Abstract:
To realize both conventional TDM-based communication typically provided by SONET and packet-based communication typically provided by Ethernet on a same optical transmission path, an integrated packet and TDM switching node apparatus is offered. This node apparatus receives wavelength-division-multiplexed optical signals of a plurality of channels incoming through a first optical transmission path and transmits wavelength-division-multiplexed optical signals of a plurality of channels over a second optical transmission path. The node apparatus comprises packet Framers, TDM Framers, and means for allocating optical signals of different wavelengths to the TDM Framers and packet Framers and wavelength division multiplexes TDM frame transmission channels and packet frame transmission channels on a same optical transmission path.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (1) Field of the Invention  
           [0002]    The present invention relates to a node apparatus for use in an optical network and, more particularly, to an integrated packet and TDM switching node apparatus that makes packet transmission compatible with TDM transmission on the same optical network.  
           [0003]    (2) Description of Related Art  
           [0004]    One of backbone network architecture for communications carriers and Internet Service Providers (ISPs) is an optical ring network configuration using a Synchronous Optical Network (SONET) Add Drop Multiplexer (ADM) that adopted Synchronous Digital Hierarchy (SDH). The SONET is network technology based on Time Division Multiplex (TDM) which the carriers have applied for long years. The SONET was developed to transmit voice traffic and traffic over leased lines at high speed. Currently, not only voice traffic and traffic over leased lines, but also data packet traffic such as IP packets is multiplexed in SONET frames.  
           [0005]    [0005]FIG. 2 shows a configuration example of a TDM (SONET) ring that is a conventional backbone network.  
           [0006]    The TDM (SONET) ring comprises a plurality of nodes of SONET ADMs  10 - 1  to  10 - 3 , connected in rings with two optical transmission paths  11 . Each node has high-speed interfaces for connection to the optical transmission paths  11  and low-speed interfaces for connection to a TDM network  2  ( 2 A or  2 B) and a packet network  3  ( 3 A or  3 B). The TDM network  2  includes a PBX  5  ( 5 A or  5 B) and a data processing system for banking online system or the like  6  ( 6 A or  6 B) that requires high-speed communication. The packet network  3  includes a router  7  ( 7 A or  7 B) via which computers are connected to the network.  
           [0007]    The backbone TDM ring network supports ring network formations such as Bidirectional Line Switched Ring (BLSR) and Unidirectional Path Switched Ring (UPSR). These network formations use two optical fibers connecting nodes; one is active for transmitting traffic and the other is standby for transmitting backup traffic, wherein the direction of transmission over one path is opposite to the direction of transmission over the other path. Thereby, highly reliable network operation can be achieved, and such networks are mainstream public communications networks.  
           [0008]    Along with explosive increase of data packet traffic due to recent development of the Internet, network technology for transmitting packets more efficiently than the above-mentioned SONET that is TDM-based transmission technology is under study. The IEEE and other various forums are discussing the standardization of such network technology.  
           [0009]    For example, 10G Ethernet featuring a higher data transmission rate of up to 10 Gb/sec has been introduced as a new version of the Ethernet (a registered trademark) which is typical packet-based network technology developed in the LAN domain. The 10G Ethernet is expected to provide a backbone ring of a network that is even larger than LAN such as MAN/WAN. The 10G Ethernet is currently under discussion at IEEE 802.3ae and scheduled to be standardized on March 2002.  
           [0010]    A Resilient Packet Ring (RPR) is a ring network for high-speed transmission of MAC-layer packets with their format extended from the Ethernet frame. The RPR is provided with the functions of packet congestion control, network topology detection, and protection, and attracts attention as the key technology of the next generation backbone networks. The RPR is currently under discussion at IEEE 802.17 and scheduled to be standardized on March 2003.  
           [0011]    These high-speed packet transmission techniques are actively discussed at RPR Alliance, 10G Ethernet Alliance, and Metro Ethernet Forum as well. As data packet traffic is expected to continue to increase in future, it is anticipated that the conventional TDM-based network architecture as the backbone network will change to new packet-based network architecture, such as RPR and 10G Ethernet.  
           [0012]    TDM-based networks such as SONET are considered remaining as they have run so far even when the above-mentioned new packet-based networks will have been used commonly in future. This is because the packet-based high-speed networks which are newly provided are intended to enhance the efficiency of transmitting variable-length packets, but it is difficult for these networks to support high-quality TDM transmission functions that the conventional TDM-based networks have.  
           [0013]    For example, in the SONET, the techniques for preventing or reducing transmission delay, preventing or reducing jitter and wander, and protection have been established, which are indispensable for high-quality communications services such as voice transmission over telephone circuits and data transmission for online transactions via leased lines.  
           [0014]    Because the SONET is based on time division multiplex/demultiplex technique in which data is transmitted in time slots that are sequenced at even intervals of time, delay of data transmitted on a same channel hardly occurs. The SONET standards prescribe the detailed specifications of jitter and wander tolerances over transmission paths and in node apparatus. The manufacturers of TDM nodes design node apparatus to conform to the SONET standards, and, therefore, jitter and wander of signals to be transmitted through the TDM nodes are very small.  
           [0015]    The SONET adopts high-speed switching technique called Automatic Protection Switching (APS) as protection technique, which requires redundant communication paths to be configured, so that communication path recovery can quickly be performed in the event of failure occurring. In packet-based networks, however, these techniques for preventing or reducing transmission delay, preventing or reducing jitter and wander, and protection are not established.  
           [0016]    Attempts to design a node by uniting packet-based high-speed network technology and TDM-based network technology are confronted by many problems.  
           [0017]    For example, a RPR node inserts a packet into a transmission frame (Add) on the ring and extracts a packet from the transmission frame (Drop) arbitrarily, which is not compatible with the TDM technology requiring synchronous manipulation. According to the specifications of WAN-PHY which is one version of 10G Ethernet, the payload of a SONET frame shall contain an Ethernet frame only. The WAN-PHY cannot support TDM technology allowing for dividing a SONET frame into a plurality of VC frames.  
           [0018]    Consequently, it is anticipated that high-speed packet nodes for RPR and 10G Ethernet (hereinafter referred to as RPR/Ethernet nodes) are provided as nodes for packet transmission only, independent of SONET ADM functions. Probably, actual network topology will be, for example, as is shown in FIG. 3 where a new RPR/Ethernet ring  16  is constructed separately from the existing TDM ring  11 .  
           [0019]    RPR/Ethernet nodes  15 - 1  to  15 - 3  are connected to the RPR Ethernet ring network  16  through their high-speed line interfaces and connected to, for example, packet networks  3 A,  3 B and routers  7 A,  7 B through their low-speed line interfaces.  
           [0020]    The RPR/Ethernet ring network  16  consists of optical fibers  17  ( 17 - 1  to  17 - 3 ) which form an outer ring and optical fibers  18  ( 18 - 1  to  18 - 3 ) which form an inner ring. The outer ring  17  is primarily used for data packet transmission and the inner ring  18  is primarily used as a transmission path for control packets. The direction of data transmission over the outer ring shall be opposite to the direction of data transmission over the inner ring. In the event of failure of either ring occurring, signaling between the nodes by control packets is performed for recovery from the failure, so that highly reliable network operation can be carried out.  
           [0021]    The network architecture of the RPR/Ethernet nodes  15  is analogous to BLSR and UPSR in a TDM ring, but different from that of SONET ADMs. The RPR Ethernet nodes are not connected to PBXs  5  and banking systems  6  which are included in TDM networks  2 , respectively.  
           [0022]    As described above, the exiting TDM network and an RPR/Ethernet network which is newly provided are physically similar in architecture, but completely different from a logical point of view. Thus, it is difficult to realize a node having both TDM functionality and RPR/Ethernet functionality. When RPR/Ethernet nodes will be put into practical use, such a network topology is anticipated that a TDM network comprising SONET ADMs and a packet network comprising RPR/Ethernet nodes exist separately as shown in FIG. 3. A problem is posed that duplex network management is required.  
         SUMMARY OF THE INVENTION  
         [0023]    It is an object of the present invention to provide a communications network making it to realize both conventional TDM-based communication typically provided by SONET and packet-based communication typically provided by RPR/Ethernet on a same optical transmission path.  
           [0024]    It is another object of the present invention to provide a new communications node apparatus having both conventional TDM-based communication functions typically provided by SONET and packet-based communication functions typically provided by RPR/Ethernet.  
           [0025]    It is yet another object of the present invention to provide a new communications node apparatus capable of selectively multiplexing TDM-based communication channels and packet-based communication channels on a same network.  
           [0026]    It is a further object of the present invention to provide an integrated packet and TDM switching node apparatus capable of dynamical switching of a part or all of TDM-based communication channels multiplexed on a network to packet-based communication channels if necessary.  
           [0027]    It is a still further object of the present invention to provide an integrated packet and TDM switching node apparatus capable of dynamical switching of a part or all of packet-based communication channels multiplexed on a network to TDM-based communication channels if necessary.  
           [0028]    In order to achieve the foregoing objects, a node apparatus according to the present invention has two communication functions of packet transmission mode and TDM transmission mode and is able to configure one physical transmission line to serve for a packet transmission network and a TDM transmission network.  
           [0029]    The present invention provides an integrated packet and TDM switching node apparatus. This node apparatus receives wavelength-division-multiplexed optical signals of a plurality of channels incoming through a first optical transmission path and transmits wavelength-division-multiplexed optical signals of a plurality of channels over a second optical transmission path. The node apparatus comprises at least one TDM Framer, at least one packet Framer, and means for allocating optical signals of different wavelengths to the TDM Framer and packet Framer. The node apparatus wavelength division multiplexes TDM frame transmission channels and packet frame transmission channels on the first and second optical transmission paths.  
           [0030]    More specifically, the node apparatus of the present invention includes optical signal circuitry which receives wavelength-division-multiplexed optical signals of a plurality of channels incoming through a first optical transmission path, converts the optical signals into electrical signals, and outputs the electrical signals to a plurality of per-channel receive ports, while converting electrical signals received from a plurality of per-channel transmit ports into wavelength-division-multiplexed optical signals of a plurality of channels and transmitting these wavelength-division-multiplexed optical signals over a second optical transmission path. The above-mentioned TDM Framer and packet Framer are connected to separate transmit/receive ports of the optical signal circuitry for different channels.  
           [0031]    In a preferred embodiment of the present invention, the node apparatus includes a plurality of TDM Framers, a TDM switching unit for switching TDM data from the plurality of TDM Framers to a TDM network and vice versa, a plurality of packet Framers, and a packet router for switching packets from the plurality of packet Framers to a packet network and vice versa. The plurality of TDM Framers and packet Framers are connected to separate transmit/receive ports of the optical signal circuitry for different channels.  
           [0032]    The integrated packet and TDM switching node apparatus according to the present invention can be applied as an ADM node for connecting a packet network and a TDM network which operate at relatively low speed to a high-speed network formed by first and second optical rings, wherein the direction of signal transmission over the first optical ring is opposite to the direction of signal transmission over the second optical ring.  
           [0033]    According to the present invention, the node apparatus includes selectors for selectively connecting one of the TDM Framers or one of the packet Framers to each of a plurality of pairs of transmit/receive ports of the optical signal circuitry. The selectors are controlled by a control unit to change the connections between the transmit/receive ports and the TDM Framers as well as the packet Framers if necessary. Thus, the number of channels operating in TDM transmission mode and the number of channels operating in packet transmission mode can be changed at any time if necessary.  
           [0034]    The node apparatus also includes means for monitoring packet traffic passing across the packet router and TDM traffic passing across the TDM switching unit. By controlling the selectors, based on traffic data collected by these monitoring means, transmission mode switchover on a per-channel basis can be implemented flexibly, according to traffic variation. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    The invention will be more particularly described with reference to the accompanying drawings, in which:  
         [0036]    [0036]FIG. 1 shows one network configuration example to which integrated packet and TDM switching nodes according to the present invention are applied;  
         [0037]    [0037]FIG. 2 shows a configuration example of a TDM ring that is a conventional backbone network;  
         [0038]    [0038]FIG. 3 shows a network topology example in which a ring network comprising high-speed packet nodes and an existing TDM ring coexist;  
         [0039]    [0039]FIG. 4 shows another network configuration example to which integrated packet and TDM switching nodes according to the present invention are applied;  
         [0040]    [0040]FIG. 5 is a structural block diagram showing one embodiment of an integrated packet and TDM switching node according to the present invention;  
         [0041]    [0041]FIG. 6 is a block diagram showing the detailed structure of an optical line interface shown in FIG. 5;  
         [0042]    [0042]FIG. 7 is a block diagram showing the detailed structure of an IP packet router shown in FIG. 5;  
         [0043]    [0043]FIG. 8 is a block diagram showing the detailed structure of a TDM switching unit shown in FIG. 5;  
         [0044]    [0044]FIG. 9 is a diagram for explaining a stack of protocols which are applied to an integrated packet and TDM switching node of the present invention;  
         [0045]    [0045]FIG. 10 is a diagram for explaining another example of a stack of protocols which are applied to an integrated packet and TDM switching node of the present invention; and  
         [0046]    [0046]FIG. 11 shows yet another network configuration example to which integrated packet and TDM switching nodes according to the present invention are applied.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0047]    The present invention now is described fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. FIG. 1 shows one network configuration example to which integrated packet and TDM switching nodes  20  ( 20 - 1  to  20 - 4 , hereinafter abbreviated to IPTS nodes) according to the present invention are applied.  
         [0048]    Each of the IPTS nodes  20 - 1  to  20 - 4  has high-speed line interfaces and low-speed line interfaces. The high-speed line interfaces of the IPTS nodes are connected to first optical fibers  100  ( 100 - 1  to  100 - 4 ) which form an outer ring for transmitting signals in a clockwise direction and second optical fibers  101  ( 101 - 1  to  101 - 4 ) which form an inter ring for transmitting signals in a counterclockwise direction. The low-speed line interfaces of the IPTS nodes are connected to low-speed networks such as TDM networks  2  ( 2 A and  2 B) or packet networks ( 3 A and  3 B).  
         [0049]    In FIG. 1, the IPTS nodes  20 - 1  and  20 - 2  are connected to a PBX  5 A and a banking system  6 A included in the TDM network  2 A and a router  7 A included in the packet network  3 A. The IPTS nodes  20 - 3  and  20 - 4  are connected to a PBX  5 B and a banking system  6 B included in the TDM network  2 B and a router  7 B included in the packet network  3 B. In this embodiment, each IPTS node  20  supports both the RPR function which is packet-based ring network technology and the BLSR and UPSR functions which are TDM-based ring network technology.  
         [0050]    [0050]FIG. 4 shows another network configuration example to which integrated packet and TDM switching (IPTS) nodes  20  ( 20 - 5  and  20 - 6 ) according to the present invention are applied.  
         [0051]    In this network configuration, a first IPTS node  20 - 5  connected to the TDM network  2 A and the packet network  3 A through its low-speed line interfaces and a second IPTS node  20 - 6  connected to the TDM network  2 B and the packet network  3 B through its low-speed line interfaces are point-to-point connected by two pairs of optical fibers: one pair of fibers  100 - 5  and  101 - 6  and the other pair of fibers  100 - 6  and  101 - 5 .  
         [0052]    In this embodiment, the IPTS nodes  20 - 5  and  20 - 6  function as the apparatuses for multiplexing/demultiplexing communication channels between the packet networks  3 A and  3 B and communication channels transmitting and receiving traffic between the TDM networks  2 A and  2 B. In this network configuration, there are two pairs of paths between the IPTS nodes, one pair consisting of optical fibers  100 - 5  and  101 - 6  and another pair consisting of optical fibers  101 - 5  and  100 - 6 . Thus, this embodiment has reliability against transmission path failure between the nodes and can provide support of the function of reconfiguring the networks such as RPR, BLSR, and UPSR.  
         [0053]    [0053]FIG. 5 shows one embodiment of an IPTS node  20  according to the present invention. The IPTS node  20  is comprised of optical line interface units  21  and  22 , an IP packet router  23 , a TDM switching unit  24 , and a control unit  25  connected to these constituent parts. The control unit  24  is connected to a control terminal  50  that is located outside the IPTS node  20 .  
         [0054]    The optical line interface unit  21  is for communicating with an adjacent node located upstream on the outer optical ring transmission path. In the case of the IPTS node  20 - 1  shown in FIG. 1, its optical line interface unit  21  is comprised of optical signal circuitry  29  to which the outer optical fiber  100 - 4  for reception and the inner optical fiber  101 - 1  for transmission are connected, a plurality of Ethernet Framers  31  ( 31 - 1  to  31 - n ) and TDM Framers  33  ( 33 - 1  to  33 - n ) which are selectively connected via selectors  35  ( 35 - 1  to  35 - n ) to transmit/receive ports Px- 1  to Px-n of the optical signal circuitry  29 , a packet traffic monitor  37  for monitoring packet traffic input to and output from the Ethernet Framers  31 , and a TDM traffic monitor  38  for monitoring TDM traffic input to and output from the TDM Framers  33 .  
         [0055]    The optical signal circuitry  29  is comprised of a wavelength division demultiplexer/multiplexer  290  and a plurality of optical/electrical (O/E) converters and electrical/optical (E/O) converters  291 - 1  to  291 - n . Optical signals of different wavelengths are input to the O/E converters and output from the E/O converters. The wavelength division demultiplexer/multiplexer  290  demultiplexes wavelength-division-multiplexed optical signals of n channels received through the outer optical fiber  100 - 4  for reception into separate optical signals of different wavelengths (per channel) and outputs them to the per-channel O/E converters. The wavelength division demultiplexer/multiplexer  290  also wavelength division multiplexes optical signals to transmit which are of n channels output from the plurality of E/O converters and output the thus multiplexed optical signals to the inner optical fiber  101 - 1  for transmission.  
         [0056]    The optical line interface unit  22  is for communicating with an adjacent node located downstream on the outer optical ring transmission path. In the case of the IPTS node  20 - 1  shown in FIG. 1, its optical line interface unit  22  is comprised of optical signal circuitry  30  to which the inner optical fiber  101 - 2  for reception and the outer optical fiber  100 - 1  for transmission are connected, a plurality of Ethernet Framers  32  ( 32 - 1  to  32 - n ) and TDM Framers  34  ( 34 - 1  to  34 - n ) which are selectively connected via selectors  36  ( 36 - 1  to  36 - n ) to transmit/receive ports Px- 1  to Px-n of the optical signal circuitry  30 , a packet traffic monitor  39  for monitoring packet traffic input to and output from the Ethernet Framers  32 , and a TDM traffic monitor  40  for monitoring TDM traffic input to and output from the TDM Framers  34 .  
         [0057]    As is the case for the optical signal circuitry  29  of the optical line interface  21 , the optical signal circuitry  30  is also comprised of a wavelength division demultiplexer/multiplexer  300  and a plurality of optical/electrical (O/E) converters and electrical/optical (E/O) converters  301 - 1  to  301 - n.    
         [0058]    The number of the selectors  35  ( 36 ) is determined by the number of channels n that are formed on one optical fiber by wavelength division multiplexing. To explain the IPTS node embodiment of FIG. 5, one Ethernet Framer  31  ( 32 ) and one TDM Framer  33  ( 34 ) are assumed to be connected to each of the selectors. In practical application, however, the number of the Ethernet Framers  31  ( 32 ) to be connected to the packet traffic monitor  37  ( 39 ) and the number of the TDM Framers  33  ( 34 ) to be connected to the TDM traffic monitor  38  ( 40 ) can be selected arbitrarily within the range of n, the number of channels.  
         [0059]    For example, if n=8, it is possible to use channels 1 to 4 for TDM only and channels 5 to 8 as common TDM/packet channels. The node may be configured to have four Ethernet Framers  31  ( 32 ) and eight TDM Framers  33  ( 34 ); in this case, the TDM transmission load on the node is weighted. Inversely, it is possible to use channels 1 to 4 for packet only and channels 5 to 8 as common TDM/packet channels. The node may be configured to have eight Ethernet Framers  31  ( 32 ) and four TDM Framers  33  ( 34 ); in this case, the packet transmission load on the node is weighted. In these cases, the hardware may be arranged such that the Ethernet or TDM Framers for the channels for packet only or TDM only are directly connected to the transmit/receive ports without the intervention of the selectors.  
         [0060]    By mode (transmission mode) switchover between TDM and packet of the selectors  35  ( 36 ), a plurality of channels formed on an optical ring transmission path by wavelength division multiplexing can be assigned to TDM transmission and packet transmission at any TDM-to-packet ratio.  
         [0061]    As concerns the packet traffic monitor  37  ( 39 ) and the TDM traffic monitor  38  ( 40 ), separate monitors per channel may be provided, or a single one may be used for monitoring packet or TDM traffic on the plurality of channels.  
         [0062]    An Ethernet Framer  31  ( 32 ) executes termination of a received frame compliant with a protocol of layer 2 of an Open Systems Interconnection (OSI) reference model (for example, an Ethernet frame pursuant to the RPR specifications), received through an optical ring transmission path (the optical fiber  100 - 4  or  101 - 2 ) The Ethernet Framer  31  ( 32 ) determines whether the MAC address specified in the received frame matches the MAC address of the IPTS node that received the frame. If MAC address matching occurs, the Ethernet Framer  31  ( 32 ) extracts a higher layer packet (IP packet) from the received frame and transfers it to the IP packet router  23  (Drop action). If a MAC address mismatch is found, the Ethernet Framer  31  ( 32 ) transfers the received frame to the corresponding Ethernet Framer  32  ( 31 ) in the other optical line interface  22  ( 21 ) (Through action).  
         [0063]    From the IP packet router  23 , when the Ethernet Framer  31  ( 32 ) receives an IP packet to transmit, it generates an Ethernet frame header by referring to an address translation table containing predefined mapping between destination IP addresses and destination MAC addresses, converts the IP packet to transmit into an Ethernet frame to transmit, and transfers the Ethernet frame to the optical signal circuitry  29  via the selector  35 - 1  (Add action). The Ethernet Framer  31  ( 32 ) receives an Ethernet frame from the other Ethernet Framer  32  ( 31 ) that serves the same channel and sends it to the optical signal circuitry  29  via the selector  35 - 1  (Through action).  
         [0064]    The IP packet router  23  switches an IP packet input from one of the Ethernet Framers  31 ,  32  to one of the low-speed I/O lines  400 - 1  to  400 - m  which are connected to the packet network  3 A or  3 B shown in FIG. 1 or an IP packet input from one of the lower-speed I/O lines to one of the Ethernet Framers  31 ,  32 , according to the destination address specified in the header of the IP packet.  
         [0065]    On the other hand, a TDM Framer  33  ( 34 ) executes termination of a SONET frame received through an optical ring transmission path (the optical fiber  100 - 4  or  101 - 2 ). The TDM Framer  33  ( 34 ) transfers such TDM data extracted from the time slots of the SONET frame that is to be forwarded to the adjacent node to the corresponding TDM Framer  34  ( 33 ) in the other optical line interface  22  ( 21 ). The TDM Framer  33  ( 34 ) transfers the TDM data to be forwarded to the TDM network to which the IPTS node that received the SONET frame is connected to the TDM switching unit  24 . The TDM Framer  33  ( 34 ) sets TDM data received from the TDM switching unit  24  and a TDM frame received from the other TDM Framer  34  ( 33 ) in predetermine time slots of a SONET frame and sends the SONET frame to the optical signal circuitry  29  ( 30 ) via the selector  35 - n.    
         [0066]    The TDM switching unit  24  executes line switching of TDM data input from one of the TDM Framers  33 ,  34  to one of the low-speed I/O lines  200 - 1  to  200 - k  which are connected to the TDM network  2 A or  2 B shown in FIG. 1 or TDM data input from one of the low-speed I/O lines to one of the TDM Framers.  
         [0067]    Traffic carried over the channels is monitored by the packet traffic monitors  37 ,  39  and the TDM traffic monitors  38 ,  40  and the control unit  25  collects the traffic data through signal lines L 37 , L 38 , L 39 , and L 40 . The control unit  25  periodically collects the traffic data for the channels and outputs traffic transition per channel to the control terminal  50  by request of the operator at the control terminal  50 .  
         [0068]    The control unit  25  controls the selectors  35 - i ,  36 - i , (i=1 to n) in the optical line interface units by request of the operator at the control terminal  50  or automatically from the result of analysis of traffic data collected from the monitors. The control unit  25  switches a channel from packet transmission mode to TDM transmission mode or from TDM transmission mode to packet transmission mode if necessary. Mode switchover of the selectors  35 - i  and  36 - i  is performed by a mode switching signal output from the control unit  25  to control signal lines L 35 - i  so that the same channel is set in the same transmission mode.  
         [0069]    The control unit  25  is connected to the Ethernet Framers  31  ( 31 - 1  to  31 - n ),  32  ( 32 - 1  to  32 - n ) and TDM Framers  33  ( 33 - 1  to  33 - n ),  34  ( 34 - 1  to  34 - n ) by control signal lines L 31  ( 131 - 1  to L 31 - n ), L 32  (L 32 - 1  to L 32 - n ), L 33  (L 33 - 1  to L 33 - n ), and L 34  (L 34 - 1  to L 34 - n ). The control unit  25  is also connected to the IP packet router  23  and TDM switching unit  24  by control signal lines L 12  and L 24 . Through these control signal lines, the control unit  25  supplies control commands to these components and updates the routing tables and other parameter tables that these components retain.  
         [0070]    [0070]FIG. 6 is a block diagram showing detailed structure of the optical line interface unit  21 . The optical line interface unit  22  also has the same structure as shown in FIG. 6.  
         [0071]    Wavelength-division-multiplexed optical signals of n channels received through the optical fiber  100 - 4  are demultiplexed into separate optical signals of different wavelengths by the wavelength division demultiplexer/multiplexer  290 A. The separate optical signals are input to the per-wavelength (per-channel) optical/electrical (O/E) converters  291 A- 1  to  291 A-n and converted to electrical received frame signals. The received frame signals are input via the receive ports PRx- 1  to PRx-n to the selectors  35 A- 1  to  35 A-n.  
         [0072]    To each of the selectors  35 A-i, (i=1 to n), at least one of the Ethernet frame termination units and TDM frame termination units. In this embodiment, assume that the TDM frame termination units are respectively connected to all selectors  35 A-i (i=1 to n) and the Ethernet frame termination units are respectively connected to selectors 1 to j (j&lt;n); therefore, (j+1)-th to n-th selectors are for TDM only.  
         [0073]    Among the Ethernet frame termination units and TDM frame termination units arranged in the optical line interface unit  21 , those selected by the associated selectors  35 - i  (i=1 to n) are enabled logically and physically and executes termination of the received frame on each channel.  
         [0074]    The Ethernet frame termination units  311 - a  to  311 - j  are enabled when their associated selectors are set in packet transmission mode and execute termination of an Ethernet frame (or RPR frame) input from one of the receive ports PRx-i (i=1 to j). Among Ethernet frames received, for an Ethernet frame to drop to a packet network (Drop) the Ethernet frame termination unit that received it extracts an IP packet from the frame and transfers the IP packet to the IP packet router  23  via one of the signal lines  201 A- 1  to  201 A-j. For an Ethernet frame to be forwarded to the Next node (Through), the Ethernet frame termination unit that received it transfers it via one of the signal lines L 311 - 1  to L 311 - j  to the Ethernet frame generation unit for the corresponding channel in the other optical line interface  22 .  
         [0075]    The TDM frame termination units  331 - 1  to  331 - j  are enabled when their associated selectors are set in TDM transmission mode, execute termination of a SONET frame input from one of the receive ports PRx-i (i=1 to j), and extract TDM data from the time slots of the frame. Among TDM data received, for TDM data to drop to a TDM network (Drop), the TDM frame termination unit that received it transfers it via one of the signal lines  202 A- 1  to  202 A-n to the TDM switching unit  24 . For TDM data to be forwarded to the next node (Through), the TDM frame termination unit that received it transfers it via one of the signal lines L 331 - 1  to L 331 - i  to the TDM frame generation unit for the corresponding channel in the other optical line interface  22 .  
         [0076]    In the optical line interface unit  21 , Ethernet frame generation units  312  to  312 - j  as many as the Ethernet frame termination units  311 - 1  to  311 - j  and TDM frame generation units  332 - 1  to  332 - i  as many as the TDM frame termination units  331 - 1  to  331 - i  are arranged.  
         [0077]    Among the Ethernet frame generation units  312 - 1  to  312 - j , those selected by the associated selectors  35 B- 1  to  35 B-j are connected to the electrical/optical converters  291 B- 1  to  291 B-j via the transmit ports PTx- 1  to PTx-n. The TDM frame generation units  332 - 1  to  332 - i  selected by the associated selectors  35 B- 1  to  35 B-i are also connected to the electrical/optical converters  291 B- 1  to  291 B-i via the transmit ports PTx- 1  to PTx-n. Optical frame signals to transmit of n channels with different wavelengths output from the electrical/optical converters  291 B- 1  to  291 B-i are multiplexed by the wavelength division multiplexer  290 B and output to the optical fiber  101 - 1 .  
         [0078]    Switchover control is exerted to concurrently switch the corresponding ones of the selectors  35 B- 1  to  35 B-n and the selectors  35 A- 1  to  35 A-n so that a pair of an Ethernet frame generation unit  312 - i  and an Ethernet frame termination unit  311 - i  (i=1 to j) or a pair of a TDM frame generation unit  332 - i  and a TDM frame termination unit  331 - i  (i=1 to n) will be connected to the same channel on the optical ring transmission path.  
         [0079]    For example, when the k-th Ethernet frame termination unit  311 - k  is connected to the receive port PRx-k by the selector  35 A-k, the selector  35 B-k connects the k-th Ethernet frame generation unit  312 - k  to the transmit port PTx-k. Similarly, when the k-th TDM frame termination unit  331 - k  is connected to the receive port PRx-k by the selector  35 A-k, the selector  35 B-k connects the k-th TDM frame generation unit  332 - k  to the transmit port PTx-k. Moreover, when transmission mode switchover of the selector  35 A-k and  35 B-k occurs in the optical line interface  21 , transmission mode switchover of the selector  35 A-k and  36 B-k occurs simultaneously in the optical line interface  22 .  
         [0080]    When the selector  35 B-k is set in packet transmission mode, the Ethernet frame generation unit  312 - k  receives an IP packet from the IP packet router  23  through the signal line  201 B-k and adds an Ethernet header to the IP packet, thus converting the IP packet into an Ethernet frame. The Ethernet frame generation unit  312 - k  writes a destination MAC address mapped to the destination IP address of the IP packet in the Ethernet header and outputs the Ethernet frame to the transmit port PTx-k. When the selector  35 B-k is set in TDM transmission mode, the TDM frame generation unit  332 - k  receives TDM data from the TDM switching unit  24  through the signal line  202 B-k, sets the TDM data in predetermined time slots of a SONET frame, and outputs the SONET frame to the transmit port PTx-k.  
         [0081]    [0081]FIG. 7 shows one embodiment of the IP packet router  23 .  
         [0082]    The IP packet router  23  is comprised of a plurality of high-speed packet line interfaces  230 - 1  to  230 - p  which are connected to the Ethernet Framers  31  (Ethernet frame termination units  311 - 1  to  311 - j  and Ethernet frame generation units  312 - 1  to  312 - j ) arranged in the optical line interface unit  21  or the Ethernet Framers  32  arranged in the optical line interface unit  22 , a plurality of low-speed packet line interfaces  234 - 1  to  234 - m  which accommodate the I/O lines from/to the packet network  3 A or  3 B, a packet switch  235  for switching IP packets from the high-speed packet line interfaces to the low-speed packet line interfaces and vice versa, and a switch control unit  236  connected to the above line interfaces and the packet switch.  
         [0083]    In this embodiment, arrangement is made so that high-speed packets input and output to/from the optical line interface units  21  and  22  will be input and output to/from the packet switch  235  at a rate as low as the rate at which packets are input and output to/from the low-speed packet line interfaces  234 - 1  to  234 - m . For this purpose, each high-speed packet line interface  230  is comprised of a plurality of Processing Units  233 - 1  to  233 - i , a demultiplexer  231  for distributing IP packets received from the Ethernet frame termination units  311  to the plurality of Processing Units, and a multiplexer  232  for multiplexing IP packets to transmit, output from the plurality of Processing Units, and supplying the thus multiplexed packets to the Ethernet frame generation units  312 .  
         [0084]    Each Processing Unit  233  has a routing table containing predefined mapping between destination IP addresses and output port numbers of the packet switch  235 . When the Processing Unit receives an IP packet from the demultiplexer, it reads the output port number mapped to the destination address of the received packet from the routing table, adds an internal header having the output port number written in it to the packet, and stores the packet into the output buffer. Each low-speed packet line interface  234  also has the same routing table as the Processing Unit  233  has. When the low-speed packet line interface receives an IP packet from the packet network, it writes the output port number mapped to the destination address of the received packet into an internal header, adds the internal header to the packet, and stores the packet into the output buffer.  
         [0085]    The packet switch  235  sequentially reads IP packets from the output buffers of the low-speed line interfaces  234  and Processing Units  233  and switches an IP packet to any line interface, according to the output port number specified in the internal header of the packet. When a low-speed packet line interface  234  receives an IP packet from the packet switch  235 , it removes the internal header that is no longer needed, and transfers the IP packet to the packet network.  
         [0086]    When an Processing Unit  233  receives an IP packet from the packet switch  235 , it removes the internal header that is no longer needed, and transfers the IP packet to the multiplexer  232 . The routing table retained on each line interface is updated by the switch control unit  236 . The switch control unit  236  is connected to the control unit  25  shown in FIG. 5.  
         [0087]    [0087]FIG. 8 shows one embodiment of the TDM switching unit  24 .  
         [0088]    The TDM switching unit is comprised of a plurality of high-speed TDM line interfaces  241 - 1  to  241 - 2   n , each of which accommodates I/O lines from/to each of the TDM Framers  33  (TDM frame termination units  331 - 1  to  331 - n  and TDM frame generation units  332 - 1  to  332 - n ) arranged in the optical line interface unit  21  and the TDM Framers  34  arranged in the optical line interface unit  22 , a plurality of low-speed TDM line interfaces  242 - 1  to  242 - k  which accommodate the I/O lines from/to the TDM network  2 A or  2 B, a TDM switch  243  for switching TDM data from the high-speed TDM line interfaces to the low-speed TDM line interfaces and vice versa, and a switch control unit  244  connected to the line interfaces and the TDM switch.  
         [0089]    As described above, the IPTS node  20  according to the present invention realizes both packet transmission and TDM transmission on a same optical ring transmission path in the following manner. For a plurality of channels wavelength-division-multiplexed on an optical ring transmission path, the per-channel selectors  35  ( 35 - 1  to  35 - n ) and  36  ( 36 - 1  to  36   n ) selectively connects the transmit/receive ports Px- 1  to Px-n (PRx- 1  to PRx-n and PTx- 1  to PTx-n) for the channels to the Ethernet Framers  31  ( 311 - 1  to  312 - j ) and  32  or the TDM Framers  33  ( 331 - 1  to  332 - n ) and  34 .  
         [0090]    The selectors  35  and  36  can be switched at any time between two modes, packet transmission and TDM transmission, by a mode switching signal that is output from the control unit  25  and carried through one of the signal lines L 35  (L 35 - 1  to L 35 - n ).  
         [0091]    In the IPTS node  20  of the present invention, traffic on the channels is monitored by the packet traffic monitors  37  and  39  and TDM traffic monitors  38  and  40 . The control unit  25  collects traffic data by, for example, periodically polling the monitors, and outputs current transmission mode and traffic transition for each channel to the control terminal  50  when the operator at the control panel  50  requests traffic data output.  
         [0092]    From the transmission mode and traffic transition for each channel displayed on the terminal screen, the operator at the control terminal  50  determines whether to take a transmission mode switchover. In consequence, given that, for example, the selectors  35 - 1  and  36 - 1  for the first channel shown in FIG. 5 should be switched from packet transmission mode to TDM mode to shift the packet transmission load on the first channel to the second channel that is still in packet transmission mode, the operator must carry out the following procedure to make a transmission mode changeover of the first channel.  
         [0093]    First, the operator must enter a first command to change the packet transfer route from the first transmit/receive port Px- 1  to the second transmit/receive port Px- 2 , and the first command is supplied from the control terminal  50  to the control unit  25 . Upon the reception of the first command, the control unit  25  notifies the Ethernet Framers  31 - 1  and  32 - 1  that are being connected to the first transmit/receive port Px- 1  of closing of the transmit/receive port through the control signal lines L 31 - 1  and L 32 - 1 . The control unit  25  notifies the switch control unit  236  in the IP packet router  23  of route change from the first transmit/receive port Px- 1  to the second transmit/receive port Px- 2 . Then, the control unit  25  returns a response to the first command to the control terminal  50 .  
         [0094]    When the control terminal  50  receives the response, the operator must enter a second command to switch the first transmit/receive port Px- 1  to TDM transmission mode. Upon the reception of the second command from the control terminal  50 , the control unit  25  sends a mode switching signal through the control signal line L 35 - 1  to the first transmit/receive port Px- 1  and returns a response to the second command to the control terminal  50 . Because the control signal line L 35 - 1  is common for the optical line interfaces  21  and  22 , the selectors  35 - 1  ( 35 A- 1  and  35 B- 1  in FIG. 6) and  36 - 1  switch to TDM transmission mode by receiving the mode switching signal, and consequently, the TDM Framers  33 - 1  and  34 - 1  are connected to the transmit/receive port Px- 1 .  
         [0095]    When the control terminal  50  receives the response to the second command from the control unit  25 , the operator must enter a third command to open the first transmit/receive port Px- 1 . Upon the reception of the third command from the control terminal  50 , the control unit  25  notifies the TDM Framers  33 - 1  and  34 - 1  which are connected to the first transmit/receive port Px- 1  of opening of that transmit/receive port through the control signal lines L 33 - 1  and L 34 - 1 . The control unit  25  notifies the switch control unit  244  in the TDM switching unit  24  of opening of the first transmit/receive port Px- 1  through the control signal line L 24  and returns a response to the third command to the control terminal  50 .  
         [0096]    When the switch control unit  236  in the IP packet router  23  receives the notification of route change from the first transmit/receive port Px- 1  to the second transmit/receive port Px- 2  from the control unit  25 , it makes packet transfer route change in the packet switch  235  so that packets so far output to the high-speed packet line interface  230 - 1  that is connected to the first Ethernet Framer  31 - 1  in the optical line interface unit  21  will be transferred to the high-speed packet line interface  230 - 2  that is connected to the second Ethernet Framer  31 - 2  and packets so far output to the high-speed packet line interface  230 -( j+ 1) that is connected to the first Ethernet Framer  32 - 1  in the optical line interface unit  22  will be transferred to the high-speed packet line interface  230 -( j+ 2) that is connected to the second Ethernet Framer  32 - 2 .  
         [0097]    The above route change updates the routing tables retained on the low-speed packet line interfaces  234 - 1  to  234 - m ; that is, the output port numbers assigned to the high-speed packet line interfaces  230 - 1  and  230 -( j+ 1) are replaced by the output port numbers assigned to the high-speed packet line interfaces  230 - 1  and  230 -( j+ 2).  
         [0098]    When the Ethernet Framers  31 - i  and  32 - i  and TDM Framers  33 - i  and  34 - i  (i=1 to n) receive the notification of opening of the transmit/receive port Px- 1  from the control unit  25 , they start transmission and reception of frames to/from the optical signal circuitry  29  or  30 . When these frame manipulating units receive the notification of closing the transmit/receive port Px- 1  from the control unit  25 , they stop transmission and reception of frames to/from the optical signal circuitry.  
         [0099]    When the switch control unit  244  in the TDM switching unit  24  receives the notification of opening of the transmit/receive port Px- 1  from the control unit  25 , it enables the high-speed TDM line interfaces  241 - 1  and  241 -( n+ 1) for the first channel in the control table of the TDM switch  243  and allocates incoming TDM connections to these high-speed TDM line interfaces  241 - 1  and  241 -( n+ 1).  
         [0100]    While the operator enters the first, second, and third commands sequentially in the above-described procedure, it is also preferable that the operator supplies these commands all together to the control unit  25 . Then, the control unit  25  sequentially executes the first, second, and third commands and returns a response to the control terminal  50  upon the completion of all commands. In stead of the first, second, and third commands, a control message in which the operator must specify parameters for switch-to-mode of transmission, port number to which the route changes, etc. may be supplied to the control unit  25  which, in turn, analyzes the control message and generates the first, second, and third commands.  
         [0101]    Channel transmission mode switchover described above must be performed synchronously on all nodes constituting the ring network, not freely on an individual node.  
         [0102]    In the case of the network shown FIG. 1, to the control units  25  of the IPTS nodes  20 - 1  to  20 - 4 , their control terminals  50  are connected. At each control terminal  50 , the operator observes the transmission mode and traffic transition per channel on the node and determines whether to take a transmission mode switchover. If observed traffic transition situation demands the transmission mode changeover of a channel as described above, in practical application, the following must be done. For example, the operators of the IPTS nodes contact with each other, determine day and time when transmission mode switchover is to be performed and what channel for which switchover is to be done, and start the operation for transmission mode switchover at the same time on all IPTS nodes.  
         [0103]    Instead of sharing information such as day and time when transmission mode switchover is to be performed among the operators of the IPTS nodes by contacting with each other, for example, the following is also preferable. From the control terminal  50  connected to one IPTS node, enter a control message in which the operator must specify control parameters for time when transmission mode switchover is to be performed, what channel for which switchover is to be done, switch-to-mode of transmission, a port to which the route changes, etc. This control message is sent to the control units  25  of all IPTS nodes through the standby path of the dual rings so that all control units  25  will execute transmission mode switchover control together at the specified time.  
         [0104]    In the ring network configuration shown in FIG. 1, if, for example, the first optical fiber  100  is an active path and the second optical path  101  is a standby path, the standby optical fiber  101  is used for transmission of control packets. The control message entered from the control terminal  50  connected to one IPTS node is converted into a control packet on the control unit  25  that received it. The control unit  25  inputs the control packet to the IP packet router  23  through the control signal line L 23  and the control packet is transferred to the appropriate Ethernet Framer  31  and output to the optical fiber  101 .  
         [0105]    By thus transmitting the control packet one by one to other IPTS nodes, the control units  25  of all IPTS nodes constituting the ring network obtain control parameters for time when transmission mode switchover is to be performed and others required for switchover, so that switchover of transmission mode of the specified channel and internal transfer route change can be performed at the same time by the control units  25  on all nodes. It is also preferable to use the broadcast addresses of the destinations so that all other IPTS nodes can receive one control packet.  
         [0106]    While transmission mode switchover is performed by the commands from the operator in the above-described embodiment, the IPTS node of the present invention can also be embodied such that the control units automatically performs transmission mode switchover, according to traffic change per channel, and dynamically changes the channel assignments for TDM transmission and packet transmission.  
         [0107]    In another embodiment, the switch control unit  236  in the IP packet router monitors packet traffic per channel and the switch control unit  244  in the TDM switching unit  24  monitors TDM traffic per channel, and the control unit  25  collects traffic data from these switch control units through the signal lines L 23  and L 24 .  
         [0108]    Automatic transmission mode switchover by the control unit  25  can be implemented as follows. For example, for TDM traffic and packet traffic, set a first threshold by which a new channel is assigned and a second threshold by which a channel is released. If TDM traffic (packet traffic) exceeds the first threshold and packet traffic (TDM traffic) is lower than the second threshold, among the channels in packet (TDM) transmission mode, one channel that carries the least traffic is switched to TDM (packet) transmission mode. The transfer router of packets (TDM) so far transmitted over that channel is switched to another channel in packet (TDM) transmission mode.  
         [0109]    The control unit  25  analyzes traffic per channel and determines what channel for which transmission mode switchover is to be done and what port to which the router changes. Thereafter, the same procedure as for transmission mode switchover by operator command described above is applied and automatic transmission mode changeover by the control unit  25  can be performed. Also in this case, notification of when transmission mode switchover is to be performed and other control parameters is sent from the control unit  25  that determined route change to other IPTS nodes on the ring network, using the standby path, so that transmission mode changeover can be performed at the same time on all IPTS nodes. Time when switchover is to be performed may be set for time after the elapse of a predetermined time from the time when route change is determined. It is also possible that the IPTS nodes autonomously determine a port to which the route changes when automatic transmission mode switchover is performed.  
         [0110]    On the IPTS node of the present invention, the transmit/receive ports Px- 1  to Px-n in the optical line interfaces  21  and  22  transmit and receive signals of frames that are physically multiplexed on a same optical transmission path. However, logically, these ports function as completely dependent TDM or packet transmission ports, and it is impossible that the same port serves both packet and TDM transmission at the same time.  
         [0111]    According to the present invention, when all the selectors  35 - i  and  36 - i  (i=1 to n) shown in FIG. 5 are set in TDM transmission mode, the IPTS node  20  can function as a TDM node. In this case, the Ethernet Framers  31  and  32  take all transmit/receive ports Px to connect to as being closed. However, higher-layer software need not care about whether the transmit/receive ports PX operate in TDM transmission mode.  
         [0112]    Inversely, when the Ethernet Framers are arranged for all channels and all the selectors  35 - i  and  36 - i  (i=1 to n) are set in packet transmission mode, the IPTS node  20  can function as an Ethernet node. In this case, the TDM Framers  33  and  34  take all transmit/receive ports Px to connect to as being closed. However, higher-layer software need not care about whether the transmit/receive ports PX operate in TDM transmission mode.  
         [0113]    When a part of the selectors  35 - i  and  36 - i  (i=1 to n) are set in TDM transmission mode and the remaining ones are set in packet transmission mode, the IPTS node  20  functions as a node serving for both TDM and Ethernet. In this case, deselected Ethernet Framers and TDM Framers simply take the transmit/receive ports Px to connect to being closed, as is the case for the above-described TDM node and Ethernet node. Therefore, TDM transmission and packet transmission by the IPTS node  20  of the present invention do not require special software and processing peculiar to the invention and ordinary applications can be applied to the operation of the IPTS node.  
         [0114]    [0114]FIGS. 9A to  9 C show a stack of protocols for running an IPTS node  20 .  
         [0115]    The node operation phases are hierarchically represented in terms of (FIG. 9A) application of layer of the OSI reference model, (FIG. 9B) protocol/media, and (FIG. 9C) a responsible portion of hardware of the IPTS node.  
         [0116]    Layer 1 (physical layer)  71 , layer 2 (data link layer)  72 , and layer 3 (network layer)  73  of the OSI reference model are respectively associated with optical fibers  100  ( 101 ), SONET/SDH  711 , RPR/Ethernet  720 , and IP/etc.  730  as shown.  
         [0117]    When packet transmission is performed, the Ethernet Framers  31  ( 32 ) manipulate variable-length packet frames of RPR or Ethernet and the Processing Units  233  in the IP packet router  23  route IP packets of layer 3. When TDM transmission is performed, the TDM Framers  33  ( 34 ) execute termination of SONET/SDH frames and manipulate fixed-length TDM frames. The RPR/Ethernet variable-length packet frames and fixed-length TDM frames are E/O converted into optical signals with different wavelengths and wavelength division multiplexed in the optical signal circuitry  29  ( 30 ) and output to the same optical fiber.  
         [0118]    [0118]FIGS. 10A to  10 C show another example of a stack of protocols applicable to the IPTS node  20  of the present invention.  
         [0119]    In this example, as seen from (FIG. 10B) protocol/media, SONET/SDH  711  is a common protocol for packet transmission and TDM transmission. SONET/SDH frames containing RPR/Ethernet variable-length packet frames and SONET/SDH frames containing fixed-length TDM frames, which are different wavelengths, are wavelength division multiplexed on the same optical fiber.  
         [0120]    In this case of embodiment, the IPTS node is configured such that SONET/SDH termination units  330  that are common for packet transmission and TDM transmission are installed between the O/E converters  291  ( 301 ) and the selectors  35  ( 36 ) shown in FIG. 5. After termination of received SONET/SDH frames, the frames are input to the Ethernet Framers  31  ( 32 ) or TDM Framers  33  ( 34 ). In this case, the TDM Framers  33  ( 34 ) need not have an SONET/SDH frame termination function, and must have only the function of manipulating fixed-length TDM frames.  
         [0121]    [0121]FIG. 11 shows yet another network configuration example to which to which integrated packet and TDM switching (IPTS) nodes  20  ( 20 - 1  and  20 - 4 ) according to the present invention are applied.  
         [0122]    In the network architecture of FIG. 11, the IPTS nodes  20  are installed instead of SONET ADMs  10  and RPR/Ethernet nodes  15  shown in FIG. 3 and already laid optical fibers are used.  
         [0123]    The IPTS nodes  20 - 1  to  20 - 3  are connected by two ring transmission paths, one consisting of optical fibers  100 - 1  to  100 - 3  and the other consisting of optical fibers  101 - 1  to  101 - 3 . The IPTS node  20 - 4  is connected to the IPTS nodes  20 - 2  and  20 - 3  by two ring transmission paths: one consisting of optical fibers  103 - 3  and  103 - 4  and the other consisting of optical fibers  104 - 3  and  104 - 4 . The existing optical fibers can be used as part of these ring transmission paths.  
         [0124]    The IPTS node  20 - 1  is connected to a TDM network  2 A and a packet network  3 A through its low-speed line interfaces. The IPTS node  20 - 4  is connected to a TDM network  2 B and a packet network  3 B through its low-speed line interfaces. Packet traffic and TDM traffic served by the IPTS node  20 - 1  are transmitted to the packet network or TDM network to which the IPTS network  20 - 4  connects via a plurality of ring networks.  
         [0125]    The IPTS nodes  20 - 2  and  20 - 3  at the junctions of two ring networks, which are different from the IPTS nodes  20 - 1  and  20 - 4 , have three optical line interfaces. For the IPTS nodes  20 - 2  and  20 - 3 , a third optical line interface is added to the node configuration shown in FIG. 5 and received packets and TDM data are passed (Through action) across three optical line interfaces. The IPTS nodes  20 - 1  and  20 - 4  can also accommodate a TDM network and a packet network and support RPR, BLSR/UPSR, and other functions.  
         [0126]    Application of the above-described IPTS node of the present invention makes it possible to integrate a packet-based network and a TDM-based network into one network and consolidate network management.  
         [0127]    In the event that a TDM node becomes failed in an existing TDM network and must be replaced by a new node, continuation of the TDM-based network operation is possible by applying the IPTS node with all channels being set in TDM transmission mode. Thus, the IPTS node of the present invention can replace a node in the existing TDM network.  
         [0128]    If the IPTS node of the present invention is used in a TDM-based network, when TDM-based traffic decreases while packet-based traffic increases, a TDM transmission channel of decreased load can be switched to a packet transmission channel. In this way, the network can be tailored to a packet-based network, using the existing optical transmission paths.  
         [0129]    As clarified from the described embodiments, a network formed by the IPTS nodes of the present invention can serve for both packet-based communication and TDM-based communication (over voice and leased lines). Thus, network management will be easier and a high-speed packet network can be built by making effective use of the existing transmission paths.