Abstract:
A logical module, referred as Load Balancer Module (LBM), is disclosed which listens to one of certain common predefined port number. These well-known ports for receiving communication video conference signaling and control protocols is thereafter load balanced and multi-plexed to a number of instances of protocol stack applications. By balancing the multi-media data stream across a multitude of application instances multiple multi-media data streams may be serviced and processed by a single internet protocol host processor. A mutipoint control unit (MCU) may therefore process multiple input data streams containing multi-media video conferencing information.

Description:
RELATED APPLICATION DATA 
     This Application claims priority to Provisional U.S. Patent Application Ser. No. 61/117,619 filed 25 Nov., 2008 titled “Method and System for Dispatching Received Sessions Between a Plurality of Instances of an Application Using the Same IP Port” by Kirill Tsym, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The subject matter of the present disclosure relates to the field of multiple application programs running on the same IP host and communicating simultaneously over the Internet, and more specifically to the need of system and method to enable multiple instances of the same application program to listen on the same IP port simultaneously. 
     BACKGROUND 
     As the network traffic continues its rapid growth and more and more developers introduce network products and solutions, there is an increasing number of application programs (processes) that use a predefined well-known network port. Some of these application programs need to listen on a single well-known predefined Transmission Control Protocol (TCP) and\or Transport Layer Security (TLS) and/or User Datagram Protocol (UDP) port number, for example. Session Initiation Protocol (SIP) and H.323 Protocol are examples of such application programs (processes) that need to listen on such a well-known TCP or UDP port number. H.323 Protocol application programs listen on TCP port number 1720, while SIP application can listen to TCP or UDP port number 5060, or over port 5061 for encrypted video and/or audio conferencing session based on TLS/TCP transport protocol, for example. In a common architecture of videoconferencing networks, SIP clients are connected via a SIP proxy to a Multipoint Control Unit (MCU). The transport protocol between the SIP proxy and the MCU can be configured by an administrator. There are some cases in which more than one transport protocol can be used between the proxy and the MCU. 
     Different types of network devices may be able to achieve better scalability, robustness and load balancing if they have the ability for two or more instances of an application program (process) to run simultaneously using the same specific port number. An example of such a network device is an MCU. An MCU is a conference controlling entity located in a node of a network or in a terminal. An MCU receives and processes, according to certain criteria, a plurality of media, signaling, and control channels from access ports and distributes these to connected channels. Examples of MCUs include the MGC-100, and RMX 2000 (Polycom Inc.). MCUs can be composed of two logical units: a media controller (MC) and a media processor (MP). A more thorough definition of an endpoint (terminal) and an MCU can be found in the International Telecommunication Union (“ITU”) standards, such as but not limited to the H.320, H.324, and H.323 standards. The MCU is required to handle a plurality of sessions between a plurality of users (clients) simultaneously. Thus, MCU may require using simultaneously more than one instance of the same application program, H.323 for example, for the different sessions. Unfortunately the Operating System (OS) has a port listening limitation in that only a single application/application instance (process) can listen on a specific port number on the same IP host. In this disclosure the terms application, application program and process may be used interchangeably. 
     H.323 is an International Telecommunications Union (ITU) standard that provides specification for computers, equipment, and services for multimedia communication over packet based networks that defines how real-time audio, video and data information is transmitted. H.323 is commonly used in VoIP, Internet Telephony, and IP-based videoconferencing. Users can connect with other users over the Internet and use varying products that support H.323. This standard includes the Internet Engineering Task Force (IETF) Real-Time Protocol (RTP) and Real-Time Control Protocol (RTCP), with additional protocols for call signaling, and, data and audiovisual communications. 
     IETF SIP is an application-layer control protocol, a signaling protocol for Internet Telephony. SIP can establish sessions for features such as audio/videoconferencing, interactive gaming, and call forwarding to be deployed over IP networks, thus enabling service providers to integrate basic IP telephony services with Internet, e-mail, and chat services. In addition to user authentication, redirect, and registration services, SIP Server supports traditional telephony features such as personal mobility, routing, and call forwarding based on the geographical location of the person being called. 
     There are techniques that provide the ability for an application program to listen for incoming calls on multiple ports. But such a system requires adding in the Operating System (OS) transport components and Network components (not always possible). Such system also may require predefining strings that a user (client) will need to transmit in order to connect to that application. A user (client) that does not know the predefined string will not be able to refer and connect to such an application program. Furthermore, such system will not enable a plurality of instances of the same application to listen on the same port. Other techniques provide the ability to dispatch connection services (multiple different application instances) to listen on a single static port. Those methods require predefining a unique ID for each application/instance and notifying the clients of these unique IDs or else the clients will not be served. In this disclosure the terms user and client may be used interchangeably 
     Therefore, there is a need in the art for a method and a system that will enable multiple application instances to operate simultaneously using the same listening port. It is desirable that such a method and system would not require that clients be informed of a predefined unique ID or special strings to be served. It is also desirable that no changes in the OS level would be required. 
     SUMMARY 
     The above-described needs are met using the disclosed methods and apparatus\systems that enable multiple application instances to use the same listening port simultaneously using a load-balancing scheme. The method and apparatus do not require any changes in the Operating System. 
     A logical module, referred as Load Balancer Module (LBM), listens to a certain common predefined port number. Port number 1720 is a well-known port for receiving communication based on H.323 protocol, for example. An exemplary H.323 LBM can be configured to listen to port number 1720 for receiving H.323 connection requests for all H.323 instances (tasks). Another exemplary LBM can be configured to listen to well-known port number 5060 and/or 5061 for communication based on SIP protocol (SIP LBM). H.323 communication is based on TCP, while SIP communication can be based on TCP, TLS/TCP or UDP. In an exemplary architecture of videoconferencing networks, SIP clients can be connected via a SIP proxy to an MCU implementing exemplary techniques as disclosed herein. The transport protocol between the SIP proxy and the MCU can be configured by an administrator, for example. In some cases more than on transport protocol can be used between the proxy and the MCU. 
     H.323 LBM is connected to a plurality of instances (tasks) of a H.323 stack. SIP LBM is connected to a plurality instances (tasks) of SIP stack. In one embodiment, the internal connection between each LBM and its associated instances can be via a connection set by the LBM using a file descriptor transferring mechanism, such as but not limited to, Unix Domain Socket, for example. In other embodiments, the connection between the LBM and the instances can be via a shared memory, for example. The connection between the different instances, such as but not limited to SIP and H.323, and the LBM can be established at power on, for example. 
     An exemplary LBM can request to listen to the relevant port. In response, a listening socket is defined by the OS. Once a request for new TCP connection is received via the relevant port, such as port 1720, the Operating System (OS) transfers the request to H.323 LBM. Thus only the H.323 LBM receives the H.323 connection request. In response for accepting the new TCP connection, a randomly chosen Socket Number is selected by the OS to be associated with the newly received TCP connection. The new socket is transferred to the H.323 LBM. Next, the H.323 LBM can locate an available H.323 instance (task) to handle the call. 
     An Active-Call Counter for each H.323 instance can assist the H.323 LBM in its decision to which H.323 instance to transfer the call. The Active-Call Counter can be a counter that counts the amount of active calls the specific H.323 instance is handling. The Active-Call Counter is updated each time an active call has been terminated or a new call has been received for that specific instance. H.323 LBM can decide to transfer the new connection request according to the H.323 instance that has the smallest Active-Call Counter value, for example. In some embodiments, if no instance (task) of the application is available, then LBM can initiate one. 
     H.323 LBM can forward the associated Socket Number using a descriptor sharing mechanism such as but not limited to UNIX Domain Socket, wherein the header indicates that a socket is transferred. In response, the selected instance will receive a new socket number for handling the call via the same IP port for receiving and sending data. According to another exemplary embodiment, in which plug-in Silicon Operating System (pSOS) is used, a sharing socket system call, “shr_socket”, can be used as socket sharing mechanism. Additionally, other methods can be used to share the same descriptor by two or more applications. 
     These and other aspects of the disclosure will be apparent in view of the attached figures and detailed description. The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure, and other features and advantages of the present disclosure will become apparent upon reading the following detailed description of the embodiments with the accompanying drawings and appended claims. 
     Furthermore, although specific exemplary embodiments are described in detail to illustrate the inventive concepts to a person skilled in the art, such embodiments are susceptible to various modifications and alternative forms. Accordingly, the figures and written description are not intended to limit the scope of the inventive concepts in any manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present disclosure will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
         FIG. 1  is a simplified block diagram illustrating a portion of an exemplary MCU. 
         FIG. 2   a &amp; b  is a time diagram illustrating an exemplary flow of a H.323 call-setup handling over TCP. 
         FIG. 3   a &amp; b  is a flowchart illustrating an exemplary method of H.323 call-setup handling over TCP. 
         FIG. 4  is a time diagram illustrating an exemplary flow of SIP, based on UDP transport protocol call-setup handling. 
         FIG. 5   a &amp; b . is a flowchart illustrating an exemplary method of SIP call-setup handling based on UDP transport protocol. 
     
    
    
     DETAILED DESCRIPTION 
     Turning now to the figures in which like numerals represent like elements throughout the several views, exemplary embodiments, aspects and features of the disclosed methods, systems, and apparatuses are described. For convenience, only some elements of the same group may be labeled with numerals. The purpose of the drawings is to describe exemplary embodiments and not for limitation. The timing interval between the different events, in the timing diagrams, is not necessarily shown to scale. 
       FIG. 1  is a simplified block diagram illustrating a portion of an exemplary Multipoint Control Unit (MCU)  100 . The described portion of MCU  100  comprises and describes relevant elements of an MCU that may handle the control and signaling based on H.323 or SIP. Other sections of a common MCU are not described, sections such as media (audio, video, data) processing, for example. Among other elements, MCU  100  can include: one or more plugs  110 , one or more Network Interface Cards  115 , and an Operating System  120 . At it&#39;s application layer, MCU  100  can include: a H.323 Load Balancer Module (LBM)  130 , a plurality of H.323 Instances  140   a - c , a SIP Load Balancer Module (LBM)  150 , and a plurality of SIP Instances  160   a - c . It will be appreciated, by those skilled in the art, that depending upon its configuration and the needs of the system, each MCU can have a number other than three instances per each protocol. However, for purposes of simplicity of understanding, three instances per protocol are shown. 
     MCU  100  can be a network device/application server working on IP network. MCU  100  is only one of many different network devices/application servers that can implement the teachings of the present description. 
     Plug  110  connects MCU  100  via an appropriate link to a LAN (Local Area Network) based on Ethernet, for example. Network Interface Card  115  processes the OSI&#39;s (Open System Interconnection) Physical Layer and Data Link Layer of the communication. Operating System (OS)  120 , among other functions, processes the Network layer and Transport Layer of the communication according to the appropriate protocols, IP protocol, TCP, UDP, etc. 
     OS  120  may include a Network Module  121 , a TCP Transport module  122   a , and a UDP Transport module  122   b . Network Module  121  can include, among other objects, an IP Network Stack for example. Network Module  121  receives its communication from the NIC  115  and processes the OSI&#39;s Network Layer. Network Module  121  parses the IP header of the packets. The IP header can include, among other things, the destination IP address, destination port number, source IP address, source port number, and the type of the transport protocol. OS  120  randomly defines a socket number  127   a - c  and\or  129  for the received communication according to the above four parameters: destination IP address, destination port number, source IP address, and source port number. Network Module  121  can transfer the communication to TCP Transport module  122   a  or to UDP Transport module  122   b , according to the protocol mentioned in the header (TCP, or UDP, for example). Over port 1720 TCP communication of H.323 call requests is transferred. Over port 5060 un-encrypted UDP or TCP communication of SIP sessions is transferred. Over port 5061 encrypted TLS communication of SIP sessions is transferred. The used transport protocols for SIP sessions can vary and can be configured by an administrator periodically. In some cases only UDP is used with a port number 5060. In other cases TCP is used with port 5060 or with port 5061 for TLS encrypted sessions. Yet in alternate embodiment, all the three options can be used. 
     TCP Transport module  122   a  processes the Transport Layer level of the OSI and can comprise, among other objects, a TCP transport stack. TCP Transport module  122   a  processes the communication from ports 1720, 5060, and 5061. TCP Transport module  122   a  can transfer the request for communication either to a H.323 Listening Socket  126  or to a SIP Listening Socket  128   a  or  128   b  or  128   c , according to the listening port from which the data was received and the used transport protocol, for example. 
     The UDP Transport module  122   b  processes the Transport Layer level of the OSI and can comprise, among other elements, a UDP transport stack. UDP Transport module  122   b  processes communication received from port 5060 and can transfer the request for communication to a Listening Socket  128   c . More information on the operation of OS  120  is disclosed below. 
     The MCU  100  Application Layer can comprise two Load Balancer modules—H.323 LBM  130  and SIP LBM  150 . Each Load Balancer includes an API (application programming interface),  138  or  158 , to communicate with H.323 Instances  140   a - c  or with SIP Instances  160   a - c , respectively. Exemplary API commands can be add, delete, clear, and so on. Each LBM may request from OS  120 , at initiation, a Listening Socket. H.323 LBM  130  may be associated with a Listening socket  126 , for TCP communication on port 1720. SIP LBM  150  may be associated with three Listening sockets  128   a - c , listening socket  128   a  for encrypted TLS/TCP communication received via port 5061, listening socket  128   b  for unencrypted TCP communication received via port 5060, and listening socket  128   c  for unencrypted UDP communication received via port 5060. The transport protocol between the SIP proxy and the MCU  100  can be configured by an administrator. There are some cases in which more than one transport protocol can be used over the connection between the proxy and the MCU  100 . 
     In another example, three LBMs can be used: one for H.323, one for un-encrypted SIP, and one for encrypted SIP based on TLS protocol. Still alternatively, a single LBM can be used for handling the three types of communication (TCP communication received via port 5060, unencrypted UDP and TCP communication received via port 5060 and encrypted communication based on TLS/TCP received via port 5061). 
     Each SIP call is associated with a Call-ID. The Call-ID (CID) represents a specific SIP call with a specific SIP client. Therefore SIP LBM  150  may include a Parser  152  that partially parses the communication received to determine the CID and transfer it to the appropriate SIP Instance  160   a - c  that handles the communication with that client. SIP LBM  150  may also include a Decrypter and TLS stack  154  to decrypt the TLS communication received from TCP Transport module  122   a  via port 5061 to enable the parsing of the communication and determining the CID. 
     A plurality of sockets  127   a - c  and\or  129   aa - cc , may be created and terminated to enable communication between different H.323 Instances  140   a - c  or SIP instances  160   a - c  and H.323 clients or SIP clients, respectively. As mentioned above, OS  120  randomly defines socket numbers  127   a - c  and\or  129   aa - cc  for communication according to four parameters: destination IP address, destination port number, source IP address, and source port number. The socket number used for SIP instances,  129   aa - cc , represents the listen socket  128   a - c  and the instance  160   a - c . The first letter represents the listen socket  128   a - c  and the second letter represents the instance number  160   a - c . Accordingly, an exemplary socket  129   bc  represent listen socket  128   b  and SIP instance  160   c , for example. So there are configurations in which the number of sockets that are used by SIP instances  160   a - c  is the product of the number of listening sockets (as function of the transport protocols and the ports) and the number of SIP instances. In the example of  FIG. 1  it can be nine sockets. 
     Yet, in another exemplary embodiment, other combinations of transport protocols can be used between MCU  100  and the SIP proxy. Some embodiments may use only TLS/TCP, for example. In such an embodiment, MCU  100  may comprise one transport protocol module, TCP transport module  122   a , one listening socket,  128   a , and three instance&#39;s sockets,  129   aa ,  129   ab  &amp;  129   ac , for example 
     At the MCU  100  Application Layer, two Socket tables are up-dated with the socket numbers. A H.323 Socket table  135  associated with H.323 communications and a SIP Call-ID (CID) table  153  associated with SIP communications. H.323 Socket table  135  is managed by H.323 LBM  130 . SIP CID table  156  is managed by SIP LBM  150 . Each entry in the H.323 Socket table  135  includes information that is relevant to an H.323 session, such as but not limited to, an entry ID, an associated socket number  127   a - c  and an associated H.323 Instance  140   a - c  allocated to handle the session. Each entry in the SIP CID table  153  comprises information that is relevant to a SIP session, such as but not limited to the CID of the SIP session, an associated SIP Instance  160   a - c  that was allocated to handle the session and the listening socket  128   a - c  from which the call is received, etc. The tables are created and managed by the appropriate LBM and are used by the relevant LBM for routing calls to appropriate instances. 
     Each LBM, H.323 LBM  130  and SIP LBM  150 , can include a plurality of Active-Call Counters. H.323 LBM  130  can include an Active-Call Counter for each H.323 Instance  140   a - c . The Active-Call Counter is incremented by one for each new incoming call for the specific H.323 Instance  140   a - c  and decremented by one for each active call that terminates at the specific H.323 Instance  140   a - c . SIP LBM  150  can include an Active-Call Counter for each SIP Instance  160   a - c , which operates in a similar manner as H.323 Active-Call Counter for the SIP instances  160   a - c . According to the values of each active call counter the communication load over the instances can be balanced. 
     An exemplary H.323 instance  140   a - c  can comprise a H.323 stack for handling the H.323 signaling and control communication with the plurality of conferees that have been associated with the relevant instance. In addition each H.323 instance  140   a - c  can include an API module  142  for communicating with the H.323 LBM  130 . An exemplary SIP instance  160   a - c  can comprise a SIP stack and an API module  162 . The SIP stack handles the SIP signaling and control communication with the plurality of conferees that have been associated with the relevant instance. The API module  162  can communicate with the SIP LBM  150 . In exemplary embodiments of SIP instance  160   a - c  in which the communication is encrypted based on TLS/TCP, the exemplary SIP instance  160   a - c  can include a TLS encryptor module. The TLS encryptor can be used to encrypt the SIP signaling and control data before sending it toward the relevant conferee. 
       FIG. 2   a &amp; b  is a time diagram illustrating relevant events in an exemplary flow of a H.323 call handling over TCP. For convenience and clarity of presentation, only a single call with few events is illustrated. However, a skilled person in the art will appreciate that a plurality of calls with a plurality of events can be handled in a similar way. During initiation T 0  to T 0   c  H.323 LBM  130  ( FIG. 1 ) establishes connection via Unix Domain Socket (UDS) with each one of the H.323 Instances  140   a - c . The new connections can be used for carrying the API commands that are transferred between API module  138  and API module  142  ( FIG. 1 ) at each instance. Other exemplary embodiments may use other communication methods between applications, such as but not limited to, a share socket mechanism in pSOS, for example. 
     At T 1 , H.323 LBM  130  requests from the OS  120  ( FIG. 1 ) to listen on TCP connection requests received via port 1720. In return, at T 2 , the OS  120  ( FIG. 1 ) sends a socket number  126  ( FIG. 1 ) to H.323 LBM  130  to serve as the Listening Socket on port 1720. Then, a TCP SYN is received T 10  from a client on port 1720 requesting to establish a new TCP connection. OS  120  responds by sending at T 11  a TCP SYN ACK (Acknowledge). Once the TCP SYN ACK has been received, the client sends T 12  a TCP ACK as an indication request to establish a H.323 communication session. 
     Next, at T 13 , OS  120  sends, via listening socket  126  the request to H.323 LBM  130  for setting a H.323 connection with the client. In return, H.323 LBM  130  sends at T 14  a H.323 accept-connection. OS  120  returns T 15  an accepted with new socket  127   a , for example, through which the session will be handled. Upon receiving the new socket, LBM can determine which H.323 instance  140   a - c  will handle the call. The selection can be based on the value of the Active-Call Counter associated with each instance. After selecting an instance, the H.323 socket table is updated with the new socket number  127   a , and the identification of the selected instance  140   a  ( FIG. 1 ), for example. 
     At T 16 , H.323 LBM  130  sends an API command to ‘ADD’ the new session, which is received via socket  127   a , to the selected H.323 Instance  140   a . The ADD command is transferred via Unix Domain Socket, wherein the header indicates that a socket is transferred and the socket number  127   a  is transferred as payload. In response, a second socket number,  127   a ′, which can be selected randomly, is delivered to the selected instance  140   a , for example. Each number,  127   a  and  127   a ′, can be used by different applications (LBM H.323  130  and the selected instance  140   a , respectively) for accessing the same file descriptor. As a result, a new socket number is allocated for the session  127   a ′ on which the selected instance can execute the session. Consequently, a pair of sockets for the session is created ( 127   a ;  127   a ′).  127   a  is used by the H.323 LBM and  127   a ′ is used by the selected instance. The rest of the H.323 session with the client is conducted by the selected H.323 instance  140   a  using the socket number  127   a ′. In a similar way, sockets  127   b  and  127   b ′ can be allocated for sessions handled by H.323 instance  140   b  and sockets  127   c  and  127   c ′ can be allocated for sessions handled by H.323 instance  140   c.    
     At T 18 , the H.323 client sends H.323 data that can include H.323 call setup information in order to establish the H.323 session. The H.323 data is transferred, at T 19 , on both sockets  127   a  and  127   a ′. However, only the selected H.323 instance,  140   a  for example, reads the H.323 data and responds to the requests. 
     Turning now to  FIG. 2   b , which is the continuation of the timetable of the same H.323 session, at T 20 , the selected H.323 instance,  140   a  for example, sends H.323 data using the Socket number  127   a ′. At T 21 , the OS  120  sends the H.323 data toward the client. At T 22 , the client sends a data (H.323 packet). OS  120  transfers the packet of H.323 data via socket  127   a ′ to the selected H.323 instance, at T 23  ( 140   a ). The session can continue via socket  127   a ′ until the end of the session. 
     At the end of the session T 30 , the client can send an H.323 end of session indication. The end of session indication can be sent at, T 32 , from the OS  120  ( FIG. 1 ) to the selected instance  140   a  via socket  127   a ′. At T 34 , a release call indication is sent, via socket  127   a ′, that closes socket  127   a ′. An API command DELETE is sent, at T 38  from H.323 instance  140   a  to the H.323 LBM  130  using UDS via the connection that was opened at T 0 . Once an API DELETE command is received, H.323 LBM  130  sends T 39  a close socket  127   a  command to OS  120 . OS  120  then sends, at T 40  a close TCP connection to the client by using TCP FIN command. It will be appreciated that similar processes can execute simultaneously for other H.323 sessions with other instances using other sockets. 
       FIG. 3   a &amp; b  illustrate an exemplary method  300  for handling a H.323 call-setup over TCP connection. Method  300  can be implemented by an exemplary embodiment of H.323 LBM  130  ( FIG. 1 ). Method  300  can be initiated  302  during power on of MCU  100  ( FIG. 1 ) and can run as long as the MCU is active. Upon initiation  304 , H.323 LBM  130  can be introduced to relevant modules or can initiate modules that are involved in the operation of H.323 LBM  130 . Exemplary modules can be the H.323 socket table  135 , a set of H.323 instances  140   a - c  ( FIG. 1 ), a set of Active-Call Counters one per each H.323 instances  140   a - c , etc. 
     After the initiation processes  302  &amp;  304 , an internal connection between H.323 LBM  130  and each one of the H.323 instances  140   a - c  is established  305 . The internal connection can be based on file descriptor transferring and/or file descriptor sharing mechanism, such as but not limited to, Unix Domain Socket, for example. 
     At this point, H.323 LBM  130  can request  306  the OS  120  ( FIG. 1 ) to listen on TCP port 1720. If a listening socket number is not received, then an error message can be sent  316  to the OS  120  and method  300  can be terminated  318 . 
     When a listen socket number is received  310 , method  300  starts a loop between steps  320  and  342  ( FIG. 3   b ) for handling H.323 communication sessions. At steps  320  and  322  method  300  waits to receive an event. An event can be received from the OS  120  ( FIG. 1 ) or from one of the H.323 instances  140   a - c  ( FIG. 1 ). If the event received  323  is a DELETE API command via one of the connections that was set in step  305  from one of the instances  140   a - c , then a relevant entry from the H.323 socket table is retrieved and parsed. The relevant entry is retrieved based on the entry ID number that can be associated with the API DELETE command. According to the content of the entry, a close-socket request  323  for closing the socket that was allocated to the LBM for handling the relevant session is issued. The Active-Call Counter that was allocated to the relevant instance is decremented by one and the relevant entry in H.323 socket table  135  is released. In response to the close socket command, OS  120  sends a TCP FIN to the relevant client for closing the TCP connection. 
     If at  322  the event is received via the listening socket  126 , which indicates a new H.323 connection request, then the LBM  130  may accept the new call, which is received via the listening socket  126  ( FIG. 1 ). In response, a new socket number is received  326  for carrying the new H.323 session and method  300  continues  330  to the steps that are illustrated in  FIG. 3   b . The new socket can be one of the sockets  127   a - c  ( FIG. 1 ), for example  127   a.    
     At step  332  ( FIG. 3   b ), method  300  may determine which H.323 instance  140   a - c  is available for handling the call. The decision can be based on checking the Active-Call Counter of each one of the instances and selecting the one with the least number of sessions, for example. If at  334  an available H.323 instance is found,  140   a , for example, its associated Active-Call counter is incremented. An entry in the H.323 socket table  135  ( FIG. 1 ) is allocated  340  for the session, the entry is updated with an entry ID, the allocated socket (e.g.,  127   a ), and the selected instance (e.g.,  140   a ). API ADD command is then sent via Unix domain Socket connection to the selected instance. The header of the Unix domain Socket message can indicate that it is a socket transferring message. The content of the message can include the new socket number,  127   a , and the entry ID number, for example. In response the selected instance,  140   a  for example, will get another socket number  127   a ′ to be used for the session. Alternatively, another file descriptor sharing mechanism can be used. At this point  342  method  300  returns to step  320  ( FIG. 3   a ) to wait for the next event. 
     If at  334  there is no available H.323 instance, then LBM  130  may create  336  a new instance  140   d  (not shown in the drawing), and set an internal connection with the new instance  140   d  as was done in step  305  above, and continue to step  340 . In an alternative embodiment, if an available instance is not found the call can be rejected. 
       FIG. 4  illustrates a time diagram with an exemplary flow of events in a SIP call handling. In the example of  FIG. 4 , the SIP call is based on UDP transport protocol and is received via UDP port 5060. For convenience and clarity of presentation only a single call via UDP port 5060 with few events is illustrated. However, a skilled person in the art will appreciate that a plurality of calls with a plurality of events can be handled in a similar way. Furthermore,  FIG. 4  illustrates the flow of an exemplary embodiment in which the clients are connected via a SIP proxy to the MCU  100  ( FIG. 1 ). In an alternate embodiment, two or more SIP proxies can be used, or alternatively clients can be connected directly to the MCU. In those cases the timing diagram can be modified according to the type of the connections. 
     At the beginning of the illustrated flow diagram, at T 100   a  to T 100   c  SIP LBM  150  ( FIG. 1 ) establishes connections with each one of the SIP Instances  160   a - c  ( FIG. 1 ). The connection with the instances can be done by file descriptor transferring mechanism, such as but not limited to, Unix Domain Socket (UDS). After setting the connection with each one of the instances  160   a - c , SIP LBM  150  can request, at T 102 , from OS  120  ( FIG. 1 ) to open a SIP transport socket over UDP port 5060. In return, at T 103 , OS  120  ( FIG. 1 ) sends a socket number  128   c  ( FIG. 1 ) to SIP LBM  150  that will serve as the SIP transport Socket (STS) on UDP port 5060 for incoming SIP data. 
     The socket number  128   c  is transferred at T 104   a -T 104   c  via Unix domain Socket connection, established before at T 100   a -T 100   c , to each one of the SIP instances  160   a - c . The header of the Unix domain Socket message can indicate that it is a socket transferring message. The content of the message can include the SIP transport socket number,  128   c , for example. Consequently, each of the SIP instances  160   a - c  receives another number,  129   aa - cc  ( FIG. 1 ), to be used as STS through which each SIP instance will send SIP data to the relevant clients via the UDP port 5060 and the SIP proxy. 
     At T 110 , a SIP client can send a SIP packet with SIP data or SIP Invite request toward UDP port number 5060. The SIP data is associated with a certain Call-ID (CID), which was allocated by the client that initiated the SIP call. At T 111 , the proxy transfers the SIP packet to MCU  100  ( FIG. 1 ). OS  120  ( FIG. 1 ), after processing the IP header and the UDP header, transfers at T 112  the SIP data to SIP LBM  150  via SIP transport socket  128   c . SIP LBM  150  can parse the SIP data by parser  152  ( FIG. 1 ) and determine whether the data is an invite request of a new SIP session or SIP data of an existing SIP session. If it is an existing SIP session, based on the CID of the session, an entry is searched in SIP CID table  153  ( FIG. 1 ). The entry is parsed for identifying the allocated SIP instance  160   a - c  that handles the session, for example instance  160   a . Then, at T 113 , the SIP data is transferred as a Unix Domain Socket message via the connection that was established during T 100   a , for example. 
     If the SIP data includes a SIP invite request, SIP LBM  150  can determine which SIP instance is available,  160   a  for example. Then an entry is allocated for the session at SIP CID table  153  and the selected instance and the CID of the session are stored in the entry. The Active-Call Counter associated with the selected SIP instance,  160   a , is incremented by one. At T 113 , the SIP invite request is transferred as a Unix Domain Socket message via the connection that was established during T 100   a  with the selected instance, for example. Then at T 113  the SIP data is transferred as a Unix Domain Socket message via the connection that was established during T 100   a  with the selected instance,  160   a  for example. 
     The selected SIP instance,  160   a , may further process the SIP data and, at T 114 , a SIP response is sent by the appropriate SIP instance ( 160   a , for example) via socket  129   ca  (the ‘c’ represent that it is a UDP session received via SIP transport socket  128   c , and ‘a’ represent SIP instance  160   a ), for example, to the client via the OS  120 . At T 116 , after adding the appropriate UDP and IP headers, the packet is sent to the proxy and from there, at T 118 , the packet is transferred to the client. The session may proceed in a similar way, until the selected instance,  160   a , determines that the received SIP data is a request to terminate the call, or the SIP instance determines to terminate the SIP session. Then at T 120  the selected SIP instance,  160   a , sends an API DELETE command with the CID of the session to SIP LBM  150 . The command is sent as a Unix Domain Socket message via the connection that was established during T 100   a  with the selected instance,  160   a  for example. Upon receiving the DELETE command with the CID of the terminated call, the relevant entry is searched in the SIP CID table  153  and the entry is released. The Active-Call Counter associated with the selected SIP instance  160   a , is decremented by one. Since a proxy is involved, the connection with the proxy is not affected by the termination of one call. The connection with the proxy remains active for serving other clients. 
     A similar flow diagram can be illustrated for a SIP session that is carried over TCP. For a TCP based SIP session the TCP transport module  122   a  will replace the UDP transport module  122   b  ( FIG. 1 ), SIP transport socket  128   b  will replace the SIP transport socket  128   c  and socket  129   ba  will replace the socket  129   ca . For a TCP and TLS based SIP session the TCP transport module  122   a  will replace the UDP transport module  122   b  ( FIG. 1 ), SIP transport socket  128   a  will replace the SIP transport socket  128   c  and socket  129   aa  will replace the socket  129   ca . In addition, a decryption process will be added at T 113  for decrypting the SIP data before parsing it. 
     An exemplary embodiment that handles SIP sessions carrying over TCP/IP (port 5060) or TLS/TCP/IP (port 5061) may need to first establish a TCP connection between the MCU and the SIP proxy. In such embodiment, to open a SIP transport Socket for carrying the SIP data over a TCP connection via ports 5060 or 5061, first a listening socket can be opened between the SIP LBM  150  and port 5060 or 5061 to establish the TCP connection between the MCU and the SIP proxy. After establishing the TCP connection, a SIP transport socket  128   a &amp; b  may be allocated for handling the SIP data and is transferred to SIP LBM  150 . An exemplary process for opening a TCP connection between the MCU and the SIP proxy and allocating the SIP transport socket can be similar to the one that is disclosed in  FIG. 2   a  from T 1  to T 14  (for setting the TCP connection) and T 15  (for allocating the SIP transport socket). In TCP based SIP sessions, the TCP connection can remain open as long as the MCU is active. 
       FIG. 5  illustrates an exemplary method  500  for handling SIP calls over three possible transport protocol options simultaneously: over TCP connection and port 5060, UDP and port 5060, or TCP on port 5061 for encrypted TLS sessions. Method  500  can be implemented by an exemplary embodiment of SIP LBM  150  ( FIG. 1 ). Another exemplary embodiment can be configured to work with a single type of SIP sessions (UDP; or TCP; or TLS/TCP). Yet another exemplary embodiment can be configured with a combination of two types of SIP sessions. In those embodiments, method  500  can be modified to match the used transport protocols. 
     Method  500  can be initiated  502  during power on of MCU  100  ( FIG. 1 ) and can run as long as the MCU is active. Upon initiation  504 , SIP LBM  150  can be introduced to relevant modules of the MCU  100  and can initiate modules that are involved in the operation of SIP LBM  150 . Exemplary modules can be the SIP CID table  153 , a set of SIP instances  160   a - c  ( FIG. 1 ), a set of Active-Call Counters one per each SIP instances  160   a - c , etc. 
     After the initiation processes  502  &amp;  504 , an internal connection between SIP LBM  150  and each one of the SIP instances  160   a - c  is established  506 . The internal connection can be based on file descriptor transferring and/or file descriptor sharing mechanism, such as but not limited to, Unix Domain Socket, for example. 
     After setting  506  a connection with each one of SIP instances  160   a - c , SIP LBM  150  can request  508  to open a SIP transport socket over one or more ports, depending on the configuration. The ports can be: TCP port 5060, UDP port 5060 and TCP port 5061. Then, the SIP LBM can wait  510  to receive a SIP transport socket number per each one of the pairs of transport-protocol and a port. If one of the socket numbers was not received, then an error message can be sent  516  to the OS  120  and method  300  can be terminated  518 . Exemplary embodiments that use TCP transport protocol for carrying the SIP communication may need to establish first a TCP connection between the MCU and the SIP proxy by opening listening socket over the appropriate port (5060 or 5061 for TLS/TCP) and only after establishing the TCP connection a SIP transport socket can be delivered. 
     When  510  the appropriate number of SIP transport sockets is received, depending on the configuration of the proxy and the MCU (sockets  128   a  for TLS/TCP on port 5061; and/or  128   b  for TCP on port 5060; and/or  128   c  for UDP on port 5060, for example), then each of the socket numbers ( 128   a - c ) is transferred  520  to each of the SIP instances  160   a - c . Sending the SIP transport socket to each one of the SIP instances can be done as a Unix domain Socket message over the connection that was established during step  506  with each one of the SIP instances. The header of the Unix Domain Socket message can indicate that it is a socket-transferring message. The content of the message can include the transferred socket number,  128   a  or  128   b  or  128   c . Consequently, the received socket number at each instance will be  129   a,a - c ; or  129   b,a - c ; or  129   c,a - c , wherein the first letter represents the SIP transport socket and the second letter represents the instance number. Therefore, sockets  129   c,a - c  represents three sockets:  129   ca  used for sessions received via socket  128   c  to instance  160   a ;  129   cb  used for sessions received via socket  128   c  to instance  160   b ; and  129   cc  used for sessions received via socket  128   c  to instance  160   c  ( FIG. 1 ). 
     After sending the one or more SIP transport sockets to a SIP instance, the SIP LBM  150  can get a response from the instance with its received socket number. The response is sent as a Unix domain socket message via the connection which was established in step  506 . The SIP LBM  150  stores the pair of sockets numbers, in a SIP socket table. An exemplary SIP socket table can includes a matrix in which the rows are associated with the SIP transport sockets  128   a - c  and the columns are associated with the SIP instances  160   a - c , for example. In this example, each cell in the matrix will include the socket  129   aa - cc  that will be used by the appropriate instance  160   a - c.    
     At step  522  and  530 , method  500  waits to receive an event. An event can be received from the OS  120  ( FIG. 1 ) or from one of the SIP instances  160   a - c  ( FIG. 1 ). If the event is received  530  from one of the instances  160   a - c , then a decision is made  536  whether it is a DELETE API command. If  536  it is a DELETE API command received over one of the connections that was set in step  506 . The API DELETE commend can point the CID of the session. Based on the session CID the relevant entry from the SIP CID table  153  ( FIG. 1 ) is retrieved  538  and is released. The Active-Call Counter that is associated with the relevant SIP instance is decremented by one and method  500  returns to step  522 . If the event is not  536  a DELETE API command, method  500  returns to step  522  to wait for the next event. 
     If  530  the received event was received from the OS  120  ( FIG. 1 ) over one of the SIP transport sockets,  128   a - c  ( FIG. 1 ), then a decision is made  540  whether the session is based on TLS. The decision can be based on the SIP transport socket. If the SIP message was received via socket  128   a , then the session is an encrypted session based on TLS. Therefore, the message is decrypted  542  by TLS DEC  154  ( FIG. 1 ) and the decrypted message is transferred to parser  152  ( FIG. 1 ) for further analysis  544 . If  540  the SIP message is not based on the TLS, the message was received via socket  128   b  or  128   c , then the message is transferred to parser  152  ( FIG. 1 ) for further analysis  544  and method  500  proceed to step  552  in  FIG. 5   b.    
     Referring now to  FIG. 5   b , at step  552  a decision is made whether the analyzed SIP message is an INVITE request from a client. The INVITE request can be sent from a client that would like to start a new SIP session. If  552  yes, then method  500  may search  554  for a SIP instance  160   a - c  ( FIG. 1 ) that is available for handling the call. The selection can be based on the Active-Call Counter of each one of the instances, looking for the one with the least number of sessions, for example  160   a . If  560  an available SIP instance is found,  160   a , for example, then an entry in the SIP CID table  153  ( FIG. 1 ) is allocated  564  for the new session. The entry is updated with the CID of the session, the selected instance (for example,  162   a ) and the relevant socket  129   a - c,a  to be used by the selected SIP instance,  160   a  for example. The relevant socket is retrieved from the SIP socket table from the cell that is in the junction of the SIP transport socket  128   a - c  from which the session received and the selected instance,  160   a  for example. The Active-Call Counter of the instance is incremented by one, and the received SIP message is sent via the appropriate Unix domain Socket connection, established in step  506  ( FIG. 5   a ) or  562  as described below, to the selected instance. The CID of the session is retrieved from the parsed SIP message. An alternate embodiment may use other file descriptor sharing mechanism instead of Unix domain socket. At this point  570  method  500  returns to step  522  ( FIG. 5   a ) to wait for the next event. 
     If  560  an available SIP instance was not found, exemplary method  500  can create  562  a new instance. A connection between the SIP LBM and the new SIP instance can be establish in a similar way as the one that is disclosed above in conjunction with step  506  ( FIG. 5   a ). After setting the connection with the new instance, the SIP LBM  150  can send each one of the SIP transport sockets  128   a - c  to the new SIP instance as it is disclosed above in conjunction with step  520  ( FIG. 5   a ). Furthermore, the SIP LBM can get and store the socket number received by the instance, update the SIP socket table in a similar way to the description of step  520  and continues to step  564 . 
     Returning now to step  552 , if the SIP data is not an INVITE request, then the SIP CID is searched  556  for an entry that is associated with the parsed CID. The entry is retrieved and parsed to determine which SIP instance was associated to the session. Then, the SIP data is transferred to the associated SIP session as a UNIX Domain Socket message via the connection that was established in step  506  and method  500  returns  570  to step  522  in  FIG. 5   a.    
     The disclosed methods and systems have been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the disclosure. The described embodiments comprise different features, not all of which are required in all embodiments. Some embodiments utilize only some of the features or possible combinations of the features. Variations of embodiments that are described and embodiments comprising different combinations of features noted in the described embodiments will be apparent to persons of skill in the art. 
     In this application the words “unit” and “module” are used interchangeably. Anything designated as a unit or module may be a stand-alone unit or a specialized module. A unit or a module may be modular or have modular aspects allowing it to be easily removed and replaced with another similar unit or module. Each unit or module may be any one of, or any combination of, software, hardware, and/or firmware. Software of a logical module can be embodied on a computer readable medium such as a read/write hard disc, CDROM, Flash memory, ROM, etc. In order to execute a certain task a software program can be loaded to an appropriate processor as needed. 
     Various changes in the details of the illustrated operational methods are possible without departing from the scope of the following claims. For instance, illustrative processing processes  300  and  500  may perform the identified steps in an order different form that disclosed here. Alternatively, some embodiments may combine the activities described herein as being separate steps. Similarly, one or more of the described steps may be omitted, depending upon the specific operational environment the method is being implemented in. In addition, acts in accordance with  FIGS. 1-5  may be performed by a programmable control device executing instructions organized into one or more program modules. A programmable control device may be a single computer processor, a special purpose processor (e.g., a digital signal processor, “DSP”), a plurality of processors coupled by a communications link or a custom designed state machine. Custom designed state machines may be embodied in a hardware device such as an integrated circuit including, but not limited to, application specific integrated circuits (“ASICs”) or field programmable gate array (“FPGAs”). Storage devices, sometimes referred to as computer readable medium, suitable for tangibly embodying program instructions include, but are not limited to: magnetic disks (fixed, floppy, and removable) and tape; optical media such as CD-ROMs and digital video disks (“DVDs”); and semiconductor memory devices such as Electrically Programmable Read-Only Memory (“EPROM”), Electrically Erasable Programmable Read-Only Memory (“EEPROM”), Programmable Gate Arrays and flash devices. 
     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the invention is defined by the claims that follow.