Abstract:
A method that uses a test system at one end of a communication link to test the communication link for high speed service by coupling the test system to the communication link, placing a telephonic call to telephonic equipment located at an other end of the communication link and testing the communication link with the test system after the call has been terminated at the telephonic equipment.

Description:
BACKGROUND OF INVENTION 
     This invention relates to high speed services, and more particularly, to methods for testing communication links for high speed services. 
     XDSL is a digital connection to a location of a customer (a.k.a. user) over standard, single twisted pair, wiring that is already connected to most premises. As a result of the increased transmission capacity of XDSL compared to standard telephone connections, XDSL promises to transmit large data files to the premises of users for computer, video and other large data operation in a fast and efficient manner. There are many different types of XDSL services such as asymmetrical digital subscriber line (ADSL), high bit rate digital subscriber line (HDSL), high bit rate digital subscriber line-2 (HDSL-2), symmetric digital subscriber line (SDSL), very high speed digital subscriber line (VDSL), ADSL-lite, and other similar high speed digital services. Additionally, there are other non-digital high speed transmission techniques. 
     Unfortunately, some potential user lines lack the capability of supporting a high speed service because of deficiencies in the loop transmission characteristics. As such, service providers offering XDSL or other high speed service to potential users must first determine if the lines of the potential user can support high speed service. Thus, there is a need to perform high speed service tests for potential users. 
     Service providers (such as telecommunication companies Ameritech, Pacific Telesis, GTE, Southwestern Bell, etc.) that have physical access to the local loops via traditional office metallic test equipment such as mechanized loop testing (MLT) equipment can easily perform these tests. The local loops are the physical wires that run from the customer premises equipment (CPE) of the user to the central office of the service provider. CPE generally relates to any telephonic equipment (telephones, key systems, private branch exchange (PBX), answering machines, etc.) that resides on the premises of the user. 
     MLT provides computer control of accurate and extensive loop testing functions in the user contact, screening, testing, dispatch and close-out phases of trouble report handling. MLT also provides full diagnostic outputs instead of just pass and fail indications. 
     As XDSL and other high speed services continue to grow, an ever increasing number of service providers will offer high speed service to potential users. Many of these service providers will not have direct access to any metallic loop testing such as MLT because these service providers do not have physical access to the local loops. 
     For service providers that do not have access to the local loops the only option available to perform high speed service tests is to perform double ended measurement techniques. Unfortunately, these double ended measurement techniques require the dispatch of test personnel from the service provider, that does not have access to the local loops, to the premises of the potential user. Thus, there is a need to perform a single ended test method that would allow a service provider to perform high speed service tests without dispatching personnel to the premises of a potential user and without requiring access to the local loop via traditional office metallic test equipment. 
     SUMMARY OF THE INVENTION 
     The above problems are solved, and a number of technical advances are achieved in the art, by using a time interval between the time that a CPE device terminates a received call and the time that the central office disconnects the call. 
     In accordance with the invention, a test unit is connected to one end (first end) of a communication link. A call is then made from a communication unit, located at a test facility, at the first end of the communication link to CPE located at a second end of the communication link. The CPE receives the call at the second end of the communication link and then terminates the call. The test unit tests the communication link within a time interval after the CPE terminates the call. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing advantageous features of the invention will be described in detail and other advantageous features will be made apparent upon reading the following detailed description that is given with reference to the several figures of the drawings, in which: 
     FIG. 1 is a functional block diagram of the implementation of the method for performing the high speed service tests by a test facility; and 
     FIG. 2 is a logic flow chart showing the steps of the process performed by the test facility. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a test facility  100  is shown implementing a high speed service (such as XDSL or a high speed analog service) test for a communication line  105  of a potential user. Communication line  105  is also connected at one end  110  to customer premises equipment (CPE)  115  (CPE generally relates to any telephonic equipment such as telephones, key systems, PBX, answering machines, etc.) of the potential user. FIG. 1 also shows that the communication line  105  is connected to a switch  120  located at a central office  125 . The switch  120  is any commercially available telecommunication switch which will allow the central office  125  to communicate to a plurality of CPEs. An example of a switch  125  is a 5ESS telephonic switch produced by Lucent Technologies, Inc. 
     A second communication line, referred to as a data line  130 , is shown to connect the switch  120 , at the central office  125 , to a test unit  135  and a communication device  140 , at a connection point  145  of the data line  130 , located at the test facility  100 . A communication link is established between the test facility  100  and the CPE  115  via data line  130 , communication line  105 , and switch  120 . The combination of the electrical paths from the connection point  145  of data line  130  to the end  110  of the communication line  105  through the switch  120  establish the communication link. Additionally, the connection point  145  of the data line  130  is herein referred to as the first end  145  of the communication link and the end  110  of the communication line  105  is referred to as the second end  110  of the communication link. 
     Additional CPEs ( 150  and  155 ) are shown connected to the switch  120  through communication lines  160  and  165  respectively. The invention will work equally well for a plurality of CPEs and communication lines without limitation as the switch  120  is enabled to communicate with multiple CPEs. 
     The communication line  105  is preferably a standard telephone line such as a single twisted pair line. However, it is appreciated that other non-standard telephone lines such as non-twisted pair, multiple twisted pair, coaxial, fiber optic, microwave or millimeter lines may suitably be employed. 
     The communication line  105  is controlled by a central office  125 . A service provider associated with the telephonic central office  125  owns, maintains and controls the communication lines  105 ,  160 ,  165  coupled with switch  120 . The central office  125  has full access to the communication line  105  and performs metallic loop access testing on the communication line  105 . 
     The central office  125  of FIG. 1 is shown with a mechanized loop testing (MLT)  170  block and the switch  120  block. The MLT  170  block represents the MLT testing units at the central office  125 . The MLT units  170  are physically connected to the communication line  105  through the switch  120 . 
     The test facility  100 , FIG. 1, is shown to posses the test unit  135  and the communication device  140  connected to the data line  130  via the first end  145  of the communication link. The data line  130  is preferably a T-1 trunk line. A trunk is a communication line between two switching systems such as equipment in the central office  125  and the test facility  100 . The T-1 line is preferably a dual twisted pair digital transmission link with a transmission capacity of 1,544,000 bits per second. 
     Although a T-1 type line may be employed, the data line  130  may selectively be any high speed digital line that is compatible with the central office  125  such as primary rate interface (PRI). PRI is the integrated service digital network (ISDN) equivalent of a T-1 line. Additionally, the data line  130  may selectively also be a whole network or part of network which includes several switches and/or different types of transmission equipment. A non-digital line may also be employed as a data line  130 . For an analog type line, the electrical properties inherent in all analog trunks will be employed. 
     As an example of operation, communication device  140  located at the test facility  100  either initiates or receives a call from the CPE  115 . If the user of the CPE  115  wishes to know if the communication line  105  is capable of supporting high speed service then the test facility  100  connects the test unit  135  to the data line  130  and the communication device  140  (either automatically or in response to user interaction) instructs the CPE  115  to terminate the call (such as hanging up a telephone). Once the CPE  115  terminates the call, the test facility  100  begins the high speed testing with the test unit  135 . 
     The high speed service testing preferably takes place within a pre-selected time interval such as a ten second time interval after the CPE  115  terminates the call. In the United States(called telephone lines stay active and connected :or approximately ten seconds after a telephone is hung up (before the switch network at the central office  125  disconnects the call.) The specification for the time interval is described in Bellcore specification GR-505-CORE section 5.4.1.3 R5-22 [214], herein incorporated by reference. 
     While testing, the test unit  135  propagates electromagnetic energy waves (signals) from the first end  145  to the second end  110  of the communication link. When the waves reach the second end  110  of the communication link the waves are then reflected back to the test unit  135  at the first end  145  of the communication link. Once the reflected waves are received by the test unit  135 , the test unit  135  analyzes the reflected waves in relation to the propagated waves and determines the electrical properties of the communication link such as calculating the frequency properties of the loop. The test unit  135  calculates the channel capacity of the communication link divided in either asymmetrical and symmetrical upstream and downstream rates for the communication link. The test unit  135  then records the various electrical properties of the communication link for future use. It is appreciated that the recorded data from the test unit  135  may selectively be stored in a memory unit located either within or external to the test unit  135 . 
     Additionally, if the communication link supports the use of a autocut function, the autocut function is preferably disabled by either the test unit  135  or the central office  125  of FIG.  1 . The autocut function is a function that prevents oscillations when the CPE  115  goes on-hook (i.e. the CPE  115  terminates the call). 
     The recorded data may selectively include the loop length, line load impedance, the presence of loading coils and analog frequency performance. The test unit  135  also records whether the communication link supports a high speed service and the upstream and downstream rates of the communication link both for digital and/or analog transmission. Once this information is recorded the test facility  100  determines if a high speed service may be supported which in a digital case supports XDSL and in an analog case selectively supports one or more of the following: television transmissions, music, voice, multiplexed voice, image and/or video transmission. 
     An example of the test unit  135  is the Lucent Technologies, Inc. Remote Measurement System—Digital unit (RMS-D), however, other manufactures also produce similar units. These units are preferably digital signal processing (DSP) based and are selectively updated with new firmware to perform multiple tests. While there are several alternatives to measuring and calculating the electrical properties of the communication link the following two example tests selectively provide the test data to the test unit  135 . 
     First, a four wire return loss measurement is selectively used to determine the approximate length of the communication link loop when the CPE  115  is on-hook. The larger the return signal (i.e. lower return loss) the shorter the loop length. The smaller the returned signal (i.e. higher return loss) the longer the loop length. 
     In the second test, a sweep of the frequency while looking at the returned signals is selectively used to determine the presence of loading coils. If this test indicates the presence of loading coils, the loading coils are selectively removed in a later operation. 
     If the return loss of the first test is low, the loop is short and supports very high data rates. If the return loss of the first test is high, the loop is long and selectively supports high data rates. A mapping is selectively generated from the return loss results versus the data rates. 
     The upstream or downstream asymmetric data rates for ADSL, ADSL Lite and VDSL are selectively mapped to the return loss values via correlation between the loop lengths and performance values as given in the XDSL standards. Similarly, the symmetric bit rates for HDSL, HDSL-2 and symmetric VDSL are selectively mapped to return loss values via correlation between loop lengths and the performance values given in the XDSL standards. 
     Referring now to FIG. 2, a logic flow chart is shown describing the process of testing the communication link. The process starts at step  175 . In step  180 , the test facility  100  of FIG. 1 connects the test unit  135  to the data line  130  at the first end  145 . Next a call is made by either the CPE  115  or the communication device  140 . In decision step  185 , FIG. 2, if the CPE  115  of FIG. 1 calls the test facility  100 , the process continues to step  190 . In step  190 , FIG. 2, the communication device  140 , FIG. 1, instructs the CPE  115  that the communication device  140  will call the CPE  115  back. The process then continues to step  195 . If instead, the communication device  140  calls the CPE  115 , the process continues directly to step  195 . 
     In step  195 , FIG. 2, the communication device  140 , FIG. 1, calls the CPE  115  which answers the call in step  200 . The communication device  140  then instructs the CPE  115 , in step  205 , to terminate the call, which the CPE  115  does in step  210 . The communication device  140  then determines in decision step  215  if there is echo canceling capabilities on the communication link. If there is echo canceling capabilities on the communication link, decision step  215  then sends the process to step  220  that disables the echo canceling capabilities of the communication link. The process then continues to step  225 . In step  225 , FIG. 2, the test facility  100 , FIG. 1, begins testing the communication link with the test unit  135 . If there is no echo canceling on the communication link, the process then continues to step  225 , FIG. 2, directly and the test facility  100 , FIG. 1, begins testing the communication link with the test unit  135 . 
     In step  230 , FIG. 2, the process then records any test data that the test unit  135 , FIG. 1, needs in order to determine performance of the communication link. Within this step, the test unit  135  determines whether the communication link is high speed service capable and then, if capable of supporting high speed service, the test unit  135  determines the upstream and downstream rates of the communication link. The process ends at  235 . 
     While the specification in this invention is described in relation to certain implementations or embodiments, many details are set forth for the purpose of illustration. Thus, the foregoing merely illustrates the principles of the invention. For example, this invention may have other specific forms without departing from its spirit or essential characteristics. The described arrangements are illustrative and not restrictive. To those skilled in the art, the invention is susceptible to additional implementations or embodiments and certain of the details described in this application can be varied considerably without departing from the basic principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are thus within its spirit and scope.