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U-Verse Technical documentation


U-Verse Technical documentation

I have U-verse, TV, Internet and phones. This is all entering my home via a system of copper twisted pairs that was buried some 50 years ago when the area was first developed. Having some 60 years experience in communications electronics (retired electrical engineer) I am having some difficulty grasping how you guys fit all that stuff onto a pair of copper wires that were buried back in the day when 75 baud data was considered state of the art.  Is there a book, or a place on the internet, that will provide some technical background on this? Specific data, not the type of stuff that Customer Service folks feed to the non-technical citizenry.  Thank you.

(I asked this a week or so ago but never got a response...)

Message 1 of 20

Accepted Solutions

Re: U-Verse Technical documentation

U-verse is fiber optics.


This is my own over simplified non technical explanation. Others feel free to give a more technical explanation.


Depending on where you live it might be fiber optics all the way to where it enters your home (typically new construction)  called FTTH or fiber-to-the-home) or more commonly the fiber optics part stops at your local VRAD and your TV/Intenet/Phone travels over copper wire the rest of the way in a loop to the VRAD, a video ready access device.


Unlike traditional all copper cable buried in the ground or on overhead wires, a TV connected to such a fiber optics network doesn't receive all your provider is sending "down the pipe" but waits till you select something on your STB then that signal goes to the VRAD and sends your requested channel along with 3 others back to you. Probably why right now why multiview is limited to just 4 channels.


The first link goes into some length how fiber optics works, the second is a short Youtube video that also explains it without getting to technical. I'm sure there's more detailed technical stuff on the web somewhere, perhaps somebody will share if they came across it. I haven't exactly been looking.

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Message 2 of 20
ACE - Expert

Re: U-Verse Technical documentation

billy-xwow did a pretty good job of explaining, I'd just touch on a few points:


1) Fiber to the home is usually abbreviated FTTP (Fiber to the Premises), though I admit FTTH seems better.


2) Sending the fiber to a central device then distributing via copper is called FTTN (fiber to the node).


3) Because of the shorter runs, higher frequencies can be used than when the signal comes all the way from the Central Office.


4) However, just to confuse everyone, AT&T introduced a few years ago a new version of Internet service under the U-verse brand.  It still usually comes from the CO (like old ADSL), can be (but rarely is) FTTN, but uses ADSL2+ (instead of the newer, higher bandwidth VDSL2 used in the original U-verse service).  This service can be combined with voice, but never with TV.  It can be deployed to subscribers a longer distance from the fiber endpoint.


*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
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Message 3 of 20

Re: U-Verse Technical documentation

For an electrical-engineering perspective on what's going on with the copper lines, have a look at the following:

The technology being used to transmit data on the copper wire is VDSL (very high rate digital subscriber line).

VDSL is a protocol that defines the framing, signaling, and manner that digital information is transmitted from one node to another. All VDSL cares about is getting a digital bitstream from point A to point B in an error-free manner. Interpretation of that bitstream is then done using a higher level protocol, like Ethernet framing (layer 2), and IP packets (layer 3).

The U-Verse services (voice over IP, IPTV, and Internet) are all in IP packets, which are encapsulated in Ethernet frames, and then transmitted via VDSL.

At the lowest level, VDSL is modulating the information onto the copper wires using the modulation scheme known as Orthogonal Frequency Division Multiplexing (OFDM):

OFDM, with appropriate error correction, can transmit information on the wires with very high bitrates comparable to the bandwidth, and in the presence of noise and signal faults. The bitrate can come within a few dB of the Shannon Limit:

The achievable bitrate of the line with an arbitrarily low probability of error is a function of the bandwidth of the line and the signal-to-noise ratio. This is given by the Shannon-Hartley theorem:

For example, for a typical VDSL subscriber line with 6 MHz of bandwidth and an average signal-to-noise ratio of 25 dB, the achievable line bitrate could be as high as:

C = B * log2 (1+ S/N)

where B is the channel bandwidth in Hz, S/N is the linear power ratio of signal to noise, and C is the achievable channel bitrate:

C = (6 MHz) * log2 (1+ (10^(25 / 10)))
C = 49.8 Mbps

Contrast this with an older transmission method: NTSC television. NTSC signals also used a 6 MHz channel, but used analog signals (amplitude modulation). Today, with modern compression techniques, an SD TV signal can be transmitted in approximately the same quality as an NTSC signal using only about 2 Mbps of bandwidth. Thus we see an approximately 25x increase in bandwidth efficiency due to the modulation scheme:

NTSC: 2 Mbps of data in 6 MHz.
OFDM: 50 Mbps of data in 6 MHz.

As modulation techniques get more complex and approach the Shannon limit, the required error correction code gets more and more complex. Error correcting codes (formally known as Forward Error Correction, or FEC) are one of several methods of encoding digital data such that if errors occur during transmission, the correct digital data can be reconstructed at the receiver's end without the data having to be retransmitted. Nearly all digital transmission methods used today use some form of FEC:

A simple FEC code might be a repetition code: Transmit each bit 3 times, one right after the other. Any single-bit error can then be corrected, by allowing 2 out of the 3 bits to "out-vote" the incorrect bit.

I don't know the exact FEC code being used with the OFDM in U-Verse's VDSL, but I suspect it's a typical concatenated code, using a convolutional code as the inner code, and a Reed-Solomon code as the outer code. This is very similar to the FEC code used on CDs and DVDs.

If you have any other questions, post here, I'll try to answer.

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Message 5 of 20
ACE - Expert

Re: U-Verse Technical documentation

rchadwic - I could be wrong, but I think of the STB (Set Top Box) communicating with a server at some distant location. The connection through the RG (Residential Gateway) to the VRAD back to the server is a pipe, making no decisions/selections. The STB tells the server what channel to select. The server applies that channel to packets sent to the IP address of the STB. Any compression takes place at the server or upstream at the content provider.

You can look into the details of the type of signal used for this communication. And, there may be software to reuse common channels for efficient distribution.  The communcation magic takes place at the IP level.

So, there are two answers to your number of channels question -

At&t can support as many channels as they create unique numbers for - currently 10,000. Since the comm pipe does not carry every channel, it is not a limiting factor.

How many channels can a house receive at the same time? - Four. There was a brief deployment of seven. But, they can be any four/seven of the 10,000 available. This seems adequate for most families and inadequate for some.

*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
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Message 9 of 20

Re: U-Verse Technical documentation

rchadwic wrote:


Third... Can I presume that the video data between the VRAD and the STB is in one of the MPEG formats? I had some dealing with this before I retired from Harris Corp a couple years ago; may have to go hat-in-hand back there and ask to borrow a couple textbooks....


Hi rchadwic,


Yes, the system works like this:


  • Video (from an analog or digital source) is encoded at the head end.  The national channels are encoded at one central location, and your local channels are encoded in a separate location near your city.
  • The encoders being used are the Motorola SE-5100 and SE-5150.
  • The output format for video is MPEG-4 AVC (H.264), using a bitrate of approximately 1.8 Mbps for SD video, and approximately 5.7 Mbps for HD video.
  • The H.264 video is combined with the audio (encoded using E-AC3, also known as Dolby Digital Plus), secondary audio (if any), and closed captions into an MPEG-2 transport stream.  This is the same stream format used in DVB systems (mostly used in Europe), on Blu-Ray discs, and in many HD camcorders.
  • The MPEG-2 transport stream is then encrypted for conditional access, and then encapsulated in both IP multicast and IP unicast packets for transmission over the network.


When you change channels on a set-top-box unit, the STB sends out two requests on the network.  First, it sends a request for an IP unicast transmission of the channel.  The unicast transmission begins coming to the STB unit within about 1/4 second, which is what gives U-Verse it's fast channel changes compared to cable or satellite.  The STB also sends out an IP multicast group join request to the next upstream router (your residential gateway), which forwards that join request to all upstream routers.  Within a few seconds, the IP multicast stream of the same channel begins coming into your house and gets received and decrypted by the STB.


The multicast stream is ahead of the unicast stream by about 3-5 seconds, so the STB buffers the multicast stream internally in memory (and also buffers it on the hard disk so that you can get FF/REW on the DVR unit and the STB units via whole-home-DVR).  It then seamlessly switches your viewing from the unbuffered unicast stream to the buffered multicast stream about 10-15 seconds after you changed the channel, and then drops the unicast stream.


You'll notice that immediately after you change channels, the trick play (FF/REW) functions are not available.  The STB doesn't enable those until the shift to the multicast stream is completed.


The system has several advantages:


  • Only the streams you're actively watching need to be sent to your house.  Thus, U-Verse is unconstrained in the number of channels that they can carry.  The only constraint on the system is the bandwidth available between your house and the main U-Verse network, which affects how many different channels can be watched simultaneously.
  • Conditional access for the viewing is very secure, because decisions regarding conditional access and sending of the stream occur in the AT&T facilities, not in the set-top-box.  This virtually eliminates piracy like older cable and satellite systems used to suffer from.
  • The set-top-box inherently has features available that many other products cannot implement or are difficult to implement because by nature it's connected to an IP network.  Whole-home-DVR is a prime example.


The VRAD box near your neighborhood is actually kind of a dumb device.  It's main purpose is a media changer, changing from 10 Gb ethernet delivered by fiber over to VDSL delivered on copper.  It has no routing functions, and doesn't participate in the multicast group joins/leaves.  The next upstream router on the network beyond the residential gateway is in the AT&T central office.



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Message 11 of 20

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ACE - Expert

Re: U-Verse Technical documentation

sandyc954 wrote:
Just a nit pock- CWA is Communicatio Workers of America, which encompasses the many variamts of supplying communications. Copper wire to coaxial cables to Fiber Opticd, to whatever the next technolgies, including the wireless edge to 4G LTE
to 5, 6, 7 etc. G, analog to digital multiplexing, fiber rings on and on and on Smiley Happy

Not sure what you're trying to say.  Communication Workers of America (CWA) is a union that covers many AT&T technical employees, as well as those of other Telephone companies.


*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 16 of 20

Re: U-Verse Technical documentation

JefferMC, the poster was nit picking on a post I had copied from a different website on some acronyms used where CWA was referred to as Cable instead of correct Communication. My fault for not proofing more accurately.
Employee Contributor*
*I am an AT&T employee and the postings on this site are my own and don't necessarily represent AT&T's position, strategies or opinions.
Message 17 of 20

Re: U-Verse Technical documentation

The reply function is lacking, it is understandable that there was confusion. I should have said to whom and what I was responding.
Perhaps the site gurus can make it automatic like some community boards do?
Sorry for nitpicking and all the typos frim my tiny keyed iPhone.
Message 18 of 20
ACE - Expert

Re: U-Verse Technical documentation

sandyc954 wrote:
The reply function is lacking, it is understandable that there was confusion. I should have said to whom and what I was responding.
Perhaps the site gurus can make it automatic like some community boards do?
Sorry for nitpicking and all the typos frim my tiny keyed iPhone.

Ah... the interface is quite different between the mobile site and the full PC site.  You do lose the ability to quote.  Even on the PC interface, the non-linear reading listing drives me crazy and I enable it only in desperation when trying to sort through whose reply goes to where.


*The views and opinions expressed on this forum are purely my own. Any product claim, statistic, quote, or other representation about a product or service should be verified with the manufacturer, provider, or party.
Message 19 of 20

Re: U-Verse Technical documentation

U-verse technician are a joke. They have been coming to install my services for two weeks. They keep reporting in the system that they have been to my house or called and left voice messages but that is not the truth. I've missed a total of 16 hours from work trying to have services installed but that is not the case. I have been told by several respresentatives that I am a valued customer yet I have been treated like an outcast. I want my services installed and I need my internet to perform part of my job duties.  I cannot express the frustation that I've expressed behind this matter. I was also informed that my services will be installed on today guranteed. I will keep you all posted.

Message 20 of 20
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