Chapter 10. Clocking Modes; Introduction - Comtech EF Data CDM-570 Installation And Operation Manual

Chapter 10. CLOCKING MODES

10.1 Introduction

When dealing with satellite modems, the subject of clocking can be a complex issue. This chapter
describes the various clocking options that are available with the CDM-570/570L. There are two
fundamentally different interfaces provided by the modem, plus the optional IP Module Ethernet
Interface:
•
Synchronous clock and data interfaces (EIA-422, V.35, etc.) that permit great flexibility
concerning the source and direction of clocks. These are complex.
•
G.703 interfaces combine clock and data into a single signal (and are referred to as self-
clocking). In their basic form these are less flexible and easier to understand.
Additionally, a G.703 Clock extension mode is available in order to provide the transport
of a high–stability G.703 (T1 or E1) timing reference to the distant end of a satellite link,
regardless of the actual data rate of that link. See Section 10.5 for detailed information.
•
For the optional IP Module Ethernet interface, clocking is internally controlled and clock
selection is not available. The G.703 Clock extension mode is also available when using
the IP interface.
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