Abstract:
To facilitate the creation of an interface between a network control layer and controlled elements in the network, on insertion of a new element to be controlled an intelligent interface creates a compatibility listing between the network control layer and the element manager, the intelligent interface carries out steps of “look around”, “try and see”, “follow instructions” and “structured questioning”. Each of these steps, in association with a dictionary of “comparable information” results in data being added to a knowledge frame which defines the element and its message format handling requirements.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a network interface and more particularly to such an interface for use in translation of coded electrical signals. The invention also relates to methods of constructing such an interface. 
     2. Related Art 
     Modern communications networks often comprise a number of layers each of which may include “intelligence”. The layers have a hierarchical structure with higher layers making use of functions provided by lower layers to complete assigned tasks. Accordingly an element (or function) in one layer may provide service to an element or function in the layer above and may demand a service from an element or function in the layer below (if any). Thus it is necessary for elements and functions to be able to pass messages between each other. Clearly there has to be some known structure for the messages sent between the layers this structure being known as a message protocol. 
     Where a complete network is supplied by a single manufacturer, the message protocols are specified by that manufacturer and provided the network does not need to communicate with any other network there is no problem. 
     However for larger networks, for example for public switched telephony networks (PSTN), it would be unacceptable if the PSTN operator were to be tied to a single manufacturer. Consequently each layer of the PSTN may contain elements from several suppliers, some of which will perform common functions but with a differing message protocol. 
     Hitherto it has been common practice for the network operator to specify to manufacturers the message protocol to be used by element managers of elements to be incorporated into particular network layers. However, this results in increased costs since each network may require bespoke element manager software to be provided. 
     An alternative is for the network operator to accept the manufacturers message protocol and to provide bespoke software in the controlling layer. Such arrangements are equally expensive and may lead to inflexibility in the network since it would not be practical to replace an element from one manufacturer with a corresponding element (having a different message protocol) from another manufacturer. The present invention seeks to alleviate the difficulties arising from message protocol incompatibility. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a method of constructing an interface between a control layer and a controlled element of the kind having an element manager arranged to control the element in response to messages from the control layer, the method comprising the steps of scanning the element manager to determine the location of data files, opening files so found and examining the respective headers thereof for field names, comparing field names with a predetermined list of field names to identify known types of fields and creating a knowledge file identifying the field locations. 
     The method may further include the steps of examining each field identified, obtaining numeric information from the fields and incorporating the numeric information in the knowledge file. Preferably the method includes identifying from the knowledge file entries relating to physical elements and transmitting to each such physical element at least one instruction to determine the correct format for the at least one instruction. 
     An interface created using the above methods may be incorporated in a translation table for use by a network control layer. 
     A communications network may be provided incorporating an interface created using the above method in particular in the network control layer thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A communications network of the type having an interface in accordance with the invention and a method of preparing such an interface will now be described by way of example only with reference to the accompanying drawing of which: 
     FIG. 1 is a block schematic diagram showing a typical OSI reference model telecommunications network; 
     FIG. 2 is a block schematic diagram showing the location of element managers within a telecommunications network; 
     FIG. 3 Shows the location of the interface of the invention with respect to the element manager of FIG. 2; 
     FIG. 4 shows an alternative implementation to that of FIG. 3; 
     FIG. 5 shows a first part of a knowledge frame used by the interface of the invention; 
     FIGS. 6 and 7 show respective sub-frames of the knowledge frame of FIG. 5; and 
     FIGS. 8 a  to  8   d  form a flow chart showing the software provided for use in creating the interface of the invention. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Referring first to FIG. 1, the open systems interconnection reference model (OSI) proposed by the International Standards Organisation (ISO) to promote network design compatibility is a seven layer design. Each layer may include sub-layers but fundamental to the proposal is that the terminal of a lower layer is compatible with (communicates with) the connection point of the higher layer and vice versa. Lower layers provide services to higher layers. Accordingly, the OSI digital communications network has a physical layer  1  which is responsible for the actual transfer of data bits to other physical layer  1  entities at other nodes. 
     The physical layer  1  activity is carried out on behalf of the data link layer  2  which arranges the transmission of data packets between nodes in response to requirements of the network layer  3  which provides for end-to-end transmission of data packets. 
     Above the network layer  3 , transport layer  4  provides end-to-end delivery of messages in response to a session layer  5  which sets up and manages end-to-end communications. 
     Presentation layer  6  formats and/or compresses data to be transferred while application layer  7  provides complete network services such as file transfer, electronic mail and the like. 
     The layers  1  to  7  of the OSI model are progressively more intelligent the higher up they are, but ultimately all rely upon the elements which make up the layers below and in particular the parts which effect and control the transfer of digital signals (whether representative of data or speech, video or graphics) in the physical to network layers  1 ,  2 ,  3 . 
     In a practical PSTN, layers  1  to  3  of nodes (A, B, C, D) are embedded in concentrators, switches, data processors and other physical communication means such as line cards for connection to lines to customer premises equipment which dictates the destination of each communication. 
     Now referring to FIG. 2, the physical layer  1  comprises elements such as line cards for connection to customers, multiplexers and other switches. The network layer  3  includes a network control layer  31  which includes element manager software  32  to allow communication between the network control layer  31  and the elements in the physical network. To select a path through the network and to cause an element to behave in a predictable manner the element manager software  32  must cause its respective element to respond in a predictable manner to an instruction from the network control  31 . 
     However, when a new element, say, a line card is provided in the system, unless it is identical to a removed element it must have a bespoke element manager  32  provided. 
     Referring also to FIG. 3, the present invention provides for an additional software layer, an intelligent interface  33 , to be located effectively between the network control layer  31  and each element manager  32 . Thus, regardless of the type of element manager  32  provided, the network control layer  31  uses a standard generic message for each task to be performed by the specified element. The interface  33  must therefore provide a translation between the control layer message and the element manager. 
     While “managers” of “managers” are known, (see for example “Integrated Network Management for Real-Time Operations” by Gary Tjaden and others, IEEE Network Magazine, March 1991, pages 10-15) these comprise translation tables manually prepared for each element manager required. The interface  33  of the present invention carries out this task with a minimum of operator intervention once an element is installed in the physical layer  1  and the corresponding element manager software  32  is provided in the network layer  3 . 
     The intelligent interface  33  is used by the operator to create a knowledge frame in relation to the specified hardware element which has been inserted. Knowledge frames are described by Marvin Minsky in “The Psychology of Computer Vision” edited by P H Winston, published in 1975, chapter 6 headed “A Framework for Representing Knowledge”. 
     In the present case, each type of element which the interface  33  may encounter could have a specified type of knowledge framework. The specific knowledge framework may be selected by the interface as part of its function during the course of scanning as hereinafter described. Alternatively, the installation operator can specify to the software of the intelligent interface  33  the kind of element which has been inserted thus limiting the requirement for software to establish the kind of framework required. 
     Referring now to FIG. 5, knowledge frames comprise data which fits particular situations. Each frame is made up of a hierarchy of nodes and relations, the higher level nodes being fixed and containing information which is always true in respect of the element represented by the frame. Lower level nodes have additional slots which are filled with data as more is learnt about the respective element manager. 
     Consider then a knowledge frame for a transmission element manager. For the software in the network control layer to function effectively allocation of hardware and the capacity of the hardware are required items. Thus, the transmission element manager framework  51  has a hardware data slot  52  and a capacity data slot  53 . In hardware  52 , for example, the hardware may be broken down into items for use in multiplexing  54 , control  55 , power  56  where in terms of capacity  53  traffic handling capability  57  or control information  58  are practical propositions. 
     Referring also to FIG. 6 the hardware frames can be further broken down, for example in multiplexed data the provided element could be line cards  61  or multiplex cards  62 , where the control comprises, for example, processing power  63 , data storage  64  and the power element  56  has specifically controller power supply data supply  65  and environmental information  66 . 
     Considering also FIG. 7, the possibility of using sub-frames rather than fixed data must be considered. Thus, for example the traffic element  57  of the capacity knowledge frame  53  may refer out to a sub-frame, for example, for asynchronous data such as an ATM network (asynchronous transfer mode) or for synchronous systems such as a time division multiplexed information. Thus, a sub-frame  71  for asynchronous data may define cell rate  73  and cell size  74  whilst a sub-frame for synchronous data  72  will refer to the number of streams  75 ,  76  and frame format  77  which the system is adapted to handle. For completeness it is noted that further frame data for control  58  includes channel associated information data  78  and non-channel specific data  79 , for example, to control remote hardware. 
     Referring additionally to FIGS. 8 a-d , the manner in which the knowledge frames of FIGS. 5 to  7  are filled by the intelligent interface  33  will now be described. The stages through which the intelligent interface proceeds may be defined as “look around”, “try and see”, “follow instructions” and “structured questioning”. Each of these stages will now be considered in turn. 
     Referring to FIG. 8 a , on installation of an element and its respective manager, the operator starts the intelligent interface software at  81  and inputs the system type at  82 . The interface establishes a link to the element manager at  83  and scans the element manager at  85  looking at lists, database records etc to search for data on commands used by the authors of the element manager. This is shown schematically as a search for directory structure  85  and, assuming that at least one database is found, at  86  the located file is opened at  87  and the header of the file is examined for the database structure. Also from the database structure and header the interface isolates field names within the database at  88  and compares these with known field names in its own dictionary at  89 . If a known field type is located then that field type and its location is stored in the knowledge frame at  91  and further investigation of the database continues in FIG. 8 b . However, if at  89  an apparent field name does not coincide with a known field name from the internal dictionary, then a query is stored for subsequent output to the man machine interface at  92  and further fields within the same database are checked. 
     Assuming that one or more correct field names are isolated and the knowledge frame updated with the location of those fields at  91 . Then, turning now to FIG. 8 b , the look around stage continues with the interface causing the database to open at  94  to examine fields for entries. Each entry located at  95  is compared with an appropriate sub-dictionary for valid field entries to determine whether a match occurs  96 . Again if there is no match a query is raised for the man machine interface at  98  and further fields are examined  99 . 
     Again if at  97  a match is determined between a current field entry and the sub-dictionary then the knowledge frame is updated with the relevant information at  100 . Using the numeric limits “highest” “lowest” attained from the field entries the knowledge frame is updated with the terminal range noted at  102 . If there are further fields to examine within the database then the procedure continues until all of the fields of an identified database have been checked using the procedure of steps  94  to  102 . Assuming that all of the fields of a particular database have been checked then the procedure recommences at step  84  of FIG. 8 a  for any other databases found. 
     Once all of the databases apparently present in the element manager have been identified and field entries checked then the software interface proceeds to the next stage at FIG. 8 c.    
     In the try and see stage, the interface  33  identifies from the knowledge gathered in the knowledge frame of FIG.  5  and FIG. 6 the entries which define hardware  105 , for example, a line card. From the dictionary, having identified the hardware, certain parameters such as on/off or other recognisable physical actions related to the hardware are identified at  106 . Using commands that the element manager might expect from a network control sequence, for example a standard enable message  107 , the interface  33  forwards a signal to try and effect one of these actions. The hardware will respond in some way, either with an acknowledge message indicating that the function has been carried out, with another message indicating a failure, for example message not understood, or with a message perhaps indicating that the parameters are out of range. 
     If the hardware response indicates that the message has been successful then the message format is stored at  111  and the same function is carried out for other hardware entries held in the knowledge frame in respect of the particular element manager. 
     Should no response or a fail response be received from the hardware, then a further different format will be tried at  110  until such time as a success is received. 
     Having completed steps  105  to  111  for each piece of identified hardware, the interface  33  checks for further operational parameters within the data entries at  113  and repeats steps  105  to  12  in respect of those parameters. At step  114 , the steps of  105  to  112  may be repeated for parameters which are stored in the dictionary area of the interface  33  rather than being stored in the data entries of the element manager. 
     Having ascertained the format for commands using try and see the interface  33  updates the knowledge frame in respect of the particular element manager at  115  and proceeds to a follow instructions stage. This stage shown in FIG. 8 d  comprises searching the element manager database for a “new command” file. If such a file is located, then each of these commands is tried in turn and the knowledge frame updated accordingly. Thus, if the element manager author indicates through a standard language such as ASN1 that additional functionality has been provided in the element, then testing of the functionality and updating of the knowledge frame occurs at steps  116  to  119 . 
     Then, in the structured questioning section, the interface opens its own questions file which contains specific pre-specified commands or queries to which the author of the element manager software will have been expected to provide standard answers. The answers to these questions will provide further information to enable updating of the knowledge frame at step  121  to  123 . 
     Finally, at step  124 , the interface  33  checks for any absence of data within the knowledge frame or for any conflict between data held therein. Any inconsistency may be passed to the man machine interface at step  125  along with other queries which have been raised in previous stages of the installation. 
     Operator responses to queries on the man-machine interface complete the task of creating an appropriate translation between the network control layer message structure and the element manager structure. 
     Whilst the interface software is shown as being in permanent communication between the network control layer  31  and the element manager  32  (in FIG. 3) it will be appreciated that effectively the intelligent interface  33  automatically creates a translation table between messages output as standard by the network control system of the PSTN operator and the element manager software provided by the manufacturer. 
     Using the various responses from the element manager, such as “I do not understand” where a message does not make sense or “I cannot do that” responses where an acceptable message has been received but the appropriate equipment is not present a translation table can be built. In most cases, as shown in FIG. 4, the interface  33  may simply create a translation table  35  which sits between the network control layer  31  and the element manager  32  to provide the functionality required.