Abstract:
A method and a system for entering data in a data processing system is provided. In this case, the data is entered in a number of steps, with a view being displayed at a step in a display region of a display means, with the entering and/or display taking place in subsequent steps at least partially as a function of the data entered in one or a number of preceding steps. To design the step-by-step entering of data in a more user friendly manner, it is proposed to simultaneously display the views of a number of consecutive steps in the display region.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority of European application No. 05001568.4 EP filed Jan. 26, 2005, which is incorporated by reference herein in its entirety.  
       FIELD OF INVENTION  
       [0002]     This invention relates to a method and apparatus for transmitting an optical signal in an optical burst switching network using arrival time.  
       BACKGROUND OF INVENTION  
       [0003]     The amount of raw bandwidth available on fiber optic links has increased dramatically with advances in dense wavelength division multiplexing (DWDM). In order to efficiently utilize this bandwidth in a cost-effective manner for IP traffic, an appropriate all-optical transport method must be developed. This transport method must be able to handle asynchronous bursty traffic by quickly provisioning resources while also minimizing the use of optical buffering.  
         [0004]     Optical burst switching (OBS) is one such method for transporting traffic directly over a bufferless optical core network. In an optical burst switched network, bursts of data consisting of multiple packets are switched through the network all-optically.  
         [0005]     The idea underlying OBS technology is to decouple the data path from the control path. In particular, IP packets are aggregated into much larger bursts before transmission through the network. This allows amortization for the switching overhead across many packets. A control message (or header) is transmitted ahead of the burst in order to configure the switches along the burst&#39;s route. The data burst follows the header after some offset time without waiting for an acknowledgment for the connection establishment. An offset time allows for the header to be processed at each node while the burst is buffered electronically at the source. Thus, no fiber delay lines are necessary at the intermediate nodes to delay the burst while the header is being processed.  
         [0006]     A key measure of performance in optical networks, particularly dynamic wavelength routed optical networks, is the blocking probability, or the probability that an incoming connection request will be denied. An appreciation of the problem of blocking in an OBS network will be appreciated from the article from M. Neuts, H. L. Vu and M. Zukerman, “Performance analysis of optical composite burst switching”,  IEEE Communications Letters,  Vol. X, NO. Y, Month 2002.  
         [0007]     Another concern in optical burst switched networks is contention, which occurs when multiple bursts contend for the same link. Contention in an optical burst switched network is particularly aggravated by the variable burst sizes and the long burst durations. Furthermore, since bursts are switched in a cut-through mode rather than a store-and-forward mode, optical burst-switched networks generally have limited buffering capabilities. A better appreciation of the problems of contention will be attained from the article from V. M. Vokkarane and J. P. Jue, “Burst segmentation: an approach for reducing packet loss in optical burst-switched networks”,  IEEE ICC &#39; 02, April 2002.  
         [0008]     There have been several proposed reservation protocols in OBS networks, such as Horizon, JIT (Just-In-Time) and JET (Just-Enough-Time) that are supposed to reduce the blocking probability and address the problem of contention. Until now, JET has been the most favored since it seems to provide the best performance, in terms of blocking probability, of the three protocols. However, as we shall see, even the JET protocol could be improved. For completeness, the various protocols shall be described and analyzed in turn.  
         [0009]     The Just-in-time (JIT) Reservation Protocol  100  will be described with reference to  FIG. 1 . There is shown in the figure, various data paths  102 , or channels, upon which the data bursts  104  and header information  106  are transmitted. In JIT, as the name implies, just as each header arrives, a bandwidth is immediately allocated. This is shown in the figure, wherein a header  108  arrives at a node (not shown) and the node immediately allocates the bandwidth  110  for a data burst  112 . A terminating block  114 , known as an inband terminator (IBT) packet, signals the end of the bandwidth to the node. The wavelength channel remains allocated until burst transmission has finished.  
         [0010]     In the case of contention, it is shown in the figure that a request from another header, for example a second burst header  116  corresponding to a second burst  118 , is received by the same node. However, the second burst header comes after the first burst header  108 . In this case, the node is already allocated to the first burst  112  and, as a result, is rejected by the node. In this case, the second burst is discarded. In addition, a third burst header  120  is shown sent to the node after the first burst but before the end of the first burst bandwidth. In this case as well, the corresponding third burst  122  is rejected.  
         [0011]     While JIT is considered to be advantageous for it&#39;s light weight approach, namely the low complexity required from both edge and core nodes, the disadvantages of this system are apparent from the above example. In the JIT case, it is apparent that there is no contention resolution. Thus, any second burst  118 , is blocked regardless of the importance of the second block. In addition, the JIT system takes up more bandwidth than is necessary to transmit the burst. This is shown in the figure, where the first burst is completed, yet the bandwidth continues to be reserved. It shall be noted that, even though the third burst actually comes after the first bandwidth, the third burst is still blocked. In other words, losses occur even in cases where there is no transmission conflict between different bursts.  
         [0012]     The reason for these deficiencies is that the only information that has to be kept record of in the network nodes in the JIT protocol is whether a wavelength channel is currently available or not. Thus, JIT is a completely “dumb” protocol that cannot correct for the problem of blocking bursts that are not actually in conflict. Nor has JIT any means of providing for contention cases.  
         [0013]     An improvement to schemes like JIT can be achieved by using a reserve limited duration (RLD) scheme such as that used by the Horizon Reservation Protocol  200  that is discussed here with reference to  FIG. 2 . Protocols based on RLD require the sender to signal the burst length in the control packet. A wavelength channel  202  that transmits bursts  204  and corresponding headers  206  is only allocated for a limited duration. Thus, subsequent burst transmission requests with a start time greater then the finishing time of an allocated burst may be accepted.  
         [0014]     This is seen here where a first header  208  is received by a node (not shown) and the node, in response, reserves the bandwidth  210  for the first data burst  212 . As in the normal case, when the node receives a header  216  corresponding to a second data burst  218 , the node rejects that burst. In contrast to the JIT case, the end is known with RLD and hence a new header  220  of a third data burst  222  can be accepted. In other words, the basic offset interval of a burst may overlap the transmission phase of a previously accepted burst. In the JIT case, the burst number  3  is lost because at the instant when the control packet arrives, the end of the previous (accepted) burst is unknown.  
         [0015]     However, despite the advantage that Horizon reduces the blocking probability of bursts in comparison to JIT, Horizon Control packets are larger than in JIT and the system grows exponentially in complexity.  
         [0016]     Higher efficiency can be achieved if start times of burst transmissions are also considered for reservation. In other words, reservation does not begin immediately when a request arrives but is delayed by the basic offset. This approach is called reserve fixed duration (RFD), as the channel is allocated for a fixed duration corresponding to the burst transmission time.  
         [0017]     One proposal of an RFD-based reservation protocol is JET. State information in JET comprises both, the starting and finishing times of all accepted bursts. However, this makes the system rather complex. On the other hand in contrast to Horizon, JET is able to detect situations where no transmission conflict occurs although the start time of a new burst is earlier than the finishing time of the already accepted burst.  
         [0018]     In the JET scheme  300  shown in  FIG. 3 , channels  302  transmit bursts  304  that have corresponding headers  306 . In this case, however, the bandwidth is independent from its header, so the burst can begin at any time. According to  FIG. 3 , when the control packet  308  arrives at a core cross-connect (or switch), capacity is reserved in the cross-connect for the burst  310  with the delay of offset time. If capacity can be reserved, the arriving burst is then switched transparently through the cross-connect.  
         [0019]     However, if the requested bandwidth is not available for the time indicated in the header, the burst is blocked and dropped. In addition, and although JET reduces the blocking probability of bursts in comparison to Horizon (and JIT), control packets are bigger than in Horizon (and JIT) and the system grows in complexity.  
         [0020]     Despite its complexity, however, JET has been generally accepted as the most promising reservation protocol in OBS networks, since it leads to the lowest blocking probability of the three protocols. This is indicative of the importance that the industry places on reducing the blocking probability in OBS networks. However, even with JET this blocking probability is unacceptably high.  
         [0021]     The problem remaining to be solved, and the challenge therein, is to define a new reservation protocol which performs even better than JET and that at the same time is simpler and easier to implement.  
       SUMMARY OF INVENTION  
       [0022]     In accomplishing this goal, the present invention takes into account at least three metrics to measure the reduced blocking probability.  
         [0023]     First, the present invention takes into account the traffic characteristics of the proposed solution in order to choose an aggregation strategy that generates traffic with special statistical properties that reduce the blocking probability. Next, the invention strives to achieve a satisfactory degree of deflection routing, that is to re-route a blocked burst through another port of an optical switch whenever the destination port is busy. In addition, the invention aims to optimize burst segmentation, that is, to lose only the IP packets of which transmission was overlapped with the transmission of another burst and to save the rest of the IP packets of the blocked burst.  
         [0024]     The invention is the proposal of a new reservation protocol, herein referred to as JAT (Just the Arrival Time), which is simpler than the best protocol of the state-of-the-art (JET) and that, at the same time, performs better in terms of blocking probability.  
         [0025]     In accordance with the objectives of the present invention, there is provided a method for transmitting an optical signal in an optical burst switching network having a data burst signal and a control signal representing the optical signal. A header packet of the control is generated signal having information indicating an arrival time of the data burst signal and no information regarding a burst size of the data burst signal and the control signal with the header packet generated is transmitted through the optical burst switching network.  
         [0026]     The invention can be used in order to build more efficient and yet cheaper and less complex OBS networks. In particular, the new concept changes OBS nodes&#39; hardware and software, OBS&#39; control plane and OBS&#39; header packet format. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The figures illustrate at least one example of the invention wherein reference numerals designate like elements.  
         [0028]      FIG. 1  illustrates a prior art protocol,  
         [0029]      FIG. 2  illustrates a prior art protocol,  
         [0030]      FIG. 3  illustrates a prior art protocol,  
         [0031]      FIG. 4  illustrates a control packet structure of the prior art protocol in  FIG. 3 ,  
         [0032]      FIG. 5   a  illustrates a control packet structure of the present invention,  
         [0033]      FIG. 5   b  is a table illustrating the differences between the present invention an prior protocols,  
         [0034]      FIG. 6   a  is an exemplary apparatus of the present invention, and  
         [0035]      FIG. 6   b  illustrates an operation of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]     The present invention proposes a new protocol for transmitting an optical signal according to an optical burst switching scheme that aims to be efficient at transmitting optical signals, yet has a lower blocking probability than JET. In addition, a protocol is provided that implements an improved contention policy than heretofore provided. To that end, there is proposed a “Just the Arrival Time” protocol.  
         [0037]     A better appreciation of the new JAT protocol can be seen by observing the control packet structure  400  in JET  FIG. 4 . The known structure includes a control packet that is headed by guard time blocks  404  and a sync block  406 . The control packet itself  402  is comprised of a label  408 , a wavelength ID  410 , a class of service (CoS) field  412 , an Offset time  414 , a burst size field  416  and a cyclic redundancy code (CRC) field  418 .  
         [0038]     In particular, it shall be noticed that the burst size field  416 , that is shown here as an 8 bit field, is present in the JET protocol. JET uses the burst size field to carry information regarding the burst size.  
         [0039]     On the other hand,  FIG. 5   a  provides a counter solution to the JET header packet format. For the new JAT reservation protocol, there shall be no burst size information. Specifically,  FIG. 5   a  illustrates the control packet structure  500  in the newly-proposed JAT protocol.  
         [0040]     As in JET, JAT comprises a control packet  502  bounded by guard blocks  504  and a sync block  506 . The guard time serves as a way of safely separating consecutive bursts. The sync field allows the receptor to synchronize the reception of the bits belonging to the burst.  
         [0041]     To continue, the label field  508  identifies the destination edge node. The wavelength ID field  510  contains the number of the wavelength on which the burst will be sent. The CoS  512  field stands for class of service and it may contain future QoS relevant information. The offset time field  514  contains the value of the offset time between header packet and burst. The CRC  516  field contains a cyclic redundancy code in order for other nodes to detect header packet transmission errors.  
         [0042]     As the name indicates, JAT sends just the arrival time. In contradistinction to JET, the JAT header packets have information regarding the arrival time of the burst, but not the burst size. In fact, as  FIG. 5   b  illustrates, none of the other reservation protocols, JIT  518 , Horizon  520  or JET  522  have this unique configuration. That is, only JAT  524  sends the arrival information of the burst but not the duration of the bandwidth reservation, i.e., the burst size.  
         [0043]     It will be appreciated that the JAT configuration leads to a simpler control plane than with JET since less information has to be processed and less state variables have to be manipulated. Indeed, only the burst arrival time is important.  
         [0044]     An exemplary apparatus  600  for transmitting such an optical data burst is shown in  FIG. 6   a.  There are two types of nodes shown here. The first are edge nodes  602  where traffic is collected from access networks  604  and assembled into larger data units, the so-called bursts. Core nodes  606  serve as transit nodes in the core network whose main task is switching the bursts without extensive processing. This is achieved according to present invention using the control information containing arrival times as will now be described with reference to the scheduling operation  608  of  FIG. 6   b.    
         [0045]     The JAT schema  610  will be described in reference to  FIG. 6   b.  A header packet  612 ( 614 ) is generated by an edge node. When a header packet  612  ( 614 ) is processed at a core node (not shown), a timer (not shown) with the value t offset −t switch  is started, where t offset    616  is the value contained in the offset time field of the header packet and t switch    618  is the switching time of the switching fabric used at the core node. When the timer is triggered the core node switches the corresponding ports according to the information contained in the header packet. In the exemplary case, this information is contained in the label and wavelength ID.  
         [0046]     With the foregoing set up, it is ensured that when the burst  1   620  arrives at the core node everything is prepared for a clean all-optical routing through it. If the core node is sending another burst, e.g., burst  2   622 , when the timer is triggered, only the tail of this burst is lost.  
         [0047]     On the other hand, JET needs both information regarding the burst arrival and duration times. In JET it is necessary to store for each wavelength of each output fiber of each core node, complex state information regarding the bandwidth reservation status. In particular, the core node has to know for each wavelength of each fiber at every time which bandwidth gaps are eventually available for future burst transmission requests. This “bandwidth reservation map” has to be updated each time a new header packet arrives at the node accordingly to its new reservation request. Depending on whether the bandwidth gap requested by the new header packet is busy or available, the control plane decides whether or not to block its associated burst.  
         [0048]     Consequently, JAT uses a much simpler method that requires with less information which allows simplifying the hardware and software of each core and edge node. This simplicity leads to cheaper OBS equipment. In particular, JAT needs neither to keep JET&#39;s “bandwidth reservation map” nor to check whether a new incoming burst fits or not in a free bandwidth gap. Indeed, in JAT it is only necessary to keep track of the arrival time of each burst. No checking for blocking is necessary since blocking naturally happens if the new burst arrives before the last burst has been completely sent. Consequently, in the basic functionality of JAT new bursts always win contention against older bursts. Of course, this would change if quality of service (QoS) is introduced.  
         [0049]     Considering again  FIG. 6   b,  the reservation contention case of JAT will now be discussed. When comparing bursts  1  and  2   620 ,  622 , since burst  2   622  arrives before burst  1   620  has finished, its transmission contention takes place in the overlapping region  624 . According to the proposed JAT protocol, only the bits of burst  1   620  in the overlapping region  624  are lost. These lost bits are shown here at  626 . In other words, with JAT at least some of the information of a block in contention is recoverable. By contrast, in JET (or JIT or Horizon, for that matter) the whole burst  2   622  is lost.  
         [0050]     In this sense, JAT in terms of blocking probability reduction could be considered a burst segmentation approach with a tail dropping policy. According to Vokkarane, cited above, an advantage of dropping the tail segments of bursts rather than the head segments is that there is a better chance of in-sequence delivery of packets at the destination, assuming that dropped packets are retransmitted at a later time. A head-dropping policy will result in a greater likelihood that packets will arrive at their destination out of order. From the Vokkarane article, it can be surmised that the new JAT proposal works as well, or better, than burst segmentation implemented on top of JET. A more in depth discussion of the burst segmentation approach, also called optical composite burst switching (OCBS), is described in Neuts.  
         [0051]     In conclusion, these and other studies show an important reduction in the blocking probability using OCBS. Given the complexity of OCBS, and further the complexity of adding OCBS on top of JET, it is clear that the much-simpler JAT protocol of the present invention is superior. The first implication of this is an important cost reduction for the whole OBS network. In particular, the control plane and the hardware of the edge and core nodes are simpler and faster.  
         [0052]     Thus, the instant invention presents a concept for a new reservation protocol for OBS networks that performs better than the state-of-the-art protocols and yet is less complex and therefore cheaper to implement. The invention realizes a reservation protocol manipulating only the burst arrival information, i.e., not the burst size. This leads to a lower blocking probability. In addition, the invention also encompasses a new definition of the details of a new protocol.