Comtech EF Data CDM-425 Advanced Satellite Modem

  • 25 Mbps Max Data Rate
  • Versa-FEC / Versa-FEC2 FEC
  • L-Band and If Band Output
  • On Board IP Packet Processor
  • Carrier In Carrier Bandwidth Cancellation
  • 5%, 10%, 15%, 20%, 25% and 35% Transmit Filter Rolloff
  • Adaptive Coding and Modulation (ACM)
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Comtech EF Data CDM-425 Advanced Satellite Modem

Comtech EF Data's CDM-425 Advanced Satellite Modem continues to build on their legacy of providing efficient and reliable satellite modems. The CDM-425 offers the most popular and powerful features of the CDM-625A in a smaller form factor with lower power consumption. The satellite modem has 18 VersaFEC® ModCods and 74 VersaFEC-2 ModCods, enabling the user to optimize for both latency and coding gain for any situation.

The CDM-425 also includes Comtech EF Data's patented DoubleTalk Carrier-in-Carrier bandwidth compression, Low Trasmit Rolloff Filters and a sophisticated IP packet processor. This combination of 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

Comtech CDM-425 Features

  • DoubleTalk Carrier-in-Carrier bandwidth compression
  • Carrier-in-Carrier Automatic Power Control
  • VersaFEC-2 High Performance LDPC with Adaptive Codingand Modulation (ACM), Short Block and Long Block – similarperformance to DVB-S2X with significantly lower latency.
  • VersaFEC FEC with Adaptive Coding and Modulation (ACM),both standard and Ultra-Low Latency (ULL)
  • 5%, 10%, 15%, 20%, 25% and 35% Transmit Filter Rolloff
  • Optional Packet Processor with header compression, payloadcompression, advanced Quality of Service (QoS) andManaged Switch Mode with VLAN support
  • Integrated 4-port managed Ethernet switch with VLAN andQoS
  • Jumbo frame support
  • Dual Band Capability: 70/140 MHz and extended L-Band(950 – 2250 MHz) in same unit
  • Data Rate: 18 kbps to 25 Mbps
  • Symbol Rate: 18 ksps to 12.5 Msps
  • Modulation: BPSK, QPSK, 8-QAM/8-ARY, 16-QAM/16-ARY,32-ARY
  • FEC: VersaFEC (low-latency LDPC) and VersaFEC-2 (highperformance LDPC)
  • Wide Range of data interfaces: EIA-422/530, V.35, G.703T1/E1, Quad G.703 E1, 4-port 10/100Base-T Ethernet
  • IEEE 1588v2 Precision Time Protocol
  • Sub Mux to multiplex IP/Ethernet traffic with serial or G.703traffic
  • Drop & insert for T1/E1
  • Enhanced D&I++ for single T1/E1 & quad E1
  • Management: 10/100Base-T Ethernet with SNMP, DistantEnd SNMP Proxy, HTTP, Telnet and EIA-232/EIA-485
  • RADIUS Client
  • ETSI compliant Carrier ID using MetaCarrier® Technology
  • Embedded Distant-end Monitor and Control (EDMAC)
  • Automatic Uplink Power Control (AUPC), and combinedAUPC and ACM
  • Standard high-stability internal reference (± 6 x 10-8)
  • L-Band TX: 10 MHz reference for BUC, FSKcommunications and optional BUC power supply
  • L-Band RX: 10 MHz reference and LNB power supply
  • L-Band: Advanced FSK for LPOD M&C
  • 1:1 and 1:10 redundancy switches available
  • Backwards compatible with CDM-625 (VersaFEC modes)and CDM-625A (VersaFEC and VersaFEC-2 modes)

Doubletalk Carrier-in-Carrier

DoubleTalk Carrier-in-Carrier, based on patented “Adaptive Cancellation” technology, allows transmit and receive carriers of a duplex link to share the same transponder bandwidth. 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.

Carrier-in-Carrier Automatic Power Control (CnC-APC)

The patent-pending Carrier-in-Carrier Automatic Power Control (CnC-APC) mechanism enables modems on both sides of a CnC link to automatically measure and compensate for rain fade while maintaining the Total Composite Power. In addition to automatically compensating for rain fade, CnC-APC also enables the modems to share link margin, i.e. a modem in clear sky conditions can effectively transfer excess link margin to a distant end modem experiencing fade, thereby further enhancing overall availability.

VersaFEC-2 High Performance LDPC Forward Error Correction

CDM-425 offers a new high performance LDPC FEC specifically design to optimize performance at low and mid-tier symbol rates. VersaFEC-2 long-block provides 38 ModCods (BPSK to 32-ARY) with performance generally comparable with DVB-S2X at significantly lower latency and short-block provides 36 ModCods (BPSK to 32-ARY) with higher coding gain than first generation VersaFEC and similar latency. All higher order constellations are circular or quasi-circular for optimal peak-to-average performance. Both CCM and ACM operation is support for long block and short block.

VersaFEC Forward Error Correction

CDM-425 offers VersaFEC, a system of high-performance short-block LDPC codes designed to provide maximum coding gain while minimizing latency. VersaFEC is designed to support ACM and CCM mode of operation.The 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 can provide significant increase in throughput as well as availability. ACM converts the fade margin into increased capacity making it possible to more than double the throughput for Ku-band operation. Even under deep fade, ACM may be able to maintain the link at the lower ModCod thereby increasing availability. It is tightly integrated with packet processor QoS which allows higher priority, mission critical traffic to be maintained even during fade.

Dual Band Capability

The CDM-425 supports 70/140 MHz and extended L-Band (950 – 2250 MHz) 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-425 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 modem supports jumbo frames with maximum Ethernet frame size of 2048 bytes.

Packet Processor

The optional high-performance Packet Processor enables efficient IP networking and transport over satellite with low overhead encapsulation, header compression, payload compression and advance Quality of Service to the CDM-425. The 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.

Packet processor supports Routed mode as well as Managed Switch Mode of operation. In managed switch mode, it operates as a layer 2 switch with VLAN support, enabling seamless integration with existing infrastructure while providing full optimization including low overhead Streamline Encapsulation, header compression and payload compression and advanced QoS.

Header Compression

The Packet Processor incorporates industry-leading header compression for Ethernet and IP traffic. In managed switch mode, header compression can reduce the 54 byte Ethernet/IP/UDP/RTP header to as little as 1 byte. For TCP/IP, the 54 byte header (including Ethernet) is reduced to as little as 3 bytes. For applications such as VoIP, header compression can provide bandwidth savings exceeding 65%. E.g. the 8 kbps G.729 voice codec requires 31.2 kbps once encapsulated into an Ethernet frame with IP/UDP/RTP. With header compression, the same voice call needs about 9 kbps – a saving of almost 70%. And, bandwidth requirements for typical Web/HTTP traffic can be reduced by 10% or more with TCP/IP header compression.

Payload Compression

The Packet Processor incorporates industry-leading GZIP based payload compression for IP/Ethernet traffic. Implemented in hardware for maximum throughput and efficiency, payload compression can typically reduce the required satellite bandwidth by 30-40%.

Streamline Encapsulation

The Packet Processor incorporates Comtech EF Data’s patent-pending 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 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 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 higherburstable rate depending on availability
  • A powerful classifier supports packet classification by Protocol, VLAN ID / range, ToS Byte, Source IP (or subnet), Destination IP (or subnet), Source Port (or Range), Destination Port (or Range) and DSCP (for DiffServ).

Quad E1 Interface (QDI) with Enhanced D&I++

The CDM-425 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.

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. IP sub mux can also be used to provision an overhead IP channel for management when using non IP/Ethernet traffic interfaces.

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-425 can also act as SNMP proxy for the distant end CDM-425. This allows distant end CDM-425 management using SNMP without requiring an end-to-end IP link.


The CDM-425 supports the Remote Authentication Dial In User Service (RADIUS) client enabling centralized user authentication for management access to the modem by web browser and telnet. RADIUS client supports Password Authentication Protocol (PAP) and Challenge-Handshake Authentication Protocol (CHAP).

IEEE 1588v2 Precision Time Protocol (PTP)

PTP has emerged as the key technology for frequency, time and phase synchronization over a packet network. The CDM-425 incorporates hardware support for PTP, thereby significantly improving synchronization accuracy for satellite backhaul.

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.

More Information
Weight 15.0000
Country of Manufacture United States
Manufacturer Comtech EF Data
Input Power 100 - 240 VAC, -48VDC
Max Data Rate 25 Mbps
Max Symbol Rate 12.5 Msps
Modulation BPSK, QPSK, 8QAM, 8ARY, 16QAM, 16ARY, 32ARY
FEC VersaFEC, VersaFEC-2
Output Frequency 70 MHz, 140 MHz, 950 - 2250 MHz
Warranty 2 Years
Dimensions 1.75 x 19.0 x 14
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101 Eagle Road Building 7. Avon, Colorado. 81620.
T : (970)-748-4250.