JPH0964901A - Address learning system for switching hub - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the access frequency to a CAM by adopting the configuration not making a retrieval for learning an address when a frame is received from a port to which only one terminal is connected so as to relieve the load of a CPU. SOLUTION: Plural terminals are connected to a port 1 of a switching hub 11a and a plural terminal connection flag is set to TRUE. Only a single terminal connects respectively to ports 2, 3. The plural terminal connection flag is set to FALSE. When the plural terminal connection flag is set to FALSE, it is discriminated that only one connection terminal is connected to the concerned port. In this case, an address this time is compared with a precedingly received address only without retrieving an address discrimination circuit memory (CAM) for learning the address to only check whether or not another connection terminal is replaced. Since the software operating time is required in a CPU and it is not required to access a memory such as the CAM whose operating speed is slow, the processing time of the CPU is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal address learning method in a switching hub, and more particularly to a switching hub for realizing a high-performance switching hub capable of receiving a large number of frames with few dropped frames. The present invention relates to an address learning method.

[0002]

2. Description of the Related Art Conventionally, a LAN represented by Ethernet
Since the (local area network) is a media sharing type, a plurality of terminals cannot simultaneously transmit. Therefore, when the number of terminals connected to one LAN increases, there is a problem that the usable band per terminal decreases. As a solution to this problem, a switching hub having a high price / performance ratio has recently been attracting attention.
Since the switching hub can simultaneously perform a plurality of sets of communication, it is possible to increase the total area by N times (an integer times).

FIG. 3 shows a configuration example of a network using a switching hub. The switching hub 11a has four network ports (port 1 to port 4), and performs communication from port 1 to port 2 while performing communication from port 3 to port 4 at the same time. It can be carried out. Terminals 13a to 13d are connected to the port 1 via the repeating hub 12, and terminals 13e and 13f are connected to the port 2 and the port 3, respectively. 4 to port 1 via repeating hub 12
Since the four terminals 13a to 13d are connected, the four terminals share a single LAN,
While one terminal is transmitting, another terminal cannot transmit. Since only one terminal is connected to the ports 2 and 3, the terminals 13e and 13f can transmit at any time. Therefore, by allocating terminals requiring high speed to 13e and 13f and connecting to ports 2 and 3, it is possible to improve the throughput of the entire system. Also, port 4
The entire system can be expanded by connecting another switching hub 11b to.

FIG. 4 shows an example of the hardware configuration in the switching hub. Switching hubs have various configurations depending on the switching method, etc., but the configuration of FIG.
It is a software-based switching system and is easy to implement. As shown in FIG. 4, the CPU 21,
Buffer memory 22, network interface units 23a to 23d corresponding to each network port, CAM
An address determination memory (also called an address registration table) 24 composed of (Content Address Memory) is the common bus 2
5 interconnected. The CAM is a memory that can perform address comparison at once, and an address determination memory 2 that determines a transfer port by address search.
Used for 4.

FIG. 5 shows an example of the structure of a transmission frame flowing on the network. The transmission frame 31 includes a destination address 32 indicating a frame destination, a source address 33 indicating a frame sender, communication data 34, and an error check 3 added to check a communication error.
It consists of 5.

FIG. 6 shows an example of registered contents of the address determination memory (address registration table) 24 composed of CAM.
Each network port number (1 to 1
4) is registered for one of the terminals, and the address of that terminal (13a-1
3f) is registered. This registered content corresponds to the network configuration example of FIG.

The operation of the switching hub will be described with reference to FIGS. The switching hub is
The frame is once stored in the buffer memory 22. When the CPU 21 confirms that the received frame is a normal frame with no error, it compares the destination address 32 with the contents of the address judging memory 24 to check which port the received frame should be transferred to. For example, if the destination address of the frame received from port 1 is 13e, the address determination memory 24 is searched with this destination address 13e, and the search result shows that the address 13e is connected to port 2. It is decided to transfer this frame to port 2.

The configuration of FIG. 3 for connecting a terminal to a switching hub may be changed due to expansion or the like. If the network configuration is changed, the registered contents of the memory for address determination will not match. To deal with this, many switching hubs have an address learning function.
The address learning function is to read the source address of a received frame to recognize the address of the terminal connected to the port that received this frame and register it in the address determination memory. As a result, the address of the terminal connected to each port can be recognized even if the network configuration changes.

FIG. 7 shows an address learning procedure at the time of receiving a frame. After receiving the frame, the source address is first extracted from the received frame. Next, it is searched whether the extracted source address is already registered in the address registration table of FIG. If this sender address is already registered, no processing is performed, but if it is not registered, it is registered in the address registration table.

[0010]

As shown in the configuration of FIG.
In the case where the CPU 21 performs all transmission / reception operations of each port and accesses to the address determination memory 24, if the frequency of reception from each port increases, there is a risk that the processing of the CPU 21 will not be in time and a frame may be dropped.

Focusing on the access to the address determination memory 24, a search for determining a transfer port and a search for learning an address are performed every time a frame is received.
You have to access it twice. Also,
Generally, the access time of CAM is longer than the access time of normal memory. Therefore, when the number of ports increases and the frequency of reception from each port increases, the address determination memory 24
The time consumed to access the device increases, and the time required for transmission and reception increases accordingly. This limitation limits the number of receive frames that can be processed.

Therefore, an object of the present invention is to solve the above problems and to provide a switching hub address learning method for realizing a high-performance switching hub capable of receiving a large number of frames with few dropped frames. Especially.

[0013]

In order to achieve the above object, the present invention has a plurality of ports connected to a network, and a destination included in a frame for transferring a frame between the ports. It has an address judgment memory that registers / searches the address of the terminal connected to each port using the address and the source address, and when the frame is received, the address judgment memory is searched and transferred by the destination address of the frame. In the switching hub that determines the port, searches the address determination memory with the source address of the frame, and registers this address if it is not registered, multiple terminals are connected to one port. Terminal connection information that sets information indicating whether or not only one terminal is connected to one port for each port Check the contents of the terminal connection information table at the time of frame reception using a table, and if the port receiving the frame is a port to which only one terminal is connected, do not perform the address search for the address learning. did.

The contents of the terminal connection information table may be set from the management terminal of the network via a transmission line of the network or a dedicated cable.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention provides a terminal connection information table in which information indicating whether a plurality of terminals are connected to one port or only one terminal is connected to one port is set for each port. When the frame is received, the contents of the terminal connection information table are checked, and if the port receiving the frame is a port to which only one terminal is connected, the address search for address learning is not performed.

The internal structure of the switching hub for the present invention is the terminal connection information table (not shown) in the structure of FIG.
Is added and the software of the CPU 24 is changed. By checking this terminal connection information table, whether multiple terminals are connected for each port,
The CPU 24 can recognize whether only two terminals are connected. When the received frame is from a port to which only one terminal is connected, the CPU 24 does not search the address judging memory for address learning. Furthermore, CPU2
4 compares the source address of this received frame with the source address of the frame previously received at this port, and confirms whether the connection terminals have been replaced.

According to the present invention, when a frame is received from a port to which only one terminal is connected, the search for address learning is not performed, the load on the CPU is reduced, and the frequency of access to the CAM is also reduced. This is intended to improve filtering and forwarding capabilities, and to support switching hubs with a larger number of ports.

FIG. 1 is a diagram showing the contents of the terminal connection information table (port setting table) of the present invention. This terminal connection information table has T
A flag that can take a logical value of either RUE (true) or FALSE (false) is provided. This flag is a multi-terminal connection flag that becomes TRUE when a plurality of terminals are connected. In the case of the network configuration of FIG. 3, the switching hub 11a has a plurality of terminals connected to the port 1, and the multi-terminal connection flag is TRUE. There is only one terminal connected to port 2 and port 3,
The multi-terminal connection flag is FALSE. Since the port 4 is connected to all terminals connected to the switching hub 11b, the multi-terminal connection flag is TRUE.

FIG. 2 shows an address learning processing procedure at the time of receiving a frame in the present invention. After receiving the frame, the multi-terminal flag on the terminal connection information table corresponding to the port number that received this frame is checked. When the multi-terminal flag is TRUE, it can be seen that the port is connected to the multi-terminals. Therefore, the address learning process by the address determination memory (CAM) search shown in FIG. 7 is performed. On the contrary, when the multi-terminal flag is FALSE, it is understood that the connected terminal is only one port. In this case, the CAM search is not performed, only the comparison with the previously received address is performed, and it is checked whether or not the connected terminal is replaced with another one. In the latter case, in the address comparison operation, only the software operation in the CPU 21 is performed, and there is no access to the slow memory such as the CAM 24. Therefore, compared with the address learning in the former case, the processing time of the CPU 21 is longer. Pretty short. Also, C
As for AM access, the CAM access when the connecting terminal receives from only one port is reduced to one time only for determining the transfer port, and the switching hub as a whole has CA
The limit value of the number of received frames that can be processed by M access can be increased.

Regarding the setting method of the terminal connection information table, there are methods such as ROM setting which is written in ROM in advance and pin setting which replaces a jumper pin with a jumper pin at a fixed time at the initial start-up. It is desirable to be able to change dynamically by setting from the network management terminal. In this case, the network management terminal and the switching hub may be connected by a dedicated cable via a management port having an interface such as RS232, or a connection method of downloading setting information via the network.

[0021]

The present invention exhibits the following excellent effects.

(1) When a frame is received from a port to which only one terminal is connected, the memory access for address learning is not performed, so the CPU load is reduced and the frequency of access to the address judgment memory is also reduced. . As a result, filtering and forwarding capabilities are improved, and it is possible to support switching hubs with more ports.

[Brief description of drawings]

FIG. 1 is a memory diagram showing a setting example of a terminal connection information table of the present invention.

FIG. 2 is a flowchart showing an address learning processing procedure at the time of receiving a frame according to the present invention.

FIG. 3 is a system configuration diagram showing a configuration example of a network using a switching hub.

FIG. 4 is a hardware configuration diagram showing an internal configuration example of a switching hub.

FIG. 5 is a frame configuration diagram showing a configuration example of a transmission frame.

FIG. 6 is a memory diagram showing an example of address registration in an address determination memory.

FIG. 7 is a flowchart showing a conventional address learning procedure at the time of receiving a frame.

[Explanation of symbols]

 11a, 11b Switching hub 13a to 13f Terminal 21 CPU 23a to 23d Network interface unit 24 Address determination memory 25 Internal bus 31 Transmission frame 32 Destination address 33 Source address

Claims (2)

[Claims] 1. Having a plurality of ports connected to a network and transferring a frame between each port,
Register the address of the terminal connected to each port using the destination address and source address contained in the frame.
It has a memory for address judgment to search, and when receiving a frame, searches the memory for address judgment with the destination address of the frame to determine the transfer port, and also searches the memory for address judgment with the source address of the frame. If it is not registered, in a switching hub that registers this address and learns the address, information indicating whether multiple terminals are connected to one port or only one terminal is connected to one port is provided for each port. When the frame is received, the contents of the terminal connection information table are checked using the set terminal connection information table, and if the port receiving the frame is a port to which only one terminal is connected, an address search for the address learning is performed. Address learning method for switching hubs characterized by not performing 2. The address learning method for a switching hub according to claim 1, wherein the contents of the terminal connection information table are set from a management terminal of the network via a transmission line of the network or a dedicated cable.