JPH0214823B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field to which the invention pertains] The present invention relates to optical fiber communication, coaxial cable communication,
It can be applied to satellite communications, mobile radio communications, etc., and relates to a communication method in which multiple stations share one transmission path or medium to communicate with each other. especially,
The present invention relates to a method in which multiple stations simultaneously send out transmission signals on one transmission path and detect that a signal collision has occurred on that transmission path. [Description of the Prior Art] In optical fiber communications, satellite communications, mobile radio communications, etc., systems are widely used in which a single transmission path is shared by a plurality of stations capable of transmitting and receiving information to communicate with each other.
One example of this is ETHERNET, which uses contention-based multi-access.
will be explained using an example. FIG. 1 shows an example of the configuration of an Ethernet. One coaxial cable 1 is a common transmission path, and a plurality of stations 2 _-1 to 2 _-o are connected to this coaxial cable 1 via adapters 3, respectively. Each station 2 _-1 ~
2 _-o includes a terminal device 5, an interface circuit 6,
It is equipped with a transmitting/receiving circuit 7, and transmits packets in broadcast format, and also receives packets to which an address addressed to itself is added. Cable termination portions 9 are provided at both ends of the coaxial cable 1. Each station can transmit its own signal at any time. Therefore, when signals are sent from multiple stations at the same time, signal collision occurs on the transmission path, making it impossible to communicate correct information.
When a collision occurs, the transmission line is occupied by the erroneous signal, so whether or not the collision can be detected immediately has a large effect on the efficiency with which the transmission line is used in this system. Therefore, a collision detection method is essential for such collision-based multiple access. FIG. 2 shows an example of the configuration of an Ethernet collision detection circuit. This is a system disclosed in US Pat. No. 4,063,220, and FIG. 2 is a block diagram of the main part of the transmitting/receiving circuit 7. The transmission signal of the terminal S is sent from the transmission circuit 11 to the adapter 3, and the reception signal is sent to the adapter 3.
The signal is then received and demodulated by the receiving circuit 12 and appears at the terminal R. The signal at terminal S and the signal at terminal R should naturally match when only this one station is transmitting, and this match is determined by the exclusive OR circuit 13.
Identification by The delay circuit 14 is the transmitting circuit 11,
It is inserted to compensate for the amount of cable delay between the receiving circuit 12 and the adapter 3. In this method, if a signal other than the signal transmitted by the own station is received during transmission by the own station, the transmitted signal and the received signal will become inconsistent and an output will be generated in the exclusive OR circuit 13, so that the signal will be sent to terminal D. When it appears, it is recognized that there is a station other than the own station that is transmitting a signal to the coaxial cable 1. This method is effective when the signal transmission speed is low and the distance from station 2 to coaxial cable 1 is short, but when the transmission speed increases or the distance from station 2 to coaxial cable 1 is long, If the delay circuit 14 is not set appropriately, it will be difficult to detect a match, resulting in false detection. To avoid this, all stations 2 _-1 ~ 2
In _-o , it is necessary to provide different delay circuits 14 depending on the conditions of each station, and the types of devices are no longer unified, and its adjustment requires a large number of man-hours. [Purpose of the Invention] The present invention improves this and is effective even when the transmission speed is high, and it is possible to use a unified device regardless of the delay time until the transmission signal from the own station is received. The objective is to provide a method capable of detecting signal collisions. [Main points of the present invention] The present invention encodes and transmits a transmission signal using a redundant code based on a certain code rule, and detects whether a received code received from a transmission path satisfies this certain code rule. It is characterized by [Description by Example] FIG. 3 is a block diagram of an optical communication system implementing the present invention. This communication method itself is a well-known method, and is described in detail in the following literature, for example. Reference 1 EGRawson, RMMetcalfe: Fibernet
Multimode Optical Fiber for Local
Computer Network, IEEE, Trans.Com.
COM-26, 7, 1978 pp983-990 This system uses an optical mixer as one common transmission line 1, and connects a plurality of stations _{2-1 to} 2 _-o to this transmission line 1 through optical fibers 21 and 22, respectively. Connecting. In FIG. 3, only two of the plurality of stations are shown.
Each station _2-1 to 2 _-o includes a transmitting/receiving circuit 7 for transmitting and receiving optical signals, an interface circuit, and a terminal device 5.
including. In the system shown in Figure 3, one station, for example station 2,
The signal sent from _-1 is transmitted to all other stations 2 _-2 ~ 2 _-o
can be received at Further, any one station can receive signals transmitted to the transmission line 1 from all other stations. One of the features of the present invention is that a redundant code based on a code rule is constantly used for signals transmitted from a plurality of stations 2 _-1 to _{2 -o} to a common transmission path 1. Part 1
One example is a CMI (code mark inversion) code. This code rule is described in detail in, for example, Document 2, "Optical Fiber Transmission," published by the Institute of Electronics and Communication Engineers, December 15, 1973, first edition, so a detailed explanation is omitted here, but the transmission code is "0" or "1"
An example of the CMI code conversion rule is shown in the table below, which is a code rule that is set with redundancy so that the numbers are not consecutive.

〔application〕

In the above example, we explained an example of optical fiber communication.
In addition to this, the system of the present invention can be applied to satellite communications, mobile communications, coaxial communications systems, etc. The above example was explained using the CMI sign rule as an example.
However, this sign rule may be any redundant sign rule. Depending on the sign rule, it is possible to configure a circuit that satisfies the sign rule or not. As another example of this coding rule, the coding rule generally referred to as mBnB code is suitable. Among these, biphase codes, DMI (differential mark inversion) codes, AMI codes, etc. can be used. Regarding these sign rules and their properties, see the above document 2.
There is a detailed description. Furthermore, if a code rule that is not currently known is used, the present invention can be similarly implemented if a means for detecting whether the received code satisfies the code rule is available. [Explanation of Effects] As explained above, the present invention provides a method that can detect collisions of signals transmitted simultaneously from multiple stations, regardless of the length of time until the transmitted signal from one's own station is received by that station again. is obtained. The method of the present invention has the advantage that the same device can be placed in each station and there is no need to make adjustments for each station, making the device extremely economical.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an Ethernet type communication network. Second
The figure is a configuration diagram of a conventional collision detection circuit. FIG. 3 is a diagram showing an example of the configuration of a communication network in which the present invention is implemented. FIG. 4 is a diagram showing an example of waveforms caused by signal collision. FIG. 5 is a diagram showing an example of the configuration of an optical receiver according to an embodiment of the present invention. FIG. 6 is a diagram showing an example of the configuration of the collision detection section of the present invention. Figure 7 is a timing chart of the collision detection section. FIG. 8 is a diagram showing actual measurement results using the collision detection section shown in FIG. 6.

Claims (1)

[Claims] 1. A plurality of stations having a transmitting circuit and a receiving circuit, and a transmission line configured such that a transmission signal from one of the plurality of stations is received by the plurality of stations other than this station. In a communication system including the above, the transmission signals transmitted from the plurality of stations to the transmission path are signals encoded with redundant codes based on a certain coding rule, and the signals received from the transmission path are identified. an identification and reproduction means for reproducing; a collision detection means for comparing a code pattern outputted by the identification and reproduction means with a code pattern based on the certain code rule and detecting whether or not the code pattern matches the code pattern; A signal collision detection method comprising: means for determining that there is a signal collision in the transmission path when the detection means detects a mismatch with a code pattern based on the certain code rule. 2. The means for determining a signal collision is a means for determining that there is a signal collision in a transmission path when the signal collision detection means detects a mismatch with a code pattern based on a certain code rule in excess of a predetermined ratio. The signal collision detection method according to claim 1, characterized in that the signal collision detection method includes: