Multiplex communications – Wide area network – Packet switching
Patent
1997-10-14
1998-12-01
Luu, Le Hien
Multiplex communications
Wide area network
Packet switching
39520057, 39520072, 370351, 370355, 370392, 370401, G06F 1300
Patent
active
058450866
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process and a system for addressing stations in a network which contains two or more segments.
BACKGROUND INFORMATION
The transfer protocol of PROFIBUS, capable of being connected to a network consisting of a plurality of segments, is described in DIN 19245, Part 1. Network junctions connecting the segments are provided between the individual segments to enable stations of different segments to communicate. In order to address the receiving station, messages contain path information providing at least the address of the receiving station. At this address, the receiving station identifies a message addressed to it. The address can be an individual address for addressing a single station or a collective address for addressing several or all members in the system. Each station has an individual address, which is unique to the particular segment to which the station is connected.
German Published Patent Application No. 40 00673 Express Mail No.: EM 271950450 US describes inputting the station address of the receiving station, which is valid in that station's segment, as well as the segment addresses of the segments through which the message is to be forwarded. According to this related art, a transmitting station wishing to communicate with a receiving station must have the required information concerning the full message path saved in a storage device and insert this information in the message. For each message, network junctions must check whether the segment numbers contained in the path information agree with the numbers of the segments they connect and, if so, forward the message. The disadvantage of this related art is that the number of segment addresses in the path information increases in the case of large networks according to the number of segments involved in the transmission, and therefore the useful data length to total message length ratio decreases. Furthermore, considerable storage space is required for storing the extensive path information for all station links in each station. To remedy this problem, the aforementioned document proposes including only the station address and station segment number in the path information when addressing a receiving station. The network junctions then carry a list of segments that can be reached through them and only forward a message if the number of a reachable segment is contained in the path information. While this process reduces the amount of data required for the path information of the messages, problems may arise if the network structure changes or a receiving station is moved to another segment.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for addressing stations in a network consisting of at least two segments, wherein a favorable useful data length to total message length ratio is achieved and wherein the segment number of a receiving station does not need to be transmitted even for messages transmitted over a plurality of segments, as well as a device suitable for carrying out the process.
According to the present invention, a message intended for a station in another segment is addressed by the transmitter of the message to the corresponding network junction connected to the same segment with a station link identifier for the network junction. The network junction can then determine the address to which the message is to be forwarded through the station link identifier with the help of the information stored in the network junction and it can forward the message. If another network junction is located in the path, it is addressed, i.e., the same principle is used again. The message is then provided with the new destination address in the network junctions and transmitted to the next network junction or from the last network junction to the receiving station.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a network with three segments, in accordance with the present invention.
FIGS. 2 shows the possible station links for a network junction,
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Buehler Reiner
Doebrich Udo
Aktiengesellschaft Siemens
Luu Le Hien
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