Cable Modem Archives

5 07, 2010

DOCSIS 3.0 Tutorial – DOCSIS Timing Interface Specification

Mia Colabrese2021-11-24T09:41:01-05:00July 5th, 2010|

Before DOCSIS 3.0 and before modular CMTS architectures, a CMTS existed in one chassis. Life was much simpler for everyone. Inside the chassis existed a 10.24 MHz clock or oscillator. This was a master time keeper that kept event in synchronization with every other event. Timing is very important in communications networks, especially when dealing with microsecond timing calculations necessary for DOCSIS transport - remember the "tick" (6.25 usec). This article is going to address the DOCSIS Timing Interface Specification (DTI) and DTI time servers that have arisen due to the distributed architectures in M-CMTSs and DOCSIS 3.0 CMTSs. In these architectures, it is possible to have the CMTS core in say the headend, with the eQAM and upstream receivers in remote hubsites. Suddenly the single 10.24 MHz clock keeping the system in synchronization is no longer an option. Three separate, free running 10.24 MHz clocks would also not work because they would not be in phase and would likely not be exactly running at the same frequency, causing the entire system to out of synchronization - there would packet collisions and lost data and VoIP packets all over the place. It would be chaos! So the smart folks at Cablelabs put together the DTI specification to resolve these issues. Here are some of the details.

1 07, 2010

DOCSIS 3.0 Tutorial – The EQAM

Mia Colabrese2021-08-17T15:58:05-04:00July 1st, 2010|

In my article on DOCSIS 3.0 M-CMTS architecture, I talked about the distributed nature of the CMTS with an M-CMTS core (the CPU of the system), a DOCSIS Timing Server, and an edge Quadrature Amplitude Modulator (EQAM). I am going to cover the EQAM in detail in this article because in the past couple of years, EQAM (also spelled eQAM) has rapidly become part of our vocabulary but its operation and value often go unappreciated. Further, in order to fully understand DOCSIS 3.0 operation, downstream channel bonding, and possible issue which may arise, a thorough understanding of the eQAM is critical.

26 06, 2010

DOCSIS 3.0 Tutorial – M-CMTS Architecture

Mia Colabrese2021-11-24T09:41:52-05:00June 26th, 2010|

In this article I am going to further explore the M-CMTS in order to describe two import elements of DOCSIS 3.0 network, the edge-Quadrature Amplitude Modulator or EQAM and the DOCSIS Timing Interface Specification Server or DOCSIS Timing Server. Before I cover these components I will show how they are integrated with the M-CMTS architecture.

12 10, 2009

DOCSIS 3.0 Tutorial – Introduction

Mia Colabrese2021-08-17T16:05:13-04:00October 12th, 2009|

This is the first of a new series of Tutorials focused on the Data Over Cable Service Interface Specifications (DOCSIS) version 3.0. I will make the assumption that you are familiar with the DOCSIS 1.x / 2.0 standards or have already reviewed my DOCSIS Basics Tutorial as I will be using many terms without explanation since they were previously covered. The DOCSIS 3.0 specification is an extension of the DOCSIS 1.x and 2.0 specification which dramatically increases the data throughput by adding a technology known as channel bonding to the DOCSIS downstream and upstream, adding increased security, adding support for IPv6, and substantially improving the back-office management support (MIBs, SNMP, IPDR, etc.) for DOCSIS. Each of these topics will covered in much greater detail in this DOCSIS 3.0 tutorial in multiple posts yet to come.

7 10, 2009

DOCSIS Upstream – Part II

Mia Colabrese2021-08-17T13:40:53-04:00October 7th, 2009|

This article will focus more specifically on DOCSIS 3.0 issues that will occur as you are deploying DOCSIS 3.0 or post -deployment.

2 10, 2009

Speeding Upstream – Part I

Mia Colabrese2021-08-18T10:19:55-04:00October 2nd, 2009|

The first part of this article (in CT's March 2009 issue) discussed downstream potential issues, while this one focuses on the potential issues associated with upstream deployments. In particular, this article covers the critical upstream areas that one should be aware of when getting ready to deploy or already deploying DOCSIS 3.0.

2 07, 2009

DOCSIS 3.0 Tips

Mia Colabrese2020-07-02T15:51:55-04:00July 2nd, 2009|

If you have not had a chance to catch the June issue of Communications Magazine, check out the article penned by John Downey, of Cisco Systems, and I on "the critical upstream areas that one should be aware of when getting ready to deploy or already deploying DOCSIS 3.0." The shortened version of this article can be found on CT's website HERE. The full version should be made available on this blog soon.

20 04, 2009

DOCSIS and Cable Modems – How it works :: Tutorial Wrap Up

Mia Colabrese2021-08-17T13:35:17-04:00April 20th, 2009|

If you have followed the "DOCSIS and Cable Modems - How it works" tutorials this far, congratulations! You now have a basic foundation of how DOCSIS networks operate and the ability to pick up the DOCSIS specification and read and comprehend it - this is hard to do for the novice. If you are just finding this blog for the first time, then I recommend that you go to the DOCSIS Tutorial Series and start at the beginning before proceeding.

9 03, 2009

DOCSIS and Cable Modems – How it works :: Quality of Service

Mia Colabrese2021-08-17T13:22:59-04:00March 9th, 2009|

DOCSIS 1.0 enabled data over coax with a "best effort" service using a data request-grant methodology. DOCSIS 1.1 and subsequent specifications added guaranteed Quality of Service (QoS) by providing Unsolicited Grant Synchronization (UGS) which means that a cable modem does not have to send a data request in order to receive a bandwidth grant from the CMTS. The new UGS service is an enabling technology which has allowed cable operators to successfully deploy the highly revenue generating Voice-over-IP (VoIP) services. In the following sections I will illustrate the differences between best-effort (request-grant) and QoS (UGS) services.

3 03, 2009

DOCSIS and Cable Modems – How it works :: Station Maintenance

Mia Colabrese2021-08-17T15:43:18-04:00March 3rd, 2009|

While the UCD provides the language of the DOCSIS network, the Station Maintenance messaging is the proverbial "heartbeat" of the DOCSIS network. A station maintenance session consists of a Range Request sent from a cable and a Range Response sent by the CMTS. The CMTS analyzes the signal quality of the Range Request message and sends back any necessary RF adjustments in the Range Response message. This "handshake" between every cable modem and the CMTS must occur once every 30 seconds as dictated by the DOCSIS specification.