Hierarchical transmission system with distributed storage of resource path information among network elements of the system

A transmission system having a plurality of network elements arranged in a tree-like hierarchical structure, and which includes means for the management and allocation of resources to the network elements. Such a system may be a communication and data transmission network consisting of a plurality of users having distributed databases. In order to enhance the efficiency and transmission speed in such a transmission system, according to the invention network elements which are situated along a resource path (P) store only the course of such resource path, but not the possessors and states of resources in lower hierarchical levels of the system.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to a transmission system which comprises a plurality
 of network elements which are arranged in a hierarchical, tree-like
 structure, and means for the management and allocation of resources to a
 network element.
 2. Description of the Related Art
 Such a transmission system is known from the publication "A primer on the
 T.120 Standard", DataBeam, 1995, P.5.
 A transmission system of this kind is used, for example for communication
 and data transmission in a network consisting of a plurality of users
 and/or in distributed data bases. The management of resources in such
 distributed environments, i.e. the management, allocation and blocking of
 resources, is a decisive factor in respect of the speed and efficiency of
 a transmission system. Resources are, for example permissions which are
 available in the transmission system, for example the permission to speak
 in a communication system or the permission to use an arbitrary system
 element. A given quality of service may also be considered as a resource.
 The infrastructure of known distributed transmission systems is organized
 in a hierarchical and tree-like manner. Starting from a main network
 element, in which the so-called top provider is localized, connections can
 be established with further network elements which are arranged at lower
 hierarchical levels. Network elements in which so-called providers are
 located offer, in addition to other services, the functionality for the
 management of resources in the transmission system. A network element can
 claim a resource as soon as a connection has been established between this
 element and the network element managing the resource. The path through
 the tree structure thus formed, extending from a first network element
 which manages a resource to a second network element which claims the
 resource offered, is referred to as a resource path.
 The allocation and the possession of a resource can be described in
 abstract terms as the allocation and the possession of a token. In known
 transmission systems the number of a token and the possessor are stored by
 appropriate means in the transmission system. In the case of distributed
 storage, storage takes place in each network element. A change of the
 state of a resource, i.e. when the possessor of a token changes, when a
 token is released or surrendered, may cause a plurality of updating
 messages between all network elements and could lead to a different state
 of the information in different network elements. Central storage of the
 information, however, has the drawback that each information concerning a
 resource, for example the requesting of a resource, must be addressed to
 the top provider and possibly transported further to the central storage
 element arranged in a different location. In large transmission systems
 this leads to very long response times for a resource request and overall
 to a reduction of the efficiency of the transmission system.
 SUMMARY OF THE INVENTION
 Therefore, it is an object of the invention to enhance the efficiency and
 the transmission speed of a transmission system of the aforesaid kind and
 to simplify the resource management.
 This object is achieved according to the invention in that network elements
 which are arranged along a resource path, extending from a first network
 element to a second network element, include means for storing the course
 of the resource path.
 As opposed to known transmission systems, not the possessor (the network
 element) of a resource itself is stored in the network elements along a
 resource path, but only an indication as to in which branch of the next
 lower hierarchical level there can be found the network element whereto a
 resource is allocated, i.e. in which branch the resource path extends. A
 central database in which the states and the possessors of all resources
 are stored can either be completely dispensed with or it may have a
 simpler construction, since the path to the network element whereto the
 resource is allocated can be found via the information stored in the
 network elements along a resource path. The request for a resource can
 thus be quickly answered, since this request need not be applied to and
 answered by a central database in all cases, but only need be transported
 as far as a network element having enough information concerning the state
 of the requested resource. Moreover, the information concerning the change
 of state of a resource need only be applied to the network elements along
 the resource path and possibly also to the central storage element, but
 not to all other network elements. Ultimately this results in a higher
 efficiency and an increased speed of the transmission system. In a further
 embodiment of the invention, the network elements along the resource path
 include a respective database in which the states of the resources in the
 branches, emanating therefrom, of the lower hierarchical levels are
 stored. When a network element requests a resource allocated to a network
 element in a neighboring branch (a branch which emanates from the same
 network element as the branch in which the requesting network element is
 situated), the request can be readily answered, without it being necessary
 to involve a central database or the top provider.
 The invention is used in transmission systems, for example in multipoint
 communication systems, in which a plurality of communication stations are
 arranged in a hierarchical network and a transmitter can communicate with
 a plurality of receivers. In that case the resources managed are, for
 example transmission channels.
 The invention also relates to a network element and to a resource
 management system. The resource management system is preferably arranged
 so as to be distributed between a plurality of network elements, via the
 transmission system.
 The invention also relates to a storage medium for use in a resource
 management system, such as notably a CD-ROM, a floppy disk, a hard disk or
 another storage device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1 shows a transmission system with a network with a tree-like
 hierarchical structure. In the top position there is located the top
 provider 1 which communicates with network elements (providers) 2, 3, 4
 arranged at the next lower hierarchical level. With the individual network
 elements 2, 3, 4 at the next lower hierarchical level, and in one case at
 an even lower hierarchical level, there are associated one or more network
 elements 5, 6, 7, 8, 9. For the sake of simplicity, FIG. 1 shows only a
 simple structure; a real transmission system may be arbitrarily larger and
 more complex.
 When the network element 9 requests a resource which has been allocated to
 the network element 6 at that instant, in the known transmission system,
 involving central resource management, the request is supplied
 (symbolically represented by arrows (a) to the top provider 1, which
 stores the information concerning the state and the possessor of the
 resource; this information is returned to the network element 9 as an
 answer (arrows (b). When the network element 7 requests a resource
 allocated to the network element 6, this request is also transported to
 the top provider 1 (arrows a') and answered thereby (arrows b').
 By way of illustration, the transmission system shown in FIG. 1 can be seen
 as a communication system between a plurality of users (network elements)
 in which always only one person can speak at a time. The permission to
 speak represents a resource which is allocated exclusively to the speaker.
 When a person receives the permission to speak, the associated network
 element receives a token so as to indicate the permission to speak. If
 another person wishes to speak, first the instantaneous possessor of the
 token must be found out in the top provider so as to request the
 permission to speak therefrom. Subsequently, the token is passed on to the
 new speaker who thus receives the permission to speak.
 The management of resources according to the invention will be described in
 detail with reference to FIG. 2. Initially, a resource is allocated
 exclusively to the network element 6. A database in the top provider 1
 stores the information that this resource has been allocated to a network
 element in the left-hand branch, so that it is not freely available. The
 possessor of the resource, i.e. the indication or number thereof, is not
 stored in the database. A database in the network element 2 stores the
 information that this resource has been allocated to a network element in
 the left branch. Because the network element 6 is situated at the lowest
 hierarchical level, along the resource path P extending from the network
 element 1, via the network element 2, to the network element 6, i.e. the
 path comprising the connections from the network element 1 to the network
 element 2 and further to the network element 6, the possessor of the
 resource can be identified by way of the information in the databases of
 the network elements 1 and 2. Additionally, the network element 6 may also
 store the information that the network element 6 is the possessor of the
 resource.
 When the network element 7 requests the resource, this request need be
 transported only as far as the network element 2 (arrow c), because that
 element already contains sufficient information for determining the
 possessor of the resource and hence the request can be answered (arrow d).
 Thus, when the resource is released by the network element 6 and allocated
 to the network element 7, the state of the resource does not change and
 the database of the top provider 1 need not be updated either, because the
 entry made thus far for the resource ("allocated in the left-hand branch")
 is still valid. Even when the resource were not exclusively allocated,
 i.e. when it were allocated to a plurality of network elements at the same
 time, for example the two network elements 6 and 7, it would not be
 necessary to update the data base of the top provider 1 but only the
 database of the network element 2.
 The overall structure shown in FIG. 2 is also referred to as a domain which
 can be subdivided into further sub-domains, for example the resource
 sub-domain 10 which includes the network elements 2, 6 and 7. The main
 network element 2 of such a sub-domain 10 is also referred to as a
 resource top provider. For as long as the possession of a resource changes
 only within a sub-domain, therefore, there will be no changes of state
 outside the sub-domain; these changes of possession are not directly
 visible outside the sub-domain.
 When the network element 9 wishes to know the state of the resource
 allocated to the network element 6, this information can be requested from
 the top provider 1 in which the state of the resource is stored. When the
 network element 9 requests this resource, the request is transported to
 the network element 6 via the top provider 1; the path to the network
 element 6 is found by means of the information stored in the network
 elements 1, 2 along the resource path P.
 By way of illustration, the network elements 2, 6, 7 may symbolize
 computers which are located in the United States of America, whereas all
 other network elements symbolize computers which are located in Europe.
 The network elements 6 and 7 involve communication partners who speak
 alternately, whereas passive listening communication partners are present
 at all other network elements. A token, representing the permission to
 speak, is passed to and from between the network elements 6 and 7, so only
 within the USA. The management information involved need only be applied
 to the network element 2, so that it is locally limited to the computers
 present in the USA. The management information need not be applied to the
 computers located in Europe, so that the management is faster and less
 expensive.
 The invention offers shorter response times in the event of resource
 requests in transmission systems having a network with a hierarchical and
 tree-like structure. The transmission system loading due to the
 establishment of connections, the loading of transmission paths and the
 updating of databases can also be reduced by the invention, resulting in a
 higher efficiency of the transmission system overall. The invention can be
 used, for example in communication systems. An example of a communication
 service is a standard defined in the ITU-T T.120 standard series. This
 communication service offers transmission channels and tokens, as
 described above, as resources within a hierarchical structure. The
 management of the resources is implemented at a central database located
 in the top provider of the structure.