Geographic redundancy for call servers in a cellular system based on a bearer-independent core network

Abstract

In a bearer-independent core network, the switching and transport of the bearer streams is separated from the processing of call sessions that control the bearer streams. The switching and transport of the bearer streams is executed by media gateways and packet switches in the switching and transport layer of the network. The processing of calls sessions that control the bearer streams is executed by call servers in the call control layer of the network. The switching and transport layer of the network may be implemented using ATM or IP technology. In order to redirect the signaling links to a backup call server, a signaling gateway is used. Each media gateway includes a signaling gateway function. The signaling gateways redirect the signaling links by encapsulating each signaling message in a new packet in one embodiment.

What is claimed is: 
     
         1 . A method of transferring communication session control from a first server controlling a first communication session to at least one backup server, the method comprising:
 storing information identifying at least one backup server for the first server;   monitoring the first server to determine whether the first server should continue to control the first communication session;   determining that the first server should no longer control the first communication session;   responsive to determining that the first server should no longer control the first communication session, forwarding signaling from a signaling gateway to the at least one backup server by addressing signaling associated with the first communication session to at least one backup server of the at least one backup server based on the stored information;   replicating respective data of the first server associated with respective communication sessions controlled by the first server in the at least one respective backup server based on the stored information; and   designating as active the respective replicated data in the at least one respective backup server.   
     
     
         2 . The method of  claim 1 , further comprising designating as inactive the replicated data in the at least one backup server when the first server hosting is in an active state. 
     
     
         3 . The method of  claim 1 , wherein storing information identifying the at least one backup server for the first server comprises storing the information identifying at least one backup server in a table identifying the at least one backup server as a backup server for the first server. 
     
     
         4 . The method of  claim 1 , wherein:
 monitoring the first server to determine whether the first server should continue to control the first communication session comprises monitoring the first server to determine an active state or an inactive state of the first server; and   determining that the first server should no longer control the first communication session comprises determining an inactive state for the first server.   
     
     
         5 . The method of  claim 4 , wherein monitoring the first server to determine an active or inactive state of the first server comprises monitoring the first server for a heartbeat signal. 
     
     
         6 . The method of  claim 5 , wherein monitoring the first server for a heartbeat signal comprises monitoring for a heartbeat signal of the first server at the signaling gateway. 
     
     
         7 . The method of  claim 4 , wherein determining the inactive state for the first server comprises determining loss of heartbeat from the first server. 
     
     
         8 . The method of  claim 1 , wherein:
 the at least one backup server comprises a plurality of backup servers; and   forwarding signaling from the signaling gateway to the at least one backup server comprises forwarding signaling associated with some communication sessions controlled by the first server from the signaling gateway to one backup server and forwarding signaling associated with other communication sessions controlled by the first server from the signaling gateway to another backup server.   
     
     
         9 . The method of  claim 1 , wherein the first server also serves as a backup server and the at least one backup server also serves as a primary server. 
     
     
         10 . The method of  claim 1 , wherein:
 the signaling gateway is one of plurality of signaling gateways connected in a ring; and   each signaling gateway has a primary signaling path to a respective primary server and at least one backup signaling path to at least one respective backup server.   
     
     
         11 . The method of  claim 1 , wherein:
 forwarding signaling from the signaling gateway to the at least one backup server comprises forwarding signaling associated with at least one communication sessions which has been at least partially established; and   replicating data of the first server in the at least one backup server comprises replicating communication session context information associated with at least one communications session for which signaling is to be forwarded to the at least one backup server.   
     
     
         12 . The method of  claim 1 , wherein addressing the signaling to the at least one backup server based on the stored information comprises mapping an address of the first server in the signaling to at least one address of at least one backup server. 
     
     
         13 . The method of  claim 1 , wherein addressing the signaling to the at least one backup server based on the stored information comprises encapsulating the signaling with at least one address of at least one backup server. 
     
     
         14 . The method of  claim 1 , wherein the respective data of the first call server that is replicated for respective communication sessions controlled by the first server comprises SS7 point codes. 
     
     
         15 . The method of  claim 1 , wherein the respective data of the first call server that is replicated for respective communication sessions controlled by the first server comprises at least one of:
 translation data for routing communication sessions;   integrated services digital network user part (ISUP) routes;   location area codes;   media gateway inventory with an indication of active/inactive status; and   signaling gateway inventory with an indication of active/inactive status.   
     
     
         16 . A system for transferring communication session control from a first server controlling a first communication session to at least one backup server, the system comprising:
 the first server;   at least one signaling gateway configured:
 to store information identifying at least one backup server for the first server; 
 to monitor the first server to determine whether the first server should continue to control the first communication session; 
 to determine that the first server should no longer control the first communication session; and 
 responsive to determining that the first server should no longer control the first communication session, to forward signaling to the at least one backup server by addressing the signaling associated with communication sessions served by the first server to the at least one backup server based on the stored information; and 
   at least one backup server configured:
 to receive signaling forwarded from the at least one signaling gateway; 
 to replicate data of the first server associated with at least one communication session controlled by the first server based on the stored information; and 
 to designate as active the replicated data when it has been determined that the first server should no longer control the first communication session. 
   
     
     
         17 . The system of  claim 16 , wherein the at least one backup server is further configured to designate as inactive the replicated data in the at least one backup server when the first server is in an active state. 
     
     
         18 . The system of  claim 16 , wherein the at least one signaling gateway is further configured to store the information identifying at least one backup server in a table identifying the at least one backup server for the first server. 
     
     
         19 . The system of  claim 16 , wherein the at least one signaling gateway is further configured to:
 monitor the first server to determine whether the first server should continue to control the first communication session by monitoring the first server to determine an active state or an inactive state of the first server; and   determine that the first server should no longer control the first communication session by determining an inactive state for the first server.   
     
     
         20 . The system of  claim 19 , wherein the at least one signaling gateway is further configured to monitor the first server to determine one of an active state and an inactive state of the first server by monitoring the first server for a heartbeat signal. 
     
     
         21 . The system of  claim 20 , wherein the at least one signaling gateway is further configured to monitor the first server for a heartbeat signal by monitoring for a heartbeat signal of the first server at the signaling gateway. 
     
     
         22 . The system of  claim 19 , wherein the at least one signaling gateway is further configured to determine the inactive state for the first server by determining loss of heartbeat from the first server. 
     
     
         23 . The system of  claim 16 , wherein the first server also serves as a backup server and the at least one backup server also serves as a primary server. 
     
     
         24 . The system of  claim 16 , wherein:
 the at least one backup server comprises a plurality of backup servers; and   the at least one signaling gateway is configured to forward signaling to the at least one backup server by forwarding signaling associated with some communication sessions controlled by the first server from the signaling gateway to one backup server and forwarding signaling associated with other communication sessions controlled by the first server from the signaling gateway to another backup server.   
     
     
         25 . The system of  claim 16 , wherein:
 the signaling gateway is one of plurality of signaling gateways connected in a ring; and   each signaling gateway has a primary signaling path to a respective primary server and at least one backup signaling path to at least one respective backup server.   
     
     
         26 . The system of  claim 16 , wherein:
 the at least one signaling gateway is further configured to forward signaling to the at least one backup server by forwarding signaling associated with communication sessions which have been at least partially established; and   the at least one backup server is further configured to replicate data of the first server in the at least one backup server by replicating communication session context information associated with communications sessions for which signaling is to be forwarded to the at least one backup server.   
     
     
         27 . The system of  claim 16 , wherein the at least one signaling gateway is further configured to address the signaling to the at least one backup server based on the stored information by mapping an address of the first server in the signaling to at least one address of at least one backup server. 
     
     
         28 . The system of  claim 16 , wherein the at least on signaling gateway is further configured to address the signaling to the at least one backup server based on the stored information by encapsulating the signaling with at least one address of at least one backup server. 
     
     
         29 . The system of  claim 16 , wherein the respective data of the first server that is replicated for respective communication sessions controlled by the first server comprises SS7 point codes. 
     
     
         30 . The system of  claim 16 , wherein the respective data of the first server that is replicated for respective communication sessions controlled by the first server comprises at least one of:
 translation data for routing communication sessions;   integrated services digital network user part (ISUP) routes;   location area codes;   media gateway inventory with an indication of active/inactive status; and   signaling gateway inventory with an indication of active/inactive status.