CDM-625 Advanced Satellite Modem
with DoubleTalk® Carrier-in-Carrier®
The CDM-625 Advanced Satellite Modem builds on Comtech EF Data’s legacy of providing the most
efficient satellite modems. It is the first modem to combine advanced Forward Error Correction (FEC) such
as VersaFEC and Low Density Parity Check (LDPC) codes with the revolutionary DoubleTalk Carrier-inCarrier bandwidth compression, allowing for maximum savings under all conditions. This combination of
advanced technologies enables multi-dimensional optimization, allowing satellite communications users to:
 Minimize operating expenses (OPEX)
 Maximize throughput without using additional transponder resources
 Maximize availability (margin) without using additional transponder resources
 Minimize capital expenses (CAPEX) by allowing a smaller BUC/HPA and/or antenna
 Or, a combination to meet specific business needs
 DoubleTalk Carrier-in-Carrier bandwidth
 Adaptive Coding and Modulation (ACM)
 IP Packet Processor with header compression,
payload compression and advanced Quality of
Service (QoS)
 Dual Band Capability: 70/140 MHz and L-Band in
same unit
 Data Rate: 18 kbps to 25 Mbps
 Symbol Rate: 18 ksps to 12.5 Msps
 Modulation: BPSK, QPSK/OQPSK, 8-PSK/8QAM, 16-QAM
 FEC: Viterbi, Sequential, Concatenated Reed
Solomon, TCM, Turbo Product Code (TPC)
(IESS-315 Compliant), LDPC Code and
VersaFEC (low-latency LDPC)
 Widest Range of data interfaces: EIA-422/530,
V.35, G.703 T1, G.703 E1, G.703 T2, G.703 E2,
Quad G.703 E1, ASI, LVDS, HSSI, 4-port
10/100Base-T Ethernet
 4-port managed Ethernet switch with VLAN and
 Sub Mux to multiplex IP/Ethernet traffic with serial
or G.703 traffic
 Drop & insert for T1/E1
 Enhanced D&I++ for single T1/E1 & quad E1
 Management: 10/100Base-T Ethernet with
SNMP, Distant End SNMP Proxy, HTTP, Telnet
and EIA-232/EIA-485
 Embedded Distant-end Monitor and Control
 Automatic Uplink Power Control (AUPC)
 Engineering Service Channel (ESC/ESC++)
 Standard high-stability internal reference
(± 6 x 10-8)
 5-tap Adaptive Equalizer
 L-Band TX: 10 MHz reference for BUC, FSK
communications and optional BUC power supply
 L-Band: Advanced FSK for LPOD M&C
 L-Band RX: 10 MHz reference and LNB power
 Open network modes
 CDM-600/L emulation mode
 1:1 and 1:10 redundancy switches available
 Backwards compatible with CDM-500/CDM-550,
CDM-550T, CDM-570/L and CDM-600/L
Satellite Modems
 Interoperable with many Comtech EF Data
Satellite Modems: CDM-Qx/L, SDM-8000, 300A,
and 300L3
Typical Users
• Mobile Operators
• Telecom Operators
• Satellite Service
• Government & Military
• Enterprise
• Offshore
Common Applications
• Mobile Backhaul
• G.703 Trunking
• IP Trunking
• Offshore & Maritime
• Enterprise
• Communications onthe-Move
• Satellite News
Doubletalk Carrier-In-Carrier
DoubleTalk Carrier-in-Carrier is based on patented bandwidth compression technology originally developed
by Applied Signal Technology, Inc. Using “Adaptive Cancellation” it allows transmit and receive carriers of a
two-way link to share the same transponder space.
Figure 1 shows the typical full-duplex satellite link, where the two carriers are adjacent to each other.
Figure 2 shows the typical DoubleTalk Carrier-in-Carrier operation, where the two carriers are overlapping, thus sharing the same
Figure 1
Figure 2
When observed on a spectrum analyzer, only the Composite is visible. Carrier 1 and Carrier 2 are shown in Figure 2 for reference only.
DoubleTalk Carrier-in-Carrier is complementary to all advances in modem technology, including advanced FEC and modulation
techniques. As these technologies approach theoretical limits of power and bandwidth efficiencies, DoubleTalk Carrier-in-Carrier utilizing
advanced signal processing techniques provides a new dimension in bandwidth efficiency.
As DoubleTalk Carrier-in-Carrier allows equivalent spectral efficiency using a lower order modulation and/or FEC Code, it can
simultaneously reduce CAPEX by allowing a smaller BUC/HPA and/or antenna. Alternatively, DoubleTalk Carrier-in-Carrier can be used
to achieve very high spectral efficiencies E.g., DoubleTalk Carrier-in-Carrier when used with 16-QAM approaches the bandwidth
efficiency of 256-QAM (8 bps/Hz).
When combined with VersaFEC or LDPC/TPC, it can provide unprecedented savings in transponder bandwidth and power utilization.
This allows for its successful deployment in bandwidth-limited and power-limited scenarios, as well as reduction in earth station
BUC/HPA power requirements.
Carrier-in-Carrier® is a Registered Trademark of Comtech EF Data
DoubleTalk® is a Trademark of Applied Signal Technology, Inc.
VersaFEC is a Registered Trademark of Comtech AHA Corp.
VersaFEC Forward Error Correction
CDM-625 is the first modem to offer VersaFEC, a patented system of high performance short-block low-latency LDPC codes designed to
support latency-sensitive applications, such as cellular backhaul over satellite. VersaFEC provides excellent coding gain with lowest
possible latency. VersaFEC’s Eb/No performance is similar to that of DVB-S2 (short block) or LDPC (16k block) with 70-90% lower
latency. Compared to TPC, VersaFEC can provide coding gain of 1.0 dB or more.
The new Ultra Low Latency (ULL) codes provide even lower latency compared to standard VersaFEC codes.
Adaptive Coding & Modulation (ACM)
Satellite users have traditionally relied on worst case link margin to overcome rain fade which leads to significant inefficiencies. ACM
converts the fade margin into increased throughput – gain of 100% or more is possible. The CDM-625 with VersaFEC was specifically
architected to support ACM for IP/Ethernet traffic. ACM maximizes throughput under all conditions – rain fade, inclined orbit satellite
operation, antenna mis-pointing, noise, interference and other impairments.
VersaFEC ACM can provide almost 85% reduction in latency compared to DVB-S2 (short block).
ACM can also be used with DoubleTalk Carrier-in-Carrier.
Low Density Parity Check Codes (LDPC) & Turbo Product Codes (TPC)
CDM-625 offers an integrated LDPC and 2nd Generation TPC codec. LDPC is an advanced Forward Error Correction technique capable
of providing performance much closer to Shannon limit. The current LDPC implementation can provide 0.7 to 1.2 dB additional coding
gain compared to an equivalent TPC code.
In order to take full advantage of the increased coding gain provided by LDPC, Comtech EF Data has developed a patented 8-QAM
modulation that allows for acquisition and tracking at much lower Eb/No compared to 8-PSK.
Dual Band Capability
CDM-625 supports 70/140 MHz and L-Band capability in the same unit with independently selectable transmit and receive IF. This
simplifies sparing and stocking in networks requiring 70/140 MHz and L-Band units.
4-Port Managed Ethernet Switch with VLAN & QoS
CDM-625 base modem incorporates a 4-port 10/100Base-T managed Ethernet switch with VLAN capability and priority-based Quality of
Service. Access (Native) Mode and Trunk Mode are supported. Traffic can be prioritized using port-based priority or VLAN priority. The
maximum Ethernet frame size is 1536 bytes.
IP Packet Processor
The IP Packet Processor enables efficient IP networking and transport over satellite by adding routing capability with very low overhead
encapsulation, header compression, payload compression and Quality of Service to the CDM-625. The advanced QoS combined with
header and payload compression ensures the highest quality of service with minimal jitter and latency for real-time traffic, priority
treatment of mission critical applications and maximum bandwidth efficiency.
Header Compression
The IP Packet Processor incorporates industry-leading header compression for IP traffic. Header compression can reduce the 40 byte
IP/UDP/RTP header to as little as 1 byte. For TCP/IP, the 40 byte header is reduced to as little as 3 bytes. For applications such as VoIP,
header compression can provide bandwidth savings exceeding 60%. E.g. the 8 kbps G.729 voice codec requires 24 kbps of IP bandwidth
once encapsulated into an IP/UDP/RTP datagram. With header compression, the same voice call needs about 8.5 kbps – a saving of
almost 65%. And, bandwidth requirements for typical Web/HTTP traffic can be reduced by 10% or more with TCP/IP header
Payload Compression
The IP Packet Processor incorporates industry-leading payload compression for IP traffic. Implemented in the hardware for maximum
throughput and efficiency, payload compression can reduce the required satellite bandwidth by as much as 40-50%.
Streamline Encapsulation (SLE)
The IP Packet Processor incorporates Comtech EF Data’s patent-pending very low overhead Streamline Encapsulation (SLE). SLE can
reduce the encapsulation overhead by as much as 65% compared to industry standard HDLC.
Advanced Quality of Service (QoS)
The IP Packet Processor incorporates multi-level QoS to ensure the highest quality service with minimal jitter and latency for real-time
traffic, priority treatment of mission critical applications and maximum bandwidth efficiency.
Supported modes are:
 DiffServ – Industry-standard method of providing QoS enabling seamless co-existence in networks that implement DiffServ
 Max/Priority – Provides multi-level traffic prioritization with the ability to limit maximum traffic per priority class
 Min/Max – Provides a Committed Information Rate (CIR) to each user defined class of traffic with the ability to allow a higher
burstable rate depending on availability
Quad E1 Interface (QDI) with Enhanced D&I++
The CDM-625 supports a Quad E1 interface that can aggregate up to four full or fractional E1s into a single carrier, with very low
overhead. This provides significant CAPEX savings by reducing the number of modems and could possibly reduce the BUC/HPA size by
eliminating the multi-carrier backoff. A proprietary, closed network drop & insert (D&I++) allows for dropping or inserting any combination
of 1 to 31 time slots on each E1. D&I++ is supported for E1-CCS only.
For QDI operation, all E1s must have a common clock source.
IP Sub Multiplexer
The IP sub mux allows multiplexing IP/Ethernet traffic with serial or G.703 traffic into a single carrier. This is particularly useful for cellular
backhaul when both E1 and IP backhaul is required. This reduces the number of modems and could possibly reduce the BUC/HPA size
by eliminating the multi-carrier backoff. The IP sub mux ratio ranges from 9:1 (IP data rate is 9 times that of the serial or G.703 data rate)
to as low as 1:59.
The CDM-625 supports EDMAC, EDMAC-2, EDMAC-3 and AUPC. EDMAC/EDMAC-2/EDMAC-3 can be used to monitor and control the
distant end of a satellite link using a proprietary overhead channel. EDMAC-3 is also used for SNMP management of the distant end
modem. AUPC enables automatic uplink power control for a duplex link.
Management & SNMP Proxy
The modem can be managed via the front panel, the remote M&C port (EIA-232/EIA-485), or the 10/100Base-T Ethernet port. With
support for SNMP, HTTP and Telnet, the modem can be easily integrated into an IP-based management system.
The CDM-625 can also act as SNMP proxy for the distant end modem. This allows distant end modem management using SNMP without
requiring an end-to-end IP link.
Advanced FSK for LPOD Monitoring & Control
The Advanced FSK allows for monitoring and control of LPOD through modem front panel menus, serial remote control and Telnet.
CDM-600/CDM-600L Emulation Mode
CDM-625 can be placed in CDM-600 or CDM-600L emulation mode. This permits easy integration into an existing CDM-600/L setup
without changes to M&C platform or redundancy switches.
Feature Enhancements
Enhancing the capability of the CDM-625 in the field is easy. Features that do not require additional hardware can be added on site,
using FAST access codes purchased from Comtech EF Data.
Data Rate
Symbol Rate
Major Operating
(See User Manual
For Details)
FEC Options
Viterbi: k=7, per
Viterbi with Reed
Reed Solomon
TCM (Per IESS-310)
Integrated LDPC
and TPC (2 Gen)
Codec (Optional
Plug-in Module)
VersaFEC Codec
(Optional Plug-in
Form C Relays
External Reference
(Input OR Output)
18 kbps to 25 Mbps, in 1 bps steps
(modulation, FEC & data interface dependant)
18 ksps to 12.5 Msps
50 – 180 MHz (standard) and
950 – 2000 MHz (Option),
100 Hz resolution, independent TX and RX
Open network, per IESS-308 / 309 / 310 / 314
transparent, closed network per IESS-315
LDPC / TPC Codec (optional plug-in module)
VersaFEC Codec (optional plug-in module) with
ACM or Constant Coding & Modulation (CCM)
EDMAC Framed with/without AUPC
RS Outer Codec
High rate ESC / Enhanced ESC (ESC++)
Drop & insert (D&I) /Enhanced D&I++
Quad E1 drop & insert (QDI)
DoubleTalk Carrier-in-Carrier (optional plug-in
Rate 3/4 16-QAM
Rate 7/8 16-QAM
See CDM-625 user manual for details
Open network and closed network modes
8-PSK/TCM Rate 2/3
LDPC Code Rates
Rate 3/4 QPSK/OQPSK/8-PSK/8-QAM/16-QAM
TPC Code Rates
Rate 5/16 BPSK
Rate 3/4 QPSK/OQPSK/8-PSK/8-QAM/16-QAM
Rate 7/8 QPSK/OQPSK/8-PSK/8-QAM/16-QAM
Rate 0.95 QPSK/OQPSK/8-PSK/8-QAM
BPSK Rate 0.488
QPSK Rate 0.533, 0.631, 0.706, 0.803
8-QAM Rate 0.576 (ECCM), 0.642, 0.711, 0.780
16-QAM Rate 0.644 (ECCM), 0.731, 0.780,
0.829, 0.853
BPSK 0.493 (ULL)
QPSK 0.493, 0.654, 0.734 (ULL)
IDR Mode, no RS, - per ITU V.35 (Intelsat variant)
IBS mode, no RS - per IESS-309, externally
frame synchronized
Transparent Closed Network mode, no RS or
Turbo coding - per ITU V.35 (Intelsat variant)
EDMAC mode, no RS coding - externally frame
synchronized - proprietary
Turbo Product Code/LDPC/VersaFEC modes externally frame synchronized - proprietary
All RS modes - externally frame synchronized per
10/100Base-T Ethernet with SNMP, HTTP and
Telnet support, EIA-232, EIA-485 (2- or 4-wire)
Hardware fault, RX and TX traffic alarms, open
network backward alarms
BNC connector
Input: 1, 2, 5, or 10 MHz, -6 dBm to
+10 dBm, 50 /75  (nominal)
Output: 10 MHz, 2.7 V peak-to-peak
± 0.4 V, low impedance output
Data Interfaces
EIA-422/-530 DCE , Up to 14 Mbps
V.35 DCE , Up to 14 Mbps
LVDS Serial , Up to 25 Mbps
HSSI Serial , Up to 25 Mbps
G.703 T1, 1.544 Mbps
(Balanced 100 )
G.703 T2, 6.312 Mbps
(Unbalanced 75  or balanced
110 )
G.703 E1, 2.048 Mbps
(Unbalanced 75  or balanced
120 )
G.703 E2, 8.448 Mbps (Unbalanced
75 )
ASI , Up to 25 Mbps
Additional 2.048 Mbps E1 Ports for
Quad-E1 (Balanced 120 )
Overhead Data
Modem Alarms
4-port 10/100Base-T Managed
Ethernet Switch
(Optional IP Packet Processor
Frequency Stability
Transmit Filtering
Transmit Filter Rolloff
Harmonics and
Transmit On/Off Ratio
Output Phase Noise
Output Power
Power Accuracy
25-pin D-sub (female)
25-pin D-sub (female)
9-pin D-sub (female)
BNC (female)
BNC (female)
9-pin D-sub (female)
44-pin High-density D-sub (male)
15-pin D-sub (male)
4 x RJ-45
± 0.06 ppm (± 6 x 10 ), 0° to 50°C (32° to
122° F) with internal reference
Per IESS-308
25%, 35%
Better than -60 dBc/4 kHz
(typically <-65 dBc/4kHz)
Measured from 1 to 500 MHz
(50-180 MHz band)
Measured F0 ± 500 MHz
(950-2000 MHz band)
-60 dBc minimum
< 0.480° rms double sided, 100 Hz to 1 MHz
(Minimum 16 dB better overall than the Intelsat
IESS-308/309 requirements)
Frequency Offset
100 Hz
1 kHz
10 kHz
100 kHz
Fundamental AC line spurious is -42 dBc or
The sum of all other single sideband spurious,
from 0 to 0.75 x symbol rate, is -48 dBc or lower
50-180 MHz:
0 to -25 dBm, 0.1 dB steps
950-2000 MHz:
0 to -40 dBm, 0.1 dB steps
50-180 MHz:
± 0.5 dB over frequency, data rate, modulation
type and temperature range of 15 to 35° C
± 0.8 dB over frequency, data rate, modulation
type and temperature range of 0 to 50° C
950-2000 MHz:
± 0.7 dB over frequency, data rate, modulation
type and temperature range of 15 to 35° C
± 1.0 dB over frequency, data rate, modulation
type and temperature range of 0 to 50° C
Output Impedance &
Return Loss
Clocking Options
External TX Carrier
BUC Reference
(10 MHz)
BUC Power Supply
(HW Option)
50-180 MHz: 50 /75 , 16 dB minimum return
loss (18 dB typical), BNC connector
950-2000 MHz: 50 , 19 dB minimum return
loss (21 dB typical), Type-N connector
Internal, ± 0.06 ppm (SCT)
External, locking over a ± 100 ppm range (TT)
Loop timing (RX satellite clock) – supports
asymmetric operation
External clock
By TTL ‘low’ signal or external contact closure
Via TX IF center conductor, 10.0 MHz
± 0.06 ppm (with internal reference), selectable
ON/OFF, 0.0 dBm ± 3 dB
24 VDC, 4.17 Amps max., 90 W @ 50° C
48 VDC, 3.125 Amps max., 150 W @ 50° C
(180 W @ 30° C)
Supplied through TX IF center conductor and
selectable on/off via M&C control.
Input Power Range,
Desired Carrier
Max Composite
Operating Level
Absolute Maximum
Adaptive Equalizer
Acquisition Range
Below 64 ksymbols/sec
Between 64 and
389 ksymbols/sec
Above 389 ksymbols/sec
Acquisition Time
Doppler Buffer
Receive Clock
Clock Tracking
LNB Reference (10 MHz)
LNB Voltage
Monitor Functions
50-180 MHz: -105 + 10 log (symbol rate) to
-70 + 10 log (symbol rate) dBm
950-2000 MHz: -130 + 10 log (symbol rate)
to -80 + 10 log (symbol rate) dBm
50-180 MHz:
94 – 10 log (symbol rate, desired carrier)
dBc, +10 dBm max., with the additional
requirement that within ± 10 MHz of the
desired carrier the composite power is
≤ +30 dBc
950-2000 MHz:
102 – 10 log (symbol rate, desired carrier)
dBc, +10 dBm max., with the additional
requirement that within ± 10 MHz of the
desired carrier the composite power is
≤ +30 dBc
+20 dBm
5-tap design, selectable on/off
Programmable in 1kHz increments
± 1 kHz to ± (Rs/2) kHz, where Rs = symbol
rate in ksymbols/sec
± 1 kHz to ± 32 kHz
± 1 kHz to ± (0.1 * Rs) kHz, up to a
maximum of ± 200 kHz
Highly dependent on data rate, FEC rate,
and demodulator acquisition range.
E.g.: 120 ms average at 64 kbps, R1/2
QPSK, ± 10 kHz acquisition sweep range,
6 dB Eb/No
Selectable from 64 to 262,144 bits, in 16-bit
steps (Additional limitations for G.704 frame
RX satellite, TX terrestrial, external
 100 ppm minimum
Via RX IF center conductor, 10.0 MHz
± 0.06 ppm (with internal reference),
selectable on/off, -3.0 dBm ± 3 dB
Selectable on/off, 13 VDC, 18 VDC per
DiSEq 4.2 and 24 VDC at 500 mA maximum
Eb/N0 estimate, corrected BER, frequency
offset, buffer fill state, receive signal level
DoubleTalk Carrier-in-Carrier
Delay Range
0 to 330 ms
Power Spectral Density
BSPK/QPSK/8-PSK/8-QAM: –7 dB to
+11 dB
(Interferer to Desired)
16-QAM: -7 dB to +7 dB
Maximum Symbol Rate
3:1 (TX:RX or RX:TX)
Eb/No Degradation
Satellite Restrictions
0 dB Power Spectral Density Ratio
8-QAM: 0.4 dB
8-PSK: 0.5 dB
16-QAM: 0.6 dB
+10 dB power spectral density ratio
Additional 0.3 dB
Satellite in “loop-back” mode (i.e., the
transmit station can receive itself)
“Non-processing” satellite (i.e., does not
demodulate or remodulate the signal)
Available Options
100 – 240 VAC, 175 W AC primary power supply
-48 VDC, 125 W primary power supply
24 VDC, 90 W @ 50° C BUC power supply, AC or DC
primary power supply
48 VDC, 150 W @ 50° C (180 W @ 30° C) BUC power
supply, AC or DC primary power supply
Integrated TPC (2 generation) and LDPC Codec module
DoubleTalk Carrier-in-Carrier module
VersaFEC Codec module
IP Packet Processor
L-Band IF (in addition to 70/140 MHz)
Modem data rate – 10 Mbps, 15 Mbps,
20 Mbps or 25 Mbps
8-PSK and 8-QAM modulation (8-QAM requires
TPC/LDPC or VersaFEC Codec)
16-QAM modulation
TPC/LDPC Codec data rate – 10 Mbps, 15 Mbps,
20 Mbps or 25 Mbps
DoubleTalk Carrier-in-Carrier license (full) – 512 kbps,
1.1 Mbps, 2.5 Mbps, 5 Mbps,
10 Mbps, 15 Mbps, 20 Mbps or 25 Mbps
DoubleTalk Carrier-in-Carrier license (fractional)
2.5 Mbps, 5 Mbps, 10 Mbps, 15 Mbps, 20 Mbps or
25 Mbps
VersaFEC Codec data rate (CCM) – 2.5 Mbps, 5 Mbps or
16 Mbps
VersaFEC Codec symbol rate (ACM) – 300 ksps,
1.2 Msps or 4.1 Msps
Open network – IBS with high rate IBS ESC, IDR and
D&I / D&I++ for single Port T1/E1
D&I++ For Quad E1 Port 2, 3 and 4
Quality of Service (requires IP Packet Processor)
Header Compression (requires IP Packet Processor)
Payload Compression (requires IP packet processor)
1:1 Modem Redundancy Switch (L-Band)
1:1 Modem Redundancy Switch (70/140 MHz)
1:10 Modem Redundancy Switch
(Not available with IP Packet Processor)
1:10 IF Redundancy Switch (70/140 MHz)
1:10 IF Redundancy Switch (L-Band)
1:N Modem Redundancy System
(For use with IP Packet Processor Only)
1:10 IF Redundancy Switch
(For use with CRS-500)
Environmental And Physical
Operating: 0 to 50ºC (32 to 122°F)
Storage: -25 to 85ºC (-13 to 185ºF)
Power Supply
100 – 240 VAC, +6%/-10%, 50/60 Hz, auto
-48 VDC (HW option)
Power Consumption
Dimensions (1RU)
(height x width x
CE Mark
48 W (typical with TPC/LDPC Codec and Carrierin-Carrier module installed), 55 W (max.)
60 W (typical with TPC/LDPC Codec, IP Packet
Processor and Carrier-in-Carrier module
installed), 67 W max.
280 W (typical with TPC/LDPC Codec, Carrier-inCarrier module and 48 VDC BUC power supply
installed), 300 W (max.)
1.75” x 19.0” x 17.65”
(4.4 x 48 x 44.8 cm) approximate
10.8 lbs (4.9 kg) maximum, with all option
modules and 48 VDC BUC power supply installed
EN 55022 Class B
EN 61000-4-4
EN 61000-4-5
EN 50082-1 (Immunity)
EN 61000-4-6
EN 60950 (Safety)
EN 61000-4-8
EN 61000-3-2
EN 61000-4-9
EN 61000-3-3
EN 61000-4-11
EN 61000-4-2
EN 61000-4-13
Part 15 Class B
CDM-625 Rear Panel
2114 West 7th Street, Tempe, Arizona 85281 USA
Voice: +1.480.333.2200 ● Fax: +1.480.333.2540 ● Email:
U.S. Patents 7,254,188, 7,353,444, 7,415,659 and other patents pending
Comtech EF Data reserves the right to change specifications of products described in this document at any time without notice and without obligation to notify any person of such changes. Information in this
document may differ from that published in other Comtech EF Data documents. Refer to the website or contact Customer Service for the latest released product information.
© 2011 Comtech EF Data