System Time-Of-Day; System Timing; Types Of System Timing - Harris CM-30 Installation & Operation Manual

NetXpress LX & CM-30 Installation & Operation Manual
Version 1, September 2010

2.6 System Time-of-Day

With the NetXpress LX system, there are two ways to set the system time-of-day: 1) manually and 2)
via NTP (Network Timing Protocol) server. If you choose the latter method, you must use the Web
server interface to enable NTP in the NIM Configuration – General Setup screen and provide the IP
address of the SNTP server (Section 4.3.3.1 – General Setup). The NetXpress LX system maintains the
time and date in a battery-backed time-of-day clock on the CM-30 module.

2.7 System Timing

2.7.1

Types of System Timing

System timing is the process of synchronizing communications and stream traffic between two or
more NetXpress LX systems in a network. Time synchronization is critical to the proper functioning of
the NetXpress LX network. It must be configured correctly.
The primary timing source for all interconnected NetXpress LX systems should trace back to the same
long-term accurate oscillator.
Primary and secondary timing are configured via the Web interface using the System Timing screen
(Section 4.3.3.5 – System Timing). You must specify the timing source for both primary and
secondary timing. If the primary timing source is unavailable, the system uses secondary timing. The
NetXpress LX system provides four timing sources from which to choose:
● Internal
● External
● Stream
● SynchroCast
Timing can be sourced through the RS-422 Timing OUT port on the MIU-201 or MIU-202-2 to feed
additional multiplexers.
2.7.1.1 Internal Timing
Internal timing is derived from an extremely accurate internal oscillator on the CM-30 module. In a
NetXpress LX network, only the master NetXpress LX system can use internal timing. Other NetXpress
LX shelves in the network must use external, stream, or SynchroCast timing derived from the network
master.
2.7.1.2 External Timing
External timing is usually a precision timing signal derived from an external device that is traceable to
a stratum-1 timing source (for example, a public network WAN interface such as T1 or E1). External
timing is input through a connection to the Timing IN port on the MIU-201 or MIU-202-2. The external
timing input accepts an RS-422/RS-485 balanced clock signal. If external timing is selected as the
primary timing source on the master NetXpress LX system, external timing, stream, or SynchroCast
timing must be selected as the primary timing method for the subordinate NetXpress LX systems.
2.7.1.3 Stream Timing
Stream timing is derived from the incoming packet stream. A timing stream must have a packet rate
of 8 packets per second or greater (1000 frames/packet or less). This type of timing uses an algorithm
inherent in the TDMoIP chip. In a NetXpress LX network, only subordinate NetXpress LX systems can
be set to stream timing mode. The NetXpress LX master system monitors stream traffic and adjusts
timing so that the subordinate shelves are synchronized with the master clock frequency. As a general
rule; the faster the packet rate, the better the stream timing. With stream timing, jitter buffer size can
be monitored and regulated to avoid buffer underflow/overflow and negate the effect of packet delay
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2 – Functional Design
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