1. Field of the Invention
The invention relates to a network system such as a local area network system using Ethernet as a protocol.
2. Description of the Related Art
A constructional example of a conventional LAN system is shown in FIG. 1. The system of FIG. 1 is a network system 10 by an Ethernet LAN (or IEEE802.3 LAN) as a typical LAN.
In FIG. 1, hub apparatuses 1-1 and 1-2 and terminal apparatuses 1-3 to 1-5, 1-20, and 1-21 are connected through LAN cables and network connecting circuits.
For example, the hub apparatus 1-1 and terminal apparatus 1-3 are connected through an LAN cable 1-12 and a network connecting circuit 1-6. Although the network connecting circuit 1-6 is positioned in the terminal apparatus 1-3 in FIG. 1, it can be arranged out of the terminal apparatus 1-3.
The terminal apparatus 1-3 is connected to one port 1-7 of a plurality of ports 1-7, 1-8, 1-14, 1-17, 1-18, and so on disposed in the hub apparatus 1-1 through the network connecting circuit 1-6 and cable 1-12.
As for ports other than the port 1-7 which the hub apparatus 1-1 have, the port 1-8 is connected to a port 1-9 of the other hub apparatus 1-2 through an LAN cable 1-13. The ports 1-17 and 1-18 are connected to the other terminal apparatuses 1-20 and 1-21.
The terminal apparatuses 1-4 and 1-5 are connected to ports 1-10 and 1-11 of the hub apparatus 1-2 through cables and network connecting circuits in a manner similar to the connecting form between the terminal apparatus 1-3 and the hub apparatus 1-1. Thus, network expansion of a star type connection constructing system is realized.
As for the ports of the hub apparatus 1-1, there is also a port connected through a cable 1-15 to a backbone network 1-16 for connecting a plurality of LANs as shown by a port 1-14. The backbone network 1-16 can be replaced with another network such as a WAN (Wide Area Network) represented by an ISDN network or the Internet.
In the network construction of the conventional LAN system 10 as mentioned above, to expand the network and the connecting terminals, it is necessary to use hub apparatuses such as the apparatuses 1-1 and 1-2.
This is because in the LAN system 10, an apparatus which is connected to one port of the hub apparatus is limited to one terminal apparatus or one hub apparatus.
How a packet (namely, LAN packet data) is transmitted and processed between the terminal apparatuses will now described in the following.
The packet which is transmitted from the terminal apparatus usually includes an address, namely a transmission destination MAC (Media Access Control) address that is peculiar to the apparatus and used to identify a terminal apparatus on the transmission destination side and an address, namely transmitting source MAC address that is peculiar to the apparatus and used to identify the terminal apparatus on the transmitting source side.
When the terminal apparatus on the transmission destination side recognizes that the transmitted packet includes data referring to a value of an transmission destination MAC address, the transmission destination terminal apparatus receives the packet, so that a data transfer is executed between the terminal apparatuses.
As a hub apparatus for transmitting and processing the packet, there are mainly two kinds of apparatuses such as a non-switching hub apparatus and a switching hub apparatus.
The non-switching hub apparatus receives a packet transmitted from a terminal apparatus at one port of a plurality of ports and transmits the received packet to all of the ports other than the port (reception port) which supplied with the received packet, without referring to the MAC address included in the received packet.
To efficiently process a traffic of a network, in the switching hub apparatus, the correspondence relation between the MAC address of each terminal apparatus connected to the hub apparatus and each port is previously held in a buffer area called an address table.
A port on the transfer destination side is determined by referring to the transmission destination MAC address included in the packet transmitted from the transmitting source terminal apparatus and comparing it with the address table and the packet is transmitted only to the decided port (hereinafter, this process is called a switching process).
The data transmission to the ports other than the port concerned with the packet transmission can be prevented by the switching process.
A case where the hub apparatus 1-1 shown in FIG. 1 is a switching hub apparatus will now be considered. Even if the hub apparatus 1-1 is the switching hub apparatus, the hub apparatus 1-2 is not necessarily a switching hub apparatus.
For example, when the transmission destination MAC address in the packet transmitted from the terminal apparatus 1-3 is equal to the MAC address of the transmitting source terminal apparatus 1-3, the port (transmission port) to transmit the packet is equal to the reception port. Thus, the packet is abandoned in the switching hub apparatus 1-1.
There is a case where the packet data is transmitted from the terminal apparatus 1-4 connected to the port 1-10 of the hub apparatus 1-2 to the terminal apparatus 1-5 connected to the other port 1-11 of the hub apparatus 1-2. In the case, the transmission destination MAC address in the packet data is equal to the MAC address of the terminal apparatus 1-5.
Further, when the hub apparatus 1-2 is assumed to be a switching hub apparatus, the hub apparatus 1-2 transmits the packet only to the port 1-11 to which the terminal apparatus 1-5 is connected by the switching hub (switching process) function and does not transmit the packet to the port 1-9 connected to the hub apparatus 1-1.
In the case, when the hub apparatus 1-2 is a non-switching hub apparatus, the hub apparatus 1-2 transmits the packet to all of the ports other than the reception port by the hub function, so that the packet is also transmitted to the port 1-9.
The port 1-8 of the hub apparatus 1-1 is connected to the port 1-9 as mentioned above. In the hub apparatus 1-1 which received the packet by the port 1-8, it is recognized that the terminal apparatuses 1-4 and 1-5 are connected to the same port 1-8, and the transmission port is equal to the reception port, so that the packet is abandoned in the hub apparatus 1-1.
Now, assuming that the hub apparatus 1-1 has a function to turn back the received packet to the reception port (turnback transfer function), the hub apparatus 1-1 transmits the packet to the port 1-8.
The terminal apparatus 1-5, therefore, receives the packet which is transmitted via the hub apparatus 1-1 and the packet that is directly transmitted from the hub apparatus 1-2.
That is, the packet of the same contents is received twice and an overlap of the reception packet occurs.
It will be obviously understood that traffic of the hub apparatus 1-1 and the network which is concerned with the hub apparatus 1-1 increases.
The conventional switching hub apparatus, therefore, does not have the turnback transfer function to turn back the received packet to the reception port, and when it is recognized that the terminal apparatus having the transmitting source MAC address and the terminal apparatus having the transmission destination MAC address in the received packet are connected to the same port, the packet is abandoned in the switching hub apparatus.
FIG. 2 shows an LAN system 20 having a connecting construction such that by cascade connecting a plurality of terminal apparatuses to one port of a hub apparatus, the network and the number of connecting terminals can be expanded without adding new hub apparatuses as mentioned above.
The LAN system 20 is disclosed in JP-A-10-190714.
In FIG. 2, in a hub apparatus 2-1 of the LAN system 20, terminal apparatuses 2-2, 2-3, 2-4, . . . , and 2-5 are cascade connected to a port 2-19 and terminal apparatuses 2-6, 2-7, 2-8, . . . , and 2-9 are also likewise cascade connected to a port 2-20. A backbone network 2-10 or the like is connected to a port 2-21 in a manner similar to the LAN system 10.
Network connecting circuits 2-11, 2-12, 2-13, . . . , 2-14, 2-15, 2-16, 2-17, . . . , and 2-18 serving as interfaces with the hub apparatus 2-1 are arranged in or out of the cascade connected terminal apparatuses, respectively.
In the LAN system 20, an LAN cable 2-22 for connecting the hub apparatus 2-1 and network connecting circuit 2-11 and connecting the network connecting circuits 2-11 to 2-14 is constructed by a pair cable (2-22A and 2-22B). An LAN cable 2-23 for connecting the hub apparatus 2-1 and network connecting circuit 2-15 and connecting the network connecting circuits 2-15 to 2-18 is also likewise constructed by a pair cable (2-23A and 2-23B).
That is, the cable 2-22 is a pair cable constructed by two cables, a cable 2-22A to transmit the packet in the direction for moving, for example, from the terminal apparatus 2-2 to the hub apparatus 2-1 (direction shown by an arrow S) and a cable 2-22B to transmit the packet in the direction for moving from the hub apparatus 2-1 to the terminal apparatus 2-2 (direction shown by an arrow R). The LAN cable 2-23 is also similarly constructed by a cable 2-23A for transmission in the direction S and a cable 2-23B for transmission in the direction R.
A twisted pair cable with a shield or a twisted pair cable without a shield can be used as the pair cable.
Each of the network connecting circuits 2-11 to 2-18 is a characteristic portion of the LAN system 20. Since internal constructions of the network connecting circuits 2-11 to 2-18 can be substantially identical, a construction around the network connecting circuits 2-11 and 2-12 will now be described with reference to FIG. 3.
In FIG. 3, the network connecting circuit 2-11 has therein: an FIFO (memory of the first-in first-out type) 11-38 to store the packet in the direction of the arrow S; an FIFO 11-31 to store the packet in the direction of the arrow R; a change-over switch 11-32; and an LANC (Local Area Network Controller) 11-34. In the diagram, a central processing unit 11-35 is an information transmitting and receiving apparatus which transmits or receives data and operates on the basis of the data, and the LANC 11-34 is a circuit for controlling data transfer in the network connecting circuit 2-11.
The network connecting circuit 2-12 and its peripheral circuits also have a construction similar to that mentioned above.
In the case where, for example, the terminal apparatus 2-2 transmits a packet in the above construction, the change-over switch 11-32 in the network connecting circuit 2-11 selects an output terminal side of the LANC 11-34. The packet to be transmitted is sent to the cable 2-22A via the change-over switch 11-32 and transmitted on the cable 2-22A in the direction of the arrow S.
When the packet sent from the LANC corresponding to the cascade connected terminal apparatuses such as terminal apparatuses 2-3 to 2-5 or the like in the direction of the arrow S passes through the network connecting circuit 2-11, the packet is once stored in the FIFO 11-38 for transmission in the direction of the arrow S provided in the network connecting circuit 2-11. The reading operation, however, of the packet from the FIFO 11-38 is performed prior to the packet transmission from the terminal apparatus 2-2 via the LANC 11-34.
When the packet is read out from the FIFO 11-38, the change-over switch 11-32 connects an output terminal 11-37 of the FIFO 11-38 for transmission in the direction S to the cable 2-22A.
By the operation of the change-over switch 11-32, it is prevented that the packet transmitted from the terminal apparatus 2-2 and the packet transmitted from the terminal apparatus 2-3 or the like collide on the cable 2-22A.
The packet which is transmitted on the cable 2-22B in the direction of the arrow R is supplied to both an input terminal of the LANC 11-34 and an input terminal of the FIFO 11-31.
The LANC 11-34 progresses the receiving process with respect to only the packet to the self terminal (terminal apparatus 2-2) from a packet stream including all packets in the direction of the arrow R.
The packet supplied to the input terminal of the FIFO 11-31 for transmission in the direction R is subjected to a buffering of a predetermined amount by the FIFO 11-31 and, thereafter, sent to the cable 2-22B in the direction of the arrow R as it is, and supplied to the network connecting circuit 2-12 of the adjacent terminal apparatus 2-3.
Since each of the other network connecting circuits 2-12 to 2-18 or the like has a function similar to that of the network connecting circuit 2-11, even if they are cascade connected as shown in FIG. 2, each terminal apparatus can certainly transmit and receive a packet.
That is, the cascade connected terminal apparatuses 2-2, 2-3, 2-4, . . . , and 2-5 can transmit and receive the packet to/from the terminal apparatuses 2-6, 2-7, 2-8, . . . , and 2-9 connected to the other port 2-20 of the hub apparatus 2-1 and the terminal apparatus in the backbone network (or WAN or the like) 2-10.
Since the cascade connection between a plurality of terminal apparatuses can be realized by the LAN system 20 having the function as mentioned above, it is possible to easily cope with a new installation or addition of a terminal apparatus. As compared with the network construction of the LAN system 10 shown in FIG. 1, a greater number of terminal apparatuses can be connected to one hub apparatus.
In the network construction of the LAN system 20 in FIG. 2, however, the terminal apparatuses connected to the same cascade cannot transmit or receive the packet mutually.
That is, the packet transmitted from the terminal apparatus 2-2 is supplied to the port 2-19 in the same cascade as that of the terminal apparatus 2-2 and the hub apparatus 1-1 does not have the turnback transfer function, so that the other terminal apparatuses 2-3 to 2-5 in the same cascade cannot receive the packet.
The packet transmitted from the terminal apparatus 2-2 can be received by the terminal apparatuses arranged out of the same cascade, for example, the hub apparatuses 2-6 to 2-9 or the terminal apparatuses enclosed in the backbone network 2-10, or the like.
This point is also similarly applied to the packets transmitted from the other terminal apparatuses 2-3 to 2-5 in the same cascade and applied to another cascade, for example, a cascade having the terminal apparatuses 2-6 to 2-9.
In other words, this means that if the transmission destination MAC address of the packet transmitted from one of a plurality of terminal apparatuses in the same cascade indicates the other one of the plurality of terminal apparatuses, the packet cannot be received by any of the terminal apparatuses in the LAN system 20.
Although the problem can be solved by installing the turnback transfer function, a problem of an increase in traffic mentioned above occurs.
It is an object of the invention to provide a network system which enables transmission and reception of a packet to be performed among terminal apparatuses in the same cascade through a hub apparatus without an increase in traffic.
To solve the problem, there is provided a hub apparatus which has a plurality of ports for connecting a network portion including one or a plurality of communicating apparatuses and relays transmission and reception of a communication packet between the communicating apparatuses through those ports. The hub apparatus has port information storing means for storing, every said port, port information regarding the network portion which includes at least information indicating whether the number of communicating apparatuses which the network portion connected to each port has is equal to 1 or a plural number, and means for determining communicating forms of transmission, non-transmission, and a state of the communication packet for transmitting on the basis of the port information corresponding to the port to which the communication packet is sent.
There is provided a network system comprising: a hub apparatus; and a communicating apparatus constructing a network portion connected to each port of the hub apparatus.