Abstract:
To take advantage of 56K modem technology, a data signal must only traverse one digital to analog (D/A) conversion and one analog to digital (A/D) conversion on the return path to a subscriber. However, current data transmission for subscribers served by a Universal DLC system requires a D/A conversion at a voice switch of a public switched telephone network (PSTN), an A/D conversion at the central office terminal of a PSTN and a D/A conversion at a remote data terminal of a DLC system. This adds a D/A and an A/D conversion which causes 56K modem technology to fail. The present invention provides a telephone call routing apparatus installed between subscribers served by a Universal type digital loop carrier system, a central office terminal of a PSTN and a data network interface. The present invention avoids an additional digital to analog conversion performed at the PSTN voice switch and an additional analog to digital conversion performed at the PSTN central office terminal, thereby enabling 56K modem data transmission.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/035,676, filed Jan. 22, 1997. 
    
    
     FIELD OF INVENTION 
     The present invention generally relates to public switched telephone networks and more particularly to a method and apparatus for providing 56K modem technology support for public switched telephone network subscribers served by universal digital loop carrier systems. 
     BACKGROUND OF INVENTION 
     Within the Public Switched Telephone Network (PSTN), some subscribers are served by Digital Loop Carrier (DLC) systems which connect subscribers to a central office (CO) voice switch via efficient high speed digital connections. The path of a telephone call in a universal type DLC system requires that the signal intended for a particular subscriber must pass through one digital to analog (D/A) conversion at the voice switch, one analog to digital (A/D) conversion at the central office terminal (COT) and another D/A conversion at the remote data terminal of the universal type DLC system. 
     The rapid growth of Internet usage has resulted in the desire for faster data transmission. Modem technology has advanced to provide users with the ability to receive data at a rate of 56 kilo bits per second (56K). An example of such technology being standardized by the International Telecommunications Union as V.PCM type modems. This rate is desirable because of the increased amount of information available via the Internet. However there exists competing technologies attempting to become the industry standard for 56K transmissions. All these competing technologies rely on the return path modem signal traversing one D/A converter and one A/D conversion at a subscriber&#39;s receiver. Thus, 56K modem technology is available to most telephone subscribers except those served by Universal type DLC systems. This is due to the additional D/A and A/D conversions between the voice switch and the COT. 
     U.S. Pat. No. 5,610,910 entitled “Access to Telecommunications Networks In Multi-Service Environment” (“the &#39;910 patent”) describes a system which utilizes a CPE connector and a module to route traffic from customer premise equipment (e.g. a computer, fax machine or telephone) to one or more networks (e.g. PSTN, data, etc.). However, the module disclosed in the &#39;910 patent decodes the received signal and analyzes the contents of the data to identify the network service requested (i.e. which ISP). The request must be reassembled (e.g. address conversion, rerouting, etc.) before re-transmitting it to the desired destination network. These additional steps compromise transmission time and provide unwanted data conversions. 
     Thus, there is a need to provide Universal DLC subscribers with the capability to use 56K modem service. 
     SUMMARY OF INVENTION 
     The invention meets these needs and avoids the above-referenced drawbacks by providing a method for enabling the operation of V.PCM modems connected to Universal type digital loop carrier systems, said method comprising the steps of monitoring telephone calls received from at least one telephone subscriber associated with a Universal type digital loop carrier system; routing at least one of the telephone calls directed to a particular one of a plurality of data networks around a central office terminal and a voice switch associated with a public switched telephone network; and transmitting data communication signals utilizing V.PCM modem technology from the data network to the subscriber associated with the Universal type digital loop carrier system. 
     In accordance with another embodiment of the present invention, a telecommunications system is provided that comprises a central office switch and a Universal type digital loop carrier network including a central office terminal and a remote terminal. The digital loop carrier network transmits and receives communication signals with a plurality of telephone subscribers associated with the Universal type digital loop carrier network. A routing unit communicates with the central office switch, the digital loop carrier network and a data service provider. The routing unit redirects the communication signals received from the data service provider away from the central office switch and the central office terminal to the remote terminal for transmission to one of the plurality of telephone subscribers. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a block diagram of a phone network with an installed data routing system between a remote terminal, a data network and a central office and a voice switch in accordance with the present invention. 
     FIG. 2 is a block diagram of a data routing system monitoring unit in accordance with the present invention. 
     FIG. 3 is a block diagram of a line card in accordance with the present invention. 
     FIG. 4 is a block diagram of a network card in accordance with the present invention. 
     FIG. 5 is a block diagram of a portion of the telephone switch relief apparatus in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Turning to the drawings in which like reference characters indicate the same or similar elements, FIG. 1 is a block diagram of a local phone network  10 . Subscribers  15   1  . . .  15   N  are connected to a first remote terminal (RT)  26   1 . Subscribers  16   1  . . .  16   N  are connected to a second RT  26   2 . The data routing system (DRS)  30  is installed between RTs  26   1 ,  26   2  and COTs  56 ,  57  via T 1  lines  31  and  47 , respectively. DRS  30  is configured to conform to the Bellcore TR-57 interface specification associated with Universal type DLC systems. DRS  30  monitors all incoming calls dialed by subscribers  15   1  . . .  15   N  and  16   1  . . .  16   N . Certain numbers, usually access numbers associated with Internet Service Providers (ISPs), are configured by the telephone service provider to be intercepted by DRS  30  and routed around COTs  56  and  57  to data network  55 . The intercepted calls are transported from data network  55  to a particular ISP. If a standard voice call is placed by a subscriber or if a data call is made to an ISP that is not configured to receive re-directed calls, DRS  30  allows the call to go through to voice switch  20  as if DRS  30  was not present. Since the intercepted calls are routed around switch  20 , D/A and A/D conversions performed at the voice switch  20  and COTs  56  and  57  are eliminated. Data transmitted in digital form from ISPs from data network  55  to RTs  26   1 ,  26   2  via DRS  30  avoids the D/A and A/D conversions performed at the voice switch  20  and COTs  56  and  57 . This, as described above enables 56K modem technology or V.PCM type modems to operate correctly, thereby allowing subscribers to take advantage of faster transmission times from ISPs. 
     DRS  30  includes a DLC monitor unit (DMU)  40  and access server  45 . FIG. 2 is a block diagram of DMU  40  which includes line cards  100   1  . . .  100   j , network cards  105   1  and  105   2  and administration card  110 . Line cards  100   1  . . .  100   j  are connected to RTs  26   1  and  26   2  via line card ports  103   1  . . .  103   j  and T 1  lines  31 . Each line card  100   1  . . .  100   j  is allocated to a certain number of T 1  lines  31 , for example 8 or 10 T 1  lines. The line cards  100   1  . . .  100   j  are also connected to COTs  56  and  57  by T 1  lines  47  and line card ports  104   1  . . .  104   j . The T 1  lines are high speed connections common in all telephony networks in the world which use standard rates and formats. For example, in the United States, Canada, Japan and select other countries T 1  lines carry 24 voice channels and operate at 1.544 million bits per second (Mb/s). In the rest of the world, these lines are called E 1  lines and carry 30 voice channels operating at 2.048 Mb/s. DMU  40  supports both E 1  and T 1  signals. Each DMU  40  can, for example, route 768 T 1  data calls and 960 E 1  data calls around voice switch  20  and COTs  56  and  57 . 
     Each line card  100   1  . . .  100   j  looks for an off-hook transition from-each of its assigned subscribers, for example subscribers  15   1  . . .  15   N  or subscribers  16   1  . . .  16   N . The off-hook condition indicates that a subscriber is preparing to place a voice or data call. When an off-hook condition is detected by a line card  100   1  . . .  100   j  associated with the subscriber&#39;s T 1  line, the subsequently dialed number is monitored by decoding the dual tone multi-frequency (DTMF) signals inserted by dialing digits on a common telephone or by dialing a telephone number via a computer modem. 
     DMU  40  also includes network cards  105   1  and  105   2 . The network cards are used to provide an interface between line cards  100   1  . . .  100   j  and data network  55  via access server  45  or directly to access server associated with an ISP. Although FIG. 2 includes two network cards in a redundant configuration, it is understood that additional network cards and/or additional interfaces may be employed to accommodate additional ISP call traffic. Network cards  105   1  and  105   2  include ports  115   1  and  115   2 , respectively which connect to lines  54  via T 1  lines  41  as shown in FIG.  1 . Lines  41  can provide, for example, D channel support for primary rate integrated services digital network (PRI). DMU  40  also includes a first data bus  120   1  which provides connectivity between line cards  100   1  . . .  100   j  and network card  105   1  and a second data bus  120   2  which provides connectivity between line cards  100   1  . . .  100   j  and network card  105   1 . It should be understood that additional data buses can be used to accommodate more network and line cards in DMU  40 . 
     DMU  40  also includes administration card  110  which is a CPU based card responsible for the management configuration of the system. Each of the line cards  100   1  . . .  100   j  and network cards  105   1  and  105   2  interface with administration card  110  via line  122 . Administration card  110  is responsible for controlling which bus  120   1  or  120   2 , which network card  105   1  and  105   2 , and which T 1  port on the selected network card an intercepted call will travel through DMU  40 . This path is determined by the administration card based on available capacity within DMU  40 . If the DTMF tones detected by one of the line cards  100   1  . . .  100   j  is associated with an ISP, the line card associated with the subscriber, for example line card  100   j , hangs-up the call to switch  20  via COTs  56  or  57  and forwards the call to one of the network cards  105   1  or  105   2  via bus  120   1  or  120   2  based upon control signals received from administration card  110 . Line card  100   j  then signals switch  20  that the subscribers line is off hook for the duration of the ISP data call. In addition, administration card  110  controls protection relays in the event of a card failure or card removal. Administration card  110  supports an ETHERNET connection  111  for communicating with external network management systems as well as accommodating downloads of stored telephone numbers associated with particular ISPs. Serial link  112  of administration card  110  is available for local management and control of DMU  40 . 
     FIG. 3 is a block diagram of an exemplary line card  100   j  having T 1  framers. The logical operation of line card  100   j  is the same whether it supports E 1  or T 1  lines. Line card  100   j  includes data-mux circuitry  140  which receives the signals from T 1  framers  150  and  155 . T 1  framer  150  receives the calls from the DLC  25  via line  103   j . Data-mux circuitry  140  interfaces with DTMF detection module  150  to decode the DTMF signals inserted in the subscriber&#39;s channel. 
     Line cards  100   1  . . .  100   j  each include a microprocessor  160 , for example an MPC860. Microprocessor  160  controls data-mux circuitry  140  via line  163  and communicates with DTMF detection module  150  via line  153 . Microprocessor  160  stores a list of destination telephone numbers the local phone service provider(s) would like to detect and re-direct. These numbers are programmable and will typically be local phone numbers associated with particular high volume ISPs. However, data calls to any destination number can be re-directed. Because the re-directing of ISP intended calls is based on their associated phone numbers, only these phone numbers need to be stored which avoids the processing associated with lengthy user profiles and routing information. All calls are passed through line cards transparently via T 1  framers  150  and  155 . T 1  framers  150  and  155  format the calls consistent with the Bellcore TR-08 digital interface specification and forward the calls to voice switch  20  via COTs  56 ,  57  where the calls are converted from D/A and A/D respectively. In this manner, standard voice calls and data calls not intended to be redirected pass transparently through line cards  100   1  . . .  100   j  to switch  20  via COTs  56 ,  57 . 
     If the DTMF signals detected are associated with an ISP&#39;s telephone number to be re-directed around switch  20  and COTs  56 ,  57 , data-mux  140  redirects the call to bus  120   1  or bus  120   2  and onto a particular network card  105   1  or  105   2  based on control signals received from administration card  110 . Once the path through the selected network card has been established, the line card, for example line card  100   j , must signal voice switch  20  to terminate the original call that the voice switch received during the detection and re-directing process. This is done by sending signaling information to the voice switch via framer  155  using an on hook signal to inform the switch that the call is terminated. Line card  100   j  then sends signaling information to framer  155  to inform switch  20  that the subscriber  15   1  . . .  15   N  has left the phone off hook. Voice switch  20  assumes that the subscriber  15   1  . . .  15   N  is permanently in the off hook condition and will periodically poll to check for on hook status. This prevents additional calls from arriving to the subscriber  15   1  . . .  15   N  while the data call is active. 
     Additionally, protect relays  170  and  175  are also included within line card  100   j  and are configured for protection path purposes in the event a particular line card is inoperable. Protect path  180  connects protect relays  170  and  175 . In the event that a hardware failure in DMU  40  occurs, protection relays  170  and  175  route the T 1  signals onto path  180  around DMU  40  as if the DMU was not installed between DLC  25  and switch  20 . Alternatively, protect relays  170  and  175  can be separate cards which interface with line cards  100   1  . . .  100   j  and perform the same function. 
     FIG. 4 illustrates a block diagram of an exemplary network card  105   1  which places the received data call into a PRI or channelized T 1  format for transmission over line  54  to data network  55  via access server  45 . It should be understood that the following description is also applicable to other network cards in DMU  30 . Similarly, network cards receive the data signals in digital form from an ISP via data network  55  and transmit these signals to RTs  26   1 ,  26   2  in digital form. In this manner, the data signals received by a subscriber  15   1  . . .  15   N ,  16   1  . . .  16   N  from an ISP via data network  55  do not undergo a D/A conversion at switch  20  and a A/D conversion at COTs  56 ,  57 , thereby taking advantage of 56K or V.PCM type modems. 
     The PRI signal from network card  105   1  is made up of 23 B and one D channel where the D channel includes, for example, on/off hook information, the subscriber dialed number, etc. Network card  105   1  includes microprocessor  210  which receives a message from administration card  110  via line  122  to allocate a slot in either bus  120   1  or  120   2  to receive the new data call. Microprocessor  210  also receives a message from administration card  110  indicating which of the particular outgoing T 1  lines  115   1 , which of the particular channels in the outgoing T 1  line, and the particular telephone number the network card  105   1  should dial using DTMF tones for channelized T 1  or Q.931 messages for PRI ISDN T 1 s respectively, to connect the data call to data network  55  via access server  45 . Microprocessor  210  receives these messages and interfaces with DTMF module  220  via line  211  to generate the appropriate DTMF signals associated with the intended ISP telephone access number. 
     Network card  105   1  includes data-mux circuitry  215  which processes the incoming data calls via bus  120   1  and  120   2 , timing signals via line  216 , DTMF signals via line  221 , control signals from microprocessor  210  via line  222 , and outputs data calls to T 1  framer  230  via line  235 . Alternatively, either robbed signaling or D-channel interfaces are used between microprocessor  210  and data-mux circuitry  215  via line  236 . By way of example, a network card  105   1  in DMU  40  in accordance with one embodiment of the present invention can handle 384 or 480 re-directed data calls for T 1  or E 1  lines, respectively. 
     FIG. 5 is a block diagram of a typical access switch/server  45 , data network  55  and ISPs  50   1  and  50   i . Access server  45  is used to place the data call into frame relay or ATM formats for transmission to data network  55 . Access server  45  receives the T 1  lines  41  from DMU  40 . Access server  45  includes a network interface  310  which receives the data calls and forwards them to digital modems  315   1  . . .  315   N , where N can be, for example, 1 to 288. Modems  315   1  . . .  315   N  are connected to L2TP client module  320  via lines  316   1  . . .  316   N . L2TP client sets up a virtual channel to communicate with a particular ISP  50   1  and  50   i . Access server  45  can be configured in one of two modes: L2TP mode where the access server knows the dialed number to put the call on appropriate tunnel to the ISP; and ISP mode where the access server just answers the call. In L2TP mode, the dialed number is passed to access server  45  by either using the basic Q.931 call control in case of ISDN PRI interface or DTMF digits in the case of channelized T 1 . 
     Data network  55  receives the redirected subscriber call in packet form via DS 1  or DS 3  lines  355 . Frame relay or ATM switch  356  forwards the call to the appropriate ISP  50   1  or  50   2  as is generally known. Similarly, data signals received from ISPs via data network  55  are forwarded to RTs  26   1 ,  26   2  via access server  45  in digital form. 
     While the foregoing invention has been described in terms of the embodiments discussed above, numerous variations are possible. Accordingly, modifications and changes such as those suggested above, but not limited thereto, are considered to be within the scope of the following claims.