Monday, March 02, 2009

FTTH beats DOCSIS beats VDSL

Comparisons of FTTH and DOCSIS usually aren't very thorough. So I got some industry intel to help me better understand the differences. Here's a first shot at providing a better comparison.

The conclusion could be that FTTH is superior, but upgraded HFC networks will go a long way. Telco incumbents have a choice: sweat the copper plant (some running into a huge problem because VDSL doesn't handle analogue TV very well); or leapfrog cable and swallow the capex pill.

Shared bandwidth
Fiber guys usually point to the fact that cable is a shared medium. Well, alas, all networks are shared. The real question is: how much bandwidth is shared among how many subscribers? Verizon answered that question recently for its FiOS network. And that's 'just' a PON network! In other words, fiber beats cable, but it is shared as well.

Symmetrical speeds
Fiber guys also tout the fact that FTTH enables symmetrical connections, and the cable guy usually retorts that DOCSIS can do that too. I'm not sure how it is in other countries, but in the Netherlands the fiber guy is 'more right' than the cable guy. Coaxial networks offer a full spectrum of some 862 MHz, which would deliver several Gb/s if it was all used for broadband (DOCSIS). Alas, most is reserved for cable TV (see below: cable TV v. IPTV). Moreover, only the bottom 60 MHz is reserved for upstream, and so upload speeds are constricted.
Even if cable operators decided to go symmetrical, it would require a large capex and opex bill. Moreover, symmetrical gear is hardly available.
Further, a quick calculation, assuming 30 TV channels (occupying 8 MHz each) leaves the equivalent of some 45 channels for DOCSIS, or around 1.8 Gb/s (shared!).

Cable TV v. IPTV
Cable TV is like pushing all TV channels all the time onto the subscriber's premises. Copper could never handle anything like that, so IPTV was invented, delivering only the channel that is being watched. It is a complicated technology and certainly in the Netherlands, analogue TV (the standard line-up of some 30 channels) sells particularly well because it doesn't require any STBs. The signal can easily be split by the subscriber, usually even without an amplifier, to service multiple TV sets in the home. Digital TV needs an STB, which is a major inhibitor in box-fobic countries such as the Netherlands. (It must be said however that people are getting used to them, because cable, DTT (Digitenne) and sat TV push them to consumers. Still, each TV set needs one, and usualy they are not all free.)
Further, cable has SDV technology to mimic IPTV, and free-up spectrum, but it looks like analogue TV is a must-have for cable, even if it were just for the profit: the total rights bill is some 2 EUR/mo/sub, whereas the retail price is around 15 EUR/mo/sub. Which is interesting for several reasons: 1. cable operators are saying that they want to switch it off; 2. Opta is preparing regulation for open access to cable TV; and 3. FTTH-networks have learned that they need to offer analogue TV (over a separate fiber!) to stand a chance of winning subscribers.

Apparently, both FTTH and DOCSIS score verry well, normally, even if FTTH is a little better (c. 1 ms).

Loop length
FTTH will work over 10 km without needing any equipment, whereas a cable network requires an amplifier no further than just 100 meters away from the subscriber. However, cable networks have had their VDSL-like upgrade long ago, pushing fiber quite deep into the networks. In the Netherlands: from Headend to Distribution Nodes and further down to the Fiber Nodes. From there coaxial cable takes over, first to a Group Amplifier, and (via a handful of amplifiers) on to a Final Amplifier and then to the subscriber's homes. On average, some 1500 homes are connected to a Fiber Node (over coax and 5-7 amplifiers).

The farther fiber is pushed, the farther weigh the benefits. FTTH is superior in that sense (see before: Loop length). The optical signal is only converted to an electrical signal in the subscriber's home. That's nice for FTTH operators, reducing their electric bill, but naturally it adds to the subscriber's electricity bill. Also, the overall electric bill is higher in FTTH networks for being less centralised.

Despite the electricity savings, opex differences apparently are small for FTTH and cable/DOCSIS. Take a look at this document.

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