Telephonic communications – Diagnostic testing – malfunction indication – or electrical... – Of data transmission
Reexamination Certificate
2002-02-01
2004-11-09
Tran, Quoc D. (Department: 2643)
Telephonic communications
Diagnostic testing, malfunction indication, or electrical...
Of data transmission
C379S001010, C379S001030, C379S022000, C379S022020, C379S022040, C379S024000, C379S027010, C379S027080
Reexamination Certificate
active
06816575
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to communication test systems and subsystems therefor, and is particularly directed to a frequency domain reflectometry-based test mechanism for measuring attenuation of a telecommunications wireline (e.g., a twisted metallic pair), and using the measured loss to estimate respective upstream and downstream bit rates at which digital subscriber line (DSL) type signals may be transported over the wireline.
BACKGROUND OF THE INVENTION
The ability to conduct high data rate communications between remotely separated data processing systems and associated subsytems and components has become a requirement of a variety of industries and applications, such as business, educational, medical, financial and personal computer uses. Indeed, it can be expected that current and future applications of such communications will continue to engender more systems and services in this technology. Associated with such applications has been the growing use and popularity of the “Internet”, which continues to stimulate research and development of advanced data communications systems between remotely located computers, especially communications capable of achieving relatively high data rates over an existing signal transport infrastructure (e.g., legacy copper cable plant).
One technology that has gained particular interest in the telecommunication community is digital subscriber line (DSL) service, which enables a public service telephone network (PSTN) to deliver (over limited distances) relatively high bandwidth using conventional telephone company copper wireline infrastructure. DSL service has been categorized into several different technologies, based upon expected data transmission rate, the type and length of data transport medium, and schemes for encoding and decoding data.
Regardless of its application, the general architecture of a DSL system essentially corresponds to that diagrammatically shown in
FIG. 1
, wherein a pair of remotely separated, mutually compatible digital communication transceivers (e.g. modems) are coupled to a communication link
10
, such as an existing copper plant. One of these transceivers, denoted as a ‘west site’ DSL transceiver
1
, is typically located at a network controller site
2
(such as a telephone company central office); the other, denoted as an ‘east site’ DSL modem
3
, may be coupled with a computer
9
located at a customer premises
4
, such as a home or office.
Within the communication infrastructure of the telephone company, the ‘west site’ DSL transceiver
1
is coupled with an associated ‘backbone’ network
5
, which communicates with other data transport paths, by way of auxiliary equipments
6
, such as routers and digital subscriber line access multiplexers (DSLAMs). Through these associated devices, the backbone network
5
may communicate with additional information sources
7
and the Internet
8
. This telecommunication fabric thus allows information, such as Internet-sourced data (which is readily accessible via the backbone network
5
), to be transmitted from the central office DSL transceiver
1
over the communication link
10
to the compatible DSL transceiver
3
at the customer site
4
.
In a DSL system of the type described above, the data rates between DSL transceivers are considerably greater than those for voice modems. For example, while voice modems typically operate at a relatively low band, e.g., from near DC up to on the order of 4 kHz, DSL data transceivers may operate in a bandwidth between frequencies on the order of 125 kHz to well over 1 MHz. This voice/data bandwidth separation allows high rate data transmissions to be frequency division multiplexed with a separate voice channel over a common signal transport path.
Moreover, the high rate data DSL band may be asymmetrically, subdivided, as shown in
FIG. 2
, into an ADSL format, which allocates a larger (and higher frequency) portion of the available spectrum for ‘downstream’ (west-to-east in
FIG. 1
) data transmissions from the central office site to the customer site, than data transmissions in the ‘upstream’ direction (east-to-west in
FIG. 1
) from the customer site to the central office. As a non-limiting example, for the case of a single twisted copper pair, a bandwidth on the order of 25 kHz to 125 kHz may be used for upstream data transmissions, while a considerably wider bandwidth on the order of 130 kHz to 1.2 MHz may be used for downstream data transmissions. This asymmetrical downstream vs. upstream allocation of DSL bandwidth is based upon the fact that the amount of data transported from the central office to the customer (such as downloading relatively large blocks of data from the Internet) can expected to be considerably larger than the amount of information (typically email) that users will be uploading to the Internet.
Fortunately, this relatively wide separation between the upstream and downstream data bands facilitates filtering and cancellation of noise effects, such as echoes, by relatively simple bandpass filtering techniques. For example, an upstream echo of a downstream data transmission will be at the higher (downstream) frequency, when received at the central office, so as to enable the echo to be easily filtered from the lower (upstream) frequency signal. Asymmetric frequency division multiplexing also facilitates filtering of near-end crosstalk (NEXT), in much the same manner as echo cancellation.
In addition to performance considerations and limitations on the transport distance for DSL communications over a conventional twisted-pair infrastructure, the cost of the communication hardware is also a significant factor in the choice of what type of system to deploy. Indeed, a lower data rate DSL implementation may provide high-speed data communications, for example, at downstream data rates on the order of or exceeding 1 Mbps, over an existing twisted-pair and at a cost that is competitive with conventional non-DSL components, such as 56 k, V.34, and ISDN modems.
In an effort to optimize the bandwidth and digital signal transport distance of their very substantial existing copper plant (which was originally installed to carry nothing more than conventional analog (plain old telephone service or POTS) signals), telecommunication service providers may perform one or more test and measurement operations on the local loop (twisted wire pair), such as, but not limited to loop loss (attenuation), the presence of bridge-taps or load coils, and data integrity at various segments of cable plant.
Loop loss has been customarily measured by placing a signal transmitter at a first (near) end of the loop and a measurement device at a second (far) end of the loop. The signal generated by the transmitter, which may comprise a tone of known frequency and power, is received by the far end measurement device to determine the insertion loss across the bandwidth of interest for the service being deployed. The measured loop loss may then be compared with existing cable records or deployment guidelines for the network access equipment.
An obvious drawback to this measurement procedure is the need to employ two pieces of test equipment at opposite ends of the loop, which may be separated by miles of communication cable. Also, some test equipment is capable of generating only a limited set of tones, which may constrain testing capabilities for new services. For a given service, the network's access equipment may assist in troubleshooting the local loop, as many different types of equipment are capable of estimating loop loss of signal power, which may be reported through a control port.
SUMMARY OF THE INVENTION
In accordance with the present invention, the need to interactively access and/or conduct a test message exchange session with a test unit installed at a far end of the loop is effectively obviated by a new and improved loop loss measurement mechanism, which employs single ended, frequency domain reflectometry (FDR)-based signal processing of the type disclosed in the above-referenced &a
Berrier Travis Lee
Lowell Alan Blair
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Harris Corporation
Tran Quoc D.
LandOfFree
Single ended loop loss measurement by frequency domain... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Single ended loop loss measurement by frequency domain..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Single ended loop loss measurement by frequency domain... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3294893