Abstract:
A digital telecommunications system, a method of reconnecting branches to a softswitch in a communications network and a program product for reconnecting branches to a softswitch in a communications network. A softswitch manages communications between devices at network endpoints, e.g., session initiation protocol (SIP) devices. When a branch is disconnected from the softswitch, the softswitch manages reconnects, prioritizing reconnects when multiple branches request reconnecting.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present invention is a continuation of Provisional U.S. Patent Application No. 61/002,913, entitled “METHOD FOR TAGGING SIP CONTACT HEADERS WHILE PRESERVING THE CONTACT HEADER FORMAT TOWARDS SOFTSWITCHES” to Johannes Ruetschi et al., filed Nov. 13, 2007 assigned to the assignee of the present invention and is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to connectivity recovery in digital communications and telecommunications systems and networks and more particularly, to managing the system/network load during connectivity in digital communications and telecommunications systems and networks. 
     2. Background Description 
     State of the art telecommunication systems are digital and, frequently, use Internet Protocol (IP) based communications. A typical such system may include softswitch located in a data center that can provide communication services to many branches or sites. The cites may be each connected to the softswitch through a high speed data connection, e.g., through a typical broadband network connection. Typically when a branch looses connectivity to the data center, a local proxy can provide a reduced set of communication features for the branch. Later, when the communications are restored between the branch and the data center, it may be necessary for branch devices to update registrations and subscriptions (e.g. to message summary events and/or line state events). Updates for a single branch may not degrade network performance. If, however, a large number of branches simultaneously recover connectivity to the data center, the simultaneous subscription and registration requests may flood the data center, forcing it into an overload state. Consequently, system communications may slow or even be non-existent during such an overload. 
     Thus, there is a need for preventing overloads in telecommunications network softswitches when a number of branches simultaneously recover connectivity to the softswitch. 
     SUMMARY OF THE INVENTION 
     It is a purpose of the invention to reduce overloads in telecommunications network softswitches; 
     It is another purpose of the invention to minimize the occurrence of overloads in telecommunications network softswitches when a number of branches simultaneously recover connectivity to the softswitch; 
     It is yet another purpose of the invention to prioritize connectivity recovery for a telecommunications network to minimize the occurrence of overloads in a network softswitch when a number of branches simultaneously recover connectivity to the softswitch; 
     It is yet another purpose of the invention to prioritize connectivity recovery for a telecommunications network to minimize the occurrence of overloads in a network softswitch when a number of branches simultaneously recover connectivity to the softswitch, giving priority to branches of higher importance or for branches with larger numbers of users. 
     The present invention relates to a digital telecommunications system, a method of reconnecting branches to a softswitch in a communications network and a program product for reconnecting branches to a softswitch in a communications network. A softswitch manages communications between devices at network endpoints, e.g., session initiation protocol (SIP) devices. When a branch is disconnected from the softswitch, the softswitch manages reconnects, prioritizing reconnects when multiple branches request reconnecting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of a preferred embodiment of the invention with reference to the drawings, in which: 
         FIG. 1  shows a simple example of a preferred system/network according to a preferred embodiment of the present invention; 
         FIG. 2  shows an example of a suitable SIP header; 
         FIG. 3  shows an example of steps  140  in determining the softswitch  118  reply to each proxy. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning now to the drawings and more particularly,  FIG. 1  shows a simple example of a preferred system/network, e.g., an Internet Protocol (IP) communications system/digital call capable network  100  according to a preferred embodiment of the present invention. In this example, the system includes 3 branches  102 ,  104 ,  106 , each with devices  108  at End Points (EP). Preferably, the EP devices  108  are typical digital telephony devices (e.g., VoIP phones) and Multimedia Terminal Adapters (MTA), e.g., keysets or session initiation protocol (SIP) phones. Since a network device defines an EP, each EP and a device(s) at the EP are referred to herein interchangeably. The branches  102 ,  104 ,  106  are networked over a suitable data network  110 , e.g., a broadband network, wide area network (WAN), or local area network (LAN). Trunks  112 ,  114 ,  116  connect a respective branch  102 ,  104 ,  106  to the data network  110 . A preferred softswitch  118 , e.g., in a general purpose computer, PC or server, in main office  120  manages network communications and is connected to the branches  102 ,  104 ,  106  through the data network  110 . Each branch  102 ,  104 ,  106  includes a survivable proxy  122 ,  124 ,  126  that provides the respective branch  102 ,  104 ,  106  with a reduced set of communication features, in the event that connection to the softswitch  118  is lost or if, for example the softswitch fails. 
     It is understood that this network is an example only and not intended as a limitation. The present invention has application to any digital telecommunications system or network with multiple branches connected to a softswitch providing communication services. Further, each branch may have any suitable number of endpoints with endpoint devices. However, for purposes of this simple example, one branch  102  (Branch A) may be a headquarters site with 6 users (each at one of 6 devices  108 ), branch  104  (Branch B) is a remote office with 4 users (each at one of 4 devices  108 ), and branch  106  (Branch C) is regional site with 5 users (each at one of 5 devices  108 ). For this example it is assumed that each device sends one subscription request for each device to register with the softswitch  118 . The softswitch  118  of this example has the capacity to process 2 requests per second and to queue up to 12 requests. 
     Even with a network error that isolates all branches from the data center, each survivability proxy  122 ,  124 ,  126  can still provide basic services in the respective branches  102 ,  104 ,  106 . While the branches  102 ,  104 ,  106  are isolated, each proxy  122 ,  124 ,  126  polls the softswitch  118  with SIP OPTIONS messages, trying to re-establish connectivity with the softswitch  118 . When the softswitch  118  responds to the OPTIONS message with a positive acknowledgement, the respective proxy  122 ,  124 ,  126  returns to normal mode and routes subscriptions and registrations for state synchronization to the softswitch  118 . According to a preferred embodiment of the present invention, the softswitch  118  avoids receiving subscription request for all devices in all branches simultaneously by selectively acknowledging the OPTIONS message if is contains specific information, e.g., in a SIP header. 
       FIG. 2  shows an example of a suitable SIP header  130 . In particular, acknowledgement may be given priority based on proxy state  132 , branch priority  134  and the number  136  of branch users. The proxy state  132 , for example, may be normal mode, backup mode or survivable mode. Branch priority  134  may be a value Q between 0 and 1. The number  136  of branch users may be the number of registered users in the branch  102 ,  104 ,  106 . 
       FIG. 3  shows an example of steps  140  in determining the softswitch  118  reply to each proxy  122 ,  124 ,  126 . First, in step  142 , the softswitch  118  determines if a request indicates that the particular proxy is in normal mode  122 ,  124 ,  126 . If so, then in step  144  the softswitch  118  positively acknowledges the message to keep the proxy  122 ,  124 ,  126  from entering survivable mode. Otherwise, in step  146 , the softswitch  118  determines if the request indicates that the proxy  122 ,  124 ,  126  is in survivable mode. If so, then in step  148  the softswitch  118  checks whether the transaction queue size (Q)+the number expected messages (for this example: registration count*number of subscriptions per device) is below a high level watermark (WM), e.g., 10. This has the form:
 
(registration-count*messages-per-device)+transaction-queue-size&lt;high-level-watermark.
 
If so, then in step  144  the softswitch  118  acknowledges the message. Otherwise, in step  150  the softswitch  118  determines whether more then one message is in the queue. If not, in step  152 , the softswitch  118  processes the sole message. Otherwise, in step  154 , the softswitch  118  selects the message with the highest Q value and in step  152  processes it first.
 
     Advantageously, the present invention prevents overloads in the telecommunications system softswitch when a number of branches simultaneously recover connectivity to the softswitch. Further, by prioritize connectivity recovery for a telecommunications network the occurrence of overloads in a network softswitch are minimized even when a large number of branches simultaneously recover connectivity to the softswitch. The softswitch efficiently manages recovery, giving priority to branches of higher importance or for branches with larger numbers of users. 
     While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims. It is intended that all such variations and modifications fall within the scope of the appended claims. Examples and drawings are, accordingly, to be regarded as illustrative rather than restrictive.