Abstract:
A method for stabilizing a connection between an xDSL modem ( 160 ) and a central office ( 120 ) is provided. The method includes detecting whether a signal on a telephone line is a ring signal; setting a ring signal flag if the signal on the telephone line is the ring signal; and maintaining a connection between the xDSL modem and the central office. An xDSL modem using the method is also provided.

Description:
FIELD OF THE INVENTION 
     The present invention relates to customer premise equipment (CPE), and particularly to customer premise equipment such as a modem. 
     RELATED OF PRIOR ART 
     A ring signal detection circuit is commonly used in an x digital subscriber line (xDSL) modem integrated with a voice over IP (VoIP) phone, for detecting ring signals. Typically, when a ring signal comes in, a connection between the xDSL modem and a central office (CO) may be prone to be interrupted due to absence or poor quality of a splitter. At this point, the XDSL modem has to reconnect to the CO, wasting approximately 60 seconds of time. 
     Therefore, a heretofore unaddressed need exists in the industry to overcome the aforementioned deficiencies and inadequacies. 
     SUMMARY OF THE INVENTION 
     An xDSL modem for stabilizing a connection with a CO is provided. The xDSL modem is connected to the CO via a public switched telephone network. The xDSL modem includes a ring signal detection module and a setting module. The ring signal detection module is used for detecting whether a signal on a telephone line is a ring signal or noise. The setting module is used for setting a ring signal flag if the signal on the telephone line is the ring signal, and maintaining a connection between the xDSL modem and the CO. 
     A method for stabilizing a connection between an xDSL modem and a CO is provided. The method includes detecting whether a signal on a telephone line is a ring signal; setting a ring signal flag if the signal on the telephone line is the ring signal; and maintaining a connection between the xDSL modem and the CO. 
     Other objectives, advantages and novel features of the present invention will be drawn from the following detailed description of preferred embodiments of the present invention with the attached drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating an application environment of an xDSL modem in accordance with an exemplary of the present invention; and 
         FIG. 2  is a flowchart of stabilizing a connection between a CO and the xDSL modem in accordance with another exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic diagram illustrating an application environment of an xDSL modem  160  of an exemplary embodiment of the present invention. 
     The xDSL modem  160  is connected to a central office (CO)  120  via a Public Switched Telephone Network (PSTN)  140 . The CO  120  is a digital subscriber line access multiplexer (DSLAM). The xDSL modem  160  includes a connection module  162 , a ring signal detection module  164 , a setting module  166 , and a status detection module  168 . 
     The connection module  162  is used for connecting to the CO  120  via the PSTN  140 . In this exemplary embodiment, the connection module  162  connects to the CO  120  based on the G.992.X standards of the International Telecommunication Union. 
     The ring signal detection module  164  detects whether a signal on a telephone line is a ring signal, and sends a detection result to the setting module  166 . The detection result indicates whether the signal is the ring signal or not. 
     The setting module  166  is used for setting a ring signal flag or a non-ring signal flag according to the detection result. In this exemplary embodiment, the setting module  166  sets the ring signal flag if the signal is the ring signal, and sets the non-ring signal flag if the signal is not the ring signal. The setting module  166  is further used for canceling the ring signal flag after the ring signal is no longer detected on the telephone line. 
     The status detection module  168  is used for detecting a connection status between the xDSL modem  160  and the CO  120  and determines whether the connection between the XDSL modem  160  and the CO  120  is to be maintained. After setting the non-ring signal flag, the status detection module  168  detects the connection status between the xDSL modem  160  and the CO  120 . 
     In this exemplary embodiment, the status detection module  168  detects the connection status by detecting a bit error rate (BER) of a physical layer, and determines whether the connection is to be maintained by verifying whether the BER exceeds a threshold, which is, for example, 100 cyclic redundancy codes (CRCs) generated in the physical layer per second defined by the G.99x standard. The BER of the physical layer includes a CRC and a head error check (HEC). 
       FIG. 2  is a flowchart of stabilizing a connection between the CO  120  the xDSL modem  160  of the exemplary embodiment of the invention. 
     In step S 202 , the xDSL modem  1   60  and the CO  120  enter a show-time mode. 
     In detail, the connection module  162  determines whether the CO  120  is ready for communicating via a handshake protocol. If the CO  120  is ready for communicating, the connection module  162  detects a distance between the xDSL modem  160  and the CO  120  by performing transceiver training. Upon performing the transceiver training, a connection between the CO  120  and the xDSL modem  160  is setup. Then the connection module  162  performs channel analysis and message exchange to determine data traffic between the xDSL modem  160  and the CO  120 . After the data traffic is successfully determined, the xDSL modem  160  and the CO  120  enter the show-time mode. 
     In step S 204 , the ring signal detection module  164  determines whether a signal on the telephone line is the ring signal. 
     In this exemplary embodiment, the ring signal detection module  164  has a preset reference voltage such as 35V, then detects a voltage of the telephone line. The detection module  164  then compares the reference voltage with the voltage of the telephone line. 
     If the voltage of the telephone line exceeds the reference voltage, then presence of the ring signal is indicated. The ring signal detection module  164  sends a detection result to the setting module  166 . The process then proceeds to step S 206  described below. 
     If the reference voltage is less than the voltage of the telephone line, that indicates the signal is not the ring signal and considered noise. The ring signal detection module  164  sends the detection result to the setting module  166 . The process then proceeds to step S 208  described below. 
     In step S 206 , the setting module  166  sets the ring signal flag. The process then proceeds to step S 216 , where the connection between the xDSL modem  160  and the CO  120  is maintained. After the ring signal disappears, the setting module  166  cancels the ring signal flag. The process then returns to step S 204 . 
     In this exemplary embodiment, the ring signal flag is represented by number “1”. If the ring signal flag is set to 1, it indicates a splitter is not present in the xDSL modem  160 , or the splitter is of poor quality. 
     In step S 208 , the setting module  166  sets the non-ring signal flag. In this exemplary embodiment, the non-ring signal flag is represented by the number “0”. The process then proceeds to step S 210 . 
     In step S 210 , the status detection module  168  detects the connection status between the xDSL modem  160  and the CO  120 . In this exemplary embodiment, the status detection module  168  detects the connection status by detecting the BER of the physical layer. The process then proceeds to step S 212 . 
     In step S 212 , the status detection module  168  determines whether the connection is to be re-established based on the connection status between the xDSL modem  160  and the CO  120 . In this exemplary embodiment, the status detection module  168  verifies whether the BER exceeds a threshold defined by the G.99x standard in order to determine whether the connection is to be maintained. For example, the threshold may be 100 CRCs generated in the physical layer per second. If the BER exceeds the threshold, that indicates a noise signal is generated on the telephone line. The process then proceeds to step S 214 . 
     In step S 214  the connection is re-established by re-connecting the xDSL modem  160  to the CO  120  at a lower BER. The process then returns to step S 204  to determine whether the signal on the telephone line is the ring signal. If the BER does not exceed the threshold, it indicates the signal is a ring signal. The process returns to step S 210 . 
     In step S 216  the connection is maintained directly without any further detection to the connection between the xDSL modem  160  and the CO  120 . 
     The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.