Abstract:
A distributed Internet Protocol communications network comprises a central control system comprising control processing means and at least one access point remote from the central control system for providing access to the packet based communications network. Under normal operating conditions the at least one access point is controlled by the control processing means. The network also comprises an emergency processing distinct from the central control system for controlling the at least one access point when there is a failure in the control processing means control of the at least one access point.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2005/008943, filed Aug. 18, 2005 and claims the benefit thereof. The International Application claims the benefits of Great Britain application No. 0422005.9 GB filed Oct. 5, 2004, both of the applications are incorporated by reference herein in their entirety. 
     FIELD OF INVENTION 
     The present invention relates to a communications network. 
     BACKGROUND OF INVENTION 
     In the past, large companies having a corporate headquarters and multiple branch offices have tended to operate independent self-contained telecommunication systems at each of the branches and at the headquarters. Naturally, these independent systems would be networked together. The administrative effort and the costs involved in running such multiple independent systems was high. 
     More recently, by using Internet Protocol (IP) internetworking between the headquarters and the various branches, it has been possible to relocate parts of the headquarters central system into the branches, whilst retaining a single point of control at the headquarters. 
     SUMMARY OF INVENTION 
     Systems based on the HiPath 4000 IP Distributed Architecture, provided by Siemens AG, are examples of such IP internetworked systems. An example of a HiPath 4000 IP Distributed Architecture system is shown schematically in  FIG. 1 . 
     Telecommunication system  1  comprises a first Local Area Network (LAN)  2  located at a company&#39;s headquarters, a second LAN  3  located at a first branch office (not shown), a third LAN  4  located at a second branch office (not shown) and a fourth LAN  5  located at a third branch office (not shown). The first LAN  2  is connected to a first router  6 , the second LAN  3  to a second router  7 , the third LAN  4  to a third router  8  and the fourth LAN  5  to a fourth router  9 . These routers connect the LANs via a Wide Area Network (WAN)  10 . 
     A first access point  11  connects to the first Lan  2 , a second access point  12  connects to the second LAN  3 , a third access point  13  connects to the third LAN  4  and fourth  14  and fifth  15  access points connect to the fourth LAN  5 . These access points  11  to  15  allow the connection of client terminals (not shown) to the LANs  2  to  5  and hence to the WAN  10 . In a typical HiPath 4000 system the client terminals may either be traditional Time Division Multiplexed (TDM) devices, for example standard telephones or cordless telephones, or IP devices, for example IP telephones. 
     A central control system  16  connects to the first LAN  2  at the headquarters (not shown) and is responsible for controlling the operation of each of the access points  11  to  15 . 
     Each of the access points  11  to  15  comprises a respective gateway card  11   a  to  15   a  and a plurality of peripheral cards  11   b  to  15   b . The peripheral cards  11   b  to  15   b  provide multiple peripheral ports for connection to client terminals, for example phones and/or trunk lines. The gateway cards  11   a  to  15   a  are the controllers of the IP based Access Point. Each of the cards  11   a  to  15   a  acts as a gateway between the LAN on one side of the card, and the client terminals on the other side of the card, converting payload data (e.g. voice data, fax data and ISDN-data) from TDM data to IP data and vice versa. Each of the cards  11   a  to  15   a  provides a local TDM switching matrix, conference units and tone generators. Each of the gateway cards  11   a  to  15   a  may be Siemens&#39; HG 3575 cards. 
     The central control system  16  comprises a plurality of gateway cards  16   a , a plurality of peripheral cards  16   b , an administration and data processor  16   c , a common control processor  16   d  and a back up common control processor  16   e.    
     Again, the plurality of peripheral cards  16   b  provide multiple peripheral ports for connection to client terminals, for example phones and/or trunk lines. The gateways  16   a  translate payload data (voice/fax/ISDN-data) from TDM data on the client terminal side of the gateways to IP data on the LAN side of the gateways and vice versa. These gateways are used for connections between the IP based access points  11  to  15  and the central system  16 . These cards  16   a  may be Siemens&#39; HG 3570 cards. 
     The Administration and Data Processor  16   c  runs administrative software and applications, whilst the common control processor  16   d  runs call processing software. The back up common control processor  16   e  provides a back up to the common control processor  16   d  and in the event of the failure of the common control processor  16   d , it can be switched into use without interrupting active calls. 
     The access points are controlled by the common control processor  16   d . Every activity of the peripheral cards, for example, tones or displays at the phones and signaling messages at trunk interfaces are controlled by the common control processor  16   d  via a control link over the IP network. A complete set of administrative parameters in a database (not shown) in the central system  16  is kept in the memory of the control processor  16   d . A persistent copy of the database is kept on hard disc which is controlled by the administration and data processor  16   c.    
     Such systems have reduced administrative outlay but an increased dependence on the availability of the network and of the central system. If the central control fails, no further telecommunication is possible—in the corporate HQ or in the branches. A very high availability of the central control is achieved by duplicating the control processors. 
     As illustrated in  FIG. 2 , in order to maintain control of access points upon failure of the WAN  10 , a modem connection may be established between the central system  16  and some or all of the access points. In  FIG. 2 , a connection between the central system  16  and the third access point  13 , the fourth access point  14  and the fifth access point  15  is made through the Public Switched Telephone Network (PSTN)  17  via a router  18  connected to the LAN  2  and a first modem  19  connected to the gateway  13   a , a second modem  20  connected to the gateway  14   a  and a third modem  21  connected to the gateway  15   a . Access points without modem connections, in this example, the second access point  12 , go out of service when their WAN connections fail. However, even back up systems such as this are useless in the event of total failure of the central system brought on by a catastrophe such as flooding or destruction of the building. 
     Embodiments of the present invention aim to alleviate the above described problems. 
     According to the present invention there is provided a distributed packet based communications network comprising: a central control system comprising control processing means; at least one access point remote from the central control system, the at least one access point for providing access to the packet based communications network, wherein under normal operating conditions the at least one access point is controlled by the control processing means; and emergency processing means distinct from the central control, system for controlling the at least one access point when there is a failure in the control processing means control of the at least one access point. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and further features of the invention are set forth in the claims and together with advantages thereof will become clearer from consideration of the following detailed description of an exemplary embodiment of the invention given with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a communication system and has already been described; 
         FIG. 2  illustrates a communication system and has already been described; 
         FIG. 3  illustrates a communications system embodying the present invention. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Referring now to  FIG. 3  of the drawings, in which identical features as those illustrated in  FIG. 1  are given like reference numerals, a communications system  100  embodies the present invention. 
     Under normal operating conditions the communications system  100  functions identically to the system  1  illustrated in  FIG. 1 . That is to say, the four access points  11  to  15  are all operated under the central control of the central system  16 . 
     The system  100  is provided with an emergency de-centralised control system for controlling access points in the event of the failure of the IP network linking access points and the central system  16  or if the central system  16  is not actually available. To this end, the first access point  11 , the third access point  13  and the fourth access point  14  are provided with their own emergency control processors labelled  11   c ,  13   c  and  14   c  respectively. 
     Each of the emergency control processors  11   c ,  13   c  and  14   c  offer the same functionality as the central control. 
     They possess the same software, the same patch status (i.e. software corrections applied to the system while running) and identical configuration data as do the administration and data processor  16   c  and the common control processor  16   d  of the central system  16 . Groups of access points are assigned to emergency control groups, each emergency control group comprising one of the emergency control processors  11   c ,  13   c  and  14   c . In the system  100 , the first access point  11  and the second access point  12  makeup a first emergency control group, the third access point  13  makes up a second emergency control group and, the fourth access point  14  and fifth access point  15  make up a third emergency control group. Each of the emergency control processors  11   c ,  13   c  and  14   c  is in contact with the gateway cards in its respective emergency group. Thus, if an access point of an emergency group loses contact with the central system the emergency processor of that group may take control of the access point. 
     A mechanism is provided for keeping the software status and the configuration data of the emergency control processors identical to that of the central system  16 . 
     A backup server  22  is connected to the WAN  10 , and in order to save on transmission bandwidth the software the software and database of the central system  16  is transmitted periodically, for example each day, to the backup server  22 . This backup server  22  is as a general rule a separate device from the central system  16  and the emergency control processors  11   c ,  13   c  and  14   c . The central system  16  and all the emergency control processors  11   c ,  13   c  and  14   c  have access via the IP network  10  to the backup server  22 . The emergency control processors  11   c ,  13   c  and  14   c  check cyclically whether updated data is present on the server  22  and download it where necessary. Thus each emergency control processor maintains an identical database to that at the central control. In an emergency the emergency control processors  11   c ,  13   c  and  14   c  can thus behave in exactly the same way as the central system processors. 
     A fault occurs when an access point can no longer be served by the central control  16 . If an access point gateway card detects a problem with the signalling connection between the access point of that card and the central system  16 , it reports that fact to the emergency processor of the emergency group to which the access point belongs. The emergency processor decides according to preconfigured rules whether to take over control of the access point or not. In one embodiment, each access point in an emergency group is assigned a weight value of between zero and one, and when the total weight value of all access points in the emergency group that have lost connection with the central system  16  equals or exceeds a predefined threshold, the emergency processor of the group takes over control of those access points. So for example, in an emergency group comprising three access points each having a weight value of 0.5 and wherein the threshold is 1, it is only when at least two access points have reported a central system connection failure that the emergency processor steps in and assumes control of those access points. Naturally, an individual access point of particular importance, for example an access point serving the telephones of senior managers, may be assigned a weight value equal to the threshold value so that if this access point loses connection with the central system, an emergency processor immediately assumes control of it. 
     In alternative embodiment, the access points in an emergency group may be configured to be taken over individually by the group&#39;s emergency processor as and when an access point loses contact with the central system  16 . 
     Naturally, the access points may be configured so that an immediate hand over to an emergency processor may be ordered by the system administrator. 
     In a preferred embodiment, to take over control of an access point, the emergency processor instructs the gateway card of the access point to restart and to start up with the emergency processor. 
     If the central system  16  succeeds in re-establishing a control connection to an Access Point in emergency operation, the access point remains under the control of the emergency processor but notifies it that it has re-established contact with the central system  16 . The emergency processor decides in accordance with pre-defined rules whether and when emergency operation can be ended. 
     For example, emergency control may be ended only if every access point in an emergency group has had a stable connection with the central system  16  for a configurable pre-determined time period. Emergency control may only be ended at configurable pre-defined times of the day. The system may be configured so that a system administrator may order the end of emergency control. 
     To end emergency control of an access point, the emergency control processor instructs the gateway card of the access point to do a restart and to start up under the control of the central system  16 . 
     Having thus described the present invention by reference to preferred embodiments it is to be well understood that the embodiments in question are exemplary only and that modifications and variations such as will occur to those possessed of appropriate knowledge and skills may be made without departure from the scope of the invention as set forth in the claims.