JP3775655B2 - Optical wireless terminal device for half-duplex optical wireless communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical wireless terminal device of an optical wireless communication system in which a star topology is configured between a collection and delivery device and a plurality of terminal devices to perform half-duplex communication by optical wireless, and in particular, from a terminal device to a collection and delivery device. The present invention relates to a method for selecting a packet transmitted by duplex communication and returned from a collection / delivery device by half duplex communication after the transmission is completed by a terminal device.
[0002]
[Prior art]
As a conventional example of this type, Japanese Patent Laid-Open No. 8-56198 proposes a full-duplex optical wireless LAN system having a transmission rate of 10 Mbps. FIG. 6 shows a standard system configuration in which a collection / delivery device C is installed on the ceiling, and information terminals such as computers 2A and 2B are connected to the terminal devices A and B through trunk lines 1A and 1B, respectively. . The collection / delivery device C is connected to another collection / delivery device C via the collection / delivery device side trunk line 1C. In this system, in order to realize full-duplex communication, the collection / delivery device C is configured to subtract the signal transmitted to the terminal devices A and B from the signals received from the terminal devices A and B to remove the reflected light. Thereby, data transmission and reception in the optical space can be performed simultaneously (in full duplex).
[0003]
Further, the signals transmitted from the terminal devices A and B are configured to be returned by the collection / delivery device C and returned to the terminal devices A and B during the transmission.
In order to prevent the packets being transmitted from the computers 2A and 2B connected to the transmitting terminal devices A and B from colliding with each other on the trunk lines 1A and 1B, the terminal device A , B holds the first few bytes at the start of packet transmission for a very short period (up to the end of packet transmission at the maximum) and compares it with a packet returned during packet transmission. It is configured not to transmit to the side.
[0004]
By the way, the above system assumes a case where the transmission rate is 10 Mbps, but considering the case of transmission at 100 Mbps (converted to 125 Mbps in the optical transmission section), the wavelength of one sample time of digital modulation is
300,000km / 125MHz = 2.4m
Thus, when reflection occurs in the vicinity of the light source, for example, 1.2 m ahead, the returning optical signal reciprocates to have an optical path of 2.4 m and a phase difference of one wavelength. Therefore, it cannot be predicted how much the reflected return light at an unspecified position has a phase difference with respect to the original transmission signal. For this reason, if the reflection cancellation is performed, a cancellation circuit corresponding to light of various phases and amplitudes is required, and it becomes very difficult to mount the reflection cancellation circuit (an optical transmission signal transmitted from the collection / distribution device C). Is transmitted over a wide range, so that various reflectors cause return light to the collection and delivery device C). For this reason, simultaneous communication cannot be performed in the optical space, and the collection / delivery device C and each of the terminal devices A and B need to perform half-duplex communication that exclusively uses the optical space.
[0005]
[Problems to be solved by the invention]
However, in such a half-duplex optical wireless communication system, one packet transmitted from the terminal devices A and B is once stored in the collecting and delivering device C, and after the packet transmission from the terminal devices A and B is completed, the collecting and delivering device When the exclusive communication in the optical space is realized by transmitting the packet stored by C to the terminal devices A and B in the service area, the terminal devices A and B are transmitted to the terminal devices A and B as in the conventional 10 Mbps full-duplex system. While the packets from the connected computers 2A and 2B are being transmitted, the packets are folded back and do not come at the same time, so no collision occurs and there seems to be no problem. For example, as shown in FIG. A problem occurs when the HUB (hub) 10 having a switch function is connected to the main line 1A side of the terminal device A.
[0006]
Here, it is assumed that the HUB 10 having a switch function has ports 1 to N. It is assumed that the server 11 is connected to the port 1 and the terminal device A is connected to the port 2. The numbers in FIG. 7 represent the movement order of the packets when the packets are transmitted from the server 11.
(1) When a packet is transmitted from the server 11 to the HUB 10 with a switch function, the HUB 10 with a switch function learns that the server 11 is connected to the port 1.
(2) The packet is transmitted from the HUB 10 to the terminal device A.
(3) The data is transmitted from the terminal device A to the collection / delivery device C in half duplex.
(4) The data is transmitted from the collection / delivery device C to the collection / delivery device A side trunk line 1A.
(5) The packet is returned from the collection / delivery device C to the terminal device A in half duplex.
(6) When a packet is transmitted from the terminal device A to the HUB 10, the HUB 10 with a switch function erroneously learns that the server 11 is connected to the port 2.
(7) A packet is transmitted from the HUB 10 to the server 11.
[0007]
That is, in (1), the HUB 10 with a switch function learns that the server 11 is connected to the port 1. However, in (6), the HUB 10 with a switching function erroneously learns that the server 11 is connected to the port 2 because the packet whose source is the server 11 arrives at the port 2. Thereafter, when a packet for the server 11 comes from another port, the packet for the server is transmitted to the port 2 and may not reach the server 11.
[0008]
In view of the above-described problems of the conventional example, the present invention provides an optical wireless terminal device of a half-duplex optical wireless communication system capable of preventing erroneous learning when a HUB with a switch function is connected to the trunk side of the optical wireless terminal device. The purpose is to provide.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention determines whether or not a packet received in half duplex is a loopback packet after finishing packet transmission in half duplex, and if it is not a loopback packet, The packet is transmitted to the information terminal, and in the case of a return packet, the packet is not transmitted to the information terminal.
[0010]
That is, according to the present invention, through a half-duplex optical wireless communications channel a plurality of optical wireless terminal device is connected to the optical wireless collection and delivery device Rutotomoni, via a communication transmission path to each of the plurality of optical wireless terminal device information terminal Te is connected, after the uplink packet transmission sent from one information terminal among the plurality of information terminals has reached the optical wireless collection and delivery device via the optical wireless terminal device, the optical wireless collection and delivery device, over Ri packet transmission described above reached, the optical wireless half-duplex optical wireless communication system for transmitting the downlink direction with respect to the respective information terminal via said respective optical wireless terminal device as a folded packet transmission A terminal device,
Received the folded packet transmission was found when those self optical wireless terminal device receives from the transmission of the uplink packet transmitted to the optical wireless pick-up device within the predetermined time, the self-light wireless terminal It is configured to prevent return communication of uplink packet transmission transmitted from the information terminal by providing downlink transmission means for prohibiting downlink transmission to the information terminal connected to the apparatus. An optical wireless terminal device of a heavy optical wireless communication system is provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing an example of a half-duplex optical wireless communication system according to the present invention, FIG. 2 is an explanatory diagram showing a communication sequence of a terminal device that is not a transmission source in the system of FIG. 1, and FIG. 3 is a transmission in the system of FIG. It is explanatory drawing which shows the communication sequence of the former terminal device.
[0012]
In the system example shown in FIG. 1, an optical wireless collection and delivery apparatus C is installed on the ceiling, and information terminals such as computers 2A and 2B are connected to the optical wireless terminal apparatuses A and B via trunk lines 1A and 1B, respectively. . The collection / delivery device C is connected to another collection / delivery device via the trunk line 1C. In such a system example, FIG. 2 and the following show the communication sequence of the terminal device B that is not the transmission source when a packet is transmitted from the computer 2A to the terminal device A.
(1) Packet transmission from the computer 2A to the terminal device A.
(2) Half-duplex packet transmission from the terminal device A to the collection / delivery device C.
(3) Packet transmission from the collection / delivery device C to the collection / delivery device side trunk line 1C side.
(4) Half-duplex loopback packet transmission from the collection / delivery device C to the terminal devices A and B.
(5) Packet transmission from the terminal device B to the computer 2B.
[0013]
Here, when half-duplex packets transmitted from the terminal devices A and B need to be returned, they are returned in the shortest time in half-duplex after the end of transmission. For this reason, it is possible to determine that a packet coming from the collection / delivery device C within a certain time after transmission from the terminal devices A and B is a return packet. In such a case, the terminal device A that has transmitted the packet does not transmit the packet to the main line side 1A. In this case, a packet reception prohibition section must be provided on the terminal devices A and B side so as not to accidentally delete packets from the collection / delivery device side trunk line 1C that are not turned back. As a situation where the return packet does not come immediately after the packets are transmitted from the terminal devices A and B, the following can be considered.
[0014]
1) The switch function is implemented in the collection / delivery device C.
In this case, the packet whose transmission destination is known to be on the trunk line 1C side of the collection / delivery device C is transmitted only to the collection / delivery device side trunk line 1C, and the return packet does not return.
2) When the signals of the terminal devices A and B cannot be recognized by the collection / delivery device C.
The collection / delivery device C does not wrap the packet when the PLL synchronization is lost or the packet start pattern cannot be recognized due to a plurality of terminal devices A and B emitting light simultaneously. In this case, it is important for the collection / delivery device C to check whether or not light is emitted from the carrier, and after the terminal devices A and B have finished emitting light, do not transmit packets for a certain period. In particular, it is necessary not to transmit a packet before the return packet reception prohibited section of the terminal devices A and B.
[0015]
Therefore, as a specific procedure of the first embodiment, as shown in FIG. 3, the terminal device A starts counting from the end of packet transmission in (2) and receives a packet from the collection / delivery device C in (4). If the counter is less than or equal to a certain value at this time, the packet is not transmitted as a return packet to the terminal apparatus A side trunk line 1A. . At this time, the counter is reset.
[0016]
<Second Embodiment>
In the second embodiment, an ID is assigned to each terminal device A, B. Then, as shown in FIG. 4, when the transmission source terminal device A receives a packet from the terminal device A side trunk line 1A side, it adds a header of such an identifiable value such as an ID and transmits it to the collection and delivery device C. I do. The collection / delivery device C deletes the header to the trunk line 1C side and transmits the packet, and transmits the packet with the header as it is to the optical space side. In the terminal devices A and B, by comparing the header information of the packets sent from the collection / delivery device C, it is possible to identify whether the packet from the collection / delivery device C is transmitted by itself. The terminal device A having an ID that matches the attached ID does not transmit to the terminal device A side trunk line 1A side.
[0017]
<Third Embodiment>
In the third embodiment, as shown in FIG. 5, when the terminal device A receives a packet from the terminal device A side trunk line 1 </ b> A side, the terminal device A holds the first few bytes of the packet and transmits it to the collection / delivery device C. The collection / delivery device C transmits the packet to the trunk line 1C and the terminal devices A and B. The terminal device A can identify whether or not the return packet is a packet transmitted by itself by comparing the head data of the previously held packet with the packet from the collection and delivery device C. If the first several bytes match, the terminal device A does not transmit to the A-side trunk line 1A side.
[0018]
【The invention's effect】
As described above, according to the present invention, it is determined by a timer or the like whether a packet received in half duplex is a folded packet after completion of packet transmission in half duplex. Since the packet is transmitted to the information terminal and the packet is not transmitted to the information terminal in the case of the return packet, the erroneous learning is prevented when the HUB with a switch function is connected to the trunk side of the optical wireless terminal device. can do.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of a half-duplex optical wireless communication system according to the present invention.
FIG. 2 is an explanatory diagram showing a communication sequence of a terminal device that is not a transmission source in the system of FIG. 1;
FIG. 3 is an explanatory diagram showing a communication sequence of a transmission source terminal device in the system of FIG. 1;
FIG. 4 is an explanatory diagram illustrating a communication sequence of a transmission source terminal device according to a second embodiment.
FIG. 5 is an explanatory diagram illustrating a communication sequence of a transmission source terminal device according to a third embodiment.
FIG. 6 is a configuration diagram illustrating an example of a general optical wireless communication system.
FIG. 7 is an explanatory diagram showing a communication sequence of a conventional half-duplex optical wireless communication system.
[Explanation of symbols]
A, B Optical wireless terminal device C Optical wireless collection and delivery device 1A Terminal device A side trunk line 1B Terminal device B side trunk line 2A, 2B Computer (information terminal)
10 HUB with switch function

Claims (1)

Optical wireless collection and delivery device via a half-duplex optical wireless communications channel a plurality of optical wireless terminal device is connected to Rutotomoni, the plurality of information terminals via the communication transmission path to each of the optical wireless terminal devices are connected, after uplink packet transmission sent from one information terminal among the plurality of information terminals has reached the optical wireless collection and delivery device via the optical wireless terminal device, said optical wireless collection and delivery device, and the reach over Ri packet transmission was to a said optical wireless terminal device of a half-duplex optical wireless communication system for transmitting the downlink via the respective optical wireless terminal device as a folded packet transmitted to each of the information terminals,
Received the folded packet transmission was found when those self optical wireless terminal device receives from the transmission of the uplink packet transmitted to the optical wireless pick-up device within the predetermined time, the self-light wireless terminal It is configured to prevent return communication of uplink packet transmission transmitted from the information terminal by providing downlink transmission means for prohibiting downlink transmission to the information terminal connected to the apparatus. An optical wireless terminal device of a heavy optical wireless communication system.

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