Abstract:
Provided is a TDMA (time division multiple access) PON (passive optical network) OLT (optical line terminal) system for a broadcast service, including packet processor determining information according to types of frames (unicast, multicast, and broadcast frames) and a switch output port using header information (an IP address of a packet header, MAC (multiple access control) addresses of Ethernet frames, and the like) of data received from an external node or the ONT (optical network terminal) and attaching the information to header parts of the frames to generate second data, a switch copying the second data by a predetermined number of times according to a transmission method and transmitting the second data to a corresponding destination output port according to the identification codes, M TDMA PON MAC processors removing the identification codes added to the second data and converting the second data into TDMA PON frames, and M optical transceivers converting the TDMA PON frames into optical signals and transmitting the optical signals to an ONT.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
       [0001]     This application claims the benefit of Korean Patent Application No. 10-2005-0121026, filed on Dec. 9, 2005, and Korean Patent Application No. 10-2006-0029083, filed on Mar. 30, 2006, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a system for a broadcast service in a passive optical network (PON) system, and more particularly, to a time division multiple access (TDMA) PON optical line terminal (OLT) system enabling a simultaneous broadcast and communications service through a single optical cable.  
         [0004]     2. Description of the Related Art  
         [0005]     Network businesses have invested heavily in triple play services (TPSs) capable of processing broadcasts, sound, and data in one network.  
         [0006]     Many more downstream bandwidths are required toward an optical network terminal (ONT) in an OLT to provide a broadcast service such as Internet protocol television (IPTV) to subscribers using a fiber to the home (FTTH) network.  
         [0007]     Downstream traffic is heavier than upstream traffic in an ultrahigh speed Internet network. Thus, if a broadcast service is additionally provided, a ratio of the downstream traffic to the upstream traffic is seriously asymmetric.  
         [0008]     However, in a gigabit PON (GPON) system recommended in ITU-T G.984.1˜2, a ratio of downstream traffic to upstream traffic may be within a range between 1:1 and 1:4. In a case of an Ethernet PON (EPON) system standardized in IEEE 802.3ah, a ratio of downstream traffic to upstream traffic is 1:1.  
         [0009]     Therefore, in a current TDMA PON system and a current network structure, network efficiency is deteriorated due to expected serious asymmetry of upstream and downstream speeds. This increases cost of OLT equipment.  
         [0010]     A multicasting method used in a TDMA-PON to solve this problem may delay a change of a channel and thus cause inconvenience to a user. Also, a broadcasting method using additional wavelength division multiplexing requires a high-priced optical transceiver and a high-priced optical amplifier to provide only a broadcast signal.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention provides a time division multiple access (TDMA) passive optical network (PON) optical line terminal (OLT) system for a broadcast service.  
         [0012]     According to an aspect of the present invention, there is provided a transmitter of a TDMA PON OLT system for a broadcast, including: a packet processor determining whether first data is received as a broadcast, multicast, or unicast based on a header of the first data and adding identification codes for determining an output port to generate second data; a switch copying the second data by a predetermined number of times and transmitting the second data to a corresponding output port according to the identification codes; M TDMA PON MAC processors removing the identification codes added to the second data and converting the second data into TDMA PON frames; and M optical transceivers converting the TDMA PON frames into optical signals and transmitting the optical signals to an ONT.  
         [0013]     According to another aspect of the present invention, there is provided a receiver of a TDMA PON OLT system for a broadcast service, including: M optical receivers receiving optical signals having burst mode characteristics, the optical signals transmitted from an ONT and extracting data from the optical signals; M TDMA PON MAC processors recovering TDMA PON frames from the extracted data; a switch multiplexing the recovered TDMA PON frames; and a packet processor recovering one of Ethernet frame data and packet data from the multiplexed frames. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
         [0015]      FIG. 1  is a view illustrating a method of transmitting frames in an existing TDMA PON OLT system; and  
         [0016]      FIG. 2  is a view illustrating a configuration of a TDMA PON OLT system for providing a broadcast service such as an IPTV according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Hereinafter, a preferred embodiment of the present invention will be described with reference to the attached drawings.  
         [0018]      FIG. 1  is a view illustrating a method of transmitting frames in an existing time division multiple access (TDMA) passive optical network (PON) optical line terminal (OLT) system.  
         [0019]     TDMA PON technology such as an Ethernet PON (EPON) and a gigabit PON (GPON) are standardized in a method of transmitting data to subscribers using a fiber to the home (FTTH) network. A TDMA PON uses continuous mode transmission technology as existing optical transmission technology during a downstream transmission of a data signal from an OLT to an optical network terminal (ONT). However, the TDMA PON uses burst mode transmission technology for transmitting packet data received from each ONT during a upstream transmission of the data signal from the ONT to the OLT.  
         [0020]     Downstream traffic for a transmission from an OLT  100  toward ONTs  120  through  130  will now be described. A packet processor  101  of the OLT  100  processes levels L 3  through L 7  of data received from an external node or the ONTs  120  through  130  and transmits the processed frames to TDMA PON medium access control (MAC) processors  102  and  104 .  
         [0021]     In the case where a packet processor having a data processing performance A is connected to TDMA PON MAC processors having a link speed of A/m, M TDMA PON MAC processors  102  and  104  are multiplexed and connected to one another to reduce the number of elements. The TDMA PON MAC processors  102  and  104  transmit TDMA PON frames having logical link identifiers (LLIDs) or optical network unit (ONU) IDs to optical transceivers  103  and  105  according to the standard recommendations of a GPON and an EPON.  
         [0022]     The optical transceivers  103  and  105  convert electric signals into optical signals and transmit the optical signals to a splitter  140  through optical lines according to the standard recommendations. The splitter  140  splits each of the optical signals into k optical signals within a splitting range according to the standard recommendations and transmits the k optical signals to the ONTs  120  through  130 .  
         [0023]     Optical transceivers  121  through  131  of the ONTs  120  through  130  convert optical signals into electric signals and transmit the electric signals to TDMA PON MAC processors  122  through  132 . The TDMA PON MAC processors  122  through  132  extract data from the electric signals to recover the TDMA PON frames transmitted from the OLT  100 .  
         [0024]     The TDMA PON MAC processors  122  through  132  convert the recovered TDMA PON frames into Ethernet frames and transmit the Ethernet frames to bridges  123  through  133  according to the standard recommendations of the GPON and the EPON. The bridges  123  through  133  transmit the Ethernet frames to destination subscriber devices.  
         [0025]     Upstream signals transmitted from the ONTs  120  through  130  to the OLT  100  will now be described. The bridges  123  through  133  of the ONTs  120  through  130  transmit Ethernet frames received from subscriber devices to the TDMA PON MAC processors  122  through  132 .  
         [0026]     The TDMA PON MAC processors  122  through  132  convert the Ethernet frames into TDMA PON frames and transmit the TDMA PON frames to the optical transceivers  121  through  131  only when a transmission of frames to the TDMA PON MAC processors  122  through  132  is allowed under the control of the OLT  100 .  
         [0027]     The optical transceivers  121  through  131  convert electric signals into optical signals and transmit the optical signal only when a transmission of frames is allowed and intercept the optical signals when the transmission of the frames is not allowed, so as to prevent signal interference among the ONTs  120  through  130 . Such a signal transmission method is called a burst mode.  
         [0028]     The splitter  140  multiplexes signals received from k ONTs and transmits the multiplexed signals to the optical transceiver  103  of the OLT  100 .  
         [0029]     The optical transceiver  103  extracts data from an optical signal transmitted in a burst mode and transmits the extracted data to the TDMA PON MAC processor  102 .  
         [0030]     The TDMA PON MAC processor  102  processes frames and transmits the processed frames to the packet processor  101  according to the standard recommendations. The packet processor  101  processes packets transmitted from a maximum number, M, of TDMA PON MAC processors  102  and  104  and transmits the processed packets to a destination port of an Uplink or a PON.  
         [0031]     More downstream bandwidths are required to provide a broadcast service such as an IPTV to subscribers using an FTTH network than in an existing network. Downstream traffic is heavier than upstream traffic in an ultrahigh speed internet network. If a broadcast service is additionally provided, a ratio of the downstream traffic to the upstream traffic is increasingly asymmetric. In an asymmetric TDMA PON system, network resources are not efficiently used due to an asymmetric traffic characteristic. Thus, cost of equipment and facilities is increased.  
         [0032]     In an existing TDMA PON system, broadcast frames requiring many bandwidths are not transmitted to all PON subscribers due to restrictions on bandwidths. However, an IPTV broadcast service is provided to all the PON subscribers by multicasting using an Internet Group Management Protocol (IGMP) or is broadcast using a wavelength division multiplexing method using a separate wavelength from a data communication signal.  
         [0033]     Multicasting may cause inconvenience to users due to a channel change delay. The broadcasting method using the wavelength division multiplexing method additionally requires a high-priced optical receiver and a high-priced optical amplifier for only a broadcast signal and thus increases cost for constituting the existing TDMA PON system.  
         [0034]      FIG. 2  is a view illustrating a configuration of a TDMA PON OLT system for providing a broadcast service such as an IPTV according to an embodiment of the present invention The TDMA PON OLT system according to the present embodiment includes a packet processor  201 , a switch  202 , TDMA PON MAC processors  203  and  205 , and optical transceivers  204  and  206 . In the TDMA PON OLT system, a means of transmission is classified into downstream transmission from an OLT to an ONT and a upstream transmission from the ONT to the OLT.  
         [0035]     The packet processor  201  of an OLT  200  processes levels L 3  through L 7  of data received from ONTs  220  through  230  or from an external node in a downstream direction, generates an internal frame including information about a destination TDMA PON port and frame identifications, and transmit the internal frame to the switch  202 .  
         [0036]     The packet processor  201  recovers frames from data received from a maximum number, M, of TDMA PON MAC processors  203  and  205  in a upstream direction and transmits the frames to an Uplink or a TDMA PON port according to address information of a packet header or an Ethernet header.  
         [0037]     The switch  202  of the OLT  200  is connected to the maximum number, M, of TDMA PON MAC processors, receives a frame having a bandwidth with a maximum amount, A, of traffic from the packet processor  201  in a downstream direction, classifies the frame into broadcast, multicast, and unicast frames, copies and transmits the broadcast frame to all of the m TDMA PON MAC processors, transmits the unicast frame to a destination TDMA PON MAC processor, and copies and transmits the multicast frame to TDMA PON MAC processors designated as destinations.  
         [0038]     The switch  202  multiplexes the frames received from the maximum number, m, of TDMA PON MAC processors in the upstream direction and transmits the multiplexed frames to the packet processor  201  having a maximum packet processing performance A.  
         [0039]     Here, M denotes the number of TDMA PON MAC processors that may be connected to a packet processor through a switch and is determined by a user by measuring upstream traffic received from the TDMA PON MAC processors. If the user does not allow any frames to be lost or corrupted, transmission speeds of upstream data of M TDMA PON MAC processors may be measured so that the largest transmission speed is divided by a maximum link speed (A) in a downstream direction so as to determine a value resulting from the division as M.  
         [0040]     However, if the user allows some low level frames to be lost, data transmission speeds may be lowered. Thus, the value of m may be increased so as to connect many more TDMA PON MAC processors to the packet processor  201 .  
         [0041]     The TDMA PON MAC processors  203  and  205  receive frames from the switch  202  in a downstream direction, process MAC functions for TDMA PON downstream signals, and transmit the frames to the optical transceivers  204  and  206 .  
         [0042]     The TDMA PON MAC processors  203  and  205  receive signals from the optical transceivers  204  and  206  in a upstream direction, process MAC functions for TDMA PON upstream signals, and transmit the signals to the switch  202 .  
         [0043]     The optical transceivers  204  and  206  of the OLT  200  receive frames from the TDMA PON MAC processors  203  and  204  in a downstream direction, convert electric signals into optical signals having speeds of A/n, and transmit the optical signals to a splitter  240 . Here, n denotes a ratio of a downstream link speed to a upstream link speed.  
         [0044]     Since an EPON has a 1 G speed in a downstream direction and a 1 G speed in a upstream direction, n=1. In the case of a GPON having a 2.5 G speed in a downstream direction and a 1.25 G speed in a upstream direction, n=2. Power to a number, k, of branches of a splitter must be appropriately adjusted during a conversion into an optical signal.  
         [0045]     The optical transceivers  204  and  206  of the OLT  200  extract data from optical signals transmitted in a burst mode in a upstream direction and transmit the extracted data to the TDMA PON MAC processors  203  and  205 . The TDMA PON MAC processors  203  and  205  process frames according to standard recommendations and transmit the processed frames to the switch  202 .  
         [0046]     The splitter  240  splits an optical signal having a transmission speed A in a downstream direction and transmits the split optical signals to the ONTs  220  through  230 . k denotes the number of branches of the splitter  240 . The splitter  240  multiplexes optical signals received from the ONTs  220  through  230  in a upstream direction and transmits the multiplexed optical signals to the optical transceivers  204  and  206  of the OLT  200 .  
         [0047]     The ONTs  220  through  230  respectively include optical transceivers  221  and  231 , TDMA PON MAC processors  222  and  232 , and bridges  223  and  233 . The optical transceivers  221  and  231  convert optical signals into electric signals and transmit the electric signals to the TDMA PON MAC processors  222  and  232 .  
         [0048]     The optical transceivers  204  and  206  convert electric signals into optical signals in a upstream direction, transmit the optical signals only when a transmission of frames is allowed, and intercepts the optical signals, so as to prevent signal interference among the ONTs  220  through  230 .  
         [0049]     The TDMA PON MAC processors  222  and  232  recover TDMA PON frames received from the OLT  200  in a downstream direction, convert only TDMA PON frames transmitted the TDMA PON MAC processors  222  and  232  into Ethernet frames, and transmit the Ethernet frames to the bridges  223  and  233 . The TDMA PON MAC processors  222  and  232  convert the Ethernet frames into TDMA PON frames and transmit the TDMA PON frames to the optical transceivers  221  and  231  only when the OLT  200  allows frames to be transmitted thereto.  
         [0050]     The bridges  223  and  233  process frames in a downstream direction and transmit the frames to destination subscriber devices according to a destination address of an Ethernet header. The bridges  223  and  233  transmit frames received from the destination subscriber devices, i.e., the frames to be transmitted to the OLT  200 , to the TDMA PON MAC processors  222  and  232 .  
         [0051]     As described above, in a TDMA PON OLT system according to the present invention, a broadcast service such as an IPTV can be efficiently broadcast using a TDMA PON-based FTTH network.  
         [0052]     Thus, a time delay of zapping caused by providing a broadcast service such as an IPTV in an existing TDMA PON OLT system can be reduced.  
         [0053]     Also, upstream and downstream transmission speeds can be asymmetrically set in the TDMA PON-based FTTH network. Thus, a maximum number of subscribers can be accommodated. As a result, network resources can be efficiently used so as to efficiently and economically provide the IPTV service in the TDMA PON-based FTTH network.  
         [0054]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.