Model 5601MSC
Model 5601MSC Master SPG/Master Clock System
MASTER CLOCK Revision 2.2 Page - 155
4.5.14.12. Accuracy
The accuracy of PTP is determined by several factors. They are the base accuracy of the MASTER, the
network, and the SLAVE and its associated hardware.
Largely, the dominating factor is the network. Accuracy can range from about 100 ns for a single hop
using a transparent switch, up to milliseconds on ordinary switches. It is up to the user to ensure the
network switches are adequate to the requirements.
Fortunately, modern facilities do not require the same levels of timing accuracy that old analogue video
networks required. It is up to the end user to determine their accuracy requirements and associated
network configurations. A careful review of the switch manuals with respect to PTP should be done
before deploying.
4.5.14.13. Parts
The parts are:
1. End point hardware and firmware: This is the firmware that generates packets and the
hardware that timestamps the outgoing and incoming packets.
2. Network switches that pass PTP packets: There are 3 types of switches. “Ordinary” switches
treat PTP packets the same as any UDP packet. “Transparent” switches, which measure the
time that the packet resides in the switch and modifies the packet to add this information, or
generates a follow-up packet to let the downstream device, have this information. “Boundary”
switches act as a PTP SLAVE, and on the other ports act as a MASTER to send PTP packets to
downstream devices.
3. Best Master Clock algorithm: This is a set of agreed rules to determine who the best master
is. It comprises of a Priority 1, which is a user configurable number. The master with the highest
Priority 1 is always the master. If all masters have the same Priority 1, then the clock quality is
looked at. This is a combination of reference type and distance from the reference. It is encoded
as a number based on ranges. If all the Priority 1s and clock qualities are the same, then it looks
at Priority 2. If Priority 1, clock quality, and Priority 2 are all the same then the master with the
lowest MAC address is the best master.
4.5.14.14. Configuring PTP
Master enable must be set to on.
Master mode should be set as appropriate. Annex J will give slower rates of sync and announce
messages. Use SMPTE if the slaves require higher packet rates.
DSCP is the PTP Differentiated Services Code Point value. Note that only 16, 18, 20, 24, 32,
24, 28, 40, 48, 52, 54, and 56 should be used. Other values are available for user defined systems.
The range is 0 to 63. It is used to tell the network to give a preference to this type of packet. Usually
this should be set to 56.
Sync rate should be set up based on the slave device requirements. It is good practice to have it
set at the same rate as all the other potential MASTERS.
Announce rate and timeout should be based on the changeover requirements. The timeout
multiplied by the announce rate gives the time the 5601MSC will go before becoming a MASTER when
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