Versions Compared


  • This line was added.
  • This line was removed.
  • Formatting was changed.
Table of Contents

Physical Layer

  1. Weather Based Interference.
    1. Cable companies that are Internet Service Providers (ISP)s don’t want to talk about it, but events like drop wires swinging in the wind can affect a cable modem connection.
  2. Aged Infrastructure.
    1. Deployment of coaxial copper wires are aged, similar to the telephone copper wires. 
      1. Some coaxial networks were built in the 1970s.
    2. Coaxial cable networks exhibit signs of aging sooner than telephone copper networks because the wires act like a huge antenna, and older networks attract so much interference and noise that it become harder to transmit the signals through the wires.
  3. Distance Limitation.
    1. Unamplified signals are not generally transmitted more than about two and a half miles over a coaxial network from a network node.
      1. This limitation is based mainly on the number of amplifiers needed on a single coax distribution route.
      2. Amplifiers are needed to boost the signal strength for coaxial distribution over a few thousand feet.
      3. Modern cable companies try to limit the number of amplifiers on a coaxial route to five or less since adding amplifiers generally reduces broadband speeds.

Upstream Bandwidth

  1. Electromagnetic Interference.
    1. In the past consumers only required sufficient download bandwidth, but not all bandwidth is the same.
    2. The upload bandwidth uses the worst spectrum inside the cable network – it uses the frequency that is most susceptible to interference.
      1. Most cable systems deploy upload broadband using the frequencies on the cable system between 5 megahertz (MHz) and 42 MHz.
        1. This represents a relatively small amount of bandwidth and it also sits at the noisiest part of cable TV frequency.
      2. Cable broadband networks are also susceptible to radio interference – a subscriber's connection will be degraded when somebody is operating a blender or microwave oven.
        1. Recall the days of analog broadcast TV and analog cable systems when somebody running a blender or a microwave would disrupt the signals on channels 2 through 5.
      3. An interference-laden 10 megabits per second (Mbps) upload stream is not going to deliver a reliable 10 Mbps connection. 
  2. Spectrum Allocation.
    1. The DOCSIS 3.0 specification assigned upload broadband to the worst part of the spectrum.
      1. Before the COVID-19 pandemic almost nobody cared about upload broadband speeds.
        1. The upload link was mostly used to send out attachments to emails or backup data on a computer into the cloud.
          1. Tended to be more for temporary and non-critical tasks – it did not matter to most folks if a file was uploaded in ten seconds or five minutes.
      2. All of the critical new uses for Internet access require a steady and dedicated upload data stream.
        1. School servers, work servers, telemedicine, and to sit on video conferencing services such as Zoom.
        2. The new upload applications can not tolerate a "best efforts" level of service, especially if using Virtual Private Network (VPN) software which is typically required to access corporate networks.
          1. What this means is that a connection to a virtual classroom either works or it does not work.
          2. If the connection hiccups then the user loses the connection, and is "booted" out of the video conferencing session.

Data Over Cable Service Interface Specification (DOCSIS)

  1. The DOCSIS 3.0 and 3.1 standards do not allow for symmetrical data speeds, meaning that download speeds are generally much faster than the upload speeds.
    1. No more than an eighth of the bandwidth can be used for upload.
  2. DOCSIS 3.0 allows bonding together enough channels to create broadband speeds as fast as about 250 Mbps download.
    1. In a digital conversion, a cable company compresses video signals and puts multiple channels into a slot that historically carried only one analog channel.
      1. This is why over-the-air (OTA) high definition television (HDTV) and over the top (OTT) content delivered via the Internet has a superior signal (as evidenced by picture quality) in comparison to video delivered via cable video programming.
  3. DOCSIS 3.1 theoretically allows all of the channels on the network to be used for data and which can produce broadband speeds as fast as 8–10 Gbps if a network carried only broadband and had zero television channels.
    1. Since there are still a lot of TV channels on a cable network, most cable companies have increased the maximum broadband speeds to between 500 Mbps and 1 gigabit per second (Gbps) using DOCSIS 3.1.
  4. DOCSIS 4.0 will allow for symmetrical gigabit data speeds.
    1. This will require even more empty channel slots on a cable network and the new standard assumes that the cable companies will increase total system bandwidth of the network to at least 1.2 gigahertz (GHz) of bandwidth.
    2. The gear needed to upgrade to DOCSIS 4.0 will not hit the market for at least two or three years.
      1. Most of the big cable companies have already said they are not interested in upgrading immediately to the new standards since the upgrades are expensive.
    3. Cable companies will ultimately face a big decision, because if they are going to upgrade to DOCSIS 4.0 they also might instead consider the leap to fiber.
      1. Most analysts think that upgrade is likely decades away, but most think that cable companies will eventually migrate to fiber.
    4. Cable companies strive to minimize capital costs and are likely to milk the current networks for as long as possible, to the detriment of the Internet experience of the end-user.
  5. Fiber.
    1. Cable companies are only going to able to provide speeds above 1 Gbps by implementing another round of expensive upgrades.
      1. There is a lot of speculation in the industry that cable companies would upgrade to fiber-to-the-home (FTTH) rather than make such an upgrade.
        1. If large cable providers ever decide that fiber is its future, major metropolitan markets will be upgraded long before secondary markets.
    2. Only 100% fiber networks allow for symmetrical download and upload speeds.
      1. Fiber networks transmit using light instead of electrical signals, and therefore, not subject to interference.

Content derived from:  "Feasibility Report for a Community Network - Falmouth, MA" | Douglas Dawson, Owner, CCG Consulting (posted )

Read more:  "The Case for Fiber to the Home, Today: Why Fiber is a Superior Medium for 21st Century Broadband" | Electronic Frontier Foundation (posted )