JP2008199399A - Communication system, gateway device, and adapter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication system capable of accommodating a synchronous network device through an IP line, and a gateway device and adapter device used for the system. <P>SOLUTION: The gateway device 10 extracts a network clock of a line switching network 100 and multiplexes IP packets to packet converting devices 30 and 31 in fixed-length frames synchronized with the network clock. The packet converting devices 30 and 31 regenerates PCM data and the network clock from the fixed-length frames and transmits them to a base station. Consequently, the clock can be transmitted in a layer closer to the physical layer between synchronous networks via the IP network without using techniques such as CES (Circuit Emulation System) etc. Namely, an STM node having an existent STM interface can be clock-synchronized with the network clock of the line switching network 100. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a gateway device for interconnecting, for example, a circuit switching network and an IP (Internet Protocol) network, and a communication system including this type of device. In particular, the present invention can be suitably used as a network clock transmission method in an optical Ethernet (registered trademark) formed by an E-PON system.

  In recent years, information communication services including voice and data communication have been diversified as information communication needs have increased and communication has been liberalized. Against this background, the number of operators (carriers) newly entering the communication service field is increasing, and service competition among carriers is becoming active. The new carrier is called NCC (New common carrier) and provides various services using a technology such as VoIP (Voice over Internet Protocol). VoIP is a technology that integrates a voice network and a data network by packetizing and transmitting digital voice data.

  NCCs often borrow equipment such as an exchange from a specific carrier that already has a subscriber line at a predetermined charge. Many NCCs build their own exchange networks such as IP networks with their own funds. In addition, a communication system is formed by adding a circuit switching network (PSTN: Public Switched Telephone Network) of a specific carrier, and these facilities are used in combination for providing services to general users.

  Gateway devices are used to interconnect different communication networks such as PSTN and IP network. This type of apparatus includes an IP conversion unit that converts voice data and binary data into IP (Internet Protocol) packets, and a packet switch unit that switches IP packets. These all play a role as a network interface for the IP network.

Some gateway devices of this type accommodate a synchronous network communication device called an STM (Synchronous Transfer Mode) node. STM nodes include base stations such as PHS (Personal Handy-phone System) and so-called mobile phone systems. As described in Patent Document 1, it is considered that this accommodated line is converted to IP because of the recent trend of communication total IP networking. However, in the IP network, there is no concept of network synchronization, and unless some solution is made, the STM node cannot be accommodated in the gateway device via the IP line.
JP 2004-336526 A

As described above, in the gateway device that interconnects the circuit switching network and the IP network, it is necessary to solve the clock distribution problem when the circuit accommodating the STM node is converted to IP. As one of the proposals, a technique called CES is known. However, there is a need to reduce the burden on the upper layer by solving the clock transmission in a layer closer to the physical layer without depending on the technology.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a communication system capable of accommodating a synchronous network device via an IP line, and a gateway device and an adapter device used in the system. .

  In order to achieve the above object, according to one aspect of the present invention, in a communication system including a subscriber network including a synchronous network node device, a synchronous communication network, and a packet communication network, the subscriber network and the synchronization A gateway device that mutually converts a communication protocol between the communication network and the packet communication network and interconnects these networks, an adapter device that accommodates the synchronous network node device via a synchronous line, and the adapter An IP conversion means for converting the interface between the device and the gateway device to IP, the gateway device terminating the synchronous communication network and generating an in-device signal, and terminating the packet communication network A packet network terminating unit that generates the in-device signal, and terminates the subscriber network via the IP interface and transmits the in-device signal. A subscriber network termination unit, a synchronous network termination unit, a packet network termination unit, a time division switch for exchanging in-device signals respectively generated at the subscriber network termination unit, and the subscriber network A packet generation unit that converts an intended data signal into an IP packet, a clock extraction unit that extracts a network clock of the synchronous communication network, and a fixed length that includes the IP packet in synchronization with the network clock extracted by the clock extraction unit A frame generation unit configured to generate a frame, and the adapter device terminates the fixed-length frame transmitted from the gateway device and extracts the data signal and the network clock from the fixed-length frame. And the extracted data signal and the network clock via the synchronization line. Communication system, comprising a transmitting means for transmitting the synchronous network node apparatus is provided.

  By taking such means, the network clock of the synchronous network is transmitted to the synchronous network node device across the IP section. As a result, the synchronous network device can be accommodated in the gateway device via the IP line. In addition, since the network clock is transmitted in synchronization with the fixed-length frame, the burden on the upper layer can be reduced.

  According to the present invention, it is possible to provide a communication system capable of accommodating a synchronous network device via an IP line, and a gateway device and an adapter device used in this system.

  FIG. 1 is a system diagram showing an embodiment of a communication system according to the present invention. The system shown in FIG. 1 includes a circuit switching network 100 as a synchronous communication network, an IP network 200 as a packet communication network, and a subscriber network 300. These networks are connected to the gateway device 10. The circuit switching network 100 is accommodated in the gateway device 10 via, for example, the I ′ interface, and the IP network 200 is accommodated via the IP.

The gateway device 10 mutually converts communication protocols among the subscriber network 300, the circuit switching network 100, and the IP network 200, and interconnects these networks. In the gateway device 10, data of each network is exchanged by a synchronous exchange connection using a time division switch.
The subscriber network 300 includes a plurality of base stations 21 to 2n. Each of the base stations 21 to 2n accommodates a mobile communication terminal PS such as PHS via a wireless line. Among these, the base station 21 has a line directly connected to the gateway apparatus 10 via the I ′ interface and a line connected to the gateway apparatus 10 via the packet conversion apparatus 30. The base station 22 is also accommodated in the gateway device 10 via the packet conversion device 31. The base station 2n includes a built-in adapter 50, and is accommodated in the gateway device 10 from the built-in adapter 50 via an IP interface.

  Between the packet converters 30 and 31 and the gateway device 10 and between the base station 2n and the gateway device 10 are accommodated in the gateway device 10 via the existing dark fiber network 400. The optical fibers F drawn from the packet conversion devices 30 and 31 are concentrated at the concentration unit 500 and connected to the gateway device 10.

  The dark fiber network 400 is an IP network using, for example, PON (Passive Optical Network) technology. The network / node interface in which each of the base stations 21 to 2n is accommodated in the dark fiber network 400 is IP-configured by the function of the base station itself or by the packet converters 30 and 31. On the other hand, some base stations 21 with two output interfaces are accommodated in the gateway apparatus 10 with the I ′ interface intact.

  The gateway device 10 includes a public network interface 11 that accommodates the circuit switching network 100 and an IP interface 12 that accommodates the IP network 200. The public network interface 11 terminates the circuit switching network 100 and generates time-division PCM (Pulse Code Modulation) data. The IP interface 12 terminates the IP network 200 and generates PCM data.

  The gateway device 10 further includes an optical switch 13a, an optical interface 13b, an optical storage unit 13, a packet conversion unit 14, and a main control unit 15. The optical switch 13 a switches the path of the optical fiber F accommodated from the dark fiber network 400. As a result, the packet conversion devices 30 and 31 and the base stations 21 to 2n can be switched and operated, and improvement of fault tolerance performance can be promoted.

  The optical interface unit 13b optical / electrically converts an optical signal coming from the dark fiber network 400. The light accommodation unit 13 accommodates the base stations 21 to 2n via the optical fibers F concentrated in the concentration unit 500. That is, the light accommodating unit 13 terminates the IP packet from the subscriber network 300 and generates PCM data.

The main control unit 15 includes a function for comprehensively controlling the gateway device 10 and a time switch 15a. The time switch 15a switches and connects the circuit switching network 100, the IP network 200, and the subscriber network 300 by switching PCM data. At this time, the signal for the IP network 200 is converted into an IP packet by the packet conversion unit 14, and the data for the dark fiber network 400 is converted into an IP packet by the light accommodating unit 13.
Inside the gateway device 10, time-division PCM data is transmitted via a PCM highway (PCM-HWY). The IP packet is transmitted via a control LAN (Local Area Network) or a data LAN.

  An optical signal introduced into the apparatus via the optical switch 13a is converted into an electric signal by an optical / electrical conversion element (not shown) provided in the optical interface 13b, and an IP packet is reproduced. The IP packet is routed by the layer 2 switch (L2SW) or the like in the light accommodating unit 13 and sent to the IP interface 12 or the control LAN. Packets that flow through the control LAN and the data LAN and time division data that flows through the PCM-HWY are mutually converted in the light accommodating unit 13.

  FIG. 2 is a functional block diagram showing the main configuration of the system shown in FIG. In this figure, packet conversion devices 30 and 31 are accommodated in the gateway device 10 via an optical coupler 500. Each of the base stations 21 and 22 has a function as a synchronous network node device (STM node). Each of the packet conversion apparatuses 30 and 31 as adapter apparatuses accommodates the base stations 21 and 22 via the STM line as a synchronous line. In FIG. 2, the gateway device 10 connected to the circuit switched network 100 and the STM node having the existing STM interface (64 kbps, 1.5 Mbps, 2 Mbps, 6.3 Mbps, etc.) are connected via the E-PON. The connected configuration is shown. E-PON is an abbreviation for Ethernet (registered trademark) -passive optical network.

  Examples of STM nodes having an existing STM interface include a base station of a mobile communication system, a PBX (Private Branch eXchange), and the like.

  FIG. 3 is a functional block diagram showing an embodiment of the light accommodating portion 13 of FIG. An STM interface (I / F) unit 62 inside the optical accommodation unit 13 is connected to the circuit switching network 100 and extracts a network clock of the circuit switching network 100. This network clock is input to a PLL (Phase Lock Loop) circuit 63 and used for network clock synchronization in the apparatus. Also, the STMI / F unit 62 converts the PCM data in the device into an IP packet.

  An OLT (Optical Line Terminal) unit 61 controls the PON. The IP packet output from the OLT unit 61 is framed by the framing unit 64, for example, every 125 microseconds (μs). That is, a fixed-length frame that includes a plurality of IP packets and is synchronized with the network clock is generated. This fixed-length frame is converted into an optical signal by the electrical / optical conversion unit 52 of the optical interface unit 13b and sent to the optical fiber F. The optical signal from the optical coupler 500 is converted into an electrical signal by the optical / electrical converter 51 and input to the OLT unit 61.

  FIG. 4 is a functional block diagram showing an embodiment of the framing unit 64. The IP packets input from the OLT unit 61 are stored in the packet buffer 641 and sequentially output to the frame buffer 644. When packets for 125 μs are accumulated, the frame buffer 644 frames these packets and outputs the generated fixed-length frame to the electrical / optical converter 52 in synchronization with the network clock from the PLL circuit 63.

  The packet accumulation amount of the packet buffer 641 is monitored by the packet buffer monitoring / control unit 642, and when the packet buffer 641 becomes empty, the data path is switched so that the dummy packet from the dummy packet adding unit 643 is output to the frame buffer 644. . As a result, even if the IP packet is interrupted and the packet buffer 641 becomes empty, the packet is input to the frame buffer 644, so that the fixed-length frame is output without interruption. Therefore, the clock can be reproduced without interruption in the device packet conversion devices 30 and 31 and the base stations 21 to 2n in the subsequent stage.

  FIG. 5 is a functional block diagram showing an embodiment of the packet conversion devices 30 and 31. The fixed-length frame that has arrived from the optical coupler 500 via the optical / electrical conversion unit 74 is input to the frame termination unit 75. The frame termination unit 75 separates and extracts the network clock and transmission data (PCM data) from the fixed-length frame. Of these, the network clock is input to the PLL circuit 76 and used for network synchronization. The transmission data is again returned to the IP packet and input to the ONU unit (Optical Network Unit) 72. The IP packet that has passed through the ONU unit 72 is converted to a time-division TDM signal by the STMI / F unit 71 based on the network-synchronized clock by the PLL circuit 76, and then output to the STM line to the STM node. The TDM signal input from the STM line follows the reverse path, is packetized from the STMI / F unit 71 via the ONU unit 72, and then output to the optical fiber F via the electrical / optical conversion unit 73.

  FIG. 6 is a functional block diagram showing the frame end portion 75 of FIG. The fixed-length frame received from the optical / electrical converter 74 is input to the clock / packet separator 751. The clock / packet separator 751 separates the fixed-length frame into a network clock and an IP packet, and the network clock is input to the PLL circuit 76. The IP packet is output to the dummy packet deleting unit 752, and if there is a dummy byte, it is deleted and only valid packets are output to the ONU unit 72.

  FIG. 7 is a diagram illustrating an example of a frame format of the fixed-length frame output from the framing unit 64. In FIG. 7, for example, a frame generated every 125 μs includes a frame header and a plurality of packets 1 to m. As the frame header, a method used in an existing STM interface can be used. Examples thereof include ISDN or SDH (Synchronous Digital Hierarchy). Of course, the number m of packets included in the fixed-length frame varies depending on the packet length of each packet.

  As described above, in this embodiment, the packet converters 30 and 31 are provided in the subscriber network 300 to convert the I ′ interface from the base station into the IP interface, and the physical layer interface is opticalized. The gateway device 10 is provided with an optical accommodation unit 13 to accommodate the optical fiber F from the packet conversion devices 30 and 31, and to convert IP packets into PCM data in the device. In this way, transmission data from the IP subscriber network 300 can also be exchanged and connected within the gateway device 10.

  At that time, the gateway device 10 extracts the network clock of the circuit-switched network 100, multiplexes the IP packet into a fixed-length frame synchronized with the network clock, and sends it to the packet converters 30 and 31. The packet converters 30 and 31 reproduce PCM data and a network clock from the fixed-length frame and transmit them to the base station. By doing so, it is possible to transmit a clock between layers synchronized with the IP network in a layer closer to the physical layer without depending on a technology such as CES (Circuit Emulation System). That is, the STM node having the existing STM interface can be synchronized with the network clock of the circuit switching network 100.

  For these reasons, the synchronous network device can be accommodated via an IP line, and various IP network services such as high-speed communication by IP and IP telephone can be enjoyed.

  The present invention is not limited to the above embodiment. For example, the frame termination unit 75 of FIG. 6 may be mounted on the base stations (STM nodes) 21 to 2n. Furthermore, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

1 is a system diagram showing an embodiment of a communication system according to the present invention. The functional block diagram which shows the principal part structure of the system of FIG. The functional block diagram which shows embodiment of the light accommodating part 13 of FIG. FIG. 4 is a functional block diagram showing an embodiment of a framing unit 64. The functional block diagram which shows embodiment of the packet converters 30 and 31. FIG. FIG. 6 is a functional block diagram illustrating a frame termination unit 75 in FIG. 5. The figure which shows an example of the frame format of the fixed length frame output from the framing part.

Explanation of symbols

  F: optical fiber, 100: circuit switching network, 200: IP network, 300: subscriber network, 400: dark fiber network, 500: concentrator, 10: gateway device, 21-2n: base station, PS: mobile communication terminal , 30, 31 ... packet conversion device, 11 ... public network interface, 12 ... IP interface, 13 ... optical accommodation unit, 14 ... packet conversion unit, 15 ... main control unit, 13a ... optical switch, 13b ... optical interface, 51 ... Optical / electrical conversion unit, 52 ... electrical / optical conversion unit, 61 ... OLT unit, 62 ... STMI / F unit, 63 ... PLL circuit, 64 ... framing unit, 641 ... packet buffer, 642 ... packet buffer monitoring / control unit 643 ... Dummy packet adding unit, 644 ... Frame buffer, 71 ... STMI / F unit, 72 ... ONU unit, 73 ... Electric / optical conversion unit, 74 ... / Electric converter, 75 ... frame termination section, 76 ... PLL circuit, 751 ... clock packet separating unit, 752 ... dummy packet deletion unit 752

Claims (12)

In a communication network comprising a subscriber network comprising a synchronous network node device, a synchronous communication network, and a packet communication network,
A gateway device that interconnects these networks by converting a communication protocol between the subscriber network, the synchronous communication network, and the packet communication network;
An adapter device accommodating the synchronous network node device via a synchronous line;
IP conversion means for converting the interface between the adapter device and the gateway device into IP (Internet Protocol),
The gateway device is
A synchronous network terminating unit that terminates the synchronous communication network and generates an in-device signal;
A packet network termination unit for terminating the packet communication network and generating the in-device signal;
A subscriber network termination unit for terminating the subscriber network via the IP interface and generating the in-device signal;
A time division switch for exchanging in-device signals respectively generated at the synchronous network termination unit, the packet network termination unit, and the subscriber network termination unit;
A packet generation unit for converting a data signal directed to the subscriber network into an IP packet;
A clock extraction unit for extracting a network clock of the synchronous communication network;
A frame generation unit that generates a fixed-length frame including the IP packet in synchronization with the network clock extracted by the clock extraction unit;
The adapter device is
A frame termination unit that terminates the fixed-length frame transmitted from the gateway device and extracts the data signal and the network clock from the fixed-length frame;
A communication system comprising: a transmitting means for transmitting the extracted data signal and the network clock to the synchronous network node device via the synchronous line. The frame generation unit inserts a dummy packet into the fixed-length frame when the IP packet from the packet generation unit is interrupted,
The communication system according to claim 1, wherein the frame termination unit extracts a valid IP packet by deleting the dummy packet from the terminated fixed-length frame. The communication system according to claim 1, further comprising: an opticalizing unit configured to connect the adapter device and the gateway device via an optical fiber to opticalize the interface. The photonization means includes:
An electrical / optical converter provided in the adapter device for electrical / optical conversion of an IP packet sent to the interface and sending it to the optical fiber;
The communication system according to claim 3, further comprising: an optical / electrical conversion unit that is provided in the gateway device and performs optical / electrical conversion on an optical signal that arrives via the optical fiber. The subscriber network comprises a plurality of the synchronous network node devices,
4. The communication system according to claim 3, further comprising: an optical concentrator that collects optical fibers that are respectively extended from the plurality of synchronous network node devices and connects the optical fibers to the gateway device. 5. The communication system according to claim 5, wherein the gateway device includes an optical switching unit for switching and operating the plurality of synchronous network node devices. The communication system according to claim 1, wherein the synchronous network node device is a base station that wirelessly accommodates a mobile communication terminal. A synchronous network node device, an adapter device that accommodates the synchronous network node device via a synchronous line, a subscriber network that includes an IP conversion means for converting an interface from the adapter device into an IP (Internet Protocol), a synchronous communication network, , A gateway device that mutually converts a communication protocol with a packet communication network and interconnects these networks,
A synchronous network terminating unit that terminates the synchronous communication network and generates an in-device signal;
A packet network termination unit for terminating the packet communication network and generating the in-device signal;
A subscriber network termination unit for terminating the subscriber network via the IP interface and generating the in-device signal;
A time division switch for exchanging in-device signals respectively generated at the synchronous network termination unit, the packet network termination unit, and the subscriber network termination unit;
A packet generation unit for converting a data signal directed to the subscriber network into an IP packet;
A clock extraction unit for extracting a network clock of the synchronous communication network;
A gateway device comprising: a frame generation unit that generates a fixed-length frame including the IP packet in synchronization with the network clock extracted by the clock extraction unit. When the adapter device includes an electrical / optical converter that electrically / optically converts an IP packet sent to the interface and sends the IP packet to the optical fiber,
The gateway device according to claim 8, further comprising: an optical / electrical conversion unit that optically / electrically converts an optical signal that arrives through the optical fiber. When the subscriber network comprises a plurality of synchronous network node devices,
The gateway apparatus according to claim 9, further comprising an optical switching unit for switching and operating the plurality of synchronous network node apparatuses. Used in a communication system comprising a subscriber network comprising a synchronous network node device, a synchronous communication network, and a packet communication network, and a gateway device for mutually interconnecting these networks by converting a communication protocol; An adapter device that accommodates a synchronous network node device via a synchronous line,
IP conversion means for converting the interface between the own device and the gateway device into IP (Internet Protocol);
A frame termination unit that terminates a fixed-length frame transmitted from the gateway device and extracts a data signal and a network clock of the synchronous communication network from the fixed-length frame;
An adapter device comprising: a transmission means for transmitting the extracted data signal and the network clock to the synchronous network node device via the synchronous line. The adapter device according to claim 11, wherein the adapter device is provided in the synchronous network node device.

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