Comtech EF Data CDM-750 - Manual (Page 26)

CDM-750 Advanced High-Speed Trunking Modem Revision 2
Introduction MN-CDM750
1–2
• Supports reception and transmission of IP data over satellite links via two fundamentally
different types of interface – IF and data:
o The IF interface provides a bidirectional link with the satellite via the uplink and
downlink equipment.
o The data interface is a bidirectional path that connects the customer’s equipment
(assumed to be the Data Terminal Equipment, or DTE) to the unit (assumed to be the
Data Communications Equipment, or DCE). All terrestrial data is connected using up
to two available 10/100/1000 Gigabit Ethernet interfaces. Two Plug‐in Interface
Card (PIIC) slots permit factory or field installation of optional data interfaces such
as G.703 E3/T3/STS‐1, Copper STM‐1, OC‐3 SONET, etc.
• Includes support for Adaptive Coding and Modulation (ACM) and Constant Coding and
Modulation (CCM):
o ACM allows optimization of throughput under all link conditions.
o CCM allows operators to define groups of remotes having different modulation and
coding parameters, as a means to improve efficiency on existing satellite capacity.
On the Tx (transmit) side: Transmit data from the Ethernet interface is converted for further
processing. Generic Steam Encapsulation (GSE) captures the Ethernet frames and prepares them
for DVB‐S2 framing and modulation and coding. Synchronous data interfaces are mapped into
the DVB‐S2 frame directly. The modulated signal is sent to the modulator output for use at
either 70/140 MHz via a BNC connector or L‐Band at a Type‐N connector. A fixed level L‐Band
sample of the modulated signal is available at the Tx Mon SMA connector depending on the
mode of operation:
• Monitor for 70/140 MHz operation: 900 + 70/140 MHz frequency;
• Monitor for L‐Band operation: L‐Band frequency.
Transmit data from non‐IP interfaces, like the G.703 data interface, are serial streams that are
not GSE encapsulated and are sent on to the rest of the modulator. In MultiStream mode, all
data interfaces are encapsulated in the low overhead GSE structure and multiplexed to form an
aggregated carrier.
On the Rx (receive) side: Signals from the link are recovered by a DVB‐S2 demodulator, and the
data is decapsulated (GSE) to extract the Ethernet frames. The data is sent to the Rx side of the
Ethernet interface for user access via an RJ‐45 connector.
A similar process without GSE for non‐IP data is used in the receive side for serial data, e.g., the
G.703 interface. Similarly, MultiStream traffic is decapsulated and demultiplexed to form the
original data streams.