A METHOD AND A SYSTEM IN CONNECTION WITH CONTROLLING RESOURCES IN A COMMUNICATION NETWORK

Abstract: The present invention relates to a method and a system in connection with controlling allocation of resources in the form of write access to time slots of frames that are transferred on a shared medium between nodes in a time division multiplexed network, preferably a circuit switched network. According to the invention, resource levels are defined for one or more nodes in the network, each resource level (517, 527, 547) designating an amount of resources (518, 528, 548) allocated to a respective node that is permissible to be temporarily allocated to other nodes of said network.

Description: A METHOD AND A SYSTEM IN CONNECTION WITH CONTROLLING RESOURCES IN A COMMUNICATION NETWORK Technical field of the invention The present invention relates to a method and a system in connection with controlling allocation of resources in the form of write access to time slots of frames that are transferred on a shared medium between nodes in a time division multiplexed network, preferably a circuit switched network. Background art An example of a circuit switched time division multiplexed network of the kind mentioned above is the so called DTM network (DTM - Dynamic Synchronous Transfer Mode). DTM is a broadband network architecture (see e.g. Christer Bohm, Per Lindgren, Lars Ramfelt, and Peter Sjδdin, The DTM Gigabit Network, Journal of High Speed Networks, 3(2), 109-126, 1994, and Lars Gauffin, Lars Hakansson , and Bjδrn Pehrson, Multi-gigabit networking based on DTM, Computer Networks and ISDN Systems, 24(2), 119-139, April 1992) . The topology of a DTM network is based upon the use of unidirectional optical fibers each connecting multiple nodes, e.g. in a bus or a ring structure. The DTM medium access protocol is a time division multi- plexing scheme. The bandwidth of each wavelength is divided into 125 μs frames, which in turn are divided into 64-bit time slots. Write access to such slots is governed by allocation of slots to different nodes. A node may write data into a specific slot, i.e. into a specific time slot position within each frame, only if the node has write access to this specific slot position, i.e. if the slot is allocated to the node. The slot access protocol guarantees the slot access to be conflict free, which means that several nodes do not write data into the same slot. In a system of this kind, a first node may have write access to a first set of slots within a frame and a second node may have write access to a second set of slots within said frame. Then, the first node is said to be the owner of the first set of slots and the second node is said to be the owner of the second set of slots. However, if the first node at some time require more transferring capacity, it may temporarily borrow slots from another node, for example the second node, presently having a surplus of slots. In such a case, one or more slots owned by the second node may be temporarily allo- cated to, i.e. borrowed by, the first node, the first node then temporarily borrowing the write access thereto. After use, said one or more borrowed slots are returned to their owner, i.e. to the second node. The published patent application WO, 97/36402, filed by the assignee of the present invention, discloses such a time multiplexed network in which time slots allocated to a primary home node may be temporarily allocated to a temporary home node. In a network designed for enabling temporary allo- cation of time slots from a node to other nodes, the temporary allocation is typically performed automatically by the network, i.e. without operator interaction, based on decisions within the network taking the current operational status into consideration. Such operational status is typically used bandwidth and bandwidth demands of the different nodes in the network. This ability of the network to temporarily allocate time slots from a node to other nodes based upon automated decisions gives the network a dynamical behaviour, which behaviour is governed by the control software and control logic internal to the network, and which, thus, is performed automatically by the network. However, when designing a network having the abilities described above, the design faces the problem of different operators having different needs and different requirements relating to a network's behaviour. For example, one operator might want the behaviour of resource allocation within the network to be static and only to be changed by the operator himself, whereas another operator might want the behaviour of the network to be fully automated in order for the behaviour to be as dynamic as possible. Also, an operator may want the network to show different levels of dynamics at different points in time or over different parts of the network. The present invention addresses the problem of how to deal with different desires, or requirements, as to whether the allocation of resources within the network should be of static or of dynamic nature. Summary of the invention An object of the present invention is to provide a mechanism for controlling to what degree resources in the form of write access to time slots allocated to a node of a time division multiplexed network should be permitted to be temporarily allocated to other nodes of the network. According to the present invention, said object is achieved by a method and a system having the features as defined in the appended claims. According to a first aspect of the invention, there is provided a method in connection with controlling allo- cation of resources in the form of write access to time slots of frames that are transferred on a shared medium between nodes in a time division multiplexed network, said method comprising defining a resource level for a node of said nodes, said resource level designating an amount of resources allocated to said node that is permissible to be temporarily allocated to other nodes of said network. According to a second aspect of the invention, there is provided a system for facilitating control of allocation of resources in the form of write access to time slots of frames that are transferred on a shared medium between nodes in a time division multiplexed network, said system including a controllable resource level parameter designating an amount of resources allocated to said node that is permissible to be temporarily allocated to other nodes of said network. Thus, the present invention provides a network operator with a simple mechanism to enable, and also disable, temporary allocation of resources between nodes within a network, which network is designed for providing such utilisation of resources, by defining resource levels as described above. In a similar way, the operator can disable existing permitted temporary allocation by removing one or more existing resource levels. Hence, an operator can control whether the allocation of resources within the network only should be static, i.e. temporary allocation not enabled, or dynamic, permitting the network to fully utilise the temporary allocation possibilities designed into the system. As referred to herein, temporary allocation of write access to a time slot means an allocation of write access with an obligation to return said write access , more specifically to return the write access the node that had write access to said slot prior to said temporary allocation. For example, if node A owns a slot, this slot may be temporarily allocated to B, i.e. borrowed by node B. Node B will temporarily have write access to said slot, but is obliged to return the write access to the slot to node A, i.e. to the owner thereof. This is as opposed to permanent allocation of write access to slots, wherein there is no obligation to return the write access of the slots to another node. Hence, in the context of the present invention, there is a difference between time slots allocated to a node and time slots owned by a node. Time slots owned by a node may at a certain point of time either be allocated to the node itself or be temporary allocated to another node. Similarily, time slots allocated to a node are either owned by the node itself or owned by another node and, thus, merely temporarily allocated. Also, note that write access to a time slot, whether owned or borrowed, only indicates the exclusive right of a node to use the time slot in a channel for transferring data to another node, it does not necessarily mean that the time slot is actually used by the node for transferring data. The actual temporary allocation of time slots is typically performed as a consequence of an automated decision by a mechanism within the network. This mechanism, controlling the allocation of time slots, and in particular the temporary allocation of time slots, is either centralized or decentralized. If the mechanism is centralized, one of the nodes within the network makes decisions relating to temporary allocation on behalf of several of the other nodes, and if the mechanism is decentralized, each node makes its own decisions based on messages that are sent between the nodes automatically or under the control of an operator. Before the above described mechanism makes its decision, it takes any relevant resource levels into consideration in order to ensure that any temporary allocation of time slots allocated to a node does not result in that the amount of resources being permissible to be temporary allocated, as defined by the node's resource level, is exceeded. Furthermore, in a network according to the invention, the respective ownership of time slots assigned to a respective node may in itself be subject to redistribution based on decisions being centralized or decentra- lized in the network. Distribution of time slot ownership, and any following redistributions, among the nodes within the network is either performed automatically or under the control of an operator. In the present invention, resources are defined as write access to time slots, which may include both slots carrying payload data and slots used for control signalling. According to an embodiment of the invention, said resource level is changed during operation of the network in order to control to what extent resources allocated to a node are permissible to be temporary allocated to other nodes within the network. An advantage with the present invention is that it provides the operator with a simple mechanism for controlling, during operation of the network, to what degree temporary allocation of resources should be permitted. Also, an operator has the option of enabling temporary allocation with respect to some of the nodes in the network, while disabling temporary allocation with respect to other nodes. Thus, an operator can control the degree of dynamical allocation behaviour of the network at his discretion. By enabling temporary allocation of resources allocated to one node in the network, a centralised pool of temporarily allocatable resources is created. If, one the other hand, temporary allocation of resources allo- cated to several nodes is enabled, a decentralised pool of temporarily allocatable resources is created. Another advantage with the invention is that it provides a simple way for presenting resource levels defined within the network to an operator, and also a simplified way for the operator to control the resource levels and, hence, the temporary allocation being permissible within the network. The presentation and the controlling of the resource levels are accomplished by means of visual displaying means and control means included in a management station connected to the network and operated by the operator. Further features and advantages of the invention will become more readily apparent from the appended claims and the follwing detailed description of a specific embodiments thereof. Brief description of the drawings Exemplifying embodiments of the invention will now be described below with reference to the accompanying drawings, in which: Fig. 1 schematically shows an exemplified network in accordance with the invention; Fig. 2 schematically shows another exemplified network in accordance with the invention; Fig. 3 schematically shows an exemplifying time multiplexed bitstream propagating along an optical fiber shown in Fig 1 and 2; Fig. 4 shows a diagram of an exemplified time slot distribution among the nodes in Fig. 1 or 2 according to an embodiment of the invention; Figs. 5a and 5b show diagrams of exemplified time slot distributions among the nodes in Fig. 1 or 2 in accordance with another embodiment of the invention; Fig. 6 shows a diagram of an exemplified time slot distribution among the nodes in Fig. 1 and 2 in accordance with yet another embodiment of the invention; and Fig. 7 schematically shows an exemplified system in accordance with an embodiment of the invention. Detailed description of preferred embodiments In Fig. 1, the basic topology of an exemplified time division multiplexed network according to the invention is shown. The network in Fig. 1 comprises four nodes Nl, N2, N3 and N4, each node connected to two unidirectional optical fibers Bl and B2 connecting all nodes in a ring structure. The optical fiber Bl carries at least one bit- stream used for communication in one direction, and the optical fiber B2 carries at least one bitstream used for communication in the other direction. In Fig. 2, another example of a time division multiplexed network according to the invention is shown. The network in Fig. 2 comprises four nodes Nl, N2, N3 and N4, each node connected to a unidirectional optical fiber B3 connecting all nodes in a bus structure. The optical fiber B3 carries at least one bitstream used for communication along the indicated direction of the bus. Each node in Fig. 1 and Fig. 2 may as such be an end user or is typically arranged to serve one or more end users (not shown) by providing access to the optical fibers of the respective network. It should be understood that the end user mentioned above may be any type of electronic equipment needing access to the network, such as printers, servers, facsimile machines, telephones, television sets, radio receivers, and the like. The structure of a time division multiplexed bit- stream of the kind propagating on the optical fibers Bl and B2 in Fig. 1, and B3 in Fig. 2, will now be described with reference to Fig. 3. The bandwidth of each wave- length, i.e. each bitstream, is divided into fixed size, e.g. 125 μs, frames F. Each frame F is in turn divided into fixed size, e.g. 64 bit, time slots. The number of time slots within a frame thus depends on the network' s bit rate. Consequently, the number of slots shown in the frame of the bitstream in Fig. 3 is merely illustrative, the actual number of slots within each frame being far greater than what is shown in Fig. 3. The time slots are in general divided into two groups, control slots C and data slots D. The control slots C are used for control signaling between nodes in the network, i.e. for carrying messages between nodes for the internal operation of the network, such as for channel establishment, slot allocation, and the like. The data slots D are used for the transfer of user data bet- ween end users connected to said nodes. The control slots C and the data slots D may be scattered within a frame. In addition to said control slots and data slots, each frame comprises one or more synchronization slots S used to synchronize the operation of each node in relation to each frame. Also, a guard band G is added after the last slot at the end of each frame in order to facilitate synchronization. As indicated in Fig. 3, the time slot frame is repeated continuously. Each node typically has write access to at least one control slot C and to a variable number of data slots D. Each node uses its control slots C to communicate with other nodes within the network. The number of data slots D to which a node has write access may typically depend upon the transfer capacity requested by the end users served by the respective node. Each node in Fig. 1 and 2 preferably includes a node controller (not shown) . The node controller performs network management operations and controls the access to slots. Messages between different node controllers are carried by the control slots. The node controller will keep track of all required information as to the allocation of time slots to different nodes and different channels. Hence, the node controller is for example used when establishing new channels on behalf of an end users or another network connected to the node. The node con- troller specifies in which slots the node may write data. The node controller also specifies from which slots the node may read control data and user data. Figs. 4, 5a and 5b, and 6 all show diagrams illustrating a current operational distribution of time slots among four different nodes in a time division multiplexed network according to the invention. The network and the nodes could, for example, be either one of the networks shown in Fig. 1 or Fig. 2 and their respective included nodes Nl - N4. In Figs. 4 - 6 each composite column represents a respective node in the network and is plotted against a vertical axis depicting resources in the form of number of time slots. Note that the scale used for the vertical axis in these figures is merely illustrative. For ease of description it could be assumed that each indicated step along the vertical axis indicates 100 time slots. The shaded part of each column in Figs. 4 - 6 illustrates the number of time slots a respective node currently has write access to, and the part of each column not being shaded illustrates the number of time slots actually owned by a respective node. The diagrams of the kind shown in Figs. 4 - 6 are typically the diagrams that are presented on a monitor to an operator of the network, as will be further described with reference to Fig. 7. Fig. 4 shows an operational situation where each node Nl has write access to 1000 slots, N2 also has write access to 1000 slots, N3 has write access to 600 slots, and N4 has write access to 1400 slots, which in the shown situation also is equal to the respective number of slots owned by the respective node. Fig. 4 hence shows a network in which no temporary allocation of write access to slots is present. This could for example be due to the fact the amount of time slots allocated to nodes of the network that are allowed to be temporarily allocated to other nodes have been set to zero by the network operator. The situation of Fig. 4 would also be constantly prevailing in a network in which temporary allocation of time slots by nodes in the network is not possible due to the design of the network nodes. In fig. 4, since none of the nodes Nl - N4 permits any temporary allocation of its resources, in the form of write access to time slots, the behavior of the network is restricted to be of static nature with respect to the possibility of temporary allocation of resources within the network. With reference to Fig. 5a, another operational situation is shown, . In the diagram illustrated in Fig. 5a, a level 517, 527, 547 defined for the node Nl, N2 and N4, respectively, is indicated. Each of these levels 517, 527, 547 has been set by the network operator and designates an amount of resources, illustrated as column areas 518, 528, 548, allocated to the node Nl, N2 and N4, respectively, that is permissible to be temporarily allocated to other nodes within the network. More explicitly, the levels 517, 527 and 547 can be seen as levels denoting the amount of resources allocated to a respective node which is not allowed to be temporarily allocated to other nodes, and the respective remaining amount of resources of each node is the amount that is permissible to be temporarily allocated to other nodes. Hence, in the situation illustrated in Fig. 5a, node Nl allows a temporary allocation of a maximum of 400 slots, illustrated as column area 518, node N2 allows a tempo- rary allocation of a maximum of 100 slots, illustrated as column area 528, and node N4 allows a temporary allocation of a maximum of 300 slots, illustrated as column area 548. According to the invention, and as mentioned above with reference to Fig. 4, each resource level is either defined as an absolute measure of resources permissible to be temporarily allocated, or as a relative measure of the resources allocated to, and owned by, the node and being permissible to be temporary allocated to other nodes. With reference to Fig. 5a, the resource levels 517, 527 and 547 would in accordance with the first case have been assigned the absolute measure 800, 200 and 600 time slots, respectively. Alternatively, if the resource levels have been defined in accordance with the latter case, the assignments would be 40%, 10% and, approximately, 21,4%, respectively. In both of these cases the resource level 537 for node N3 have been assigned to 0 or 0 %, or, alternatively, not defined at all. Thus, the system, or an operator of the system, does not allow any resources allocated to node N3 to be temporary allocated to other nodes within the network. Fig. 5a furthermore illustrates a situation in which node N2 has borrowed write access to 100 slots from node Nl. In this example, since no other temporary allocations of write access to time slots has been performed among the nodes Nl - N4, the result is that node Nl still has write access to 900 slots, which is less than the 1000 slots that it owns, and node N2 has write access to 1100 slots, which is more than the 1000 time slots actually owned by node N2. The reason for this temporary allo- cation could, for example, be that a user connected to the second node N2 has requested more bandwidth, and thus access to more time slots, resulting in that the total bandwidth needed by node N2 exceeded the bandwidth which it had access to prior to the temporary allocation of time slots from node Nl. Moreover, note that none of the time slots allocated to node N4 has been temporarily allocated to other nodes, even though so permitted. In Fig. 5a, only the nodes Nl, N2, and N4 have a defined level 517, 527 and 547. These three nodes con- stitute a confined set of nodes within the network. By only defining resource levels for a confined set of nodes, the resources within the network is controlled in such a way that resources allocated to other nodes, i.e. node N3 in Fig. 5a, is excluded from the possibility of being temporary allocated to other nodes. However, nodes outside the confined set may still borrow resources from nodes within the confined set, if such need should arise. Such a situation is described with reference to Fig. 5b below. With reference to Fig. 5b, the distribution of write access to time slots among the nodes within the network has been further changed. As can be seen in the diagram, the nodes N2 - N4 has now borrowed write access to 100, 100 and 200 time slots, respectively. As is shown, all resources 518 of node Nl, being permissible to be temporarily allocated to other nodes, have been subject to such temporary allocation. The defined resource level 517 of node Nl does not permit any more of its allocated resources to be temporary allocated to other nodes. Node Nl is therefore left with an amount of allocated resources corresponding to the amount of resources 518 temporarily allocated to other nodes subtracted from the amount of resources actually owned by node Nl. Also, in accordance with the description above, it can be seen in Fig. 5b that node N3, being a node outside the confined set of the nodes Nl, N2 and N4 and not per- mitting any of its allocated resources to be temporarily allocated to other nodes, temporarily has borrowed write access to 100 time slots from other nodes. In Fig. 5b , the operator could, for example, change the defined level 517 in order to increase, or decrease, the amount of resources, illustrated as column area 518, being permissible to be temporary allocated from node Nl to other nodes. By increasing the amount of resources represented by column area 518, the operator enables more resources, of the resources that node Nl owns and have write access to, to be temporarily allocated to nodes N2 - N4. This could be interesting if node Nl does not use the bandwidth provided by its current allocation of write access to time slots. However, the operator could alternatively decrease the amount of resources represented by column area 518 if, for some reason, a greater part of the bandwidth associated with the write access to time slots owned by node Nl should be restricted to only be possible to be utilized by node Nl. With reference to Fig. 6, another embodiment of the present invention is illustrated. This embodiment differs from the embodiment described with reference to Figs. 5a and 5b in respect of the number of resource levels being able to be defined for a node within the network. In this exemplified embodiment, two resource levels 617 and 619 have been defined for node Nl. Each of these resource levels 617 and 619 defines a respective amount of resources, represented by column areas 618 and 620, respectively, being permissible to be temporarily allocated to other nodes within the network. Generally, according to the invention, a node in need of bandwidth capacity sends a message to another node including a request for resources that are allocated to said another node. In the embodiment of Fig. 6, such a request is associated with a priority level indicating the priority of the request in relation to other node internal or external bandwidth demands. In Fig. 6, the resource level 617 defines an amount of resources, represented by column area 618, comprising 200 time slots as indicated in Fig. 6, which may be temporarily allocated to nodes from which requests associated with any priority are received. The resource level 619 defines another amount of resources, represented by column area 620, comprising 100 time slots, which may be allocated to nodes from which requests associated with only a first priority are received. The amount of resources, write access to 300 time slots, potentially at the disposal for temporary allocation requested with this first priority is therefore higher than the amount of resources, write access to 200 time slots, at the disposal for requests associated with priorities lower than said first priority. With reference to Fig. 7, an exemplifying system according to an embodiment of the invention is described. Each node Nl - N4 in the network 700 includes a respective mechanism making decisions relating to temporary allocations of resources in the network 700. Such a mechanism is implemented by processing means 710 executing appropriate software for controlling the temporary allocation of a node's Nl, N2, N3, N4 resources in accordance with a resource level defined for the node, said level designating the amount of resources that may be temporarily allocated to other nodes of the network. This mechanism, or processing means, 710 is preferably part of a node's previously described node controller. The software which is executed within a node Nl, N2, N3, N4 have access to one or more resource level parameters defined for the node. Each resource level parameter within a node Nl, N2, N3, N4 is thus implemented as a software parameter storing the value of a defined resource level. Fig. 7 also shows a management station, for example a personal computer or a workstation, connected to, and communicating with, the network 700. The management station includes a monitor 720, i.e. visual displaying means, and control means 730. The control means 730 comprises processor hardware executing appropriate software and are used by an operator for defining resource level parameters for the nodes Nl - N4 in the network 700. The monitor 720 presents the resource level parameters of the respective node in the network 700 to the operator. The monitor 720 also continuously presents the current actual amount of resources of a respective node Nl, N2, N3, N4 that are being temporary allocated to other nodes Nl, N2, N3, N4 within the network 700. Preferably, the monitor 720 presents the resource levels and the present actual amount of resources, or time slots, allocated to a respective node, as well as the amount of resources owned by the node, in the form of a diagram of the kind shown in Figs. 4 - 6. The operator may also use the diagrams presented on the monitor 720 as an interface to the control means 730 for changing, as well as defining, resource levels by manipulating the graphical levels in the diagrams using a mouse or, for example, the numerical keypad of a keyboard (neither shown) . A defined or changed resource level may then immediately be visually inspected in the diagram presented on the monitor. Even though the invention has been described with reference to specific exemplifying embodiments, many different alterations and modifications will become apparent for those skilled in the art. The described embodiments are therefore not intended to limit the scope of the invention, as defined by the appended claims.

Claims: CLAIMS 1. A method in connection with controlling allocation of resources in the form of write access to time slots of frames that are transferred on a shared medium between nodes in a time division multiplexed network, said method comprising defining a resource level for a node of said nodes, said resource level designating an amount of resources allocated to said node that is per- missible to be temporarily allocated to other nodes of said network. 2. A method as claimed in claim 1 , wherein said amount is defined as a number of time slots. 3. A method as claimed in claim 1 or 2, comprising changing said resource level in order to control to what extent resources allocated to said node are permissible to be temporarily allocated to other nodes within said network. 4. A method as claimed in any of claims 1 - 3, wherein whether or not to actually perform said temporary allocation is based upon a decision by a mechanism controlling the temporary allocation of resources in accordance with said defined resource level. 5. A method as claimed in any of claims 1 - 4, comprising defining two or more resource levels, wherein each resource level designates an amount of resources permissible to be temporarily allocated to other nodes in dependence upon a priority associated with a request for resources . 6. A method as claimed in any one of claims 1 - 5, wherein said step of defining a resource level is performed for at least one node of a confined set of nodes within said network, thereby excluding resources allocated to nodes outside said confined set from the possibility of being temporarily allocated to other nodes within said network. 7. A method as claimed in any one of claims 1 - 5, wherein said step of defining a resource level is performed for two or more nodes within said network. 8. A method as claimed in any one of claims 1 - 7, wherein said resource level is presented on visual displaying means arranged in communication with said network. 9. A method as claimed in claim 8, wherein the actual amount of resources of said set being temporarily allocated to other nodes within said network is presented on said visual displaying means. 10. A method as claimed in any one claims 1 - 9, wherein said network is a circuit switched network. 11. A method as claimed in any of claims 1 - 10, wherein said amount is an absolute measure. 12. A method as claimed in any one of claims 1 - 10, wherein said amount is a relative measure of the resources allocated to, and designated to be owned by, said node. 13. A method as claimed in any one of claims 1 - 12, wherein said network is a Dynamic Synchronous Transfer Mode (DTM) network. 14. A system for facilitating control of allocation of resources in the form of write access to time slots of frames that are transferred on a shared medium between nodes in a time division multiplexed network, said system comprising a controllable resource level parameter designating an amount of resources allocated to a node of said nodes that is permissible to be temporarily allo- cated to other nodes of said network. 15. A system as claimed in claim 14, including control means for defining said resource level parameter in order to control to what extent resources allocated to said node are permissible to be temporarily allocated to other nodes within said network. 16. A system as claimed in claim 14 or 15, said system including means for controlling said temporary allocation of resources and for deciding whether or not to actually perform said temporary allocation based upon said defined resource level. 17. A system as claimed in any one of claims 14 - 16, said system including two or more resource level parameters, wherein each one of said two or more resource level parameter designates a respective amount of resources permissible to be temporarily allocated from a node to other nodes in dependence upon a respective priority associated with a request for resources. 18. A system as claimed in any one of claims 14 - 17, including visual displaying means for presenting said resource level parameter. 19. A system as claimed in claim 18, wherein said visual displaying means are further arranged for presenting the actual amount of resources of said node being temporary allocated by other nodes within said network. 20. A system as claimed in any one of claims 14 - 19, wherein said node is included in a Dynamic Synchronous Transfer Mode (DTM) network.

Inventors: BOHM CHRISTER, BOHM, CHRISTER
Applicants: BOHM CHRISTER, NET INSIGHT AB, BOHM, CHRISTER
Application year: 2000
Main classification: H04L12
IPC codes: H04Q11