Abstract:
A connection between an external host and a host internal to a network (e.g., VPN or LAN) and located behind a firewall and/or NAT-enabled device is established and maintained. A dynamic DNS server is updated with the remote location (RL) information associated with the internal host. This information includes the dialed number (i.e. the number assigned to the internal host), the physical address of the internal host, the private IP address corresponding to the internal host, the public IP address corresponding to the firewall, and the port on which voice data is to be communicated. Each time the internal host&#39;s location changes, a new and updated record is sent to the dynamic DNS server. The call placed by an external host reaches its final destination based on the record information in the DNS server table. Once the connection between the external host and the internal host is established, voice traffic is “cut-through” the firewall on this channel associate with the port designated by the RL record.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of IP telephony. More specifically, the present invention is related to IP telephony behind firewalls. 
     2. Discussion of Prior Art 
     Deployment of IP telephony has been slow and thus far, not particularly widespread because of compatibility issues with firewalls and network address translators (NAT). Provisions for roaming IP telephony devices within a network or networks have been limited, as most organizations, from large corporations to small businesses, employ the use of these network devices. Thus, users residing in these networks are often precluded from fully utilizing and benefiting from IP telephony. Networks protected by firewalls that allow persistent, un-monitored channels become highly vulnerable since an unmonitored channel makes the network susceptible to inbound, unfiltered, malicious traffic. Additional complications arise due to the fact that IP telephony solutions for networks having NAT require the discovery of NAT translations. This achieves less than optimal performance, since an additional piece of software must discover compression and de-compression techniques as well as NAT translations to allow for the discovery of prematurely closed telephony connections through the firewall. Thus, additional software, processing, memory, and disk storage space are required. 
     The following patents provide a general teaching of IP telephony. 
     U.S. Pat. No. 6,161,008 discloses a method for establishing communications with a user that employs multiple heterogeneous networks. A personal mobility application receives a request from a calling user containing the personal identifier of a called user. The personal identifier is used to retrieve a user record containing a plurality of terminal records, with each of the terminal records having a respective terminal address. Analyzing network usage profiles or user profiles determines the terminal address to which the calling user connects. This method does not guarantee that a terminal device will receive the call placed by the calling user. Rather, the method provides for a way to select the most likely choice of terminal address to which the user is connected. 
     U.S. Pat. No. 6,144,671 discloses a personal mobility method for allowing a called user having a personal host connected to a packet-based communications network at a home address to receive, at a foreign host connected to the network having an in-care-of address, a multimedia call from a calling user originally directed towards the personal host of the called user. Also disclosed is an application-layer solution for distributing multimedia calls among a plurality of peer computing devices, each of which has an address. 
     U.S. Pat. No. 6,359,880 discloses a localized wireless gateway offering cordless telephone service, including voice communication service, via a public packet network. The system includes a plurality of base station transceivers that provide two-way wireless voice frequency communications for wireless terminals and a packet service gateway that selectively couples the base station transceivers to the public packet data network. Also disclosed is an access manager that controls registration and validation of roaming wireless terminal devices, as well as transmission of location information for registered terminals to a home location register database via a public packet data network. 
     U.S. Pat. No. 6,345,294 discloses a method that allows a network appliance to boot-up remotely by obtaining configuration information from a remote source. The network appliance is able to contact a remote appliance registry to obtain information about its local environment, regardless of whether a local DHCP server or boot server exists on the local network. The appliance adheres to a principle of self-organization; it boots and observes the local environment of the LAN. The appliance broadcasts a request and waits to see whether there are responses. This method provides for a single remote configuration source that is known to the network appliance upon boot-up. It does not provide for the network appliance to obtain configuration information from a plurality of remote configuration sources. 
     U.S. Pat. No. 6,154,839 discloses a method for allowing a remote client to connect to a VPN through a firewall from an unknown network address. Also disclosed is a method for load balancing across multiple VPN units that couples a private network to a public network. A data packet sent from a source node to a destination node is translated and delivered on the basis of a user identifier field in the packet. The allows the data packet to be forwarded to the destination node if the user identifier is allowed communication privileges with the destination node. Thus, a list of user identifiers corresponding to all possible calling parties needs to be maintained. This method fails to provide communication privileges with the destination node in the event the user identifier is unknown, even if the network address is unknown. 
     U.S. Pat. No. 6,233,234 discloses a convenient and secure method of Internet telephony communication. Selectable security is provided for telephony applications through the use of an access gateway between the LAN and the packet switched data network. Information obtained from a party seeking to connect to a telephone terminal connected to the LAN is used to filter traffic on the basis of incoming or outgoing addresses or protocol. The destination terminal may only be reached first reaching the centralized access gateway, which eventually uses further information to use translation and filter tables to effect a connection to the telephone station. 
     The above-mentioned prior art references seek to provide IP telephony services in a secure environment by utilizing lookup tables for the purposes of: translation, identification of the user, or filtration of communications requiring additional software, processing, memory, and disk storage space. There is a need, however, for a system to provide a method to reliably establish and maintain connection with an internal host behind a firewall, regardless of the location of the host. Whatever the precise merits, features, and advantages of the above-cited references, they fail to achieve or fulfill the purposes of the present invention. 
     SUMMARY OF THE INVENTION 
     The present invention provides for a system and method for facilitating communication between IP phones (with an assigned phone number) over a packet-based communication protocol, wherein the IP phones are located behind a firewall. The present invention&#39;s IP phone comprises DHCP client software and IP agent software. The DHCP client software, upon an initial power up of the IP phone, communicates with its firewall to receive an IP address. The IP agent software, upon receiving said IP address from said firewall, registers the IP phone with a DNS switch based upon at least the following parameters: the assigned phone number, the received IP address, a public IP address associated with the firewall, or a MAC address associated with the IP phone. Upon successful registration with said DNS switch, the IP agent software receives a port number and address over which future communications are to be performed. 
     In one embodiment, communications between the IP agent and the DNS switch is via the Transmission Control Protocol/Internet Protocol (TCP/IP) protocol. 
     In another embodiment, the IP agent additionally monitors and detects changes to the public IP address associated with the corresponding firewall; upon detecting such a change, the IP agent identifies a new public IP address of said firewall and reregisters the newly identified public address with the DNS switch based upon at least the following parameters: the assigned phone number, the received IP address, the identified new public IP address associated with corresponding firewall, or the MAC address associated with said IP phone. In an extended embodiment, the IP agent monitors changes to the public IP address associated with the corresponding firewall at pre-set time intervals. In yet another embodiment, the DNS switch is behind an Internet Service Provider (ISP) gateway. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an overview of the present invention system for facilitating communication between an IP phone (behind a firewall) and a dynamic DNS switch over a network. 
         FIG. 2  illustrates a timeline diagram outlining a method associated with the preferred embodiment of the present invention. 
         FIG. 3  illustrates a further extension to the scenario depicted in  FIG. 2 , wherein a timeline diagram shows the interaction between two IP phones and a dynamic switch. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While this invention is illustrated and described in a preferred embodiment, the invention may be produced in many different configurations. There is depicted in the drawings, and will herein be described in detail, a preferred embodiment of the invention, with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention and the associated functional specifications for its construction and is not intended to limit the invention to the embodiment illustrated. Those skilled in the art will envision many other possible variations within the scope of the present invention. 
       FIG. 1  illustrates an overview of the present invention system for facilitating communication between an IP phone  102  behind firewall  104  and a dynamic DNS switch  108  over a network  106 . The IP phone of the present invention comprises DHCP client software  110  and IP agent software  112 . Network  106  is any of, but is not limited to, the following networks: a local area network (LAN), wireless networks, or the Internet. 
     DHCP client software  110 , upon an initial power up of IP phone  102 , communicates with firewall  104  to receive an IP address. Upon receiving the requested IP address from firewall  104 , IP agent software  112  registers with dynamic DNS switch  108  based upon at least the following parameters: the assigned phone number of IP phone  102 , said received IP address, a public IP address associated with said firewall, or a MAC address associated with said IP phone. Upon successful registration with dynamic DNS switch  108 , IP agent software  112  receives a port number and address over which future communications are to be performed. Hence, all future communications addressed to IP phone  102  are routed through the received port number and address. 
       FIG. 2  illustrates a timeline diagram outlining a method associated with the preferred embodiment of the present invention. Specifically,  FIG. 2  illustrates various interactions between IP phone  202 , firewall  204 , ISP gateway  206 , and dynamic DNS switch (DNS/SW)  208 . 
     At power up, as shown in steps  210  and  212 , IP phone  202  and firewall  204  establish connections to their respective DHCP servers (i.e.,  214  and  216 , respectively). In steps  218  and  220 , the DHCP servers  214  and  216  issue a lease and an IP address for the respective clients (i.e., clients IP phone  202  and firewall  204 &#39;s DHCP client  215 ). In step  222 , IP phone  202  detects its media access control (MAC) address. The MAC address to ensure the correct phone is registered. Dialed Number (DN), i.e., the number assigned to the phone, is programmed in and associated with by the Dynamic DNS/SW. This association is made during provisioning of the service. IP agent residing in IP phone  202  establishes a TCP/IP connection to the Dynamic DNS/SW  208 which remains up as long as the phone is in service with keep-alive messages. 
     In step  224 , after firewall  204  has assigned the IP address (e.g., 172.198.X.X—private address) to the IP phone  202 , the IP agent residing in the IP phone  202  queries firewall  204  for its public IP address. It is envisioned that step  224  can be implemented via various ways. For example, in one embodiment, a custom browser is used to make an HTTP GET( ) query to the HTTPD service, running on almost any commercial firewalls today. It should be noted that although this is one method, there are others—including the maintenance channel using CLI interfaces on larger firewall-routers. Thus, in step  226 , a public IP associated with firewall  204  is returned to the IP phone  202 . 
     Once the IP agent has determined the public IP address, it sets a timer which is configurable (e.g., a timer in the range of 515 seconds). In step  228 , the IP agent is able to register with the Dynamic DNS/SW  208  by sending a message comprising the following information:
     1. DN Dialed Number   2. MAC Address   3. Private IP address   4. Public IP address   5. Port (this is the port which will be used for bearer communication on calls)   

     Dynamic DNS/SW  208 , upon receipt of this information, validates that the number is in service and updates its DNS database with the routing information required to communicate with the phone. In step  230 , Dynamic DNS/SW  208  sends back an acknowledgment message to the phone and then initiates a listen (PORT) on the port indicated in the registration message. 
     A TTL (time to live) timer is set in the dynamic DNS/SW  208  to indicate for how long this address is valid for, before dynamic DNS/SW  208  should re-query the hosting platform for address information. Information regarding the IP phone is stored as an “RL” (remote location) record in DNS. 
     As shown in steps  232 - 236 , if a change in firewall  204 &#39;s public IP is detected, the new public address for firewall  204  is detected, and such information is used to reregister the IP phone with the dynamic DNS/SW  208 . 
     The dynamic DNS/SW  208  also stores the original home location so, if any of the following occurs, calls will revert to the home location and be processed as would be expected.
     1. Signaling channel dropped or not responsive.   2. New registration attempted but old registration not dropped.   

     At this point, incoming calls can be properly routed to the IP phone  202 . For example, in step  238 , when the dynamic DNS/SW  208  receives an incoming call request, it forwards that request over the signaling channel to the IP phone  202  and waits for a CONNECT( ) to be received on the port it is listening to (i.e., the port that was identified for communication at registration time). This allows all connections to be established from behind the firewall out to the network, thus avoiding the typical NAT/NAT (network address translation) problems that occur when communication is established in the other direction. Once the CONNECT( ) is received by the dynamic DNS/SW  208 , it is answered and the bearer traffic is cut through. 
       FIG. 3  illustrates a further extension to the scenario depicted in  FIG. 2 , wherein a timeline diagram shows the interaction between two IP phones  302  and  304  and dynamic switch  306 . At powerup, IP phones  302  and  304  activate the DHCP client software (not shown) to receive an IP address from their respective firewalls (i.e.,  308  and  310 . In steps  312  and  314 , IP phones  302  and  304  activate the IP agent software, which opens a socket connection (via, for example, the TCP/IP protocol) to dynamic DNS/SW  306 on a port (e.g., port  32787 ). The connection made via TCP/IP to the soft switch is maintained as the soft switch makes the connection between the incoming side and the out going side. In steps  316 and  318 , the IP agent software of each phone sends a register message to the dynamic DNS/SW  306  containing the corresponding MAC addresses, the Private IP address the Phone, the Public IP address assigned to the corresponding firewall, and its corresponding assigned phone number. 
     Once the registration is complete and validated (by sending acknowledgement signals in steps  320  and  322 ) by the dynamic DNS/SW  306 , a port and address (over which future communications are to be addressed to) are sent by DNS/SW  306 . This is maintained by the IP agent in phones  302  and  304   
     In step  324 , dynamic DNS/SW  306  receives an incoming request (call) for the phone number associated with registered IP phone  302 . Next, in step  326 , dynamic DNS/SW  306  sends an alert message to registered IP phone  302  on the signaling channel. IP phone  302 , in step  328 , establishes a bearer connection from the phone back to the dynamic DNS/SW on the assigned port (e.g., port  70 ). 
     Once the connection has been received by dynamic DNS/SW  306  on the assigned port, it then connects the incoming port to the port of the called party&#39;s phone (i.e., IP phone  304 ). At this point, the dynamic DNS/SW monitors the communication link for disconnections. It should be noted that port connections are made using any standard protocol, including but not limited to: Session Initiated Protocol (SIP) or Media Gateway Control Protocol (MGCP). 
     Furthermore, the present invention includes a computer program code based product, which is a storage medium having program code stored therein which can be used to instruct a computer to perform any of the methods associated with the present invention. The computer storage medium includes any of, but is not limited to, the following: CD-ROM, DVD, magnetic tape, optical disc, hard drive, floppy disk, ferroelectric memory, flash memory, ferromagnetic memory, optical storage, charge coupled devices, magnetic or optical cards, smart cards, EEPROM, EPROM, RAM, ROM, DRAM, SRAM, SDRAM, and/or any other appropriate static or dynamic memory or data storage device. 
     Implemented in computer program code-based products are software modules for: (a) communicating with said firewall to receive an IP address; (b) registering with a DNS switch based upon at least the following parameters: said assigned phone number, said received IP address, a public IP address associated with said firewall, or a MAC address associated with said IP phone; and (c) computer readable program code, upon successful registration with said DNS switch, receiving a port number and address over which future communications are to be performed. 
     CONCLUSION 
     A system and method has been shown in the above embodiments for the effective implementation of a method and system facilitating remote location VOIP roaming behind firewalls. While various preferred embodiments have been shown and described, it will be understood that there is no intent to limit the invention by such disclosure but, rather, it is intended to cover all modifications falling within the spirit scope of the invention as defined in the appended claims. For example, the present invention should not be limited by specific port numbers used for communication with the dynamic DNS/SW, specific duration of time to live timer, number of IP phones behind a firewall, method used to obtain public IP of a firewall, software/program, computing environment, or specific networking hardware. 
     The above enhancements are implemented in various computing environments. For example, the present invention may be implemented on a conventional IBM PC or equivalent, multi-nodal system (e.g., LAN) or networking system (e.g., Internet, WWW, wireless web). All programming and data related thereto are stored in computer-memory, static or dynamic, and may be retrieved by the user in any of: conventional computer storage, display (i.e., CRT) and/or hardcopy (i.e., printed) formats. The programming of the present invention may be implemented by one of skill in the art of networking.