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AT&T U-verse service

Doug Kerr

Well-known member
By definition, all here are users of Internet access, and we may be interested in new developments in access service and technology.

AT&T now offers in many of its operating areas their new U-verse service, which can provide any or all of:

• Telephone service (1 or 2 lines).

• Internet access at a number of optional nominal rates, including 6 Mb/s downstream,1 Mb/s upstream and (in many areas) 18 Mb/s downstream, 1.5 Mb/s upstream.

• Television program service, with a wide variety of channels and (in most packages) a central digital video recorder (DVR).

In one form of the service, the service is delivered to the individual residence from a "neighborhood" fiber terminal (up to perhaps a half mile away) over very high speed digital subscriber line (VHSDL) operating over a single cable pair. In another form, the service is delivered over fiber all the way from the serving central office to the residence over fiber, using a BPON (broadband passive optical network).

We recently had all three aspects of U-verse installed at our home. Before committing to this change, I new little of the technical details of the service. Now, I know enough to be dangerous.

As usual, to make sure this newfound information doesn't get away from me, I have captured it in a new technical article, "The AT&T U-verse Service", available here:

http://doug.kerr.home.att.net/pumpkin/index.htm#U-verse

The article describes the overall architecture and operation of the service, summarizes the functions of the various system units, explains the vary flexible arrangements for interconnecting the various system units over a range of wiring media, and (in an appendix) describes the DMT (discrete multi-tone) modulation scheme used for the VDSL.
 

nicolas claris

OPF Co-founder/Administrator
Hi Doug
thanks for posting.
In the "old" Europe as described by your former President, we have all this (at least in France) since 5 years… but thru DSL. Yes at home, we have 100 TV chanels (+ uncountable # of radios), 2 # phone numbers and Internet access. All of that with 20 Mb downstream and 1.5 Mb upstream…

Bien évidemment, when we use the TV the bandwith dedicated to computers for Internet is lowered to 6-7 Mb… still fair enough!

We have one "box" connected to the copper line, sending thru WIFI to another "box" connected to the TV, wifi to our home networked laptops (2)
the phones are connected to the initial "box" (in fact we use one only)

But don't ask me how it works! Lol!
 

Doug Kerr

Well-known member
Hi, Nicolas,

Hi Doug
thanks for posting.
In the "old" Europe as described by your former President, we have all this (at least in France) since 5 years… but thru DSL. Yes at home, we have 100 TV chanels (+ uncountable # of radios), 2 # phone numbers and Internet access. All of that with 20 Mb downstream and 1.5 Mb upstream…

Bien évidemment, when we use the TV the bandwith dedicated to computers for Internet is lowered to 6-7 Mb… still fair enough!

We have one "box" connected to the copper line, sending thru WIFI to another "box" connected to the TV, wifi to our home networked laptops (2)
the phones are connected to the initial "box" (in fact we use one only)

But don't ask me how it works! Lol!
Thanks for the interesting description. It sounds very comparable to what I describe (although we do not have the opportunity for a WiFi link from the "main box" to the TV boxes).

In the case of U-verse, using the TV capability doesn't reduce the bitrate available for Internet access since that is "throttled" to a modest rate all the time!

I suspect the DSL there uses a similar modulation scheme as for U-verse (it is an international standard).

Best regards,

Doug
 

nicolas claris

OPF Co-founder/Administrator
In the case of U-verse, using the TV capability doesn't reduce the bitrate available for Internet access since that is "throttled" to a modest rate all the time!

We even have some of the TV chanels in HD… :) and 6 Mb downstream seems enough for me !

However, one need to mention that this level of stream demivery is dependant of the distnace between boxes and mainframe at the phone company…
i.e. with the same contract we have about 1/3 of that stream only at office… because we're about 2 km from the mainframe.

One have also to mention, that one of the phone line is an IP phone (goes threu Internet but reaches any kind of phone system (mobile, Internet, land etc…), so most of calls except mobiles and some "special numbers" are completely free (even for abroad)…
 

Doug Kerr

Well-known member
Hi, Nicolas,
We even have some of the TV chanels in HD… :) and 6 Mb downstream seems enough for me !

However, one need to mention that this level of stream demivery is dependant of the distnace between boxes and mainframe at the phone company…
i.e. with the same contract we have about 1/3 of that stream only at office… because we're about 2 km from the mainframe.
Interesting.

In U-verse (the form that uses the VDSL), the VDSL is never longer than 2000 ft (formerly was 2500 ft, earlier was 5000 ft - known by cynics as "the incredible shrinking radius"!). The traffic is carried by fiber from the central office to the "neighborhood" terminal from which the VDSLs issue.

The available Internet access bitrate ("throttled") is not dependent on the length of the cable pair involved (even though the potential overall link transmission rate would differ).

One have also to mention, that one of the phone line is an IP phone (goes threu Internet but reaches any kind of phone system (mobile, Internet, land etc…), so most of calls except mobiles and some "special numbers" are completely free (even for abroad)…
In U-verse, the telephone line(s) operate on an IP basis, but not in the sense that the traffic is carried over the Internet. Rather, to the extent practical, they are carried over a dedicated AT&T IP network.

We have a plan in which calls within the US are "free". (We had that before, when our telephone service was provided in the traditional fashion.)

Thanks again on your insight on the comparable service there.

In any case, I am grateful that "HD" photos of those lovely boats, and the lovely girls on them, are able to successfully traverse these VDSLs at both ends.

Best regards,

Doug
 

Doug Kerr

Well-known member
Bitrates of the U-verse ADSL

Aficionados of the U-verse system often obsess over bitrate values that characterize the actual, or potential, operation of the ADSL link. Sadly, the careless use of terminology often makes it difficult to understand what is being discussed. I'l excerpt here the discussion of this from my article on the U-verse service.

Background

The U-verse ADSL is adaptive and adaptable. By adaptive, I mean that at system startup, the ADSL modems (in a process called "modem training") make a detailed assessment of the properties of the bearing cable pair, in terms of the presence or absence of interfering tones, the attenuation, and the noise level, in each of almost two thousand narrow frequency bands.

Then, if left to their own devices, the modems establish a customized discrete multitone modulation scheme, in terms of which of those slots will actually carry a subcarrier ("tone") and at what bitrate will that subcarrier operate (that is, what modulation constellation it will carry). The result would be a certain overall gross bitrate capacity for the link. It is the highest attainable bitrate over that cable pair in the light of a certain established error performance criterion.

By adaptable, I mean that the served system (the U-verse gateway, in this case) may invite the modems to adopt a "less aggressive" modulation scheme - one that will provide an overall bitrate that will accommodate (including overhead needs) the highest bitrate at which the system plans to transmit.

That "utilization limit" (referred to as the "profile bitrate" for the system) is based on the user's service package, reflecting the amount of transmission resources - not just through the ADSL, but through the entire network - that the service provider commits to a subscriber with that particular package.

The result of the modems adopting a less aggressive modulation scheme than would otherwise be supportable by the cable pair is improved error performance.

Bitrates

The bitrate provided by an ADSL link operating under a specific modulation plan is called its sync bitrate. The term reminds us that the link operates as a synchronous channel - it carries the same number of bits per second (again assuming some particular modulation plan), whether or not the served applications at the moment make use of any or all of those bits.

There are two sync rates that are often of interest:

• The operating sync rate. This is the bitrate of the ADSL link as it has been configured for operation - under the modulation plan actually in effect. Recall that this modulation plan has been put into effect by the modems at the direction of the served system, in support if its stated profile bitrate.

• The maximum sync rate. This is the sync rate that the link would have if the modems would put into effect the "most aggressive workable" modulation scheme, based on the measured characteristics of the cable pair.

If we use the term "sync bitrate" in connection with an operating VDSL link, without further elaboration, it should reasonably be taken to mean the sync bitrate of the link as it is operating.

Careless usage

But, for some reason, ADSL aficionados have taken to using the term "sync bitrate" (without further qualification) to mean the maximum sync bitrate that would pertain to the cable pair involved.

Ordinarily, the operating sync bitrate is set a a bit over the stated profile bitrate (the excess being to accommodate certain transmission overhead, and to provide a little margin of safety). Yet we find reports by aficionados that on their system, "the downstream profile rate is 25,216 and the downstream sync bitrate is 47,508 kb/s."

In fact, the downstream sync bitrate of their ADSL link is probably about 27,000 kb/s.

What they usually mean is that the cable pair being used would support a sync bitrate of 47,508 kb/s if we asked the modems to operate in the most aggressive workable modulation scheme (with an attendant worse, but still "acceptable", error performance).

Incidentally, the screen in which the U-verse VDSL modem reports it operation to the user (on a connected computer) gives the profile rate labeled as "current rate" and the maximum sync rate (based on the latest assessment of the cable pair) labeled as "maximum rate". The current sync rate is not reported (but can be determined from detailed information given on the modulation plan currently in use).

Well, I see our Sunday breakfast is ready, so - aren't you glad you asked?

Best regards,

Doug
 

Gary Ayala

New member
I ripped out the hard-line phone years ago. Voice communications is cellular, TV signals and internet communications is vis-a-vis cable which delivers hundreds of channels and a ton of HD channels. The computers and printers are networked wireless and the internet is distributed through wireless as well. It is nice to grab a laptop and work in the garden.

Gary

PS- I also have computer type speakers coupled with MP3 docking stations in many rooms and in the patio. They deliver excellant quality and take up a small footprint and the docking stations are operated with a wireless control.
G
 
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