Multiplex communications – Duplex
Reexamination Certificate
1996-05-24
2002-06-04
Zimmerman, Brian (Department: 2635)
Multiplex communications
Duplex
C370S241000, C714S717000
Reexamination Certificate
active
06400694
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention generally relates to a duplex communication path switching system, and more particularly to a duplex communication path switching system applicable to a ring network which can effectively switch a duplex communication path for data transmitted at any speed.
(2) Description of the Related Art
In a ring network, a communication path is duplicated in order to improve reliability of communication. That is, a clockwise transmission line and a counterclockwise transmission line link respective nodes together, at which nodes terminals are accommodated. A direction in which data is transmitted through the clockwise transmission line is opposite to a direction in which data is transmitted through the counterclockwise transmission line. At each node, signals from terminals are supplied to both the clockwise transmission line and the counterclockwise transmission line so as to be transmitted through both the transmission lines in opposite directions. At a node accommodating destination terminals, normal signals are selected from among signals received from the clockwise transmission line and the counterclockwise transmission line. The above communication system is referred to as a transmission-hybrid/receive-selecting system. At a receiver-side node, to select the normal signals, the communication path is switched from the clockwise transmission line to the counterclockwise transmission line or from the counterclockwise transmission line to the clockwise transmission line. A system for switching the communication path between the clockwise transmission line and the counterclockwise transmission line is referred to as a duplex communication path switching system.
FIG. 1
shows an example of the ring network. Referring to
FIG. 1
, the ring network has a clockwise transmission line L
R
and a counterclockwise transmission line L
L
which link nodes A, B, C and D. For example, at the node A, a signal received from a terminal
100
is supplied to both the clockwise transmission line L
R
and the counterclockwise transmission line L
L
via a hybrid connector
101
. The communication path is switched by use of a selective connector
102
between the clockwise transmission line and the counterclockwise transmission line so that a normal signal is selected, as a signal to be received by the terminal
100
, from among signals transmitted through the transmission lines L
L
and L
R.
At the node B, in the same manner as at the node A, a signal received from a terminal
200
is supplied to the clockwise transmission line L
R
and the counterclockwise transmission line L
L
via a hybrid connector
201
, and the switching operation between the clockwise transmission line L
R
and the counterclockwise transmission line L
L
is performed by use of a selective connector
202
so that a normal signal is selected as a signal to be received by the terminal
200
from among signals transmitted through both the transmission lines L
R
and L
L
. The other nodes C and D have the same structure as the nodes A and B described above.
In order to determine which received signal is to be selected as the normal signal from the clockwise transmission line or from the counterclockwise transmission line, a frame signal added to the received signal or error checking information is checked. This checking operation is performed for every unit of transmission signal (this unit is referred to as a switched-signal unit).
In a case of the conventional PDH (Presynchronous Digital Hierarchy), a Handling Group (HG) of 64 kbps×6, a unit of 1.5 Mbps or a unit of 6.3 Mbps is used as the switched-signal unit. In a case of the SDH (Synchronous Digital Hierarchy), a unit of multiplexed signals, such as VC
1
or VC
22
, is used as the switched-signal unit.
At each node, signals from a plurality of terminals are multiplexed. To multiplex the signals, circuits (e.g., multiplexers) for multiplexing the signals are hierarchically coupled to each other. Circuits in the lowest hierarchy are coupled to the respective terminals and output signals each corresponding to the switched-signal unit. A circuit in the highest hierarchy is coupled to the communication path (both the clockwise transmission line and the counterclockwise transmission line). Each of the circuits is duplicated to improve the reliability. If an error is detected in a multiplex signal in a circuit, an alert signal is supplied to circuits in lower side hierarchies so that the circuits in the lower side hierarchies are respectively switched to other circuits. If an error is detected in a signal in a circuit in the lowest hierarchy, only the circuit in which the error has occurred is switched to another circuit.
Meanwhile, when the communication path is switched between the clockwise transmission line and the counterclockwise transmission line in a receiving-side node, an accurate communication signal must be obtained in the receiving-side node. Thus, in the conventional duplex communication path switching system, a transmission speed in the communication path between nodes is limited to the speed (bps:bits per second) of the switched-signal unit of the signal.
There are two kinds of switching logic, 0/1-system switching logic and N(normal)/E(emergency)-system switching logic.
In the 0/1-system switching logic, one of a 0-system and a 1-system is selected as a normal system. For example, the 0-system is selected as the normal system. When the 0-system malfunctions, the 0-system is switched to the 1-system. After this, the 1-system is continuously selected as the normal system although the 0-system is recovered. In the N/E-switching logic, an N-system is usually selected as the normal system. When the N-system malfunctions, the N-system is switched to the E-system. After this, if the N-system is recovered, the E-system is switched back to the N-system.
The communication path may be switched between the clockwise transmission line and the counterclockwise transmission line in accordance with the 0/1-system switching logic. In this case, the clockwise transmission line and the counterclockwise transmission line are used as the 0-system and the 1-system flexibly. As a result, if a signal in a line with a transmission speed corresponding to a plurality of switched-signal units is transmitted through the communication path, switched-signal units from the 0-system and the 1-system may be arranged at random in a received signal.
The communication path may be switched between the clockwise transmission line and the counterclockwise transmission line in accordance with the N/E-system switching logic. In this case, the clockwise transmission line and the counterclockwise transmission line are used as the N-system and the E-system fixedly. As a result, when the N-system malfunctions and is then recovered, switched-signal units from the N-system and the E-system are mixed in a received signal.
A delay time in the clockwise transmission line between nodes differs from a delay time in the counterclockwise transmission line between the nodes. Therefore, a received signal in which switched-signal units from the clockwise transmission line and the counterclockwise transmission line are mixed may be incorrect. That is, communication between terminals accommodated at different nodes coupled to the clockwise transmission line and the counterclockwise transmission line may be not accurately performed.
For example, in a case where the HG (the Handling Group in the PDH) is used as the switched-signal unit, a communication path having a speed greater than 384 (64×6) Kbps corresponding to the HG cannot be formed in the ring network. However, in recent years, a data communication speed is improved, and it is desired that a communication path in which switched-signal units corresponding to various speeds (from a low speed to a high speed) are formed.
SUMMARY OF THE INVENTION
Accordingly, a general object of the present invention is to provide a novel and useful duplex communication path switching system in which the d
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Zimmerman Brian
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