Abstract:
A method and apparatus for transmitting data from an optical network unit (ONU) to an optical line termination (OLT) in a Gigabit Ethernet passive optical network (GE-PON) on the basis of a time division multiple access (TDMA) scheme are provided. A measurement of a data transmission time when the data is transmitted to the OLT is obtained, and the measured data transmission time is compared with a predetermined normal transmission time. The transmission of the data is maintained if the measured data transmission time is determined to be less than or equal to the normal transmission time from the comparison result. However, if the measured data transmission time is determined to be greater than the normal transmission time, the transmission of the data is stopped.

Description:
CLAIM OF PRIORITY 
     This application claims priority to an application entitled “METHOD AND APPARATUS FOR TRANSMITTING DATA IN GIGABIT ETHERNET PASSIVE OPTICAL NETWORK,” filed in the Korean Intellectual Property Office on Feb. 24, 2003 and assigned Serial No. 2003-11523; filed on Mar. 5, 2003 and assigned Serial No. 2003-13753; and filed on Mar. 14, 2003 and assigned Serial No. 2003-16222, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a Gigabit Ethernet passive optical network (GE-PON) and, more particularly, to an apparatus and method for transmitting data from optical network units (ONUs) to an optical line termination (OLT) in a GE-PON. 
     2. Description of the Related Art 
       FIG. 1  shows the configuration of a GE-PON being standardized in IEEE802.3ah EFM to which the present invention is applicable. As shown, a plurality of ONUs  110 - 1 ,  110 - 2  and  110 - 3  are configured to communicate with one OLT  100 . During downstream transmission from the OLT  100  to the ONUs  110 - 1 ,  110 - 2  and  110 - 3 , the OLT  100  broadcasts data to all the ONUs  110 - 1 ,  110 - 2  and  110 - 3 , and each of the ONUs  110 - 1 ,  110 - 2  and  110 - 3  is configured to receive the intended data from the OLT  100 . However, during upstream transmission from the ONUs  110 - 1 ,  110 - 2  and  110 - 3  to the OLT  100 , the ONUs  110 - 1 ,  110 - 2  and  110 - 3  transmit a frame to the OLT  100  based on a time-division multiple access (TDMA) scheme. 
     Referring to  FIG. 9 , if a malfunction occurs in any one of the ONUs during the upstream transmission, the transmission times allocated to the other ONUs may be affected. As can be seen from this drawing, the ONU 1   110 - 1  may succeed in transmitting an ONU 1  data frame during a first period, and the ONU 2   110 - 2  fails to transmit an ONU 2  data frame within a second period due to the occurrence of an error therein, thereby continuously occupying the transmission line thereafter. As the ONU 2   110 - 2  continuously transmits the erroneous ONU 2  data for more than the predefined time, it causes a data collision in a third period, during which the ONU 3   110 - 3  is permitted to transmit an ONU 3  data frame. As a result, the entire transmission of the GE-PON will be disabled if such data collusion occurs continuously. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been made in view of the above problems and provides additional advantages, by providing a method and apparatus for stably transmitting data from ONUs to an OLT in a GE-PON. 
     In accordance with an aspect of the present invention, a method for transmitting data from an optical network unit (ONU) to an optical line termination (OLT) in a Gigabit Ethernet passive optical network (GE-PON) on the basis of a time-division multiple access (TDMA) scheme is provided. The method includes the steps of: a) measuring a data transmission time when transmitting the data to the OLT; b) comparing the measured data transmission time with a predetermined normal transmission time; and c) maintaining the transmission of the data if the measured data transmission time is determined to be less than or equal to the normal transmission time based on the comparison outcome, and stopping the transmission of the data if the measured data transmission time is determined to be greater than the normal transmission time. 
     In accordance with another aspect of the present invention, an apparatus for transmitting data from an ONU to an OLT in a GE-PON on the basis of a TDMA scheme is provided. The apparatus includes a transmission control function block having a switch for outputting the data to be transmitted to the OLT to a transmission line coupled to the OLT in response to an external control signal; and a transmission controller for measuring a data transmission time elapsing from the moment when the transmission of the data has been started, and controlling the switch to maintain the output of the data if the measured data transmission time is less than or equal to a predetermined normal transmission time and stopping the output of the data if the measured data transmission time is greater than the normal transmission time. Preferably, the transmission control function block is located in any one of a physical coding sub-layer (PCS), physical medium attachment (PMA) sub-layer and physical medium dependent (PMD) sub-layer of a physical layer of the ONU. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram showing the configuration of a GE-PON to which the present invention is applied; 
         FIG. 2  is a block diagram showing the configuration of an ONU according to a preferred embodiment of the present invention; 
         FIG. 3  depicts the arrangement of a transmission control function block in the ONU according to the embodiment of the present invention; 
         FIGS. 4 to 6  illustrate different locations of the transmission control function block in a physical layer of the ONU according to the embodiment of the present invention; 
         FIG. 7  is a block diagram showing the structure of the transmission control function block according to the embodiment of the present invention; 
         FIG. 8  is a flow chart illustrating the operation of the ONU according to the embodiment of the present invention; 
         FIG. 9  is a view illustrating the effects of an ONU error on the GE-PON; 
         FIG. 10  illustrates the blockage of an ONU error according to the embodiment of the present invention; 
         FIGS. 11 to 13  illustrate different configurations of an ONU according to an alternative embodiment of the present invention; and, 
         FIG. 14  shows the structure of a laser control block according to the alternative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted as it may make the subject matter of the present invention unclear. 
       FIG. 1  is a block diagram showing the configuration of the GE-PON to which the present invention is applied. As shown, the GE-PON includes an OLT  100 , a plurality of ONUs  110 - 1  to  110 - 3  coupled to the OLT  100 , and a plurality of end users (network devices)  120 - 1  to  120 - 3  in communication with the ONUs  110 - 1  to  110 - 3 , respectively. Although a limited number of ONUs is shown in  FIG. 1  for illustrative purposes, it is to be understood that the GE-PON can support concurrent communications between a much larger number of ONUs. Thus, the number of ONUs in the drawing should not impose limitations on the scope of the invention. 
     In operation, the end users  120 - 1  to  120 - 3  transmit their respective data  131  to  133  to the OLT  100 , respectively, via the ONUs  110 - 1  to  110 - 3 , and the OLT  100  transmits data to the end users  120 - 1  to  120 - 3 , respectively, via the ONUs  110 - 1  to  110 - 3 . In the GE-PON, an Ethernet frame, for example, may be transmitted at a bit rate of 1 Gbps or higher. During the upstream transmission of the GE-PON, the OLT  100  accesses the respective data from the ONUs  110 - 1  to  110 - 3  and multiplexes them according to a time-division multiplexing (TDM) scheme. During the downstream transmission of the GE-PON, each of the ONUs  110 - 1  to  110 - 3  selects and receives only the intended data out of the data broadcast from the OLT  100 . 
     During the upstream transmission of the GE-PON as stated above, the ONUs  110 - 1  to  110 - 3  have to assemble their data and transmit the assembled data over an upstream channel without a collision in their respective TDM timeslots. To this end, according to the teachings of the present invention, if each ONU  110  starts to transmit data to the OLT  100  in the upstream direction, a measurement of the time required to transmit the data is measured, and, if the measured time exceeds a predetermined normal transmission time, the data transmission is stopped. Here, the normal transmission time is the time required for the ONU  110  to transmit the maximum amount of data transmittable at a given time when it occupies a transmission line to the OLT  100 . Note that OLT assigns the transmission time to each ONU in the GE-PON protocol. 
     The configuration of the ONU  110  operated in the above manner is shown in  FIG. 2 . The ONU  110  includes a media access control (MAC) layer and a physical layer. The physical layer includes a physical coding sub-layer (PCS)  160 , a physical medium attachment (PMA) sub-layer  150 , and a physical medium dependent (PMD) sub-layer  190 . The PCS  160  performs an 8B/10B-coding operation for transmission and a 10 B/8 B-decoding operation for reception. The PMA sub-layer  150  performs a data serialization/deserialization operation, and the PMD sub-layer  190  performs a modulation/pulse shaping operation to transmit data while loading it onto the transmission line. This configuration of the ONU  110  shown in  FIG. 2  is conformable to the IEEE802.3 standard. 
     Because the present invention is related to data transmission of the ONU  110  or OLT  100 , only constituent elements of the respective sub-layers associated with the data transmission are shown in  FIG. 2 . In connection with the data transmission, the PCS  160  includes an encoder  10  for encoding data from an upper layer, the PMA sub-layer  150  includes a multiplexer  20  for multiplexing data from the encoder  10 , and the PMD sub-layer  190  includes a modulator  30  for modulating the multiplexed data and a pulse shaping filter  40  for generating a pulse signal of the modulated data. 
     Referring to  FIG. 3 , the physical layer further includes a transmission control function block  310  for sensing and blocking the transmission of erroneous data from the upper layer in addition to the PCS  160 , PMA sub-layer  150  and PMD sub-layer  190 . The transmission control function block  310  can be located at a desired position of the physical layer  400  with the PCS, PMA sub-layer, and PMD sub-layer for data transmission/reception of the physical layer  400 . 
       FIGS. 4 to 6  show different locations of the transmission control function block  310  in the physical layer  400  according to the embodiment of the present invention. The transmission control function block  310  can be located in the PCS  160  to sense and block erroneous data coming downstream from the MAC layer  170 , as shown in  FIG. 4 , or in the PMA sub-layer  150  to sense and block erroneous data from the PCS  160 , as shown in  FIG. 5 . Alternatively, the transmission control function block  310  may be located in the PMD sub-layer  190 , as shown in  FIG. 6 . In this manner, the transmission control function block  310  according to the present invention is located, not in every sub-layer of the physical layer, but in any one sub-layer thereof. 
       FIG. 7  is a block diagram showing the structure of the transmission control function block  310  according to the embodiment of the present invention. As shown, the transmission control function block  310  includes a switch  153  and a transmission controller  155 . 
     In operation, the switch  153  is turned on/off under the control of the transmission controller  155  to output input data to the transmission line, or stop the data output. The transmission line interconnects the OLT  100  and the ONU  110 . The transmission controller  155 , if output data from the upper layer is transmitted to the switch  153 , is adapted to drive a timer to measure the time required for the data transmission and determine from the measured result whether or not the transmitted data is normal. In particular, if the measured data transmission time is less than or equal to the predetermined normal transmission time, the transmission controller  155  determines the transmitted data to be normal and thus keeps the switch  153  on. However, if the measured data transmission time is greater than the predetermined normal transmission time, the transmission controller  155  determines the transmitted data to be abnormal and thus turns the switch  153  off so as to stop the data output to the transmission line. 
     Accordingly, the transmission controller  155  acts to recognize the occurrence of an error in the upper layer based on the time required for data transmission. In the present embodiment, the transmission controller  155  may be, for example, a jabber controller. 
     Referring to  FIG. 8 , the operation of the ONU  110  will be described in detail. First, the ONU  110  determines at step  201  whether the transmission of data to the OLT  100  has been started, and then proceeds to step  203  if the data transmission has been started. At step  203 , the ONU  110  measures a data transmission time elapsing from the moment when the data transmission has been started, and then proceeds to step  205 . The ONU  110  compares the data transmission time measured at step  203  with the predetermined normal transmission time at step  205 . The ONU  110  proceeds to step  207  if the measured data transmission time is determined to be less than or equal to the normal transmission time from the comparison result, and to step  209 , otherwise. Here, the fact that the measured data transmission time is less than or equal to the normal transmission time signifies that the transmitted data is normal and the data transmission is performed normally. If the measured data transmission time exceeds the normal transmission time, it signifies that the transmitted data is abnormal and the data transmission may be in error. As a result, at step  207 , the ONU  110  successfully completes the data transmission and then ends it. However, at step  209 , the ONU  110  stops the data transmission and then ends the operation. 
     As stated above, according to the present invention, the ONU  110  can sense and block erroneous data during the upstream transmission, thereby enabling the entire data transmission of the GE-PON to be smoothly carried out, as will be described in further detail with reference to  FIG. 10 . 
       FIG. 10  illustrates the blockage of an ONU error according to the embodiment of the present invention, wherein it is assumed that abnormal data occurs in the ONU 2   110 - 2 . As shown in this drawing, the ONU 1   110 - 1  successfully transmits ONU 1  data for a first period where it performs the data transmission. In a second period where the ONU 2   110 - 2  performs the data transmission, it senses erroneous ONU 2  data via the transmission controller  115  and then drives the switch  153  to stop the data transmission of the ONU 2  at a start point of a third period where the ONU 3   110 - 3  is scheduled to perform the data transmission. As a result, the ONU 3   110 - 3  can normally transmit ONU 3  data during the third period, and the entire data transmission of the GE-PON can thus be smoothly carried out. 
     As described above, the transmission control function block  310  including, for example, a jabber controller can be randomly located in the PCS, PMA sub-layer, and PMD sub-layer of the physical layer for the data transmission and reception of the physical layer to sense and block erroneous data coming downstream from the upper layer. 
     Note that an EPON MAC layer, more specifically a multipoint MAC control layer that is an upper layer of the MAC layer  170 , generates a laser control signal to turn on/off a laser of the PMD sub-layer, which is the lower layer of the PMA sub-layer. When transmitting no data, it is preferable for an ONU/ONT to turn off a laser, which is operable as a noise source during data transmission of other ONUs/ONTs, such that it does not disturb the data transmission thereof. Therefore, in the case where the transmission controller is applied to the EPON, it is preferable to turn off the laser when the data transmission is disabled by the transmission control function block  310  for the above reason. 
     In the above-described embodiment of the present invention, the transmission control function block  310  is operated irrespective of the laser control. For this reason, provided that the transmission control function block  310  is operated under the condition, the laser is turned on. 
     In an alternative embodiment of the present invention, the laser has the same state as that of a laser control when data is transmitted by the transmission control function block  310 , so that the data transmission is disabled by the transmission control function block  310 . A function block including such a laser and laser controller will be hereinafter referred to as a laser control block. 
       FIGS. 11 to 13  show different configurations of an ONU according to the alternate embodiment of the present invention. As shown, the transmission control function block  310  is shown to be located in any one of the PCS, PMA sub-layer, and PMD sub-layer of the physical layer, while a laser control block  320  is located in the PMD sub-layer  190 . 
     Referring back to  FIG. 3 , the ONU  110  includes the MAC layer  170  and the physical layer  400 , which includes the PCS  160 , PMA sub-layer  150 , and PMD sub-layer  190 . This configuration of the ONU  110  is based on a hierarchical structure of the IEEE802.3 standard. The ONU  110  further includes the above-described transmission control function block  310  located in any one of the PCS  160 , PMA sub-layer  150  and PMD sub-layer  190  of the physical layer  400 , and the laser control block  320  interoperable with the transmission control function block  310  and located in the PMD sub-layer  190 . 
     The laser control block  320  has the same control state as the laser control state when data is transmitted from the transmission control function block  310 , thus it always keeps the laser off irrespective of a laser control command coming downstream from the upper layer when no data is transmitted from the transmission control function block  310 . 
       FIG. 14  is a block diagram showing the structure of the laser control block  320  according to the alternate embodiment of the present invention. As shown, the laser control block  320  of the PMD sub-layer  190  includes a laser  193  for transmitting data from the upper layer to the transmission line, and a laser controller  195  for controlling the laser  193 . The laser  193  is turned on under the control of the laser controller  195  to transmit data from the upper layer to the transmission line. 
     The laser controller  195  receives a laser control signal from the multipoint MAC control layer that is the upper layer of the MAC layer  170 . The laser controller  195  further receives a transmission control signal from the transmission control function block  310 . 
     The transmission control signal from the transmission control function block  310  is a control signal that the block  310  outputs as a result of a determination based on the time required for data transmission as to whether data is normal or not, as stated previously. This control signal is applied to the switch  153  to turn it on/off. The turning-on of the switch  153  is performed to continue the output of data to the transmission line, and the turning-off of the switch  153  is performed to stop the output of data to the transmission line. 
     In the alternate embodiment of the present invention, the laser controller  195  of the laser control block  320  is adapted, when the upper layer is normally operated, to control the laser  193  in response to the laser control signal since the transmission control signal from the transmission control function block  310  is outputted to turn on the switch  153 . That is, upon determining on the basis of the control signal from the transmission control function block  310  that the upper layer is normally operated, the laser controller  195  of the laser control block  320  outputs the same value as that of the laser control signal, the output of the multipoint MAC control layer, to have the same control state as the existing laser control state. 
     According to the alternate embodiment of the present invention, the laser controller  195  of the PMD sub-layer  190  is also adapted, when an abnormal data frame is transmitted from the upper layer, to keep the laser  193  off irrespective of the laser control signal from the multipoint MAC control layer since the transmission control signal from the transmission control function block  310  is outputted to turn off the switch  153 . 
     In other words, upon determining on the basis of the control signal from the transmission control function block  310  that the upper layer is abnormally operated, the laser controller  195  keeps the laser  193  off irrespective of the laser control signal from the multipoint MAC control layer. 
     As apparent from the above description, the present invention provides a method and apparatus for transmitting data from ONUs to an OLT in a GE-PON, wherein, during data transmission, the occurrence of abnormal data is sensed and the transmission thereof is blocked, so that the remaining data transmission can be smoothly performed. 
     Furthermore, according to the present invention, if it is determined on the basis of a control signal from a transmission controller that an upper layer is abnormally operated, a laser, which is operable as a noise source, is turned off so as not to disturb data transmission of other units. 
     Furthermore, according to the present invention, a transmission control function block can be located in any one of a PCS, PMA sub-layer and PMD sub-layer of a physical layer to output a control signal that is available in connection with a laser control. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible without departing from the scope and spirit of the invention as disclosed in the accompanying claims.