JPH0771100B2 - Network priority determination method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system in a network in which various computers, terminal devices, etc. are connected to a transmission path and information is mutually transmitted. More specifically, the present invention relates to a network priority determining method for determining the priority of terminals transmitting in such a network and operating the network efficiently with the shortest waiting time.

2. Description of the Related Art At present, a network system in which various computers, terminal devices, etc. are interconnected via a transmission path to mutually transmit information is used in various fields. Such networks have the form of sharing one or more lines. In this type of network, transmission collisions occur when multiple terminals transmit at the same time. Therefore, there is a need for a method of deciding how the transmission right is sequentially given to each node (called an access method).

One of the access methods is the token method. This token method is. This is a method in which a predetermined frame (referred to as a free token) is sequentially circulated to each node, and a node having a transmission request captures the token, converts it into a busy token, and then attaches a data packet and transmits.

In this method, a terminal that receives a token early can transmit quickly. However, the priority of the transmission request of each terminal may be postponed to the transmission of the terminal having the transmission data of high priority regardless of whether the token is received early or not.

Therefore, for example, the draft of the IEEE 802 Committee, dated September 23, 1983, "Draft IEEE Standard 802.5 Token Ring access method and its physical layer specifications" (Draft IEEE Standard
802.5 Token Ring Access Method and Physical Layer
As can be seen from the specifications), in the token system, a method of prioritizing transmission packets and giving a high priority packet an opportunity to transmit as soon as possible is considered.

The outline will be described below.

FIG. 2 is a schematic configuration of a loop network that can adopt the above token method. That is, a loop-shaped transmission line 10 made up of a coaxial cable or an optical fiber.
A terminal 14 is coupled to each of the nodes via a node 12.
Then, the token and data on the transmission line are transferred to each node 12
When the received data is not transmitted to the terminal, it is transmitted as it is, that is, relayed, and as a result, the token and the data circulate on the transmission path.

IE used in the above loop network
The frame structure described in EE802.5 is shown in FIG. FIG. 3 (a) shows a free token. That is, the free token is the start delimiter SD and the access control unit AC.
And an end delimiter ED, the access control unit AC of the token bit T (in this case, T =
0) and the monitor bit M, there are a priority field P and a reserved field R.

If the priority of the free token is P and the priority Pm of the transmission request packet of the node that received the free token is higher than or equal to that, the node changes the free token into the busy token, and FIG. Data is transmitted in a packet structure as shown in FIG.

That is, the data packet includes a start delimiter SD, an access control unit AC, a data unit, a frame check sequence FCS, an end delimiter ED, and a frame status FS. The access control unit AC has a priority field P, a token bit T (however, In this case it has T = 1), monitor bit M and reserved field R.

Each node that relays such a data packet compares the value of the reserved field in the busy token of the data packet with the priority of its own transmission standby data, and changes the reserved field when the following conditions are satisfied. To do.

That is, when the priority of the transmission request packet is lower than the priority of the priority field in the busy token of the data packet being transferred, and the value Rr of the reserved field is lower than the priority value of the transmission request packet, Update reserved fields.

The above is the basic idea of the priority determination method of the token ring method by IEEE, the details and the implementation device thereof have been widely known in the past, and the applicant has proposed a method improved from the IEEE method described above. Japanese Patent Laid-Open No. 61-33
Since it is described in detail in Japanese Patent Publication No. 043, description thereof will be omitted.

Problems to be Solved by the Invention The conventional IEEE system described above has the following problems.

When the transmitted data packet is large, as can be seen from FIG. 3, a long data section follows the access control section AC. In this case, after updating the reserved field R of the access control unit AC in each node, a transmission request with a high priority may occur before the end of the transmission of the data relaying the transmission. However, such a high priority generated after updating the reserved field R is not written in the reserved field, and when the transmission of the above-mentioned data packet is completed, a low priority is registered in the priority field of the free token. As a result, a node having a transmission request with a priority equal to or slightly higher than the low priority recorded in the priority field receives the free token and starts transmission. Therefore, a node that actually has a transmission request with a higher priority than that priority cannot transmit.

That is, when the frequency of updating the maximum value of the priority of the data packet to be transmitted while waiting for the transmission of each node is larger than the length of the data packet being transmitted, the value of the reserved field is Will not show the exact value of. Therefore, the priority field of the token to be output next becomes substantially lower than the required value, and the high-priority transmission queue packet is not prioritized.

The present invention solves the above-mentioned problems of the conventional method, and even if the data packet being transmitted is long, the highest priority is recorded in the reserved field at that time, and it is possible to always transmit in the order of high priority. It is intended to provide a priority determination method.

Means for Solving the Problems According to the present invention, a ring-shaped transmission line and a plurality of terminals, each of which is coupled to the transmission line via a node, are provided. In the network configured so that the plurality of terminals can communicate with each other by sequentially giving the transmission right to each node, the priority indication for the token to control the priority of the transmission right. Including a field and a reserved field for reserving transmission, each terminal determines the transmission priority of its own transmission-waiting data based on the received token,
A network priority determining method for transmitting or waiting the data waiting to be transmitted, wherein the priority display field is arranged at a head portion of a data packet and the reserved field is arranged at a last end of a data packet including an end delimiter. A network priority determining method is provided, wherein the priority determining process for writing to the reserved field is performed when the transmission of the data packet including the end delimiter is completed.

The network transmission method by the network priority determining method according to the present invention will be described.

The free token has a priority field P and a reservation field R. When the priority Pm of the transmission request packet of the node receiving such a free token is higher than the priority P of the free token, the node transmits data by using the free token as a busy token. At this time, the priority field of the busy token is placed at the beginning of the data, and the reserved field is placed at the end.

Then, in each node receiving such a busy token, the reserved field is updated when the following conditions are satisfied.

That is, when the priority of the transmission request packet is lower than the priority of the priority field of the busy token and the value Rr of the reserved field is lower than the priority of the transmission request packet, the reserved field is updated.

Thus, after the packet has been sent, the sending node outputs a free token. The reserved field at the end of transmission of the packet is updated by the node on the way according to the priority of the transmission request. Therefore, when the free token is output, the priority field P is set in the same manner as in the conventional method with reference to the value of the reserved field R.

In the above data transmission, when the reserved field of the busy token is arranged at the end of the data, the priority of the reserved field is updated by comparing it with the latest priority of the relayed node. Therefore, priority control is appropriately performed, a higher priority packet priority is recorded in the reserved field, and the next data transmission is performed from the transmission request having the higher priority.

Embodiment FIG. 1 shows an example of a frame structure according to the present invention in the case of a free token and a data packet (including a busy token).

The free token consists of a start delimiter SD, an access control unit AC and an end delimiter ED, as shown in Fig. 1 (a).
The access control unit AC has a priority field P and a reserved field R before and after the token bit T (T = 1 in this case) and the monitor bit M. Therefore, the structure of the free token in the network priority determination method of the present invention is basically the same as that of the conventional IEEE802.5 method.

Each node that receives such a free token or a busy token described later, receives a priority field P and a reservation field R included in the token every time the token is received.
Are written in the priority field register Pr and the reserved field register Rr provided in each node.

If the priority of the free token is P and the priority Pm of the transmission request packet of the node that has received the free token is higher than or equal to that, the node changes the free token to the busy token, and FIG. Data is transmitted in a packet structure as shown in (b).

That is, the data packet includes the start delimiter SD, the access control unit AC1, the data unit, the frame check sequence FCS, the end delimiter ED, and the frame status F.
The access control unit AC2 includes a priority field P, a token bit T (where T = 0 in this case), and a monitor bit M. The access control unit AC2 includes a reserved field R.
Consists of. The position of AC2 can also be placed between FCS and ED.

The data packet (piggy token) as described above is relayed and transmitted at each node on the way. that time,
Each node writes the priority field P and the reserved field R included in the received token in the priority field register Pr and the reserved field register Rr. On the other hand, it also holds the priority Pm for its own transmission request.
Then, the reserved field R of the access control unit AC2 of the data packet (busy token) being transferred is updated in each node when the following conditions are satisfied.

(I) The priority Pm of the transmission request packet is lower than the priority of the priority field P.

(Ii) The value Rr of the reserved field is lower than the value of the priority Pm of the transmission request packet.

As described above, the reserved field R of the transfer data packet (busy token) is updated. However, the reserved field R is located after the data part of the transfer data packet. Therefore, even if the data section is long, the maximum priority Pm of its own transmission request and the priority of the reserved field R, which change from moment to moment after the transfer of the data section, are compared,
Since it is updated when necessary, the highest priority is recorded in the reserved field R at that time.

When the data packet transmission is completed as described above,
This node outputs a free token.

Free token priority field P sent at this time
The value of the reserved field R and the value of the reserved field R are determined according to the following standard similar to the conventional method.

(I) In the case of Pr ≧ max (Rr, Pm) P = Pr R = max (Rr, Pm) (ii) Pr <max (Rr, Pm) P = max (Rr, Pm), R = O where Pr : Priority field register value (indicating the current priority) Rr: Reserved field register value Pm: Priority of transmission request packet P: Token priority field setting value to be transmitted R: Token reservation field to be transmitted The setting value of "O" indicates the lowest priority.

At this time, since the highest priority is recorded in the reserved field R among the transmission requests in each node when the data packet transmitted immediately before passes through each node, Pr <max ( If Rr, Pm), then P = max (Rr, P
m) and R = 0.

In this way, the node that converted the value of the priority field in the token from a small value to a large value is
Stored in the stack Sr of its own storage means and changed value P
Is stored in the stack Sx. Each stack is prepared by the number of priority levels. Here, this node is called a stacking station.

Thus, the above-mentioned free token circulates in the transmission line through the node provided in the transmission line. As a result, if the priority Pm of the transmission request packet is higher than or equal to the priority P of the free token during the process,
The node converts the free token into a busy token and transmits the data. That is, the node having the transmission request with the highest priority P can transmit.

Thus, the request data packet with the highest priority is always transmitted.

However, if Pr ≧ max (Rr, Pm), the free token may return without any change. In that case, the node that has become the stacking station confirms that none of the nodes output a packet with a priority higher than that of the stacking station. As a result, the priority is lowered. The method is as follows as in the prior art.

When a free token whose priority field value is equal to the stack Sx value is received, (i) if Sr ≧ Rr, the stack Sx is popped, the tokens P = Sr, R = Rr are transmitted, and the stack Sr is popped. The stacking station is released when the contents of the stack Sr are exhausted.

(Ii) When Rr> Sr The stack Sx is popped, a free token of P = Rr, R = O is transmitted, and the value of P is stacked on the stack Sx. In this case, the stacking station is continued.

A method for determining the values of the priority field P and the reserved field R of the free token has been proposed by the applicants.
The method according to 61-33043 can also be replaced.

EFFECTS OF THE INVENTION As described above, according to the network priority determining method of the present invention, the value of the reserved field is written in each node after the data portion has passed through each node. By comparison, the value of the reserved field becomes new by the passage time of the data part. Therefore, even if a data packet with a large data part length is transmitted, the number of data packets waiting to be transmitted increases during the time when the data packet passes through the entire network, and the maximum priority value also changes, the next free token At the time of output, the priority recorded in the priority field follows the maximum priority of the entire network. Therefore, a packet waiting to be transmitted having a high priority is always prioritized and transmitted.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration example of a free token and a busy token in a network priority determination method according to the present invention, FIG. 2 is a schematic diagram showing a basic configuration of a loop network, and FIG. It is a figure which illustrates the structural example of a free token and a busy token in a network priority determination system. [Main reference numbers] 10 …… Transmission line 12 …… Node 14 …… Terminal

Claims (1)

[Claims] 1. A node comprising a ring-shaped transmission line and a plurality of terminals each coupled to the transmission line via a node, wherein a token composed of a predetermined frame is circulated around the transmission line to make each node In a network configured to allow communication between the plurality of terminals by sequentially giving the transmission right to the token, the token reserves a priority display field for controlling the priority of the transmission right and transmission. Reservation field of each of the terminals, each of the terminals determines the transmission priority of its own data waiting to be transmitted based on the received token, and transmits or waits for the data in the transmission. The priority indication field is placed at the beginning of the data packet and the reservation field is placed at the end of the data packet including the end delimiter. Network priority determination system priority determining process for writing to field, characterized in that the transmission of data packets including said termination identifier is performed at the time of completion.