Activation of multiple XDSL modems with channel probe

Details Activation of multiple XDSL modems with channel probe Activation of multiple XDSL modems with channel probe

1998-12-21

2004-05-11

Chin, Stephen (Department: 2734)

Pulse or digital communications

Transceivers

Modems

C375S260000

Reexamination Certificate

active

06735245

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention is directed to a communications device, such as, for example, a modem and a method for enabling data communication, and in particular, to an apparatus and method that detects various communication configurations and selects an appropriate communication configuration to establish a communication link.
2. Discussion Of Background And Other Information
Traditionally, data communication devices, such as, for example, modems (both analog and digital), have been employed over public switched telephone networks (PSTN) to transmit data between a first location and a second location. Such modems operate within a conventional voice band (e.g., approximately 0 through 4 kHz bandwidth) of the PSTN. Early modems transmitted data over the PSTN at a speed of approximately 300 bits per second (bps), or less. Over time, and with the increased popularity of the Internet, faster communication schemes (e.g., modems) were demanded and developed. Currently, the fastest analog modem available (referred to as an ITU-T V.34 modem, as defined by the International Telecommunication Union (ITU)), transmits data at a rate of approximately 33,600 bps under ideal conditions. These modems continue to exchange data within the approximate 4 kHz bandwidth of the PSTN.
It is not uncommon to transfer data files that are several megabytes (MB) in size. A modem that operates utilizing the V.34 modulation requires a long time to transfer such a file. As a result, a need has developed for even faster modems.
Accordingly, many new communication methods are being proposed and/or developed to transmit data on the local twisted wire pair that uses the spectrum above the traditional 4 kHz band. For example, various “flavors” (variations) of digital subscriber line (DSL) modems have been/are being developed, such as, but not limited to, for example, DSL, ADSL, VDSL, HDSL and SDSL (the collection of which is generally referred to as xDSL). Several of the various xDSL schemes permit simultaneous communication on a single twisted pair in the voice band and the band above the voice band. Each xDSL variation employs a different communication scheme, resulting in different upstream and/or downstream transfer speeds, and utilize differing frequency bands of the twisted pair communication channel. In addition, some xDSL variations require filters including low pass filters, high pass filters and combinations of filters that are sometimes referred to as “splitters”, which may differ between the installations. The filters separate the frequency band that carries voice band communication from the frequency band above the voice band carrying data communication. The line environments surrounding the xDSL data communication schemes, such as, for example, their ability to co-exist with a conventional analog modem that communicates within the conventional voice band (e.g., 0-4 kHz bandwidth), differences in central office equipment, quality of the line, etc., are numerous, differ significantly, and are complicated. Accordingly, it is essential to be able to determine the capabilities of the communication channel in addition to being able to determine the capabilities of the communication equipment in order to establish an optimum and non-interfering communication link.
Conventional start-up sequences (such as, for example, V.8 and/or V.8bis protocols, as established by the ITU-T), as implemented by, for example, V.34 modems, use a sequence of bits transmitted from each modem to identify and negotiate the varying equipment capabilities, such as the modulation scheme employed, protocol, etc. These startup sequences are applicable only to the conventional voice band communication methods. These conventional startup sequences do not test (or disclose) the constitution and/or condition of the communication channel.
However, for xDSL modems, line condition information, such as, for example, frequency characteristics, noise characteristics, presence or absence of a splitter, etc., is useful at the time that two modems are negotiating prior to connecting to each other, if the communications link is to be successfully established.
Voice band line probing techniques are known in the art and can be used to determine voice band line condition information. Such techniques have been used effectively to optimize a given modulation method, such as, for example, V.34. In a set of devices with multiple modulation methods, V.8 or V.8bis has been used to negotiate and then select a particular modulation, and after that modulation initiation sequence has started, line probing techniques are used to receive some indication of the condition of the communication channel. If it is determined at that point that a given communication channel could not effectively support a chosen modulation method, time consuming heuristic (i.e., self-learning) fallback techniques are employed by the prior art to try and find a modulation method that works.
Accordingly, what is required to establish an improved communication link is a method to observe (or examine) the line conditions before attempting to select the most appropriate communication method. Thus, while techniques have been established to increase the data rate for a given modulation, the prior art does not provide a method for using channel information to aid in the selection of the communication method.
Unfortunately, in the current state of the art, capability negotiations occur without knowledge of the prevailing channel configuration. Explicit knowledge of spectrum, splitting, etc. is vital to the selection of the appropriate communication mechanism (modulation) decision process.
SUMMARY OF THE INVENTION
Based on the foregoing, the overall purpose of the present invention is to develop a communication method, modem device and a data communication system that detects various configurations, capabilities and limitations of a communication channel and associated equipment in order to determine a specific (xDSL) communication standard appropriate for the existing line conditions. To accomplish this goal, the invention employs several individual techniques as a system.
According to one aspect of the present invention, a method and apparatus are provided to negotiate between modems that embody a multiple (plural) communication methods (e.g., DSL standards), so as to select a single common communication standard to be used for a communication session. A communication control section executes a handshake procedure (protocol) in a negotiation channel to obtain information concerning high speed data communication, including type identification information of xDSL used in the communication exchange. A communication standard refers to any type of standard, whether defacto, proprietary, or issued by an industry or government body.
In another aspect of the instant invention, a method is provided for determining characteristics of the communication channel between a central communication system and a remote communication system by using an examination signal. The examination signal detects impairments, such as, but not limited to, frequency rolloff and noise, that are identified and disclosed between the central system and the remote systems. Information pertaining to the quality of the communication channel enables the present invention to make a more informed decision concerning the selection of the subsequent communication standard. (e.g., whether to use CDSL instead of ADSL, or use CDSL instead of VDSL.)
In another aspect, the invention provides a method and apparatus to determine the presence of equipment used to split frequency bands. In many cases, the presence of such equipment is necessary to provide communication in the frequency above the voice band. The lack of such splitting equipment may necessitate the use of different communication methods. The present invention includes a method for detecting the presence of such splitters that is non-intrusive, so as not to interfere with any communication (such as, for example, a voice communication o

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