An ATM network controller

The present invention relates generally to asynchronous transfer mode (ATM) networks. A particular embodiment, illustrative of the invention by way of example, will be described below in relation to the reservation of network resources in an ATM network in response to user's requests.

Japanese Laid-Open Patent Specification Hei-6-30021 proposes time-scheduled communications in a switched network in which ATM switching nodes individually perform the reservation of a bandwidth according to a user's reservation requests by storing reservation requests in a memory and monitoring the stored requests, in order to establish a connection at a requested time of day, if a network resource is available. After a connection has been established, the ATM switches monitor a stored request in order to release it at the expiry of the reservation.

Since the previously proposed resource reservation system is implemented individually on a per-node basis and no facility is available to link the reservation data between ATM switches, network reservation cannot be performed on an end-to-end basis. In addition, network resource reservation is attempted at the very instant at which the scheduled communication begins. Although in the previous proposal means is provided for rejecting some calls if they occur during a predetermined interval prior to the scheduled communication, there is some degree of uncertainty with regard to satisfying a reservation request at the beginning of a scheduled communication. Furthermore, if the ATM switches fail to satisfy a reservation request at the beginning of a scheduled communication, there is no fall back procedure for continuing the search for the requested network resource.

Features of embodiments to be described below by way of example in illustration of the invention are that they minimise the effect of the above problems associated with ATM switches for making a reservation of a network resource.

In one particular arrangement to be described below, by way of example in illustration of the invention there is a network controller for making a resource reservation in a network formed by a plurality of ATM switches interconnected by communication links. The network controller includes a data base for holding data pertaining to network topology and the remaining network resource, a supervisory circuit for monitoring the communication links, a registration memory, and route decision and resource reservation logic circuitry. The logic circuitry updates the data base if a faulty condition is detected by the supervisory circuit and receives, from a source terminal, a reservation request indicating a reservation of an end-to-end network resource between a scheduled start time and a scheduled end time, making a search through the data base to reserve the network resource in the data base if the network resource is available. The logic circuit causes the ATM switches to establish an end-to-end connection using the reserved network resource at the scheduled start time, informs the source terminal of a virtual channel identifier/virtual path identifier of the established connection to be used for the subsequent transmission of messages, releases the established connection when the request stored in the registration memory indicates the scheduled end time and removes the request from the registration memory.

In another arrangement to be described below by way of example in illustration of the present invention, the reservation request further indicates one of first and second reservation classes, and the logic circuitry is arranged to make a search through the data base, if the request indicates the first class, to determine whether the network resource is available immediately following the receipt of the request, to reserve the network resource and to cause the ATM switches to establish the connection using the reserved network resource at the scheduled start time if the network resource is available, and is further arranged to make a search through the data base, if the request indicates the second class, to determine whether the network resource is available at the scheduled start time, and to cause the ATM switches to establish the connection using the network resource if the network resource is available.

In yet another arrangement to be described below, by way of example in illustration of the invention, the logic circuitry is arranged to store the request in a waiting memory if the network resource is determined to be unavailable, to make a search through the data base to determine, when an existing connection is released, whether the network resource is available, and to cause the ATM switches to establish the connection using the network resource and to remove the request from the waiting memory if the network resource is available.

The following description and drawings disclose, by means of an example, the invention which is characterised in the appended claims, whose terms determine the extent of the protection conferred hereby.

In the drawings:- <ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 is a block schematic diagram of an ATM switched network,</li><li>Fig. 2 is a block schematic diagram of the network management apparatus of Fig. 1,</li><li>Fig. 3 is a flowchart illustrating the operation of a route decision and bandwidth reservation (RDBR) logic circuit,</li><li>Fig. 4 is a block schematic diagram of a modified embodiment in which a mapping table is located in the network controller for translating a user-transmitted code name to a corresponding set of reservation data items, and</li><li>Fig. 5 is a block schematic diagram of the ATM network in which the mapping table is located in the user's premises.</li></ul>

Referring to Fig. 1, an ATM (asynchronous transfer mode) switched network is illustrated by means of a simplified example for the purpose of disclosure. Two ATM switches 3 and 4, interconnected by a communication link 7, are illustrated as switching nodes of the network for serving many end user terminals. Only two user terminals 1 and 5 are illustrated for simplicity, these terminals being connected to the switching nodes 3 and 4 via subscriber lines 6 and 8, respectively. All ATM nodes and user terminals are connected to a network controller 2 via logical (virtual) links 9,10,11 and 12. Logical links 9 and 12 of the user terminals are established via ATM nodes 3 and 4.

As shown in Fig. 2, the network controller 2 comprises a line receiver 20 to which the logical links 9 and 12 are terminated for receiving reservation requests from the user terminals. A supervisory circuit 21 is connected to the logical links 10 and 11 to monitor lines and switching equipment. A route decision and bandwidth reservation (RDBR) logic circuit 22 is provided to receive reservation requests from line receiver 20 and a monitor report from the supervisory circuit 21. The RDBR logic circuit 22 is associated with a network topology memory 23, a remaining resource memory 24, a connection status memory 25, a registration memory 26, and a waiting memory 27. A monitor circuit 28 is connected to the registration memory 26 to monitor reservation requests stored in memory 26 and supplies an interrupt command to the logic circuit 22 when one of the start and end times of a reservation matches the time of day. Monitor circuit 28 is further connected to the connection status memory 25 to monitor the status of established connections and supplies an interrupt command to the logic circuit 22 when any of the established connections is released.

A signalling circuit 29 is provided for transmitting signalling packets to the ATM switches via logical links 10 and 11 to establish switched virtual connections along routes determined by the RDBR logic circuit 22 using the Simple Network Management Protocol (SNMP) which is currently in use for establishing permanent virtual connections (PVC). In this particular arrangement, each ATM node responds to the signalling packet for establishing a switched virtual connection to the destination terminal and informing the source terminal of a virtual channel identifier/virtual path identifier (VCI/VPI) to be used during the subsequent transmission of ATM message cells. After a switched virtual connection is established by the ATM switches under control of the network controller 2, each ATM switch examines the header of user-transmitted ATM message cells for routing them along the established connection.

In a further arrangement, reservation requests are classified into a high-cost, priority reservation class and a low-cost, normal reservation class, for making a reservation of an end-to-end communication through the ATM network. The priority reservation class ensures a high degree of certainty for obtaining the requested bandwidth. If this class is requested, the RDBR logic circuit 22 immediately begins hunting for a route having the requested bandwidth. The normal reservation class, on the other hand, provides a low degree of certainty for obtaining the requested bandwidth. On receiving this request, the RDBR logic circuit 22 waits until the start of the requested communication before hunting for a route having the requested bandwidth.

The operation of the RDBR logic circuit 22 will be explained with the aid of a flowchart shown in Fig. 3. When a reservation request is received (step 30), flow proceeds to step 31 to store the request in the registration memory 26. The reservation request indicates the identity of the source user terminal (source address), the identity of a destination user terminal (destination address), a network resource, such as bandwidth, to be reserved, times of day respectively indicating the beginning and expiry of a communication to be reserved over a route between the source and the destination terminals, and a priority/normal reservation class.

At step 32, the stored request is examined to determine whether it demands the priority class or the normal class. If the request demands the normal class, flow returns to the starting point of the routine to wait until the logic circuit 22 is triggered by the monitor circuit 28 in order to serve reservation requests from other user terminals.

If the request demands the priority class, flow proceeds from step 32 to step 33 to hunt for a route having the requested bandwidth using network topology data stored in the network topology memory 23 and currently available network resource data stored in the remaining resource memory 24. If there is one (step 34), flow proceeds to step 35 to reserve the bandwidth of the detected route in the remaining resource memory 24. If the decision at step 34 is negative, the reservation request is stored in a queue in the waiting memory 27 (step 36), and flow returns to the starting point of the routine.

When the beginning of a communication requested by either class of a request stored in the registration memory is detected by monitor circuit 28, the logic circuit 22 is triggered and starts its operation at step 40 by determining which reservation class the request is demanding. If the priority class is requested, flow proceeds from step 40 to step 41 to check to see if the requested route is reserved. If so, flow proceeds from step 41 to step 42 where the logic circuit 22 commands the signalling circuit 29 to operate the ATM switches to establish a connection over the reserved route. In addition, the logic circuit 22 stores the connection status of the request into connection status memory 25, and returns to the starting point of the routine. If the decision at step 41 is negative, flow returns to the starting point of the routine.

If the request stored in the registration memory demands the normal class, flow branches at step 40 to step 43 to hunt for a route having the requested bandwidth. If such a route is found (step 44), a connection is established over the detected route and the remaining resource memory 24 and connection status memory 25 are updated accordingly (step 45). Otherwise, the request is placed into a queue in the waiting memory 27 (step 36).

The reservation requests stored in the waiting memory 27 are served by the logic circuit 22 whenever any of the already established connections is released. When this occurs, the logic circuit 22 is triggered by the monitor circuit 28 and starts its operation at step 50 by making a search through the waiting memory 27 for a stored request. If a request is found in the waiting memory (step 51), flow proceeds to step 52 to hunt for a route having the bandwidth requested by the request stored in the waiting memory. If such a route is detected (step 53), a connection is established over the detected route and the remaining resource memory 24 and connection status memory 25 are updated accordingly (step 54) and the request is removed from the waiting memory (step 55). If the decision at steps 51 and 53 are negative, flow returns to the starting point of the routine.

When the expiry of a communication of a request of either normal or priority class is detected in the registration memory 26 by the monitor circuit 28, the logic circuit 22 is triggered to start its operation at step 60 by releasing the connection established for the request and removing the request from the registration memory 26 (step 61), and flow returns to the starting point of the routine.

Since the reservation request contains a number of reservation data items, it is a time-consuming and tedious affair manually to enter reservation data if calls are frequently set up using different patterns of reservations. Therefore, from the customer service viewpoint, it is important to simplify the reservation procedure. Fig. 4 illustrates an embodiment that simplifies the reservation procedure.

In the embodiment of Fig. 4, the network controller, indicated at 70, additionally includes a mapping table 71 connected between line receiver 20 and the RDBR logic circuit 22. In the table 71, a plurality of code names are mapped to corresponding reservation data items each including a source address, a destination address, times of day for the beginning and expiry of a scheduled communication, a desired bandwidth and a reservation class. When transmitting a reservation request, the user terminal only needs to enter a desired code name, instead of entering the reservation data. The code name is transmitted to the network controller 70, where it is translated by the mapping table 71 to corresponding reservation data and applied to the logic circuit 22.

The mapping table may be located at a customer's premises. As illustrated in Fig. 5, each of the user terminals 1 and 5 includes a mapping table 81 connected to the data terminal equipment 80. When transmitting a reservation request, each user terminal enters a desired code name which is translated by the mapping table 81 to corresponding reservation data, which is then transmitted to the network controller 2.

It will be understood that although particular embodiments have been described by way of example in illustration of the invention, variations and modifications thereof as well as other embodiments may be employed within the scope of the appended claims.