock
̃
̃
Combining the above two equations, we find that:
̃
The clock now knows the offset õ during this transaction and can correct itself by this amount to bring it into
agreement with their other master.
Network protocols
IEEE1588 standard defines the network layers where the PTP protocol will be applied. It is possible to use
PTP protocol in a network layer with IEEE 802.3 Ethernet (layer 2) or UDP/IPv4 (layer 3) connection.
The layer 3 (UDP/IPv4) is used in more environments facilitating the compatibility of sending and receiving
messages between the devices connected to the network.
To use the layer 2 it is necessary that the network has E connections between all master and slave
THERNET
clocks, which are not common when the network is divided into subnets and there is not an interconnection
between them. The advantage of using layer 2 is that the traffic through the network is smaller because the
sent packets do not require including IP and UDP address.
Once the PTP protocol has low traffic when compared to other protocols, the network traffic is not limiting
factor of the use of layer 3.
RT430 uses PTP protocol in its UDP/IPv4 (layer 3) network layer.
Clock operation mode
PTP protocol requires the master clock sending synchronism messages periodically to all slave clocks
connected to the network. Furthermore, master clocks must register and communicate to the slave clocks
the exact timestamp in which the data packets were sent. This information can be sent in a single packet or
two packets separately.
In One-step operation mode, the synchronism information is sent in in the same data packet as the
timestamp of the message. In Two-step operation mode, the synchronism information is sent in a data
packet and the timestamp information of the message is sent in another one. The accuracy of both modes is
the same.
RT430 allows sending messages in both One-step and Two-step modes.
90 RT430-TM-EN-5