JPH06261048A - Method and device for branching branch line - Google Patents

Abstract

PURPOSE:To connect a branch line cable to a branch connecting point on a trunk line cable without installation of excess trunk line cable by inserting a specific branch line branching device between branch connecting points of the branch line cable. CONSTITUTION:A branch line branching device 8 has an impedance equal to a characteristic impedance of a trunk line cable 3 and a length not causing signal reflection between adjacent branch connecting points and an attenuation equivalent to that of a trunk line cable. The insertion of the branch line branching device 8 as above between branch connecting points is electrically equivalent to the connection of a trunk line cable with a required length between branch connection points on the trunk line cable 3. Thus, it is not required to secure the attenuation depending on the length of the trunk line cable and installation of an excess trunk line cable is not required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention branches and connects a branch cable for connecting a terminal device to a trunk cable which is a transmission medium of a two-wire twisted pair LAN system using CSMA / CD as a medium access control system. The present invention relates to a branch line branching method and device.

[0002]

2. Description of the Related Art LANs (Local Area Networks) have become widespread in offices and factories in various fields. This LA
There are various types of N, but CSMA / CD (Carrier S
In the LAN of ense Multipul Access with Collision Detection) method, each terminal device detects whether a signal is flowing on the network (main cable), starts transmission if there is a space, and waits if there is no space. It is a system that.

In such a CSMA / CD type LAN, two twisted pair wires are used as a trunk cable to connect a terminal device such as a personal computer (hereinafter referred to as a PC) to the two twisted pair wires. Bus type CSMA / CD in the form of branching as a branch cable
There is a method.

In this bus type CSMA / CD system two-wire twisted-pair wire LAN system, a transmission signal is generated at the connection point (hereinafter referred to as a branch connection point) between the trunk cable and the branch cable due to disturbance of the line impedance of the trunk cable. Distortion and signal reflection.

Therefore, in the specification of the 2-wire type twisted pair wire LAN system of the bus type CSMA / CD system, the maximum trunk cable length is limited to 400 m and the maximum number of connectable terminal devices is limited to 32 units.

Further, the interval between branch connection points required to prevent reflection at each branch connection point on the main cable in the maximum specification, that is, the length of the main cable connected between adjacent terminal devices, is determined by the inventor. According to the experiment, about 12m
Has become.

FIG. 3 is a system configuration diagram of a bus type CSMA / CD system two-wire twisted pair wire LAN.

As shown in FIG. 3, this two-wire twisted-pair wire LAN system has a bus type structure using two twisted-pair wires and has 1-1, 1-2 to 1-n (n is an integer). ) Is a terminal device PC, 2 is a terminating resistor, 3 is a main cable of a two-wire twisted pair LAN system, 4 is a branch line cable for connecting the main cable 3 to the terminal device, and 5 is transmission from PC 1-1. The signal 5a is a signal transmitted from the branch connection point a to the left side of the drawing, and the signal 5b is a signal transmitted from the branch connection point a to the right side.

The access control system from each PC 1-n to the trunk cable 3 is IEEE802.3 CSMA / CD.
The method is used.

In FIG. 3, for example, the signal 5 transmitted from the PC 1-1 is transmitted in the direction of the arrow shown in FIG. 3, and the branch connection point a with the trunk cable 3 is transmitted via the branch cable 4.
To reach.

This signal 5 is further divided into a signal 5a to the left of the main cable 3 from the branch connection point a and a signal 5a to the right.
It is transmitted as b, and is transmitted to all PC1-n connected to the trunk cable 3 via the branch cable 4.

Each PC 1 that has received this rightward signal 5b
-N judges whether it is a signal addressed to its own PC,
If the signal is addressed to C, this is taken in.

On the other hand, since each PC 1-n is supposed to be able to transmit signals asynchronously, a plurality of PCs may transmit signals almost simultaneously. In such a case, a signal collision occurs on the main cable 3.

This signal collision is detected by determining that the signal collision has occurred when the own PC receives a signal from another PC while transmitting the signal, and at this time, the own PC Transmits a JAM signal which is a collision strengthening signal.

This JAM signal is transmitted to all PC1-n connected to the trunk cable 3 to notify the occurrence of collision.

Each of the other PC1s that have received this JAM signal
After waiting for a certain period of time, n again detects whether or not a signal is flowing on the trunk cable 3, starts transmission of the signal if there is a space, and waits if there is no space.

By the way, such a signal collision can occur not only by a signal from another terminal device but also by a signal transmitted from its own terminal device. The generation mechanism will be described below.

FIG. 4 is a diagram showing a state in which the PC 1-1 and the PC 1-2 are connected to the branch connection points a and b on the main cable 3 via the branch cable 4.

In FIG. 4, it is assumed that the distance between the branch connection points a and b (distance between branch connection points) is short. According to the experiments conducted by the inventor, the trunk cable 3 having a length of 5 to 12 m is required, but the length is shorter than this.

Assuming now that the signal 5 is transmitted only from the PC 1-1, the signal 5 transmitted from the PC 1-1 is transmitted by the branch cable 4 as shown by the arrow in FIG.
To reach a branch connection point a with the main cable 3.

This signal 5 is further transmitted from the branch connection point a to the left of the main cable 3 as a signal 5a and to the right as a signal 5b. The signal 5a transmitted from the branch connection point a to the left is No reflection occurs because it is absorbed by the terminating resistor 2.

However, the signal 5b transmitted to the right is
Reflection occurs at the branch connection point b on the trunk cable 3 of the branch cable 4 to which the adjacent PC1-2 are connected.

When the reflected signal 6 is large, the transmitting PC1-1 transmits the reflected signal 6 to the PC1-2.
The JAM signal is transmitted by erroneously recognizing it as a signal transmitted by the JAM signal and determining that a signal collision has occurred on the main cable 3.

As described above, when the distance between the branch connection points on the trunk cable 3 between the adjacent terminal devices is short, the signal 5 transmitted by the own terminal device is reflected at the branch connection point on the trunk cable 3 and is reflected. The signal 6 may be mistaken for a signal from another terminal device.

Therefore, as described above, it is necessary to ensure a sufficient distance between the branch connection points on the trunk cable 3 of the terminal device connected adjacently. According to the experiment by the inventor, 5 to 1
2m long trunk cable is required.

Therefore, conventionally, for example, even when a terminal device is placed on the same desk, the length of the trunk cable between the terminal devices is set such that reflection does not occur between the branch connection points, that is, 5 m to 12 m. There is no choice but to install it extra.
This extra trunk cable is unavoidable to be laid under a desk or the like in a state of a tuna roll.

FIG. 5 shows such a state.
PC with sufficient space between branch connection points on the main cable 3
It is a figure which shows the state in which 1-1 and PC1-2 are connected.

Further, the trunk cable 3 connected between the branch connection points a and b is shown in a tongue-wound state as indicated by reference numeral 7 in order to secure a length such that reflection does not occur at the branch connection point. is there.

In FIG. 5, the signal 5 transmitted from the PC 1-1 reaches the branch connection point a through the branch cable 4 and is further transferred to the left of the main cable 3 as a signal 5a.
Further, it is transmitted to the right as 5b.

As in the case of FIG. 4, the signal 5a transmitted to the left on the main cable 3 is absorbed by the terminating resistor 2, so that the signal 5a is not reflected.

As in the case of FIG. 4, the signal 5b transmitted to the right is first transmitted from the PC 1-1 and then from the branch connection point a, although the signal 5b is reflected at the branch connection point b. The signal 5b transmitted in the right direction is attenuated to some extent by the time it reaches the branch connection point b because the length of the trunk cable 3 from the branch connection point a to the branch connection point b is sufficiently long. However, the absolute value of the signal is small.

The signal 6 reflected at the branch connection point b is further attenuated by the time it returns to the branch connection point a.
The collision with the signal 5b transmitted to the right of the signal 5 transmitted from the PC 1-1 does not occur.

[0033]

However, when a trunk cable having a length such that reflection does not occur between the branch connection points is secured as in the method shown in FIG. 5, the trunk cable is installed under the desk. Since it has to be installed in a state of being wound with a tongue, there is a problem in that it is difficult to install cables in an area where many terminal devices must be installed close to each other, and the appearance is not preferable.

An object of the present invention is to provide a branch line branching method and a branch line branching device which can connect a branch line cable to a branch connection point on the main line cable without laying an extra main line cable. .

[0035]

In order to achieve the above object, the present invention divides a branch cable for connecting a terminal device into a trunk cable of a bus type two-wire twisted pair LAN system using the CSMA / CD system. In the branch line branching method to be connected, attenuation equivalent to the characteristic impedance of the main line cable between the branch connection points of the branch cable, and equivalent to the attenuation amount of the trunk cable of a length that does not cause signal reflection between adjacent branch connection points Insert branch line branching device with quantity.

The branch line branching device is inserted between the branch connection points of the branch cable, has a length equal to the characteristic impedance of the main cable, and has a length such that signal reflection does not occur between adjacent branch connection points. It is composed of a circuit element having an attenuation amount equivalent to the attenuation amount.

[0037]

According to the above means, the branch line branching device is equal to the characteristic impedance of the main line cable and is equivalent to the attenuation amount of the main line cable, and therefore is required between the branch connection points on the main line cable. It is electrically equivalent to connecting a length of trunk cable.

Therefore, it is not necessary to secure the amount of attenuation depending on the length of the main cable, and it is not necessary to lay an extra main cable.

[0039]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a LAN system constructed by connecting branch line branching devices of the present invention.

In FIG. 1, 1-1 to 1-n are PCs as terminal devices, 2 is a terminating resistor, and 3 is a trunk cable for connecting each terminal device to construct a LAN system.

Further, 4 is the trunk cable 3 and PC1-1 to PC1-1.
A branch cable for connecting the PC1-n, 5 is a signal transmitted from the PC 1-1, 5a is a signal transmitted in the left direction on the trunk cable, and 5b is a signal transmitted in the right direction as well. . Reference numeral 8 is a branch line branching device of the present invention.

FIG. 2 is a block diagram showing the details of the branch line branching device 8 of the embodiment.

In the branch line branching device 8 shown in FIG. 2, the impedance Zin seen from the left and right is equal to the characteristic impedance of the trunk cable 3, and has a length required to prevent reflection between adjacent terminal devices. Trunk cable 3
Is designed so that the amount of signal attenuation due to the signal and the amount of signal attenuation due to passing through the branch line branching device 8 become equal.

In FIG. 2, 8a, 8b, 8c and 8
d is a constituent element of the branch line branching device 8 (Z1, Z2, Z3,
Z4), and passive elements such as an inductance (L), a capacitor (C), and a resistance (R) are used.

Further, as the constituent elements 8a, 8b, 8c, 8d, active elements such as transistors may be used as necessary for signal attenuation correction.

In FIG. 2, since the impedance Zin seen from the left and right of the branch line branching device 8 is equal to the characteristic impedance of the trunk cable 3, this branch line branching device 8 is connected to each branch connection point (a, b, ... y, z) is electrically equivalent to connecting the trunk cable 3 having the length required between the adjacent terminal devices between the branch connection points.

Further, in FIG. 1, for example, a branch connection point a
If a signal is sent from the side, the amount of signal attenuation by the branch line branching device 8 inserted between the branch connection points a and b, and the trunk cable 3 having the required length are connected to the branch connection points a and b.
Since the amount of signal attenuation due to the connection between the branch lines is equal, the branch line branching device 8 is inserted between the branch connection points as shown in FIG. 1 and the trunk cable 3 having the required length is used.
Is completely electrically equivalent.

Therefore, the trunk cable 3 having a length required to prevent reflection between adjacent terminal devices is connected between the branch connection points, and the branch line branch device 8 is provided on the trunk cable 3. Insertion between the branch connection points is electrically equivalent to each other, and the same effect as that in FIG. 5 is obtained, so that the signal reflection at each branch connection point (a, b, ... Y, z) is prevented. It won't happen.

As a result, many terminal devices can be connected close to each other on the main cable.

[0051]

As described above, according to the present invention, C
In the branch line branching method of branching the branch line cable for terminal equipment to the main line cable of the bus type 2-wire twisted pair LAN system using the SMA / CD method, the characteristic impedance of the main line cable is provided between the branch connection points of the branch line cables. Since a branch line branching method of inserting a branch line branching device having an attenuation amount equivalent to that of a main line cable of a length that does not cause signal reflection between adjacent branch connection points is adopted, an extra trunk line cable is used. No need to lay.

The branch line branching device is inserted between branch line connection points of the branch line cable, and has a length equal to the characteristic impedance of the main line cable and of a length such that signal reflection does not occur between adjacent branch connection points. Since the circuit element is configured to have an attenuation amount equivalent to the attenuation amount, signal reflection does not occur between the branch connection points.

Therefore, by inserting the branch line branching device between the branching connection points on the trunk cable, even if the number of terminal devices is increased, reflection does not occur at each branching connection point, so that the transmission quality of the entire LAN system is improved. Does not fall.

Further, since it is not necessary to lay an extra trunk cable, the cable cost can be reduced.

Furthermore, by using this branch line branching device, the line impedance of the trunk cable can be corrected, and therefore, the disturbance of the waveform of the transmission signal can be suppressed.

[Brief description of drawings]

FIG. 1 is an LA constructed by using a branch line branching device of the present invention.
It is a system block diagram which shows one Example of N system.

FIG. 2 is a diagram showing details of a branch line branching device of the embodiment.

FIG. 3 is a system configuration diagram of a bus type CSMA / CD type two-wire twisted pair wire LAN.

FIG. 4 is an explanatory diagram for explaining an influence when a distance between main cables is short.

FIG. 5 is an explanatory diagram for explaining an influence when the distance between the main cables is sufficiently long.

[Explanation of symbols]

1-1 to 1-n ... PC as terminal device, 2 ... terminating resistor, 3 ... trunk cable, 4 ... branch cable, 5 ... PC1
-1 signal, 5a ... signal transmitted leftward on main cable, 5b ... signal transmitted rightward on main cable, 6 ... signal reflected by branch connection point b, 7 ... Cable, 8 ... Branch line branching device, 8a,
8b, 8c, 8d ... Constituent elements of the branch line branching device 8.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04B 3/40 9199-5K

Claims (2)

[Claims] 1. A branch line branching method of branching a branch line cable for connecting a terminal device to a trunk line cable of a bus type two-wire twisted pair LAN system using a CSMA / CD system, between branch line branching points. Insert a branch line branching device having an attenuation amount equivalent to the characteristic impedance of the main line cable and equivalent to the attenuation amount of the main line cable of a length that does not cause signal reflection between adjacent branch connection points. A branch line branching method, characterized in that a branch line cable is connected to the branch line. 2. A branch line branching device for branch-connecting a branch line cable for connecting a terminal device to a trunk line cable of a bus type two-wire twisted pair line LAN system using the CSMA / CD system, and between branch connection points of the branch line cable. A branch line branching device that is inserted into a cable and has a circuit element having an attenuation amount equivalent to the characteristic impedance of the main line cable and having an attenuation amount equivalent to the attenuation amount of the main cable that does not cause signal reflection between adjacent branch connection points. .