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`
`US008432956B2
`
`(12) United States Patent
`Krinsky et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 8,432,956 B2
`*Apr. 30, 2013
`
`(54)
`
`(75)
`
`(73)
`< * >
`
`(21)
`
`(22)
`
`(65)
`
`(63)
`
`(60)
`
`(51)
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`(52)
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`(53)
`
`MULTICARRIER MODULATION
`MESSAGING FOR POWER LEVEL PER
`SUBCHANNEL INFORMATION
`
`Inventors: David M. Krinsky, Acton, MA (US);
`Robert Edmund Pizzano, .lr.,
`Stoneham, MA (US)
`
`Assignee: TQ Delta, LLC, Austin, TX (US)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(1)) by 0 days.
`This patent is subject to a terminal dis-
`claimer.
`
`Appl. No.: 13/476,310
`
`Filed:
`
`May 21, 2012
`Prior Publication Data
`
`Sep. 13, 2012
`US 2012/0230476A1
`Related U.S. Application Data
`Continuation of application No. 12/779,660, filed on
`May 13, 2010, now Pat. No. 8,238,412, which is a
`continuation of application No. 12/477,742, filed on
`Jun. 3, 2009, now Pat. No. 7,835,430, which is a
`continuation of application No. 10/619,691, filed on
`Jul. 16, 2003, now Pat. No. 7,570,686, which is a
`continuation of application No. 09/755,173, filed on
`Jan. 8, 2001, now Pat. No. 6,658,052.
`
`Provisional application No. 60/224,308, filed on Aug.
`10, 2000, provisional application No. 60/174,865,
`filed on Jan. 7, 2000.
`Int. Cl.
`H04B 1/38
`H04L 1206
`U.S. Cl.
`USPC ......................................... .. 375/222; 370/252
`Field of Classification Search ...................... .. None
`See application file for complete search history.
`
`(2006.01)
`(2006.01)
`
`230
`/V
`Diagnostic
`lniormallan
`Monitoring
`Device
`
`(ATU-C)
`
`5
`220
`/V
`
`210
`/V
`CRC
`Checker
`
`Dlagnastic
`
`Device
`
`2°
`]/V
`
`5\Nl|ch
`Phone
`
`POTS-0
`4/
`
`(56)
`
`EP
`GB
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,836,726 A
`9/1974 Wells et al.
`4,385,384 A
`5/1983 Rosbury et al.
`(Continued)
`FOREIGN PATENT DOCUMENTS
`0889615
`"1/2009»
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`
`(Continued)
`OTHER PUBLICATIONS
`
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`XP000343913 ISBN: 0-7803-0640-6.
`
`(Continued)
`
`Primary Examiner — Khanh C Tran
`(74) Attorney, Agent, or Firm —Jason H. Vick; Sheridan
`Ross, PC
`
`ABSTRACT
`(57)
`Upon detection ofa trigger, such as the exceeding ofan error
`threshold or the direction of a user, a diagnostic link system
`enters a diagnostic information transmission mode. This
`diagnostic information transmission mode allows for two
`modems to exchange diagnostic and/or test information that
`may not otherwise be exchangeable during normal commu-
`nication. The diagnostic information transmission mode is
`initiated by transmitting an initiate diagnostic lin.k mode mes-
`sage to a receiving modem accompanied by a cyclic redun-
`dancy check (CRC). The receiving modem determines, based
`on the CRC, ifa robust communications channel is present. If
`a robust communications channel is present, the two modems
`can initiate exchange of the diagnostic and/or test infonna-
`tion. Otherwise, the transmission power of the transmitting
`modem is increased and the initiate diagnostic link mode
`message re—transrnittedto the receiving modem until the CRC
`is determined to be correct.
`
`10 Claims, 2 Drawing Sheets
`
`Remote Terminal
`
`300
`
`1o
`,,/
`Splitter
`
`30
`
`_L5‘_/VSplitiar
`
`,j,‘°
`Message
`Determination
`Device
`
`330
`(ATU-R)
`Dlagnestlc
`Davlee
`
`/V
`
`34°
`A/
`lnfnnnatlon
`Diagnostic
`storage
`Delvce
`
`Power
`
`//
`
`Phone
`
`ARRIS-1 001
`
`Arris Group, Inc. v. T0 Delta
`
`Page 1 of 10
`
`

`
`US 8,432,956 B2
`Page 2
`
`4,566,100
`5,023,873
`5,128,619
`5,313,197
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`5,388,252
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`6,073,179
`6,075,821
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`6,188,717
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`6,404,774
`6,411,678
`6,445,773
`6,449,307
`6.512.789
`6,631,120
`6,633,545
`6,636,603
`6,658,052
`6,725,176
`6,781,513
`7,570,686
`7,835,430
`
`7,889,784i>J>gggwwgwwe-wwwu-wwwwwi>D>>i>i>>>i>il>>i>il>
`
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`
`Page 2 of 10
`
`

`
`US 8,432,956 B2
`Page 3
`
`Supplemental Notice ofAllowabi1ity for US. Appl. No. 10/61 9,691 ,
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`
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`including translation) for Japanese Patent
`Application No. 2011—012155. mailed Feb. 25. 2013.
`
`Page 3 of 10
`
`

`
`U.S. Patent
`
`Apr. 30, 2013
`
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`
`US 8,432,956 B2
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`

`
`U.S. Patent
`
`Apr. 30, 2013
`
`Sheet 2 of2
`
`US 8,432,956 B2
`
`Commence
`Initialization
`
`Diagnostic
`Mode
`?
`
`Enter Normal
`Steady State
`Data
`Transmission
`
`Error
`
`Threshold
`Exceeded
`7
`
`Re-transmit
`?
`
`For Predetermined Number Of
`
`Herations S220
`V
`Transmit Diagnostic Link
`Message With CRC
`
`3230
`
`I
`Determine
`CRC
`
`CRC
`Correct
`'2
`
`Increase
`Transmission
`Power
`
`Page 5 of 10
`
`

`
`US 8,432,956 B2
`
`1
`MULTICARRIER NIODULATION
`MESSAGING FOR POWER LEVEL PER
`SUBCHANNEL INFORMATION
`
`RELA'l'El_) APPLICATION DATA
`
`This application is a continuation of U.S. application Ser.
`No. 12/779,660, liled May 13, 2010, 11ow U.S. Pat.No. 8,238,
`412, which is a continuation of U.S. application Ser. No.
`12/477,742, filed Jun. 3, 2009, now U.S. Pat. No. 7,835,430,
`which is a continuation of U.S. application Ser. No. 10/619,
`691, filed Jul. 16, 2003, now US. Pat. No. 7,570,686, which
`is a continuation of U.S. application Ser. No. 09/755.173,
`filed Jan. 8, 2001, now US Pat. No. 6,658,052, which claims
`the benefit of and priority ur1der 35 U.S.C. §119(e) to U.S.
`Provisional Application No. 60/224,308, filed Aug. 10, 2000
`entitled "Characterization of transmission lir1es using broad-
`band signals in a multi-carrier DSL system,” and U.S. Provi-
`sional Application No. 60/174,865, liled Jan. 7, 2000 entitled
`“Multicarrier Modulation System with Remote Diagnostic 0
`Transmission Mode”, each of which are incorporated herein
`by reference in their entirety.
`
`FIELD OF THE INVENTION
`
`This invention relates to test and diagnostic information. In
`particular,
`this invention relates to a robust system and
`me hod for communicating diagnostic information.
`BACKGROUND OF THE INVENTION
`
`he exchange of diagnostic and test information between
`transceivers in a telecommunications environment
`is an
`important part of a telecorrnnunications, such as an ADSL,
`deployment. In cases where the transceiver connection is not
`performing as expected, for example, where the data rate is
`low. where there are many bit errors. or the like, it is necessary
`to collect diagnostic and test information from the remote
`transceiver. This is performed by dispatching a technician to
`the remote site, e.g., a truck roll, which is time consuming and
`expensive.
`In DSL technology, communications over a local sub-
`scriber loop between a central oflice and a subscriber pre-
`mises is accomplished by modulating the data to be transmit-
`ted onto a multiplicity of discrete frequency carriers wl1icl1
`are summed together and then transmitted over the subscriber
`loop. Individually, the carriers form discrete, non-overlap-
`ping communication subcharmels of limited bandwidth. Col-
`lectively, the carriers form what is effectively a broadband
`communications charmel. At the receiver end, the carriers are ,
`demodulated and the data recovered.
`DSL systems experience disturbances from other data ser-
`vices on adjacent phone lines, such as, for example, Al')SI,,
`HDSL, ISDN, T1. or the like. These disturbances may com-
`mence after the subject ADSI, service is already initiated and,
`since DSL for internet access is envisioned as an always-or1
`service, the effect of these disturbances must be ameliorated
`by the subj ect ADSL transceiver.
`SUMMARY OF THE INVENTION
`
`The systems and methods of this invention are directed
`toward reliably exchanging diagnostic and test infonnation
`between transceivers over a digital subscriber line in the
`presence ofvoice communications and’or other disturbances.
`For simplicity of reference, the systems and methods of the
`invention will hereafter refer to the transceivers generically as
`
`2
`modems. One such modem is typically located at a customer
`premises such as a home or business and is “downstream”
`from a central ollice with which it communicates. The other
`modem is typically located at
`the central office and is
`“upstream” from the customer premises. Consistent with
`industry practice, the modems are often referred to as “ATU-
`R“ (“ADSL transceiver unit, remote,” i.e., located at the cus-
`tomer premises) and “ATU-C” (“ADSL transceiver unit, cen-
`tral office” i.e., located at the central office). Each modem
`includes a transmitter section for transmitting data and a
`receiver section for receiving data, and is of the discrete
`r11ultitone type, i.e., the n1oden1 transmits data over a r11ulti-
`plicity of subchannels of limited bandwidth. Typically, the
`upstream or Al'U-C modem transmits data to the downstream
`or ATU-R modem over a first set of subchannels, which are
`usually the higher-frequency subchannels, and receives data
`from the downstream or ATU-R modem over a second, usu-
`ally smaller, set of subchannels, commonly the lower—fre—
`quency subchannels. By establishing a diagnostic link mode
`' between the two modems, the systems and methods of this
`invention are able to exchange diagnostic and test infonna-
`tion in a simple and robust manner.
`In the diagnostic link mode, the diagnostic and test infor-
`mation is communicated using a signaling mechanism that
`has a very high immunity to noise and/or other disturbances
`and can therefore operate effectively even in the case where
`the modems could not actually establish an acceptable con-
`nection in their normal operational mode.
`For example, if tl1e A'l'U-C and/or ATU-R modem fail to
`complete an initialization sequence, and are thus unable to
`enter a normal steady state corrnnunications mode, where the
`diagnostic
`and test
`information would normally be
`exchanged, the modems according to the systems and 1neth—
`ods of this invention enter a robust diagnostic link mode.
`Alternatively, the diagnostic link mode can be entered auto-
`matically or manually, for example, at the direction of a user.
`In the robust diagnostic link mode, the modems exchange the
`diagnostic and test information that is, for example, used by a
`technician to determine the cause of a failure without the
`technician having to physically visit, i.e., a truckroll to, the
`remote site to collect data.
`information ca11 include, for
`The diagnostic and test
`example, but is not limited to, signal to noise ratio infonna-
`tion, equalizer information, programmable gain setting infor-
`mation, bit allocation information, transmitted and received
`power information, margin information, status and rate infor-
`mation, telephone line condition information, such as the
`length of the line, the number and location of bridged taps, a
`wire gauge, or the like, or any other known or later developed
`diagnostic or test information that may be appropriate for the
`particular communications enviromnent. For example, the
`exchanged diagnostic and test information can he directed
`toward specific limitations of the modems, to information
`relating to the modem installation and deployment environ-
`ment, or to other diagnostic and test information that can, for
`example, be determined as needed which may aid in evaluat-
`ing the cause of a specific failure or problem. Alternatively,
`the diagnostic and test information can include the loop
`length and bridged tap length estimations as discussed inU.S.
`patent application Serial No. 09/755,172, now U.S. Pat. No.
`6,865,221, liled herewith and incorporated herein by refer-
`ence in its entirety.
`For example, an exemplary embodiment of the invention
`illustrates the use of the diagnostic link mode in the commu-
`nication of diagnostic information from the remote terminal
`OKT) transceiver, e.g., ATU-R, to the central office (CO) trans-
`ceiver, e.g., ATU—C. Transmission of information from the
`
`Page 6 of 10
`
`

`
`US 8,432,956 B2
`
`3
`remote terminal to the central oflice is important since a
`typical ADSL service provider is located in the central office
`and would therefore benefit from the ability to determine
`problems at the remote terminal without a truckroll. However,
`it is to be appreciated, that the systems and the methods oftl1is
`invention will work equally well in communications from the
`central ofiice to the remote terminal.
`These and other features and advantages of this invention
`are described in or are apparent from the following detailed
`description of the embodiments.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The embodiments of the invention will be described in
`detail, with reference to the following figures wherein:
`FIG. 1 is a functional block diagram illustrating an exem-
`plary communications system according to this invention;
`and
`FIG. 2 is a flowchart outlining an exemplary method for
`communicating diagnostic and test information according to '
`this invention.
`
`’
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`For ease of illustration the following description will be
`described in relation to the CO receiving diagnostic and test
`information fror11 the R'f. lr1 the exemplary embodiment. the
`systems and methods of this invention complete a portion of
`the normal modem initializationbefore entering ir1to the diag-
`nostic link mode. The systems and methods of this invention ,
`ca11 enter the diagnostic li11k mode manually, for example, at
`the direction of a technician or a user after completing a
`portion of initialization. Alternatively, the systems and meth-
`ods of this invention can enter the diagnostic link mode auto-
`matically based on, for example, a bit rate failure, a forward
`error correction or a CRC error during showtime, e.g., the
`normal steady state transmission mode, or the like. The tran-
`sition into the diagnostic link mode is accomplished by trans-
`mitting a message from the CO modem to the RT modem
`indicating that the modems are to enter into the diagnostic
`ink mode, as opposed to transitioning into the normal steady
`state data transmission mode. Alternatively, the transition into
`he diagnostic link mode is accomplished by transmitting a
`message from the RT modem to the CO modem indicating
`hat the modems are to enter into the diagnostic li11k mode as
`opposed to transitioning into the normal steady state data
`ransmission mode. For example, the transition signal uses an
`ADSL state transition to transition from a standard ADSL
`state to a diagnostic link mode state.
`In the diagnostic link mode, the RT modem sends diagnos-
`ic and test information in the form of a collection of infor-
`mation bits to the CO modem that are, for example, modu-
`ated by using one bit per DTM symbol modulation, as is used
`in the C—Ratesl message in the ITU and ANSI ADSI, stan-
`dards, where the symbol may or may not include a cyclic
`’1I'CfiX. Other exemplary modulation techniques include Dif-
`ferential Phase Shift Keying (DPSK) on a subset or all the
`carriers, as specified in, for example, ITU standard G.994.1,
`iigher order QAM modulation (>1 bit per carrier), or the like.
`In the one bit per DMT symbol modulation message
`encoding scheme, a bit with value 0 is mapped to the
`ZZVERBI signal and a bit with a value of 1 mapped to a
`SEGUEI signal. The REVERB1 and SEGUE1 signals are
`defined in the ITU and ANSI ADSL standards. The
`2'33/FRBI signal is genera ed by modulating all of the car-
`riers in the inulticarrier system with a known pseudo -random
`sequence thus generating a wideband modulated signal. The
`
`4
`SEGUEl signal is generated fror11 a carrier by 180 degree
`phase reversal ofthe REVERBI signal. Since both signals are
`wideband and known in advance, the receiver can easily
`detect the REVFRBI and SEGUEI signal using a simple
`matched filter in the presence of large amounts of noise and
`other disturbances.
`
`TABIF, l
`
`Exemplary Message Variables
`Dam Sent in die Diag Link
`Train Type
`ADSL Standard
`Chip Type
`Vendor ID
`Code Version
`Average Reverb Received Signal
`Programmable gain auiplifier (PGA) Gain - Training
`Programmable gain amplifier l’GA Gain - Showtime
`Filter Present during Idle Channel Calculation
`Average Idle Channel Noise
`Signal to Noise during Training
`Signal to Noise during Showtime
`Bits and Gains
`Dam Rate
`Framing Mode
`Margin
`Reed—Selomon Coding Gain
`QAM Usage
`Frequency Domain Equalizer (PDQ) Coefficicnts
`Gain Scale
`Ti.me domain equalizer (TDQ) Coeflicients
`Digital Echo Canceller (DEC) Coetficients
`
`Table I shows an example of a data message that can be
`sent by the RT to the CO during the diagnostic link mode. In
`this example, the RT modem sends 23 different data variables
`to the CO. Each data variable contains different items of
`diagnostic and test information that are used to analyze the
`condition of the link. The variables may contain more than
`one item of data. For example, the Average Reverb Signal
`contains the power levels per tone, up to, for example, 256
`entries, detected during the ADSL Reverb signal. Conversely,
`the PGA Gain Training is a single entry, denoting the gain
`in dB at the receiver during the ADSL training.
`Many variables that represent the type of diagnostic and
`test information that are used to analyze the condition of the
`link are sent from the RT modem to the CO modem. These
`variables ca11 be, for example, arrays with different lengths
`depending on, for example, information in the initiate diag-
`nostic mode message. The systems and methods ofthis inven-
`tion can be tailored to contain many different diagnostic and
`Q test information variables. Thus, the system is fully config-
`urable, allowing subsets of data to be sent and additional data
`variables to be added in the future. Therefore, the message
`length can be increased or decreased, and diagnostic and test
`information customized, to support more or less variables as,
`for example, hardware, the environment ar1d/or the telecom-
`munications equipment dictates.
`'fherefore, it is to be appreciated, that ir1 general the vari-
`ables transmitted from the modem being tested to the receiv-
`ing modem can be any combination ofvariables which allow
`for transmission of test and/or diagnostic information.
`FIG. 1 illustrates an exemplary embodiment of the addi-
`tional modem components associated with the diagnostic link
`mode. Inparticular, the diagnostic link system 100 comprises
`a central office modem 200 and a remote terminal modem
`300. The central office modem 200 comprises, in addition to
`the standard ATU-C components. a CRC checker 210, a diag-
`nostic device 220, and a diagnostic information monitoring
`
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`US 8,432,956 B2
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`5
`device 230. The remote terminal n1oden1 300 comprises, in
`addition to the standard components associated with anATU-
`R, a message determination device 310, a power control
`device 320, a diagnostic device 330 and a diagnostic infor-
`mation storage device 340. The central ollice modem 200 and
`the remote terminal model 300 are also connected, via link 5,
`to a splitter 10 for a phone switch 20, and a splitter 30 for a
`phone 40. Alternatively, the ATU-R can operate without a
`splitter, e.g., splitterless, as specified in ITU standard G.992.2
`(G.lite) or witl1 an in-li11e filter in series witli the phone 40. In
`addition, the remote terminal modem 300, can also be con-
`nected to, for example, one or more user terminals 60. Addi-
`tionally, the central office modem 200 can be connected to
`one or more distributed networks 50, via link 5, wl1icl1 may or
`may not also be connected to one or more other distributec
`networks.
`While the exemplary embodiment illustrated in FIG. 1
`shows the diagnostic link system 100 for an embodiment in
`which the remote terminal modem 3 00 is communicating tes
`and diagnostic information to the central office 200, it is to be ’
`appreciated that the various components ofthe diagnostic link
`system can be rearranged such that the diagnostic and tes
`information can be forwarded from the central office 200 to
`the remote terminal modem 300, or, altematively, such tha
`botl1 modems can send and receive diagnostic and/or tes
`information. Furthermore, it is to be appreciated, that the
`components oftlie diagnostic link system 100 can be locatec
`at various locations within a distributed network, such as the
`POTS network, or other comparable telecommunications net-
`work. Thus, it should be appreciated that the components 0
`the diagnostic link system 100 can be combined into one
`device for respectively transmitting, receiving, or transmit-
`ting and receiving diagnostic and/or test information. As wil
`be appreciated from the following description, and for rea-
`sons of computational efficiency, the components ofthe diag-
`no stic link system 100 can be arranged at any location within
`a telecommunications network and’or modem without affect-
`ing the operation of the system.
`The links 5 can be a wired or wireless link or any other
`known or later developed element(s) that is capable of sup-
`plying and communicating electronic data to and from the
`coimected elements. Additionally, the user terminal 60 can
`be, for example, a personal computer or other device allowing
`a user to interlace with a11d communicate over a modem, such
`as a DSL modem. Furthermore, the systems and method of
`this invention will work equally well with splitterless and
`low-pass multican*ier modem technologies.
`In operation, the remote terminal 300, commences its nor-
`mal initialization sequence. The diagnostic device 330 moni-
`tors the initialization sequence for a failure. If there is a
`failure, the diagnostic device 330 initiates the diagnostic link
`mode. Alternatively, a user or, for example, a technician at the
`CO, ca11 specify that the remote terminal 300 enter into the
`diagnostic link mode after completing a portion ofan initial-
`ization. Alternatively still, the diagnostic device 330 can
`monitor the normal steady state data transmission of the
`remote terminal, and upon, for example, an error threshold
`being exceeded, the diagnostic device 330 will initiate the
`diagnostic link mode.
`Upon initialization of the diagnostic link mode, the diag-
`nostic device 330, in cooperation with the remote terminal
`300 will transmit an initiate diagnostic link mode message
`from the remote tenninal to the central office 200 (RT to CO).
`Alternatively, the central office modem 200 can transmit an
`initiate diagnostic link mode message to the remote terminal
`modem 300. If the initiate diagnostic li11k mode message is
`received by the central office 200, the diagnostic device 330,
`
`6
`in cooperation with the message determination device 310,
`determines a diagnostic link message to be forwarded to the
`central office 200. For example, the diagnostic link message
`can include test information that has been assembled during,
`for example, the normal ADSL initialization procedure. The
`diagnostic and/or test information can include. but is not
`limited to, the version number ofthe diagnostic link mode, the
`length of the diagnostic and/or test information, the commu-
`nications standard, such as the ADSL standard, the chipset
`type, the vendor identifications, the ATU version number, the
`time domain received reverb signal, the frequency domain
`reverb signal, the amplifier settings, the CO tran smitter power
`spectral density, the frequency domain received idle charmel,
`the signal to noise ratio, the bits and gains and the upstream
`and downstream transmission rates, or the like.
`Ifthe initiate diagnostic link mode message is not received
`by the central office 200, the initiate diagnostic link mode
`message can, for example, be re-transinitted a predetermined
`number ofiterations until a determination is made that it is not
`possible to establish a connection.
`Assuming the initiate diagnostic link mode message is
`received, then, for a predetermined number of iterations, the
`diagnostic device 330, in cooperation with the remote terrni—
`nal modem 300 and the diagnostic information storage device
`340, transmits the diagnostic link message with a cyclic
`redundancy check (CRC) to the central office modem 200.
`However, it is to be appreciated that in general, any error
`detection scheme, such as bit error detection, can be used
`,, without affecting the operation of the system. The central
`ollice 200, iii cooperation with the CRC checker 210, deter-
`mines if the CRC is correct. If the CRC is correct, the diag-
`nostic information stored in the diagnostic information stor-
`age device 340 has been, with the cooperation of the
`diagnostic device 330, and the remote terminal modem 300,
`forwarded to the central oflice 200 successfully.
`If, for example, the CRC checker 210 is unable to deter-
`mine the correct CRC, the diagnostic device 330, in coopera-
`tion with power control device 320, increases the transmis-
`sion power of the remote terminal 300 and repeats the
`transmission of the diagnostic link message from the remote
`tenninal 300 to the central oflice 200. lhis process continues
`until the correct CRC is determined by the CRC checker 210.
`The maximum power level used for transmission of the
`diagnostic link message can be specified by, for example, the
`user or the ADSL service operator. If the CRC checker 210
`does not determine a correct CRC at the maximum power
`level and the diagnostic link mode can not be initiated then
`other methods for determining diagnostic information are
`, ' utilized, such as dispatching a technician to the remote site, or
`the like.
`Alternatively, the remote terminal 300, with or without an
`increase in the power level, can transmit the diagnostic link
`message several times, for example, 4 times. By transmitting
`the diagnostic link message several times, the CO modem 200
`can use, for example, a diversity combining scheme to
`improve the probability of obtaining a correct CRC from the
`received diagnostic link message(s).
`Alternatively, as previously discussed, the central ollice
`200 comprises a diagnostic information monitoring device
`230. The remote terminal 300 can also include a diagnostic
`information monitoring device. One or more of these diag-
`nostic information monitoring devices can monitor the nor-
`mal steady state data transmission between the remote termi-
`nal 300 and the central office 200. Upon, for example, the
`normal steady state data transmission exceeded a predeter-
`mined errorthreshold, the diagnostic information monitoring
`
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`7
`device can initiate the diagnostic lir1k mode with tl1e coopera-
`tion of the diagnostic device 300 and/or the diagnostic device