A personal evaluation of AT&T's Uverse FTTN (fiber to the node)
May 2nd 2011 has arrived, all of AT&T broadband customers now have uveruse CAPs.
Many of our blog visitors reach our site as the result of a search from a search engine such as Google, Bing and others. All the search engine queries are logged by our servers and the most common search phrase (or keywords) regarding uverse other than keywords that indicate a problem is: "How does uverse work"
This entry in our blog is for people asking this particular question, if additional information is required we encourage our visitors to read our new blog or our original blog by clicking on the links to the left or by clicking the direct links to our new blog or to the original blog.
One of the most common misconceptions is that uverse is the equivalent to Verizon's FIOS and nothing can be further from the truth as comparing uverse to FIOS. So what is uverse?
The big picture:
Uverse now come in three very different flavors or versions. The third flavor (uverse ADSL2+) added at some point at the start of 2010.
- The first flavor, the flavor that everybody wants is a 100% pure fiber installation that terminates at one of the subscriber's home external walls. This version is called FTTP/FTTH fiber-to-the-premises or fiber-to-the-home and it is used only in brand new and affluent subdivisions and not in existing dwellings. AT&T doesn't say what percentage of their uverse customers are on 100% pure fiber (FTTH/FTTP) but estimates place these numbers at less than 5%.
- The second flavor, the flavor that everybody will get is called FTTN fiber-to-the-node and is fiber to a distribution device called VRAD (video ready access device) and from the VRAD to the subscriber's home using existing twisted pair copper cables... in short phone wires. The very same cable type that Alexander Graham Bell used more than 100 years ago when he first 'invented' the telephone, the very same corroded and decaying cables that everybody have in their homes today.
- The third flavor, the other flavor that everybody will get is ADSL2+. AT&T is secretly and silently pushing this version of uverse and hoping their users will not notice the difference. AT&T is promoting this new flavor under the very same uverse brand as VDSL. Uverse ADSL2+ a much lesser version of uverse FTTN (VDSL) .
A simple technical explanation:
Uverse (the FTTN version) use a system called VDSL or VDSL2 (very high speed digital subscriber line).
The radio frequency spectrum used by VDSL range from 25 KHz up to 12 MHz (uverse only use up to 8.5 MHz). The VDSL2+ specification allow frequencies up to 30 MHz but due to severe attenuation at higher frequencies, bad physical condition of the phone cables and degradation of the signal as distance increases it is unlikely that the VDSL2+ spectrum will be used by uverse.
VDSL/VDSL2+ use a modulation method called DMT (discrete multi tone) This modulation method optimizes the spectrum by dividing it in smaller channels called tones. The spacing therefore the width of each tone depends on the profile in use and can be 4.3125 KHz or 8.625 KHz wide, uverse use profile 12a with 4.3125 KHz wide tones. Profiles are pre arranged band plans designed to fit specific application requirements basically it is a form of standardization.
Each tone use a rectangular 4x4 16-QAM modulation technique that can carry a small limited amount of data. The final 'product' is the sum of all the individual tones. DMT have big advantages over QAM in that it is the perfect solution for noisy environments like in the telco telephone lines. During the VDSL modem boot up process each tone is evaluated for signal quality and interference and given a number of 'bits' depending on the carrying capacity of that particular tone. The number of bits assigned is dependent on the 16-QAM constellation ( 4 x 4 = 16 ) and the ability of that particular tone to carry data. In the case of 16-QAM the number of bits can be 0 for tone disabled (tone cannot carry data) and from 2 ~ 15 (2 being the worst and 15 the best).
The tones are grouped into distinct bands for upstream, downstream and control. The first downstream band overlaps with the ADSL's spectrum and start at 25 KHz and end at 3.75 MHz. The second band is used in upstream and start at 3.75 MHz and end at 5.2 MHz the last band is used in downstream and start at 5.2 MHz and end at 8.5MHz. Uverse use profile 12a which allows frequencies up to 12 MHz but uverse's implementation only use up to 8.5 MHz.
Error correction and buffering:
In 'traditional' services like Internet communications occasional packet loss is not a something to be concerned about, the client just requests the lost packets and the server acknowledges and retransmit the lost information. In video systems or streams lost data can cause severe service disruptions mainly in the form of pixelation and screen freezes. To mitigate this problem uverse use strict error correction schemes, mainly in the form of forward error correction (FEC) and the use of an interleaved path buffer (not to be confused with buffering explained below). The trade off is that these error correction schemes add a considerable amount of latency to the system and in severe packet loss environments not all of the lost data can always be recovered resulting in unrecoverable cyclic redundancy check errors (CRC).
For the system to recover from packet loss the lost information has to be retransmitted. Depending on the severity of the lost information and the sequential and uninterrupted nature of video streams the delay involved can be from a few seconds to tenths of seconds. To mitigate this problem Uverse FTTN use a technique called buffering. Buffering like its name suggests is a first in first out buffer (FIFO) where video data is temporarily stored prior to being displayed. This technique assures the system that there will be enough time to retransmit lost video stream information for a continuous and uninterrupted video playback. The trade off is what the subscriber is watching has a delay from a few seconds to tenths of seconds or even minutes from the original broadcast.
Distance to the VRAD. The haves and have not's:
The most important factor in uverse service quality and features is the distance from the VRAD to the subscriber's home. Distance to the VRAD can be the decisive factor for subscribers in getting 1, 2 or 3 HD video streams and 3, 6, 12, 18 or 24 Mbps Internet tiers. AT&T use these numbers to assign gateway profiles (not to confuse with Internet speed tiers) according to distance. The top gateway profile maximum distance limit is less than 2,200 ft, for the middle profile less than 3,000 ft and for the low profile less than 3,400 ft. These distance limits are by no means guaranteed and subject to many external factors such as quality of the cooper wires, interference and electrical noise environments. As a rule of thumb real world numbers are less than 1,500 ft for the top profile, less than 2,200 ft for the middle profile and up to 3,600 ft for the low profile. We like to refer to this disparity in service as the haves and have not's as not all uverse subscribers can get or receive the same homogeneous service quality across the board. In short the distance between getting the best and the middle gateway profile is only 700 feet, between the middle and the low gateway profile is 1,400 feet. All profiles are priced identically, so users on the low profile pay the same as users in the top profile.
Uverse equipment oddities:
Uverse business and advanced residential subscribers will find the equipment used in uverse installations odd and hard to work with especially when the service use static IPs. Currently AT&T use two kind of routers and gateways Motorola and 2Wire.
In uverse VDSL2 installations (you'll get this one if you order TV) the service comes with the 2Wire 3800-xxx gateway. The 2Wire is an odd and obtuse device incapable of correctly handle static IPs. Yes there are specific instructions on how to configure this gateway for static IPs but the end results are totally unsatisfactory in a business environment as the gateway is not capable of true bridged mode and the device's firewall cannot be completely disabled. Uverse subscribers looking forward to use a router behind the 2Wire gateway always end up scratching their heads and asking for ideas and support in popular bulletin boards.
If you are planning to buy the ADSL2+ modem of your choice to use with uverse you are out of luck as AT&T will not allow subscribers to use non AT&T approved equipment.
Update 2010-05-15 (yyyy-mm-dd). Yet another face of uverse:
Over the last year AT&T have introduced an new player into the uverse arena. The new player comes in the form of ADSL2+, the performance and capabilities of ADSL2+ is middle ground between ADSL and VDSL. This relatively old but newly deployed technology have the advantage of reach, the drawback of ADSL2+ is the lack of performance when compared to VDSL. ADSL2+ is capable of offering up to 24 Mbps depending on distance. AT&T is silently pushing this technology to their customers under the same uverse brand. Like uverse FTTN uverse ADSL2+ continue to use twisted copper pairs as the delivery method.
Usage based billing aka. CAPS.
Starting on May 2nd, 2011 all of AT&T Internet products will come with usage based billing aka CAPS. For u-verse the limit will be a 250 GB per month allowance. U-verse subscribers will get warning letters for the first two offences and afterward they will be hit with overuse fees of $10 per 50 GB over the limit.
If you are looking for short answers here is the compendium.
- More than 95% of AT&T's Uverse subscribers are not fiber installations. If a uverse salesperson tells you that you'll get fiber to your home and your home is not brand new and in a expensive subdivision it is probably a lie.
- VDSL/2+ is very sensitive to distance. The closer the subscriber is to the distribution device (VRAD) the better the system will work for him/her. Based in the data gathered by our tools the sweet spot is less than 1,500 ft.
- VDSL/2+ is very sensitive to interference. Thunderstorms, strong or nearby radio stations (commercial and HAM), electrical noise and other sources of interference can cause severe service disruptions.
- Due to lack of shielding copper twisted pair cables are highly vulnerable to ingress interference, RFI (radio frequency interference) and electrical noise.
- Due to strict error correction schemes used by VDSL/2+ Uverse FTTN will add a considerable amount of latency to the system. Some uverse subscribers say that the latency is around 25 ~ 30 ms more than comparable services, others have experience latency of 65 ~ 95 ms or more. It depends on who you ask but latency is definitely a significant part of Uverse FTTN the only question should be: How much?
- Depending on distance and electrical environmental conditions potential uverse subscribers can now be placed in the much lesser uverse ADSL2+ version without even knowing it. The price for the much lesser uverse ADSL2+ service? The same.
- Overuse CAPS of 250 GB per month.
We reiterate, if you want to learn more about uverse FTTN problems and history read our old or new uverse blogs.