WO2001010105A1

WO2001010105A1 - Method for fast retrain for g. lite

Info

Publication number: WO2001010105A1
Application number: PCT/US2000/020468
Authority: WO
Inventors: A. Joseph Mueller
Original assignee: 3Com Corporation
Priority date: 1999-07-30
Filing date: 2000-07-27
Publication date: 2001-02-08
Also published as: GB2358324A; GB2358324B; GB0110582D0; AU6383600A

Abstract

A method and system for improving the fast retrain procedure on a telephone line such as a digital subscriber line. The improvement may include transmitting application requirements or profiles to be used in selecting appropriate communication profiles for changing line conditions. In certain instances when no profiles are appropriate, a best-fit profile is selected and modified according to the current line conditions and/or the application requirements. Exemplary methods of modifying the selected profiles to help adapt to changing line conditions are described.

Description

METHOD FOR FAST RETRAIN FOR G LITE

FIELD OF THE INVENTION

This invention relates to electronic communication systems, and more particularly to a system and method for enhancing a fast retrain sequence to optimize communication in a digital modem communication system, such as a digital subscriber line communication system

BACKGROUND OF THE INVENTION

A significant effort has been undertaken to use existing telephone lines for high-speed digital data communications As part of this effort, a number of Digital Subscriber Line (DSL) systems have been proposed For example, an Asymmetπc Digital Subscπber Line (ADSL) provides a system that supports "plain old telephone service" (POTS) and high-speed duplex (simultaneous two-way) digital services over a single twisted-wire pair Generally, DSL systems use special digital modems to encode digital data as analog signals at significantly higher data rates than voice band systems

DSL line conditions may vary significantly over peπods of time and from subscriber to subscriber For example, each user's DSL line is carried over twistedpair conductors bundled together with a large number of other twisted-pair conductors, each used at different times and for different purposes (e g , voice only, data only, and both voice and data) The length and characteristics of wire run from a central office transceiver to a user's remote transceiver may vary greatly from subscriber to subscriber In addition, the physical channel over which the system communicates vanes over time due to, for example, temperature and humidity changes, fluctuating crosstalk interference sources, and phones transitioning on-hook and off-hook on the line in sp tterless configurations Consequently, the analog DSL signals exist in a noisy, time varying environment

To cope with these factors, DSL systems use sophisticated equalizer training, echo canceller training, and synchronization techniques (collectively, training), all of which lequire retraining from time-to-time to adapt to changing line conditions Additionally, DSL system equipment may go offline at any time, such as when powered down or placed into an idle or sleep mode Retraining may be necessary or desirable to adapt to the line conditions when such equipment goes back online

Figure 1 is a block diagram of one embodiment of a prior art DSL system such as a typical architecture using the G lite ADSL standard A user's computer or customer premise equipment ("CPE") 10 is coupled to a DSL modem 12 through an optional band splitter 14 to a conv entional twisted pair telephone line 16 and thence to a telephone company ("telco") system 18 The telco system 18 includes a DSL modem and necessary communication equipment to establish a link to, for example, the Internet or other communication equipment

The optional splitter 14 separates voice band frequencies from higher data band fiequencies The splitter 14 typically provides voice band frequencies for communication to a conventional telephone 20 while providing higher band frequencies to computer equipment CPE 10 The splitter 14 also isolates the ADSL system from the effects of CPE devices that are connected to the telephone line 16 Thus, when the splitter 14 is present, G lite compliant ADSL systems typically do not require retraining to transition from an off-hook state to an on-hook state, or vice versa

For the G lite standard, however, the splitter 14 is optional and the intention of the standard is that the splitter 14 is not required in the majority of installations With such a "sphtterless" system, however, the ADSL system is not isolated from the CPE 20 Thus, telephone on-hook/off-hook transitions may cause channel disruptions and have an adverse effect on the system Furthermore, although G lite systems are "always available", they may actually be put into a low power idle state between sessions of user activity "Waking up" from these low power states may require retraining to compensate for any changes and disruptions in line conditions that may have occurred during the idle period

At present, G lite DSL modems attempt to recover from a channel disruption or low power idle state {e g , caused by an on-hook/off-hook transition or renewed user activity) by using a procedure known as a fast retrain sequence The fast retrain sequence relies on stored profiles containing modem operating parameters appropπate for particular line characteristics In response to a change in line conditions, the fast retrain attempts to determine if anv one of the previously stored profiles, each corresponding to a previous run-time channel condition, is appropriate for the current channel condition and, if so, selects that profile Duπng a fast retrain sequence between two transceiver units, if both units have maintained their stored profiles, then each unit's receiver may invoke a stored profile to set the modem characteπstics appropriately for the far-end unit's transmitter, thereby permitting data transmission, referred to as the "SHOWTIME" state, to resume rapidly

In addition, the CPE devices 10, 20 may be using the telephone line 16 for different applications For example, the computer device 20 may be using the telephone line 16 for a high bandwidth communication application such as high-grade video, or at other times a lower bandwidth communication application such as high- grade voice Each of these different applications may have different service requirements

If application requirements change or the channel conditions change due to on- hook/off-hook transitions, temperature fluctuations, etc., a fast retrain may be initiated In certain situations, however, none of the stored profiles may match or be suitable for the current application requirements or channel conditions.

If none of the stored profiles are appropπate, then either a full initialization is required to obtain a new profile or an existing sub-optimal profile must be selected. Using a sub-optimal profile may limit the data rate, latency or reliability of the connection A full initialization adds 6-10 seconds of additional training, introducing a noticeable delay in restoring the communication link Needed is a way to select more suitable profiles

SUMMARY OF THE INVENTION

In accordance with preferred embodiments of the present invention, some of the problems associated with changing line conditions on DSL connections using stored profiles are addressed and overcome Methods for retraining using stored profiles and optimizing the stored profiles using profile modification parameters are provided

In an exemplary embodiment, a fast retraining procedure with particular application requirements and profile modification is provided Upon determining a fast retrain is necessary, an ATU initiates the fast retrain procedure in the usual manner During the fast retrain sequence, activation, channel measurement, transceiver retrain, and profile selection are executed along with transmitting application requirement and profile modification parameters

According to an embodiment of the invention, application requirements or application profiles can be transmitted to assist in determining the appropπate profile for the current line conditions according to the particular application using the communication link Application requirements preferably indicate the desired data rate, error rate and latency required for the application to be successfully transported In addition, application profiles defining different types of applications such as low- grade voice, high-grade voice, low-grade video, high-grade video, etc can also be defined to imply certain application service requirements If the fast retrain is defined to include application profiles, or the more geneπc application requirements, they can be conveyed during the fast retrain procedure, typically from the initiating ATU to the responding ATU

According to another aspect of the invention, stored profiles with modification profiles are provided to optimize profiles for the particular line conditions Profiles preferably include such information as bits and gain tables, Reed-Solomon coding parameters, interleaver depth, etc Stored profiles generally correspond to the operating parameters of a previous session that were saved using a profile management procedure According to an embodiment of the invention, a best-fit profile is selected and profile modification commands are issued to improve any sub- optimahties The profile modification commands may, for example, add or remove bits to adjust the profile gain for specific earners The present invention may help adapt ADSL transmission characteπstics to changing line conditions and application requirements without decreasing the quality of service If none of the profiles match the current application and/or channel lequirements, they can be modified such that a non-optimal profile may be modified and optimized (or made near optimal) avoiding a loss in quality of service A full initialization to obtain a new profile is not required, saving 6-10 seconds in retraining time In addition, profiles can be tailored to particular application requirements and may allow for a reduction in the number of profiles (and thus storage space) given that profiles which exactly match the channel are no longer necessary

The foregoing and other features and advantages of preferred embodiments of the present invention will be more readily apparent from the following detailed description The detailed description proceeds with references to the accompanying drawings

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present inventions are described with reference to the following drawings, wherein

Figure 1 is a block diagram illustrating a prior art asymmetnc data transmission system,

Figure 2 is a block diagram illustrating an exemplary asymmetric digital subscriber line data transmission system utilizing an embodiment of the present invention,

Figure 3 is a diagram illustrating a method for profile modification in the system of Figure 2 according to a present embodiment, and

Figure 4 shows a diagram of the overall communication process

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Exemplary asymmetric data transmission s\ stem

Figure 2 is a block diagram illustrating an exemplary asymmetnc data transmission system 30 for a preferred embodiment of the present invention In the asvmmetπc data transmission system 30, data is transmitted at a higher data rate in a downstream direction than in an upstream direction The asymmetric data transmission system 30 includes a first asymmetπc network device or ATU 32, a connection 34, and a second asymmetric network device 36 However, the asymmetric data transmission system 30 is not limited to the network devices and the connection illustrated in Figure 2, and more or fewer network devices and connections can also be used Splitters are not illustrated in Figure 2, and may or may not be used in the asymmetric data transmission system 30

In one exemplary preferred embodiment of the present invention, the connection 34 is a conventional twisted pair of copper wires The first asymmetnc network device 32 is an Asymmetric Digital Subscnber Line ("ADSL") Transmission Unιt-Remote("ATU-R") The second asymmetπc network device 36 is an ADSL Transmission Unit-Central ("ATU-C") Howev er, the present invention is not limited to this exemplary preferred embodiment and other network devices and connections can also be used

The asymmetric network devices 32, 36 for preferred embodiments include network devices that can interact with the asymmetnc network system 30 based on all or part of standards proposed by the Institute of Electrical and Electronic Engineers ("IEEE"), International Telecommunications Union-Telecommunication Standardization Sector ("ITU"), Internet Engineenng Task Force ("IETF"), or American National Standard Institute ("ANSI") However, network devices based on other standards could also be used IEEE standards can be found on the World Wide Web at the Universal Resource Locator ("URL") "www leee org " The ITU, (formerly known as the CCITT) standards can be found at the URL "www ltu ch " IETF standards can be found at the URL "www letf org " The ANSI standards can be found at the URL "www ansi org " The ANSI standard "Network and Customer Installation Interfaces - Asymmetric Digital Subscriber Line (ADSL) Metallic interlace,^" ANSI-T1 413-1995, and the ITU standards "asymmetrical digital subscriber line (ADSL) transceiver." ITU-G 992 1 -1999. and "Sphtterless Asymmetrical Digital Subscriber Line Transceivers," ITU-G 992 2-1999, are incorporated herein by reference

Two of the ADSL standards are set forth in the ANSI Tl 413 Issue 2 ADSL Standard ( 1998), and in the ITU G 992 2 G lite Standard (1999). both of which are hereby incorporated by reference The G lite standard is a variant of the Tl 413 ADSL standard, with modifications directed primarily to work in a sphtterless environment (i e , without a splitter at the remote user end)

An operating environment for asymmetric network devices 32, 36 include a processing system with one or more high speed Central Processing Unιt(s) ("CPU") and a memory In accordance with the practices of persons skilled in the art of computer programming, the present invention is descπbed below with reference to acts and symbolic representations of operations or instructions that are performed by the processing system, unless indicated otherwise Such acts and operations or instructions are referred to as being "computer-executed" or "CPU executed " It will be appreciated that acts and symbolically represented operations or instructions include the manipulation of electπcal signals by the CPU An electπcal system represents data bits which cause a resulting transformation or reduction of the electrical signals, and the maintenance of data bits at memory locations in a memory system to thereby reconfigure or otherwise alter the CPU's operation, as well as other processing of signals The memory locations where data bits are maintained are physical locations that have particular electrical, magnetic, optical, or organic properties corresponding to the data bits

The data bits may also be maintained on a computer readable medium including magnetic disks, optical disks, organic memory, and any other volatile (e g , Random Access Memory ("RAM")) or non-volatile (e g , Read-Only Memory ("ROM")) mass storage system readable by the CPU The computer readable medium includes cooperating or interconnected computer readable medium, which exist exclusively on the processing system or be distπbuted among multiple interconnected processing systems that may be local or remote to the processing system

The general timing sequence of a proposed fast retrain sequence for two transceiver units of a standard digital modem communication system in accordance with the present embodiment is described below. The fast retrain timing sequence generally includes the following steps:

( 1 ) Activation: The G.lite fast retrain uses activation tones in a manner similar to Tl .413 initialization to initiate a connection.

(2) Channel measurement: The channel is measured to (a) ensure that the channel is stable (i.e., any transients due to on or off hook transitions have subsided), (b) determine power cut-back levels, and (c) begin characterizing the channel in order to select the appropriate profile (if one exists). Timing recovery should be performed here as well (the system may either fine-tune the timing if the previous state was the SHOWTIME data transmission state or may reacquire timing if previous timing information is not available or no longer valid). If either end has no stored profiles, a Fast Retrain Truncate is signaled via the C-MSG-FR1 and/or R-MSG-FR1 and entry into the full initialization procedure commences.

(3) Transceiver Retraining: Echo cancellers and equalizers are trained and timing may be further tuned. Additional information stored in the profile from a previous session (such as previous equalizer taps) may be used to speed the process. In addition, some channel analysis may be done to assist with final profile selection.

During channel measurement or transceiver retraining, channel characterization is preferably performed using the wide band REVERB signal, and signal-to-noise ratio (SNR) measurements are preferably performed using the wide band MEDLEY signal. Using this information, each ATU should be capable to determine to some extent, what bit loading configuration the channel will support. Given this information and any application information that may have also been exchanged, the stored profiles are examined to determine a suitable match.

(4) Profile Selection: If a suitable match is determined, the profile number corresponding to that match is exchanged via the C-MSG-FR2 and R-MSG-FR2 messages and entry into SHOWTIME data transmission commences. Up to 16 profiles corresponding to up to 16 different channel configurations can be saved and reference the information exchanged in previous executions of the initialization exchange procedure. According to another embodiment of the invention, application requirements or application profiles are used in the profile selection process. The profile is selected according to the requirements of the application using the communication channel For example, by decreasing the interleaver depth, the latency is reduced, but the error rate increased By increasing the Reed-Solomon overhead, the bit eπor rate is decreased, but the data rate is also decreased. Decreasing the SNR margin increases the data rate but also increases the error rate. Application Requirements and Application Profiles

Typically, the initiating ATU will know the particular application using the communication channel to be supported Although G hs can be used to convey application requirements, it currently is not sufficiently comprehensive and is significantly more time consuming than performing the application requirement selection in the fast retrain procedure Furthermore, G hs is not always invoked pπor to a fast retrain such that application requirements may be exchange When performing a fast retrain to compensate for channel changes, the application requirements will typically remain unchanged from those pπor to the fast retrain. However, when transitionmg from a power management state using fast retrain, it is likely that the application requirements may have changed Furthermore, the application requirements may change while in SHOWTIME data transmission.

To account for application requirement changes of the DSL line, it is proposed that application requirements be exchanged between the ATUs duπng the fast retrain. Limited application requirements are exchanged in G hs, however, additional application requirements and application profiles may be added in addition to those m G hs Preferably, Application Requirements would indicate, at a minimum, the desired data rate, bit error rate and latency required for the application to be transported In addition, the Application Requirements could also include signal to noise ratio margin, average and peak latency, minimum and average data rate requirements, average and peak error rates, maximum burst error tolerance, etc This mfonnation could be conveyed individually with no reference to the particular application or could also be conveyed by further defining Application Profiles describing particular applications

In an exemplary embodiment. Application Profiles may include low-grade voice, high-grade voice, CD-quality audio, low-grade video, internet browsing, etc Each Application Profile implies the necessary service requirements Table 1 identifies several typical applications along with potential quality of service requirements Additional quality of service requirements imposed by the higher layer transport protocols are not reflected here and may alter the overall requirements

TABLE 1 Example Quality of Service Requirements for Various Applications

To account for Application Requirement changes, it is proposed that Application Requirements be exchanged dunng C-MSG-FR1 and R-MSG-FR1 messages m this exemplary embodiment Occumng near the start of the fast retraining, the C-MSG-FR1 and R-MSG-FR1 messages are 16 bit messages modulated using one bit per symbol C-MSG-FR1 and R-MSG-FR1 include 16 data bits followed by a 16-bit CRC parity check

R-MSG-FR1 messages (m) are typically defined by m = {u7, uό, , ul , u0, d7, d6, ,dl, dO)

Bits d4 to dO (LSB) indicate the relative downstream Fast Retrain Power Cutback PSD level and represent the power cutback in 2 dB steps (maximum of 62 dB power cutback) Bit d5 is the "Fast Retrain Truncate" bit and is used to indicate that the ATU-R requests to truncate the fast retrain sequence and exit to the full initialization sequence Bits d7 and d6 are reserved and set to 0_b In this embodiment of the invention, these two unassigned bits along with u5-u7 may be used to carry the application requirement and profile information, if sufficient In another alternate of the invention, these two unassigned bits along with u5-u7 may be used to carry the application requirement and profile information, if sufficient In another alternate embodiment, a fixed or \ anable number of additional bytes may be added to specifically convey application requirements or profiles The least significant bit dO is transmitted first Table A below defines the relationship between the PSD level and the values for {d4, d3, d2, dl, dO}

Relative Downstream Fast Retrain Power Cutback

Table A

Bits u4 to uO (LSB) indicate the Absolute Fast Retrain Power Cutback PSD level and represent the power cutback in 2 dB steps (maximum of 62 dB power cutback) Bits u7 to u5 are reserved and set to Ob The least significant bit, uO, is transmitted first Table B below defines the relationship between the PSD levels and the values for {u4, u3, u2, ul , and uOJ

Absolute Upstream Fast Retrain Power Cutback

Table B

C-MSG-FR1 messages, m are defined by m = { b l 5, bl 4 b2, b l , b0)

Bits b4 to bO indicate the Fast Retrain Politeness Power Cutback PSD level to a maximum of 62 dB power cutback with respect to the nominal downstream PSD level as used by the preceding C-REVERB-FR1 signal. Bit b5 is the "Fast Retrain Truncate" bit and is used to indicate the ATU-C requests to truncate the Fast Retrain procedure and exit the initialization procedure. The other Bits are reserved and set to Ob. In this embodiment of the invention, these unassigned bits may be used to carry the application requirement and profile information, if sufficient. In another alternate embodiment, a fixed or variable number of additional bytes may be added to specifically convey application requirements or profiles. The least significant bit, uO, is transmitted first. The Table C below defines the relationship between the decimal value of {b4, b3, b2, bl , bO } to the Fast Retrain Politeness Power Cutback.

Fast Retrain Politeness Power Cutback

Table C

The C-MSG-FR1 and R-MSG-FR1 messages are preferably augmented to convey this information. For example, a single 16-bit word is added to select an application profile between predefined application profiles 1 and 2^{I 6}-1 . If the current application requirements are not represented by any of the predefined application profiles, profile 0 is selected, signaling that an additional, 16 bytes will follow to specify the particular application requirements.

It should be understood that Application Requirements and Application Profiles are not required for profile modification, and other embodiments may be practiced without Application Requirements. Profile Modification

During the last stage of the fast retrain sequence, each receiver selects a single stored profile comprising stored modem operating parameters appropπate for the current line characteristics and exchanges the corresponding profile identification number using the C-MSG-FR2 and R-MSG-FR2 signals. Each of the signals includes 16-bιts used to identify the profile selection and are followed by a 16-bit CRC panty check The data and parity bits are encoded using the wide band SEGUE and REVERB symbols The REVERB symbol is a phase reversed SEGUE symbol and each symbol represents one bit at a 4000 symbols/second bit rate.

Generally, stored profiles correspond to the operating parameters of a previous session that were saved using the AOC profile management procedure. For example, new profiles are typically created and exchanged using the full initialization procedure (one profile for the upstream direction and one profile for the downstream direction). Either or both receivers may request that the current profile be saved if (a) the current profile is performing adequately, (b) the profile is not already saved and (c) there is enough memory to store another profile or that an existing saved profile can be overwritten. Since both ATU transceivers are already using both profiles, it is only necessary to indicate that the current profile be saved and assign a profile identification number that can later be used to reference that profile. The AOC (ADSL Overhead Channel) protocol currently defines two profile management messages: the Profile Management Request message which requests that the current profile be stored as profile number xxxx_b (from 0 to 15), and the Profile Management Acknowledge message which confirms that the profile was saved (by echoing the profile number xxxx_b) If the profile cannot be saved, the Unable to Comply (UTC) message is sent. The stored profiles include such information as bits and gains tables, Reed-Solomon coding parameters and interleaver depth and are known to those skilled in the art

If the channel conditions change due to, for example, on-hook or off-hook transitions, temperature fluctuations, increases or decreases in crosstalk due to adjacent pair services or changes in RFI ingress, or the application requirements change, none of the stored profiles may match the current needs In this embodiment, rather than sending an "unknown Profile" indicator in the C-MSG-FR2 and R-MSG- FR2 message(s) and initiating a full initialization, the "best-fit" profile is selected. Profiles, typically and at a minimum, contain two bytes for Reed Solomon parameters, a single byte for interleaver depth and 32 16-bit words for the upstream bits and gains table and 128 16-bit words for the downstream bits and gains table. Thus, when selecting the 'best fit profile', the profile w hich requires the least number of modifications to the bits and gains table parameters is generally chosen in order to minimize the time it takes to communicate the profile modifications

The best-fit profile, however, may be sub-optimal. In a preferred embodiment, Profile Modification commands are issued to improve any sub-optimahties of the selected profile. The Profile Modification Commands may be earned in the C-MSG- FR2 and R-MSG-FR2 messages and could include a set of commands similar to that used by the bit swap procedure The bit swap procedure is a method of either moving one bit from one DMT earner to another DMT earner or adjusting the gam of a particular DMT carrier duπng SHOWTIME without interrupting the flow of data. In essence, it is an on-line method of modifying a currently used profile. The bit swap messages and protocol are transported over the AOC and are descπbed in § 9 of the ITU G 992 2 (G.hte) standard

The R-MSG-FR2 message is a 16-bit message indicating the downstream line profile selected by the ATU-R. The R-MSG-FR2 message (m) is defined by. m = {ml5, ml4, . m2, ml. mO) Bits m3 to mO represent the line profile index up to 16 profiles, with profile index LSB in mO Bit m4 is used to indicate a "Known Profile" (Ob) or a "Unknown Profile" ( l_b) The other bits are reserved and set to O_b The most significant bit, mO is transmitted first

The C-MSG-FR2 message is a 16-bit message indicating the upstream line profile selected by the ATU-C The C-MSG-FR2 message (m) is defined by m = jml5, ml4, m2, ml , m0) With mO. the least significant bit, being transmitted first Bits m3 to mO represent the line profile index up to 16 profiles, with profile index LSB in mO Bit m4 is used to indicate a "Known Profile" (O_b) or a "Unknown Profile" ( l_b) The other bits are reser ed and set to O_b The most significant bit. mO is transmitted first According to this embodiment, an extension of the R-MSG-FR2 and C-MSG-FR2 messages is utilized to transmit profile modification messages The first 16 bits are utilized as defined above, although the reserved bits can be utilized to indicate, for example, the number of profile modification commands to follow (see 'N' in Table D) The profile modification commands could be formatted as descnbed below

In the preferred embodiment, the profile modification commands are sent similar to bit swap commands sent during C-MSG-FR2 and R-MSG-FR2 Shown in Table D below is a format of an exemplary profile modification message consisting of N profile modification commands

Table D

As seen above, the profile modification message begins with a Message Header indicating the number of profile modification commands to follow Message Fields 1- N each includes an eight bit Command followed by a related eight bit Subcarner Index for a total of 16 bits per modification The 8 bit sub-carrier index is counted from low to high frequencies with the lowest frequency sub-carrier having the number zero Preferably, the sub-earner index zero should not be used for data In this prefeπed embodiment, setting the sub-earner index to zero indicates that the profile command is not specific to any particular earner and represents a general command Shown in Table E below is an exemplary set of general profile modification commands

Table E Shown in Table F below is an exemplary set of profile modification commands that are specific to the particular subcarner indexed

Table F

Other more efficient Command or command sets could easily be denved if deemed necessary For example, 8 bits could be used to identify the earner, 4 bits to identify the bits/carrier and 4 bits to identify the gain in dB relative to the nominal

Referring now to Figure 3, shown is an exemplary method 48 of optimizing sub-optimal profiles using profile modification according to an exemplary embodiment The method of Figure 3 is exemplary of a particular embodiment and many other embodiments are possible

At Step 50, the initiating ATU commences the fast retraining sequence in response to user activity, a change in conditions such as a change in line conditions or application requirements as previously described For example, the fast retraining sequence may be initiated in response to a change in line conditions such as that due to on-hook/off-hook or a change in power conditions or in response to a change in application such as that due to changing from transporting only low-grade digitized voice to transporting both low-grade digitized voice and Internet data

At Step 52, it is determined whether any Application Requirements or Application Profiles are available by interaction with higher level application layers For example. Application Requirements or Profiles are preferabh transmitted in the C-MSG-FRl and R-MSG-FRl messages during the beginning of the retrain sequence or may be transmitted during a preceding G hs session If Application Profiles or Requirements are available, they can be exchanged at Step 54

At Step 56, the retraining sequence proceeds, culminating in knowledge of the current line conditions At Step 58, it is determined during the retrain sequence whether a stored profile is suitable for the current line conditions If a suitable profile for the line conditions has been found, then that profile is identified in the C-MSG- FR2 or R-MSG-FR2 messages and is used for communication SHOWTIME at Step 60

If none of the stored profiles are suitable for the current line conditions or application requirements, then, according to this embodiment, a best fit stored profile is determined from the available profiles at Step 62 The selected best fit profile is preferably identified by use of a flag or signal as best fit and thus possibly sub-optimal for the current line conditions or application requirements and that profile modification commands are to follow

At Step 64, the profile modification of the selected best fit profile is performed The selected best fit stored profile is sub-optimal for the current line conditions Profile modification commands are utilized to modify the stored profile according to the line conditions or application requirements/profile

Figure 4 shows a diagram illustrating a number of paths where application profiles or profile modification may be used Figure 4 shows an embodiment where profile modification and application requirement identification are utilized as part of the fast retrain procedure and how the fast retrain sequence and profile modification procedure are utilized during the communication process

At Step 404, the link is m the idle state until the user becomes active and the channel is utilized Depending upon the history of the link, either the Full Initialization starting with G hs at Step 408 or the Fast Retrain at Step 406 will execute, ideally culminating in the SHOWTIME state 402 At Step 408, the first phase of G hs is performed including rudimentary link establishment and capabilities exchange Based on the capabilities exchanged, either the ATU-R or ATU-C selects a mode of operation at Step 412 During mode select, application requirements may be exchanged G Handshake is terminated at Step 416 and depending on the mode selections, proceeds to G lite Fast Retrain Step 406, G lite Full initialization Step 420 or some other DSL mode Step 422

At Step 420, Full Initialization is performed, in part, to create a new upstream and downstream profile This profile is used upon entry into Step 402, the SHOWTIME state Alternatively, from G Handshake Step 416 or from the Idle State Step 404, a fast retrain may be performed At Step 406, the first phase of the fast retrain procedure is performed including rudimentary link establishment, preliminary channel characterization and pow er level adjustments

At Step 410, the R-MSG-FRl and C-MSG-FRl messages are exchanged identifying power level cutbacks and may indicate truncating the Fast Retrain Process to perform G Handshake Step 408 for example, if no stored profiles are available Application Profiles and/or Requirements are exchanged at Step 410 The second phase of the Fast Retrain Step 414 includes further channel characterization Upon completion of the channel characterization, the R-MSG-FR2 and C-MSG-FR2 messages are exchanged at Step 418 These messages identify a particular best fit profile and provide profile modification commands if necessary such that SHOWTIME Step 402 may commence Alternatively, if no suitable profiles can be selected, even when profile modification commands are supplied, the Full Initialization starting with Step 408 may be performed to determine new upstream and downstream profiles Once in SHOWTIME Step 402, the ATU-R and ATU-C can autonomously request that the current operating profile be saved as a stored profile for future G lite sessions

The embodiments of the invention help adapt ADSL transmission characteristics to changing line conditions while maintaining the quality of service requirements of the applications being transported If the profiles do not match the current application and/or channel requirements, they can be modified such that a non-optimal profile may be optimized (or made near optimal) avoiding a loss in qualitv of service A full initialization to obtain a new profile is not required, saving 6-10 seconds in retraining time In addition, profiles can be tailored to particular application requirements and may allow for a reduction in the number of profiles (and thus storage space) given that profiles which exactly match the channel are no longer necessary It should be understood that the programs, processes, methods and systems described herein are not related or limited to any particular type of computer or network system (hardware or software), unless indicated otherwise Vanous types of general purpose or specialized computer systems may be used with or perform operations in accordance with the teachings descnbed herein

In view of the wide vaπety of embodiments to which the pπnciples of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only The illustrated embodiments should not be taken as limiting the scope of the present invention

For example, the steps of the flow diagrams may be taken in sequences other than those described, and more or fewer elements may be used in the block diagrams. While \ aπous elements of the preferred embodiments have been described as being implemented in software, in other embodiments hardware or firmware implementations may alternatively be used, and vice-versa

The claims should not be read as limited to the described order or elements unless stated to that effect. Therefore, all embodiments that come within the scope and spmt of the following claims and equivalents thereto are claimed as the invention.

Claims

I Claim

1 A method of adapting communication parameters to changing line conditions, the communication parameters defined in profiles, the steps compπsing detecting a change in conditions such as a change in line conditions or application requirements, determining the current line conditions, comparing the current line conditions to the profiles, selecting a best-fit profile according to the current line conditions, and modifying the profiles according to the current line conditions to optimize the profile for communication according to the current line conditions

2 The invention of claim 1 wherein the profile comprises bits and gains tables, Reed-Solomon coding parameters and interleaver depth

3 The invention of claim 1 wherein the step of modifying profiles is transmitted within the C-MSG-FR2 and R-MSG-FR2 messages

4 The invention of claim 1 wherein the best-fit profiles is selected according to the profile which requires the least number of modifications to the profile parameters to match the current line conditions and/or application requirements

5 The invention of claim 1 further compnsing the steps of identifying application requirements for the line condition, and selecting the appropπate profile according to the application requirements

6 The invention of claim 4 wherein the application requirements are determined according to application profiles

7 The invention of claim 4 wherein the application requirements are transmitted during the C-MSG-FRl and R-MSG-FRl messages 8 The inv ention of claim 4 wherein the application requirements compnse the desired data rate, bit error rate and latency desired for the application to be transported

9 The invention of claim 4 wherein the application requirements compnse signal to noise ratio, noise margin, average and peak latency, minimum and average data rate requirements, average and peak error rates, and maximum burst error tolerance

10 The invention of claim 1 wherein the steps are stored on a computer readable medium

1 1 A method of adapting communication parameters to changing line conditions in an digital subscriber line system, the communication parameters defined in profiles, the steps comprising detecting a change in conditions such as a change in line conditions or application requirements, determining the current line conditions, transmitting application requirements of the communication channel, comparing the current line conditions to the profiles, selecting a best-fit profile according to the current line conditions and the application requirements, and modifying the profiles according to the current line conditions and application requirements to optimize the profile for communication according to the current line conditions

12 The invention of claim 1 1 wherein the application requirements compnse the desired data rate, bit error rate and latency desired for the application to be transported

13 The invention of claim 1 1 wherein the application requirements comprise signal to noise ratio, noise margin, average and peak latency, minimum and average data rate requirements, average and peak error rates, and maximum burst error tolerance.