DOCSIS 3.0 Tutorial – Introduction

DOCSIS 3.0 Gets Fast

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.

First and foremost, DOCSIS 3.o is most recognized for its dramatic downstream and upstream IP data throughput capabilities.  Typically these are four times those that DOCSIS 2.0 can support in the downstream / upstream and 12 times what DOCSIS 1.x can support in the upstream.  Without getting into the details yet, this is accomplished by using a rather simple concept called “channel bonding”.  In DOCSIS 1.x and 2.0, the CMTS transmits data to cable modems using one downstream QAM RF upconverted channel (“DS channels” for short).  The DOCSIS 3.0 specification has developed some unique methods to allow new CMTS architectures to communicate with DOCSIS 3.o modems using four DS channels.  So if a 256-QAM channel can transport 38 Mbps, then four 256-QAM bonded channels can transport 152 Mbps.  Similarly, DOCSIS 1.x/2.0 cable modems transmit data to the CMTS using one upstream RF channel using a number of different digital modulation schemes in a TDMA (or S-CDMA) format.  In DOCSIS 3.0, the specification allows for up to four upstream channels to be bonded together.

The following table shows the speed increases that can be expected for the downstream and upstream in both DOCSIS and Euro-DOCSIS systems when channel bonding is used in a DOCSIS 3.0 system.

DOCSIS 3.0 Speed Comparison

Note that this chart also shows a DOCSIS 3.o downstream with “(8 channels)” bonded, yielding a data throughput of 343.04 Mbps.  When I stated channel bonding allowed four DS channels to be bonded, that indicated this was just a minimum.  Broadcom, one of the chipset vendors that makes cable modem chipsets, currently has a chipset solution which supports eight bonded downstreams.  Many cable operators are looking at using more than four bonded downstream channels.  Either to have the ability to provide more data bandwidth to the end user or to provide both data and MPEG/IPTV set top box capabilities in the same chipset solution.  It is important to understand this capability of the DOCSIS standard, the CMTS, the home (premise) equipment and potentially the test equipment used for installation, all of which will be covered later.

Summary

DOCSIS 3.0 offers tremendous capabilities over previous revisions to the specification.  The drivers for the new specification have been part do to new data intensive applications, but much more as a response to competitive threats such as Verizon’s FIoS and AT&T’s U-Verse.  DOCSIS 3.0 does offer much more than just speed, such as a distributable architecture, enhanced security, support for IPv6, enhanced back office management support and much more.  DOCSIS 3.0 does require a fork-lift upgrade if existing headend equipment is very old, however some vendors have migration paths for their carrier class platforms such as Cisco’s ubr10k, Motorola’s BSR 64k and Arris’ C4 CMTSs.  In either case, the future (at least for the next five years) is DOCSIS 3.0 and there are significant business cases to justify the investment in migrating to the new technology.