Loop certification and measurement for ADSL

Details Loop certification and measurement for ADSL Loop certification and measurement for ADSL

2000-09-12

2002-11-05

Nguyen, Duc (Department: 2643)

Telephonic communications

Diagnostic testing, malfunction indication, or electrical...

Of trunk or long line

C379S001030, C379S001040, C379S022020, C370S248000, C370S249000

Reexamination Certificate

active

06477238

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a technique for measuring the performance of wire pairs used for high speed digital subscriber line (xDSL) services, for example for Asymmetrical Digital Subscriber Line (ADSL) services and the like. The measurement technique enables a network carrier to test a line. typically a twisted-wire copper pair, to determine if the line characteristics will permit a particular level of digital service. The carrier can then certify the line for that service.
ACRONYMS
The written description uses a large number of acronyms to refer to various services and system components. Although generally known, use of several of these acronyms is not strictly standardized in the art. For purposes of this discussion, acronyms therefore will be defined as follows:
ADSL—Asymmetrical Digital Subscriber Line
ATM—Asynchronous Transfer Mode
ATU-C—ADSL Terminal Unit-Central Office
ATU-R—ADSL Terminal Unit-Remote
CO—Central Office
CP—Customer Premises
CPU—Central Processing Unit
DSL—Digital Subscriber Line
DSLAM—Digital Subscriber Line Access Multiplexer
EEPROM—Electronically Erasable/Programmable Read Only Memory
EOC—Embedded Operations Channel
HDSL—High data rate Digital Subscriber Line
I/O—Input/Output
IP—Internet Protocol
ISDN—Integrated Services Digital Network
LAN —Local Area Network
LCD—Liquid Crystal Display
MDF—Main Distribution Frame
MLT—Mechanized Loop Test
MPEG—Moving Pictures Experts Group digital encoding
NID—Network Interface Device
PC—Personal Computer
POTS—Plain Old Telephone Service
QoS—Quality of Service
R—Ring
RAM—Random Access Memory
ROM—Read Only Memory
SMDS—Switched Multi-Megabit Data Service
T—Tip
TCP—Transmission Control Protocol
TLS—Total Least Squares
VDSL—Very high data rate Digital Subscriber Line
xDSL—Generic class of Digital Subscriber Line Services
BACKGROUND
Modern society continues to create exponentially increasing demands for digital information, and the communication of such information creates increasing needs for ever-faster data communication speeds. The most common form of computer-to-computer communication in use today relies on modems and analog telephone network connections. The telephone network, however, was designed to provide approximately 3.3 kHz of analog voice bandwidth. Such a bandwidth provides adequate voice communication, at low cost, but does not support high-speed data communications. Integrated Services Digital Network (ISDN) offers somewhat faster data communications and the capacity for concurrent data and voice telephone services. However, this technology has some drawbacks, and data rates offered by ISDN already may be too slow. The high-speed and wide availability of modem personal computers (PCs) continually gives rise to ever more sophisticated multimedia applications. Communications for such applications, typically between the PC and the Internet, are driving the need for speed to rates far above those available on analog telephone lines and on normal ISDN lines.
A number of technologies are being developed and are in early stages of deployment, for providing substantially higher rates of data communication, for example ranging form 640 kb/s to 9 Mb/s. Of particular note, after considering several other options, a number of the local telephone carriers are working on enhancements to their existing copper-wire loop networks, based on various xDSL technologies. xDSL here is used as a generic term for a group of higher-rate digital subscriber line communication schemes capable of utilizing twisted pair wiring from an office or other terminal node of a telephone network to the subscriber premises. Examples under various stages of development include ADSL (Asymmetrical Digital Subscriber Line), HDSL (High data rate Digital Subscriber Line) and VDSL (Very high data rate Digital Subscriber Line).
Consider ADSL as a representative example. For an ADSL related service, the user's telephone network carrier installs one ADSL modem unit at the network end of the user's existing twisted-pair copper telephone wiring. Typically, this modem is installed in the serving central office or in the remote terminal of a digital loop carrier system. The user obtains a compatible ADSL modem and connects that modem to the customer premises end of the telephone wiring. The user's computer connects to the modem. The central office modem is sometimes referred to as an ADSL Terminal Unit—Central Office or ‘ATU-C’. The customer premises modem is sometimes referred to as an ADSL Terminal Unit—Remote or ‘ATU-R’.
For digital data communication purposes, the ATU-C and ATU-R modem units create at least two logical channels in the frequency spectrum above that used for the normal telephone traffic. One of these channels is a low speed upstream only channel; the other is a high-speed downstream only channel. Two techniques are under development for dividing the usable bandwidth of the telephone line to provide bidirectional transmission. Currently, the most common approach is to divide the usable bandwidth of a twisted wire pair telephone line by frequency, that is to say by frequency division duplexing. The frequency division approach uses one frequency band for upstream data and another frequency band for downstream data. The downstream path is then divided by time division multiplexing signals into one or more high-speed channels and one or more low speed channels. The upstream path also may be time-division multiplexed into corresponding low speed channels. The other approach uses Echo Cancellation. With Echo Cancellation, the upstream band and the downstream band substantially over-lap. The modems separate the upstream and downstream signals by means of local echo cancellors, in a manner similar to that used in V.32 and V.34 modems.
The telephone carriers originally proposed use of ADSL and similar high-speed technologies to implement digital video services, for example in networks sometimes referred to as video ‘dialtone’ networks. The ADSL line technology provided a mechanism for high-speed transport of MPEG encoded video information to video terminal devices in the customers' homes. Examples of such ADSL-based video dialtone networks are disclosed in U.S. Pat. Nos. 5,247,347, 5,410,343 and 5,621,728. Interest in such video services has waned, but the recent explosion in Internet and other PC-based services has sharply rekindled the carriers' interest in xDSL technologies. The carriers are now proposing a range of xDSL data services targeted at high-speed Internet access and high-speed access to private data networks. U.S. Pat. No. 5,790.548 to Sistanizadeh et al. discloses an example of an ADSL based data network, e.g. for high-speed access to the Internet and to corporate LANs.
In the last year or so, considerable attention has focused on one version of ADSL with somewhat reduced capabilities but which does not require a separate splitter/combiner at the customer premises to segregate the telephone traffic from the data traffic. The ADSL ‘Lite’ modem can plug directly into the customer's telephone wiring, without a special installation by a telephone company technician. The customer's ‘Lite’ modem does not need or include a frequency splitter/combiner to segregate the voice and data traffic. The ‘Lite’ modem uses a more restricted frequency band, in order to reduce interference with telephone service. Although this reduces the downstream data rate somewhat, particularly for longer lines, the ‘Lite’ implementation still provides downstream speeds ranging from 640 b/s to 1.5 Mb/s, which are substantially higher than provided by analog modems or ISDN.
Thus, ADSL modems today are providing downstream data rates in ranges from 640 kb/s to as high as 9.1 Mb/s. The precise data rate depends on many factors, such as line length, copper wire gauge, cross-coupled interference, and the like. As a general rule, the shorter the distance, and/or the smaller the wire gauge, the higher the rate can be on the particular telephone line. These rates provide an order of magnitude improvement over telephone

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