Abstract:
A method for enhancing transmission efficiency of burst data by estimating a void between burst data and filling the void with new burst data in an optical burst switching (OBS) network. To this end, a node in the OBS network receives burst data (BD) aggregated from data packets, and a burst control packet (BCP) that is received prior to the BD by an offset time. The BCP contains information relating to the offset time and the BD. To predict the void between the BDs, a void filling time is defined within the offset time using the BCP. The present invention provides the method for determining whether to fill the void and filling the void by directly monitoring the BD over a preset time.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit under 35 U.S.C. § 119 (a) from Korean Patent Application No. 2004-112977 filed on Dec. 27, 2004 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method for transmitting optical burst data by inserting new burst data into a void between the optical burst data on a channel so as to reduce errors of the optical burst data and improve availability of the channel over an optical burst switching (OBS) network.  
         [0004]     2. Description of the Related Art  
         [0005]     Over optical burst switching (OBS) networks, typically, IP packets coming into an optical domain are aggregated to burst data at an edge node, and such burst data is routed to their destination nodes via a core node according to their destinations or quality of service (QoS). A burst control packet (BCP) and a payload (burst data:BD) are separated by an offset time and transmitted on different channels. In more detail, the BCP precedes the burst data by the offset time to reserve in advance a path for the transmission of the burst data. Accordingly, the burst data can be transmitted over the optical network without buffering. Hereafter, the transmission of the optical data is explained in reference to  FIG. 1 .  
         [0006]      FIG. 1  illustrates nodes that transmit and receive or switch the burst data over the OBS network, which is described in detail.  
         [0007]     As for incoming IP packets, the node A  100 , which is an edge node, generates burst data by aggregating the IP packets. Edge nodes  100 ,  106 , and  108  serve to generate and transmit optical burst data packets by aggregating IP packets, or receive the optical burst data packets and divides them into IP packets. Core nodes  102  and  104  are responsible to optically switch the optical burst data. Upon generating the burst data in a desired size, the node A  100  generates and transmits a burst control packet (BCP) to the node B  102  which is the core node. After the offset time, the node A  100  transmits the burst data to the node B  102 . The BCP contains information relating to a destination address and a source address of the burst data, a size of the burst data, and the offset time.  
         [0008]     The node B  102  checks the destination address of the burst data to be received from the received BCP, determines an optical path, and reserves a time for the optical switching. While the BCP is converted optic-electronically or electro-optically at the node B  102 , the burst data follows the optical path only by the optical switching, without the optic-electronic conversion. The node B  102  can optically switch the burst data to the node D  106  or the node C  104  depending on whether the destination of the burst data provided from the node A  100  is either the node D  106  or the node E  108 .  
         [0009]     It has been described that the node B  102  relays the burst data from the node A  100  to either the node D  106  or the node E  108 . Meanwhile, the node B  102  may be the destination of the burst data originated from the node A  100  or may generate burst data to be transmitted to the node D  106  or the node E  108 . In other words, the node B  102  being the core node can function as the edge node. In this case, a method is demanded for the node B  102  to relay the burst data received from the node A  100  to the node D  106  or the node E  108  on one channel by inserting its generated burst data between the received burst data so as to save resources.  
         [0010]      FIG. 2  illustrates transmission of the BCP and the burst data over a conventional OBS network. Descriptions are provided of a problem occurring when the void between burst data is filled with other burst data on a conventional channel in reference to  FIG. 2 .  
         [0011]     Referring to  FIG. 2 , the BCP is transmitted and received on a channel λ BCP , and the burst data BD is transmitted and received on a channel λ BD . As mentioned earlier, the BCP contains information relating to the offset time and the BD size. The offset time is a temporal difference between the receiving time point of the BCP and the receiving time point of the BD.  
         [0012]     In  FIG. 2 , the offset time between the BCP 1  and the BD 1  is T_offset 1 , and the offset time between the BCP 2  and the BD 2  is T_offset 2 . The channel λ BD  is not filled with the burst data all the time, but a non-transmission time period without data signals is present between the burst data, which is called a void time T_void.  
         [0013]     A node performs the optic-electronic conversion and electrical processing to the received BCPs. As for the BDs, the node conducts switching or add/drop function. The node may have data ready to be transmitted on the same channel as the channel of the BD 1  and the BD 2 . In  FIG. 2 , it is exemplified that the node transmits the BD 3  on the same channel as the BD 1  and the BD 2 . The node serves as the core node with respect to the BD 1  and the BD 2 . Yet, the node serves as the edge node for the BD 3 . When the BCP 3  and the BD 3 , which are locally generated without the offset time, are transmitted from the node, the BCP 3  precedes the BD 3  by the offset time T_offset 3 . In case that the BCP 3  and the BD 3  are transmitted from another node, rather than generated locally, the BCP 3  and the BD 3  are received at the node with the offset time defined from the very first.  
         [0014]     However, a general node in the OBS network cannot learn the size of the time interval T_void betwen the BD 1  and the BD 2  until the BCP 2  is input. In this regard, when T_void is longer than the BD 3  regardless of the input of the BCP 2 , a method is demanded to fill the time interval between the BCP 1  and the BD 1  with the BCP 3  and the BD 3 , respectively, without collisions with other BDs.  
       SUMMARY OF THE INVENTION  
       [0015]     The present invention has been provided to solve the above-mentioned and other problems and disadvantages occurring in the conventional arrangement, and an aspect of the present invention provides a method for enhancing a transmission efficiency of burst data by predicting T_void between the burst data and filling the void between the burst data with new burst data in an optical burst switching or optical burst add/drop network.  
         [0016]     Another aspect of the present invention provides a method for filling voids between burst data with new burst data without incurring collisions by predicting T_void between the burst data in an optical burst switching or optical burst add/drop network.  
         [0017]     To achieve the above aspects and/or features of the present invention, a method for transmitting a burst control packet (BCP) that contains time offset information of burst data (BD) to be received by a node in an optical burst switching (OBS) network, and transmitting the BD that is received at an interval of the offset time from the BCP, includes predefining a void filling time within the offset time, the void filling time to be filled with new BD; determining whether second BCP is received within the void filling time based on received first BCP; inserting third BD to be transmitted when the second BCP is not received within the void filling time; and transmitting the first BD by delaying the first BD as long as the void filling time.  
         [0018]     In accordance with the above aspects of the present invention, a method for transmitting a burst control packet (BCP) that contains time offset information of burst data (BD) to be received by a node in an optical burst switching (OBS) network, and transmitting the BD that is received at an interval of the offset time from the BCP, includes checking whether second BD is received within a predefined void filling time after the reception of the first BD; and transmitting third BD after the first BD in succession. The third BD is transmitted with a predefined offset time maintained from third BCP corresponding to the third BD.  
         [0019]     Additional and/or other aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0020]     These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawing figures of which:  
         [0021]      FIG. 1  illustrates an optical burst switching (OBS) network constructed with a plurality of nodes;  
         [0022]      FIG. 2  illustrates insertion and transmission of burst data at a core node in a conventional OBS network;  
         [0023]      FIGS. 3A through 3C  illustrate insertion and transmission of burst data at core node of an OBS network according to a first embodiment of the present invention;  
         [0024]      FIG. 4  is a flowchart outlining the insertion and transmission of the burst data at the core node in the OBS network according to the first embodiment of the present invention;  
         [0025]      FIG. 5  illustrates insertion and transmission of burst data at core node of an OBS network according to a second embodiment of the present invention;  
         [0026]      FIG. 6  is a flowchart outlining the insertion and transmission of the burst data at the core node in the OBS network according to the second embodiment of the present invention 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0027]     Reference will now be made in detail to the exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.  
         [0028]     Hereinafter, descriptions are made in reference to attached drawings on a method for filling voids between burst data (BD) with new BD in an optical network according to embodiments of the present invention.  
       First Embodiment  
       [0029]     According to a first exemplary embodiment of the present invention, a void filling method using a offset time is suggested, which is now set forth in detail in reference to  FIGS. 3A-3C  and  FIG. 4 .  
         [0030]     According to the first embodiment of the present invention, a void filling time is defined as a threshold within an offset time. The offset time includes the void filling time in addition to its primary time required to process a burst control packet (BCP) received at a destination node. The offset time can be calculated from Equation 1. 
 
new offset time=void filling time+processing time+extra time  [Equation 1]
 
         [0031]     The void filling time is a time required to fill T_void with new burst data. The void filling time needs to be longer than a maximum time period of the burst data to fill with. When minimum and maximum sizes of the burst data are determined in an optical network, the void filling time is set to be longer than the maximum burst data size so as to fill voids between burst data with new burst data without incurring collisions. In other words, to fill the voids between the burst data with the new burst data, the void T_void between the burst data has to be longer than the void filling time and the void filling time has to be longer than the size of the new burst data.  
         [0032]     The first embodiment of the present invention is described in reference to  FIGS. 3A-3C .  FIG. 3A  illustrates BCPs and BDs transmitted to a node,  FIG. 3B  illustrates processing of the BCPs and the BDs received at the node, and  FIG. 3C  illustrates BCPs and BDs output from the node.  
         [0033]     Referring first to  FIG. 3A , the node receives the BCP 1  and the BCP 2  on a channel λ BCP , and receives the BD 1  and the BD 2  on a channel λ BD . The BCP 1  and the BD 1  have an offset time T_offset 1  therebetween, and the BCP 2  and the BD 2  have an offset time T_offset 2  therebetween. The BD 1  and the BD 2  are transmitted to the node with T_void maintained. However, as set forth earlier, the node cannot estimate T_void until receiving the BCP 2 .  
         [0034]     Referring to  FIG. 3B , after waiting for the void filling time ‘T_void filling’, the node receives BCP 1 . Since the void filling time is included in the offset time, the offset time between the BCP 1  and the BD 1  reduces.  
         [0035]     A determination is made on whether a new BCP is received within the void filling time. As aforementioned, it is required that the void filling time be longer than the maximum size of the burst data to fill with so as to insert the burst data even with the maximum size. In case that the burst data is inserted when a new BCP, that is, BCP 2  is received within the void filling time, blocking (collision) occurs. In this situation, the node cannot transmit its new burst data on the channel λ BD . Conversely, when a new BCP is not received within the void filling time, the node can transmit its new burst data on the channel λ BD . In  FIG. 3B , as a new BCP is not received after the BCP 1  receiving time point and the void filling time, the node determines to transmit the BD 3  on the channel λ BD . The determination to insert the BD 3  on the channel λ BD  can be made after the elapse of the void filling time, but the reservation of the BD 3  is conducted substantially after the BD 1 . The reservation of the BCP 3  is made in advance by a time calculated by subtracting the void filling time from the offset time.  
         [0036]      FIG. 3C  exemplifies that the node outputs the BD 3  on the channel λ BD  in addition to the BD 1  and the BD 2 . As shown in  FIG. 3C , the offset time is recovered to an original offset time before inputting to the node. The recovery of the offset time can be achieved by delaying the BD as long as the void filling time when the BD departs the node. In  FIG. 3C , it can be seen that the offset time between BCP 1  and the BD 1  recovers its original offset time before inputting to the node as T_offset 1 , and that the offset time between the BCP 3  and the BD 3  is transmitted as T_offset 3 .  
         [0037]     It has been exemplified that the new BD is generated and reserved together with the new BCP when the new BD is inserted. It should be appreciated that appropriate time can be reserved for the new BD and the new BCP in the same manner as set forth above even when the new BD and the new BCP are input with the offset time defined.  
         [0038]      FIG. 4  illustrates an operation of the node according to the first embodiment of the present invention, to be explained.  
         [0039]     The node receives the BCP 1  (S 400 ). The BCP 1  waits for a predefined void filling time (S 402 ).  
         [0040]     The node checks whether another BCP (BCP 2 ) is received within the void filling time after the receiving time point of the BCP 1  (S 404 ).  
         [0041]     When another BCP (BCP 2 ) is received within the void filling time, the node proceeds to operation S 406 . Otherwise, the node proceeds to operation S 408 .  
         [0042]     If BCP 2  is received within the void filling time, the node cannot add the new BD 3  and the new BCP 3  (S 406 ), but only transmits the received BCP  1 , BCP 2 , BD 1 , and BD 2 .  
         [0043]     When BCP 2  is not received within the void filling time, the node can insert the BD 3  after the BD 1  (S 408 ). In addition, the node can insert the BCP 3  after the BCP 1 . That is, the node makes reservations in order of the BD 1  and the BD 3 . Note that the BCP 1  and the BCP 3  precede their corresponding BDs by the offset time from which the void filling time is subtracted.  
         [0044]     The node sends the BCPs and the BDs by restoring their offset times to the original offset times before inputting the node (S 410 ). This can be achieved by delaying the offset times as long as the void filling time by use of an optical delay line (ODL) or an optical delay buffer with respect to the channel λ BD .  
       Second Embodiment  
       [0045]     According to a second embodiment of the present invention, the void is filled with the received BDs, rather than with the offset time and the BCPs as in the first embodiment of the present invention. Herebelow, the second embodiment of the present invention is described in detail in reference to  FIG. 5  and  FIG. 6 .  
         [0046]      FIG. 5  depicts BCPs and BDs transmitted and received at a node according to the second embodiment of the present invention. The node receives the BCPs on a channel λ BCP , and receives the BDs on a channel λ BD . As set forth above, the BCP contains information pertaining to the offset time between the BCP and the BD, and the BD size. As shown in  FIG. 5 , the node receives BCP 1  and BCP 2  on the channel λ BCP , and receives BD 1  and BD 2  on the channel λ BD . The offset time between the BCP 1  and the BD 1  is T_offset 1 , and the offset time between the BCP 2  and the BD 2  is T_offset 2 .  
         [0047]     It has been explained that the channel λ BD  does not carry the BD all the time, but is divided into a transmission time period in which the BD is delivered and a non-transmission time period in which the BD is not delivered. In  FIG. 5 , the non-transmission time period is the interval between the transmission time period of the BD 1  and the transmission time period of the BD 2 , and represented as T_void.  
         [0048]     Referring to  FIG. 5 , a BD detector  500  of the node determines whether the BD is received on the channel λ BD . A first buffer  502  delays the received BD for filling a new BD when the BD detector  500  detects the received BD. In specific, the BD detector  500  monitors whether next BD is received within a void filling time which is predefined from the end point of the BD. If the next BD is not received, it is feasible to insert new BD after the existing BD. If the next BD is received, the node cannot insert new BD after the existing BD. Thus, the first buffer  502  is an optical delay element corresponding to the void filling time and needs to be greater than the maximum BD size, similarly to the first embodiment of the present invention.  
         [0049]     A switching element  504  switches or add/drops the transmitted BDs according to their destinations. In specific, when the node is not the destination of the BD, the switching element  504  switches the BD. When the node is the destination of the BD, the switching element  504  performs the drop function. Additionally, the switching element  504  performs the add function to insert new BD.  
         [0050]     A second buffer  506  is an optical delay of the BD for providing the offset time between the BCP and the BD even when the BCP and the BC are received at the same time.  
         [0051]      FIG. 5  illustrates a case when the BD 2  is not received within the void filling time. Hence, the node transmits the BD 3  using the interval between the BD 1  and the BD 2 . When the BCP 3  and the BD 3  are output from the node, T_offset 3  is defined between the BCP 3  and the BD 3  by means of the second buffer  506 .  
         [0052]      FIG. 6  is a flowchart outlining the operation of the node according to the second embodiment of the present invention, to be explained below.  
         [0053]     The node receives the BD 1  (S 600 ). The BD detector monitors whether next BD is received within the void filling time that is predefined from the end point of the BD 1 , and the BD 1  is delayed at the first buffer (S 602 ).  
         [0054]     The BD detector checks whether another BD (BD 2 ) is received within the void filling time after the end point of the BD 1  (S 604 ).  
         [0055]     When another BD (BD 2 ) is received within the void filling time, the node proceeds to operation S 606 . When another BD (BD 2 ) is not received within the void filling time, the node proceeds to operation S 608 .  
         [0056]     If BD 2  is received within the void filling time, the node cannot insert the new BD 3  and the new BCP 3  but transmits only the received BCP 1 , BCP 2 , BD 1 , and BD 2  (S 606 ).  
         [0057]     If BD 2  is not received within the void filling time, the node inserts the BD 3  after the BD 1  and the BCP 3  after the BCP 1  (S 608 ). That is, the node makes reservations in order of the BD 1  and the BD 3 .  
         [0058]     As transmitting the BCPs and the BDs, the node recovers the original offset times that are defined before inputting to the node (S 610 ). This can be achieved by delaying as long as the offset time on the channel λ BD  by means of an optical delay line or the second buffer.  
         [0059]     In light of the foregoing as set forth above, the transmission efficiency can be improved because the node fills the non-transmission period between the BDs with the new BD in the optical communication network. Furthermore, the estimation of the non-transmission period between the BDs can avoid the collisions that may occur when the new BDs are inserted.  
         [0060]     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.