JPH0385940A - Communication network system - Google Patents

Abstract

PURPOSE: To make data transmission efficient by forming allocable channels and a control channel for performing allocation in the data transmission of a communication network having plural nodes. CONSTITUTION: This system is equipped with the nodes 1 to 5 for communicating via a single broadband cable 6 connected to a head end remodulator 8 with its head end 7, and each node transmits information to the other nodes only when having 'token' transmitted from the preceding node. Then, this network includes the plural allocable channels for data communication between the nodes and the control channel for allocating an allocable channel to the respective nodes, and the one of the channels operates under a token path protocol having a limited message packet length, and transmits a selected message between the nodes with the prescribed maximum delay. Thus, the token holding time of each node is kept in short, and a further longer message can be effectively transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION A. INDUSTRIAL APPLICATION The present invention relates to communication networks for communicating between a plurality of nodes via a communication medium.

B. PRIOR ART AND ITS PROBLEMS To control the exchange of information over a network where multiple nodes are competing for use of the network,
Traditionally, some form of network protocol has been used.

An example of a network based on a class of protocols commonly referred to as token-pass protocols is the 1L)-Kun Bus Local Area Network (Token Bus LAN). In a token bus network, each node of the network has (
It can only send information to other nodes when it is in possession of the "token" sent by the previous node (logically, not necessarily physically). The node in possession of the token passes as many messages as necessary, subject to the restrictions imposed by the protocols under which the network operates, and then passes the message containing said token to the next node in the network. By sending to a node, it busses the token to the next node (again, not necessarily physically, but logically), which in turn sends as needed and sends the token to its next node. The relationship between previous and subsequent nodes is configured in the network to define a logical ring such that tokens are bussed circularly within this logical ring.

This mechanism allows only one node to transmit at a time, thus avoiding collisions that would normally occur if two or more nodes try to transmit at the same time (elimination of error conditions). Furthermore, if each node is subject to a maximum token holding time limit upon receipt of the token, then the total token circulation time around the logical ring is guaranteed to be less than or equal to some maximum number. This number depends on the maximum token holding time at each node, the transmission delay and the number of nodes in the network. Therefore, the delay between when a node needs to send some information and when it successfully sends that information is a known amount. This is an important advantage, for example, in a LAN in a manufacturing environment where one node is the machine controller and the other node is the control computer that issues machine instructions.

There are many competing requirements for a communications network to be successful, such as compatibility, performance, flexibility, and reliability among connected devices. As an example, consider a situation involving an industrial LAN. The desire to ensure compatibility was recognized in 1978 by the International Standards Organization. The organization uses the Open Systems Interconnection (
O8I) model was proposed and defined. Based on this model, an industrial LAN standard called Manufacturing Automation Protocol (MAP) was proposed. The MAP protocol is J,
Dwyer (1) vyer and Ioan A.
rMAP and TOP (MAP an
dTOP)J (ISBNI-850913552)
It is described in. Although the MAP protocol achieves the compatibility requirements very well, it does Ainscow) paper rMAP milestone (
Other requirements are sacrificed, as discussed in the former 1stones in MAP) J.

In pure information processing applications and interactions with people, a delay of a few seconds in the transmission of a message over a communications network is often acceptable.

In contrast, when computers are used to control the operation of mechanical devices, it is necessary to guarantee "real-time" operation, that is, maximum latencies on the order of a few milliseconds rather than hundreds of milliseconds or more. It may become. As indicated above, token bus technology that provides access to a communication channel has the potential to guarantee maximum response time. MAP is based on the Token Pass protocol. However, due to the need to efficiently process long files under this protocol, the token retention time is relatively high, resulting in a guaranteed time of only about 1 second for even medium-sized networks. No.

One technique to reduce warranty time is to divide the network into multiple smaller networks. This approach is not without its drawbacks; it introduces inter-network communication problems at gateways, increases transmission delays to nodes on other networks, and requires finding a compromise between compatibility and flexibility.

In communication networks where guaranteed maximum response time is not a requirement, carrier sense multiple access/collision detection (C8M
There is a class of protocols called A/CD protocols. An example of such a protocol is “Ethernet”.
hernet) J protocol. C8MA/CD
In a network, any node that needs access can also attempt to transmit when the network is not active. Collisions between two or more nodes attempting to transmit at the same time are handled by having all nodes cease transmitting and then attempting to transmit. The delay before attempting a retransmission is
Two or more nodes repeatedly issue conflicting transmissions,
It is variable to avoid transmission being impossible. This type of network has the advantage that, at low traffic levels, message transmission delays are generally short. However, the disadvantage is that at high traffic levels, collisions often occur, resulting in very long delays in message transmission, which can result in unacceptable delays in transmission. ,At high traffic levels, the high frequency of collisions makes the use of the communication channel very inefficient when high capacity is desired.Especially for low-priority nodes, it is important to avoid too much delay. Complex algorithms are often used to prevent this.

In JP-A-81-102842, C8 uses frequency division multiplexing to provide a fixed control channel and several data transfer channels, each occupying a different frequency band.
MA/CD networks have been proposed. Two nodes wishing to establish a one-to-one communication path negotiate over a control channel to discover a free data transfer channel and agree to communicate over this channel. In this way, several one-to-one communications occur simultaneously,
Allowing high priority nodes (assuming these nodes always have an assigned data transfer channel) the necessary rapid access to the network. However, the time it takes to establish a one-to-one communication link is variable. This is because, as with all C8MA/CD-type communication channels, the time it takes to communicate over the C8MA/CD control channel cannot be guaranteed, and therefore the time taken to negotiate the use of the data channel over the control channel cannot be guaranteed. This is because the time it takes is not constant.

As a result, at least some nodes, such as high-priority nodes that use communications infrequently and to which it would be uneconomical to permanently allocate a data channel, will may be subject to unpredictable delays. An example of such a node is an error monitoring node designed to signal the system when a particular parameter (eg, conveyor speed, furnace temperature, etc.) exceeds its tolerance. This is for example an industrial L
This is not acceptable in many network application fields such as AN.

An object of the present invention is to provide a communication network that alleviates the problems of prior art networks.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a network for communicating between multiple nodes via a multi-channel communication medium. The network includes a plurality of allocatable channels for data communication between nodes and a control channel for allocating the allocatable channels to individual nodes, wherein at least one channel has a limited message packet length. It is characterized in that it operates under a token pass protocol with which selected messages can be sent between nodes with a predetermined maximum delay.

By limiting the message packet length on a token-passing channel, the token holding time of each node and thus the token cycle time of that channel can be kept short. Due to the limited message packet length on token-pass channels and the availability of allocatable channels for large information transmissions,
Efficient transmission of longer messages may still be possible.

That is, the network according to the invention can provide a guaranteed maximum delay time for any node wishing to communicate a selected short message over the communication medium. This guaranteed maximum delay can be kept short because only short messages are sent to the token bus channel, so each node's token hold time can be set to a low level on this channel. . In prior art single channel, token bus networks, the token retention time must be kept large enough to accommodate the nodes necessary to transmit large amounts of data. It is undesirable to divide the data into small packets and send one each time a token is received, as this would make the transmission of this data very slow and complicate the protocol. Prior art multi-channel networks based on C8MA/CD protocols cannot provide a guaranteed maximum delay due to the nature of these protocols.

A control channel is a channel that operates under a token-pass protocol with a limited message packet length, and message packets transmitted by nodes over the control channel are allocatable channels to individual nodes. Preferably, it includes a message negotiating the allocation of. In this way, a maximum guaranteed delay can be provided for the allocation of allocatable channels for transmitting data messages between nodes.

Additionally, message packets transmitted by nodes over the control channel contain data messages that are unrelated to negotiating the allocation of allocatable channels; It is preferable to enable communication between the nodes via the . By allowing the control channel to also carry information packets that are not related to the allocation of allocatable channels, nodes that are not currently allocated channels can use channels without incurring allocated channel setup delays and especially for emergency communications. It is possible to send emergency messages (eg, error messages) without having to reserve a message.

However, by providing a dedicated channel other than one control channel operating under a token pass protocol with a limited message packet length, messages containing data messages that are unrelated to negotiation of the allocation of allocatable channels are provided. - Packets can be transmitted by the node via this dedicated channel. In this way, urgent data messages (eg, error messages) can be communicated between nodes over this dedicated channel without having to wait for allocation of an allocatable channel.

In the particular example of a communication network described below, three or more nodes may communicate on an allocatable channel, thus establishing a subnetwork on this channel. These nodes communicate using any protocol they wish over this channel, such as MAP or Ethernet, or a token pass protocol with limited message packet length as described above.
The specific requirements of the 7-bands on this subnetwork can be met. This configuration allows for easy and flexible establishment of multiple sub-networks on a single physical communication medium. That is, multiple subnetworks each operate on a separate allocatable channel, and each subnetwork can operate under the same or different protocols or no protocol. Even if the network operates under a token-pass protocol with a limited message packet length,
There can be more than one channel. One is a control channel, and one is the above-mentioned dedicated channel dedicated to serving nodes with a high destination order that rarely use communication.

If each channel operates in its own frequency band, the channels can be configured in such a way that token bus channels can provide additional channels while maintaining compatibility with existing single-channel equipment. It is possible to perform the separation of

The number of channels that can be provided varies depending on the bandwidth of the communication medium. For reasons of compatibility and reliability, the frequency band of the token bus channel is preferably fixed. However, it is not necessary to do so, and the bandwidth and frequency of the channel can be made variable so that the channel can be flexibly allocated according to the needs of the nodes on the network.

Preferably, one or more nodes each include a communications adapter switchable between frequency bands, allowing said one or more nodes to communicate via multiple channels. Alternatively, one or more of said nodes may be provided with a plurality of fixed communication adapters, one for each channel. However, this would be a more costly solution and would have limited flexibility.

The node may further include a second communication adapter operable in the frequency band of at least one channel operating under a token pass protocol with a limited message packet length; One node can communicate on this token bus channel and another channel simultaneously. These nodes operate efficiently because they communicate permanently over the token bus channel. By providing a second communication adapter, potential delays and other complications due to nodes leaving and re-entering the token bus ring are avoided. If necessary, e.g. 2 as above
If there are more than two token bus channels and multiple allocatable channels, a node can
May include an adapter.

If the node contains only a single switchable communication adapter, a ring maintenance flag indicating whether the node underwent ring maintenance during the last round of tokens on the token bus channel, the token bus channel It is preferable to maintain a logical ring formed by busing tokens at a node, and ring maintenance is performed if the ring maintenance flag is not set when the token is accepted by that node.

Not all nodes in the network need to operate on allocatable channels. For example, a very short (
Nodes that only issue messages (e.g., indicating an error condition) are allowed to do so by sending information packets on the token bus channel as described above. Such nodes have the advantage of simplicity (and therefore low cost) since they only require a single non-switchable communications adapter. Therefore, some nodes include a fixed frequency band communication adapter that operates only in the frequency band of a channel operating under a token pass protocol with a limited message packet length; Communication occurs only on this token bus channel.

The invention has particular, but not limited, application in local area networks where the communication medium is a broadband cable and the communication adapter is a modem. The invention is equally applicable to other types of networks using multi-channel communication media, such as optical fiber-based communication networks.

D. EXAMPLE FIG. 1 is a schematic diagram of a typical node configuration on a token-pass communication network, as is well known in the art. For convenience of explanation, only five nodes are shown. In reality, the number of nodes may be much higher or less than five. The illustrated communication network includes nodes 1 communicating via a communication medium (e.g. broadband cable) 6.
5 to 5. Each node in the network receives a "token" sent to it by the previous node in the network.
A node can send information to other nodes only when it owns it. The node before node 2 is, for example, node 3. A token is a unique identifier that a node recognizes as granting it permission to send.

When a node (e.g., node 2) owns a token, it can send as many messages as necessary to other nodes in the network, according to the restrictions imposed by the protocols under which the network is operating. and then busses the token to the next node (eg, node t is the node after node 2) by sending a message containing the token to the next node. The latter node (e.g., node 1) then similarly transmits as needed and then busses the token to its next node (the node after node 1 is node 5).
.

It can therefore be seen that the relationship between the previous and subsequent nodes is arranged to define a logical ring such that tokens are bussed circularly within the logical ring. The relationship between the previous node and the subsequent node is not originally a physical relationship (
, it can also be seen that there is a logical relationship. The communication medium of the present invention is assumed to be a single broadband cable 6 connected at one end, the so-called head end 7, to a head end remodulator 8. Broadband cables typically used in token bus LANs, including repeaters and other equipment, have a bandwidth of approximately 400 MH2. In a single cable system as shown, the edge bandwidth is divided into a high region and a low region for transmission in opposite directions, and the signal is Hera 1! It is transferred between nodes by an end-to-end modulator 8. Dual cable systems have the full bandwidth available in both directions and use repeaters instead of head-end remodulators. In networks with fiber optic communication media, the available bandwidth is greater. In optical fiber networks, it is possible to configure the network in a star shape, as is well known to those skilled in the art.

Consider a LAN with 100 nodes spread over a 5 km radius based on the token pass protocol. Keeping geographic spread in mind, the worst case propagation time from the head end to the most remote node is approximately 35 microseconds. The maximum time it takes to send a token between nodes is the worst case propagation time plus the time for the receiving node to respond to receipt of the token. This total time is called transmission time (TT). Other parameters of the network that directly affect performance are the maximum retention time (MRT) that a node can hold a token before bussing it;
It is. Once these times are known, the maximum access time of the network can be determined from the following relationship.

Maximum access time = number of nodes
It can be determined assuming that the operation of the node is arbitrarily fast due to sufficiently high processing speed and large bandwidth usage. This leaves propagation time as the only limiting factor. Thus, for a 5 km radius network containing 100 nodes, the transmission time would be approximately 35 microseconds, the token retention time could be considered zero, and the worst case maximum access time would be 3.5 milliseconds.

Real networks do not reach this limit for two reasons. First, the bandwidth cannot be expanded arbitrarily. The standard channel bandwidth for wideband systems is 12MHz,
The data rate is therefore 10 Mbits per second. Transmitting one byte takes 819.2 microseconds, whether it's data or protocol overhead. To allow transmission of large data files without excessive fragmentation, the maximum token hold time must be set to a large value, typically 5 to 10 milliseconds.

Second, if the time taken for node operation is variable, the transmission time will be approximately 40 microseconds. With these values and a network with a radius of 5 km with 100 nodes, the performance is more than two orders of magnitude lower than the theoretical maximum performance, and as a result, a MAP network of this size is not suitable for real-time control systems such as industrial LANs. cannot be used as

Next, an industrial LAN with 100 nodes in a radius of 5 krn will be described as an example of a communication network according to the present invention. However, the present invention is not limited to industrial LANs or to networks of this size.

If the cable bandwidth is 400 MHz, a single broadband cable will carry about 12 channels simultaneously, each carrying about 10 Mbits per second, and a dual cable will carry about 3 channels simultaneously.
Can accommodate 0 pieces.

Again, the number of optical fibers will be several orders of magnitude larger.

Prior art token bus networks underutilize this available bandwidth.

The present invention takes advantage of this available bandwidth by providing multiple allocatable channels for message communication between nodes in addition to the control channel. Because bulk data transferred between nodes can be sent over allocatable channels, it is possible to limit the length of individual messages on the control channel to a low value, shorten the node's token hold time, and therefore the total token hold time, and It is also possible to increase the response speed of the communication network.

The characteristics of this example industrial LAN are summarized in Table 1 below.

Transmission time 10. .

Control channel maximum message length Control channel maximum token hold time Token transfer time per node.

If the lOO node's guaranteed access time is 10 ms, then each node on the network can send short messages 100 times per second. This number is sufficient for controlling industrial machinery.

FIG. 2 is a schematic diagram of the architecture of this example communication network according to the invention. The structure of the Open Systems Interconnection (O8I) model is adapted for both token-pass channels and allocatable channels. This diagram is self-explanatory to those familiar with the O8I standard and will therefore not be described further. The token pass channel follows the O8I standard to maintain compatibility with existing LAN equipment based on the O8■ standard. However, since allocatable channels are dynamically allocated through negotiation between nodes, any protocol used on a once-allocated channel can be used if there is a mechanism to close the channel upon completion and make it available for reallocation. It may be used or it may not be used.

FIG. 3 shows the architecture of a node 20 incorporated into an example communication network according to the invention.

This node contains the following components:

- a switchable channel adapter or modem 22 operable over a range of frequencies, preferably the entire range of frequencies provided by the communication medium, and a second channel adapter or modem operable at the frequency of the control channel 26; A fixed modem 24 implements the protocol selected for one control channel 26, in this case IEEE 802.4, and transfers it to a second modem 24.
Logical functions in communication controller 28 associated with 4-allocated channels 30.30', 30''...
A logical function that implements whatever protocol is used by the above terminals and connects them to the switchable modem 22, recognizes the need for a channel, and negotiates its provision using a control channel protocol, also a communication The supervisory logic function of the controller 28 is a task that operates on a terminal and initiates or responds to a transmission on the network (
The machine 32) terminal serves, for example, to handle the download of a partial program from a central database (not shown) to a numerically controlled machine tool (i.e. machine 32 containing the machine tool and appropriate processing logic functions). , periodically send machine tool temperature readings to a remote monitoring program. The terminal also needs to process urgent messages, such as notifications of refrigerant outages. A suitable protocol for the first task is MAP FTAM, and for the second
For this task, a simple serial point-to-point message service may be sufficient. The communication controller 28 of this terminal is therefore capable of implementing both of these protocols and using the switchable modem 22 to assign one of them to an allocable channel 30.3.
0° 30”, .... This controller also implements IEEE 802.4 and uses the second modem 24 to associate it with a control channel 26 and use it to perform the necessary For emergency messages, the terminal can send short messages on the control channel 26 using the second modem 24. In the figure, double connections represent data and control information paths or channels, and single connections represent control paths, i.e., internal paths 34.3B, 38 represent functional mechanisms shown in terminal 20. The control path 40 is used for channel selection by the switchable modem 22.

Communication control device 28 (communication control device 2 in FIGS. 4 and 5)
8" and 28") can typically be implemented in the form of software logic running on general purpose computer hardware, such as a microprocessor and associated memory. Also, in these figures, the communication control device and the machine tool may be separated or may be separate logical entities within the same physical device. For example, they may be separate tasks running in a general purpose computer.

Using the architecture shown in FIG.
can still be part of the token-pass ring while transferring data using other channels. The switchable modem is frequency sensitive so that it can be switched between channels, but the second modem 24 is permanently allocated to the control channel and therefore does not need to be frequency sensitive. High priority short messages can be sent on the control channel without interrupting the sending or receiving of lower priority long messages on the allocatable channel.

FIG. 4 is a schematic diagram of a lower cost alternative to the network node architecture of FIG. The node 42 shown in FIG. 4 includes a single switched IIJ modem 22 and does not include the second modem shown in FIG. This modem 22 can communicate only on one channel at a time, but can switch between channels. The switchable modem of FIG. 4 is normally set to the frequency of control channel 26, so that the node is part of the token ring on that channel. Once the node is allocated to an allocatable channel, the communication controller of node 42 uses control signals on path 44 to change the modem frequency to the frequency of the allocated channel (
(i.e., any frequency of channels 30, 30', 30", etc.), and change the token of the control channel to
Fall from the pass ring. Providing t modems of this type provides a relatively low cost way of connecting nodes to the network since only one modem is required. The sequence of events related to channel allocation, described below, is the same for the node architectures shown in either FIG. 3 or FIG. However, with a single switchable modem, there is a delay in abandoning the allocated channel and rejoining the token ring. This is due to the characteristics of IEEE802.4, as will be explained later.

It may also be desirable to have several nodes on the network including a single non-switchable modem 48 in the form of a simple node 46 as shown in FIG. For example, a node that only issues very short messages (eg, indicating an error condition) need not use allocatable channels. Such nodes can be implemented using an architecture such as that shown in FIG. If the communication controller 28" determines that an error message should be sent, it sends the error message as a short message on a channel designated for this purpose. The channel for this purpose may be a control channel or It may also be a dedicated channel reserved specifically for error messages.

In this way, it has been found that full plug-in compatibility can be maintained from prior art token protocol networks based on the Manufacturing Automation Protocol (MAP) to single-channel devices such as the one shown in Figure 5. sea bream.

The simplest procedure is to have prior art devices communicate only on control channels. Legacy nodes use control channels for all purposes, including communicating with new nodes. However, the presence of such conventional equipment on the network degrades network performance because the token retention time must account for the amount of data that nodes containing such equipment put on the token pass channel.

Another method is to keep the new control channel separate from the old operating channel and use a protocol to allocate the channel to the old equipment. In that case, a gateway must be provided to interconnect the two sets of nodes. The gateway computer is responsible for requesting and maintaining allocated channels. This allows new equipment to realize the full potential of the protocol, while older equipment continues to operate on logically separate LANs over the same physical communication medium.

Of course, it is possible for one node to include more than two channel adapters. The two channels shown in Figure 3
An example of when it may be desirable to provide a third channel adapter in addition to the adapter is when a channel separate from the control channel is specifically dedicated to error messages. This separate dedicated channel can operate under the token pass protocol described above. 3
Another example of a node where it is desirable to have more than one channel adapter is a node that acts as a gateway between different logical networks built on a single physical communications medium.

The communication controller 28.28°, 28'' of each terminal participating in the token bus system on the control channel maintains information about the state of the network in the form of addresses of previous and subsequent nodes and a channel status table.

The addresses of the previous and subsequent nodes are maintained according to IEEE 802.4. If a node has two modems, one for connecting only to the control channel and one for allocable channels, as shown in Figure 3, or permanently to the control channel, as shown in Figure 5. With a single non-switchable modem allocated, these addresses are not used for any purpose other than ring maintenance as in IEEE 802.4. However, if there is a single switchable modem as shown in FIG. 4, their addresses are also used to initiate changes taking into account when neighboring nodes leave the channel.

The channel status table (not shown) is a compact table and is preferably implemented in a memory connected to the communication controller. The channel status table requires only one bit per channel to store the occupancy status of each channel that may be allocated. This table is maintained by the communication controller, which interprets all channel allocation messages passing through the network, regardless of their destination address.

The protocol used on the control channel in this example is I
Same as that specified by EEE Standard 802.4, with the additional requirement that the maximum length of any transmission, including token transfers, on the control channel be set to a small value (e.g., Table 1
75 bytes). This restriction is possible because the transmission of longer messages is moved from the control channel to one of the allocated channels. This limit does not break compatibility with other 080 equipment, since if a node on the network exceeds the limit, it does not cause an error and only reduces the degree of performance improvement.

A message packet or frame transmitted on the control channel in this table has the fields shown in Table 2 below.

Briasiple Start Delimiter (SD) Frame Control (FC) Destination Address (DA) Source Address (SA) Control Channel Cheek Unit (CCDU) Frame Check Unit 1 (FCS) End Delimiter (ED) SD FC=)-X Note that the address of the token node before the identifier uses a 6-neutral address according to the SAFCS D 081 global addressing standard. Note also that the message packet shown in Table t is valid with two messages concatenated, thus two start delimiters and two end delimiters. Fields 9-14 are omitted if the token is not bussed immediately after the message is transmitted. Generally, this only occurs during ring maintenance.

A control channel data unit (CCDU) contains the fields shown in Table 3 below.

1 1 6 4 Maximum 26 1 Zfi Big 3 Big Money 3 Maximum 34 Cheek Unit Type Channel Number (CM) Previous Token Node Address Allocated Channel Protocol Cheek or Data Unit Type Non-confidential Data The unit type field indicates whether the data unit is a channel allocation request, channel allocation response, channel release request, channel release response, channel abort,
or a short message. The first five cases contain the associated channel number in the second field and the address of the token node before the source node for passive ring maintenance if necessary in the third field.

This packet format is fully within the constraints of IEEE 802.4, with the additional constraint of a very short length limit.

The functions performed by the control channel participation seed include those required by IEEE 802.4 and others required to maintain a channel status table.

The communication controller of each participating mate in the control channel that does not currently own a token monitors the traffic on the bus in order to maintain an internal table of information regarding the current state of the network.

The communication controller maintains a record of the addresses of the previous and next nodes in the ring as required by IEEE 802.4. When one of these addresses appears in a channel allocation request or response, the node is considered to leave the ring. Therefore, its address is replaced with the address of the previous or subsequent node obtained from the channel allocation request or response message.

The communication controller node also maintains its channel status table indicating the age of each reassignable channel.

When a channel number appears in a channel allocation request, the channel is flagged as occupied at that position in the channel status table; when a channel number appears in a channel release response or a negative channel allocation response message, the channel status table is flagged as occupied. An unoccupied flag is set for that channel at the relevant position. These terms will be explained later.

For nodes with one switchable modem and no second modem, this table becomes inaccurate when the nodes leave the ring to use other channels. Therefore, when rejoining the ring, this table is restored using the information sent by the authorization node. This is IE
This can be performed using the EE802.4 ring maintenance procedures.

However, as mentioned above, there may be some delay at this stage.

Channel negotiation/short message functions are performed when the node wishes to transport data using the network, either by allocating a channel or by using a control channel to carry messages in the CCDU file field.

A short message is a single packet on a control channel that may or may not require a response. this is,
Contains the fields shown in Table 4 below.

1 3 Preamble 2 1 Start delimiter (SD) 3
1 Frame control (FC)
4 6 Destination Address (DA) 5 6 Source Address (SA) 6 1
Data unit type = short mef t-shift
Maximum 33 Meft-ji Text 8 4 Frame Check 1 (FCS) 9 1 End Delimiter (E
D) 10 1 5D 11 1 FC=)
-Poppy identifier 12 6
Later token node address 13
6 5A14
4 FCS15 1
When an ED node attempts to use an allocatable channel for a point-to-point link, the following sequence of operations is performed.

1. The initiating node examines its channel status table to identify unoccupied channels. If there are no unoccupied channels, wait until one becomes available.

2. Upon receiving the token, the node issues a channel allocation request message specifying the channel to the intended receiver and immediately passes the token. after that,
Other nodes interpret this packet and identify that the channel is occupied. Since only the node that owns the token can transmit, there is no possibility that the same channel will be requested by two nodes at the same time. If there are no unoccupied channels available, the initiating node, upon receiving the token, sends a short message to the receiving node indicating that a long message is pending.

3. The receiver receives the channel allocation request message, recognizes the address of the message, waits until the receiver receives the token, and then sends a channel allocation response message. The message may be positive or negative, indicating acceptance or rejection, respectively, to the starting node.

In the case of a positive response, the receiving node switches its switchable modem to the allocated channel. This response message is interpreted by other nodes and used to confirm or cancel occupancy of the channel. When the initiating node receives the response message, it switches its switchable modem to the designated channel and begins transmission.

In the case of a single modem, if for some reason communication is not established on the allocated channel within the timeout period, neither the initiating node nor the receiving node returns to the control channel after completing communication on the allocated channel in any case. Return and rejoin the ring.

When the point-to-point link is no longer needed, the following series of messages are issued to release the channel.

1. Either participating node in the link sends a channel release request message addressed to the other.

2. When the other participating node receives the message, it sends a channel release response message to the first participating node after sending standby traffic on the allocated channel. Other nodes interpret this packet and flag the specified channel as unoccupied.

3. Additionally, as a confirmation of the channel release, either participating node may broadcast a channel release message on the control channel specifying the channel that has just been released. This confirmation is necessary in the case of a single modem where the channel release transmissions of steps 1 and 2 occur on the allocated channel.

Alternatively to the above procedure, either participating node can also send a channel termination message to the other node. Both participating nodes must immediately terminate using the allocated channel and abandon any pending traffic. The channel abort message informs the other node that the channel is free and available for the option 1 confirmation procedure. In this case, in the case of a single modem, confirmation is required to inform the other node via the control channel that the channel is free.

When allocatable channels are needed in a multi-node network using protocols such as the Token Pass protocol or the C8MA/CD protocol, a different set of steps are performed. As always, all such networks usually have a special terminal called a network manager. It is responsible for managing networks, directory services, etc. The sequence of steps is as follows.

1. When a node, including the network manager of a logical network, finds an unoccupied channel, it sends a channel allocation request packet followed by a channel allocation response packet, both addressing that node. This has the effect of reserving a channel and informing other nodes that the channel is occupied.

2. Every node that subsequently wants to join the logical network sends a channel number request packet addressing the network manager.

3. The network manager responds with a channel number response packet containing the number of the channel assigned to that logical network and a code identifying the protocol used on that channel.

4. The node then joins the network on the allocated channel using whatever joining procedure is set by the protocol. You can then leave the logical network in the same way.

A channel number request packet is actually a special case of a channel allocation request packet and can be implemented as a channel allocation request packet with an empty address field. Similarly, the channel number response packet may be the same as the channel allocation response packet.

When a logical network is closed, and all participating nodes in the logical network except the network manager leave it, the network manager sends channel release request and response frames addressed to itself, if appropriate. A channel can be released by sending a channel termination packet to itself, or by simply broadcasting a channel release packet.

FIG. 6 is a schematic diagram of an example of channel allocation on a communication network according to the invention. In this example, assume that there are 100 nodes on the network as described above, and that the nodes are numbered from 0 to 99. Note that in addition to control channels, there are currently unallocated channels and channels that support communication under the MAP protocol, Ethernet protocol, and point-to-point communication. Allocation of these channels is done as described above (ie, under the token pass protocol on the control channel). It should be noted that FIG. 6 is purely schematic and the channel congestion shown does not represent its relative bandwidth. The bandwidth of each channel may be the same. Similarly, channels of different bandwidths may be provided and allocated according to the bandwidth requirements of the communications to be carried out. this is,
This can be done by pre-selecting multiple channels of different bandwidths or by dynamically determining the bandwidth of the channels.

Above, a specific example of a communication network according to the invention has been described in the form of an industrial local network (LAN). However, the invention is clearly applicable to other environments such as satellite communications and wide area networks. Accordingly, the present invention relates to a LAN, particularly the L
It is not limited to AN. The communication medium in the preferred embodiment described above is broadband cable. However, it should be understood that the present invention divides a communication medium into channels (e.g., by frequency division multiplexing (FDM)) such that all messages are received by all receivers connected to the transmission medium. It is also applicable to communication networks using other communication media, such as electromagnetic communication through free space or fiber optic cables, which are broadcast simultaneously into the medium in a manner that allows communication.

It should be understood that modifications and additions may be made to the communication network described above within the scope of the invention. For example, in the particular example above, dual modems are used, the control channel protocol is IEEE 802.4, there are no acknowledgments, and the message length limit is set to 75 bytes. However, in other examples of communication networks according to the invention - instead of or in addition to the dual modem nodes of the above network, a single switchable modem
Nodes can also be used.

- Non-IEEE 802.4 token pass protocols can be used on the control channel.

- The message length limit on the control channel can be set to other values chosen to optimize performance in a particular environment.

Acknowledged messaging can be used on the control channel rather than non-acknowledged message transmission.

In summary, the present invention provides a communication network as follows.

Broad compatibility can be achieved because one control channel can be tailored to follow existing protocols (e.g., in the network above, higher-level layers of the architecture follow the standards of the O8I model, at the expense of software compatibility). do not have to).

High performance is achieved because bulk transfers of data are handled by allocated channels and do not interfere with the process of gaining access to the network and sending short, high-priority messages.

- Its performance is high enough to eliminate physically separate sub-network structures for real-time control, and to integrate devices using non-standard protocols into the network, allowing for token bus operation protocols. provides the opportunity to keep the system under control, allowing for a high degree of flexibility.

- Provides an opportunity to improve reliability and maintainability by introducing redundancy into the network in the form of distributed processing that takes advantage of high performance.

Furthermore, the communication system according to the present invention includes a computer
It offers the possibility of bringing the total management of the cable system, not just the channels allocated to the network, under control of the protocol. This is a significant advantage when cables are needed to carry non-computer signals such as video or voice communications. Permanently allocating channels for these purposes does not allow for rapid channel removal in the event of equipment failure; instead, channels can be allocated dynamically, either by a node in the network or under the control of a controlling computer. or both.

Methods of using the functionality that can be provided in a communication network according to the invention include the following methods.

1 on the control channel, which requires channel allocation between the sender and all intended receivers for each data transmission.
Point-to-point communication.

A multiple network configuration that establishes multiple logical networks over a common transmission medium, each using the same protocol on an individual channel.

- A multi-protocol configuration that establishes multiple logical networks using different protocols on individual channels over a common transmission medium.

Short message transmission on a control channel for the following purposes:

(i) Rapid transmission of high priority messages.

(ii) communication with one or more nodes not belonging to a particular logical subnetwork to provide a means of inter-network communication (this does not provide the data transformation functionality of O3I, and therefore communication (Note that separate processing by the application program is required to start the process.)

(iii) Communication between network management agents and network managers (most O8Is require a network management agent on each node on the network).

A low cost operating only on the control channel for connecting simple sensors or actuators to the network so that they can be addressed by a data collection/distribution mechanism that is also, for example, a component of a logical MAP network at the same time. Provide a node.

Dealing with errors on one logical subnetwork (for example, if a node becomes "jabbered", i.e. constantly sending noise on the network, by moving nodes one by one to other channels) (can be found and corrected).

In the above specific example of a communication network according to the invention:
Maintenance of the ring is performed according to IEEE 802.4. This can cause a delay when a node with a single switchable modem attempts to rejoin a token bus channel when releasing an allocated channel. This is to update the information of the previous and next nodes during ring maintenance in order to add the node to the token bus channel, and it does not occur during the token ring cycle under IEEE802.4. do not. Ring maintenance is performed by I
Optimized according to EEE 802.4.

For token bus channels with messages containing limited message packages in the network according to the present invention, the performance of nodes with a single switchable modem is further improved by adopting a modified ring maintenance scheme. I can do it. By adopting the scheme outlined below, the interval between ring maintenance operations can be shortened.

As part of this modified scheme, each node maintains a flag called the IT ring maintenance (RM) flag. This flag indicates whether ring maintenance was performed during the last round of tokens. The RM flag is set whenever the token is abandoned, except when ring maintenance is performed by the relinquishing node, and is set when ring maintenance is observed to be performed by another node.

Ring maintenance using this modified method 1'! , is executed in the following cases:

If there is no response within l slot times after busing one token (error condition), or - If the RM flag is not set when the token is received.

This causes ring maintenance to be performed by each node in turn in the absence of errors, with tokens cycling between occurrences. Its main goal is to make the time it takes to rejoin the ring more predictable.

The function performed by this ring maintenance method is the IEEE 802.4 "post-node solicitation" well known to those skilled in the art.
The function is almost the same as that of the procedure. However, one additional function is performed in addition to the post-node solicitation procedure. That is, when a node is admitted to the ring, the channel status table is transferred to the newly admitted node. At the same time that the token is bused, the table can be sent as a short message to the new node.

E3 Effects of the Invention As described above, according to the present invention, in data transmission in a communication network having multiple nodes, an allocatable channel and a control channel for allocating are formed, so that it is possible to improve the efficiency of data transmission. .

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a typical configuration of nodes on a token bus communication network. FIG. 2 is a schematic diagram of the architecture of an example communication network according to the present invention. FIG. 3 is a schematic block diagram of an example architecture of a high performance network node for simultaneous transmission on two channels. FIG. 4 is a schematic block diagram of the architecture of a network node with a single switchable communication adapter. FIG. 5 is a schematic block diagram of the architecture of a low cost network node for transmission on a single fixed channel. FIG. 6 is a schematic diagram of an example of channel allocation in a communication network according to the invention. 1-5...Node, 6...Broadband cable, 8
...Head end remodulator. FIG, 3 FIG, 4

Claims (3)

[Claims] (1) In a communication network that performs communication between a plurality of nodes via a multi-channel communication medium, the network allocates a plurality of allocatable channels for data communication between the nodes and an allocatable channel to each of the nodes. at least one channel operating under a token pass protocol with a limited message packet length to transmit selected messages between the nodes with a predetermined maximum delay; A communication network system characterized by: (2) A channel that operates under the token pass protocol with a limited message packet length is a control channel, and message packets transferred between nodes via the control channel include The communication network system according to claim 1, characterized in that the communication network system includes allocation information of allocatable channels. (3) Message packets transferred between nodes via a control channel contain data messages that are separate from allocation information of allocatable channels, and can be transferred via the control channel without having to wait for allocation of allocatable channels. 2. The communication network system according to claim 1, wherein the communication network system enables inter-node transfer of emergency messages.