Abstract:
Transmitting data in a synchronous Ethernet passive optical network employs a synchronous Ethernet for ensuring QoS during transmission of multi-media data, thereby specifying transmission of synchronous data and asynchronous data, respectively. The Ethernet passive optical network has an optical line terminal, which is a central base station, and a plurality of optical network units. The method includes the steps of forming a synchronous frame using the OLT to transmit synchronous data for the ONUs, forming an asynchronous frame using the OLT to transmit asynchronous data for the ONUs, forming a super frame including the synchronous and asynchronous frames using the OLT, and transmitting the super frame using the OLT.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims the benefit under 35 U.S.C. 119(a) of an application entitled “Method for Transmitting Data in Synchronous Ethernet Passive Optical Network” filed with the Korean Intellectual Property Office on Jan. 27, 2005 and assigned Serial No. 2005-7597, the contents of which are incorporated herein by reference.  
       BACKGROUND OF INVENTION  
       [0002]     The present invention relates to a passive optical network. More particularly, the present invention relates a passive optical network using residential synchronous Ethernet.  
         [0003]     A conventional passive optical network (PON) employs a time-division scheme or a wave-division scheme.  
         [0004]     A PON employing the time-division scheme is known as an Ethernet PON. Due to the characteristics of the PON, the Ethernet PON uses a particular scheme for media access control (MAC) in order to prevent collision between upstream signals.  
         [0005]     A typical Ethernet PON has a separate time domain for each subscriber that allows subscribers to transmit upstream signals at respective times so as to avoid collision between the signals of different subscribers. However, since the time domain is established regardless of signal type, competition arises between upstream signals if more than one type of upstream signals exists. In the latter case, a time delay may occur. Since multi-media signals are sensitive to the time delay, the conventional Ethernet PON is unsuitable for transmitting multi-media signals requiring exact time information without time delay.  
         [0006]     Recently, a technique for transmitting multi-media data such as video/voice data using the conventional Ethernet has been actively discussed. The Ethernet for transmitting multi-media data is referred to as synchronous Ethernet.  
         [0007]      FIG. 1  is a view illustrating the structure of a transmission cycle in a conventional synchronous Ethernet.  
         [0008]     As shown in  FIG. 1 , the conventional synchronous Ethernet transmits data with a transmission cycle of 125 μsec. The transmission cycle includes an Async frame  12  for transmitting asynchronous data and a Sync frame  11  for transmitting synchronous data.  
         [0009]     According to the proposal under the discussion (although the proposal is subject to change), the Sync frame  11  for transmitting the synchronous data has the highest priority in the transmission cycle and includes 738-byte sub-Sync frames  11 - 1 ,  11 - 2 , . . . ,  11 -M. The Async frame  12  for transmitting the asynchronous data includes sub-Async frames having a variable length in a corresponding area. Each of the sub-Sync frames  11 - 1 ,  11 - 2 , . . . ,  11 -M includes n Sync packets  101 - 1  to  101 - n.    
         [0010]     However, in order to apply the above synchronous Ethernet to the Ethernet PON, it is necessary to perform the MAC in a manner discretely different from that of the conventional Ethernet PON, which competitively grants access onto a communication medium using the CSMA/CD (carrier sense multiple access/collision detect) protocol defined in IEEE 802.3.  
         [0011]     More specifically, it is necessary to provide an Ethernet PON using a synchronous Ethernet capable of transmitting multi-media signals, which require exact time information, separately from general signals in such manner that the Ethernet PON can support various multi-media without degrading QoS (quality of service).  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention addresses the above-mentioned problems occurring in the prior art.  
         [0013]     In one aspect, the present invention transmits data in a synchronous Ethernet passive optical network (PON), which employs a synchronous Ethernet for ensuring QoS during transmission of multi-media data, thereby specifying transmission of synchronous data and asynchronous data, respectively.  
         [0014]     The present invention accordingly provides a method for transmitting data in an Ethernet passive optical network (PON) including an optical line terminal (OLT), which is a central base station, and a plurality of optical network units (ONUs), the method comprising the steps of: forming a synchronous frame using the OLT to transmit synchronous data that is for the ONUs; forming an asynchronous frame using the OLT to transmit asynchronous data that is for the ONUs; using the OLT to form a super frame so as to include the synchronous and asynchronous frames; and transmitting the formed super frame using the OLT.  
         [0015]     According to another aspect of the present invention, there is provided a method for transmitting data in an Ethernet passive optical network (PON) including an optical line terminal (OLT), which is a central base station, and a plurality of optical network units (ONUs), the method comprising the steps of: using each ONU in forming a respective sub-synchronous frame to transmit synchronous data that is for the OLT; using each ONU in forming a respective asynchronous frame to transmit asynchronous data that is for the OLT; scheduling and transmitting the sub-synchronous frames using the ONUs such that the sub-synchronous frames are combined as one synchronous frame in a splitter connecting the OLT with the ONUs; and scheduling and transmitting the asynchronous frames using the ONUs such that the asynchronous frames are combined as one asynchronous frame in the splitter connecting the OLT with the ONUs.  
         [0016]     According to still another aspect of the present invention, there is provided a method for transmitting data in an Ethernet passive optical network (PON) including an optical line terminal (OLT), which is a central base station, and a plurality of optical network units (ONUs), the method comprising the steps of: using each ONU in forming respective time slots to transmit synchronous data that is for the OLT; using each ONU in forming respective asynchronous frames to transmit asynchronous data that is for the ONUs; using the ONUs in scheduling said respective time slots, and transmitting in correspondence with said respective time slots, such that resulting transmissions are combined as one sub-synchronous frame in a splitter connecting the OLT with the ONUs; and using the ONUs in scheduling and transmitting said respective asynchronous frames such that the transmitted asynchronous frames are combined as one asynchronous frame in the splitter connecting the OLT with the ONUs. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The above and other objects, 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:  
         [0018]      FIG. 1  is a view illustrating the structure of a transmission cycle in a conventional synchronous Ethernet;  
         [0019]      FIG. 2  is a view illustrating a layer structure of a synchronous Ethernet according to the present invention;  
         [0020]      FIG. 3  is a detailed view illustrating a synchronous frame process unit, which is a part of a data link layer for processing a synchronous frame in a conventional Ethernet layer structure;  
         [0021]      FIG. 4  is a view illustrating a downstream transmission scheme in a conventional Ethernet PON;  
         [0022]      FIG. 5  is a view illustrating a downstream transmission scheme in a synchronous Ethernet PON according to a first embodiment of the present invention;  
         [0023]      FIG. 6  is a view illustrating a downstream transmission scheme in a synchronous Ethernet PON according to a second embodiment of the present invention;  
         [0024]      FIG. 7  is a view illustrating an upstream transmission scheme in a conventional Ethernet PON;  
         [0025]      FIG. 8  is a view illustrating an upstream transmission scheme in a synchronous Ethernet PON according to a first embodiment of the present invention; and  
         [0026]      FIG. 9  is a view illustrating an upstream transmission scheme in a synchronous Ethernet PON according to a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0027]     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanied drawings. Note that the same or similar components in drawings are designated by the same reference numerals as far as possible although they are shown in different drawings. In the following description of the present invention, detailed description of known functions and configurations incorporated herein is omitted for clarity of presentation.  
         [0028]      FIG. 1  is a view illustrating the structure of a transmission cycle in a conventional synchronous Ethernet.  
         [0029]     As shown in  FIG. 1 , the conventional synchronous Ethernet transmits data with a transmission cycle of 125 μsec. The transmission cycle includes an Async frame  12  for transmitting asynchronous data and a Sync frame  11  for transmitting synchronous data.  
         [0030]     According to the proposal under the discussion (although the proposal is subject to change), the Sync frame  11  for transmitting the synchronous data has the highest priority in the transmission cycle and includes 738-byte sub-Sync frames  11 - 1 ,  11 - 2 , . . . ,  11 -M. The Async frame  12  for transmitting the asynchronous data includes sub-Async frames having a variable length in a corresponding area. Each of the sub-Sync frames  11 - 1 ,  11 - 2 , . . . ,  11 -M includes n Sync packets  101 - 1  to  101  - n . Each of the Sync packets  101 - 1  to  101 - n  can be represented as one time slot.  
         [0031]      FIG. 2  is a view illustrating a layer structure of a conventional synchronous Ethernet. The layer structure includes a PHY layer  21 , which is a lowermost layer of an OSI layer structure and directly relates to hardware so as to allow input/output of an Ethernet frame. An xMII (x media independent interface) layer  22  is an 802.3 MAC-PLS (physical layer signaling) interface layer for connecting the PHY layer  21  with a data link layer. A Sync frame process unit  26  is designed for processing Sync frames, and an Async frame process unit  27  is designed for processing Async frames. Similar to the conventional layer structure, the Async frame process unit  27  includes a MAC layer  23 , which converts a packet from an upper layer (MAC client)  25  into an Ethernet frame so as to transmit the Ethernet frame into the PHY layer  21 . The unit  27  also converts an Ethernet frame from the PHY layer  21  into a packet so as to transmit the packet into the upper layer  25 . Additionally included in the unit  27  is a bridging layer  24 , which analyzes the received Ethernet frame and determines the relay of the Ethernet frame to the destination based on information contained in the Ethernet frame.  
         [0032]     The xMII layer  22 , according to the present invention, includes a parser  221 , which divides the synchronous Ethernet frame into sub-Sync frames and sub-Async frames so as to transmit them to upper layers  23 ,  25  according to the contents thereof. The layer  22  further includes a MUX  222  for multiplexing, in one cycle, the sub-Sync frames and sub-Async frames from the Sync frame process unit  26  and the Async frame process unit  27 , respectively.  
         [0033]      FIG. 3  is a detailed view illustrating the Sync frame process unit  26 , which is a part of a data link layer for processing the Sync frame in the conventional Ethernet layer structure. The Sync frame process unit  26  includes a Sync buffer  34  connected to an upper layer, which processes multi-media information, so as to perform a buffering operation for ensuring continuous data input/output. The unit  26  further includes a Sync frame-frame section  33  for creating a Sync header with respect to Sync data transmitted from the upper layer through the Sync buffer  34  A Sync frame-inverse frame section  32  erases the Sync header in a sub-Sync frame transmitted from a lower layer (e.g., parser) and transmits the sub-Sync frame to the Sync buffer  34 . A slot routing process section  31  connected to the Sync frame-frame section  33 , the Sync frame-inverse frame section  32 , and lower layers  221  and  222  provides a transmission route for the sub-Sync frame. The Sync frame-frame section  33 , the Sync frame-inverse frame section  32 , and the slot routing process section  31  can be implemented in software.  
         [0034]     In the case of a downstream signal (i.e., a signal from an upper layer of an OLT to a lower layer), the multi-media data (i.e., Sync packet), such as broadcast data having an interface (ASI or the like), are received through a corresponding interface and stored in the Sync buffer  34  of the Sync frame process unit  26 . A Sync header is created, in the form of software, for the data stored in the Sync buffer  34  by means of the Sync frame-frame section  33  and the slot routing process section  31 . Slots are allocated to a payload, thereby forming the sub-Sync frame. The Sync header includes information related to a frame counter for counting the sub-Sync frames and a cycle counter for counting transmission cycles, as well as slot routing information for slot allocation and slot reservation information.  
         [0035]     The sub-Sync frame formed in the Sync frame process unit  26  is transmitted to the MUX  222  of the xMII layer  22 . A number of the sub-Sync frames, together with the sub-Async frames transmitted to the MUX  222  through the Async frame process unit  27 , are combined into a synchronous Ethernet frame allocated to one cycle. Then, the synchronous Ethernet frame is transmitted to other equipment through the PHY layer  21 . The Async frame process unit  27  consists of the bridging layer  24  and the MAC layer  23  and operates as a typical IEEE 802.3 data link layer.  
         [0036]     In the case of an upstream signal, the synchronous Ethernet frame received through the PHY layer  21  is divided into a Sync frame part and an Async frame part by means of a parser  221  of the xMII layer  22 . The Sync frame part is transferred to the Sync frame process unit  26  and the Async frame part is transferred to the Async frame process unit  27 . As mentioned above, the Async frame process unit  27  consists of the bridging layer  24  and the MAC layer  23  and operates as a typical IEEE 802.3 data link layer.  
         [0037]     The sub-Sync frame of the Sync frame part transferred to the Sync frame process unit  26  is transmitted, in the form of software, to the Sync frame-inverse frame section  32  and through the slot routing process section  31 . Then, after extracting multi-media data from the sub-Sync frame based on information related to the slot of the payload contained in the Sync header, the multi-media data are transmitted, through the Sync buffer  34 , to an upper layer for processing the multi-media data while ensuring QoS.  
         [0038]     Signal transmission in the synchronous Ethernet PON, whose layer structure is discussed immediately above, may be performed as downstream transmission and as upstream transmission.  
         [0039]      FIG. 4  is a view illustrating a downstream transmission scheme in the conventional Ethernet PON. When an OLT (optical line terminal)  41  transmits data  401 ,  402 ,  403 ,  404  that is destined for, UEs (user equipments)  44 - 1 ,  44 - 2 ,  44 - 3 , the data are transferred to respective ONUs (optical network units)  43 - 1 ,  43 - 2 ,  43 - 3  through a splitter  42 . The ONUs  43 - 1 ,  43 - 2 ,  43 - 3  extract data for the UEs  44 - 1 ,  44 - 2 ,  44 - 3  based on destination address information of the MAC header and transmit the data to the UEs.  
         [0040]     The synchronous Ethernet PON according to the present invention performs the downstream transmission differently and in two ways.  
         [0041]     One of them is to transmit Sync data by allocating the sub-Sync frames among respective UEs  44 - 1 ,  44 - 2 ,  44 - 3 , and the other is to transmit Sync data by allocating the time slots of the sub-Sync frame to respective UEs.  
         [0042]      FIG. 5  is a view illustrating downstream transmission in the synchronous Ethernet PON according to a first embodiment of the present invention. The Sync data are transmitted to UEs  44 - 1 ,  44 - 2 ,  44 - 3  by allocating the sub-Sync frames among respective UEs. In this case, transmission of the Async data is identical to that of the conventional Ethernet PON shown in  FIG. 4 .  
         [0043]     The Sync frames and Async frames to be transmitted to UEs  54 - 1  to  54 -M from an OLT  51  are prepared in the form of super frames  501 ,  502 ,  503 . The super frames  501 ,  502 ,  503  are each transferred to each of the ONUs  53 - 1  to  53 -M through a splitter  52 . Portions of the super frame  501  are selectively transmitted by each of the ONUs  53 - 1  to  53 -M to the UEs  54 - 1  to  54 -M. In effect, the ONUs  53 - 1  to  53 -M distinguish the Sync frames from the Async frames, and select the respective sub-Sync frame for transmission to the UE  54 - 1  to  54 -M.  
         [0044]     In summary, the super frames  501 ,  502 ,  503  each include sub-Sync frames  511 - 1 ,  511 - 2 .,  511 -M, which are allocated to the UEs  54 - 1  to  54 -M. The Async frames  512 - 1 ,  512 - 2 ,  512 - 3  are, likewise, respectively allocated.  
         [0045]     Referring to the downstream transmission in the synchronous Ethernet PON according to the first embodiment of the present invention shown in  FIG. 5 , the ONUs  53 - 1  to  53 -M distinguish the Sync signals according to sub-Sync frame unit, but it is not necessary for the ONUs  53 - 1  to  53 -M to distinguish signals in the sub-Sync frame by slot unit.  
         [0046]      FIG. 6  is a view illustrating a downstream transmission scheme in a synchronous Ethernet PON according to a second embodiment of the present invention.  
         [0047]     According to the second embodiment of the present invention, the Sync data are transmitted to UEs  64 - 1 ,  64 - 2 , . . .  64 -M by allocating the time slots of the sub-Sync frame to respective UEs. In this case, transmission of the Async data is identical to that of the conventional Ethernet PON shown in  FIG. 4 .  
         [0048]     The Sync frames and Async frames to be transmitted to UEs  64 - 1  to  64 -M from an OLT  61  are prepared in the form of super frames  601 ,  602 ,  603 . The super frames  601 ,  602 ,  603  are each transferred to each of the ONUs  63 - 1  to  63 -M through a splitter  62 . Then, the ONUs  63 - 1  to  63 -M selectively transmit respective portions of the super frame  601  to the UEs  64 - 1  to  64 -M. This involves distinguishing the Sync frames from the Async frames, and selecting time slots for respective UEs  64 - 1  to  64 -M.  
         [0049]     The super frames  601 ,  602 ,  603  each include a plurality of sub-Sync frames  611 - 1 ,  611 - 2 .,  611 -N for transmission of the Sync data. The sub-Sync frames  611 - 1 ,  611 - 2 ,  611 -N respectively include Sync time slots  611 - 11  to  611 -IM,  611 - 21  to  611 - 2 M, . . . , and  611 -N 1  to  611 -NM. Async frames  612 - 1 ,  612 - 2 ,  612 - 3  are also included in each of the super frames  601 ,  602 ,  603 . Content of each super frame  601 ,  602 ,  603  is allocated among the UEs  64 - 1  to  64 -M.  
         [0050]     Referring to the downstream transmission in the synchronous Ethernet PON according to the second embodiment of the present invention shown in  FIG. 6 , the ONUs  63 - 1  to  63 -M distinguish the Sync signals for the UEs  64 - 1  to  64 -M in view of a time slot unit in the sub-Sync frame. Therefore, it is necessary for the ONUs  63 - 1  to  63 -M to distinguish signals in the sub-Sync frame in view of a slot unit.  
         [0051]     Meanwhile, upstream transmission in the conventional Ethernet PON is shown in  FIG. 7 .  
         [0052]      FIG. 7  is a view illustrating an upstream transmission scheme in the conventional Ethernet PON. Data  741 - 1 ,  741 - 2 ,  742 - 1 ,  743 - 1 ,  743 - 2 ,  743 - 3  from UEs  74 - 1 ,  74 - 2 ,  74 - 3  are transmitted to ONUs  73 - 1 ,  73 - 2 ,  73 - 3 . The latter combine the data to form packets  741 ,  742 ,  743 . In addition, the ONUs  73 - 1 ,  73 - 2  and  73 - 3  schedule the packets  741 ,  742 ,  743  and sequentially transmit the packets to an OLT  71 .  
         [0053]     Different from the upstream transmission in the conventional Ethernet PON shown in  FIG. 7 , the synchronous Ethernet PON according to the present invention performs the upstream transmission in two ways.  
         [0054]     One of them is to allow UEs to transmit Sync data by allocating one respective sub-Sync frame per one cycle to each UE, and the other is to allow UEs to transmit Sync data including time slots for UEs by allocating the time slots of the sub-Sync frame among the UEs.  
         [0055]      FIG. 8  is a view illustrating an upstream transmission scheme in a synchronous Ethernet PON according to a first embodiment of the present invention.  
         [0056]     According to the first embodiment of the present invention, one sub-Sync frame per one cycle is allocated to each UE so as to allow the UE to transmit the Sync data.  
         [0057]     Sync Ethernet data to be transmitted to ONUs  83 - 1  to  83 -M from UEs  84 - 1  to  84 -M are prepared by a splitter  82  to form a super frame  801 , and the super frame is transmitted to the OLT  81 .  
         [0058]     The super frame  801  formed through the splitter  82  has  15625  octets per one cycle. The super frame  801  includes sub-Sync frames  831 - 1 ,  832 - 1 , . . . ,  83 M- 1  and Async frames  831 - 2 ,  832 - 2 , . . . ,  83 M- 2  transmitted from the UEs  84 - 1  to  84 -M.  
         [0059]     The sub-Sync frames  831 - 1 ,  832 - 1 , . . . ,  83 M- 1  created in ONUs  83 - 1  to  83 -M and transmitted to the splitter  82  are scheduled in such a way that they can be allocated to a single super frame  801 .  
         [0060]      FIG. 9  is a view illustrating an upstream transmission scheme in a synchronous Ethernet PON according to a second embodiment of the present invention. Time slots of the sub-Sync frame are allocated among the UEs so as to allow the UE to transmit the Sync data by means of its respective time slots. Sync Ethernet data transmitted to ONUs  93 - 1  to  93 -M from UEs  94 - 1  to  94 -M are prepared through a splitter  92  to form a super frame  901  and the super frame is transmitted to an OLT  91 . The super frame  901  formed through the splitter  92  has  15625  octets per one cycle and includes sub-Sync frames  931 - 1 ,  932 - 1 , . . .  93   n - 1  and Async frames  931 - 2 ,  932 - 2 , . . . ,  93 M- 2 . The sub-Sync frames  931 - 1 ,  932 - 1 , . . . ,  93   n - 1  allow the upstream Sync data to be transmitted with the time slots allocated to the UEs  94 - 1  to  94 -M.  
         [0061]     Hereinafter, the upstream transmission for the Sync data according to the second embodiment of the present invention is described in relation to the UE  194 - 1 .  
         [0062]     The UE  194 - 1  transmits Sync data and Async data to the ONU  93 - 1 . Upon receiving the Sync data and Async data from the UE  194 - 1 , the ONU  93 - 1  creates and transmits the Async frame  931 - 2  and time slot data  931 - 11 ,  931 - 12 , . . . ,  931 -In for sub-Sync frames.  
         [0063]     The splitter  92  sequentially receives time slot data  931 - 11 ,  931 - 12 , . . . ,  931 - 1   n ;  932 - 11 ,  932 - 12 , . . . ,  932 - 1   n ; . . . and  93 M- 11 ,  93 M- 12 , . . . ,  93 M- 1   n  transmitted from the ONUs  93 - 1  to  93 -M for the sub-Sync frames, and thereby forms the sub-Sync frames. In particular and by way of example, one sub-Sync frame may include the time slot data transmitted from the ONUs  93 - 1  to  93 -M for the sub-Sync frames. If the time slot data  931 - 11  have been input into the splitter  92  from the ONU  193 - 1 , the next time slot data  932 - 11  is then input into the splitter  92  from the ONU  293 - 2 , and so on in sequence. In this manner, if the time slot data  93 M- 11  have been input into the splitter  92  from the final ONU  93 -M, the sub-Sync frame  1   931 - 1  is created. After that, sub-Sync frames  2  and  3  are sequentially created. When the final sub-Sync frame has been made, the splitter  92  receives Async data  931 - 2 ,  931 - 2 , . . . , and  93 M- 2  from the ONUs  93 - 1  to  93 -M, thereby forming the Async frame. The Async frame, in combination with the Sync frame  931 - 1 ,  932 - 1 , . . .  93   n - 1 , are transmitted as a super frame  901  to the OLT  91 .  
         [0064]     As described above, the present invention provides a data transmission method in the PON using a synchronous Ethernet, so that the Sync and Async signals can be transmitted through the PON.  
         [0065]     In addition, according to the present invention, the Sync signal is transmitted in a frame unit if the Sync signal has a large size. It is also possible to transmit the Sync signal in a slot unit if the Sync signal has a small size or the Sync signal is frequently transmitted. Thus, the present invention offers improved communication efficiency.  
         [0066]     The data transmission method according to the present invention can be realized in the form of a program, so that the data transmission method can be stored in a computer-readable record medium, such as CD ROM, RAM, floppy discs, hard discs, or optical magnetic discs.  
         [0067]     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. Consequently, the scope of the invention should not be limited to the embodiments, but should be defined by the appended claims and equivalents thereof.