JP2753346B2 - Communication network access method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a communication network access method for information communication using a common line network, and particularly to a case where a common line network is used for an access system to an exchange in a configuration in which a subscriber line termination is provided by a distributed NT2 function. A communication network access method suitable for

[Prior art]

With the development of optical communication technology, a network for transmitting broadband signals such as images and high-speed data has become feasible. As a transmission switching method for such a broadband network, there is a method called an asynchronous transfer mode (ATM). ATM is a system in which all information is divided into fixed-length packets, which are called data, and are transmitted and exchanged. Since ATM is a kind of packet transmission switching system, a distributed switching system conventionally used in a local area network can be applied. This means that all terminals are connected to a common line via a device called an access unit and access the network via the access unit. The access unit obtains the right to access the common line when there is a transmission request from the terminal,
The information from the terminal is transmitted to the common line as a packet.
Each access unit checks the address of the information packet on the common line and copies the packet addressed to the access unit. However, in such a distributed switching system, since all access units are involved in all communication, efficient communication cannot be performed when the number of access units increases. For this reason, a centralized switching system in which switching is performed by an exchange is applied to communication over a wide area in an ATM. The distributed switching system is used in an area limited to an area such as a home or a premises. That is, the distributed switching system is used as a so-called extension connection. In such a case, conventionally, the connection between the exchange and the common line for distributed switching is as shown in FIG. That is, the exchange was connected to the common line via the access unit like other terminals. Such a configuration is
Sea C 89, Conference Record (1989) 39
Pages 4 to 398 (ICC89, Conference Record, (1989), p.
p394-398).

[Problems to be solved by the invention]

In the above conventional example, the following problem occurs. In the access to the common line, it is necessary to access after obtaining the access right. The same applies to a packet arriving from a switch to a terminal connected to a common line. For this reason, if the common line is used for communication between terminals at the time of an incoming call from the exchange, the incoming call from the exchange is put on standby. This is shown in FIG. No problem occurs when the sum of the incoming call volume and the extension call volume is within the transmission band of the common line. However, if the total exceeds the transmission band, either an extension call or an incoming call is waiting to be sent. When an extension call is waiting to be sent, it is easy for the terminal that is the information generation source to cope with it by reducing the information generation speed. On the other hand, when an incoming call is waiting to be sent, it is generally difficult for the exchange to reduce the information generation speed. This is because the exchange is not an information source, and in order to reduce the information generation rate, the information generation rate of a terminal located far away must be reduced. However, at the time when the exchange is waiting to be transmitted to the common line, the information packet has been transmitted from the terminal, and such control is impossible.
In such a case, it may happen that a part or all of the incoming information packet is discarded due to overflow of the buffer while waiting for transmission. SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems, and to prevent a loss of incoming information packets even in a case where incoming information packets from an exchange and extension information packets between terminals are mixed on a common line. It is an object of the present invention to provide a configuration of a line and distributed switching means.

[Means for Solving the Problems]

The above problem can be solved by giving an access right to the access from the exchange to the common line preferentially. In this case, it is necessary to give a higher priority than the normal priority access control between terminals. Focusing on this point, the following configuration can be a means for solving the above problem with a simple configuration. That is, a bus-type common line is used, an access unit is not used for access from the exchange, and a function of discarding an extension call packet is added to the entrance of the exchange when the terminal accesses the exchange.

[Action]

Giving the access from the exchange a higher priority than the terminal-to-terminal priority means that an incoming call from the exchange is unconditionally transmitted to a common line. In such a case, there is no need to use an access unit for common line access from the switch. For example, as shown in FIG. 4, a band required for a switched call among the common line bands may be secured, and the remaining band may be used for an extension call. If the bandwidth of the common line is equal to or higher than the maximum information rate from the exchange, there is no transmission wait for the exchanged call. In order to enable unconditional access to the common line for a switched call in this way, the form of the common line (connection form of a plurality of terminals by the common line) must be such that the exchange has a special arrangement. No. That is, in the ring type configuration as shown in FIG. 2, all the access units connected to the common line are equivalent. That is, in the ring type common line, each access unit can receive all signals from the upstream and transmit an information signal only when there is a fall in the common line band or when the access right has been acquired in advance. If an exchange is inserted and a signal is sent unconditionally in a ring-type configuration, some or all of the information packets from the upstream may be replaced by information packets from the exchange. The form of the common line in which the exchanges have a specific arrangement is generally a bus type form. Here, the bus-type configuration means that the common line has an end point, and includes a ring-type configuration in which a part thereof is cut off, and the like. If an exchange is arranged at the end point of this bus, there is no upstream of the exchange, so that the above-mentioned inconvenience does not occur. On the other hand, since the exchange is at the end point of the common line, the information packet to the exchange, that is, the information packet transferred from the terminal connected to the common line via the access unit to a wide area by the exchange flows into the exchange,
An information packet corresponding to an extension call that should not flow into the exchange also flows into the exchange. If the exchange accesses the common line via the access unit, such unnecessary information packets are not copied by the access unit, so that such a problem does not occur. For this reason, in the present invention, among the information packets flowing into the exchange from the common line, those corresponding to the extension call are discarded at the entrance of the exchange. According to the above configuration, it is possible to transfer the incoming information packet from the exchange to the terminal without waiting for transmission, and it is possible to solve the problem that the incoming information packet is discarded due to the transmission wait.

【Example】

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. Common track 14a, 14
The access units 11a, 11b, 11c, and 11d are connected as shown by b and 14c. Terminals 13a, 13b, 13c, and 13d are connected to the respective access units. An extension information cell erasing circuit 18 is provided between the transmission lines 16 and 17 only between the exchange 12 and the access unit 11d facing the exchange, only on the up line (the line going to the exchange).
In this embodiment, the common lines 14a, 14b, 14c, the transmission lines 15, 1
6 and 17 constitute a bus-type common line, and one end of an exchange 1
2 is connected. The access unit has a configuration as shown in FIG. In this configuration, the access unit uses an access method to a common line called DQDB. FIG. 5 shows only information transfer in one direction of a bidirectional bus for the purpose of explanation. In FIG. 5, there is an exchange on the right side of the figure. For the sake of explanation, FIG. 5 shows the access unit 11c in FIG. Common track 1
It is assumed that the right side of the access units 41 and 142 corresponds to the common line 14b in FIG. 1, and the left side corresponds to the common line 14c in FIG. The access unit has two types of counters, a request counter 51 and a down counter 52. The request detection circuit 53 in the access unit has a common line 142 in the opposite direction to the common line 141 in the direction in which information is to be transferred.
The request display section of the information cell column 57 to which the request is transferred is constantly monitored, and the request counter 51 is incremented by one each time a request displayed there is detected.
The value of the request counter 51 is the common line on the information sending side.
It is decremented by one each time an empty cell is detected in the cell column 58 passing through 141. Empty cell detection circuit is empty cell detection circuit
155 is performed by detecting that the empty cell display section of each cell indicates that it is an empty cell.
The request here is a common line 141 on the information cell sending side.
Is transmitted by the access unit 11a or the like on the downstream side every time there is a transmission request from the terminal 13a or the like, and the value of the request counter 51 that counts this becomes a transmission waiting state on the 141 downstream side at that time. Indicates the number of information cells present. When there is a transmission request from the terminal 13c, the access unit 11c makes a request indication mark on the request display section of one cell in the cell column 57 flowing through the common line 142 in the direction opposite to the transmission direction by the request transmission circuit 54. Sends a request. At the same time, the value of the request counter 51 at that time is copied to the down counter 52. The down counter 52 decrements the value by one each time an empty cell is detected in the cell column 58 passing through the common line 141 on the sending side, and when the value becomes 0, the value is changed to the empty cell passing immediately thereafter. The information is sent to the common line 141 by copying the information signal from the terminal 13c. With the above-described access unit configuration, even if information from the exchange is unconditionally transmitted as a switching call cell to the common line, the operation in each access unit simply requires information transfer from the terminal to be a transmission wait. Only the ratio increases, and no change occurs in the operation itself. Also, if the exchange 12 in FIG. 1 is located at the most upstream of the common line 141, it is clear that all information cells transmitted by the access unit located downstream therefrom are for the extension. It can be seen that the information cells are transferred with priority over the extension information cells. As described above, as shown in FIG. 4, a method of using the common line in which the band of the common line is preferentially assigned to the switched call and the remaining portion is assigned to the extension call can be realized. On the other hand, when each terminal sends outgoing information to the exchange, there is no need to set priorities among the terminals, so if any terminal sends an information cell to a common line going to the exchange via an access unit. Good. However, in this case, an extension information cell and a transmission information cell to the exchange are mixed on the common line toward the exchange. Since the flow of the extension information cells into the exchange may complicate the processing in the exchange and cause inconvenience, it is necessary to provide the extension information cell erasing circuit 18 as shown in FIG. FIG. 6 shows an embodiment of the extension information cell erasing circuit. In this embodiment, the virtual channel identifier (VCI) present in the header of the information cell is used for identifying the extension information cell. The VCI associates an information cell with a virtual channel for performing information transfer, and can thereby identify which call the information cell belongs to.
That is, the information cell for the extension and the information cell for transmission to the exchange can be distinguished by the VCI. In the embodiment shown in FIG. 6, the VCI latch circuit 61 controls the VCI of the header of the information cell.
The value is latched. The VCI comparison circuit 62 checks whether or not the VCI matches the VCI assigned to transmission to the exchange registered in the latched VCI registration table 63. If the VCI matches, the VCI comparison circuit 62 notifies the exchange call cell selection circuit 64 of the coincidence. The switching call cell selection circuit 64 drives the gate circuit 65 so as to send the switching call information cell to the exchange based on this. In the above embodiment, the access to the common lines 14a, 14b, and 14c uses a so-called DQDB access method.
In this embodiment, each access unit 11a, 11b, 11c, 11d
In this configuration, the incoming information cell from the exchange is preferentially transferred without any change to the DQDB as the access method in the above. For this reason, the access unit used here has the effect that no change is necessary when connecting to the exchange or in other cases. FIG. 7 shows another embodiment of the extension information cell erasing circuit. In this embodiment, a portion for indicating that the cell is an extension information cell is provided in the header of the information cell, and the extension information cell is erased based on the portion. That is, the extension display detecting circuit 71 examines the extension display portion of the information cell header, and if the extension is not displayed, that is, if the information cell is a transmission information cell to the exchange, it notifies the exchange call cell selection circuit 64. The switching call cell selection circuit 64 drives the gate circuit 65 so as to send the switching call information cell to the exchange based on this. The extension information cell erasing circuit according to the present embodiment is characterized in that the circuit is simplified because the exchange call information cell can be detected only by examining the extension display portion of the information cell header. FIG. 8 shows another embodiment of the present invention. In the present embodiment, a statistical multiplexer 81 is provided between the exchange 12 and the extension information cell erasing circuit 18. Statistical multiplexer 81
Is connected not only to a pair of common lines 15 and 17, but also to a plurality of other similar common lines 15 ', 17' and the like. The statistical multiplexing device 81 increases the use efficiency of the transmission line 82 by statistically multiplexing the information cells from the plurality of uplinks 17, 17 'and the like. In this configuration, extension information cells that do not need to be transferred to the exchange 12 are deleted before being input to the statistical multiplexer 81.
That is, since the extension information cells are not input to the statistical multiplexing device 81, the present embodiment has an effect that the use efficiency of the transmission line 82 is further increased. FIG. 9 shows another embodiment of the present invention. In the present embodiment, a speed conversion circuit 91 is inserted between the exchange 12 and the extension information cell erasing circuit 18. Speed conversion circuit
91 is the common line 17 ″ and 15 ″ on the access unit side
This is a circuit for converting the speed of the switch to be higher than the speed of the exchange side lines 92 and 93. This can be easily realized by performing a so-called store-and-forward transfer through a buffer memory. This configuration secures a band for transferring extension information cells by setting the band of the common lines 14a ", 14b", and 14c "connecting the access units to be larger than the input / output band of the exchange 12. According to the configuration of the example, there is an effect that the terminal-to-terminal communication is possible even when the incoming call from the exchange 12 and the outgoing call to the exchange 12 occupy the transmission band of the input / output lines 92 and 93.

【The invention's effect】

As described above, according to the present invention, according to the present invention, when the incoming information from the exchange and the outgoing information to the exchange are mixed in the communication using the common line, the information from the exchange is preferentially transferred. It is not possible for the incoming signal from the exchange to wait for access to the common line. For this reason, a large-capacity buffer for buffering signals from the exchange is unnecessary, and even if a large-capacity buffer is used, information cells that may occur may not be discarded. There is an effect that can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic embodiment of the present invention. Second
The figure shows an example of the prior art. FIG. 3 is a diagram for explaining the prior art. FIG. 4 is a diagram for explaining the effect of the present invention. FIG. 5 is a diagram showing a configuration example of the access unit in FIG. 1, and FIGS. 6 and 7 are diagrams showing an embodiment of the extension information cell erasing circuit in FIG.
8 and 9 show another embodiment of the present invention. Explanation of reference numerals 11a, 11b, 11c, 11d, 11a ', 11b', 11c ', 11d', 11
a ″, 11b ″, 11c ″, 11d ″: access unit 12: exchange, 13a, 13b, 13c, 13d, 13a ′, 13b ′, 13c ′, 13
d ', 13a ", 13b", 13c ", 13d": terminals 14a, 14b, 14
c, 141, 142, 14a ', 14b', 14c ', 14a ", 14b", 14
c ″: Common line connecting access units, 15, 1
6, 17, 15 ', 16', 17 ', 15 ", 16", 17 ", 82, 1
8, 18 ', 18 ": extension information cell erase circuit, 83, 92, 93:
Transmission line, 81: Statistical multiplexer, 91: Speed conversion function

Claims (6)

(57) [Claims] 1. A communication network in which a plurality of access units are interconnected by a common line and a plurality of terminals access the common line via the access unit, wherein the common line is in the form of a bus. An exchange switch is connected to one end of the common unit in a direction from the access unit to the exchange, and the access unit is provided between the access unit facing the exchange and the exchange. A function for erasing information relating only to communication between the terminals via a communication network. 2. A communication network access method according to claim 1, wherein said access unit accesses said common line by means of a distributed queue dual bus (Di-bus).
A communication network access method characterized by the method of distributedQueue Dual Bus (DQDB). 3. The communication network access method according to claim 1, wherein the function of deleting information related only to the terminal-to-terminal communication is performed only for the terminal-to-terminal communication by using a virtual channel identifier included in a header portion of the information. A communication network access method characterized by identifying relevant information. 4. The communication network access method according to claim 1, wherein the function of erasing the information related only to the terminal-to-terminal communication includes the step of deleting the information related to the terminal-to-terminal communication included in the header part of the information. A communication network access method, wherein information related to only the terminal-to-terminal communication is identified by a display function. 5. The communication network access method according to claim 1, wherein a statistical multiplexing function is provided between the function of erasing information relating only to the terminal-to-terminal communication and the exchange. Communication network access method to be. 6. The communication network access method according to claim 1, further comprising an information transfer rate conversion function provided between the function of erasing information related to the terminal-to-terminal communication and the exchange. The information transfer speed between the information transfer speed conversion function and the function for erasing information related only to the terminal-to-terminal communication is set to be higher than the information transfer speed between the speed conversion function and the exchange. A communication network access method, characterized in that: