Communications: electrical – Continuously variable indicating – With meter reading
Patent
1991-01-31
1994-06-21
Yusko, Donald J.
Communications: electrical
Continuously variable indicating
With meter reading
34082516, 370 8513, H04L 100
Patent
active
053231449
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to duplexing of a bus type network.
BACKGROUND ART
Hitherto, LANs (local area networks) with a bus type structure using coaxial cables, such as CSMA/CD (IEEE 802.3) type LANs and token bus (IEEE 802.4) type LANs, have been widely used. Recently, bus type networks using optical fibers and optical star couplers as transmission media have been studied.
These bus type LANs are characterized, like a ring type LAN, by freedom from the possibility that turning off the power supply of a node station may exert an influence on the total system. The bus type LANs, however, have the drawback that the total system runs down or the system must be stopped when the transmission line is broken or at the time of providing an additional station. In the ring type LAN, on the other hand, duplexing the transmission line and providing a loopback function will prevent the system from running down upon breakage of the transmission line at one place.
Concerning a bus type network, therefore, attempts have been made to duplex the transmission line and modem portions so that normal operation of the system will be secured even upon breakage of the transmission line or failure in a modem.
FIG. 8 shows a conventional duplexed structure in a bus type LAN which employs coaxial cables. Modems 11A, 11B, 11C and modems 21A, 21B, 21C are connected to a main transmission line 10 and a stand-by transmission line 20 through branching devices 13 and 23 and node stations 3A, 3B and 3C can selectively connect themselves to either the main transmission line 10 or the stand-by transmission line 20 by their own switches 4B, 4B and 4C, respectively. Designated by numerals 12 and 22 are terminating resistors, each of which has an impedance equal to the characteristic impedance of the transmission line.
FIG. 9 shows a duplexed structure in a broadband bus type network. A main transmission line 10 and a stand-by transmission line 20 are terminated on one end side thereof respectively by terminating resistors 12 and 22, each having an impedance equal to the characteristic impedance of the transmission line. Head end remodulators 41 and 42 are provided at the other ends of the transmission lines, and two-way amplifiers 43 and 44 are provided at intermediate points of the transmission lines.
Normally, node stations 3A to 3C are connected to main modems 11A to 11C through switches 4A to 4C thereof and perform data transmission using the main transmission line 10. That is, in normal state, data output from a data terminal of one of the node stations 3A, 3B and 3C, for instance, the node station 3A is transmitted through the main modem 11A and the main transmission line 10 to the other node stations 3B and 3C.
In FIGS. 8 and 9, if a certain mode, e.g., 11A fails, the respective switches 4A, 4B and 4C at the stations are simultaneously set to the dotted line side to resume the data transmission through the modems 212A, 21B and 21C and the stand-by transmission line 20.
When the main transmission line 10 is broken, for instance, between the modem 11A and the modem 11B as indicated by the mark "X" in FIG. 8, the switches 4A to 4C are changed over to connect the stations 3A-3C to the stand-by modems 21A-21C, whereby data transmission can be performed by use of the stand-by transmission line 20.
FIG. 10 shows a duplexed bus type LAN using optical fibers and optical star couplers as transmission media. A main transmission line 10 and a stand-by transmission line 20 are constructed by use of optical fiber cables 10a, 20a and star couplers 10b, 20b, and duplexed by providing modems 11A, 11B, 11C and modems 21A, 21B, 21C. Switching between the main and the stand-by system is performed by switches 4A, 4B and 4C.
The switching is carried out in the same manner as in the bus type LANs of FIGS. 8 and 9, that is, in the following manner.
In normal state, data output from a data terminal of one of the node stations 3A, 3B and 3C, for example, the node 3A is sent through the main modem 11A into the main star coupler 10a. In the
REFERENCES:
patent: 4748560 (1988-05-01), Kataoka
patent: 4977557 (1990-12-01), Phung et al.
Aoki Teruaki
Imai Mitsuo
Imai Yasumasa
Suzuki Yasuo
Giust John
Hitachi Cable Limited
Yusko Donald J.
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