Abstract:
A data bypass system for removing data traffic from a public switched telecommunications network designed for carrying voice traffic includes a remote access concentrator for receiving a modulated signal corresponding to the data traffic, demodulating the signal to recover the link layer frames that comprise the data traffic, and tunneling the link layer frames through a data network to a network access controller for extracting compressed data contained within the link layer frames, decompressing the compressed data, performing error correction, performing protocol processing, and transmitting the decompressed data to a data terminal device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of data communications. 
     2. Related Art 
     With the advent of the personal computer and the tremendous popularity of the Internet and on-line services, the number of computers connected to the public switched telephone network (PSTN) has grown immensely over the past decade. It is estimated that 20-30% of all calls placed on the telephone network are established for the purpose of allowing one terminal or computer device to communicate with another computer device. These calls are known as data calls. The characteristics of a data call are unlike the characteristics of voice calls. A voice call normally lasts for 3 centennial call seconds (CCS), which is about five minutes, whereas a data call normally lasts for 36 CCS (about an hour). This presents a problem because the telephone network was not designed for handling the relatively long duration data calls. Consequently, as result of the tremendous increase in the number of data calls served by the phone network, the network is increasingly being overloaded. 
     FIG. 1 illustrates a representative overloaded PSTN  102 . PSTN  102  comprises a plurality of central office switches (CO)  110 ,  112 ,  114 ,  116  and at least one STP/SCP node  118 . Each CO has a serving area, which is the geographical area in which the CO is located: all subscribers in that area are served by that CO. 
     FIG. 1 shows a user  103  that desires to connect data terminal device  104  with remote data terminal device  124  using PSTN  102 . Data terminal device  104  is connected to PSTN CO  110  through data communication device  106 , such as a modem, and dial media  108 . 
     In order to establish a connection between data terminal device  104  and remote data terminal device  124 , data terminal device  104  directs data communication device  106  to place a call to remote access server (RAS)  120  using PSTN  102 . Data communication device  106  places a call to RAS  120  by sending a call request to PSTN CO  110 . Upon receiving the call request from data communication device  106 , the PSTN establishes a circuit from the originating CO  110  to RAS  120  through terminating CO  114 . RAS  120  is connected to data network  122 , which is connected to remote data terminal device  124 . 
     RAS  120  provides full data call establishment by performing the reverse of the processes performed by data communication device  106 . The processes performed by data communication device  106  includes the processes of: (1) data compression; (2) error correction; (3) link layer framing; and (4) modulation, in that order. Thus, RAS  120  provides full data call establishment by performing the following steps in the following order: (1) demodulation; (2) link layer framing; (3) error correction; and (4) data decompression. 
     Modulation refers to the conversion of a binary bit stream into a modulated signal within the voice frequency range. The facilities of a PSTN are designed to handle voice traffic, not binary data. Thus, to transmit binary data through the phone network it is necessary to perform the process of modulation. The modulated signal is then used to “carry” the binary data through the phone network. Demodulation refers to the process of converting a modulated signal back into the original binary data. Consequently, a modulator/demodulator (i.e., modem) is necessary to transmit binary data from one computer to a second computer through the phone network. 
     The process of link layer framing refers to a process of encapsulating data within a frame for transmission on the physical layer. Encapsulating data within a frame enables the error correction processing. 
     After the call is established by RAS  120 , data communication device  106  accepts user data from data terminal device  104  for transmission to RAS  120 . Data communication device  106  prepares the user data for transmission over the PSTN by first encapsulating the data in a protocol (such as PPP), compressing the encapsulated data, applying error control, framing the data in a link layer frame, and modulating the link layer frame. RAS  120  receives the modulated signal, demodulates the signal to recover the link layer frame, removes the link layer framing, checks for errors, decompresses the data, and de-encapsulates the call to recover the user data in its original form. The user data is then forwarded to remote data terminal device  124  through data network  122 . 
     The circuit set up between CO  110  and CO  114  remains in use until data communication device  106  terminates the call and releases the circuit, regardless of whether actual data is being transmitted. Thus, valuable PSTN circuits are consumed from data communication device  106  to local CO  110 , between originating CO  110  to terminating CO  114 , and from terminating CO  114  to the RAS. 
     To conserve valuable PSTN circuits, what is needed is a system to bypass the PSTN by capturing data calls at the originating CO and transmitting the compressed user data associated with the data call through a data network to a device that will then decompress the data and transmit the decompressed data to the intended destination. 
     SUMMARY OF THE INVENTION 
     In a system wherein a data communication device receives user data from a data terminal device, compresses the user data, encapsulates the compressed user data within a link layer frame, and transmits a modulated signal corresponding to the link layer frame to a switch within a telephone circuit switch network, the present invention provides a system for transporting the compressed form of the user data through a data network, thereby bypassing the telephone network. 
     The present invention includes a remote access concentrator (RAC) connected to a network access controller (NAC) through the data network. The RAC is connected to the switch within the telephone network and includes a network interface for receiving the modulated signal from the switch. The RAC also includes a demodulator to demodulate the modulated signal so as to recover the link layer frame. After recovering the link layer frame, the RAC tunnels the link layer frame through the data network to the NAC. Since the link layer frame contains the compressed form of the user data, the compressed user data is transported through the data network. 
     The NAC receives the tunneled link layer frame from the RAC and extracts the compressed user data from the link layer frame. The NAC then decompresses the compressed user data to recover the user data in its original form. The user data is then processed by the NAC according to the user data type. Finally, the NAC forwards the user data to the remote data terminal device. 
     The invention supports a variety of user data types, including: Asynchronous data, Point to Point Protocol (PPP), and Serial Line Internet Protocol (SLIP). The invention&#39;s ability to support a variety of data types is based on the RAC tunneling the link layer frame to the NAC, such that the RAC does not directly process the user data. 
     In a first embodiment of the present invention, the switch within the telephone network is a CO. In a second embodiment of the present invention, the switch is a Competitive Local Exchange Carrier (CLEC) switch. 
     Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. 
     FIG. 1 illustrates a representative public switched telephone network. 
     FIG. 2 illustrates a network configuration according to a first embodiment of the present invention. 
     FIG. 3 illustrates a procedure, according to the present invention, for providing call establishment. 
     FIG. 4 illustrates the flow of data from data terminal  104  to remote data terminal  124 , according to the present invention. 
     FIG. 5 illustrates a second embodiment of the present invention. 
     FIG. 6 is a diagram further illustrating a remote access concentrator. 
     FIG. 7 is a diagram further illustrating a network access controller. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The system of the present invention captures data calls at an entrance of the public switched telephone network (PSTN) (e.g., the originating CO) and transports the compressed form of the user data associated with the data call through a data network, thereby bypassing the PSTN. The advantage of this invention is that the consumption of PSTN interconnect circuitry is reduced and that the user data is transported in its compressed form though a data network. 
     FIG. 2 illustrates an overview of an embodiment of the present invention. The present invention includes a remote access concentrator (RAC)  210 , a data network  220 , and a network access controller (NAC)  230 . 
     RAC  210  is connected to data terminal device  104  though originating CO  110  and to NAC  230  through data network  220 . RAC  210  is locally connected to CO  110 . Although it is not shown, each CO  112 ,  114 ,  116  can have a locally connected RAC to service users in each COs respective geographic areas. NAC  230  is connected to remote data terminal device  124  through data network  122 . Because RAC  210  is locally connected to CO  110 , the only PSTN circuits that will be consumed are the circuits from data communication device  106  to originating CO  110 , and the circuits between originating CO  110  and RAC  210 . 
     Data terminal device  104  includes but is not limited to such devices as personal computers, laptop computers, and workstations. Similarly, data communication device  106  includes but is not limited to such devices as analog or digital modems, ISDN terminal adapters, or wireless modems. It should also be noted that data terminal device  104  and data communication device  106  can form one integral unit or can exist as two separate units. 
     The invention essentially splits the functionality of the typical RAS  120  into two new parts: RAC  210  and NAC  230 . RAC  210  performs the link layer and modulation/demodulation functions of RAS  120 , while NAC  230  performs the link layer functions and all functions existing above the link layer, such as error correction and data compression/decompression. 
     The link layer is the optimum area in which to split the RAS  120  functionality because the users data is compressed at that layer and the link layer consists of uniform frames. Because RAC  210  does not perform any functions above the link layer (e.g., RAC  210  does not perform data decompression) RAC  210  is able to transmit the compressed user data to NAC  230  for further processing. Consequently, the system of the present invention utilizes fewer data network resources than a system where the user data is transported in its uncompressed form. Substantial cost savings and efficiency gains are thereby realized. Additionally, RAC  210  is completely protocol independent because it does not process above the link layer. 
     FIG. 3 illustrates a procedure, according to the present invention, for providing call establishment when data terminal device  104  initiates a data call to remote data terminal  124 . 
     The procedure begins at step  302  where control immediately passes to step  304 . In step  304  data terminal device  104  directs data communication device (DCD)  106  to place a call to RAC  210  using PSTN  102 . In step  306  a call request is received at CO  110  and in step  308  CO  110  will set up a local circuit connecting DCD  106  to RAC  210 . After step  308  control passes to steps  310  and  312  in parallel. In step  310 , RAC  210  receives the call and uniquely provides partial data call establishment by demodulating the modulated signal transmitted by DCD  106  and by performing link layer framing. In step  312 , RAC  210  contacts the associated NAC  230  over data network  220  to request a virtual port for the continuation of matching and completing the remainder of call establishment. Instep  314  NAC  230  signals RAC  210  instructing RAC  210  which virtual port will continue and complete the call establishment. After step  314 , RAC  210  and NAC  230  are connected via data network  220 . In step  316 , RAC  210  forwards the link layer frames transmitted by DCD  106  to NAC  230  so that NAC  230  can complete call establishment. RAC  210  forwards the link layer frames through data network  220 . In step  318 , NAC  230  completes call establishment on its virtual port by processing the link layer frames received from RAC  210 . 
     After the call is established by RAC  210  and NAC  230 , DCD  106  will begin accepting user data from terminal device  104  for transmission to RAC  210 , and ultimately for transmission to remote data terminal  124 . 
     FIG. 4 illustrates the flow of data from data terminal  104  to remote data terminal  124 , according to the present invention. FIG. 4 also illustrates how the functionality previously performed by RAS  120  is now performed by RAC  210  and NAC  230 . 
     Data terminal device  104  generates user data  402 , which is sent to DCD  106  for transmission to remote data terminal  124 . The present invention supports a variety of user data  402  types, including: Asynchronous data, Point to Point Protocol (PPP), and Serial Line Internet Protocol (SLIP). 
     Upon receiving user data  402 , DCD  106  performs data compression  408 . A compression algorithm commonly implemented in data communication devices is the V.42bis compression standard. However, other compression algorithms are contemplated by the present invention. 
     After compressing the data, DCD  106  typically adds error correction information  414  to the compressed data  412 . As an example, DCD  106  employs the V.42 error correction standard. The compressed data and the error correction information  414  are then encapsulated within a link layer frame  418 . Link layer frame  418  is modulated  420  to produce modulated signal  422  for transmission on to dial media  108 . Dial media  108  can include, for example, plain old telephone service (POTS), integrated services digital network (ISDN) services, and analog and digital wireless services. A variety of modulation schemes  420  can be used by DCD  106 . An example modulation scheme is the V.34 standard. Other modulation schemes are contemplated by the present invention, such as ISDN modulation schemes. 
     Modulated signal  422  passes through CO  110  and is received at RAC  210 . RAC  210  performs demodulation  424  and link layer processing  428  so as to recover link layer frame  418 . After recovering link layer frame  418 , RAC  210  will tunnel link layer frame  418  through data network  220  to NAC  230 . RAC  210  tunnels link layer frame  418  through data network  220  by encapsulating it in a data network protocol. A variety of protocols may be used to tunnel link layer frame  418 . Such protocols include but are not limited to TCP, ATM, and Frame Relay. 
     NAC  230  will receive the data network protocol encapsulated link layer frame and remove the protocol encapsulation to recover link layer frame  418 . NAC  230  will then extract the compressed user data and error correction information  414  from link layer frame  418 . Next, NAC  230  will use the error correction information  414  to fix errors that may have occurred during transmission. Following that step, NAC  230  will decompress the compressed user data. Next, NAC  230  will perform protocol processing corresponding to the type of user data  402  transmitted by data terminal device  104 . For example, if user data  402  is of the PPP protocol type, NAC  230  will perform PPP processing. Finally, NAC  230  forwards user data  402  to remote data terminal  124  via data network  122 . 
     As is evident from data flow diagram  400 , the compressed form of user data  402  is transported through data network  220 . By transporting the compressed form of user data  402  through data network  220 , as opposed to the un-compressed form, cost savings and efficiency gains are realized because a smaller amount of data traverses data network  220 . For example, the V.42bis compression algorithm yields approximately a 4:1 compression ratio. 
     FIG. 5 illustrates another environment in which the present invention is useful. In this environment, RAC  210  is connected to a competitive local exchange carrier (CLEC) switch  510  instead of a CO. CLEC  510  is connected to a plurality of local access and transport areas (LATA). The present invention functions exactly the same in the environment illustrated in FIG. 5 as it does in the environment shown in FIG.  2 . Thus, the process of FIG.  3  and the data flow diagram of FIG. 4 require no modification to operate in the environment shown in FIG.  5 . 
     FIG. 6 is a diagram illustrating a more detailed view of RAC  210 . RAC  210  includes: network interface  610  for connecting to a PSTN switch, such as a CO  110  or CLEC  510 ; network interface  612  for connecting to a data network; processor  620 ; control logic  622  for enabling processor  620  to demodulate the signal received from DCD  106 ; memory  630  for storing link layer frames  418 ; and encapsulator  640  for removing frames from memory and encapsulating the frames within a data network protocol so that the frame can be tunneled through a data network to a virtual port of NAC  230 . In the preferred embodiment, processor  620  is a digital signal processor. The implementation of control logic  622  is well known in the art. 
     FIG. 7 is a diagram illustrating a more detailed view of NAC  230 . NAC  230  includes: network interface  710  for connecting to data network  220 ; network interface  712  for connecting to Internet type network  122 ; processor  720 ; control logic  722  for enabling processor  720  to process the tunneled link layer frames received from RAC  210  and to decompress user data; memory  730  for storing user data; and routing mechanism  740  for forwarding user data to data terminal device  124  connected to data network  122 . 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be understood by those skilled in the relevant art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the following claims. Thus the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.