Abstract:
An OAM capability discovery method in Ethernet passive optical network is disclosed. An OLT assigns identifications according to a registration request of the plurality of ONUs connected to the OLT. In response, the OLT transmits an OAM capability information message of the OLT to a random ONU from among the registered plurality of ONUs, and the random ONU transmits an OAM capability information message of the random ONU to the OLT, then finally the OLT transmits an OAM capability discovery completion message to ONU.

Description:
CLAIM OF PRIORITY 
   This application claims priority to an application entitled “OAM capability discovery method in Ethernet passive optical network,” filed in the Korean Intellectual Property Office on Sep. 19, 2002 and assigned Serial No. 2002-57296, the contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an Ethernet passive optical network (EPON), and more particularly to an OAM (Operations, Administration and Maintenance) capability discovery method that may be implemented in a passive optical network. 
   2. Description of the Related Art 
   The standardization of Gigabit Ethernet and MAC technology for the ATM-PON (Asynchronous Transfer Mode Passive Optical Network) has been completed. In the ATM-PON, upward or downward transmission of frames, each of which consists of a predetermined number of ATM cells, is used for communication purposes. In particular, an OLT (Optical Line Termination) inserts downward cells in the transmission frame, and then the downward cells are distributed to each ONU (Optical Network Unit) in the PON having a tree-shaped structure. Other details of the Gigabit Ethernet and the ATM-PON protocols are described in the IEEE 802.3z dated Jan. 23, 1997. and ITU-T G.983.1 dated Oct. 13, 1998, from which the contents of both documents are incorporated herein by reference. 
     FIG. 1  is a block diagram showing the physical network structure of a general passive optical network (PON). As shown, the PON includes an OLT  100  and a plurality of ONUs  110 - 1  to  110 - 3  connected to the OLT  100 .  FIG. 1  is an example in which three ONUs  110 - 1  to  110 - 3  are connected to one OLT  100  in the Ethernet Passive Optical Network, which transmits 802.3 Ethernet frames via a point to multi-point network. Here, multiple users  120 - 1  to  120 - 3  (users or network equipments) may be connected to the ONUs  110 - 1  to  110 - 3 , respectively, so that data  131 - 1  to  133 - 1  transmitted by the users  120 - 1  to  120 - 3  can be transmitted to the OLT  100  via the ONUs  110 - 1  to  110 - 3 . 
   As shown in  FIG. 1 , in the case of upward transmission, all data of the ONUs are accessed by means of a TDM (Time Division Multiplexing) method. An ODN (Optical Distribution Network), which is a passive element, enables the data not to be collided with each other by means of a ranging method. In the case of downward transmission, each of the ONUs  110 - 1  to  110 - 3  receives data broadcasted by the OLT  100 . Each frame in upward or downward transmission has a field arranged in a dedicated ATM cell or a general ATM cell, by which messages can be sent or received at predetermined intervals. 
   However, with the development of the Internet technology, more bandwidth at the subscriber&#39;s ends are required, and to address this need, a point-to-point transmission by means of Gigabit Ethernet, which is relatively low-priced and can secure a higher bandwidth in comparison to the ATM technology, is utilized. In this regard, the ATM has drawbacks in that it requires relatively expensive equipment, has limited bandwidth, and requires the segmentation of IP packets. As such, even in the PON structure of the subscriber network, the Ethernet type is more favored rather than the ATM technique. 
   In order to provide services by means of Ethernet-based passive optical network, it is necessary for the provision of OAM capability, which does not exist in the existing Ethernet. The OAM has been defined recently in an EPON standardization but still being developed in IEEE 802.3ah EFM TF, Draft v1.0. The OAM capability defined in the Draft v1.0 up to now is a basic function, which supports Remote Failure Indicating function, Remote Loop-back function, and Link Monitoring function, as described in IEEE 802.3ah EFM. However, since detailed operation processes for the OAM discovery method are not defined in the Draft v1.0, some problems may occur in attempts to perform the OAM protocols effectively. In other words, no uniform discovery process for the OAM capability is available between the OLT  100  and the ONU  110 . As a result, any OAM capabilities defined and used by different vendors will not cooperate with each other as the frames may be unrecognizable to each other. 
   SUMMARY OF THE INVENTION 
   Accordingly, there is a need for a new scheme to provide an OAM capability discovery method, which enables an OLT and an ONU to perform discovery for their OAM capabilities. 
   The present invention is related to an OAM capability discovery method for performing an OAM effectively after setting the OAM capabilities that can be supported by both an OLT and an ONU. 
   In one preferred embodiment of the present invention, there is provided an OAM capability discovery method in which an OLT performs the OAM discovery method for multiple ONUs connected to the OLT in an Ethernet passive optical network. The method includes the steps of: assigning by the OLT identifications for identifying each of the ONUs according to registration requests from the ONUs connected to the OLT, and starting by the OLT an OAM capability discovery operation for the OAM capabilities of the ONUs by transmitting first OAM capability information messages; and receiving by the OLT second OAM capability information messages for reporting the OAM capabilities of the ONUs from the ONUs having received the first OAM capability information message. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram showing the physical network structure of a general passive optical network; 
       FIG. 2  is a view showing the placement where OAM capability discovery process occurs between OLT and ONU; 
       FIG. 3  a view showing detailed steps of the OAM capability discovery process according to an embodiment of the present invention; 
       FIG. 4  is a flow chart illustrating an operation state of the OLT in an OAM capability discovery process according to an embodiment of the present invention; 
       FIG. 5  is a flow chart illustrating an operation state of the ONU in an OAM capability discovery process according to an embodiment of the present invention; 
       FIG. 6  is a view showing a data field structure of an OAM state PDU_according to an embodiment of the present invention; 
       FIG. 7  is a view showing a bit encoding structure of a local/far_end_state field according to an embodiment of the present invention; and 
       FIG. 8  is a view showing the kinds of messages classified by bit encoding of a local/far_end_state field according to an embodiment of the present invention; and 
   

   APPENDIX A is a copy of ITU-T Standard G.983.1. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In the following description, for purposes of explanation rather than limitation, specific details are set forth such as the particular architecture, interfaces, techniques, etc., in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments, which depart from these specific details. For purposes of simplicity and clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail. 
   Referring to  FIG. 2 , an OAM capability discovery processes according to the teachings of the present invention are performed just after the discovery process between an OLT (Optical Line Termination)  100  and an ONU (Optical Network Unit)  110  have been completed. In particular,  FIG. 2  shows the operation steps by which the OAM capability discovery process between the OLT  100  and the ONU  110  is performed according to an embodiment of the present invention. Briefly, the OLT  100  performs a discovery process, which assigns an ID for identifying the ONU  110  according to a registration request of the connected ONU  110  in step  10 . In step  20 , the OLT  100  and the ONU  110  perform an operation for discovering the capability of each other, and then in step  30 , a number of other subsequent steps are performed. 
   Referring to  FIG. 3 , the OAM capability discovery process according to the embodiment of the present invention is realized on a three-way handshaking. As shown, messages transmitted/received according to the operation procedure includes an OAM capability information message of the OLT Initiate_OAM_Discovery, an OAM capability information message of the ONU Report_OAM_Discovery, and OAM capability discovery completion message Complete_OAM_Discovery. In addition, in order to improve the reliability in the exchange of all messages, reception wait time (discovery_time) for waiting for a message received corresponding to a transmitted message is set in advance in the present invention. 
   The process in which the OLT  100  and the ONU  110  transmit/receive the messages according to the OAM capability discovery processes is described hereinafter with reference to  FIG. 3 . 
   As shown in  FIG. 3 , the OLT  100  starts the OAM capability discovery by transmitting an OAM capability of the OLT  100  to the registered ONU  110  by means of “Initiate_OAM_Discovery” message in step  21 . Herein, when the “Report_OAM_Discovery” message is not received from the ONU  110  within a predetermined time period (discovery_time), the OLT  100  retransmits the “Initiate_OAM_Discovery” message until the “Report_OAM_Discovery” message is received within the predetermined time period (discovery_time). 
   The ONU  110  having received the “Initiate_OAM_Discovery” message from the OLT  100  transmits an OAM capability of the ONU  110  to the OLT  100  by means of the “Report_OAM_Discovery” message in step  23 . Herein, when the “Complete_OAM_Discovery” message is not received from the OLT  100  within the predetermined time period (discovery_time), the ONU  110  retransmits the “Report_OAM_Discovery” message until the “Complete_OAM_Discovery” message is received within the predetermined time period (discovery_time). 
   In step  25 , the OLT  100  having received the “Report_OAM_Discovery” message from the ONU  110  transmits the “Complete_OAM_Discovery” message to the ONU  110 , and then informs the ending of the OAM capability discovery between the OLT  100  and the ONU  110 . 
   Now, detailed operation processes for each of the OLT  100  and the ONU  110  according to the above-mentioned steps are shown in  FIGS. 4 to 5 . 
   First, an operation of the OLT  100  in an the OAM capability discovery process according to the present invention is described with reference to  FIG. 4 . In step  101 , in order to start the OAM capability discovery, the OLT  100  transmits to the registered ONU  110  the “Initiate_OAM_Discovery” message in which the OAM capability of the OLT  100  has been stored, and then step  103  is performed. In step  103 , the OLT  100  waits for the reception of the “Report_OAM_Discovery” message from the ONU  110  within a predetermined time period. Next, in step  105 , when the “Report_OAM_Discovery” message is received from the ONU  110  within the predetermined time period, step  107  is performed. If the “Report_OAM_Discovery” message is not received from the ONU  110  during the predetermined time period, the step  101  to step  105  are repeated. Finally, in step  107 , the OLT  100  transmits the “Complete_OAM_Discovery” message to the ONU  110 , and then ends the OAM capability discovery process. 
   Next, an operation of the ONU  110  in an OAM capability discovery process according to the present invention is described with reference to  FIG. 5 . The ONU  110  receives the “Initiate_OAM_Discovery” message from the OLT  100  in step  111 , and then step  113  is performed. In step  113 , the ONU  110  transmits to the OLT  100  the “Report_OAM_Discovery” message in which the OAM capability of the ONU  110  has been stored, and then step  115  is performed. In step  115 , the ONU  110  waits for the reception of the “Complete_OAM_Discovery” message from the OLT  100  within a predetermined time period. Next, in step  117 , when the “Complete_OAM_Discovery” message is received from the OLT  100  during the predetermined time period, the ONU  110  ends the OAM capability discovery process. If the “Complete_OAM_Discovery” message is not received from the OLT  100  during the predetermined time period, the step  113  to step  117  are repeated. 
   Referring to  FIGS. 6-8 , a data field structure of each message transmitted/received during the OAM capability discovery process described above is described. 
     FIG. 6  illustrates the data field structure of an OAM state PDU, which is a data field structure of each message that is actually transmitted/received through out the OAM capability discovery processes. The table includes a column on the left which indicates the quantity of OCTETS (8 bits each) that each field comprises. As shown, each message according to an embodiment of the present invention includes not only data fields of an OAM state PDU of a general structure, but also a Local_Allocated_channel field  203  having a size of one byte and a Far_End_Allocated_channel field  209  having a size of one byte, a Local_Topology field  205 , a Far_End_Topology field  211 , a Local_State field  201  and a Far_End_State field  207 . 
   The Local_Allocated_channel field  203  and the Far_End_Allocated_channel field  209  are fields in which a static allocated bandwidth information is stored in order to transmit OAM capability information when the OAM capability discovery is performed. In addition, the Local_Topology field  205  and the Far_End_Topology field  211  are fields for storing transmission information regarding a network topology, i.e., a point-to-point network structure or a point-to-multi-point network structure during the OAM capability discovery. 
   The Local_State field  201  and the Far_End_State field  207  are defined newly according to the embodiment of the present invention and represent fields including information regarding the type of messages transmitted/received through the OAM capability discovery process. Bit encoding structure of the Local_State field  201  and the Far_End_State field  207  is shown in  FIG. 7 . As shown, the Local_State field  201  and the Far_End_State field  207  represent the classification of each message transmitted/received through the OAM capability discovery process by newly defining D6 bit and D7 bit as CD state (Capability Discovery State) field in a bit encoding structure of a conventional Local_State field and the Far_End_State field. 
   The type of messages classified by the CD state field values are shown in  FIG. 8 . As shown in  FIG. 8 , the CD state value of the “Initiate_OAM_Discovery” message is 01, the CD state value of the “Report_OAM_Discovery” message is 10, and the CD state value of the “Complete_OAM_Discovery” message is 11. Further, a CD state value of an OAM message, which utilizes OAM Status PDU [0×00] after the OAM capability discovery has completed, is 00. 
   As described above, the present invention can perform the OAM information exchange effectively by defining a 3-way handshaking-based OAM capability discovery procedure. Moreover, the present invention can provide a high reliability for messages (Initiate_OAM_Discovery, Report_OAM_Discovery, Complete_OAM_Discovery) transmitted/received when the OAM capability discovery is performed, by setting the discovery_time, which is a reception waiting time period for waiting a message. 
   While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.