Patent Application
20100158520
This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2008-0131700, filed on Dec. 22, 2008, the disclosure of which is incorporated herein in its entirety by reference.
1. Field
The following description relates to optical network technology, and more particularly, to a local area network (LAN) emulation method in a wavelength division multiplexing (WDM)-passive optical network (PON) and an information storage medium.
2. Description of the Related Art
As next-generation optical network technology using a WDM technique, WDM-PONs have overcome poor scalability and security of conventional Ethernet PONs (EPONs) and provide high-capacity and high-quality service.
In such a WDM-PON, data transmission from an optical network unit (ONU) is based on point-to-point (P2P) connection with an optical line terminal (OLT). All frames transmitted from an ONU are only received by an OLT, and ONUs cannot directly transmit and receive frames transmitted by other ONUs. Thus, in order to provide a conventional LAN function of using a shared medium in the WDM-PON, a LAN emulation function reflecting a characteristic of the WDM-PON is required.
The following description relates to a local area network (LAN) emulation method in a wavelength division multiplexing (WDM)-passive optical network (PON).
According to an exemplary aspect, there is provided a local area network (LAN) emulation method of an optical line terminal (OLT) for a wavelength division multiplexing (WDM)-passive optical network (PON). The method includes receiving a data frame from an optical network unit (ONU) or an external network; checking a PON tag of the data frame received from the ONU including a mode bit and a logical link identifier (LLID) or a destination address (DA) of the data frame received from the external network, and identifying a transmission type of the received data frame; and generating a new data frame based on the result of the identification operation, and transmitting the new data frame to the ONU or the external network.
According to another exemplary aspect, there is provided a data frame receiving method of an optical network unit (ONU) for a wavelength division multiplexing (WDM)-passive optical network (PON). The method includes checking a mode bit and a logical link identifier (LLID) of the data frame when a new data frame arrives; receiving the new data frame when it is found that the mode bit is 0; and receiving the new data frame when it is found that the mode bit is 1 and a source address (SA) is not a media access control (MAC) address of the ONU.
According to still another exemplary aspect, there is provided a logical link identifier (LLID) assignment method of an optical line terminal (OLT) for a wavelength division multiplexing (WDM)-passive optical network (PON). The method includes broadcasting a discovery message including port information and transmission wavelength information to optical network units (ONUs); receiving a registration request message including the port information, the transmission wavelength information and source address (SA) information of the ONU from an ONU receiving the discovery message; transmitting a registration message assigning a LLID to the ONU according to the received registration request message to the ONU; and receiving a registration response message including the assigned LLID from the ONU receiving the registration message.
According to yet another exemplary aspect, there is provided an information storage medium storing a local area network (LAN) emulation layer data structure of an optical line terminal (OLT) for a wavelength division multiplexing (WDM)-passive optical network (PON). The medium includes a media access control (MAC) layer that is a lower layer receiving a data frame transmitted from an optical network unit (ONU), removing a MAC frame header, transmitting a PON tag and data to a shared LAN emulation layer that is an upper layer, receiving a data frame generated from the shared LAN emulation layer, and transmitting the data frame to the ONU; and the shared LAN emulation layer checking a mode bit and a logical link identifier (LLID) of the data frame received through the MAC layer, and transmitting the data frame generated according to the result of the check operation to the MAC layer.
According to yet another exemplary aspect, there is provided an information storage medium storing a structure of a data frame transmitted between a media access control (MAC) layer of an optical line terminal (OLT) for a wavelength division multiplexing (WDM)-passive optical network (PON) and a local area network (LAN) emulation layer that is an upper layer of the MAC layer. The medium includes a preamble; a destination address (DA) field indicating a DA; a source address (SA) field indicating a SA; a type field indicating a type of the data frame; a PON tag including a mode bit for distinguishing between point-to-point (P2P) and broadcast or multicast, and a logical link identifier (LLID) indicating a logical link between the OLT and an optical network unit (ONU); a data field containing data; and a frame check sequence (FCS) field containing information for detecting an error.
Other objects, features and advantages will be apparent from the following description, the drawings, and the claims.
Elements, features, and structures are denoted by the same reference numerals throughout the drawings and the detailed description, and the size and proportions of some elements may be exaggerated in the drawings for clarity and convenience.
The detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses and/or systems described herein. Various changes, modifications, and equivalents of the systems, apparatuses, and/or methods described herein will likely suggest themselves to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions are omitted to increase clarity and conciseness.
In telecommunication using optical fibers, a WDM technique employed in exemplary embodiments simultaneously transmits a plurality of channels using light of different wavelengths. In a WDM-PON according to an exemplary embodiment, the single OLT 10 and a plurality of the ONUs 30 are connected through the RN 20 in a tree form.
In particular, the RN 20 according to an exemplary embodiment may be configured in the form of an arrayed-waveguide grating (AWG). An AWG is a passive device having a wavelength-selection routing function, and an output port is determined according to a wavelength and an input port. The RN 20 may consist of a single AWG or a plurality of AWGs. Also, the WDM-PON can be connected to a plurality of input ports of an N×N AWG to reuse limited wavelengths. Here, the OLT 10 may transmit data to n of the ONUs 30 using W wavelengths.
When LAN emulation is performed at a reconciliation sublayer (RS), a part of a preamble can be used as a PON tag. However, a multiplexing function is required because an OLT must operate as if it had n logical MAC entities corresponding to n ONUs in order to communicate with the n ONUs. Thus, a delay may vary due to multiplexing, and a bit error rate (BER) may be high due to additional buffering. However, the LAN emulation function performed at the upper layer of the MAC layer according to an exemplary embodiment does not require multiplexing. Thus, it is possible to provide a low BER, and simplify an 802.1D bridge by a single MAC.
Referring to
The LAN emulation layer 12 according to an exemplary embodiment receives a data frame transmitted from the ONU 30 through the MAC layer 14, which is a lower layer. At this time, MAC header frame information (a DA and source address (SA)) collected by the MAC layer 14 is stored in an address mapping table of the OLT and used in the LAN emulation layer 12 according to necessity. And, a data frame generated in the LAN emulation layer 12 is transmitted to the ONU 30 through the MAC layer 14. Meanwhile, the LAN emulation layer 12 checks a mode bit and a logical link identifier (LLID) of a PON tag in a received data frame, and transmits a data frame generated according to the result of the check operation to the MAC layer 14.
A LAN emulation process of the LAN emulation layer 12 according to an exemplary embodiment will be described in detail now. When registration of an ONU and LLID assignment are completed through a registration process that will be described later with reference to
The LAN emulation layer 12 checks the mode bit and the LLID of the PON tag in the received frame. At this time, when the mode bit is 0 and the LLID is the LLID of the is transmission ONU, the frame transmitted from the ONU is a P2P frame. When the mode bit is 0 and the LLID is a broadcast_ID, the transmitted frame is a broadcast frame to be transmitted out of a PON. Also, when the mode bit is 1 and the LLID is a broadcast_ID, the transmitted frame is a broadcast frame to be transmitted in the PON. When the mode bit is 1 and the LLID is a multicast_group_ID, the transmitted frame is a multicast frame to be transmitted in the PON. Meanwhile, a frame transmitted from an external network is determined to be a P2P frame, broadcast frame, or multicast frame based on the DA field of the frame.
In a network architecture, different wavelengths are assigned to respective ONUs. Thus, P2P frames are transmitted with only a mode bit contained therein such that the ONUs can classify and process traffic. On the other hand, a PON tag is included in multicast frames and broadcast frames. In particular, in the case of a multicast frame, the LLID of a PON tag is a multicast_group_ID, and thus only ONUs belonging to the corresponding multicast service group receive the frame.
Referring to
The PON tag 101 includes a mode bit M 102 for distinguishing between P2P and broadcast or multicast, and a LLID 103 indicating a logical link between an OLT and an ONU. The mode bit M 102 is used as a flag for distinguishing between P2P (M=0) and broadcast or multicast (M=1), and the LLID 103 is given while the ONU or a user is registered. Here, the frame 100 including a PON tag is a multicast or broadcast frame.
Referring to
The OLT according to an exemplary embodiment receives a data frame from an ONU or external network, and checks a PON tag of the data frame received from the ONU including a mode bit and a LLID or the DA of the data frame received from the external network, thereby identifying the transmission type of the received data frame. Here, when the data frame received from the ONU is a P2P frame, a data frame including only a mode bit is transmitted to the ONU. When the data frame received from the ONU is a broadcast frame, a data frame is transmitted to the external network with a PON tag removed, or transmitted into a PON without change. Also, when the data frame received from the external network is a multicast or broadcast frame, a data frame into which a PON tag is inserted is transmitted to the ONU, and when the data frame received from the external network is a P2P frame, a data frame into which a mode bit is inserted is transmitted to the ONU.
A data frame processing process of an OLT according to an exemplary embodiment will be described in detail now with reference to
Meanwhile, when it is found in operation 703 that the LLID is an ONU_ID, the LLID is removed (710). Then, port information and wavelength information of a destination ONU are searched for based on the DA of the frame (711), and the data frame is transmitted to the ONU (712). Also, when it is found in operation 702 that the mode bit M is 1, the frame is transmitted to ONUs without change by broadcasting or multicasting (713).
When it is found in operation 701 that no PON tag is included, the received frame is processed based on the DA field. The DA of the received framed is checked (720). When the DA of the received frame is broadcast, the mode bit M is set to 1, and the LLID is set to a broadcast_ID (721). Subsequently, a PON tag is inserted (722), and the frame is broadcast or multicast to all ONUs (723).
Meanwhile, when it is found in operation 720 that the DA of the received frame is not a broadcast_ID, it is checked whether the DA of the received frame is a multicast_ID (730). When the DA of the received frame is a multicast_ID, the mode bit M is set to 1, and the LLID is set to a multicast_ID (731). Subsequently, a PON tag is inserted (722), and the frame is broadcast or multicast to all ONUs (723). On the other hand, when it is found in operation 730 that the DA of the received frame is an ONU MAC address, the mode bit M is set to 0 (740) and inserted into the data frame (741). Subsequently, port information and wavelength information of the corresponding ONU are searched for based on the DA of the data frame (711), and the data frame is transmitted to the ONU (712).
When a new data frame arrives, the ONU according to an exemplary embodiment checks a mode bit M and a LLID of the data frame. When the mode bit M is 0, or when the mode bit M is 1 and a SA is not the MAC address of the ONU, the ONU receives a new data frame.
A data frame processing process of an ONU according to an exemplary embodiment will be described in detail now with reference to
On the other hand, when the mode bit M is 1, the ONU checks whether a LLID is a broadcast_ID (820). When it is found that the LLID is a broadcast_ID, a SA is checked. When the SA is the same as the MAC address of the ONU, the frame is discarded (850), and when the SA is not the same as the MAC address of the ONU, the frame is received (860). When the LLID is not a broadcast_ID, the ONU checks whether the LLID is a multicast_ID (830). When it is found that the LLID is not a multicast_ID, a frame is discarded (850). Otherwise, the SA field is checked (840). When a value of the SA field is the same as the MAC address of the ONU, the ONU discards the frame (850), and when the value is not the same as the MAC address of the ONU, the ONU receives the frame (860).
Referring to
A LLID assignment process of an OLT according to an exemplary embodiment will be described in detail now with reference to
Each ONU receiving the discovery message 200 records its own MAC address in a SA field 211 of the registration request message 210, records port and wavelength information obtained from the discovery message 200 in a port field 212 and a wavelength field 213, and transmits the registration request message 210 to the OLT.
The OLT receiving the registration request message 210 from the ONU assigns a LLID and manages the assigned LLID, the MAC address, and the port and wavelength information using a table. The OLT records the assigned LLID in a LLID field 221 of the registration message 220 and transmits the registration message 220 to the ONU. In response to the received registration message 220, the ONU records the assigned LLID in a LLID field 231 of the registration response message 230 and transmits the registration response message 230 to the OLT.
The LLID assignment process may additionally include an operation of releasing the registration and the LLID after the transmission is completed. To be specific, after the transmission is completed, the ONU transmits a registration release request message RELEASE_REQUEST 240 to the OLT in order to release the registration and the LLID. The OLT receiving the registration release request message 240 transmits a registration release message RELEASE 250 to the ONU. When the OLT receives a registration release response message RELEASE_ACK 260 from the ONU, it removes the LLID and all information of the ONU from the table.
Referring to
The present invention can be implemented as computer readable codes in a computer readable record medium. The computer readable record medium includes all types of record media in which computer readable data are stored. Examples of the computer readable record medium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, and an optical data storage. Further, the record medium may be implemented in the form of a carrier wave such as Internet transmission. In addition, the computer readable record medium may be distributed to computer systems over a network, in which computer readable codes may be stored and executed in a distributed manner.
As apparent from the above description, an exemplary embodiment can provide a LAN emulation function of a WDM-PON. In particular, in an AWG-based WDM-PON, the LAN emulation function can be provided using a mode bit and LLID regardless of the number of AWGs constituting a RN, the number of input ports of the AWGs, or the number of wavelengths.
It will be apparent to those of ordinary skill in the art that various modifications can be made to the exemplary embodiments of the invention described above. However, as long as modifications fall within the scope of the appended claims and their equivalents, they should not be misconstrued as a departure from the scope of the invention itself.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2008-0131700 | Dec 2008 | KR | national |
