1. Field of the Invention
This invention relates to a node device for use in the token ring LAN (Local Area Network) of the FDDI (Fiber Distributed Data Interface).
2. Related Background Art
The FDDI token ring LAN is a 100-Mbps (Megabit per second) data rate LAN based on the use of a optical fiber and the LAN is being standardized by ANSI (American National Standards Institution)/X3T9.5. The token ring LAN has the following characteristics. In this LAN, a data path, along which is transmitted a packet of data containing, for example, one or a plurality of frames in one direction, interconnects a plurality of nodes in a ring. Each node obtains a priority of transmitting along the data path by capturing a token rotating along the data path. And each node loses the priority by issuing the token when it finishes transmitting a packet. The node erases the packet when it finds the source address(sender) it receives agrees with its own address, without relaying (hereinafter "relay" means to receive and transmit a packet without erasing.) the packet to a next node.
Recently, a plurality of networks are sometimes connected to one another, and in these cases, when the FDDI LAN is used as it is, the following problems take place.
When a packet come from other network such as ethernet or others is transmitted by a concentrator node to the FDDI LAN, since the packet has a node address of the other network as its source address, the concentrator node of the FDDI LAN has no means for identifying a packet which has made one round trip along the data path ring. Thus, it has been impossible to connect different types of networks to the FDDI LAN as it is.
An object of this invention is to provide a node device which is able to function properly as a node of the FDDI LAN.
Another object of this invention is to provide a node device which, in the case a plurality of network are connected to one another, is able to relay correctly a packet from one network to another.