KR20070111024A - Method of routing for interworking between local network and global network based on session initiation protocol, alg device and nat device thereof - Google Patents

Abstract

An SIP(Session Initiation Protocol) message routing method for SIP-based interworking between a private network and a public network, an application layer gateway device applied with the method, and an NAT(Network Address Translation) device are provided to suggest alterations necessary for an SIP message to solve an NAT-traversal problem of an SIP-based service, thereby being directly usable for development/implementation of a related node. A message transmission subject of a received SIP message and a method thereof are confirmed(S101). NAT based on the confirmed message transmission subject and method is applied to RTCP(Real Time Control Protocol) reception address information and media of the SIP message(S103). An address of a node selected on the basis of the confirmed message transmission subject is specified in routing path information of the SIP message(S105). The SIP message is routed to the corresponding destination address(S107).

Description

SIP message routing method for SPI-based interworking between private network and public network, application layer gateway device and network address translation device applying the same THEREOF}

1 is a diagram schematically illustrating a SIP message routing method according to an embodiment of the present invention.

2 is a diagram illustrating in detail a SIP message routing method according to a first embodiment of the present invention.

3 is a diagram illustrating in detail a SIP message routing method according to a second embodiment of the present invention.

4 is a diagram illustrating classification information according to a subject and a method of transmitting a SIP message according to an embodiment of the present invention.

5 and 6 are diagrams for comparing before and after converting a SIP message for SIP message routing according to an embodiment of the present invention.

7 is a diagram illustrating a SIP-based network interworking configuration according to the first embodiment of the present invention.

FIG. 8 is a block diagram illustrating an application layer gateway device of FIG. 7.

9 is a diagram illustrating a SIP-based network interworking configuration according to a second embodiment of the present invention.

FIG. 10 is a block diagram of the network address translation apparatus of FIG. 9.

The present invention relates to a SIP message routing method for SIP-based interworking between a private network and a public network, an application layer gateway device and a network address translation device using the same.

As IP network applications expand, their utilization increases, and public IP addresses are in very low demand.

Therefore, most carriers use NAT (Network Address Translation) technology for securing insufficient public IP address and securing network stability.

NAT translates a private IP address into a public IP address and a public IP address into a private IP address. In addition, as one NAT, Port Address Translation (PAT) translates not only IP addresses but also port numbers of TCP / UDP. This solves the problem of lack of public IP address by allowing a large number of public IP addresses to be used together.

However, since this NAT technology can only analyze up to the 3rd and 4th layer headers of the OSI model and not the upper layers, it can't be converted to a public IP address by NAT. I mean. Therefore, the Internet application including the identification information (source address, origination port) of the packet generating host in the payload in the 4th layer header of the packet is not supported. This is called a problem with NAT-Traversal.

In particular, the Session Initiation Protocol (hereinafter referred to as SIP), which is currently actively discussed for supporting multimedia services in IP networks, performs multimedia session negotiation between both ends using host information included in payload. Communication takes place.

Therefore, to connect a multimedia session using a SIP message between a private network and a public network, an application layer gateway (hereinafter referred to as ALG) capable of analyzing SIP messages is required.

However, there is no conventional proposal about what part of the SIP message should be converted.

Accordingly, the present invention provides a SIP message routing method for interworking a private network and a public network based on SIP.

Another object of the present invention is to provide an application layer gateway device implementing a SIP message routing method on a network node for interworking a private network and a public network based on SIP.

Another object of the present invention is to provide a network address translation apparatus implemented by integrating a SIP message routing method for interworking a private network and a public network based on SIP with existing NAT technology.

According to a feature of the present invention in order to achieve the above problems,

SIP message routing method,

A SIP message routing method of a node interworking a private network and a public network based on a Session Initiation Protocol (SIP), comprising: (a) identifying a message transmission subject and a method of a received SIP message; (b) applying network address translation (NAT) address translation based on the identified message transfer subject and method to the media and Real Time Control Protocol (RTCP) reception address information of the SIP message; (c) specifying an address of the node selected based on the identified message transmission subject in a routing path of the SIP message, where the routing path determines a routing path of a next request message; And (d) routing the SIP message to a corresponding destination address.

According to another feature of the invention,

Application layer gateway device,

In an Application Layer Gateway (ALG) device that performs routing of SIP messages for interworking a private network and a public network based on SIP, a node is configured in the private network, and a SIP message is received by receiving a SIP message. And a message receiving unit confirming the method; A message translator configured to perform NAT address translation on the media and RTCP reception address information of the SIP message and include address information of the node in a SIP message routing path based on the confirmation content; And a message transmitter for transmitting the converted message to a suitable routing path.

According to another feature of the invention,

Network address translation device,

A network address translation apparatus located at a boundary between a private network and a public network to perform routing of SIP messages, the apparatus comprising: a packet analyzer configured to analyze a received packet and determine whether a SIP message is present; And an application layer gateway driver for performing network address translation of host information for media reception and RTCP reception with reference to the NAT translation table for the SIP message, and including its address information in a routing path to route to a corresponding destination. .

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

In addition, the term module described herein refers to a unit for processing a specific function or operation, which may be implemented in hardware or software, or a combination of hardware and software.

In addition, when a part is said to "include" a certain component, this means that it may further include other components, except to exclude other components unless otherwise stated.

A SIP message routing method for SIP-based interworking between a private network and a public network according to an embodiment of the present invention, an application layer gateway device and a network address translator applying the same will be described in detail with reference to the accompanying drawings.

 1 is a diagram schematically illustrating a SIP message routing method according to an embodiment of the present invention.

According to FIG. 1, first, a message transmission subject and a method of a received SIP message are checked (S101). In this case, the message transmission subject indicates an incoming / outgoing subject and the method indicates whether the message is a request message or a response message. At this time, the SIP message is composed of a request message or a response message.

The NAT address translation suitable for the content checked in step S101 is applied to the media of the received SIP message and the RTCP (Real Time Control Protocol) reception address information (S103). That is, NAT address translation is performed according to whether the originating subject of the received SIP message is a private network or a public network and whether it is a request message or a response message. In addition, NAT address translation may be performed on the transport information of the SIP message, but this is not necessary since the SIP message routing node is assigned a public IP address. Here, the transport includes any one of a host name or network address information of a subject that transmits a SIP message, that is, a SIP client.

The address of the node corresponding to the content checked in step S101, that is, the address of the node that performs the SIP message routing, is included in the routing path of the SIP message (S107). Here, the routing path determines the routing path of the next request message (UPDATE, PRACK, etc.). That is, according to the routing path determined as described above, the SIP message received thereafter receives a SIP service request message using the private IP address of the node when the sender is a private network. In addition, when the transmission subject is a public network, the SIP service request message is received using the public IP address of the node.

The SIP message converted through the steps S103 and S105 is routed to the corresponding destination address (S107).

Hereinafter, a SIP message routing method according to a subject and a method of transmitting a SIP message will be described in detail with reference to FIG. 4.

First, FIG. 2 is a diagram illustrating a SIP message routing method according to a first embodiment of the present invention in detail. FIG. 4 illustrates a case corresponding to 'Case (1)' (P101) in FIG.

According to Figure 2, the message transmission subject receives a SIP message that the public network in the private network and the method is a session invitation request (S201).

In step S201, the media and the RTCP address allocated by the source specified in the Session Description Protocol (SDP) field of the SIP message received are extracted (S203). At this time, the extracted address is in the form of IP, that is, private IP.

Then, the allocation and translation of the public IP address for the address extracted in step S203 is performed (S205).

Then, the address allocation information performed in step S205 is temporarily stored (S207).

Then, the public IP address of the node performing SIP routing is specified in the routing path of the converted SIP message in step S207 (S209).

Then, in step S211, the SIP message specifying the routing path is transmitted to the destination address (S211).

In this case, in step S205, the public IP address may be allocated using a NAT address translation table. In addition, public IP address allocation may be performed by using a query method using an external server. As a query method using such an external server, a STUN (Simple Traversal of UDP through NAT) binding protocol may be used. At this time, the public IP address allocation using the stun binding protocol may obtain a NAT binding value by substituting the media and RTCP receiving address of the SIP message with the IP header information of the stun binding message.

Next, FIG. 3 is a diagram illustrating in detail a SIP message routing method according to a second embodiment of the present invention, which shows a case corresponding to 'Case (2)' (P103) in FIG.

According to Figure 3, the message transmission subject is a private network in the public network and the method receives a SIP message that is a response to the session invitation request (S301).

In step S301, the media and the RTCP address corresponding to the destination specified in the SDP field of the received SIP message are extracted (S303).

Then, the private IP address of the extracted address in step S303 is searched for and mapped to the extracted address and stored in the SIP address allocation table (S305).

Then, in step S307, including the private IP address of the node that performs the SIP message routing in the routing path of the SIP message that passed through the step S305.

The SIP message, which has passed through the step S307, is transmitted to the destination address (S309).

5 to 6 are diagrams for comparing before and after converting a SIP message for SIP message routing according to an embodiment of the present invention, which shows a case corresponding to 'Case (1)' (P101) in FIG. to be.

5 and 6, specifically, fields converted for routing in a SIP message are an SDP field (P205), a Via header field (P201), and a record-route field (P203).

In this case, the SDP field P205 is more specifically, a 'media receiving port (m attribute)' field (P207), a 'media receiving IP address (c attribute)' field (P209), and an RTCP receiving IP address and port ( a attribute) 'field P211 is converted.

In the 'media receiving port (m attribute)' field (P207), the media receiving port value assigned by the source is changed to the NAT converted value. At this time, all media types are converted, i.e., audio, video, and text (P213, P215, P217). This is a conversion necessary for receiving media from an external network, that is, a public network.

In the 'media destination IP address (c attribute)' field (P209), the media destination IP address assigned by the source is changed to NAT converted value. At this time, similarly, all media types are converted for audio, video, and text (P213, P215, and P217). This is a transformation necessary to enable media reception from external or authorized network.

The 'TCP TCP IP address and Port (a property)' field (P211) is changed from NAT to the IP address and port for RTCP. At this time, it is also converted for all media types, that is, audio, video, text (P213, P215, P217). This is necessary conversion in order to be able to receive RTCP from external network.

At this time, compared with FIG. 5, the converted part of each field P207, P209, P211 of FIG. 6 is shown in bold.

The Via header field P201 is for supporting the rport function in the Via header, and should include the 'rport' parameter in the message already sent from the calling terminal. In this case, it is preferable to extract the 'IP address' of the Via header field including the 'rport' parameter and the 'Source Port' value of the message, and specify the 'received' and 'rport' parameters, respectively, that is, rewrite the Via header. Do. In this case, the node performing SIP message routing has a public IP address statically mapped by NAT, so this is not a necessary translation.

The Record-Route field P203 is a field for specifying a proxy address so that the next request (eg, UPDATE, PRACK, etc.) message can be routed according to the message transmission subject. In this case, a next-request message is required because it must be routed through the node that performs the SIP ALG function.

Here, according to the message transmission subject, the message transmitted from the private network to the public network specifies the public IP address. In addition, the message sent from the public network to the private network specifies the private IP address.

5 and 6, the media destination address (private) is 10.10.10.14 (audio: 20000, video: 20002, text: 20004). The media destination address (authorized) is 200.200.200.1 (audio: 20000, video: 20002, text: 20004). The rtcp destination address (private) is 10.10.10.14 (port 20001) and the rtcp destination address (authorized) is 200.200.200.1 (port 20001).

Since the originating terminal (ue1) has a private IP address, the private receiving address is 10.10.10.14 (port is audio: 20000, video: 20002, text: 20004), and the NAT converted value of this IP address / port is 200.200.200.1 (ports are audio: 20000, rtcp: 20001, video: 20002, text: 20004).

Here, the address (private) of the node that performs the routing of the SIP message is 10.10.10.11 and the address (authorized) is 200.200.200.201.

FIG. 7 is a diagram illustrating a SIP-based network interworking configuration according to a first embodiment of the present invention, showing an example of implementing a SIP message routing method described with reference to FIGS. 1 to 6 at a node of a network. At this time, NAT address translation uses the stun binding protocol.

According to FIG. 7, an interworking configuration between a private network and a public network includes an originating terminal 100, an application layer gateway device 200, a NAT 300, a stun server 400, and a called terminal 500.

The originating terminal 100 and the terminating terminal 500 are terminating hosts on a communication line of the network. At this time, the originating terminal 100 is located in the private network 10 and is assigned a private IP address. In addition, the called terminal 500 may be a terminal that is located in the authorized network 20 and is assigned a public IP address or a terminal that is located in another private network and assigned a corresponding private IP address.

The application layer gateway device 200 changes the media reception information and the RTCP reception address information in the form of a private IP address from the SIP messages transmitted by the terminals 100 and 500 to the public IP address type obtained by the stun binding. It includes its address applied according to the transmission subject in the routing path and routes it to the corresponding terminal (100, 500). At this time, the public IP address by the stun binding may obtain the NAT binding value by replacing the media and RTCP receiving address information specified as the private IP in the received SIP message with the IP header information of the binding message.

The NAT 300 is located at the boundary between the private network 10 and the public network 20, and based on the Open System Interconnection (OSI) model, address translation for network layers and transport layers corresponding to layers 3 and 4 is performed. Do this.

Stern server 400 is connected to the public network 20 and provides binding information of the public IP address by the network address translation means 300. That is, when the stun binding request is received from the application layer gateway device 200, the information converted to the public IP address is extracted through the network address translation means 300 and provided to the application layer gateway device 200.

Here, the operation of the application layer gateway will be described in more detail with reference to FIG. 8.

FIG. 8 is a block diagram illustrating an application layer gateway device of FIG. 7.

According to FIG. 8, the application layer gateway device 200 includes a message receiver 210, a message converter 220, and a message transmitter 230.

The message receiving unit 210 receives the SIP message and checks the message transmission subject and method.

The message translator 220 performs NAT address translation on the media and RTCP reception address information of the SIP message based on the confirmation information of the message receiver 210 and includes the address information of the node in the SIP message routing path.

Here, the message conversion unit 220 includes a SIP address assignment storage unit 222, a SIP address assignment module 224, a SIP address mapping module 226, and a SIP message conversion module 228.

The SIP address assignment storage unit 222 stores information mapped to information before and after NAT address translation.

The SIP address assignment module 224 performs public IP assignment of the host information for RTCP reception and media of the received SIP message whose sender is a private network and the method is a session invitation request. More specifically, this includes the stun binding drive module 224a and the address assignment module 224b.

The stun binding drive module 224a replaces the media and the RTCP receiving address information of the session invitation request message with the IP header of the stun binding request message to obtain the stun bound address information.

The address assignment module 224b performs the SIP address assignment using the stunbound address information obtained by the stun binding drive module 224a.

The SIP address mapping module 226 stores the host information for RTCP reception and media of the SIP message in which the sender is a public network and the method is a response to the session invitation request, and the SIP address pre-assignment information by the SIP address assignment module 224. The data is mapped and stored in the SIP address allocation storage unit 222.

SIP message translation module 228 works in conjunction with SIP address assignment module 224 and SIP address mapping module 226 to perform appropriate SIP address translation. In addition, the public IP address of the application layer gateway device 200 is specified in the routing path of the session invitation request message. In addition, the private IP address of the application layer gateway device 200 is specified in the routing path of the response message for the session invitation request.

More specifically, this includes a first address translation module 228a, a second address translation module 228b, and a routing path creation module 228c.

The first address translation module 228a performs address translation of media of SIP messages and host information for RTCP reception.

The second address translation module 228b performs address translation of the transport information of the SIP message, where the transport includes either the hostname or the network address of the sender.

The routing path creation module 228c creates a routing path of a response to the SIP service request message as a public IP address or a private IP address of the application layer gateway device 200 according to the message transmission subject.

Here, the service request message or the service response message is received through the message receiving unit 222 using the private IP address or the public IP address thus prepared.

The message transmitter 230 transmits the message converted by the message converter 220 to an appropriate routing path.

FIG. 9 is a diagram illustrating a SIP-based network interworking configuration according to a second embodiment of the present invention. The SIP message routing method described with reference to FIGS. 1 to 6 is applied to an existing NAT technology. At this time, NAT address translation uses a NAT translation table.

According to FIG. 9, the SIP-based network interworking configuration diagram includes a calling terminal 600, a network address translation apparatus 700, and a called terminal 800.

Since the calling terminal 600 and the called terminal 800 are the same as the contents of FIGS. 7 to 8, detailed description thereof will be omitted.

The network address translation apparatus 700 is located at the boundary between the private network 30 and the public network 40 to perform a NAT function, and performs a SIP application layer gateway function to enable SIP-based network interworking.

More specifically, the packet analyzer 720 and the application layer gateway driver 740 are included.

The packet analyzer 720 analyzes the received packet and checks whether a SIP message is present. At this time, the source address and the port number of the packet are analyzed to determine whether the SIP message. That is, since SIP uses 5060 as the default port number, there is a way to check whether it is a SIP message using this port number.

If the message received as a result of the packet analyzer 720 is a SIP message, the application layer gateway driver 740 performs NAT translation of host information for media reception and RTCP reception with reference to a NAT translation table. It includes its address information in the routing path and routes it to its destination.

In this case, when the received packet is not a SIP message as a result of the analysis of the packet analyzer 720, the existing NAT operation of converting an IP header or other additional elements and transferring the same to other layers is performed.

The detailed configuration of the application layer gateway driver 740 is as shown in FIG. 10.

According to FIG. 10, the application layer gateway driver 740 may include a message analysis module 742, a SIP address assignment module 744, a first message translation module 746, and a second message translation module 748. ).

The message analysis module 742 analyzes the method and the message transmission subject of the SIP message received from the packet analyzer 710.

The SIP address assignment module 744 uses the NAT address translation table to perform SIP address assignment and mapping suitable for the analyzed method and message transfer subject. This more specifically includes allocator 744a and mapper 744b.

The allocator 744a uses the NAT address translation table to assign a public IP corresponding to the media and RTCP destination address information of the SIP message.

The mapper 744b configures the SIP address allocation table by mapping the public IP address allocated to the media and RTCP address information with the private IP address before allocation.

The first message translation module 746 performs SIP message translation using the address assigned by the SIP address assignment module 744. In this case, the allocated public IP may be applied to transport information of the SIP message, that is, information including any one of a host name or a network address of the sender.

The second message conversion module 748 includes its public IP address in the routing path when the subject of the SIP message is a private network. In addition, if the sender is a public network, the private IP address is included in the routing path.

Based on the above description, the necessary address translation of the SIP message header is minimized by the 'm', 'c' parameter of the SDP, the 'a' parameter of the RTCP, and the 'record-route' parameter. Therefore, SIP-based communication between the private network and the public network is required without the need to convert multiple fields such as Request-URI, Via, Contact, Route, From, To, Error-info, Proxy-authenticate, WWW-authenticate, and Warning of SIP messages. Network interworking can be implemented.

The embodiments of the present invention described above are not implemented only through the apparatus and the method, but may be implemented through a program for realizing a function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded. Implementation may be easily implemented by those skilled in the art from the description of the above-described embodiments.

The scope of the present invention is not limited to the above-described embodiments, but various modifications and improvements of those skilled in the art using the basic concept of the present invention as defined in the following claims are also within the scope of the present invention.

By the above-described configuration, by providing the necessary changes in the SIP message substantially for solving the NAT-Traversal problem of the SIP-based service, it provides an effect that can be directly utilized in the development / implementation of the relevant node.

Claims (19)

In a SIP message routing method of a node in which a private network and a public network are interworked based on a Session Initiation Protocol (SIP), (a) identifying the message transmission subject and method of the received SIP message; (b) applying network address translation (NAT) address translation based on the identified message transfer subject and method to the media and Real Time Control Protocol (RTCP) reception address information of the SIP message; (c) specifying an address of the node selected based on the identified message transmission subject in a routing path of the SIP message, where the routing path determines a routing path of a next request message; And (d) routing the SIP message to a corresponding destination address SIP message routing method comprising a. The method of claim 1, Step (b) is Extracting an m / c / a attribute value in a Session Description Protocol (SDP) of the SIP message; And Converting the extracted m / c / a attribute value into a public IP address SIP message routing method comprising a. The method according to claim 1 or 2, Step (b) is When the transmitting entity is a private network and the method is a session invitation request message, converting the reception address information of the media and the RTCP into a public IP, mapping the information with the pre-conversion information, and temporarily storing the information; And Storing the temporarily stored mapping information in a SIP address allocation table when the transmitting entity is a public network and the method is a response message to the session invitation request message SIP message routing method comprising a. The method of claim 3, Step (c) is Specifying the public IP address of the node when the message transmission subject is a private network; And Specifying the private IP address of the node if the message transmission subject is a public network; SIP message routing method comprising a. The method of claim 4, wherein After the step (d), If the sender is a private network, receiving a SIP service request message using the node's private IP address; Receiving a SIP service request message by using a public IP address of the node when the transmitting entity is a public network; And Routing the received message to a corresponding destination SIP message routing method further comprising. The method of claim 5, Step (b) is Applying the NAT address translation to transport information of the SIP message, wherein the transport includes either hostname or network address information of the sender; SIP message routing method further comprising. The method of claim 6, Step (b) is SIP message routing method using the NAT address translation table to perform the NAT address translation. The method of claim 6, Step (b) is SIP message routing method characterized in that for performing the NAT address translation using a query method using an external server. The method of claim 8, Step (b) is Performing the NAT address translation using a STUN (Simple Traversal of UDP through NAT) binding protocol, The NAT address translation Extracting the media and Real Time Control Protocol (RTCP) reception address information specified as a private IP from the received SIP message; And Substituting the extracted information with IP header information of a binding message to obtain a NAT binding value for the extracted information; SIP message routing method comprising a. In the Application Layer Gateway (ALG) device that performs the routing of SIP messages for interworking a private network and a public network based on SIP, Configure one node in the private network, A message receiver for receiving a SIP message and checking a message transmission subject and a method; A message translator configured to perform NAT address translation on the media and RTCP reception address information of the SIP message and include address information of the node in a SIP message routing path based on the confirmation content; And Message transmitting unit for transmitting the converted message to the appropriate routing path Application layer gateway device comprising a. The method of claim 10, The message conversion unit A SIP address assignment storage unit for storing information mapped to the NAT information before / after NAT address translation; A SIP address assignment module for allocating a public IP for the media of the SIP message and the host information for RTCP reception, wherein the sender is a private network and the method is a session invitation request; The SIP address assignment is stored by mapping the host information for RTCP reception and media of a SIP message in which the sender is a public network and the method is a response to the session invitation request. SIP address mapping module for storing in the unit; And Perform appropriate SIP address translation by the SIP address assignment module and the SIP address mapping module, specify the public IP address of the node in the routing path of the session invitation request message, and route the response message to the session invitation request SIP message conversion module specifying the node's private IP address in the path Application layer gateway device comprising a. The method of claim 11, The message receiving unit Application layer gateway device for receiving a service request message and a service response message using the private IP address and the public IP address of the node. The method according to any one of claims 10 to 12, The SIP message conversion module A first address translation module for extracting an m / c / a attribute value in SDP of the SIP message and performing address translation thereof; A second address translation module for performing address translation of the transport information of the SIP message, wherein the transport includes either a host name or a network address of the sender; And Routing path creation module which creates routing path of response to SIP service request message as public IP or private IP node of the node according to message transmission subject Application layer gateway device comprising a. The method of claim 13, The SIP address assignment module The application layer gateway device, characterized in that for performing the SIP address assignment using the NAT binding information of the address information of the conversion target obtained by querying an external server. The method of claim 14, The SIP address assignment module A stun binding driving module for obtaining the stub bound address information by replacing the m / c / a attribute value of the session invitation request message with an IP header of the stun binding request message; And An address allocation module for performing the SIP address allocation using the obtained stunbound address information Application layer gateway device comprising a. In the network address translation apparatus located at the boundary between the private network and the public network to perform the routing of SIP messages, A packet analyzer for analyzing a received packet to determine whether a SIP message is present; And An application layer gateway driver for performing network address translation of host information for media reception and RTCP reception by referring to the NAT translation table for the SIP message, and including its address information in a routing path to route to a corresponding destination. Network address translation apparatus comprising a. The method of claim 16, The application layer gateway driver A message analysis module for analyzing a method and a message transmission subject of the SIP message received from the packet analyzer; A SIP address assignment module which calls a NAT address assignment module and performs SIP address assignment and mapping suitable for the analyzed method and message transmission subject; A first message translation module applying the address assigned by the SIP address assignment to the SIP message; And A second message conversion module configured to include its own public IP address in the routing path when the sender of the SIP message is a private network and to include its private IP address in the routing path when the sender is a public network; Network address translation apparatus comprising a. The method of claim 17, The SIP address assignment module, An allocator for allocating a public IP assigned from the NAT address assignment module to an m / c / a attribute value in the SDP of the SIP message; And A mapper that configures a SIP address allocation table by mapping public IP information allocated to the m / c / a attribute value and private IP address before allocation. Network address translation apparatus comprising a. The method according to any one of claims 16 to 18, The first message conversion module And the transport information of the SIP message, the assigned public IP, wherein the transport includes any one of a host name and a network address of the sender.

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