Method of implementing multimedia protocol passing through network address transform device

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DESCRIPTION

Method of implementing multimedia protocol passing through a network address translation device.

Field of the invention

The present invention relates to multimedia communication technology, particularly to a method for implementing multimedia protocol passing through a Network Address Translation device.

Background of the invention

All multimedia communication protocols involve the transmission of multimedia streams (audio / video streams); and for the transmission of multimedia streams in IP networks it is more suitable to use the UDP protocol. For this reason, today, most multimedia communication protocols use UDP to carry multimedia streams. However, since UDP is a connectionless transport layer protocol, Network Address Translation (NAT) devices cannot determine to which private network incoming UDP packets should be forwarded; as a consequence, UDP packets transmitted from a public network to a private network will be rejected by NAT devices, resulting in the final failure of multimedia communication.

The modes for the address translation of the NAT device can be classified: static NAT, dynamic NAT, and NAPT (Network Address and Port Translation). Currently, solutions are available for passing the multimedia communications protocol through NAT in either of the first two NAT modes described above: the static NAT solution and the dynamic NAT solution.

The static NAT solution is implemented as follows: The IP addresses of the private terminal network that request multimedia communication are matched with IP addresses of the public network in the NAT, that is, the NAT reserves IP addresses in advance of the public network for multimedia terminals in private networks.

Based on the static NAT solution, a dynamic NAT solution is introduced: when multimedia communication occurs (detected on a known port, for example, the known calling port for the H.323 protocol is 1720), the NAT assigns a certain IP address of the public network to the multimedia terminal in the private network dynamically, until the multimedia communication has ended. Although there have been improvements to this solution compared to the static NAT solution, it is still impossible to reserve IP address resources on public networks. This is because once a certain IP address of a public network has been assigned to a certain terminal of a private network, other terminals cannot use this IP address of the public network before the multimedia communication of this terminal has finished. terminal.

US Patent Application Publication No. 2002/114319 A1 discloses a method of communication of audio signals between a first telephony client located behind a network address translation server and a second remote telephony client, in which a calibration datagram is sent from the first telephony client to the second telephony client over an identified User Datagram Protocol (UDP) channel to send audio data, the second telephony client extracts the source address and port number to identify a reverse UDP channel to send audio data to the first telephony client.

US Patent Application Publication No. 2003/048780 A1 discloses an arrangement to allow continuous real-time data flows through a network address translator, in which the existing configuration of a network address translator is used to perform protocol preparation. After a TCP connection is established, user datagram protocol preparation establishes a data channel, Through which continuous data streams can be sent between two end points of the network through an existing network address translator.

International Patent Application Publication No. WO 01/30036 A1 discloses an arrangement for H.323 proxies, with which a network adapter is provided. The network adapter provides mechanisms to let H.323 traffic pass through firewalls and a wide range of functionalities such as firewall support, NAT, multiplexing of multimedia streams, QoS mechanisms, performance improvements for signaling connections, eavesdropping , bridging, interaction with media channels, and integrity, authentication and privacy between network adapters.

However, for NAPT mode, there is still no solution for passing a multimedia communication protocol through NAT. NAT devices are designed to reserve IP address resources from a public network. However, in existing solutions, it is impossible for an IP address of a public network to be shared by multiple multimedia communication terminals in a private network. In many cases involving private network endpoints (or other H.323 nodes), the waste of public network IP addresses is unavoidable, which means that the primary function of NAT devices - reserving public network IP addresses - does not have sense in multimedia applications.

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Summary of the invention

The objective of the present invention is to provide a method to implement the passage of multimedia protocols through a Network Address Translation device, to solve the problem that multimedia communication protocols cannot traverse a NAT device in the mode NAPT in the prior art.

The present invention provides a technical solution to solve the mentioned problem, the technical solution is as follows:

Method to implement the passage of multimedia protocols through a Network Address Translation device, the Network Address Translation (NAT) device establishes a correspondence relationship between the address of a terminal in a private network and the address of a terminal on a public network, and allows the terminal on the private network to access the public network with a common address, to implement the interaction of multimedia flows between the terminal in the private network and the terminal in the public network, in which the common address is an address of the private network to access the public network, in which the method comprises the following stages:

The terminal in the private network acquires the address of the terminal in the public network to send multimedia streams;

The terminal in the private network sends a redirection packet, in which the destination address of the redirection packet is the address of the terminal in the public network to send streaming media;

The NAT device substitutes the source address in the redirection packet with the common address and sends the substituted redirect packet to the public network terminal, and maps the addresses in the redirect packet before substitution and the addresses in the redirect packet after the replacement;

The terminal in the public network sends a multimedia stream, in which the destination address of the multimedia stream is the common address. The NAT device replaces the destination address in the multimedia stream with the address of the terminal in the private network according to the correspondence relationship, in which the terminal in the private network sends (4) redirection packets periodically to update the time of timing for the mapping.

According to the solution described above:

The source address in the redirect packet is the receiving port number and the private network IP address of the private network terminal.

The terminal in the private network sends a request message to the terminal in the public network to acquire the address of the terminal in the public network to send multimedia streams.

The private network terminal sends the request when the multimedia stream sent from the public network terminal has not been received in a previously set period of time after the "Open Media Channel" signaling has been received from the terminal. the public network.

The previously set period of time is less than the time for which the terminal will automatically disconnect from the private network when no continuous stream of code is received.

The terminal of the private network sends redirection packets periodically, to update the timing time for the mapping in the NAT device.

The private network terminal performs the interaction through an extension field in the protocol message when the private network terminal sends a request to the public network terminal to obtain the source address to send multimedia streams.

The present invention implements a successful protocol passthrough without the need to modify the firewall (FW) / NAT device. With the present invention, users can execute multimedia communication (eg H.323 communication) between public networks and private networks without the need to buy any new device; Therefore, not only can the problem of communication failure of multimedia communication protocols passing through NAT be solved, but a common IP address of the public network can also be used to reserve IP address resources. of public networks.

Brief description of the drawings

Fig. 1 is a schematic diagram of a network connection for carrying out the present invention;

Fig. 2 is a flow chart of one embodiment of the present invention.

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Detailed description of the realizations

Hereinafter, the present invention is described in an embodiment with the H.323 protocol, which is the most widely used multimedia communication protocol as an example.

Referring to Fig. 1, terminals T1 and T2 are two H.323 terminals in a private network; terminal T3 is an H.323 terminal in a public network; GK is a Gatekeeper in the H.323 protocol.

Referring to Fig. 2, the process in which the terminal T1 of the private network makes a call towards the terminal T3 of the public network is as follows:

The terminal T1 of the private network sends a setup signaling towards the terminal T3 of the public network;

When it receives the setup signaling from the terminal T1 of the private network, the terminal T3 of the public network returns a connection signaling to the terminal T1 of the private network;

The T1 establishes an H.245 connection with the T3 using the H.245 address of the terminal T3 of the public network carried in the connection signaling; then T1 and T3 perform a mutual H.245 signaling interaction.

The above process is fully compliant with the H.323 protocol specification. For detailed information on the process, see “ITU-T Recommendation H.323”.

As the interaction fully conforms to the standardized protocol, it is impossible for multimedia streams to reach terminals of the private network from the public network. The present invention achieves the objective of a free communication between terminals of the public and private network executing an interaction of certain extension information (not specified in the protocol) on the basis of the standardized protocol. The extension information interaction process is detailed as follows:

1. When a terminal of the private network receives an “Ack Open Media Channel (OMC Ack)” signaling from an opposite terminal (that is, the terminal of the public network with which it connects), Timer 0 is started, in which the time interval of the timer should be less than the time for which the terminal is automatically disconnected when no code stream is received, preferably 5 s.

Timer 0 will stop if a successful media stream is received before the Timer 0 timing. That the terminal has received the multimedia stream means that there is no NAT device that does not support the H.323 protocol, and normal communication can be performed without using the method provided in the present invention; therefore, the calling process after Timer 0 has been stopped follows the standard H.323 protocol, and the following steps are not necessary.

If the terminal T1 of the private network has not received any multimedia stream from the terminal T3 of the public network after the timing of Timer 0, this situation means that there is a NAT device (s) that does not support (s) the H.323 protocol; therefore, the method provided in the present invention must be used to allow multimedia streams to pass through the NAT device (s) successfully, and the process must continue to stage 2.

2. T1 requests the source IP address (that is, the source IP of the UDP packet header that carries the media stream) and the source port (that is, the source port of the UDP packet header that carries the media stream ) of the multimedia stream through an extension field in the H.245 message after the Timer 0 timeout.

3. Similarly, the public network terminal T3 notifies the private network terminal of the source IP address and source port (ip_b, port_b1) of the multimedia stream through the extension field in the H.245 message when it receives the request sent from the terminal T1 of the private network.

Four. The terminal of the private network periodically sends redirection packets, which are defined in the following table, to the source address (ip_b, port_b 1) of the multimedia stream of the opposite terminal when it receives the H.245 message that carries the field of extension sent from opposite terminal:

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<td>UDP header</td><td>Value</td><td>Description</td>

<td>Source IP address</td><td>ip_a</td><td>IP address of the T1 terminal of the private network (an address in the private network)</td>

<td>Destination IP address do not</td><td>ip_b</td><td>the receiving IP address of the redirection packet, of the terminal T3 of the public network (extracted from the extension field in the H.245 message, that is, the source IP address when T3 sends a multimedia stream to T1)</td>

<td>Port of Origin</td><td>Port a</td><td>Rtp receive port number of T1</td>

<td>port of destination</td><td>Port_b1</td><td>The port of reception of the redirection packet, of the terminal T3 of the public network (extracted from the extension field in the H.245 message, that is, the number of the source port when T3 sends a multimedia stream to T1)</td>

NAT replaces the source address of the redirect packet with the common address of the public network and establishes the mapping relationship between the source address and the destination address before substitution, and the source address and destination address of the redirect packet after replacement, when the redirect packet passes through the NAT device. If the firewall also uses NAT processing, the method can also be applied to pass through the firewall. The following table shows the relationship formed by address mappings:

<td colspan="2">Before the firewall</td><td colspan="2">os / NAT</td><td colspan="4">After firewall / NAT</td>

<td>src ip</td><td>src port</td><td>dst ip</td><td>dst port</td><td>src ip</td><td>src port</td><td>dst ip</td><td>dst port</td>

<td>ip to</td><td>port a</td><td>ip b</td><td>port b1</td><td>ip t</td><td>port t</td><td>ip b</td><td>port b1</td>

Where, ip_t and port_t are public network addresses.

As there is a time-out in the address correspondence relationship in the firewall / NAT device, the terminal T1 of the private network updates the time-out periodically sending redirection packets, and it is possible to guarantee that the terminal of the public network it can receive the redirect packets even when some of the redirect packets are lost.

5. The terminal T3 of the public network sets the destination address to which a certain multimedia stream is sent to the source IP (ip_t) and the source port (port_t) that are extracted from the UDP header of a redirection packet from of the redirection packet when T3 receives the redirection packet at the broadcast address (ip_b, port_b1) of the multimedia stream. Then, the multimedia stream sent by Terminal T3 of the public network after redirection will reach the terminal T1 of the private network through the reverse correspondence of addresses of the firewall / NAT device.

Although the present invention has been described in the above embodiment with the H.323 protocol as an example, the calling process in other multimedia communication protocols, such as the SIP protocol, is similar, except that the signaling naming and naming specific fields are different; therefore, the present invention can also be applied to other multimedia communication protocols.