When I first began using the Internet, I used a dialup modem to connect and still remember the nice noise the modem made when establishing a connection. That was over 16 years ago, but for the past 14 years I have been using a broadband Internet connection through my cable provider. Over the years I have seen my Internet connection speeds increase for both download and upload. Recently I have been contemplating switching Internet providers – mainly because of price – and have begun researching cable modems.
The one thing that I have learned about cable Internet is the connectivity standard that is used by cable companies when it comes to offering Internet service. This standard is called the “Data Over Cable Service Interface Specification”, or more popularly known as DOCSIS. As I am at times, I became curious as to this specification and began doing some basic research.
Brief History of DOCSIS
When cable companies began offering broadband Internet connectivity there was an issue. This issue was that each cable company had their own proprietary connection, meaning that when someone signed up for Internet service from one cable company, they would use a modem that would only work for that cable company.
As with most things that are proprietary, Internet connections became expensive since each cable company needed to use a modem that was able to connect to their proprietary connection. In order to keep costs down, an Internet connection specification needed to be adopted by the cable companies.
CableLabs
In 1988, a not-for-profit consortium of cable television companies founded Cable Television Laboratories, Inc., which is usually shortened to CableLabs. Any cable system operator from around the world can become a member of CableLabs.
One of the mandates for CableLabs is to conduct research and development for new cable telecommunications technologies that help cable operators use the technical advancements into their business.
One of these technologies was the creation of the DOCSIS specification that is used by the CableLabs members as a means for providing Internet connectivity.
DOCSIS
CableLabs currently as released four versions of DOCSIS, with each version being backward compatible with all the previous versions. This means that a version 3.0 cable modem will be able to work with a version 2.0 Internet connection. If you use a version 2.0 (maximum downstream through of 37 Mbit/s) modem on a network that supports version 3.0, you will be limited by the speed of the modem, even if your ISP provides 50 Mbits/s.
Note:
Downstream is the transfer of data to the subscriber (user), while upstream is the data being transferred from the subscriber.
Version 1.0
The first version of DOCSIS was released in March 1997. This version provided basic connectivity support. In order to control the download and upload speeds for the customers of cable companies, this version provided support to limit a customer’s data rate.
Version 1.1
Released in April 1999, version 1.1 added full standardization for Internet connectivity by cable operators. Quality of service (QoS) capabilities were also added.
The maximum throughput for version 1.1 was 38 Mbits/s downstream and 9 Mbits/s upstream.
Version 2.0
The biggest difference between version 2.0, which was released in December 2001, and its predecessors was the increase in upstream throughput. With this version of DOCSIS, the maximum upstream throughput was 27 Mbits/s. The downstream throughput remained unchanged at 38 Mbits/s.
Another change, through a firmware update, was that this version also supports Internet Protocol version 6 (IPv6), which is important as version 6 Internet addresses begin to appear.
Version 3.0
While only the upload throughput increased with version 2.0, both downstream and upstream throughput dramatically increased with version 3.0.
All previous versions used one channel for downstream and one channel for upstream, the version 3.0 specification specified that a device supporting this specification must support a minimum of 4 channels for both downstream and upstream channels.
Each downstream channel can transfer data at a rate of 38 Mbits/s, which makes for a total downstream rate of 152 Mbits/s (4 times 38 Mbits/s). For upstream, the data rate for each channel is 27 Mbits/s for a total data rate of 108 MBits/s (4 times 27 Mbits/s).
In order for modems to achieve even faster speeds, it must support more channels.
In addition to the additional channels for transferring data, version 3.0 also introduced support for Internet Protocol version 6 (IPv6).
EuroDOCSIS
There is a European consortium called EuroCableLabs that certifies devices for use with cable networks in Europe using their specification called EuroDOCSIS. EuroDOCSIS is essentially the DOCSIS standards that have been adapted for Europe. The biggest difference between DOCSIS and EuroDOCSIS is the throughput speeds.
Version 1.x
The downstream maximum throughput for version 1.x is 50 Mbits/s while the upstream throughput is 9 Mbits/s.
Version 2.0
The downstream maximum throughput for version 1.x is 50 Mbits/s while the upstream throughput is 27 Mbits/s.
Version 3.0
With the additional channels support in version 3.0, the minimum downstream rate is 200 Mbits/s (4 times 50 Mbits/s). The minimum upstream throughput is 108 Mbits/s (4 times 27 Mbits/s).
In terms of modems, I recommend that if you are looking to purchase your own cable modem, you should buy one that is at least DOCSIS version 2.0 certified. If your Internet package is faster than 38 Mbits/s second, you should purchase a DOCSIS version 3 modem to handle the faster data rates. Most cable modems are about $50-$100, so they aren’t too expensive.
While many cable companies do rent modems, usually about $5/month, if you plan on staying with a company for a few years it could be more cost effective to spend the $100 and buy a modem.