12 Essential CMTS Lessons From Worldwide Supply

12 Essential CMTS Lessons

With today’s emerging cable technologies, it’s critical to stay up to date on what’s happening in the industry. That’s why we’ve compiled 12 essential CMTS lessons from our knowledgebase. Below is a brief summary of each lesson:

Interested in learning more about CMTS? Check out our full 12 lesson CMTS training course today.

Learn More


What is Data Over Cable Service Interface Specification (DOCSIS)? It’s the standard for providing internet access through a cable modem. DOCSIS goes back more than 20 years, with new versions focusing on improving upstream and downstream data rates, as well as supporting Internet Protocol version six (IPv6).

2. Electrical

Most chassis require DC voltage or an AC rectifier with a -48 voltage at around 60 Amps.

3. Basic Operations

Basic operations include your cable modem receiving an IP address from the Dynamic Host Configuration Protocol (DHCP) server, as well as a modem file from the Trivial File Transfer Protocol (TFTP) server.

4. RF and Cable Plant

Radio Frequencies (RF) and Cable Plant describe how data moves to and from a cable modem. For a Cable Plant, amplifiers connect to hardline coax cables. For RF, your average return frequency range is 5-42Mhz upstream with a 6Mhz wide downstream channel for domestic use, and 8Mhz wide channel for Euro DOCSIS. Multiple channels in both directions are combined together to create a bonding group that allows for higher speed internet services.

5. IP Networking

Most cable modems use a private network while most PC’s and routers use a public network to pass traffic onto the web.

6. Modem Registration

Different cable modem models follow a similar process for registration. They run a self-diagnostic before scanning for a downstream frequency from the CMTS and then an upstream frequency. Once both are locked in, your cable modem requests its IP address and modem file.

7. Cable Modem Configuration Files

Configuration files are small binary files that end in either .cfg or .bin. The file sets the speeds the modem will be allowed to run at, as well as the number of PC’s that can be connected to the modem. Most use just one, but they can support up to 32 different public IP devices.

8. Provisioning

Every cable modem has a unique Media Access Control (MAC) address (just like PC’s and routers). The DHCP server checks its database to give the modem the correct modem file and private IP address with a specific lease time.

9. Configuration

IP networks, routes, frequencies and channel width, as well as SNMP would need to be considered to match your cable plant’s capabilities and back office network.

10. SNR

Signal to noise (SNR) is the power level from the modem carrier to the noise floor (noise is a byproduct of amplifiers as well as other factors like bad grounding and interfering frequencies). ATDMA modulation requires an SNR of 28 and higher. Lower SNR would result in retransmit of data packets, slower speeds and well as modem deregistration.

11. Video

Both DOCSIS 2.0 and 3.0 support video through DSG, or DOCSIS set-top Gateway, or IP multicast. For higher video support on downstream Qam channels.

12. Monitoring

SNMP, simple network monitoring protocol can be used to monitor everything from network connectivity to environmental conditions. Most use mrtg to monitor network utilization and modem count. You need to load a MIB for the specific CMTS used to get the correct data.

Learn More About the Best Practices for CMTS

Understanding the best practices for CMTS is essential, plus it offers several benefits. When you k now its role, as well as how to monitor its performance, you can deliver an improved experience for your company or clients, which leads to a range of advantages, such as growth and productivity.

To learn more about CMTS, start your CMTS training course today. Once you’ve completed these 12 lessons test out your knowledge with the lab portion as well!

Contact Us