Comtech EF Data CDM-625 - Manual (Page 393)

CDM-625 Advanced Satellite Modem Revision 15
Ethernet Network Configuration MN-CDM625
16–15
16.7 Advanced Network Timing
16.7.1 Overview
The Advanced Network Timing (ANT) feature provides IP-based protocols to synchronize the
modem's internal time-of-day clock to an external device such as a time server, Base Station
Controller (BSC), or Radio Network Controller (RNC).
16.7.2 SNTP (Simple Network Time Protocol)
The Simple Network Time Protocol (SNTP), defined in RFC-1361, provides millisecond-
resolution time synchronization with a time server. When the modem synchronizes its time, it also
synchronizes the time of all connected EDMAC devices, such as slave LPODs or CSATs. When all
devices are synchronized, administrators can better correlate logged events between devices.
SNTP is a UDP protocol that works on port 123. If the modem is not updating its time, verify that
there are no network devices between the modem and time server that might block UDP packets
on that port.
16.7.3 PTP (Precision Time Protocol)
1. At present, PTP is not supported in modems in which the optional IP
Packet Processor is installed and enabled .
2. For better PTP clock accuracy, ingress and egress port sync interval shall
be at least 2 seconds.
The Precision Time Protocol is used to synchronize clocks throughout a computer network.
Based on the IEEE 1588v2 (2008) standard, PTP achieves clock accuracy in the nanosecond range
– much more accurate than what is attainable by NTP (Network Time Protocol) – and it is also
used in network applications where GPS is either unaffordable or inaccessible.
Comtech EF Data’s implementation of PTP in the CDM-625 operates over IP, without the
presence of the optional IP Packet Processor. To achieve high accuracy time and frequency
synchronization, PTP relies on hardware time stamping at the ingress and egress ports of the
network; therefore, all devices in the network must support PTP.
Figure 16-13 shows a typical network configuration. Here, the RNC/BSC (Radio Network
Controller/Base Station Controller) at the near-end side of the network and the BTS (Base
Transceiver Station) on the distant-end side of the network are the IEEE 1588v2-capable devices.
In this topology the RNC/BSC serves as the Grandmaster – the root timing reference that
transmits synchronization information to the clocks residing on its network segment – or slave
to the Grandmaster.