Hyperconnectivity: October 2009 Archives
In addition, whatever the type of the NGA network architecture that will benefit from State aid, it should support effective and full unbundling and satisfy all different types of network access that operators may seek (including but not limited to access to ducts, fibre and bitstream). In this respect it should be noted that "multiple fibre" architecture allows full independence between access seekers to provide high-speed broadband offers and is therefore conducive to long-term sustainable competition. In addition, the deployment of NGA networks based on multiple fibre lines supports both "point-to-point" and "pointto-multipoint" topologies and is therefore technology neutral. [ bold added later ]
Since 2008 I have been presenting the view that topology matters. You can build a topology that is specific for a technology, or design one that can support many technologies. A technology neutral topology. See the image below for an explanation.
"In our approach, every premise is "home-runned" to a "fiber aggregation point (FAP) " which is an actual building--with power, HVAC, light, security etc. Anything up to 4000 or so subs. can home in on one such FAP, or "remote hub"....(which are trunkedback to the main hub--and to each other--using carrier grade 10G/40G-E systems). All electronics are in the FAPs--where they can be both easily maintained/repaired AND replaced--incrementally or entirely, as desired. You can patch past the splitters and provide mega-circuits if you want to (dedicated Terrabit circuit, anyone?). You can replace specific customer OLT's with something else (later vintage PON, customized active elements etc)--in small batches or all at once. In fact, you can do most anything you want--including change out the whole system. You can do all these things without ever touching the main infrastructure and main cost item--the fiber distribution network itself. The fact that there are NO stategic (let alone active) components in the field not only greatly improves maintenance (ease and cost) but also increases the ease and efficiency of upgrading/changing/migrating AND inserting other signals should that be desired."
The Guidelines as published by the EC show that this very significant insight has been understood and adopted in Brussels.
The Internet access specifications for residential cable-internet-access and ADSL-internet-access are always asymmetrical: the downloadspeed is larger (much larger) than the uploadspeed. Internet access over fiber shows higher speeds and quite often (but not always) the same assymetry where the download is much faster than the upload.
A lot of people wonder why. What is the driver for this difference? Technology? Costs? Marketing? Based upon a recent discussion between experts I have tried to summarize the geeky details.
We have to keep in mind that Internet access was piggybacked upon networks designed for quite different purposes: cable for distributing TV-channels, copper network for telephony. So the engineers charged with creating Internet access had to work with what they got.
The key engineering issues involved in creating Internet access over these lines are attenuation, noise and cost of equipment.
Attenuation is the weakening of signal strength as you get farther away from the source. If the strength of a signal starts to drop to the same level as the noise on the line you start to lose information carrying capacity (down to zero: no information). If you send information over a cable/telephone wire/fiber the signal strength weakens with the distance travelled.
The rule of thumb is: higher frequencies weaken earlier than low frequencies ( compare it to driving to a band playing on a festival ground: you hear the base player from far, the high notes only when you are close).
The second rule-of-thumb is: the higher the frequency you can carry over a wire over a distance, the more information (bandwidth) you can send per second.
Telephone wires are difficult to work with: high frequencies weaken very fast with distance. Coaxial cable is much better (that's why Siemens invented it : transatlantic telegraphs through normal wires was terrible) but anything over 1 Ghz weakens very fast. Fiber is way, way better (a million times better), you easily get 40-50 miles at extremely high frequencies before you have to repeat the signal. (Wireless behaves more or less the same and at the same time different: the signal weakens with distance but the sensitivity to anything inbetween you and the sending antenna is very dependent on the (carrier)frequency used.).
Fiber (again) has much less problems: it does not send anything, does not pick up anything. (But bad engineering, construction or maintenance can reduce its capabilities).
A lot of extremely clever engineering has been thrown at the problem to maximize the use any bit of untainted bandwidth/spectrum, but you cannot defy the laws of physics.
So VDSL was introduced: reduce the wire length to a couple of hundred meters so you can use higher frequencies (which would weaken too much otherwise) and gain bandwidth. The problem of not being able to predict the noise and crosstalk levels remains, so the predictability of the preformance is not good. Again the design choice in VDSL washow to split the available bandwidth. You can go for symmetric if you want to, but 40 Mbps down and 10 Mbps up advertises better than 25/25.
As the medium is shared by users (couple of hundred on one coax cable as a rule) you share the available bandwidth.
The standard upstream channel is limited in bandwidth and placed at the low end: again with a "content consumer" frame of mind and the objective to reduce the sensitivity for noise. Most hybrid fiber coax networks have not been designed for more upload capacity to begin with. Modyfiing the hardware is required as a start.You could also change the allocation of capacity in a spectrum (quite an effort but doable) or split up the coax network more so you end up with less shared users (messy, means digging and investing in hardware).
Again: physics and historical engineering choices have biased the access network towards asymmetrical bandwidth.
There might be a commercial reason not to offer symmetry. If you are a telco who has been serving high-end business customers with dedicated fiber lines, you have a problem explaining the difference in price between what they charge now and the consumer FttH offerings.
There is a reason why the business lines are/have been much more expensive (as a start: a dedicated dig is terribly expensive compared an FttH roll-out spreading all costs over many users) but it is a very difficult sell. An asymmetric offer makes the explaining a bit easier.





















