JPH1032578A - Communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication system in which the efficiency of the communication system capable of multimedia communication is improved and noise immune and economical multimedia communication is attained in a 2-way communication network. SOLUTION: In this communication system, one central station and a plurality of terminal stations 5-1, 5-2 are tied via a 2-way communication line and the communication between the terminal stations is conducted via the central station. In this case, the system is provided with an exclusive communication channel assigned fixedly between one terminal station and the other terminal station and a common communication channel assigned multiplexingly and simultaneously to a plurality of the terminal stations 5-1, 5-2, and part of an optional traffic channel is used for a logic control channel. A control means 104 to assign a plurality of terminal equipments to each of the traffic channel in response to a communication request of the terminal stations 5-1, 5-2 and a plurality of terminal equipments assigned to each traffic channel configure wait type data communication with a means preventing collision in each traffic channel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a central office,
The present invention relates to a communication system in which a plurality of terminal stations are connected via a bidirectional communication path, and communication between the terminal stations is performed via a central station. In particular, the present invention relates to a communication system suitable for using multimedia of various information forms such as audio information, computer output data, text information and graphics or moving images, and quasi-moving images.

[0002]

2. Description of the Related Art In recent years, a communication system using a CATV network has attracted attention both inside and outside the country as a new communication infrastructure.
As a communication system corresponding to this trend, an MCA / C called "analog CATV telephone" at a practical level is used.
There is a telephone system. This MCA / C telephone system
Multi-channel access (hereinafter abbreviated as MCA) based on FM radio technology proven in the wireless field.
Because it was applied to the ATV network, on-cable (on C
able) and named MCA / C.

In the MCA / C telephone system, as shown in FIG. 11, as shown in the main specifications, a 2.5-MHz band for each of the upstream and downstream in the CATV transmission line is used, and 200 MHz at a carrier frequency interval of 12.5 KHz. The communication channel of the channel is obtained. FIG. 7 shows an example of the MCA / C telephone system.

FIG. 7 is a block diagram showing a conventional example of an MCA / C system in which a part of the facilities of the CATV system is operated in common, wherein 1 is a head end,
It is located at the center of the CATV system, and a plurality of trunk cables 2-1 to 2-n extend from the head end 1 for each route.

The head end 1 has a trunk cable 2-1.
An input / output distribution device 101, which is a branch coupling unit of .about.2-n, is provided. A CATV broadcast facility 102 and a block converter 103 are connected to the input / output distribution device 101. Further, a line control device 104, The communication management device 105 is connected.

The trunk cables 2-1 to 2-n are provided for each route, but are generally divided into a plurality of routes in order to limit the number of accommodated subscribers and the cable length. is there.
And the trunk cables 2-1 to 2-n of these respective routes are
Is extended by connecting the bidirectional relay amplifiers 3-1 and 3-2 in multiple stages.

[0007] The branch cables branched from the bidirectional relay amplifiers 3-1 and 3-2 have tap-offs 4-1 and 4-2, and are configured to branch to subscribers 5-1 and 5-2. , As a whole, constitute a tree-like network.

[0008] A distributor 501, a television receiver 502, a network terminating device 50 are installed in the homes of the subscribers 5-1 and 5-2.
3. Telephone 505 and FAX / PC 506 are provided.
With the reception of multi-channel television broadcasting, telephone, F
Intra-region communication by AX, PC, etc. can be performed. In this intra-area communication, a bidirectional transmission system is used in which the direction from the subscriber to the headend is set as up, and the direction from the headend to the subscriber is set as down.

In response to the digitalization trend of the MCA / C telephone system, a system called a "digital CATV telephone" has recently been developed in various fields. As a system for realizing this digital CATV telephone, a time division multiplexing (hereinafter abbreviated as TDMA) system is adopted.

In the TDMA system of the digital CATV telephone system which is currently under development, the communication path has a bandwidth of one TV channel of the NTSC system.

TDM for digital CATV telephone system
An example of the A method is shown below.

[0012] Four-phase phase modulation (hereinafter abbreviated as QPSK modulation) is performed using the entire area of the 6 MHz band, and about 8 Mb
There is an example in which a transmission rate of ps is secured, and TDMA is implemented in units of 64 Kbps as a transmission rate per terminal.

There is an example in which QPSK modulation is performed for each 1.5 MHz subchannel obtained by dividing a 6 MHz band into four, about 2 Mbps is secured for each subchannel, and TDMA in units of 64 Kbps is realized.

FIG. 10 shows a TDMA using a CATV network.
FIG. 2 is a conceptual block diagram for explaining a line connection operation in a system telephone communication. ts1, ts2,... tsn and Ts1, Ts2
.., Tsn are shown.
The terminal station 51 uses a time slot of ts1 for uplink (transmission) and a time slot of Ts1 for downlink (reception). Terminal station 5
2 uses a time slot of ts3 for uplink (transmission) and a time slot of Ts3 for downlink (reception). The conversion of the time slot from upstream to downstream indicated by the dashed arrow is performed by the exchange 41 and the multiplexer 42 in the head end 40.
The terminal station 52 has network termination devices 513 and 52, respectively.
3 and telephones 515 and 525 are connected.

FIG. 12 is a main specification table of the TDMA system of FIG. According to the table, sub-channels consisting of 4 carriers are configured at a carrier frequency interval of 1.5 MHz using up and down 6 MHz bands in the CATV transmission line, and 24 channels per sub channel, for a total of 96 channels Are obtained.

The MCA / C telephone system first put into practical use as a general-purpose communication system using a CATV network has a limit in its use. On the other hand, digital CATV telephones currently under development are in a transitional period of development. Published TDMA for digital CATV telephones
The method has the following features, problems, and the like in relation to the characteristics of the CATV network, the use form, the business form, and the like.

First, the characteristics of the CATV network will be described.

(1) Bidirectional C composed of a tree-like network
In the ATV network, there is upstream ingress noise (a noise mixed into a distribution system or a home wiring system which flows into a head end) peculiar to the CATV network in an upstream transmission band. In the upstream transmission band, a transmission system with higher noise resistance is required as compared with the transmission of television video signals and the like in the downstream transmission band.

(2) Upstream ingress noise occurs in a specific band due to interference by a radio device or the like. Generally, the upstream ingress noise is caused by contamination of noise generated from home electric appliances and industrial equipment. When noise is observed with a spectrum analyzer or the like, a situation in which narrow-band, short-duration, impulse-like noise is randomly generated on the frequency axis is observed. From this situation, it can be said that a transmission scheme using a wide band has a high probability of being disturbed by noise.

(3) In the conventional CATV, even if the equipment is bidirectional, the use of the upstream transmission band including the end of the cable is less than that of the downstream transmission band. Therefore, no attention has been paid to the countermeasure for upstream ingress noise, and various experiments have revealed that the level of upstream ingress noise is generally poor in existing CATV networks.

In order to improve this, all the terminals are visited and
It is necessary to confirm the source of the mixed noise and to strengthen the shield of the cable itself and the coaxial connector. However, in CATV, since thousands to tens of thousands of terminals are targeted per system, it is expected that significant cost will be generated for noise countermeasures.

(4) In the CATV network, it is necessary to cope with noise generated in the network in addition to the noise mixed from outside as described above. The noise generated in the network is mainly caused by the nonlinearity of the transmission path.

In a CATV network, multistage relay amplification is performed to compensate for line loss. Inter-channel interference, which depends on the characteristics of the relay amplifier and the number of relay stages and is caused by the non-linearity of the amplifier, caused by cross-modulation, inter-modulation, etc., is a problem.
As measures to prevent the influence from exceeding the limit, the total transmission power per TV channel is limited, and the number of channels is limited when the band of one TV channel is further used in the frequency multiplexing system. .

On the other hand, in the CATV network, as the trunk line becomes an optical cable, the nonlinearity of the entire network tends to be improved by reducing the number of relay stages.

(5) It has been known that, when performing wideband, high-speed digital transmission in a CATV network, a reflected wave caused by impedance mismatch of a transmission line has an effect. In order to improve this problem as well, the range extends to in-home wiring and terminal equipment, and it is expected that ideal improvement is difficult in terms of cost.

(6) In the CATV network, up / down signals pass through one coaxial cable. In the Japanese CATV network, the upstream band: 10 MHz to 50 MH
z, downstream band: 70 MHz to 450 MHz (or 750
MHz) is common. Even if the entire upstream band can be used, the total number of possible channels with a 6 MHz bandwidth as one channel is as small as 6 channels. In addition, the above-mentioned upstream inflow noise is not uniform in all bands, and is 10 MHz.
It is often found in the band of ２０20 to several MHz. Channels in a noisy band cannot be used. In the United States, the upstream band is narrower than in Japan, at 10 to 30 MHz.

[0027] Under such circumstances, the upstream channel is very valuable, and efficient use is required.

Next, the problems of the MCA / C are as follows: (7) Compared with the characteristics of the transmission line such as the above-mentioned CATV network, the MCA / C is a narrow band transmission system, so that considerably good transmission is achieved. There is an advantage that the number of channels can be increased. However, MCA / C is 9600 bp for data transmission.
There is a drawback that the service level is limited, and services beyond this can not be provided.

Next, the problems of the TDMA are as follows: (8) Digital C
For ATV phones, as mentioned above, 6 MHz or 1.5
Since a wide band such as MHz is used, it is easily affected by upstream ingress noise having the above-described properties. In addition, there is a drawback that since the transmission is broadband and high-speed, it is easily affected by reflection due to impedance mismatch.

(9) The noise level at each terminal station dispersedly arranged in the tree-like CATV network is not uniform, and there is considerable variation depending on the route of the trunk line. In order to ensure uniform transmission quality throughout the system, it is desirable that the ratio of carrier level to noise level (C / N) be the same at each terminal station. In a system in which a carrier is divided for each communication channel, within a permissible value of the total transmission power of one TV,
Weighted power distribution is possible in which a high transmission level is assigned to communication with a terminal station on a path having a high noise level. However, it is difficult to use a method of transmitting a plurality of communication channels using one carrier such as TDMA.

(10) In the TDMA system, 64 Kbps by PCM transmission is set to 1ch and connected to an analog telephone. As a result, in terms of the frequency utilization efficiency per 6 MHz, the MCA / C is 200 when compared with the number of channels constituting the voice transmission band (0.3 to 3.4 kHz).
TDMA is inferior to 96 channels. In addition,
In this case, the MCA / C uses 2.
It is limited to 5 MHz.

(11) In the CATV telephone system, a fixed-rate system is adopted in order to avoid a high facility cost of the telephone charge management system. The flat-rate system is a system in which telephone charges for a predetermined period are constant regardless of the usage amount. There is a need for a CATV telephone system that can accommodate many subscribers at low cost. The following two methods are conceivable as telephone communication methods. One is the immediate connection type, in which the terminals occupy the line once, and the other terminals cannot enter the line until the communication ends, as in the line connection method of the existing subscriber telephone system. Communication method. the other one is,
There is a waiting-type communication system such as a LAN (Local Area Network) in which a common line is allocated to a plurality of terminals and a waiting time until each terminal can access the common line is given to each terminal. In personal computer communication, the data transmission speed is determined by the signal transmission speed of the terminal device even if the maximum signal transmission speed of the communication line is high. Further, there is a period during which data is not actually transmitted even while the communication line is connected between the computer terminals. Therefore, the line utilization rate of data communication between personal computers generally shows a small value. For a subscriber who connects a data processing device such as a computer to the CATV telephone system, the latter communication method such as LAN is suitable.

In order to increase the line utilization rate, it is advantageous to use a system such as a LAN in which many terminals are accommodated in one channel and communication is performed in a waiting mode. In such a LAN type communication system, the line speed is effectively absorbed by absorbing the speed difference between the terminal and the line, and making other terminals use the non-operation time when the line is held but not used. It will be available. It is difficult to realize such communication in the TDMA system based on the instantaneous circuit switching system.

(12) Further, in the TDMA system, a full-duplex communication system (full-duplex) is used in the same manner as the voice channel allocation of the MCA / C system described later.
Up / down two time slots, each 2ch
Need to be allocated. In the case of the LAN type, half-duplex communication is premised, so that a line can be configured by allocating one channel.

There are various forms of data communication, and most of the forms involve data transmission from one terminal to the other terminal. A system in which a line is always open while simultaneous transmission can be performed in both directions is disadvantageous in line use efficiency.

(13) TDMA of CATV telephone system
Is based on 64 Kbps / ch. Generally, a terminal having a transmission rate different from the transmission rate of a line requires an adapter for performing rate conversion because the network terminating device of the terminal does not have a rate conversion function. In a LAN, the line speed is basically different from the terminal speed, and it is possible to flexibly cope with a difference in transmission speed.

Finally, problems of the LAN will be described.

(14) For example, the IE of the LAN standard
In a LAN system such as EE 802.3, a terminal connected to a node can make outgoing calls at any time under certain conditions, and has means for controlling the total amount of network traffic, such as outgoing calls. Not.

When a LAN communication system is applied to a CATV network, it is necessary to provide a system that assumes that the number of subscribers is very large. For example, in a traffic state where the waiting time exceeds a certain time, a new communication request is restricted (assignment to the channel is restricted).
It is necessary to have a function that can do it.

(15) Some data transmissions using the CATV network are required to transmit high-speed and continuous data, such as moving image transmission. There is a problem that high-speed continuous data transmission is not suitable for a system such as a LAN that assumes intermittent data transmission in packet units. In order to solve such a problem, it is necessary to occupy the channel in a state similar to circuit switching, depending on the type of information to be transmitted, so that a continuous data transmission service can be provided.

Such services are not intended for all ordinary subscribers. For example, in the home welfare service, it can be limited to a specific use such as a communication system connecting a hospital or a welfare center and a solitary elderly home.

(16) In a LAN system, a baseband transmission system using the entire band of one cable, which is a common transmission line, is generally used. The band is divided to provide a plurality of channels, and for each channel, There are no examples of enabling different services.

[0043]

The use of a communication network in a multimedia environment includes voice information, facsimile,
Various types of data information, such as text information, graphics, moving images, or computer output data, may be transmitted using one communication network, for example, a CATV network as a transmission medium. These various forms of information can be
It is desirable that data can be efficiently transmitted between terminals of many subscribers in a V network. The service area of the CATV network has been expanding in recent years. In the existing CATV network, broadcasting of video information is mainly performed.

For communication of information such as computer data, it is desirable to use a waiting communication system in which a common communication channel is allocated to a plurality of different terminals, such as a LAN system, as described above.

An object of the present invention is to provide a communication system which enables efficient multimedia communication in a two-way communication network such as a CATV network.

Another object of the present invention is to provide a communication system which is robust against noise and enables economical multimedia communication.

Suitable for CATV in a multimedia environment,
According to the embodiment of the present invention, from the viewpoint of efficient use of the line, the above two methods can be used properly according to the information form. C
The frequency band of the communication path of the ATV network is allocated to a band for the immediate communication system and a band for the queuing communication system.

Further, by dividing the bandwidth of the queuing type communication system into a plurality of channels and narrowing each channel, noise can be reduced and the line can be economically used.

Further, the object of the present invention is to commercialize a communication service using a CATV network, while considering a general purpose multimedia communication system including a telephone service, while focusing on a data transmission service. There are also realistic voices who want a simplified, multimedia communication system.
The reasons are, for example: (1) Given an existing CATV network, the number of TV channels available for communication services is small, and it is expected that it will be difficult to accommodate telephone service traffic.

(2) To realize a telephone service connected to a public network, which guarantees advanced service functions and reliability,
Large-scale capital investment and maintenance systems are required.

(3) As for the usage fee of the existing communication carrier, the data transmission service is more expensive than the telephone service, and the investment effect is high. And so on. Therefore, the present invention aims at a simpler multimedia communication system specialized in data transmission to meet such a demand.

[0052]

According to the communication system of the present invention, one central station and a plurality of terminal stations are connected via a bidirectional communication path. A communication system performed via a central office, wherein a dedicated communication channel allocated between a terminal station and another terminal station,
In a system having a common communication channel multiplexed and allocated to a plurality of terminal stations simultaneously, the communication path has a plurality of traffic channels in which the common communication channel and the dedicated communication channel are set, and an arbitrary traffic channel. Is used as a logical control channel.
The present invention further provides a frequency multiplexed narrow band single carrier per channel system (hereinafter referred to as S
Communication may be performed by a CPC scheme or a multi-carrier per-channel scheme (hereinafter abbreviated as MCPC scheme). Further, in a communication system in which a bidirectional multiplex communication network is configured between the one central station and a plurality of terminal stations, a plurality of traffic channels are provided in a certain bandwidth including an upstream transmission band and a downstream transmission band. Control means for arranging and allocating a plurality of terminals to each of a plurality of traffic channels using the logical control channel in response to a communication request of the terminal; and allocating the traffic channels by the control means. The plurality of terminals thus set may form a queued data communication by means for preventing collision in each traffic channel. The collision preventing means may control the common communication channel so that only one signal is transmitted when a plurality of different signals are present in the common communication channel to avoid a signal collision. Further, the configuration may be such that the logical control channel is used to perform communication based on a service type and a traffic condition based on a means capable of limiting use, limiting communication time, and the like on a traffic channel basis. good. Further, the frequency band of the communication path is divided into a plurality of bands, and the plurality of traffic channels are set by frequency division multiplexing on each of the divided bands, and the plurality of traffic channels have different bandwidths from each other. Is also good.

Further, a unique code may be assigned to each of the plurality of terminal stations on the communication path, and the plurality of traffic channels may be set by a code multiplexing method.

[0054] The central station may have service management means for setting an upper limit of the use time of the common signal channel to be allocated to the terminal station when there is a communication request from the terminal station. Further, the central station may have a service management means for setting the waiting time of the common signal channel for each terminal station, or a service management means for setting the data transmission rate of the common signal channel for each terminal station. Means may be provided.

The upper limit of the use time is provided with a plurality of groups each consisting of one or more terminal stations, and the service management means of the central office sets the upper limit of the use time for each group. You may do it.

A plurality of groups each consisting of one or more terminal stations are provided for the waiting time, and the service management means of the central office sets the waiting time for each group. good.

The data transmission rate is provided with a plurality of groups each including one or more terminal stations, and the service management means of the central office sets the data transmission rate for each group.

[0058]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a multimedia communication system according to the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 shows an embodiment of the present invention, wherein 1 is a head end, 2-1 to 2-n are trunk cables, and 3-1 to 3-n.
2 is a relay amplifier, 4-1 and 4-2 are tap-off, 5-1
5-2 are terminal stations.

Here, as shown in the figure, 101 is an input / output distribution device, and 102 is a CATV.
The broadcasting equipment, 103 is a block converter, 104 is a line control device, and 105 is a communication management device. As shown in the figure, the internal configuration of the terminal stations 5-1 to 5-2 includes a distributor 501, a television receiver 502, a network termination device 504, and a personal computer (PC) 507.
2A and 2B are frequency arrangements of the communication system according to the embodiment of the present invention.

FIG. 2A is an arrangement diagram of a frequency band used for a communication path in a communication system to which the present invention is applied. Headend 1 from terminals 5-1 and 5-2
The total bandwidth 10 of the upstream signal transmitted to the
MHz, and conversely, the whole use band 20 of the downlink signal transmitted from the head end 1 to the terminal side is 70 to 450 MHz.
It has become. In the multimedia communication system according to the present invention, among the frequency bands for uplink and downlink signals,
Originally, it is set for CATV for TV signals.

Further, in this embodiment, a frequency-multiplexed narrow band single carrier per channel system (hereinafter abbreviated as SCPC system) or a multi carrier per channel system (hereinafter MCP system)
The communication is performed according to the C method. Further, FIG. 2B shows an example of the arrangement of signal bands in each of the bands 15 and 25 indicated by hatched portions in FIG.

The arrangement shown in FIG. 2 (B) shows two arrays at 300 KHz intervals within a 6 MHz band for one NTSC television set.
This is an arrangement of traffic channels of channel 0.

As an example, in a traffic channel:
384 Kbps by built-in QPSK modulation mode modem
Data transmission.

FIG. 3 shows the internal configuration of the network terminating device 504. Reference numeral 514 denotes a high-frequency input / output line (hereinafter referred to as an RF input / output line), 511 denotes a high-frequency unit (hereinafter referred to as an RF unit),
31 is an intermediate frequency unit (hereinafter referred to as an IF unit), 532 is a modulation / demodulation unit, 533 is a communication control unit, 534 is a terminal interface unit (hereinafter referred to as a terminal I / F unit), and 515 is a terminal interface line (hereinafter referred to as a terminal I / F unit). F line).

FIGS. 4A and 4B show the structure of a packet according to the embodiment of the present invention. FIG. 4A shows the basic structure of a packet, FIG. 4B shows a control packet, FIG. 4C shows a data packet, and FIG. 3 shows a frame of an F signal. Also, PA and pa are preambles, SFD and sfd are frame start delimiters, DA and da are destination addresses, SA and sa are transmission addresses, LF and lf are information field lengths, INFO,
info is an information field, and FCS and fcs are flag check sequences. These frame configurations are IE
It is basically the same as EE 803.2.

Next, the function of each section will be described.

The RF unit 511 is a frequency band used in the CATV network, 10 to 50 MHz (up), 70 to 450
It operates using each 6 MHz band in MHz (downstream) (see FIG. 2A).

As described above, this network terminating device
Data transmission of 384 Kbps is performed in a bandwidth of 0 KHz, and the IF unit 531 and the modulation / demodulation unit 532 correspond to this.

The reason is that the bandwidth of 300 kHz is 384.
As data transmission at Kbps, digital transmission in a wireless section of a personal handyphone system (hereinafter abbreviated as PHS) is employed.

Communication control section 533 and terminal I / F section 534
Has the following features:

The interface with the terminal is RS232C
18. Supports synchronous / asynchronous transmission of / RS422, and the transmission rate exceeds the rate that can be supported by the voice channel.
2 kbps, 64 kbps, 128 kbps, etc. are assumed. Therefore, synchronous / asynchronous conversion, speed conversion to 384 Kbps, or the reverse conversion is performed.

At the start of communication, the operation for receiving the assignment of the traffic channel depends on the transmission operation of the terminal. The terminal makes a call according to a procedure corresponding to an AT command which is widely used in personal computer communication. Terminal I / F unit 53
Reference numeral 4 has a function of monitoring this procedure, receives a destination number, etc., and uses it in a calling operation.

In the communication after receiving the “channel designation” and capturing the traffic channel, it is necessary to generate a data packet independent of the terminal protocol in order to enable connectionless communication.

This means is performed by means for monitoring the frame without intervening in the protocol of the terminal as employed in a bridge, which is one of the LAN connection devices.
That is, terminal I / F transmitted and received by terminal I / F section 534
Recognize the frame of the signal and generate a new data packet using the frame as user data. When the frame length is long, conversion for dividing into a plurality of data packets is also performed. FIG. 4C shows an example of a data packet.
FIG. 4D shows a frame of the terminal I / F signal.

The logical control channel for responding to the outgoing / incoming call operation has the same format as the above data packet, and the header part can distinguish the data packet and the control packet. FIG. 4D shows an example of the control packet.

Another operation after capturing the designated traffic channel is that a plurality of terminals in one traffic channel are connected to the IEEE 802.3 CSMA /
Communication is performed by a waiting type communication system in which collision is prevented by a function equivalent to a CD.

Under the control of the communication control unit 533, the RF unit 511 and the IF unit 531 can transmit and receive signals by selecting a transmission and reception traffic channel.

The details of the operation will be described below with reference to FIGS.

FIG. 5 is a conceptual diagram of a multiplex communication path of a traffic channel using a virtual cross-point switch in a frequency according to an embodiment of the present invention, and FIG. 6 shows an operation sequence.

In FIG. 5, reference numeral 103 denotes a block converter,
04 is a line controller, 5-1 to 5-2 are terminal stations, 504
Is a network terminator, 507 is a personal computer, t-d1 to t-d4
Indicates a downlink traffic channel, and tu1 to tu4 indicate uplink traffic channels.

Now, the originating terminal station 5-1 is changed to the terminating terminal station 5-2.
When the originating terminal station 5-1 uses the communication software of the personal computer 507 to make a dial call using an AT command, the network terminating device 504 sends the terminal I / F
The signal is received by the terminal I / F unit 534 via the line 515 (see FIG. 3), and the communication control unit 533 transmits the signal to the IF unit 531 and the RF unit 511.
To capture the uplink traffic channel tu1 by the cross point “a” (see FIG. 5), and
The control packet shown in FIG.
Send by A traffic channel for transmitting this connection request uses a predetermined channel.

FIG. 4 shows a control packet in this case.
In (b), the address of the line control device 104 is set to the destination address DA, the own station number is set to the transmission address SA, and the other station number is set to the INFO information field INFO, and transmitted. The control packet shown in FIG. 4B and the data packet shown in FIG.
This is done in the FO.

To prevent collision at the time of transmission, the Slotted ALOHA system is adopted in the MCA / C system, but in the present embodiment, the IEEE 803.2 CSMA is used.
/ CD method.

The inside of the line control device 104 of the head end 1 has the same configuration as the internal configuration of the network termination device of FIG. 3, and receives this via the cross point “b”.
The downlink traffic channel t-d1 is captured by the cross point “c”, and “control channel designation” is transmitted as the control packet shown in FIG. 4B. This t-d1 is also a predetermined channel, and all the waiting terminal stations wait on this channel.

The channel designation control packet is transmitted to the originating terminal station and the terminating terminal station based on service conditions and traffic conditions determined in advance by a subscription contract or the like.

Channel designation control packet FIG.
In the transmission method (b), as shown in FIG. 6, the sender and the destination can receive at the same time as in the MCA / C. To enable simultaneous reception, the line controller 1
FIG. 4 (b) shows a control packet transmitted by the terminal 04. A destination address DA is set to a global address (means known in IEEE 802.3) which can be received by all terminal stations at the same time, and a line control is set to a source address SA. Apparatus 1
04, and set the INFO information field I
The local station number, the partner station number, the traffic channel number based on the service condition and the traffic situation, the designation of the time limit, and the like are set and transmitted to the NFO.

In the terminal stations 5-1 and 5-2, the control packet FIG. 4 (b) is received by the network terminating device 504 via the cross points "d" and "e".

The terminal equipment of the terminal station captures a traffic channel according to the designated traffic channel number. For example, if the designated numbers are tu-u3 and t-
Assuming d3, the transmission (T) of the terminal station 5-1 receives the cross point “f”, the reception (R) receives the “i”, and the transmission (T) of the terminal station 5-2 receives the cross point “h”. (R) captures each designated traffic channel via "g". After the capture, the receiving terminal station directly transmits a "response" control packet to the transmitting terminal station as shown in FIG. In this case, the contents of the control packet include the destination address DA, the source terminal station number, the source address SA, the destination terminal number, and the response information in the information field INFO.

When the originating terminal station receives this packet,
The connection procedure based on the AT command is completed, and communication is possible. For example, in a general dial-up type communication software, “CONNECT” is displayed on the screen of the personal computer, and the process proceeds to the next stage and is performed according to a protocol such as TCP / IP. It is in a state where communication can be started.

Although not shown, the other terminal stations which have made a communication request at the same time operate under the same operation as the line controller 104.
According to the instructions, capture the specified traffic channel.

The line control device 104 is the communication management device 10
5 and assigning a traffic channel to a pair of terminal stations communicating with each other in accordance with service conditions and traffic conditions determined in advance by a contract at the time of subscription. Give instructions about.

In the "communication" state, the communication control unit 533 of the network termination unit 504 monitors the TCP / IP frame and generates the data packet shown in FIG. 4C as described above. The data packet generated here is based on the IEEE 802.3 CS in units of each traffic channel.
A queuing type, connectionless type communication in which collision is prevented by a function corresponding to MA / CD is performed.

Next, IEEE 8 for preventing a collision.
The operation of the function corresponding to CSMA / CD in 22.3 will be described.

The communication control unit 533 monitors the carrier of the traffic channel captured via the modem unit 532,
If no carrier is detected on the traffic channel, transmission can be started immediately.

When a carrier is detected, transmission is waited until the transmission becomes empty, and after a certain period of time, the transmission is started after confirming the empty state.

Even if the above control is performed, a collision occurs due to simultaneous transmission with a probability. Therefore, as a means for early discarding a data packet having a collision, a terminal station transmitting a data packet, for example, The terminal station 5-1 receives the transmission signal at the cross point “f” via the cross point “i”, checks the data signal being transmitted, and if the mismatch exceeds a certain amount, It is determined that a collision has occurred, and transmission of the data packet is interrupted halfway.

Next, the LAN in the CATV system will be briefly described with reference to FIG.

Compared to LAN used in general premises, CAT
Since the V system has a wide area, a large transmission delay occurs in proportion to the cable length. In the collision prevention control of CSMA / CD, it is necessary to prevent collision including the terminal station closest to the center and the terminal station farthest from the center. Therefore, the timing from the detection of no carrier to the packet transmission (FIG. 8) T1) and the packet transmission timing by the retransmission algorithm after detecting the collision (T2 in FIG. 8)
It is necessary to set the time in consideration of the round trip transmission delay (Trtd) at the maximum cable length in the CATV system.

For example, if the cable length of the terminal station farthest from the center is 20 km and the wavelength shortening rate of the cable is 0.9, the round trip delay time (Trtd) is about 120 μs. At a low transmission rate of 384 Kbps divided into 300 KHz bands as in the embodiment of the present invention, 120 μs is about 46 bits long, but at a high transmission rate using the entire 6 MHz band, for example, at 10 Mbps, it is about 1200 bits long. I do.

If the packet length is 1024 bytes, 3
The case of 84 Kbps corresponds to 0.6%, and the case of 10 Mbps corresponds to 15%. The higher the percentage, the lower the throughput and the lower the line utilization rate.

Generally, since there are many shorter packets, a CSM in a wide area CATV network having a large transmission delay is used.
When performing A / CD, it is more advantageous to divide the band to a lower transmission rate than to use a high transmission rate using the entire 6 MHz band.

In a CATV system having a long cable length and a large transmission delay, the line rate becomes high.

The communication is terminated by the AT command “on hook”, and each terminal station transmits a “end request” to the line controller 104 as shown in FIG. In order to transmit to the line control device 104, the traffic channel is returned to tu-1 and t-d1 in FIG. Also, the terminal that has forgotten "on-hook" automatically returns to tu1, t-d1 and enters a standby state by monitoring the timer.

As described above, as a method of using a part of an arbitrary traffic channel as a logical control channel, as shown in FIG. 4, the control packet is controlled by the INFO information field INFO in the header of the packet. And a configuration that can be identified as a data packet. As for an arbitrary traffic channel, the embodiment of FIG. 5 shows an example in which predetermined channels tu1 and t-d1 are used. However, the channel is moved to another arbitrary channel in accordance with an instruction from the line control device 104. be able to. The movement method is as follows. The control packet using the global address (IEEE 802.3) is transmitted from the line control device 104 to each traffic channel by the control packet shown in FIG. It is possible to realize the movement of the traffic channel for transmitting the control packet including the terminal station.

In the above description, a traffic channel used as a logical control channel is tu.
Although an example in which a pair of channels such as 1, t-d1 is used has been described, the line controller 104 can be configured to handle a plurality of channels, and a part of the plurality of traffic channels can be used as a control channel. By doing so, it is possible not only to improve the reliability against the failure of the line control device, but also to cope with heavy traffic and the like. It is common for commercial systems to have a plurality. According to the present invention, allocation corresponding to various communication services can be freely performed. As a method for allocating channels corresponding to various service modes, a method of registering in advance at the time of a subscription contract and performing a fixed operation using a subscriber number of the terminal station (the own station number) or the like is generally used. . On the other hand, in the present invention, various types of different service conditions can be given to communication between terminal stations. For example, the head end 1 may have a function of setting and managing communication service conditions for each terminal station. The setting of service conditions includes setting the upper limit of the use time of the data channel allocated to the terminal station, setting the waiting time of the data channel for each terminal station,
And setting the data transmission rate of the data channel for each terminal station. Furthermore, a plurality of groups each including one or a plurality of terminal stations may be set, and service conditions may be set for each group. If the subscriber is given more favorable service conditions to the terminal, higher rates will be set.

The management of the service conditions for each terminal station or each group is performed on the head end 1 side, for example, as follows. Network termination devices 503 and 5 for all subscribers
A table indicating identification information for identifying a terminal station, such as an identification code 04 or a subscriber number of the terminal station, and corresponding service conditions is registered in a memory (not shown) in the communication management apparatus 105 in advance. deep. When receiving a connection request from a terminal station, the head end 1 detects identification information from a signal transmitted from the terminal station, and reads a given service condition with reference to a table. Headend 1
Based on the service condition, the communication time between terminals, the waiting time or the data transmission speed is managed. Also,
To enable contracts for multiple service types when subscribing,
If a number indicating the service type is added after the destination station number when dialing, the service form can be switched by one network termination device 504 according to the usage status of the subscriber. The service provider can also charge for each service type.

In the above embodiment, the case where all traffic channels are accommodated in the 6 MHz band has been described. However, when a large-capacity system is required, another 6M band is required.
It is possible to expand the number of traffic channels using the Hz band.

In a CATV network having a lot of upstream ingress noise, narrow band transmission is advantageous.
C, MCPC, but improved CATV
In the case of a network, it is also possible to increase the bandwidth of the traffic channel so as to support higher-speed data transmission.

For example, as employed in the above-described TDMA system, 1.5 MHz obtained by dividing the entire 6 MHz region into four
Therefore, a system in which a transmission speed of about 2 Mbps is added to a part of the traffic channel, and a uniform control is performed using the logical control channel (control packet) described above. can do.

As means for managing the traffic of the traffic channel by the line control device and the communication management device at the headend, the number of packets generated per unit time, the average value of the waiting time, the maximum It is possible to measure values and the like, and report them to the line control device in a certain cycle by a control packet, so that the traffic situation of the entire system can be grasped and managed at the head end.
In a more advanced system, there is a method in which a network management device is installed at the head end, and a packet transmitted to each traffic channel is constantly monitored to grasp the traffic situation.

The flat-rate charge may be used continuously for a long time. To prevent this, a “communication time limit” function that can instruct the terminal to set the communication time at the “channel designation” point is set. have. The above-mentioned control can be performed by setting the communicable time in the head-end communication management device 105 as needed.

The means for limiting the upper limit of the transmission rate that can be used by the terminal for each subscriber is provided by the terminal I / O of the terminal equipment of the terminal station.
This can be handled by changing the upper limit of the clock speed of the data of the terminal I / F signal frame passed from the F unit 534 to the communication control unit 533. As a method of changing the setting, switching by a switch in the network termination device of the terminal station, or from the communication management device of the headend,
There is a method of switching the network terminating device of the terminal station by remote control via the line control device, but the latter is desirable in order to prevent the user from changing it independently.

As means for configuring a plurality of traffic channels in a certain bandwidth, there is a code multiplexing system (hereinafter abbreviated as CDMA system) in addition to the frequency multiplexing system described above. This CDMA system is also one of the above-mentioned SCPC systems, and a channel can be divided by a pseudo-noise code to easily configure a multiplex communication channel as shown in FIG.

The CDMA system has the highest frequency utilization efficiency in the field of radio, and has already been adopted in some radio systems in the United States. If devices and the like are made more economical due to future spread, application to the system as shown in this embodiment is also possible.

Further, a new attention as a narrow-band digital transmission system belongs to the above-mentioned MCPC system, and is an OFDM (Orthogonal Frequency Division Multiple Multiple Access) which is one of multi-carrier multi-level modulation.
xing). OFDM is a digital modulation method using a number of orthogonal carrier waves, and its application to digital terrestrial television broadcasting is being studied. However, it is also effective when applied to the present invention.

[0117]

According to the present invention, since a control channel using a band equivalent to a voice channel such as MCA / C is not required, the configuration of the network termination device can be simplified. Further, in addition to such effects, according to the present invention, it is possible to support various data communication services from low-speed to high-speed data transmission. A high system can be realized.

It is resistant to the influence of upstream ingress noise and reflected waves, which is unique to the CATV network. Therefore, it is possible to reduce the cost for improving the existing CATV network.

[0119] The waiting communication system similar to the LAN enables effective use of the speed difference between the line and the terminal and the non-operation time of the terminal.

Further, the traffic channel of the present invention can perform communication by the half-duplex communication method, and is compared with the circuit switching type requiring two channels because of the full-duplex communication method.
Since it can be configured with one channel, it is possible to realize a system with extremely high line utilization.

When the band of 1.5 MHz is used, the number of terminals that can operate simultaneously is 64 Kbps, 3
Calculations are performed for three types of terminals, 2 Kbps and 19.2 Kbps, and a comparison between TDMA and the system of the present invention is as follows.

As a condition, TDMA uses the data shown in Table 2. In the system of the present invention, the data channel is 300 KHz, 384 Kbps shown in the embodiment, and
It is assumed that the maximum waiting time is allowed up to ten times the packet length.

In TDMA, the line capacity in the 1.5 MHz band is 64 Kbps × 24 channels. One opposing terminal has 2 channels regardless of the transmission speed of the terminal as described above.
Use Therefore, the number of devices that can operate simultaneously is 24 (12 facing) regardless of the type of terminal.

In the system of the present invention, the line capacity in the 1.5 MHz band is 30 channels in 64 Kbps conversion. Assuming that the utilization rate of CSMA / CD that allows the maximum waiting time up to 10 times the packet length is 0.8, and the loss associated with packet generation (addition of header and trailer sections) is 0.9, 64 Kbps 42 terminals (21 facing), 84 units (42 facing) at 32 Kbps,
At 19.2 Kbps, the number is 168 (84 facing).

According to the present invention using a plurality of traffic channels and a logical control channel,
Since the allocation to traffic channels can be managed freely, for each traffic channel, services that are equivalent to circuit switching that allows channel occupation, services that are ranked according to the length of waiting time, or classification by terminal transmission speed, etc. In the introduction of the flat-rate system, it is possible to set a fee category corresponding to various services, so that a unique business development not available in the conventional communication business is possible.

In a plurality of traffic channels, it is possible to change the bandwidth and the transmission speed for each channel, and it is possible to expand to a higher-speed service.

In the bandwidth of the traffic channel, the 300 KHz band expected to have the largest number of users, 384 Kb
Since the modulation and demodulation unit of ps can use the same one as the modulation and demodulation unit of the PHS which is expected to be widely used in the future, economical production by mass production can be expected.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram showing an entire system of an embodiment of a multimedia communication system according to the present invention.

FIG. 2 is an explanatory diagram showing a frequency arrangement in one embodiment of the present invention.

FIG. 3 is a block diagram showing an internal configuration of a data channel network termination device according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a configuration of a packet in one embodiment of the present invention.

FIG. 5 is a conceptual diagram of a data channel multiplex communication channel according to an embodiment of the present invention.

FIG. 6 is a diagram showing an operation sequence of a data channel in one embodiment of the present invention.

FIG. 7 is a configuration diagram of a conventional MCA / C telephone system.

FIG. 8 is an explanatory diagram of CSMA / CD collision prevention control.

FIG. 9 is a conceptual diagram of a conventional TDMA telephone system.

FIG. 10 is a diagram showing main specifications of a conventional MCA / C telephone system.

FIG. 11 is a diagram showing main specifications of a conventional TDMA telephone system.

[Explanation of symbols]

1 headend, 3 relay amplifier, 4 tap-off,
5 terminal, 102 CATV broadcasting equipment, 103 block converter, 104 line control device, 105 communication management device, 502 TV receiver, 503, 504 network termination device, 505TEL, 506 FAC / PC, 507P
C.

Claims (8)

[Claims] 1. A communication system in which one central office and a plurality of terminal offices are connected via a bidirectional communication path, and communication between the terminal offices is performed via the central office. The communication system has a dedicated communication channel allocated between a terminal station and another terminal station, and a common communication channel multiplexed and allocated to a plurality of terminal stations simultaneously. A plurality of traffic channels are arranged, and a part of an arbitrary channel among the traffic channels is used as a logical control channel. According to the logical control channel, in response to a communication request of the terminal station, A communication system comprising control means for assigning a plurality of terminal stations to each of a plurality of traffic channels. 2. The communication system according to claim 1, wherein said control means responds to a communication request from one or more of said plurality of terminal stations, and controls said one or more of said plurality of traffic channels. Allocating the communication request to the terminal station, having a means for transmitting a control signal for specifying the allocated traffic channel to the terminal station via the logical control channel,
A communication system, further comprising means for controlling the common communication channel so that only one signal is transmitted when a plurality of different signals are present in the common communication channel to avoid signal collision. 3. The communication system according to claim 1, wherein the communication path includes a plurality of traffic channels in which the common communication channel and the dedicated communication channel are set.
One or more control channels through which a control signal is transmitted, wherein the control means responds to a communication request from one or more of the plurality of terminal stations to control one of the plurality of traffic channels. A communication system for allocating at least one or more to the terminal station that has made the communication request, and transmitting a control signal for specifying the allocated traffic channel to the terminal station via the logical control channel. . 4. The communication system according to claim 3, wherein
A communication system, wherein a frequency band of the communication channel is divided into a plurality of bands, and the plurality of traffic channels are set in each of the divided bands by frequency multiplexing. 5. The communication system according to claim 3, wherein
A communication system, wherein a unique code is assigned to each of the plurality of terminal stations on the communication path, and the plurality of traffic channels are set by a code multiplexing method. 6. The communication system according to claim 3, wherein
The communication system according to claim 1, wherein said central station has a service management means for setting an upper limit of a use time of said common signal channel allocated to said terminal station when a communication request is received from said terminal station. 7. The communication system according to claim 3, wherein
The communication system according to claim 1, wherein said central station has service management means for setting a waiting time of said common communication channel for each terminal station. 8. The communication system according to claim 3, wherein
The communication system according to claim 1, wherein said central station has service management means for setting a data transmission rate of said common signal channel for each terminal station.