JPS60256248A - Information transmission system - Google Patents

Abstract

PURPOSE:To improve the reliability of system by allowing a medium attachment unit MAU to receive a signal on a unidirectional transmission line and detecting the collision of signals on the unidirectional transmission line from the result of reception so as to detect surely the collision on the carrier bad transmission line. CONSTITUTION:A reception line 3 and a transmission line 2 are connected by a head end 4 on the unidirectional transmission line 1 of the information transmission system and a high-order protocol (not shown in figure) is connected to the transmission line 1 via plural MAU 6a-6n. An FM modulation section 11 of each MAU modulates the transmission information from the protocol by using the packet data, the result is transmitted from a transmission amplifier 13 to the transmission line 1 and to a reception line 3 via the head end 14. This signal is received by the reception amplifier 14, demodulated by an FM demodulator 16 via a BPF15 and inputted to the protocol. Moreover, the collision detecting circuit 17 detects the collision of the signal on the transmission line 1, the result of detection is outputted from a collision display generating circuit 18 to the protocol as a display signal so as to detect surely the collision on the transmission line 1.

Description

[Detailed Description of the Invention] (Technical background of the invention and its problems) Recently, completely distributed peer-to-peer protocol transmission systems, That is, C8MA/CD (Carrier Sense
multiple access/collision detection)
A method has been developed. This method performs baseband transmission via a coaxial cable as a transmission path.
Recently, in order to use the coaxial cable more efficiently, the baseband signal is modulated into a carrier band signal and transmitted.
Development of so-called broadband networks is underway to effectively utilize the transmission band.

By the way, on such a carrier band transmission path, C8MA/C
Challenges in realizing the D method include ensuring the same level of collision detection characteristics as conventional baseband transmission paths and ensuring compatibility with higher-level protocols.

Of these, for the collision detection method mentioned above, if the level of the beat signal generated by the overlap of signals sent from two medium attachment units (MAU) is in the same phase, the peak value will be doubled. The RA signal level detection method is attracting attention because it determines whether or not there is a collision by detecting the presence or absence of the collision. This signal level detection method has the advantage of being able to easily detect signal collisions on a transmission path using only the received signals in a normal MAU, and that the detection is reliable.

However, in a network using a unidirectional transmission path, there is a delay in the transmission signal on the transmission path, so it takes a certain amount of time for the beat signal generated by one collision to disappear from the transmission path. This results in problems such as those of the method. That is, when focusing on a specific point on the transmission path, a signal whose level intermittently increases will pass for a predetermined period of time in response to one signal collision. For this reason,
As described above, in the method of detecting a collision based only on the level of the received signal, when a signal whose level intermittently decreases as described above is received, the collision is detected as if a plurality of collisions had occurred. Each modem then generates its collision detection signal to the upper layer protocol each time.

On the other hand, when the upper level block o1-col receives a collision indication signal from MAtJ during data transmission, it sends a Jim↑・Mu signal onto the transmission path for a predetermined period of time in order to strengthen the collision state. , a beat signal due to a collision is present on the transmission path for a predetermined period of time, thereby ensuring that all MAUs detect the signal collision. For this reason, the problem that one collision is detected multiple times as described above becomes noticeable. And like this I
In the upper protocol that receives the I collision detection signal, the protocol that is in the data sending state incorrectly counts the number of collisions, resulting in problems such as buckets being discarded.

[Purpose of the invention]

The present invention has been made in consideration of these circumstances, and its purpose is to provide a highly practical information transmission system that can reliably detect collisions on a carrier band transmission path. .

(Summary of the Invention) The present invention provides a medium connection to a unidirectional transmission line consisting of a transmission line and a reception line coupled via a head end, for example.
In an information transmission system in which information is transmitted by a completely distributed peer-to-peer protocol transmission method between a plurality of upper protocols connected via attachment units, the medium attachment unit is connected to a signal on the unidirectional transmission path. and means for detecting a collision of signals on the unidirectional transmission path from the reception result by, for example, comparing the amplitude of the received signal with a predetermined value, and transmitting a collision detection signal to the upper protocol at the time of detecting the collision. and a means for generating a collision indication signal for a predetermined period of time, and the upper protocol transmits the collision indication signal to the unidirectional transmission path via the medium attachment unit for a predetermined period of time in order to strengthen the collision state. The jam signal is generated over a period i that is longer than the jam signal transmission period.

〔Effect of the invention〕

Thus, according to the present invention, once a collision is detected on the transmission path, the collision display signal indicating the collision is continuously transmitted for a longer period than the jam signal sent to strengthen the collision state. Since it is output to the lower level protocol, even if the beat signal caused by the collision is interrupted, this will not be erroneously detected as a new collision occurrence and a collision indication signal will not be output to the upper protocol. In other words, when a collision occurs on the transmission path, a collision indication signal indicating collision detection is continuously sent to the upper protocol for a period longer than the output period of the jam signal that is output to strengthen the collision condition. Therefore, the upper protocol can reliably and accurately detect one collision on the transmission path as one collision occurrence. Therefore, it becomes possible to effectively avoid malfunctions of the upper layer protocol, and there are great practical effects such as improving the reliability of the network.

(Embodiment of the invention) An embodiment of the invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of the information transmission system.

The unidirectional transmission line 1 has a configuration in which a transmission line 2 and a reception line 3 are coupled via a head end 4.

Multiple upper protocols (not shown) connect MAtJ6a, 6b, ~6n to this unidirectional transmission path 1.
An information transmission system is being built horizontally through connections.

The upper protocol consists of various information processing B units.
Each of them executes predetermined information processing, and also mutually transmits necessary information from the modem 6 to other upper protocols via the transmission path 1. This information transmission is controlled by the C8MA/'CD system.

As shown in FIG. 2, for example, the MAU 6 inputs transmission information from an upper protocol, such as packet data, to an FM modulator 11 for modulation, and transmits the modulated signal to a band bus filter 12. Transmit via amplifier 1
3 to the transmission line 1 (transmission line 2). Further, the signal sent to the transmission line 1 is transmitted from the transmission line 2 to the reception line 3 via the head end 4.
transmitted above. The data receiving section of the modem 6 includes a receiving amplifier 14 that receives the signal on the receiving line 3, and an FM tI modulator 16 that inputs this received signal via a band bus filter 15 and demodulates it. ing.

Packet data received and demodulated by this data receiving section is output to its upper protocol.

The MAU 6 is also provided with a collision detection processing section. This collision detection processing unit 1, the band bass filter 1
A collision detection circuit 17 detects a signal collision on the transmission line 1 from the output (received signal) of 5, and when this collision detection circuit 17 detects a collision, it generates a collision indication signal and sends it to the upper protocol. The collision display signal generation circuit 18 outputs a collision display signal. The jam signal that the upper protocol sends in place of the transmission data in order to strengthen the collision state upon receiving the collision indication signal is, for example, a 32-bit signal, and is sent to the data transmitter via the FM modulator 11. given to.

That is, as shown in FIG. 3, in the MAU 6, when a signal collision occurs on the transmission line 1 when transmission data is input from the upper protocol and an attempt is made to send the data, this collision is detected by the collision detection circuit 17. Detected by According to the collision detection result, the upper protocol generates a 32-bit jam signal, and at the same time, the collision indication signal generation circuit 18 continuously generates a collision indication signal having a longer time width than the jam signal. ing. Therefore, the collision indication signal is continuously given to the upper layer protocol for a predetermined period of time even after the transmission of the jam signal is finished.

Thus, the MAU6 that generates such a collision indication signal
According to the above, one signal collision 9- occurs on the transmission path 1, and during the period when the jam signal is being transmitted to strengthen this collision state, even if a beat occurs in the received signal due to the collision, that beat is ! It is no longer necessary to detect intermittent signals as individual collision occurrences and generate a surface collision display signal each time. In other words, since one collision causes the collision indication signal to be continuously given to the upper protocol for longer than the jam signal transmission period, the upper protocol can correctly detect the occurrence of the collision. Therefore, the 10-bit protocol does not cause accidents such as erroneously detecting the occurrence of a collision and erroneously discarding transmitted data (packets) according to the counting result.

By the way, before &! The collision detection circuit 17 is configured as shown in FIG. 4 or 5, for example.

The collision detection circuit 17 shown in FIG.
A received signal inputted through the filter 15 is detected through an envelope detection circuit 20, and the level of the received signal is determined. This detection output is given to an amplifier 22 via a low-pass filter 21, and is also sent to two comparators 23.2.
4 and 10- respectively. Each of these comparators 23 and 24 compares a predetermined signal level outputted from the IA semi-multiplying signal generator 2526 and the signal level of the detection output. The reference signal generator 25 sets a signal level slightly higher than the received signal level which is substantially constant over time when data is sent from only one M A Cl 6 and no collision occurs as a threshold value. and the reference signal generator 2
6 sets a threshold value of a signal level slightly lower than the above-mentioned temporally substantially constant signal level. Said comparator 23.2
4 compares the two thresholds and the received signal level, and outputs a signal when the signal level falls outside the range of the two thresholds. In other words, two or more MAU8
When the two transmit data simultaneously, the amplitude of the beat signal caused by the collision changes more than twice that of each transmitted signal, so the collision is detected by detecting the level of the received signal.

Therefore, each output of each comparator 23, 24 is connected to the OR circuit 27.
The signal is applied to the AND circuit 28 through the instep, and is applied to the instep stable multivibrator 29 only when a received signal is present. The output of the monostable multivibrator 29 drives the collision indication signal generation circuit 18, and the collision indication signal 1 mentioned above is generated.

Incidentally, the collision detection circuit 17 shown in FIG. 5 uses a clock of a predetermined frequency generated by a clock generator 30 at a counter 3 instead of the monostable multivibrator 29 shown in FIG.
1 to generate a signal with a predetermined time width. That is, when the occurrence of a collision is detected from the received signal level, the counter 31 is reset with a signal obtained by differentiating the detection signal via the differentiating circuit 32, and the AND circuit 33 is opened at this reset i timing. A clock of a predetermined frequency generated by the clock generator 30 is input to the counter 31 and counted. Then, when the counter 31 obtains a predetermined count value, its output (carry)
Thus, the AND circuit 33 is closed. Note that 34 is an inverter circuit that inverts the output of the counter 31.

Even if the collision detection circuit 17 is configured in this manner, a signal similar to that of the circuit shown in FIG. 4 can be obtained.

As described above, in the information transmission system according to the present invention, a collision in data transmitted via the unidirectional transmission path 1 is detected from the level of the received signal, and the collision is outputted to the upper layer protocol according to the collision detection result. Since the display signal is continuously generated in a time period longer than the transmission time of the jam signal that is sent to strengthen the collision state when the collision is detected, the upper level protoful will not erroneously count the number of collisions. It disappears. Therefore, effects such as being able to perform stable information transmission ti control can be achieved.

Note that the present invention is not limited to the embodiments described above. For example, the collision detection method, jam signal transmission time width, etc. may be determined according to the specifications of the network, and in short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of drawings]

13- The figures show one embodiment of the present invention. Figure 1 is a schematic diagram of the fR configuration of an information transmission system, Figure 2 is a configuration diagram of MAU, and Figure 3 is a diagram of collision detection, jam signal, and collision. FIGS. 4 and 5 are diagrams illustrating the timing of generation of display signals, and are diagrams each illustrating an example of the configuration of a collision detection circuit. DESCRIPTION OF SYMBOLS 1... Unidirectional transmission line, 2... Transmission line, 3... Receiving line, 4... Head end, 6 (6a, 8b, ~
60)... Medium attachment interface (M△U), 11... FM modulator, 12.15
...Band pass filter, 13...Transmission amplifier, 14...Reception amplifier, 16...FM demodulator, 17
...Collision detection circuit, 18...Collision display signal generation circuit. Applicant's agent Patent attorney Takehiko Suzue-14=

Claims (3)

[Claims] (1) In an information transmission system in which information is transmitted using a completely distributed peer-to-peer protocol transmission method between multiple upper protocols connected to a unidirectional transmission path via medium attachment units, respectively, The medium attachment unit receives the signal on the unidirectional transmission path, and detects a collision of the signals on the unidirectional transmission path based on the reception result, and upon detecting this collision, the medium attachment unit receives the signal on the unidirectional transmission path, means for generating a collision indication signal for the collision indication signal, and the upper protocol, upon receiving the collision indication signal, transmits the collision indication signal to the above-mentioned one via the medium attachment unit in order to strengthen the collision state. An information transmission system characterized in that the jam signal is set to occur over a longer time period than a jam signal transmission period to be transmitted to a directional transmission path. (2) The information transmission system according to claim 1, wherein collision of signals on the unidirectional transmission path is detected by comparing the amplitude of the received signal with a predetermined value. (3) The soft information transmission system according to claim 1, wherein the unidirectional transmission path consists of a transmission line and a reception line coupled through a head end.