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A Guide to Data Over Cable Interface Specification and Why it Matters for Modems
Data Over Cable Service Interface Specification, or DOCSIS, is an international telecommunications standard that allows for the addition of high-bandwidth data transfer to an existing coaxial cable TV system.
This is important for Internet users and Internet providers because it allows Internet speeds to increase without having to completely replace coaxial cable networks. In an ideal world, everyone would have Fiber to the Home service. In reality, that would cost billions of dollars to make happen.
On a practical level, DOCSIS matters for consumers because you’ll have to decide which DOCSIS standard you need when purchasing a modem for your cable Internet connection. Depending on the quality of your connection, the answer isn’t necessarily just “the newest one.”
First created in March of 1997, the DOCSIS standard has been through multiple rounds of improvements and iterations since its inception. It was initially developed by CableLabs in conjunction with a multitude of contributing companies, including 3Com, ARRIS, BigBand Networks, Broadcom, Cisco, Conexant, Correlant, Harmonic, Hitron Technologies, Intel, Motorola, Netgear, Technicolor, Terayon, Time Warner Cable, and Texas Instruments.
As an overarching technology, DOCSIS includes several different pieces of actual hardware, including but not limited to a cable modem located at the user’s premises, as well as a cable modem termination system located elsewhere, usually at a cable company’s headend or hubsite. Think of these hubsites as “wells” from which all of the water (Internet connectivity) flows from, heading directly to the consumer to be consumed.
Of course, it’s a bit more complicated than that, but for the purposes of this overview, the example should suffice. In the following section, we’ll take a closer look at how the DOCSIS specification actually works in order to enable this connectivity, from both a hardware and software perspective.
There are two main components of DOCSIS: the physical (PHY) layer and the media access control (MAC) layer. The physical layer is a bit easier to understand, but each is an important part of how the overarching technology actually works to deliver you your cable connection to the Internet.
For instance, the physical layer pertains to the wiring and routing equipment used, as well as the frequency at which data is transmitted through these various physical systems. In general, faster transmission speeds means better performance, but there are a few limitations in terms of physical distance that can change this. These distance restrictions affect the areas where DOCSIS-based cable modems and other infrastructure can be installed, which in turn affects their resulting speed and price.
The MAC layer, by contrast, is designed to intelligently handle the massive amount of information being processed at any given time, allowing for a crucial level of organization that prevents frequent “traffic jams” caused by signals colliding with one another. Continuing the analogy, each device on a network has a MAC address tied to it, which acts as its own personal stoplight in a massive metropolis of other devices, all vying for access to the same information.
In this fictional “city”, the only thing standing in the way of everything falling into chaos and disorder are these MAC addresses, as well as the overarching DOCSIS network itself that supports this entire infrastructure.
Going cross-eyed yet? Obviously, we realize that this level of depth might be outside the wheelhouse of many, and to be honest, if all you’re concerned with is ensuring that you stay up to date and get the fastest speeds possible for the money, you might not need to know all of the intricacies of how this complicated system works in practice. However, understanding the basic systems underpinning the technology can help you decide what hardware and service options are right for you based on your location, lifestyle, and budgetary needs.
In the following section, we’ll look into a few other reasons why understanding at least the basic mechanisms and terms employed by DOCSIS might be a good idea overall.
If you’re reading this, you might be thinking to yourself, “Okay, this all makes sense, but why do I care about it? I just want quality internet services.” After all, something like DOCSIS doesn’t appear to affect the daily lives of cable internet users all over the world at first glance, but dig a bit deeper and you’ll discover that it is actually a very important aspect of your network setup. Why?
Simply put, depending upon what DOCSIS standard your equipment uses, you may or may not be able to take advantage of the latest internet speeds offered by your cable internet provider. In certain areas, this may not be an issue, as the speed limitations of the infrastructure may not be able take advantage of these newer technologies.
In general, there have been three different major iterations of DOCSIS over the years; 1.x, 2.x, and 3.x. The original specs, 1.0 and 1.1, had a working limit of 38 Megabits per second (Mbps) for the down speed and just 9 Mbps for the up speed. Obviously, as technology progressed throughout the next several years, there was a need to allow for cable providers to have more flexibility as their speeds improved and additional service tiers became possible. This eventually led to the creation of DOCSIS 2.0 in 2002. DOCSIS 2.0 introduced no new capacity for the down speed of a network, but it did triple the up speed, allowing for 30 Mbps connections.
The most significant changes, however, came in 2008 with the introduction to DOCSIS 3.0. This new iteration represented a departure for the format, significantly increasing both up and down speeds to 1.2 Gigabits per second (Gbps) and 200 Mbps, respectively. This was a huge leap on its own, but 3.0 also included the introduction of something referred to as channel bonding.
Channel bonding allows for the aggregation or combination of several downstream and upstream channels to deliver these much-improved speeds across the board. With channel bonding, the more channels that are present, the better, so for instance, while a 16 downstream by 4 upstream setup is fast, a 24 x 8 system can be even faster.
To put this into perspective, let’s say you’re still using a DOCSIS 2.x cable modem. In this example, you’d be limited to just one download and one upload channel. During times of peak congestion, this may slow you to a crawl, whereas with a newer 3.x channel bonding modem, you’d be able to take advantage of multiple channels, resulting in faster speeds during these heavy-use periods.
So, to recap, while you can generally still use your older 2.x equipment for most providers, you’ll be limiting yourself in terms of what top speeds you can achieve, especially during hours of peak activity in your area.
In 2016, DOCSIS 3.1 was released, bringing with it another massive leap in both up and downstream speeds. This iteration brought the cap to 10 Gbps for download speed and 1 Gbps for upload speed. Today, work is already underway to develop a new iteration, commonly referred to as DOCSIS 3.1 Full Duplex. This version, when released, will bring support for symmetrical down and up speeds of 10 Gbps, allowing upload speeds to “catch up” to down speeds for the first time since DOCSIS’ inception.
As time marches onward and the rate of technology progression only seems to accelerate, it is inevitable that DOCSIS will continue to evolve to accommodate new services, technologies, and demands from users all over the world. As informed consumers, it’s our task to stay up to date with these changes in order to determine which ones might benefit us the most. As 4K and UHD video become increasingly common, and both wireless and wired networks increase in terms of scope and convenience, it’s probably fair to assume that there are plenty of exciting developments still yet to be made to the specification over the coming decades.