Path to Gigabit Cable Systems

UHDTV_resolution_chartI saw an article yesterday where Pat Essex, the president of Cox talked about offering gigabit cable modem speeds to customers later this year. This conflicts with what the Cox CTO told Fierce Cable, and who said that the company has a five-year plan to free up enough bandwidth on their systems to be able to fully implement such a conversion. I think the CTO has it right. Perhaps later this year Cox might find a way to offer a gigabit to a handful of customers as a press release opportunity.

The article estimated that it would take ‘hundreds of millions’ for Cox to make this upgrade. What sorts of changes will Cox have to make on their networks to have speeds this fast? They will have to do most or all of the following network upgrades:
• Convert everything to digital. One of the biggest upgrades that benefit a cable network is to get rid of all analog channels. Analog channels can transmit only one TV channel in a 6 MHz slot, but once converted to digital you can fit as many as twelve channels in the same slot. Cox is probably mostly digital now, but anywhere they are not would need to finish this conversion.
• Convert to all MPEG4. MPEG4 is a compression scheme and it is the most efficient way to squeeze a cable channel into the least amount of bandwidth. A lot of channels are still delivered in an older compression technology called MPEG2. The big cost of making this kind of conversion is that any settop boxes that still can’t receive MPEG4 would have to be replaced.
• Split Nodes. A node is the number of customers in a geographic area that share the network. This is important when talking about data speeds, because whatever speeds is delivered to the node is then shared with all of the customers on that node. Passive fiber-to-the-home networks have nodes that are no greater than 32 homes. Active Ethernet fiber networks effectively have a node size of one home. But cable systems normally have nodes around 200 – 250 homes. Cable companies have to build more fiber to get closer to homes to get the node sizes smaller and closer in size to what fiber can deliver.
• Upgrade to DOCSIS 3.1. DOCSIS is the acronym for the technology that operates the cable modem network. This new standard was just released in October 2013. The standard lays forth a technology that will support capacities of 10 Gigabits downstream and 1 Gigabit upstream using 4096 QAM, if all of the capacity is used for data. The DOCSIS 3.1 specification does away with 6 MHz and 8 MHz wide channel spacing and instead use smaller (20 kHz to 50 kHz wide) orthogonal frequency division multiplexing (OFDM) subcarriers; these smaller pieces of spectrum can then be bonded together to create one large data path that could end using multiple 200 MHz wide frequency paths.

The new standard is expected to be fully deployable by 2016, so I don’t quite understand the timing mentioned by Cox. The biggest issue with deploying DOCSIS 3.1 is that unless you change every cable modem to be DOCSIS 3.1 compatible you will need to have enough system bandwidth to operate both the new and old cable modems side-by-side using two sets of network bandwidth. There is no sensible logistical path to flash-cut from one to the other and so cable networks will have to operate two large swaths of data simultaneously.
• Upgrade the whole network. In order for a network to have enough bandwidth to make the conversion it will have to be at least 1,000 MHz, and possibly larger. Today many cable networks are smaller than this and there is a lot of work needed to make such an upgrade that includes such things as changing taps and repeaters throughout the network, and even in some cases replacing the coaxial cable and many of the drops.

These changes can all be made. Each of these are major upgrades and require a lot of changes in the network. There are parts of the cable plant that will need to be rebuilt. Fiber must be built. Settop boxes and cable modems all have to be swapped. There are major electronics upgrades needed.

But one thing that this upgrade path doesn’t consider is that there is still an ever-increasing need to add more channels to a cable system. Cable customers want more and more HD channels which are much larger than standard channels. And now we are looking at the threat of having to offer super HD channels using 4K which are many times larger than today’s HD channels. At the end of the day there is only so much bandwidth in a cable network. Cable network engineers spend all of their time making tradeoffs between programming and cable modem bandwidth and it’s a challenging job. Do I think Cox can eventually offer gigabit service to everybody and not just to a small number of people for the press releases? Yes, but they have a whole lot of work to do and a whole lot of money to spend first.

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