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The present invention relates to methods and apparatuses for allocating time slots to circuit-switched channels established to comprise one or more respective time slots in a recurrent frame of a time division multiplexed network. According to the invention, a time slot allocated to said channel is

The present invention relates to methods and apparatuses for allocating time slots to circuit-switched channels established to comprise one or more respective time slots in a recurrent frame of a time division multiplexed network. According to the invention, a time slot allocated to said channel is associated with a selected level, of at least two available levels of priority. Decisions as to whether or not to deallocate said time slot from said channel is then based upon a comparison of said selected level of priority and a level of priority associated with a request for a time slot for another channel.

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The invention claimed is: 1. In a time division multiplexed network in which a recurrent frame thereof is divided into time slots, and in which circuit-switched channels are allocated respective sets of time slots in said recurrent frame of said network, a method comprising: controlling the allocat

The invention claimed is: 1. In a time division multiplexed network in which a recurrent frame thereof is divided into time slots, and in which circuit-switched channels are allocated respective sets of time slots in said recurrent frame of said network, a method comprising: controlling the allocation of time slots in said recurrent frame to said circuit-switched channels; said controlling comprising: allocating a set of time slots in said recurrent frame to a circuit-switched first channel; associating the allocated set of time slots to said first channel with a first level of priority; receiving a request for time slots in said recurrent frame for a circuit-switched second channel associated with a second level of priority; comparing said first and second levels of priority, and determining whether or not to deallocate a subset of said set of time slots from said first channel, and allocate the deallocated subset of time slots to said second channel, based upon said comparison. 2. A method as claimed in claim 1, wherein in said determining step it is determined to perform a deallocation if said second level of priority is higher than said first level of priority. 3. A method as claimed in claim 1, wherein said second level of priority is identified in said request. 4. A method as claimed in claim 1, wherein in said step of determining it is determined to perform a deallocation only if there are insufficient non-allocated slots available to satisfy said request. 5. A method as claimed in claim 1, wherein in said step of determining it is determined to perform a deallocation only if the first level of priority is lower than a highest level of priority. 6. A method as claimed in claim 1, wherein said step of determining whether or not to deallocate a subset of said set of time slots from said first channel is further based upon an evaluation regarding to which channel a time slot was last allocated. 7. A method as claimed in claim 1, wherein said step of determining whether or not to deallocate a subset of said set of time slots from said first channel is further based upon an evaluation regarding to which channel a time slot has been allocated the longest period of time. 8. A method as claimed in claim 1, wherein said step of determining whether or not to deallocate a subset of said set of time slots from said first channel is further based upon an evaluation regarding from which channel a time slot was last deallocated. 9. A method as claimed in claim 1, wherein said associating step comprises associating the allocation of all time slots allocated to said first channel with the same level of priority. 10. A method as claimed in claim 1, wherein said associating step comprises associating said first channel with said first level of priority, thereby associating the allocation of each time slot allocated to said first channel with the same level of priority. 11. A method as claimed in claim 1, wherein said associating step comprises associating the allocation of different time slots allocated to said first channel with different levels of priority and wherein said determining step comprises to deallocate from said first channel, and allocated to said second channel, only such time slots that have been allocate to said first channel with a level of priority that is lower than said second level of priority. 12. A method as claimed in claim 1, wherein said associating step comprises associating the allocation of time slots allocated to said first channel over a first portion of said network with one level of priority and associating the allocation of time slots allocated to said first channel over another portion of said network with another selected level of priority. 13. A method as claimed in claim 1, wherein said associating step comprises changing the level of priority associated with the allocation of time slots to said first channel as a consequence of changing bandwidth requirements. 14. A method as claimed in claim 1, comprising the step of determining the priority by which said first and second channels are to be re-established in case of channel failure based upon their respective levels of priority. 15. A method as claimed in claim 1, comprising the step of determining a degree of redundancy requested for the channels based upon their respective levels of priority. 16. A method as claimed in claim 1, wherein said channels carry traffic, comprising selecting said levels of priority based upon the identity of a physical or virtual port or interface to/from which traffic pertaining to the respective channel is delivered. 17. A method as claimed in claim 1, wherein said channels carry traffic, comprising selecting said levels of priority based upon an identification of the type of application that traffic to be transported in the respective channel pertains to. 18. A method as claimed in claim 1, comprising transmitting information on said level of priority associated with the allocation of a set of time slots to the first channel to one or more other nodes of the network in order for said other nodes to be able to switch said first channel taking said level of priority into consideration. 19. In a time division multiplexed network in which a recurrent frame of the network is divided into time slots and in which circuit-switched channels are established to comprise respective sets of time slots in said recurrent frame of said network, a method comprising: controlling the allocation of time slots in said recurrent frame to said circuit-switched channels said controlling comprising: specifying levels of priority associated with the allocation of time slots in said recurrent frame to respective established channels; receiving a request for time slots in said recurrent frame for a circuit-switched channel in need of bandwidth, said request being associated with a requested level of priority; determining if there are slots available that are not allocated to any other channel and, if so, allocating such time slots to said circuit switched channel; and, if the amount of time slots so allocated to said circuit-switched channel is insufficient to meet the request; determining if there is a subset of the time slots allocated to said established channels at a level of priority that is deemed lower than the requested level of priority and, if so, deallocating the subset of the time slots from said established channels and allocate said deallocated subset of time slots to said circuit switched channel. 20. Use of a method as claimed in claim 1, for specifying different traffic service classes based upon said priority levels when operating a communication network. 21. Use of a method as claimed in claim 1, for providing channel prioritization based upon said priority levels when interconnecting ports of a data switching or routing apparatus. 22. A method as claimed in claim 1, wherein said method is performed at a node of the network and wherein said request is received from another node of the network. 23. A method as claimed in claim 1, wherein said method is performed at a node of the network and wherein said request is received from a user connected to said node. 24. A method as claimed in claim 1, wherein said request is a request for more bandwidth to an already established channel. 25. A method as claimed in claim 1, comprising the step of reestablishing said channels in case of channel failure in a highest level of priority of first order. 26. A method as claimed in claim 1, comprising defining the level of priority for the allocation of time slots to one or more of said channels so that a higher level of priority is assigned for allocation of time slots to channels carrying traffic pertaining to real-time applications, such as voice or video applications, whereas a lower level of priority is assigned for allocation of time slots to channels carrying bursty data traffic. 27. In a node of a network comprising a plurality of nodes, a method for allocating time slots to channels in a time division multiplexed network in which a bitstream divided into frames is propagating, wherein a recurrent frame thereof is divided into time slots, and in which circuit-switched channels are allocated respective sets of time slots in said recurrent frame of said network, said method comprising: controlling the allocation of time slots in said recurrent frame to said circuit-switched channels; said controlling comprising: allocating a set of time slots in said recurrent frame to a circuit-switched first channel; associating the allocated set of time slots to said first channel with a first level of priority; receiving, from one of an end user and another node, a request for time slots in said recurrent frame for a circuit-switched second channel associated with a second level of priority; comparing said first and second levels of priority; and determining, based upon said comparison, whether or not to deallocate a subset of said set of time slots from said first channel, and, if it is determined to deallocate a subset of said set of time slots from said first channel, allocate the deallocated subset of said set of time slots to said second channel. 28. A method as claimed in claim 27, wherein in said determining step it is determined to perform a deallocation if said second level of priority is higher than said first level of priority. 29. A method as claimed in claim 27, wherein said second level of priority is identified in said request. 30. A method as claimed in claim 27, wherein said step of determining to deallocate time slots from said first channel is performed only if there are insufficient non-allocated slots available to satisfy said request. 31. A method as claimed in claim 27, wherein said step of comparing is preceded by the steps of: checking whether or not there are any free time slots available, and if there are free time slots, allocate the free time slots to said second channel; and if there are no free time slots available, proceeding with said step of comparing, which comprises checking whether or not some time slots of said set of time slots are associated with a lower priority than said second priority, and wherein, in said step of determining, said deallocation is performed if there are such lower priority time slots; and wherein the method further comprises the step of: if there are not a sufficient number of lower priority time slots performing one of rejecting said request and sending said request to another node of the network. 32. A method as claimed in claim 27, wherein in said step of determining it is determined to perform a deallocation only if there are insufficient non-allocated slots available to satisfy said request.