# Patent

## Title
System and method for distributed call processing using load sharing groups

## Abstract

A switch for handling call connections between calling devices and called devices on trunk lines of the switch. The switch comprises a main processing unit for executing call process client applications. Each call process client applications is associated with a call connections. The switch also comprises N call application nodes for executing call process server applications. A first call process server application executed on a first call application node is associated with a similar second call process server application executed on a separate second call application node. The first and second call process server applications form a first load sharing group server application. Each call process client application sends a call process service request to the first load sharing group server application, which selects one of the first and second call process server applications to perform the requested call process service according to a load distribution algorithm.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present invention is related to those disclosed in the following United States Non-Provisional Patent Applications:

    1) U.S. patent application Ser. No. 10/039,186 filed concurrently herewith, entitled “SYSTEM AND METHOD FOR DISTRIBUTED CALL PROCESSING USING A DISTRIBUTED TRUNK IDLE LIST”;
    2) U.S. patent application Ser. No. 10/038,872 filed concurrently herewith, entitled “DISTRIBUTED IDENTITY SERVER FOR USE IN A TELECOMMUNICATION SWITCH”;
    3) U.S. patent application Ser. No. 10/038,879 filed concurrently herewith, entitled “SYSTEM AND METHOD FOR PROVIDING A SUBSCRIBER DATABASE USING GROUP SERVICES IN A TELECOMMUNICATION SYSTEM.”


The above applications are commonly assigned to the assignee of the present invention. The disclosures of these related patent applications are hereby incorporated by reference for all purposes as if fully set forth herein.


TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to telecommunication systems and, more specifically, to a telecommunication system that uses group services to distribute call processing functions and call traffic in a telecommunication switch.
BACKGROUND OF THE INVENTION
Wireless service providers continually try to create new markets and to expand existing markets for wireless services and equipment. One important way to accomplish this is to improve the performance of wireless network equipment while making the equipment cheaper and more reliable. Doing this allows wireless service providers to reduce infrastructure and operating costs while maintaining or even increasing the capacity of their wireless networks. At the same time, the service providers are attempting to improve the quality of wireless service and increase the quantity of services available to the end-user.
The mobile switching of a wireless network provides connections between a number of wireless network base stations and the public switched telephone network. Calls originated by or terminated at a cell phone or other mobile station are handled in the mobile station by a number of call processing client applications. A conventional mobile station typically contains a large switching fabric controlled by a main processing unit (MPU) that contains a large number of data processors and associated memories, often in the form of ASIC chips. Each of these MPU processors contains a call process client application for controlling the flow of control signals of a single call. Each call process client application in turn communicates with a call process server application that controls the flow of control signals for a large number of calls.
Thus, when a particular event occurs during a phone call (e.g., the call set-up, the invocation of three-way calling, call disconnection, or the like), control signals associated with the event are relayed from the mobile station to the call process client application in the mobile switching center (MSC). This call processing client application then relays the control signals to the call process server application, which actually performs the call processing service requested by the control signals.
Unfortunately, in large capacity systems, bottlenecks may develop around the call process server applications. Each call process client application must communicate with a particular piece of server hardware that is executing the call process server application. Due to the random nature of the start and stop of phone calls, in large systems, some servers may be near capacity and develop bottlenecks, while other servers still have plenty of adequate bandwidth. Moreover, a system failure in a particular piece of server hardware results in the loss of all call processes being handled by a call process server application being executed on the failed server.
Therefore, there is a need for improved wireless network equipment and services. In particular, there is a need for mobile switching centers that are highly reliable and minimally susceptible to bottleneck conditions during periods of high call traffic volume. More particularly, there is a need for a distributed call processing architecture for use in mobile switching centers and other similar switching devices.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a switch capable of handling call connections between calling devices and called devices on a plurality of trunk lines associated with the switch. According to an advantageous embodiment of the present invention, the switch comprises: 1) a main processing unit capable of executing call process client applications, wherein each of the call process client applications is associated with one of the call connections; and 2) N call application nodes capable of executing call process server applications, wherein a first call process server application is executed on a first one of the N call application nodes and is associated with a similar second call process server application executed on a second one of the N call application nodes separate from the first call application node, the first and second call process server applications thereby forming a first load sharing group server application, wherein the each call process client application sends a call process service request to the first load sharing group server application and the first load sharing group server application selects one of the first and second call process server applications to perform the requested call process service according to a load distribution algorithm.
According to one embodiment of the present invention, the load distribution algorithm distributes new call process services requests in an alternating manner between the first and second call process server applications.
According to another embodiment of the present invention, the load distribution algorithm distributes new call process service requests according to a current call process load of the first call process server application and a current call process load of the second call process server application.
According to still another embodiment of the present invention, the load distribution algorithm distributes the new call process service requests in order to maintain the current call process load of the first call process server application at a level substantially equal to the current call process load of the second call process server application.
According to yet another embodiment of the present invention, the first call process server application comprises a first primary-backup group server application, wherein the first primary-backup group server application comprises a first primary call process executed on the first call application node and a first backup call process associated with the first primary call process.
According to a further embodiment of the present invention, state information associated with the first primary call process is mirrored to the first backup call process associated with the first primary call process.
According to a still further embodiment of the present invention, the first backup call process resides on the first call application node.
According to a yet further embodiment of the present invention, the first backup call process resides on a call application node separate from the first call application node.
In one embodiment of the present invention, the second call process server application comprises a second primary-backup group server application, wherein the second primary-backup group server application comprises a second primary call process executed on the second call application node and a second backup call process associated with the second primary call process.
In another embodiment of the present invention, state information associated with the second primary call process is mirrored to the second backup call process associated with the second primary call process.
In yet another embodiment of the present invention, the second backup call process resides on the second call application node.
In still another embodiment of the present invention, the second backup call process resides on a call application node separate from the second call application node.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.



BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, wherein like numbers designate like objects, and in which:
FIG. 1 illustrates an exemplary wireless network according to one embodiment of the present invention;
FIG. 2 illustrates an exemplary mobile switching center in greater detail according to one embodiment of the present invention;
FIG. 3 illustrates selected portions of a mobile switching center that perform distributed call processing using group services according to the principles of the present invention;
FIG. 4A is an illustration of server side internal group policy classes according to an exemplary embodiment of the present invention;
FIG. 4B is an illustration of a client side internal client policy architecture according to an exemplary embodiment of the present invention; and
FIG. 4C is an illustration of a load sharing client side policy internal architecture according to an exemplary embodiment of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
FIGS. 1 through 4, discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be implemented in any suitably arranged telecommunications network.
In the disclosure that follows, a group services framework for performing various distributed call processing functions is implemented in a mobile switching center of a wireless communication network. This is by way of illustration only and should not be construed so as to limit the scope of the invention. Those skilled in the art will understand that the group services framework descried below may be implemented in other types of telecommunication devices, including many varieties of switches, routers and the like.
FIG. 1 illustrates exemplary wireless network 100 according to one embodiment of the present invention. Wireless network 100 comprises a plurality of cell sites 121-123, each containing one of the base stations, BS 101, BS 102, or BS 103. Base stations 101-103 communicate with a plurality of mobile stations (MS) 111-114 over, for example, code division multiple access (CDMA) channels. Mobile stations 111-114 may be any suitable wireless devices, including conventional cellular radiotelephones, PCS handset devices, personal digital assistants, portable computers, or metering devices. The present invention is not limited to mobile devices. Other types of access terminals, including fixed wireless terminals, may be used. However, for the sake of simplicity, only mobile stations are shown and discussed hereafter.
Dotted lines show the approximate boundaries of the cell sites 121-123 in which base stations 101-103 are located. The cell sites are shown approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the cell sites may have other irregular shapes, depending on the cell configuration selected and natural and man-made obstructions.
As is well known in the art, cell sites 121-123 are comprised of a plurality of sectors (not shown), each sector being illuminated by a directional antenna coupled to the base station. The embodiment of FIG. 1 illustrates the base station in the center of the cell. Alternate embodiments position the directional antennas in corners of the sectors. The system of the present invention is not limited to any one cell site configuration.
In one embodiment of the present invention, BS 101, BS 102, and BS 103 comprise a base station controller (BSC) and one or more base transceiver subsystem(s) (BTS). Base station controllers and base transceiver subsystems are well known to those skilled in the art. A base station controller is a device that manages wireless communications resources, including the base transceiver stations, for specified cells within a wireless communications network. A base transceiver subsystem comprises the RF transceivers, antennas, and other electrical equipment located in each cell site. This equipment may include air conditioning units, heating units, electrical supplies, telephone line interfaces, and RF transmitters and RF receivers. For the purpose of simplicity and clarity in explaining the operation of the present invention, the base transceiver subsystem in each of cells 121, 122, and 123 and the base station controller associated with each base transceiver subsystem are collectively represented by BS 101, BS 102 and BS 103, respectively.
BS 101, BS 102 and BS 103 transfer voice and data signals between each other and the public switched telephone network (PSTN) (not shown) via communication trunk lines 131, mobile switching center (MSC) 140, and communication trunk lines 132. Trunk lines 131 also provide connection paths to transfer control signals between MSC 140 and BS 101, BS 102 and BS 103 that are used to establish connections for voice and data circuits between MSC 140 and BS 101, BS 102 and BS 103 over communication trunk lines 131 and between MSC 140 and the Internet or the PSTN over communication trunk lines 132. In some embodiments of the present invention, communication trunk lines 131 may be several different data links, where each data link couples one of BS 101, BS 102, or BS 103 to MSC 140.
Trunk lines 131 and 132 comprise one or more of any suitable connection means, including a T1 line, a T3 line, a fiber optic link, a network packet data backbone connection, or any other type of data connection. Those skilled in the art will recognize that the connections on trunk lines 131 and 132 may provide a transmission path for transmission of analog voice band signals, a digital path for transmission of voice signals in the pulse code modulated (EPCM) format, a digital path for transmission of voice signals in an Internet Protocol (IP) format, a digital path for transmission of voice signals in an asynchronous transfer mode (ATM) format, or other suitable connection transmission protocol. Those skilled in the art will recognize that the connections on trunk lines 131 and 132 may provide a transmission path for transmission of analog or digital control signals in a suitable signaling protocol.
FIG. 2 illustrates exemplary mobile switching center 140 in greater detail according to one embodiment of the present invention. MSC 140 includes interconnecting network 200, among other things. Interconnecting network 200 comprises switch fabric 205 arid switch controller 210, which together provide switch paths between communication circuits in trunk lines 131 and 132. MSC 140 provides services and coordination between the subscribers in wireless network 100 and external networks, such as the PSTN or Internet. Mobile switching centers similar to MSC 140 are well known to those skilled in the art.
When a wireless network subscriber turns on his or her mobile station (e.g., cell phone) or fixed access terminal, radio messages over the air interface inform the base station that the mobile station (or fixed access terminal) is joining the network. However, a connection is not automatically made to voice or data traffic carrying circuits in trunk lines 131-132. A voice or data traffic connection to the public switched telephone network (PSTN) or the Internet is not needed until the subscriber places a call (e.g., dials a phone number) or accesses the Internet.
However, even when the phone is idle, certain information about the subscriber (i.e., subscriber data) must be retrieved and stored in either the base station or in MSC 140, or both, in order to authenticate the subscriber, gather billing information, identify the services available to the subscriber, determine capabilities of the mobile station, and the like. The control signals (as opposed to voice and data traffic) required to do this are also carried over trunk lines 131 and 132. After the subscriber data is stored in memory in MSC 140, it is available for use by a variety of call processing client (CPC) applications that may be initiated by the subscriber or another device while the it mobile station is still active.
For example, when MS 111 is first turned ON, a call process is set up in MSC 140 for MS 111 and subscriber data (e.g., billing information) is stored in MSC 140 that may be accessed by the call process or other call applications that provide particular types of call services. If the subscriber dials a phone number on MS 111 or a call is received from the PSTN directed to MS 111, the call process for MS 111 handles the establishment of a call connection on one of the trunk lines in trunk line 131 and one of the trunk lines in trunk line 132. The MS 111 call process executed in MSC 140 maintains all state information related to the call and to MS 111 and handles all other applications required by MS 111, including three-way calls, voice mail, call disconnection, and the like.
In order to handle a large amount of call traffic, it is necessary to distribute the many active call processes and call service applications handled by MSC 111 across a number of call application nodes. The call services may include application for accessing a subscriber database, selecting (or de-selecting) trunk, lines, retrieving and maintaining call identity information, and the like. The present invention provides methods and apparatuses for distributing call processes and call service applications across multiple call application nodes in a highly reliable and redundant manner. This is accomplished by a distributed network of redundant servers in which call traffic is distributed in order to increase the call-handling capacity of MSC 140. The redundancy of the distributed servers is transparent to both the call process client applications that require a service and the call process server applications that provide the service. It also decreases the complexity of both the client and server applications.
FIG. 3 illustrates in greater detail selected portions of exemplary mobile switching center 140 that perform distributed call processing using group services in accordance with the principles of the present invention. MSC 140 comprises main processing unit (MPU) 310, system manager node 1 (SYSMGR1), optional system manager node 2 (SYSMGR2), and master database 320. MSC 140 also comprises a plurality of call application nodes (CANs), including CAN1, CAN2, and CAN3, and a plurality of local storage devices (SDs), namely SD1, SD2, and SD3, that are associated with CAN, CAN2 and CAN3. Master database 320 may be used as a master software repository to store databases, software images, server statistics, log-in data, and the like. SD1-SD3 may be used to store local capsules, transient data, and the like.
Each one of system manager nodes 1 and 2 and CAN1-CAN3 executes a configuration management (CM) process that sets up each node with the appropriate software and configuration data upon initial start-up or after a reboot. Each node also executes a node monitor (NM) process that loads software and tracks processes to determine if any process has failed. System manager nodes 1 and 2 execute a first arbitrary process, P1, and system manager node 1 also executes a second arbitrary process, P2.
In accordance with the principles of the present invention, call application nodes 1-3 (CAN1-CAN3) also execute a number of call process (CP) server applications organized as primary and backup processes that are available as distributed group services to 1 to N call process client (CPC) applications, namely CPC APP1-CPC APPn in main processing unit 310. The N call application nodes (e.g., CAN1-CAN3) are separate computing nodes comprising a processor and memory that provide scalability and redundancy by the simple addition of more call application nodes.
Each of the N call process client (CPC) applications, namely CPC APP1-CPC APPn in MPU 310 handles the control signals and messages related to a single call associated with a mobile station. Each of CPC APP1-CPC APPn establishes a session with a load sharing group, which assigns the call to a particular one of the primary-backup group call process server applications, CP1, CP2, or CP3. The selected call process server application actually performs the call process services/functions requested by the call process client application.
In the illustrated embodiment, three exemplary call process server applications are being executed, namely CP1, CP2, and CP3. Each of these processes exists as a primary-backup group. Thus, CP1 exists as a primary process, CP1(P), and a backup process, CP1(B). Similarly, CP2 exists as a primary process, CP2(P), and a backup process, CP2(B), and CP3 exists as a primary process, CP3(P), and a backup process, CP3(B). In the illustrated embodiment, CP1(P) and CP1(B) reside on different call application nodes (i.e., CAN1 and CAN2). This is not a strict requirement: CP1(P) and CP1(B) may reside on the same call application node (e.g., CAN1) and still provide reliability and redundancy for software failures of the primary process, CP1(P). However, in a preferred embodiment of the present invention, the primary process and the backup process reside on different call application nodes, thereby providing hardware redundancy as well as software redundancy. Thus, CP1(P) and CP1(B) reside on CAN1 and CAN2, CP2(P) and CP2(B) reside on CAN2 and CAN3, and CP3(P) and CP3(B) reside on CAN3 and CAN1.
Together, CP1, CP2 and CP3 form a supergroup for load sharing purposes. Thus, CP1(P) and CP1(B), CP2(P) and CP2(B), and CP3(P) and CP3 (B) are part of a first load sharing group (LSG1), indicated by the dotted line boundary. Additionally, CAN1-CAN3 host three other load sharing groups, namely, LSG2, LSG3, and LSG4. LSG2 comprises two trunk idle list (TIL) server applications, namely TIL1 and TIL2. TIL1 exists as a primary process, TIL1(P), on CAN2 and a backup process, TIL1(B), on CAN3. TIL2 exists as a primary process, TIL2(P), on CAN3 and a backup process, TIL2(B), on CAN2. Similarly, TLSG3 comprises two identity server (IS) applications, namely IS1 and IS2. IS1 exists as a primary process, IS1(P), on CAN1 and a backup process, IS1(B), on CAN2 and IS2 exists as a primary process, IS2(P), on CAN2 and a backup process, IS2(B), on CAN1. Finally, LSG4 comprises two subscriber database (SDB) server applications, namely SDB1 and SDB2. SDB1 exists as a primary process, SDB1(P), on CAN2 and a backup process, SDB1(B), on CAN3 and SDB2 exists as a primary process, SDB2 (P), on CAN3 and a backup process, SDB2(B), on CAN2.
A group service provides a framework for organizing a group of distributed software objects in a computing network. Each software object provides a service. In addition, the group service framework provides enhanced behavior for determining group membership, deciding what actions to take in the presence of faults, and controlling unicast, multicast, and groupcast communications between members and clients for the group. A group utilizes a policy to enhance the behavior of the services provided by the group. Some of these policies include primary-backup for high service availability and load sharing for distributing the loading of services within a network.
Call processing server applications, such as CP1-CP3, IS1-IS2, and TIL1-TIL2, located within a computing network provide services that are invoked by client applications, such as CPC APP1-CPC APPn. As shown in FIG. 3, the call processing server applications are organized into primary-backup groups configured as a 1+1 type of primary-backup group. There are multiple numbers of these primary-backup groups and the exact number is scalable according to the number of processes and/or computing nodes (CANs) that are used. All of the primary-backup groups are themselves a member of a single load sharing group (e.g., LSG1, LSG2, LSG3, LSG4).
It is important to note that while the call process client applications, CPC APP1-CPC APPN, are clients with respect to the call process; server applications, CP1, CP2, and CP3, a server application may be a client with respect to another server application. In particular, the call process server applications CP1-CP3 may be clients with respect to the trunk idle list server applications, TIL1 and TIL2, the subscriber database server applications, SDB1 and SDB2, and the identity server applications, IS1 and IS2.
A client application establishes an interface to the load sharing group. When a new call indication is received by the client application, the client application establishes a session with the load sharing group according to a client-side load sharing policy. The initial policy is round-robin (i.e., distribution of new calls in sequential order to each CAN), but other policies may be used that take into account the actual loading of the different primary-backup groups.
The client application associates the session with the new call and sends messages associated with the call over the session object. The client application also receives messages from the primary-backup group via the session established with the primary-backup group. Only the primary process (e.g., CP1(P)) of the primary-backup group joins the load sharing group (e.g., LSG1). For a variety of reasons, the application containing the primary may be removed from service. The server application may elect to not accept any new calls by leaving the load sharing group. However, the client applications may still maintain their session with the primary-backup group for existing calls. This action is taken because new call traffic may be lost if the singleton primary also fails. New calls are not distributed to the primary-backup group if it leaves the load sharing group.
If the primary of the primary-backup group that is a member of the load sharing group should fail, the backup member is informed that the primary member has failed (or left) and then assumes the role of primary member. The responsibility for these actions must be performed by the server application. It is the responsibility of the Group Service to inform the backup member that the primary member has failed or left.
As part of an online software upgrade process, one or more applications containing primary-backup groups may be removed from service, brought down, and then brought back up using a new version of software code. These groups, if their interface has not changed, join the existing load sharing group. When first started, it is required that the client interface be capable of throttling the call traffic to specific primary-backup groups. The traffic throttling is expressed as a percentage varying from 0% (no calls) to 100%. All new calls that would have been scheduled according to the scheduling algorithm are handled by this session. The throttling factor is initialized to 100% for any primary-backup group that joins the load sharing group. During on-line software upgrades, the throttling factor is adjusted to start with the no-calls case for the new software version. Any client application for the load sharing group may establish a session with a specific primary-backup group. The client may then change the throttling factor at any time. When the throttling factor is changed, all client session interfaces receive via multicast the changed throttling factor. As the throttling factor is increased, the call process server applications with the new software version may receive increasing amounts of call traffic.
Call processing communications from the client applications to the call processing server primary-backup groups must support a very high volume of calls. The group software utilizes an internal transport consisting of a multicasting protocol (simple IP multicast) and optionally a unicasting protocol. The unicasting protocol may be TCP/IP, SCTP, or other transport protocol. The multicast protocol is used for internal member communications relating to membership, state changes, and fault detection. In the absence of unicast transport, the multicast protocol is used for client/server communication streams. The unicast protocol, when provided, is used to provide a high-speed stream between clients and servers. The stream is always directed to the primary of a primary-backup group, which is transparent to both the call processing client application and the call process (e.g., CP1, CP2, CP3, TIL1, TIL2, IS1, IS2).
AS noted above, the call processes on the call application nodes (CANs) are organized into a load sharing group. Each call process (e.g., CP1, CP2, CP3, TIL1, TIL2, IS1, IS2) is itself a primary-backup group. Both members of the primary-backup group may provide the service but only the primary of the group receives messages and thus actually provides the service. When a member of the group is selected as the primary, it registers one or more interface streams for the group. Each stream is a separate interface for some call processing service.
The call processing client application (e.g., CPC APP1, CPC APP2) in MSC 140 receives a new call indication and uses the group service to select an interface with a call application node (i.e., server) to handle the new call. The call process on each server (CAN) is a member of a load sharing group and a particular call application node (CAN) is selected using a round-robin algorithm from the perspective of the call process client application. For the particular primary-backup group that is selected a session is returned to the call processing client application. When the session is established with the primary-backup call process server group, the call processing client application then opens an interface to a particular member (representing an interface to a primary-backup group) and obtains a session interface. Each call processing server sends a message related to the new call over the session interface. Any subsequent transactions associated with the call are sent over the same session object.
The call process server (i.e., primary-backup group) may send asynchronously messages over the session using one or more of the defined stream interfaces. The primary member of the call processing server group receives the transactions. The backup group member does not receive transactions. The primary group member sends updates to the backup group member. The primary group member decides when updates are sent to the backup group member. The primary starts sending updates when a call has been answered. Prior to the call being answered, the call is defined as being a transient call. After the call has been answered, the call is defined as being a stable call.
If the primary group member should fail, then the backup group member becomes the new primary member. All transient call information during the fail-over period (the time between when the primary fails and the backup is changed to be the new primary) can be lost. All stable call information must be maintained by the backup. However, some stable call information may be lost if the backup has not received updates.
Advantageously, the present invention has no limitations on the scalability of the system and the system size is hidden from both and the primary-backup group server applications and call process client applications. The present invention eliminates any single point of failure in the system. Any failure within the system will not affect the system availability and performance.
New call application nodes (CANs) and additional primary-backup group server applications (e.g., CP1, CP2, CP3, TIL1, TIL2, IS1, IS2) may be added dynamically to the load sharing groups and can start servicing new call traffic. Call process client applications are not affected by the additions of new servers. If a server should fail, its backup assumes responsibility for the load. This provides high availability for the servicing of each call and minimizes dropped calls.
FIG. 4A is an illustration of server side internal group policy classes according to an exemplary embodiment of the present invention. FIG. 4B is an illustration of a client side internal client policy architecture according to an exemplary embodiment of the present invention. FIG. 4C is an illustration of a load sharing client side policy internal architecture according to an exemplary embodiment of the present invention.
Server applications create a primary-backup group and then join the primary-backup group. This action creates the server side policy containing the objects shown in FIG. 4A. The group policy distributes invocations from clients, participates in a distributed election of the primary in the group, maintains group membership, and monitors for group member failures. Server applications join a load sharing group using a group adaptor object as a proxy member of the load sharing group. The group adaptor object is set with the name of the primary-backup group prior to joining the load sharing group.
Client applications establish a client interface to the load sharing group and begin by opening a session. The act of opening a session utilizes a client side load sharing policy to select one of the members of the load sharing group. The internal load sharing client policy architecture is shown in FIG. 4C. The session object itself encapsulates a client side policy that connects to a particular primary-backup group. The internal architecture for this client policy is shown in FIG. 4B.
Call processing client application communicate with the selected server (which is the primary within a primary-backup group). As the primary call process receives messages from the call processing client application, the primary call process sends state updates to the corresponding backup call process. If the primary call process should fail, the backup call process is automatically selected as the new primary. During the fail-over period to the new primary, the call processing client application receives an indication of the failure and may retry the send until the new primary call process is ready to receive messages. This minimizes the lost message traffic during the fail-over period. Once the call processing client application is through with the session, the call processing client application may release the session.
The PBUNIGroupPolicy group policy has the following internal member:
1) PBUNIConfiguration—identifies the group policy name as being “PBUNI” and specifies the QoS requirements for the communication stack for this policy.
2) PolicyGroupMembership—maintains the membership for the group and provides a membership protocol for adding new members, removing members that have left, and marking members that have failed as “FAILED”.
3) PBPolicyEventNotification—provides the behavior for event notifications, such as i) when a member joins the group (recovered), ii) leaves the group (left), iii) fails (failed), or iv) has a state change.
4) PBMemberStateControl—has the state machine for primary selection in the presence of joins, exits, and failures of group members. Each local instance of this class decides which member is the primary. It is possible, due to network partitions, that there can be more than one primary at the same time.
5) PBSessionControl—controls the session establishment between call processing client applications for a primary-backup group and the group members.
6) PBPolicyIOControl—provides the primary-backup policy behavior for multicasting and sending to group members.
7) GroupSendProtocol—provides the group member protocol for sending to other members of the group and to clients of the group.
8) UnicastGroupInterface—is a group interface that provides separate interfaces to each capsule in which a group member resides.
PBUNIClientPolicy is a primary-backup client policy in which unicast links are used to communicate with the group. General sending is sent only to the primary member and is not redundantly sent to the backup member(s). The PBUNIClientPolicy has the following members:
1) ClientMembershipView—provides a local view of the group membership but unlike GroupMembershipView, does not participate in the protocol associated with group membership.
2) PBUNIClientPolicyIO—handles I/O over unicast links to the primary member.
3) GroupSendProtocol—provides the Group Member protocol for sending to other members of the group and to clients of the group.
4) ClientSessionControl—manages sessions on the client side with group members.
5) PBUNIClientStateControl—maintains a local view of which member is the primary in a primary-backup group.
6) ClientSessionControl—manages sessions on the client side with group members.
7) UnicastGroupInterface—provides separate interfaces to each capsule in which a group member resides.
LSIClientPolicy is a load sharing policy for group members who are themselves groups. LSIClientPolicy provides client-side round-robin selection of members when a session to a member is opened. Each session provides a group interface to a particular group. LSIClientPolicy also provides support of message throttling to each session. Throttling can vary from 0% (no messages) to 100% (all messages are sent that would normally be selected using round-robin scheduling). LSIClientPolicy overrides what is in the base ClientPolicy. LSIClientPolicy contains the following members:
1) LSIClientNotification—notifies both the ClientPolicy notifier and the local notifier of events.
2) LSIClientSessionControl—returns a session using a round-robin algorithm. The session provided is an interface to another group. LSISessionControl has a running index that is used to select a new session for each open session request. LSISessionControl has a list of known interfaces called “Member Known”. Member Known is a map that is indexed by the Member ID and contains a SessionCount object which contains the actual session and a reference count of the number of users of the session instance. The sessions in known are maintained even though members may leave the group. When members leave the group they are removed from being available but kept in known. This permits clients to continue to use the group interface even though they have left the load sharing group.
3) GroupSendProtocol—provides the Group Member protocol for sending to other members of the group and to clients of the group.
4) GroupInterface—is the interface class to the multicast and/or unicast protocol stack(s) that are utilized by the group interfaces.
5) ClientPolicyIO—is responsible for handling client I/O.
6) ClientStateControl—is used to control the event state of the group and to retrieve the event state of the group.
Although the present invention has been described in detail, those skilled in the art should understand that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the invention in its broadest form.

## Claims

1. A switch capable of handling call connections between calling devices and called devices on a plurality of trunk lines associated with said switch, said switch comprising:
a main processing unit capable of executing call process client applications, wherein each of said call process client applications is associated with one of said call connections; and 
N call application nodes capable of executing call process server applications, wherein a first call process server application is executed on a first one of said N call application nodes and is associated with a similar second call process server application executed on a second one of said N call application nodes separate from said first call application node, said first and second call process server applications thereby forming a first load sharing group server application, 

wherein said each call process client application sends a call process service request to said first load sharing group server application and said first load sharing group server application selects one of said first and second call process server applications to perform said call process service request according to a load distribution algorithm.

2. The switch as set forth in claim 1 wherein said load distribution algorithm distributes new call process services requests in an alternating manner between said first and second call process server applications.

3. The switch as set forth in claim 1 wherein said load distribution algorithm distributes new call process service requests according to a current call process load of said first call process server application and a current call process load of said second call process server application.

4. The switch as set forth in claim 3 wherein said load distribution algorithm distributes said new call process service requests in order to maintain said current call process load of said first call process server application at a level substantially equal to said current call process load of said second call process server application.

5. The switch as set forth in claim 1 wherein said first call process server application comprises a first primary-backup group server application, wherein said first primary-backup group server application comprises a first primary call process executed on said first call application node and a first backup call process associated with said first primary call process.

6. The switch as set forth in claim 5 wherein state information associated with said first primary call process is mirrored to said first backup call process associated with said first primary call process.

7. The switch as set forth in claim 6 wherein said first backup call process resides on said first call application node.

8. The switch as set forth in claim 6 wherein said first backup call process resides on a call application node separate from said first call application node.

9. The switch as set forth in claim 1 wherein said second call process server application comprises a second primary-backup group server application, wherein said second primary-backup group server application comprises a second primary call process executed on said second call application node and a second backup call process associated with said second primary call process.

10. The switch as set forth in claim 9 wherein state information associated with said second primary call process is mirrored to said second backup call process associated with said second primary call process.

11. The switch as set forth in claim 10 wherein said second backup call process resides on said second call application node.

12. The switch as set forth in claim 10 wherein said second backup call process resides on a call application node separate from said second call application node.

13. A wireless network comprising:
a plurality of base stations capable of communicating with a plurality of mobile stations in a coverage area of said wireless network; and 
a mobile switching center coupled to said plurality of base stations and to a public switched telephone network by a plurality of trunk lines, wherein said mobile switching center is capable of handling call connections between calling devices and called devices on said plurality of trunk lines, said mobile switching center comprising: 
a main processing unit capable of executing call process client applications, wherein each of said call process client applications is associated with one of said call connections; and 
N call application nodes capable of executing call process server applications, wherein a first call process server application is executed on a first one of said N call application nodes and is associated with a similar second call process server application executed on a second one of said N call application nodes separate from said first call application node, said first and second call process server applications thereby forming a first load sharing group server application, wherein said each call process client application sends a call process service request to said first load sharing group server application and said first load sharing group server application selects one of said first and second call process server applications to perform said call process service request according to a load distribution algorithm.

14. The wireless network as set forth in claim 13 wherein said load distribution algorithm distributes new call process services requests in an alternating manner between said first and second call process server applications.

15. The wireless network as set forth in claim 13 wherein said load distribution algorithm distributes new call process service requests according to a current call process load of said first call process server application and a current call process load of said second call process server application.

16. The wireless network as set forth in claim 15 wherein said load distribution algorithm distributes said new call process service requests in order to maintain said current call process load of said first call process server application at a level substantially equal to said current call process load of said second call process server application.

17. The wireless network as set forth in claim 13 wherein said first call process server application comprises a first primary-backup group server application, wherein said first primary-backup group server application comprises a first primary call process executed on said first call application node and a first backup call process associated with said first primary call process.

18. The wireless network as set forth in claim 17 wherein state information associated with said first primary call process is mirrored to said first backup call process associated with said first primary call process.

19. The wireless network as set forth in claim 18 wherein said first backup call process resides on said first call application node.

20. The wireless network as set forth in claim 18 wherein said first backup call process resides on a call application node separate from said first call application node.

21. The wireless network as set forth in claim 13 wherein said second call process server application comprises a second primary-backup group server application, wherein said second primary-backup group server application comprises a second primary call process executed on said second call application node and a second backup call process associated with said second primary call process.

22. The wireless network as set forth in claim 21 wherein state information associated with said second primary call process is mirrored to said second backup call process associated with said second primary call process.

23. The wireless network as set for in claim 22 wherein said second backup call process resides on said second call application node.

24. The wireless network as set forth in claim 22 wherein said second backup call process resides on a call application node separate from said second call application node.