Method for void-filling and transmitting burst data over optical burst switching network

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.

CROSS-REFERENCE TO RELATED APPLICATIONS

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

1. Field of the Invention

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.

2. Description of the Related Art

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 toFIG. 1.

FIG. 1illustrates nodes that transmit and receive or switch the burst data over the OBS network, which is described in detail.

As for incoming IP packets, the node A100, which is an edge node, generates burst data by aggregating the IP packets. Edge nodes100,106, and108serve 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 nodes102and104are responsible to optically switch the optical burst data. Upon generating the burst data in a desired size, the node A100generates and transmits a burst control packet (BCP) to the node B102which is the core node. After the offset time, the node A100transmits the burst data to the node B102. 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.

The node B102checks 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 B102, the burst data follows the optical path only by the optical switching, without the optic-electronic conversion. The node B102can optically switch the burst data to the node D106or the node C104depending on whether the destination of the burst data provided from the node A100is either the node D106or the node E108.

It has been described that the node B102relays the burst data from the node A100to either the node D106or the node E108. Meanwhile, the node B102may be the destination of the burst data originated from the node A100or may generate burst data to be transmitted to the node D106or the node E108. In other words, the node B102being the core node can function as the edge node. In this case, a method is demanded for the node B102to relay the burst data received from the node A100to the node D106or the node E108on one channel by inserting its generated burst data between the received burst data so as to save resources.

FIG. 2illustrates 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 toFIG. 2.

Referring toFIG. 2, the BCP is transmitted and received on a channel λBCP, and the burst data BD is transmitted and received on a channel λBD. 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.

InFIG. 2, the offset time between the BCP1and the BD1is T_offset1, and the offset time between the BCP2and the BD2is T_offset2. The channel λBDis 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.

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 BD1and the BD2. InFIG. 2, it is exemplified that the node transmits the BD3on the same channel as the BD1and the BD2. The node serves as the core node with respect to the BD1and the BD2. Yet, the node serves as the edge node for the BD3. When the BCP3and the BD3, which are locally generated without the offset time, are transmitted from the node, the BCP3precedes the BD3by the offset time T_offset3. In case that the BCP3and the BD3are transmitted from another node, rather than generated locally, the BCP3and the BD3are received at the node with the offset time defined from the very first.

However, a general node in the OBS network cannot learn the size of the time interval T_void between the BD1and the BD2until the BCP2is input. In this regard, when T_void is longer than the BD3regardless of the input of the BCP2, a method is demanded to fill the time interval between the BCP1and the BD1with the BCP3and the BD3, respectively, without collisions with other BDs.

SUMMARY OF THE INVENTION

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.

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.

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.

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.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

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

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 toFIGS. 3A-3CandFIG. 4.

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]

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.

The first embodiment of the present invention is described in reference toFIGS. 3A-3C.FIG. 3Aillustrates BCPs and BDs transmitted to a node,FIG. 3Billustrates processing of the BCPs and the BDs received at the node, andFIG. 3Cillustrates BCPs and BDs output from the node.

Referring first toFIG. 3A, the node receives the BCP1and the BCP2on a channel λBCP, and receives the BD1and the BD2on a channel λBD. The BCP1and the BD1have an offset time T_offset1therebetween, and the BCP2and the BD2have an offset time T_offset2therebetween. The BD1and the BD2are transmitted to the node with T_void maintained. However, as set forth earlier, the node cannot estimate T_void until receiving the BCP2.

Referring toFIG. 3B, after waiting for the void filling time ‘T_void filling’, the node receives BCP1. Since the void filling time is included in the offset time, the offset time between the BCP1and the BD1reduces.

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, BCP2is received within the void filling time, blocking (collision) occurs. In this situation, the node cannot transmit its new burst data on the channel λBD. Conversely, when a new BCP is not received within the void filling time, the node can transmit its new burst data on the channel λBD. InFIG. 3B, as a new BCP is not received after the BCP1receiving time point and the void filling time, the node determines to transmit the BD3on the channel λBD. The determination to insert the BD3on the channel λBDcan be made after the elapse of the void filling time, but the reservation of the BD3is conducted substantially after the BD1. The reservation of the BCP3is made in advance by a time calculated by subtracting the void filling time from the offset time.

FIG. 3Cexemplifies that the node outputs the BD3on the channel λBDin addition to the BD1and the BD2. As shown inFIG. 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. InFIG. 3C, it can be seen that the offset time between BCP1and the BD1recovers its original offset time before inputting to the node as T_offset1, and that the offset time between the BCP3and the BD3is transmitted as T_offset3.

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.

FIG. 4illustrates an operation of the node according to the first embodiment of the present invention, to be explained.

The node receives the BCP1(S400). The BCP1waits for a predefined void filling time (S402).

The node checks whether another BCP (BCP2) is received within the void filling time after the receiving time point of the BCP1(S404).

When another BCP (BCP2) is received within the void filling time, the node proceeds to operation S406. Otherwise, the node proceeds to operation S408.

If BCP2is received within the void filling time, the node cannot add the new BD3and the new BCP3(S406), but only transmits the received BCP1, BCP2, BD1, and BD2.

When BCP2is not received within the void filling time, the node can insert the BD3after the BD1(S408). In addition, the node can insert the BCP3after the BCP1. That is, the node makes reservations in order of the BD1and the BD3. Note that the BCP1and the BCP3precede their corresponding BDs by the offset time from which the void filling time is subtracted.

The node sends the BCPs and the BDs by restoring their offset times to the original offset times before inputting the node (S410). 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 λBD.

Second Embodiment

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 toFIG. 5andFIG. 6.

FIG. 5depicts 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 λBCP, and receives the BDs on a channel λBD. 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 inFIG. 5, the node receives BCP1and BCP2on the channel λBCP, and receives BD1and BD2on the channel λBD. The offset time between the BCP1and the BD1is T_offset1, and the offset time between the BCP2and the BD2is T_offset2.

It has been explained that the channel λBDdoes 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. InFIG. 5, the non-transmission time period is the interval between the transmission time period of the BD1and the transmission time period of the BD2, and represented as T_void.

Referring toFIG. 5, a BD detector500of the node determines whether the BD is received on the channel λBD. A first buffer502delays the received BD for filling a new BD when the BD detector500detects the received BD. In specific, the BD detector500monitors 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 buffer502is 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.

A switching element504switches or add/drops the transmitted BDs according to their destinations. In specific, when the node is not the destination of the BD, the switching element504switches the BD. When the node is the destination of the BD, the switching element504performs the drop function. Additionally, the switching element504performs the add function to insert new BD.

A second buffer506is 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.

FIG. 5illustrates a case when the BD2is not received within the void filling time. Hence, the node transmits the BD3using the interval between the BD1and the BD2. When the BCP3and the BD3are output from the node, T_offset3is defined between the BCP3and the BD3by means of the second buffer506.

FIG. 6is a flowchart outlining the operation of the node according to the second embodiment of the present invention, to be explained below.

The node receives the BD1(S600). The BD detector monitors whether next BD is received within the void filling time that is predefined from the end point of the BD1, and the BD1is delayed at the first buffer (S602).

The BD detector checks whether another BD (BD2) is received within the void filling time after the end point of the BD1(S604).

When another BD (BD2) is received within the void filling time, the node proceeds to operation S606. When another BD (BD2) is not received within the void filling time, the node proceeds to operation S608.

If BD2is received within the void filling time, the node cannot insert the new BD3and the new BCP3but transmits only the received BCP1, BCP2, BD1, and BD2(S606).

If BD2is not received within the void filling time, the node inserts the BD3after the BD1and the BCP3after the BCP1(S608). That is, the node makes reservations in order of the BD1and the BD3.

As transmitting the BCPs and the BDs, the node recovers the original offset times that are defined before inputting to the node (S610). This can be achieved by delaying as long as the offset time on the channel λBDby means of an optical delay line or the second buffer.

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.