Abstract:
A method and system for provisioning remote user data access over digital subscriber lines (DSL&#39;s) through connection-oriented packet networks is described. According to a preferred embodiment, DSL terminal units are directed to train at a rate that is not substantially greater than the subscribed data rate, thereby avoiding network congestion due to data rate mismatches between the DSL connection and a corresponding permanent virtual circuit (PVC) channel through the connection-oriented packet network. According to another preferred embodiment, the DSL units are directed to test for the maximum trainable data rate before settling to the subscribed data rate, and to communicate this information to a network operations center computer, thereby allowing the maximum allowable DSL data rate to be compared to actual client traffic usage patterns and to the client&#39;s subscribed data rate. According to another preferred embodiment, in the event that the maximum trainable rate lies substantially below the subscribed data rate, the network operations center automatically re-provisions the permanent virtual circuit (PVC) channel through the connection-oriented packet network to a corresponding lower level, thereby conserving network resources.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of digital communications. In particular, the present invention relates to an optimal method for provisioning a high-speed data connection between a user and a destination over a connection-oriented packet network having digital subscriber line access to the user premises. 
     BACKGROUND OF THE INVENTION 
     With the explosive growth of the Internet and with the increasing desirability of telecommuting, the need for more reliable and higher speed data access over the “last mile” to homes and small businesses has become apparent. In particular, it has become desirable to provide high-speed data communications (1) between remote users, such as users at homes or small businesses, and corporate networks for telecommuting purposes, and (2) between remote users and the Internet. A traditional method of remote user access, and still the most common, involves the use of two-wire modems, such as V.90 modems, to establish a dial-up connection between the remote user and their company&#39;s dial-in server, or between the remote user and their Internet Service Provider (ISP). Although still having certain cost advantages, the traditional dial-up modem has many practical disadvantages including dial-up delay and including a limited data access rate, which is currently 56 Kbps for V.90 modems. 
     FIG. 1 shows a block diagram of an emerging technology and service solution that provides numerous advantages over traditional remote access methods. FIG. 1 shows a connection-oriented packet network  100  for providing a connection between a remote user and a destination where a DSL (Digital Subscriber Line) link is used to access the remote user premises. As used herein, “remote user” indicates a customer at a home, small business, or other location whose primary method of data connection to the outside world is through ordinary telephone system “last mile” copper connections to the telephone company central office (CO). 
     As known in the art, connection-oriented protocols rely on end-to-end connections through virtual circuits. The virtual circuits are either Permanent Virtual Circuits (PVC&#39;s) that are permanently “nailed up”, or Switched Virtual Circuits (SVC&#39;s) that are established on a per-call basis. In a connection-oriented protocol, successive packets travel from the source to the destination over the same path, whereas for connectionless protocols each individual packet finds its own way through the network to its destination. Examples of connection-oriented protocols include Asynchronous Transfer Mode (ATM), Frame Relay, and X.25 Virtual Circuit Mode. Examples of connectionless protocols include the Internet Protocol (IP), X.25 Datagram Mode, and SMDS (Switched Multimegabit Data Service). 
     From a connectivity and throughput perspective relevant to the remote access network of FIG. 1, the newer connection-oriented protocols such as Frame Relay and ATM are advantageous for reasons including (a) higher data rates over the newer and more reliable hardware that is now available, as compared to connectionless lower-level protocols, and (b) the opportunity to define specific grades of service, such as CIR (Committed Information Rate) for Frame Relay and QoS (Quality of Service) metrics for ATM. See generally McDysan and Spohn, ATM:  Theory and Application, Signature Edition,  McGraw-Hill Series on Computer Communications (1998), the contents of which are hereby incorporated by reference into the present disclosure. 
     As known in the art, DSL technology affords the opportunity to establish high bit rate access over ordinary copper lines between remote user premises and the telephone company CO. DSL technology has been described as creating high-speed “dumb pipes” over ordinary copper lines, allowing high bandwidth to remote users at reduced cost. See K. Taylor, “Converting Copper: How xDSL Paves the Way for ATM”, in Gadecki and Heckart, ATM . . . , IDG Books Worldwide (1997) at pp. 91-93. The contents of the Gadecki and Keckart text are are hereby incorporated by reference into the present disclosure. 
     DSL technology, often named xDSL technology, comes in several different variations. High Bit Rate DSL (HDSL) is the oldest DSL technology, which arose from problems in transmitting T 1  (1.544 Mbps) over long copper loops, offers symmetric (same speed both ways) data rates up to 1.544 Mbps in a 4-wire implementation, and up to 768 Kbps in 2-wire implementations. Symmetric DSL (SDSL) offers, in a single 2-wire implementation, a symmetric data rate of up to 1.1 Mbps and even 1.544 Mbps in light of recent improvements. Asymmetric DSL (ADSL) offers, in a single 2-wire implementation, the combination of a high-speed downstream channel that can deliver a one-way downstream rate of 1.5-8 Mbps to the remote user, along with a duplex channel that can deliver a symmetric data rate of up to 640 Kbps. Other types of DSL services have emerged including Rate Adaptive DSL (RADSL), ISDN DSL (IDSL), and Very High-Speed DSL (VDSL). See generally Chen, DSL:  Simulation Techniques and Standards Development for Digital Subscriber Line Systems,  MacMillan Technology Series (1998), the contents of which are hereby incorporated by reference into the present disclosure. 
     As shown in FIG. 1, the connection-oriented packet network  100  provides connectivity between a remote user or client premise  102 , such as a home or small business, and a corporate LAN  104 . Alternatively, or in conjunction therewith, the connection-oriented packet network  100  provides connectivity between the client premise  102  and the Internet  106  via ISP  108 . As used herein, for simplicity and clarity of disclosure, the remote user is denoted as the “client” of the remote data access service. It is to be appreciated that the “customer” of the remote data access service of FIG. 1, i.e. the party that requests the service and pays the service invoices, may actually be the client, the client&#39;s employer, the ISP, or a different party depending on bundling, reselling, or other business and marketing factors. Unless otherwise indicated herein, and for purposes of clarity of disclosure and not by way of limitation, the “client” shall correspond to a single entity at the remote user premise who requests, uses, and pays the remote data access service of FIG.  1 . 
     In the case of the corporate LAN  104  as the destination, the connection-oriented packet network  100  provides a permanent virtual circuit (PVC) between the client premise  102  and the corporate LAN  104 . Physically, (1) a DSL link  110  is provided between the client premise  102  to the CO  112 , (2) a standard Time Division Multiplexed (TDM) link  114  (e.g., DS- 3  or STS- 3   c ) is provided between the CO  112  to an ATM network switch  116  of an ATM Network  118 , (3) facilities of ATM Network  118  are provided between ATM network switch  116  and an ATM network switch  120  near the corporate LAN  104 , and (4) a standard TDM link  122  (e.g., DS- 1  or DS- 3 ) is provided between ATM network switch  120  and the corporate LAN  104 . The DSL link  110  is provisioned between (a) a remote DSL terminal unit  132  such as a DSL modem at the client premise  102 , and (b) a CO DSL terminal unit  134  such as a DSL Access Multiplexer at the CO  112 . The TDM link  122  between ATM network switch  120  and the corporate LAN  104  terminates at a router  107  at the corporate site. 
     Using the above facilities, in FIG. 1 an ATM circuit is provisioned between remote DSL terminal unit  132  and router  107 , traversing the DSL link  110 , the CO DSL terminal unit  134 , the TDM link  114 , the ATM switch  116 , the ATM Network  118 , the ATM switch  120 , and the TDM link  122 . For purposes of disclosing features and advantages of the preferred embodiments infra, the portion of the ATM circuit between the remote DSL terminal unit  132  and the CO DSL terminal unit  134  may be referred to as a digital subscriber line portion, while the portion of the ATM circuit between the CO DSL terminal unit  134  and the router  107  may be referred to as a connection oriented packet network portion. 
     In the case of the ISP  108  as the destination, the connection-oriented packet network  100  provides a similar PVC except that connectivity is provided between the ATM network switch  116  and a different ATM network switch  124  closer to the ISP  108  over a TDM link  126  to ISP  108 . The TDM link  126  terminates at a router (not shown) at ISP  108  which provides connectivity to the Internet  106 . Thus, in this case, an ATM circuit is provisioned between remote DSL terminal unit  132  and a router at ISP  108 , traversing the DSL link  110 , the CO DSL terminal unit  134 , the TDM link  114 , the ATM switch  116 , the ATM Network  118 , the ATM switch  124 , and the TDM link  126 . 
     It is to be appreciated, of course, that the router  107  at the interface to the corporate network, as well as the router (not shown) at the interface to ISP  108 , represent endpoints of the connection-oriented packet network  100 . The Internet  106  and LAN  104  are not in themselves part of the connection-oriented packet network  100 . It is to be further appreciated that the ATM Network  118  is exemplary of a network that provides PVC and SVC services, but may contain, in whole or in part, portions that use a different connection-oriented protocol such as Frame Relay without departing from the scope of the preferred embodiments. 
     The connection-oriented packet network  100  of FIG. 1 is similar to a currently available service named TeleSpeed® offered by Covad Communications, the assignee of the present invention. As described on the Covad web site www.covad.com, the entirety of which is hereby incorporated by reference into the present disclosure as of the filing date, exemplary TeleSpeed® subscription services include: TeleSpeed® 144, which uses an IDSL connection between the customer premise and the CO that allows a symmetric 144 Kbps data rate, TeleSpeed® 192, which uses an SDSL connection between the customer premise and the CO that allows a symmetric 192 Kbps data rate; TeleSpeed® 384, which uses an SDSL connection for a symmetric 384 Kbps data rate; TeleSpeed® 768, which uses an SDSL connection for a symmetric 768 Kbps data rate; TeleSpeed® 1.1, which uses an SDSL connection for a symmetric 1.1 Mbps data rate; and TeleSpeede® 1.5, which uses an ADSL connection for offering of a downstream channel of up to 1.5 Mbps in combination with an upstream channel of up to 384 Kbps. It is to be appreciated, however, that the scope of the preferred embodiments is not limited to such implementations. For purposes of the present disclosure, the providers of high speed remote access using digital subscriber lines through connection-oriented packet networks, such as Covad Communications, may generically be referred to as end-to-end service providers. 
     As shown in FIG. 1, the client premise  102  usually contains one or more client computers, two such client computers  128  and  130  being shown in FIG.  1 . Client computers  128  and  130  are each equipped with LAN access equipment such as  10 BaseT Ethernet cards (not shown) for coupling to a client LAN  113 . Any of a variety of protocols may be used for establishing data communications among client computers  110  and  112  over client LAN  113 , including standardized protocols such as TCP/IP over Ethernet, proprietary protocols such as Novell IPX, or other protocols. 
     Connection-oriented packet network  100  comprises a DSL link  110  between a remote DSL terminal unit  132  and a CO DSL terminal unit  134 . Remote DSL terminal unit  132  is coupled to the user LAN  113 . The type of DSL terminal units  132  and  134  that are used will depend on the subscribed service and the type of equipment on the user LAN  113 . For example, in the case of TeleSpeed® 144 service from Covad Communications, remote DSL terminal unit  132  may be an Ascend Pipeline 50/75, a Cisco 700 series router, a Cisco 1604 router, or a Flowpoint 144 router, while the CO DSL terminal unit  134  may be a Cisco 90i IDSL Channel Unit. In the case of TeleSpeed® 192, 384, 768, or 1.1 service from Covad Communications, remote DSL terminal unit  132  may be a FlowPoint 2200 SDSL router. In the case of TeleSpeed® 1.5 service from Covad Communications, remote DSL terminal unit  132  may be a Flowpoint 2100 ADSL router. CO DSL terminal unit  134  may be a Diamond Lane DSL Access Multiplexer. It is to be appreciated, of course, that the above exemplary equipment is listed for completeness of disclosure and so as not to cloud the features and advantages of the preferred embodiments. As line speeds increase and/or other technological advances are made, the implementations may use different equipment without departing from the scope of the preferred embodiments. 
     It is also to be appreciated that remote user premise  102  is one of tens, hundreds, or even thousands of client premises that may be connected over DSL lines similar to DSL line  110  for termination at the telephone company CO  112 . Accordingly, the CO DSL terminal unit  134  may be one of many such units at the CO  112 , and each CO DSL terminal unit may be coupled to several DSL lines depending on its capabilities. For simplicity and clarity of disclosure, however, only one such DSL line  110 , remote DSL terminal unit  132 , and CO DSL terminal unit is shown in FIG.  1 . 
     At the telephone company CO  112 , the network sides of the multiple DSL lines are multiplexed onto a high-capacity transmission line using, for example, a DSL Access Multiplexer for providing an ATM protocol connection between the DSL lines and the ATM network switch  116 . The ATM network switch  116  may be, for example, a Cisco BPX® ATM switch. Between the ATM network and the corporate LAN  104  or ISP  108 , data packets are delivered in accordance with the appropriate protocols, the details of which are beyond the scope of the present disclosure but which are described, at least in part, in the McDysan and Spohn text supra. 
     Provisioning refers to the process of configuring hardware and software to establish a virtual circuit between the client premise and the destination. Provisioning includes the process of establishing the DSL link  110  between the client premise  102  and the CO  112 , as well as the process of establishing a virtual circuit between the CO  112  and the destination. In the case of permanent or “nailed up” data connections, as is the case with the exemplary TeleSpeed® services described supra, the service remains in its provisioned configuration unless changes occur. Such changes include, but are not limited to, interruptions in the ATM network such as link outages, interruptions in the DSL line such as the inadvertent unplugging of the client DSL unit, and maintenance interruptions in either portion. Upon such occurrences, the ATM network is designed to automatically reroute traffic and/or reestablish PVC connections, and the DSL units are designed to automatically re-train to establish DSL connectivity as soon as possible. 
     A problem occurs in the remote user data access network of FIG. 1 due to present-day provisioning processes. In particular, in prior art provisioning processes the DSL terminal units are configured to train at the highest obtainable speed, independent of the rate that is subscribed to by the customer. Often, the actual trained data rate between the DSL terminal units is much higher than the subscribed rate, simply because the facilities between the customer premise and the CO allow this higher trained rate to happen. As an example, it has been observed in some circumstances that the DSL terminal units will train as high as several megabits per second (Mbps), even though the subscribed rate was only 384 Kbps. However, the ATM network has only provisioned 384 Kbps for that remote user&#39;s PVC. In this case, unwanted congestion can occur between the CO DSL terminal unit and the ATM network switch during bursts of data greater than the subscribed rate of 384 Kbps. 
     As described in ATM:  Theory and Application,  supra, at Chapter 23, the ATM protocol is designed to respond to the unwanted congestion through various means, which may include the invocation of Selective Cell Discard, i.e. the “bit-bucketing” of lower priority cells. Although higher-level protocols will ensure overall data integrity, e.g. by requesting re-send of the data by the client and/or destination computers, the overall efficiency of the end-to-end network is compromised, and a lower overall throughput may result. 
     FIG. 2 shows a diagram of a training sequence between DSL terminal units that causes the above congestion problem in prior art implementations of remote user access over DSL through connection-oriented packet networks. FIG. 2 shows a generic user DSL Modem  232  located at the remote user premises coupled to a generic DSL Access Multiplexer  234  located at the CO. In the example of FIG. 2, an SDSL symmetric connection of 384 Kbps is provisioned. In accordance with the prior art, the exemplary DSL Access Multiplexer  234  is capable of training to speeds 300, 400, 500, 600, 700, and so on, up to a maximum of several Mbps. The speeds 300, 400, 500, etc. represent the speed increments at which the DSL Access Multiplexer  234  can train. Due to hardware considerations, typical DSL Access Multiplexers  234  are incapable of training at speeds that lie between these speed increments. The user DSL Modem  232  is programmed to attempt to train at whatever speed attempted by the DSL Access Multiplexer  234 . It is to be appreciated that the specific numbers 300, 400, 500, etc. used in this example were selected for clarity of disclosure, and are not intended to precisely represent the actual training speed steps of the existing physical devices. Actual training speeds of the existing physical devices vary depending on brand and other factors, but will generally vary in a manner analogous to this example. 
     In accordance with this prior art example, when the SDSL connection is first established, the DSL Access Multiplexer  234  will first attempt to train with the user DSL Modem  232  at the lowest data rate, that is, 300 Kbps. If copper facility conditions and loop length allow successful training with user DSL Modem  232  at 300 Kbps, then DSL Access Multiplexer  234  will increase the attempted training rate to the next speed increment, 400 Kbps. If successful, i.e. if copper facility conditions and loop length allow training with user DSL Modem  232  at 400 Kbps, then DSL Access Multiplexer  234  will increase the attempted training rate to the next level, 500 Kbps, and so on until the increase in attempted training speed causes training failure. Such a failure level is shown as 700 Kbps in FIG.  2 . In this case, the DSL Access Multiplexer  234  and the DSL Modem  232  “settle” on a training rate of 600 Kbps. 
     Disadvantageously, in this prior art example where the DSL terminal units have trained at 600 Kbps, which is substantially higher than the subscribed rate of 384 Kbps, problems can occur. In particular, if the client transmits a substantially long burst of data at, say, 550 Kbps, then the ATM network will respond with congestion recovery measures, because it has only provisioned 384 Kbps for that PVC. These congestion recovery measures can include the “bit bucketing” described above, which results in retransmission requests from the higher order protocols and reduced end-to-end efficiency of the network. 
     Accordingly, it would be desirable to provision data access over DSL through connection-oriented packet networks, such that network congestion due to data rate mismatches between the DSL connection and the provisioned PVC channel is minimized. 
     It would further be desirable to provision data access over DSL through connection-oriented packet networks, such that enhanced services may be offered to the remote user in the event that the DSL connection is capable of training at a data rate substantially greater than the subscribed rate, based upon automatically learned knowledge of the difference between the maximum actual trainable DSL rate and the subscribed rate. 
     It would be even further desirable to provision data access over DSL through connection-oriented packet networks, such that resources in the connection-oriented packet network may be more efficiently utilized in the event that the actual trained DSL rate is substantially less than the subscribed rate provisioned rate. 
     It would be even further desirable to provision data access over DSL through connection-oriented packet networks, such that differences in available speed increments between the DSL link and the provisioned PVC channel are accommodated in a manner that does not “punish” the remote user by excessively discarding cells during periodic bursts of data at speeds lying between respective speed increments. 
     SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment, a method and system for provisioning remote user data access over DSL through connection-oriented packet networks is provided, wherein the DSL terminal units associated with the DSL link are directed to train at a rate that is not substantially greater than a subscribed data rate. In this manner, network congestion due to data rate mismatches between the DSL connection and the corresponding PVC channel through the connection-oriented packet network is minimized or avoided. 
     According to another preferred embodiment, a provisioning process is provided wherein the DSL terminal units are directed to test for the maximum trainable data rate before settling to a trained data rate not substantially greater than the subscribed data rate, and to communicate the maximum trainable data rate to a network operations center computer. In this manner, the maximum allowable DSL data rate to each specific client premise is known by the network operations center, and can advantageously be used by the end-to-end service provider. For example, the maximum allowable DSL data rate may be compared to the client&#39;s subscribed data rate and to the client&#39;s actual traffic usage patterns, permitting enhanced services to be offered to the client by marketing personnel when appropriate. As another example, knowledge of the maximum allowable DSL data rates for a plurality of client premises may be used for facility routing and community data planning applications, and may be sold to digital content providers as valuable marketing data. 
     According to another preferred embodiment, in the event that the maximum trainable rate between DSL terminal units lies substantially below the subscribed data rate, the network operations center causes the automatic re-provisioning of the permanent virtual circuit (PVC) channel through the connection-oriented packet network such that the resulting PVC has a corresponding data rate lower than the subscribed data rate. In this manner, bandwidth that would otherwise go unused is released for allocation to other ATM channels, thereby conserving network resources and enhancing network efficiency. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a connection-oriented packet network for providing a connection between a remote user and a destination where a digital subscriber line link is used to access the remote user premises; 
     FIG. 2 shows a diagram of a training sequence between two digital subscriber line terminal units; 
     FIG. 3 shows steps for provisioning data access over digital subscriber line through a connection-oriented packet network in accordance with a preferred embodiment; 
     FIG. 4 shows steps for provisioning data access over digital subscriber line through a connection-oriented packet network in accordance with a preferred embodiment; 
     FIG. 5 shows a portion of a connection-oriented packet network in accordance with a preferred embodiment including a data link between a central office digital subscriber line terminal unit and a network operations center; and 
     FIG. 6 shows steps for provisioning data access over digital subscriber line through a connection-oriented packet network in accordance with a preferred embodiment. 
    
    
     DETAILED DESCRIPTION 
     FIG. 3 shows steps for provisioning data access over a digital subscriber line through a connection-oriented packet network in accordance with a preferred embodiment. At step  302 , the client order is received for remote user access at a subscribed rate (SR). The subscribed rate SR will depend primarily on the marketing strategy and physical plant available to the end-to-end service provider as communicated to the client in advertising material, service orders, customer relations sessions, and so forth. Importantly, neither the client nor the end-to-end service provider is aware of the exact maximum DSL link data rate that will be permitted by the copper facilities between the client premise  102  and the CO  112 . Generally speaking, however, the end-to-end service provider will expect the maximum DSL link data rate to be greater than the subscribed rate SR, or else such rate would not have been offered for sale. If, in fact, the subscribed rate SR is not achievable, a renegotiation of the subscription rate will usually be offered to the customer. 
     At step  304 , the physical plant including the client remote DSL terminal unit  132  and the CO DSL terminal unit  134  (or, more particularly, the DSL Modem  232  at the client premises and DSL Access Multiplexer  234  at the CO as shown in FIG. 2) are physically installed using methods known in the art. For example, the DSL Modem  232  will be programmed at the customer premises to have certain transmission parameters through a management link to a Network Operations Center NOC or through a direct link such as an RS-232 interface to a field technician. Likewise, the DSL Access Multiplexer  234  will be programmed at the CO to have certain transmission parameters, through a standard RS-232 interface to a technician laptop computer or through a management link to the NOC. Alternatively, the DSL Modem  232  and DSL Access Multiplexer  234  are simply installed using the default parameters that are programmed at the factory, and are not modified by the installation technician. As discussed supra, in prior art systems among the default settings are generally (a) for the DSL Access Multiplexer  234 , to the train at the highest possible speed increment, and (b) for the DSL Modem  232 , attempt to train at whatever speed attempted by the DSL Access Multiplexer  234 . 
     At step  306 , in accordance with a preferred embodiment, the DSL Access Multiplexer  234  is programmed to train at a speed that is not substantially higher than the subscribed rate SR. Because the subscribed rate SR will depend on the specific customer and the specific end-to-end service provider, this programming is to be performed by the installation technician at the CO or by the NOC through the management link, and is not custom-programmed at the equipment factory, although the scope of the preferred embodiments is not so limited. Thus, for example, the end-to-end service provider may maintain an inventory of DSL Access Multiplexers that are pre-programmed to different speed increments without departing from the scope of the preferred embodiments. 
     By way of example, and not by way of limitation, the subscribed rate SR may be selected by the client as 384 Kbps. The speed increments for the specific DSL Access Multiplexer  234 , which corresponds to CO DSL terminal unit  134  of FIG. 1, may be 100, 200 Kbps, 300 Kbps, 400 Kbps, 500 Kbps, etc., up to a maximum of several Mbps. In accordance with a preferred embodiment, the DSL Access Multiplexer  234  will be programmed to train at 400 Kbps. Although 400 Kbps is higher than the subscribed rate of 384 Kbps, it is not substantially higher in that it represents the next DSL speed increment available, and any occurring bursts of data at 400 Kbps are not expected to cause significant congestion in the ATM link  114  and ATM network  118 . Nevertheless, the probability exists that congestion may occur in the ATM link  114  and ATM network  118  because of bursts of data between 384 Kbps and 400 Kbps, an issue which is addressed in another preferred embodiment infra. 
     It is to be appreciated that the selection of a training speed not substantially higher than the subscribed rate SR may involve a choice between the first DSL speed increment less than SR (300 Kbps in the above example) and the first DSL speed increment greater than SR (400 Kbps in the above example). Each selection would have its own advantages and disadvantages, and represents a tradeoff in performance. If 400 Kbps is chosen as the training speed, the client will generally enjoy the full 384 Kbps bandwidth, but may experience congestion problems when sending extended bursts between 384 Kbps and 400 Kbps causing retransmission delays in the higher protocol layers that may result in a throughput far less than 384 Kbps at those times. In contrast, if 300 Kbps is chosen as the training speed, the client will not experience the above congestion problems but is, of course, limited to the lower 300 Kbps speed. While tradeoffs exist between the two choices, it is to be appreciated, that the selection of either 300 Kbps or 400 Kbps in this example represents a selection of a training speed not substantially higher than the subscribed rate SR in accordance with a preferred embodiment. 
     It may occur, of course, that there is precise correlation between the subscribed rate SR and the speed increments for the DSL terminal unit. Thus, using the above subscribed rate SR of 384 Mbps for a hypothetical DSL terminal unit that offers speed increments of 184, 284, 384, 484, 584, etc., the appropriate selected DSL training speed that is not substantially higher than the subscribed rate SR would be 384 Mbps. 
     At step  308 , the ATM channel (that is, the permanent virtual circuit established using the ATM protocol) involving the DSL Modem  232 , the DSL Access Multiplexer  234 , and the ATM network  118  is provisioned using methods known in the art. As known in the art, the specific definition of the traffic parameters and QoS parameters for the ATM channel will depend on the specific network equipment providers, although general interoperability standards are provided by standards organizations and industry forums (e.g., the ITU-T, ATM Forum). Generally speaking, the traffic descriptors for the ATM channel will include: a Peak Cell Rate (PCR), the reciprocal of the time between the first bit of one cell to the first bit of the next cell; the Cell Delay Variation (CDV) Tolerance, the variation from the nominal per-cell time spacing that the source may transmit; the Maximum Burst Size (MBS), the maximum number of cells that are allowed to be sent at the Peak Cell Rate (PCR); and the Sustainable Cell Rate (SCR), the maximum average rate. 
     As used herein, and as commonly used in art, the Sustainable Cell Rate (SCR) corresponds to the expected rate of cell transmission across the network, and it is the SCR that is used as the nominal ATM channel rate. Accordingly, when the ATM channel involving the DSL Access Multiplexer  234  and the ATM network  118  is provisioned at step  308 , parameters are chosen such that the SCR is set equal to the subscribed rate SR. Finally, at step  310 , the DSL link and the ATM channel are enabled, allowing service to begin. 
     FIG. 4 shows steps for provisioning data access over digital subscriber line through a connection-oriented packet network in accordance with a preferred embodiment. The embodiment of FIG. 4 is directed to those circumstances in which the speed increments of the DSL Access Multiplexer  234  do not align with the subscribed rates SR. As shown in FIG. 4, steps  402  and  404  are performed in a manner similar to steps  302  and  304  of FIG. 3, respectively. At step  406 , however, the DSL link is programmed to train at the first DSL speed increment greater than the subscribed rate SR. 
     As mentioned supra, when the DSL link is programmed to train at the first DSL speed increment (e.g., 400 Kbps) greater than the subscribed rate SR (e.g., 384 Kbps), congestion problems may occur when sufficient bursts of data are sent at a rate that lies between the two rates, causing retransmission delays in the higher protocol layers that may result in a throughput far less than the nominal subscribed rate SR at those times. In accordance with a preferred embodiment, at step  408  the ATM channel is provisioned with a nominal data rate of SR, but with relaxed congestion reduction parameters that reduce the number cells that are “bit-bucketed” when the congestion condition occurs for this ATM channel. 
     One exemplary method for relaxing the congestion reduction parameters in the ATM channel at step  408  involves the use of larger buffers at the ATM network switch  116 , although other methods may be used. In this manner, there is less “punishment” to the client for the lack of alignment between DSL speed increments and subscription rates SR, which is a factor that is often beyond the client&#39;s technical control. Finally, at step  410 , the DSL link and the ATM channel are enabled, allowing service to begin. 
     FIG. 5 shows a portion of a connection-oriented packet network in accordance with a preferred embodiment, including a DSL Access Multiplexer  534 , an ATM network  518 , and a Network Operations Center (NOC)  502 . DSL Access Multiplexer  534  is coupled to the ATM network  518  through an ATM link  514 , and NOC  502  is coupled to the ATM network  518  through an ATM link  506 . NOC  502  generally comprises a network of computers used to provision and maintain services for the end-to-end service provider. 
     In accordance with a preferred embodiment, a two-way data link  504  is included between the DSL Access Multiplexer  534  and the NOC  502  for allowing readout and programming of DSL access multiplexer parameters from the NOC. The two-way data link  504  may take any of several forms in accordance with the preferred embodiments, including that of a separate connection to the NOC or as a part of a channel on a group of control connections between the CO and the NOC. Indeed, it is within the scope of the preferred embodiments to provide data link  504  in the form of a ATM channel between the DSL Access Multiplexer  534  and the NOC  502  across the ATM network  518 , or for data link  504  to be a DS- 1  circuit. 
     FIG. 6 shows steps for provisioning data access over digital subscriber line through a connection-oriented packet network in accordance with a preferred embodiment using the network shown in FIG.  5 . As shown in FIG. 6, steps  602  and  604  are performed in a manner similar to steps  402  and  404  of FIG.  4 . However, at step  606 , instead of training up to a predetermined rate, the DSL Access Multiplexer  534  trains with remote DSL terminal unit  132  (e.g., a DSL Modem at the client premises) to a maximum actual training rate TRMAX. 
     Importantly, the training rate TRMAX is not a theoretical or historical value, but is rather the current maximum practical value under the present facility conditions. It may be greater, equal to, or less than its theoretical or historical values for any of a variety of reasons, such as rerouting of copper facilities by the telephone company, or the deactivation of an unrelated T 1  circuit that lies in the same copper bundle as the DSL copper pair (thus reducing crosstalk and increasing DSL bandwidth). At step  608 , the value TRMAX is transmitted to the NOC  502  over data link  504 . 
     Subsequent to step  608 , steps  610  and steps  612  are shown in FIG. 6 as being carried out in parallel, although the ordering of these parallel steps does not affect the operation of the preferred embodiments. At step  610 , the DSL Access Multiplexer  534  trains with remote DSL terminal unit  132  at a required training rate. If TRMAX is less than the subscription rate SR, the required training rate is TRMAX. If TRMAX is greater than or equal to the subscription rate SR, the required training rate is set according to steps described supra in connection with step  306  of FIG. 3 or step  406  of FIG.  4 . 
     At step  612 , in accordance with the preferred embodiments, the value TRMAX is stored in a NOC database for future technical or commercial advantages. For example, the maximum allowable DSL data rate may be compared to the client&#39;s subscribed data rate and to the client&#39;s actual traffic usage patterns, permitting enhanced services to be offered to the client by marketing personnel when appropriate. Thus, if the client&#39;s subscribed rate SR is 192 Kbps but TRMAX is 768 Kbps, a marketing call may be made to the client to sell the additional bandwidth, especially if congestion reduction activity has been recently invoked on the client&#39;s ATM channel. As another example, knowledge of the maximum allowable DSL data rates for a plurality of client premises may be used for facility routing and community data planning applications. As yet another example, data regarding the maximum allowable DSL data rates for a plurality of client premises may be sold to interested parties, such as digital content providers, who would consider knowledge of available bandwidth to customer premises as a valuable marketing tool. 
     At step  614 , the NOC determines whether the value TRMAX is greater than or equal to the subscribed rate SR. If yes, a variable PVCR (Permanent Virtual Circuit Rate) is set to the subscribed rate SR at step  616 . If no, the variable PVCR is set to TRMAX at step  618 . At step  620 , the ATM channel involving the DSL Access Multiplexer  534  and the ATM network  118  is provisioned to a data rate corresponding to the value of PVCR. Advantageously, the steps  606 - 620  provide for the conservation of network resources in the event that the maximum trainable rate between DSL terminal units TRMAX has degraded to a value substantially below the subscribed data rate SR. This is because when the DSL link is trained to a rate less than the ATM channel, there will always be excess unused capacity in the ATM channel. Accordingly, it would be more efficient to allow allocation of this extra bandwidth to other ATM channels by reducing its nominal data rate. 
     At step  622 , the DSL link and the ATM channel are enabled, allowing service to begin. In accordance with a preferred embodiment, however, at step  624  the NOC  502  continues to monitor the DSL Access Multiplexer  534  over the data link  504  to detect whether the DSL link has been interrupted or reset, either intentionally or accidentally, causing the need for retraining. As long as there is no resetting of the DSL link, no action is taken. However, if the DSL Access Multiplexer  534  has reset, it is instructed at step  606  to test for the maximum DSL training rate TRMAX possible as of the time of the retraining, and the provisioning steps  608 - 622  are repeated. Of course, if the rate TRMAX has not changed since the last resetting interval, the steps  614 - 618  may be skipped. Advantageously, the method of FIG. 6 provides for automatic updating of the maximum DSL training rate TRMAX whenever the DSL link resets, while also providing for the automated conservation of ATM network resources when the maximum DSL training rate TRMAX falls below the subscribed rate SR. 
     While their salient features have been described, these descriptions are merely illustrative and are not intended to limit the scope of the preferred embodiments. Indeed, the preferred embodiments are applicable to a wide variety of digital communications systems.