Information transmission system and method based on one-way channel for physical isolation between internal and external networks

Abstract

The present application relates to the physical isolation information transmission system of one-way channel-based inner and outer network, it includes: source side outer network content host, source side display capability management module, audio and video main link sending unit, one-way transmission link, decoding and re-timing unit and inner network receiving end;Source side outer network content host includes display card and standard audio and video output port, standard audio and video output port includes audio and video output pin, display data channel pin, hot plug detection channel pin and consumer electronics control pin;Source side outer network content host outputs standard audio and video signal through audio and video output pin;Source side outer network content host reads the simulated hot plug detection timing signal from source side display capability management module, expands display identification data and mode strategy, to lock mode output audio and video signal, which is transmitted to inner network receiving end through one-way transmission link.The present application can realize the safety requirement of absolute one-way, physical break.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of information transmission, and in particular to a device and method for physical isolation of information transmission between internal and external networks based on a one-way channel. BACKGROUND

[0002] In the context of "internal and external network security isolation", common cross-network data exchange methods include: application layer gatekeeper, protocol stack proxy, file import / export gateway (U disk / CD manual over-gateway), and "data diode" type devices.

[0003] Network gatekeeper: mostly dependent on protocol parsing and dual-machine isolation, but still has risks such as protocol implementation defects, policy misconfiguration, zero-day vulnerabilities, etc.; and once the minimum necessary backhaul (such as ACK / retransmission / session control) is opened, a "soft circuit" is generated.

[0004] File over-gateway: high labor cost and delay, and does not have the ability to publish "quasi-real-time, stable bandwidth".

[0005] Traditional data diode: mostly for internal to external data leakage protection, and often through the Ethernet physical layer / link layer; for "external to internal quasi-real-time information publishing (such as announcements, media, data dashboards, task instruction boards, etc.)", the current network general-purpose product does not match, or requires complex protocol / drive adaptation and secondary development.

[0006] In addition, taking HDMI as an example, the HDMI protocol and control signal are bidirectional, and in actual use, the core "video" signal source always flows from the source side (computer host) to the receiving side (display device), but this one-way flow mechanism does not really rule out the possibility of HDMI being used as a bidirectional transmission medium, allowing the signal on the receiving side to be leaked to the source side, for the following reasons:

[0007] The HDMI standard link includes:

[0008] • TMDS (Transition-Minimized Differential Signaling) main data channel (video / audio / accessory data, source→display);

[0009] • DDC / I²C (Display Data Channel, display data channel; SCL / SDA, display→source interactive reading of EDID); EDID: Extended Display Identification Data;

[0010] • HPD (Hot-Plug Detect, hot-plug detection; display→source);

[0011] • CEC (Consumer Electronics Control; single-wire bus, bidirectional);

[0012] • 5V power supply and ground, etc.

[0013] The above DDC / HPD / CEC essentially forms a backhaul / bidirectional control path. In order to normally handshake, the common HDMI optical / electrical extender multiplexes / forwards DDC / CEC / HPD on the optical link, which is still a "reversible channel" in essence and cannot meet the safety requirements of "absolute unidirectional, physically broken". SUMMARY

[0014] In view of the problems in the prior art, the present application proposes a unidirectional channel-based internal and external network physical isolation information transmission system, which is characterized by comprising: a source-side external network content host, a source-side display capability management module, an audio / video main link sending unit, a unidirectional transmission link, a decoding and retiming unit, and an internal network receiving end.

[0015] The source-side external network content host comprises a graphics card and a standard audio / video output port, and the standard audio / video output port comprises audio / video output pins, display data channel pins, hot plug detection channel pins, and a consumer electronics control pin. The source-side external network content host outputs standard audio / video signals through the audio / video output pins. The source-side external network content host is connected to the source-side display capability management module to read the pre-stored signed display capability profile and the simulated hot plug detection timing signal from the source-side display capability management module. The display capability profile comprises extended display identification data and mode strategy. The source-side external network content host also outputs audio / video signals in a locked graphics card output mode according to the mode strategy. The display data channel pins, the hot plug detection channel pins, and the consumer electronics control pin are empty.

[0016] The source-side display capability management module is used to return the display capability profile and the simulated hot plug detection timing signal to the source-side external network content host.

[0017] The audio / video main link sending unit is connected to the audio / video output pins to receive audio / video signals and send them to the unidirectional transmission link.

[0018] The unidirectional transmission link is used to send the audio / video signals to the decoding and retiming unit.

[0019] The decoding and retiming unit is used to demodulate and retime the received signals into standard audio / video signals.

[0020] The internal network receiving end is used to receive and play standard audio / video signals.

[0021] According to some embodiments of the present application, the locked graphics card output mode of the source-side external network content host includes fixed resolution and refresh rate, disabled high dynamic range, display stream compression, dithering, scaling and consumer electronics control functions.

[0022] According to some embodiments of the present application, the standard audio and video output port includes HDMI, VGA, DVI, DP and USB-C output port.

[0023] According to some embodiments of the present application, the display data channel pin and the hot plug detection channel pin are connected to the source-side display capability management module to respectively read the pre-stored extended display identification data and the simulated hot plug detection timing signal from the source-side display capability management module; and the consumer electronics control pin is empty.

[0024] According to some embodiments of the present application, the consumer electronics control pin is cut off or sealed.

[0025] According to some embodiments of the present application, the system further comprises a unidirectional transmission link, which comprises: an electro-optical conversion unidirectional optical transmitter for receiving audio and video signals and converting them into optical signals; a unidirectional optical fiber for unidirectional transmission of optical signals to an opto-electric conversion unidirectional optical receiver; and an opto-electric conversion unidirectional optical receiver for receiving optical signals and outputting them after converting the optical signals into electrical signals.

[0026] The present application also proposes an information transmission method of an internal and external network physically isolated information transmission system, characterized in that it comprises:

[0027] The source-side external network content host initiates an extended display identification data reading request to the source-side display capability management module;

[0028] The source-side display capability management module returns the pre-stored signed display capability profile and the simulated hot plug detection timing signal to the source-side external network content host in response to the request, wherein the display capability profile includes extended display identification data and mode strategy;

[0029] The source-side external network content host outputs audio and video signals to the audio and video main link sending unit according to the locked graphics card output mode according to the mode strategy;

[0030] The audio and video main link sending unit receives the audio and video signals and sends them to the unidirectional transmission link;

[0031] The unidirectional transmission link sends the audio and video signals to the decoding and retiming unit;

[0032] The decoding and retiming unit demodulates and retimes the received signals into standard audio and video signals; and

[0033] The internal network receiving end receives and plays the standard audio and video signals.

[0034] According to some embodiments of the present application, the standard audio and video output port includes HDMI, VGA, DVI, DP and USB-C output port.

[0035] According to some embodiments of the present application, the source-side external network content host reads the extended display identification data from the source-side display capability management module through a local I2C bus, and the extended display identification data is read-only data.

[0036] According to some embodiments of the present application, the source-side external network content host reads the pre-stored extended display identification data and the simulated hot plug detection timing signal from the source-side display capability management module through the display data channel pin and the hot plug detection channel pin, respectively; and the consumer electronics control pin is left empty.

[0037] Through the present application, the following effects can be achieved:

[0038] 1. Realize "outside-in" one-way transmission, and physically cut off all backhaul (DDC / HPD / CEC / hidden modulation).

[0039] 2. Under the condition of zero backhaul, complete source display mode locking (fixed resolution and refresh rate, disable high dynamic range, display stream compression, dithering, scaling and consumer electronics control function, avoid graphics card "pixel tampering / bandwidth dithering".

[0040] 3. Can help to realize a general, safe, bandwidth controllable, plug and play cross-network information publishing link, taking into account maintainability and acceptance.

[0041] 4. No need to re-construct complex transmission protocol / drive adaptation and secondary development. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings used:

[0043] Figure 1 The architecture diagram of the internal and external network physical isolation information transmission system based on one-way channel according to some embodiments of the present application is shown.

[0044] Figure 2 The signal transmission flowchart of the source side according to some embodiments of the present application is shown.

[0045] Figure 3 The information transmission method flowchart according to some embodiments of the present application is shown.

[0046] The correspondence of the reference numerals in the drawings is as follows:

[0047] 100 source-side external network content host

[0048] 110 source-side display capability management module

[0049] 120 main-link sending unit

[0050] 130 electro-optical conversion unidirectional optical transmitter

[0051] 140 unidirectional optical fiber

[0052] 150 photo-electric conversion unidirectional optical receiver

[0053] 160 decoding and re-timing unit

[0054] 170 intranet receiving end DETAILED DESCRIPTION

[0055] To make the purposes, technical solutions and advantages of the present application clearer, the embodiments of the present application will be further described in detail below with reference to the drawings.

[0056] Figure 1 A schematic diagram of a system according to some embodiments of the present application is shown.

[0057] As shown in the figure, the system comprises a source-side extranet content host 100, a source-side display capability management module 110, a main-link sending unit 120, a unidirectional transmission link, a decoding and re-timing unit 160 and an intranet receiving end 170.

[0058] According to some embodiments of the present application, the unidirectional transmission link can comprise the illustrated electro-optical conversion unidirectional optical transmitter 130, unidirectional optical fiber 140 and photo-electric conversion unidirectional optical receiver 150. The electro-optical conversion unidirectional optical transmitter 130 is used to receive the audio and video signals and convert them into optical signals. The unidirectional optical fiber 140 is used to transmit the optical signals unidirectionally to the photo-electric conversion unidirectional optical receiver. The photo-electric conversion unidirectional optical receiver 150 is used to receive the optical signals and output them after converting them into electrical signals. In the present application, the electro-optical conversion unidirectional optical transmitter can convert electrical signals into optical signals but cannot convert optical signals into electrical signals; the photo-electric conversion unidirectional optical receiver can convert optical signals into electrical signals but cannot convert electrical signals into optical signals. The unidirectional transmission link can also be any link that can realize physical unidirectional transmission of signals, including but not limited to unidirectional serial port lines and the like.

[0059] The source-side external network content host 100 includes a display card and standard audio-video output ports, which include audio-video output pins, display data channel pins (DDC pins), hot plug detection channel pins (HPD pins), and consumer electronics control pins (CEC pins). The source-side external network content host 100 outputs standard audio-video signals to the outside through the audio-video output pins. The source-side external network content host also connects a source-side display capability management module to read a pre-stored signed display capability profile and a simulated hot plug detection timing signal from the source-side display capability management module, the display capability profile including extended display identification data and mode policy. The display data channel pins, the hot plug detection channel pins, and the consumer electronics control pins are empty. In the present application, the empty means that the pins are not connected to any object, and the standard audio-video output ports mean various audio-video output ports that can realize audio-video transmission based on existing protocols.

[0060] According to some embodiments of the present application, the display data channel pins and the hot plug detection channel pins of the standard audio-video output ports are connected to the source-side display capability management module 110 to respectively read pre-stored extended display identification data (EDID) and a simulated hot plug detection timing signal (simulated HPD timing signal) from the source-side display capability management module 110, and the consumer electronics control pins are kept empty. Here, the DDC pins in the output ports of the source-side external network content host 100 are designed as local loops only. The DDC pins are "handshake" channels, and in the prior art, the source-side external network content host normally reads the EDID of a display device through the DDC. In the present application, the design of the DDC pins as "local loops only" means that the DDC pins are designed to be connected to the source-side display capability management module only, so that the source-side external network content host 100 cannot read the EDID of a truly remote receiving-side display device, but reads a locally "counterfeit" EDID. When the source-side external network content host 100 attempts to read signals through the DDC, the DDC handshake is "intercepted", and the source-side display capability management module 110 locally replies to the pre-stored (or counterfeit) EDID.

[0061] The source-side display capability management module 110 is configured to return a display capability profile and emulated hot plug detection timing signal to the source-side external network content host, the display capability profile including extended display identification data and mode policy, the mode policy being used to lock the output mode of the graphics card of the source-side external network content host, so as to prevent the graphics card bandwidth / pixel side channel from being shaken. The locking of the output mode of the graphics card of the source-side external network content host includes fixing the resolution and refresh rate, disabling high dynamic range, display stream compression, dithering, scaling and consumer electronics control functions. If there are other functions that may affect the output mode of the graphics card, they are also within the scope of the present application, and here the most common ones are selected because it is impossible to enumerate all. The source-side display capability management module 110 can include a policy firmware, and the above functions are realized through the policy firmware.

[0062] According to some embodiments of the present application, the source-side display capability management module 110 is built-in with a signed “display capability profile” (including EDID and mode policy), and the EDID and emulated HPD timing signal are provided in a local I2C read-only manner. The source-side external network content host reads the EDID data and emulated HPD timing signal in the source-side display capability management module 110. That is, as described above, when the source-side external network content host 100 reads the signal through DDC, the DDC handshake is “intercepted” by the source-side display capability management module 110, and the pre-stored (or fake) EDID is replied locally by the source-side display capability management module 110.

[0063] According to some embodiments of the present application, the “display capability profile” (EDID content and mode policy) is issued in an asymmetric signature and version management.

[0064] According to some embodiments of the present application, the “display capability profile” supports “read-only OTP / PUF binding” to prevent on-site tampering.

[0065] The audio and video main link sending unit 120 is configured to connect the audio and video output pins of the standard audio and video output port, receive the audio and video signals, and send them to the unidirectional transmission link.

[0066] The unidirectional transmission link is configured to send the audio and video signals to the decoding and retiming unit 160.

[0067] The decoding and retiming unit 160 is configured to demodulate and retime the received signals into standard audio and video signals.

[0068] The internal network receiving end 170 is configured to receive and play the standard audio and video signals. The internal network receiving end 170 only displays or collects data locally in the internal network, and no longer sends signals to the outside.

[0069] According to some embodiments of the present application, the standard audio-video output port comprises an HDMI output port (HDMI port for short). The CEC pin in the prior art allows users to control devices connected through HDMI with a remote control, but in the present application, the CEC pin is cut off or sealed. Since the present application physically cuts off (or seals) the CEC pin in the HDMI port. This means that the source-side external network content host 100 will never respond or send any CEC control commands. It cannot control other devices, nor can it be controlled by other devices, completely eliminating such "backhaul control". The source-side external network content host 100 sends standard TMDS signals (transmission minimized differential signaling) to the main link sending unit 120 after completing a local handshake with the source-side display capability management module 110 and being locked by the policy firmware. The decoding and retiming unit 160 demodulates and retimes the optical signal to a standard TMDS.

[0070] Figure 2 A signal transmission flowchart of the source side according to some embodiments of the present application is shown.

[0071] Please refer to the drawings, the source side external network comprises a source-side external network content host 100; a source-side display capability management module 110; a main link sending unit 120; and an electro-optical conversion one-way optical transmitter 130.

[0072] The source-side external network content host 100 is in communication connection with the source-side display capability management module 110. According to some embodiments of the present application, the source-side external network content host 100 reads the EDID from the source-side display capability management module 110 through a local I 2 C bus, the EDID being read-only data. At the same time, the source-side display capability management module 110 also provides a local emulated HPD timing signal (hot plug detection timing signal) and a mode policy to the source-side external network content host 100. The source-side display capability management module 110 can also contain a policy firmware. The policy firmware is used to execute a predetermined mode policy, that is, under zero backhaul conditions, fixed resolution and refresh rate, disable HDR, DSC, dithering, scaling, and CEC.

[0073] On the main signal path, the source-side external network content host 100 sends standard audio-video signals (such as TMDS signals, i.e. transmission minimized differential signaling) to the main link sending unit 120 after completing a local handshake with the source-side display capability management module 110 and being locked by the policy firmware. The main link sending unit 120 receives the electrical signal input and transmits it to the electro-optical conversion one-way optical transmitter 130. The electro-optical conversion one-way optical transmitter 130 is a TX-only device that is responsible for converting the electrical signal into an optical signal and transmitting it outward.

[0074] Through this architecture, the output of the source-side external network content host 100 is strictly limited by the policy firmware, and the control channel thereof is physically isolated from the downstream device.

[0075] In addition to the HDMI transmission line described above, there are also VGA, DVI, DP, and USB-C video transmission lines. These transmission lines also contain similar audio and video output pins, display data channel pins, hot plug detection channel pins, and consumer electronics control pins. Therefore, the above-mentioned embodiments of the present application are also applicable to VGA, DVI, DP, and USB-C video transmission lines, and the standard audio and video output port includes HDMI, VGA, DVI, DP, and USB-C output ports. For the sake of simplicity, they will not be described here.

[0076] The present application also provides an information transmission method based on the internal and external network physical isolation information transmission system. This method realizes a secure one-way video transmission link through hardware isolation and local emulation mechanisms. The method comprises the following steps:

[0077] The source-side external network content host 100 initiates an extended display identification data reading request to the source-side display capability management module 110;

[0078] The source-side display capability management module 110 responds to the request and returns the pre-stored signed display capability profile and emulated hot plug detection timing signal to the source-side external network content host 100, the display capability profile including extended display identification data and mode policy;

[0079] The source-side external network content host 100 outputs audio and video signals to the audio and video main link sending unit according to the locked graphics card output mode of the mode policy;

[0080] The audio and video main link sending unit 120 receives the audio and video signals and sends them to the one-way transmission link;

[0081] The one-way transmission link sends the audio and video signals to the decoding and retiming unit 160;

[0082] The decoding and retiming unit 160 demodulates and retimes the received signals into standard audio and video signals; and

[0083] The internal network receiving end 170 receives and plays the standard audio and video signals.

[0084] As mentioned earlier, the one-way transmission link includes an electro-optical conversion one-way optical transmitter 130, a one-way optical fiber 140, and an opto-electric conversion one-way optical receiver 150. The one-way transmission link can also be any link that can achieve physical one-way transmission of signals, including but not limited to a one-way serial port line, etc.

[0085] Further example embodiments are described below.

[0086] As shown in FIG. 1, at 1, the source-side external content host 100 initiates an EDID read request to the source-side display capability management module 110. The EDID is local read-only data. Figure 3

[0087] At 2 and 3, the source-side display capability management module 110 returns a signed display capability profile and emulated HPD timing signal (local emulation) to the source-side external content host in response to the request. The source-side display capability management module 110 generates the emulated HPD timing signal by using local MCU emulation to simulate the access state of the display device on the receiving side.

[0088] The sequence of 1, 2, and 3 above does not necessarily strictly follow as described above, and can be adjusted as needed.

[0089] At 4, after receiving the emulated HPD timing signal and the signed display capability profile, the source-side external content host 100 selects and locks a fixed mode, such as 1080p60 or 4K30, according to the mode strategy (such as "mode lock").

[0090] At 5, after the display mode is locked, the source-side external content host 100 outputs a main link video signal, such as a TMDS signal, to the main link transmission unit 120 with stable parameters.

[0091] At 6: the video main link transmission unit receives the audio and video signal and transmits it to the electro-optical conversion unidirectional optical transmitter, which receives the audio and video signal and converts it into an optical signal and emits it unidirectionally;

[0092] At 7, the unidirectional optical fiber unidirectionally transmits the optical signal to the photoelectric conversion unidirectional optical receiver;

[0093] At 8, the photoelectric conversion unidirectional optical receiver receives the optical signal and converts it into an electrical signal, and the decoding and retiming unit demodulates and retimes the electrical signal into a standard TMDS audio and video signal.

[0094] At 8, the internal network receiving end collects the electrical signal and reconverts it into an audio and video signal for display.

[0095] ​As shown in the highlighted area at the bottom of the figure, in the entire transmission link from the source side external network content host 100 to the internal network receiving end 170, there is no "backhaul" channel for control signals such as DDC, HPD or CEC. Moreover, the receiving side device (such as the optical-electric conversion one-way optical receiver 150 and the decoding and retiming unit 160) does not contain any optical transmitter, thereby completely eliminating the possibility of data backhaul at the hardware level, achieving strict one-way data flow and security isolation.

[0096] According to some embodiments of the present application, the locked graphics card output mode includes a fixed resolution and refresh rate, and disables high dynamic range, display stream compression, dithering, scaling and consumer electronics control functions.

[0097] According to some embodiments of the present application, the source side external network content host reads the extended display identification data from the source side display capability management module through a local I 2 The C bus is used to read the extended display identification data from the source side display capability management module, and the extended display identification data is read-only data.

[0098] According to some embodiments of the present application, the consumer electronics control pin is cut off or sealed.

[0099] According to some embodiments of the present application, the source side external network content host reads the pre-stored extended display identification data and the simulated hot plug detection timing signal from the source side display capability management module through the display data channel pin and the hot plug detection channel pin, respectively; and the consumer electronics control pin is left empty.

[0100] In addition to the above-mentioned HDMI transmission line, there are also VGA, DVI, DP and USB-C video transmission lines. These transmission lines also contain similar audio and video output pins, display data channel pins, hot plug detection channel pins and consumer electronics control pins. Therefore, the above-mentioned embodiments of the present application are also applicable to VGA, DVI, DP and USB-C video transmission lines, and the standard audio and video output port includes HDMI, VGA, DVI, DP and USB-C output ports. For the sake of simplicity, they will not be described here.

[0101] Through the present application, the following effects can be achieved:

[0102] 1. Absolute one-way, physically irreversible: the source side has no DDC / HPD / CEC / optical RX / electric RX devices and wires connected to the receiving side; the receiving side has no light emitting / electricity emitting devices that can be used for backhaul; therefore, even if the internal network side is compromised, it cannot affect the external network host configuration and pixel output from the physical layer.

[0103] 2. Plug and play, bandwidth predictable: source EDID / HPD local simulation, make the graphics card think that a fixed-capability display device is connected; prohibit HDR / DSC / shake / zoom / gamut switching, etc. Dynamic negotiation, output mode stable, link bandwidth constant and measurable.

[0104] 3. Consideration of engineering practicability and acceptance: through anti-disassembly pouring seal, remove RX device / wiring, no test point (CEC pin is cut off or sealed) and other "visible physical evidence", it is convenient for third-party safety evaluation / military inspection; support common resolutions such as 1080p / 4K, and the internal network end can be selected for direct display or collection into the warehouse, covering information release / command look board / security control and other scenes.

[0105] 4. Anti "soft circuit" and "side channel": not dependent on upper layer protocol plugging (such as TCP / UDP / DNS, etc.), directly eliminate the loop at the physical layer; through mode locking and pixel path, weaken the feasibility of pixel-level covert encoding.

[0106] It should be noted that, for the convenience of understanding, each step in the method and each module in the system is carefully split in this application, but those skilled in the art understand that, according to the actual implementation needs, each step and module can be further split or reorganized, which is within the scope and protection range of the present application.

Claims

1. A physical isolation information transmission system for internal and external networks based on a unidirectional channel, characterized in that, include: Source-side external network content host, source-side display capability management module, audio and video main link sending unit, one-way transmission link, decoding and retiming unit, and internal network receiver; The source-side external network content host includes a graphics card and a standard audio / video output port. The standard audio / video output port includes audio / video output pins, display data channel pins, hot-plug detection channel pins, and consumer electronics control pins. The source-side external network content host outputs standard audio / video signals through the audio / video output pins. The source-side external network content host connects to the source-side display capability management module to read pre-stored signed display capability profiles and simulated hot-plug detection timing signals from the source-side display capability management module. The display capability profile includes extended display identification data and mode policies. The source-side external network content host also outputs audio / video signals in a locked graphics card output mode according to the mode policy. The mode policy is used to lock the graphics card output mode of the source-side external network content host. The display data channel pins, hot-plug detection channel pins, and consumer electronics control pins are left unused. The source-side display capability management module is used to return display capability profiles and simulated hot-plug detection timing signals to the source-side external network content host; The audio / video main link transmitting unit is connected to the audio / video output pin to receive audio / video signals and send them to the unidirectional transmission link; A one-way transmission link is used to send the audio and video signals to the decoding and retiming unit; The decoding and retiming unit is used to demodulate the received signal and retime it to a standard audio and video signal. The intranet receiver is used to receive and play standard audio and video signals. Among them, the display data channel pin and the hot-plug detection channel pin are connected to the source-side display capability management module to read the pre-stored extended display identification data and the simulated hot-plug detection timing signal from the source-side display capability management module, respectively; And the aforementioned consumer electronics control pins are unused.

2. The system according to claim 1, characterized in that, The graphics card output mode of the locked source-side external network content host includes fixed resolution and refresh rate, and disables high dynamic range, display stream compression, jitter, scaling and consumer electronics control functions.

3. The system according to claim 2, characterized in that, The standard audio and video output ports include HDMI, VGA, DVI, DP, and USB-C output ports.

4. The system according to claim 2, characterized in that, The consumer electronics control pins are cut off or sealed.

5. The system according to claim 2, characterized in that, The system also includes a unidirectional transmission link, which comprises: an electro-optical conversion unidirectional optical transmitter for receiving audio and video signals and converting them into optical signals; a unidirectional optical fiber for transmitting the optical signals unidirectionally to an opto-optical conversion unidirectional optical receiver; and an opto-optical conversion unidirectional optical receiver for receiving the optical signals and converting them into electrical signals before outputting them.

6. An information transmission method based on the internal and external network physically isolated information transmission system according to any one of claims 1-5, characterized in that, include: The source-side external network content host initiates an extended display identifier data read request to the source-side display capability management module; In response to the request, the source-side display capability management module returns a pre-stored signed display capability profile and a simulated hot-plug detection timing signal to the source-side external network content host. The display capability profile includes extended display identification data and mode strategy. The source-side external network content host outputs audio and video signals to the audio and video main link sending unit in the locked graphics card output mode according to the mode policy; The audio / video main link transmission unit receives audio and video signals and sends them to the unidirectional transmission link; The one-way transmission link sends the audio and video signals to the decoding and retiming unit; The decoding and retiming unit demodulates and retims the received signal into a standard audio and video signal; as well as The intranet receiver receives and plays standard audio and video signals. Specifically, the source-side external network content host reads pre-stored extended display identifier data and simulated hot-plug detection timing signals from the source-side display capability management module through the display data channel pin and the hot-plug detection channel pin, respectively; and leaves the consumer electronics control pin idle.

7. The method according to claim 6, characterized in that, The standard audio and video output ports include HDMI, VGA, DVI, DP, and USB-C output ports.

8. The method according to claim 6, characterized in that, The source-side external network content host communicates through a local I / O network. 2 The C bus reads extended display identifier data from the source-side display capability management module. The extended display identifier data is read-only data.

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