Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-07-01
2003-11-04
Swarthout, Brent A. (Department: 2632)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06643041
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical network. Particularly, the present invention relates to an optical network using a wavelength-division multiplexing transmission system or a time-division multiplexing transmission system.
2. Description of the Related Art
In order to improve the reliability of circuit service, a network has recently been proposed which is capable of healing a signal of a failure developed in an optical network. The circuit failure includes an unintentional cutoff of a transmission line, signal degradation, repeater's trouble, etc. This type of optical network is normally designed so as to automatically detect the circuit failure and automatically perform switching between transmission lines. Such an optical network is called “survival network”.
There is also provided a survival network capable of performing switching to an SDH system or a SONET system corresponding to a synchronous network in particular to improve the healing capability of such a transmission network. The SDH system is an abbreviation of the Synchronous Digital Hierarchy System. Further, the SONET system is short for the Synchronous Optical Network.
As examples of its use, there are known (1) a 1:N type NPS (Nested Protection Switching) system which performs switching between a plurality of working lines and a plurality of protection lines, (2) a
4
Fiber type BLSR (Bidirectional Line Switching Ring) system connected in a ring form by working lines and protection lines, etc.
The former example is described in, for example, Fiber Network Service Survivability, 1992 Artech House, INC,and T1X1.5/90-132. The latter example is described in Bellcore SONET BLSR Genertic Criteria GR-1230-CORE, 1993.
FIG. 2
is a diagram for describing the 1:N type NPS system. In
FIG. 2
, reference numerals
101
through
104
indicate transmission equipment respectively. Working lines
105
through
108
indicate bidirectional lines respectively. The bidirectional lines described herein are formed by two optical fibers. In
FIG. 2
, the bidirectional lines are shown by arrows indicated by bidirectional solid lines corresponding to respective one reference numerals.
The example shown in
FIG. 2
has the following connections. The working line
105
is connected to terminating equipment
112
lying in the transmission equipment
101
and an add-drop multiplexer (branch-insertion equipment) lying in the transmission equipment
102
. The line is connected to the terminating equipment or add-drop multiplexer by using an optical transmitter on the transmitting side and using an optical receiver on the receiving side. Further, the working line
105
is connected to the working line
106
through the add-drop multiplexer lying in the transmission equipment
102
. The working line
107
is connected to the transmission equipment
102
and terminating equipment lying in the transmission equipment
104
. The working line
107
is relayed by the transmission equipment
103
. Reference numeral
113
indicates a repeater. Namely, the transmission equipment
103
does not have the ability to switch the bidirectional line
107
to a protection line. On the other hand, protection lines
109
through
111
are indicated by dotted lines in
FIG. 2
respectively. The protection lines
109
through
111
connect all the transmission equipment
101
through
104
to one another through the use of the add-drop multiplexers within the respective transmission equipment. The respective transmission equipment have the ability to switch the working lines to the protection lines, respectively.
An example of switching to be done by the NPS system will next be described. A description will be made of how to perform switching when a failure occurs in the bidirectional line
107
, for instance. Since the bidirectional line
107
is terminated by the transmission equipment
102
and the transmission equipment
104
, these transmission equipment respectively have the ability to perform line switching. Therefore, when the failure occurs in the bidirectional line
107
, the transmission of a signal is done using the protection line
110
and the protection line
111
. The 1:N type NPS system shown in
FIG. 2
lays or strings the working lines according to the capacity of a traffic (main signal) and can select the corresponding add-drop multiplexer or repeater within each transmission equipment.
FIG. 3
is a diagram for describing the
4
Fiber type BLSR system. In
FIG. 3
, reference numerals
201
through
204
indicate transmission equipment respectively. Working lines
221
through
224
and protection lines
211
through
214
are respectively connected to one another in a ring form through add-drop multiplexers within the transmission equipment. The respective transmission equipment have the ability to switch the working lines to the protection lines, respectively.
A description will be made of a basic operation of the
4
Fiber type BLSR system, which is related to line switching for a circuit failure. When a failure occurs in the working line
221
in
FIG. 3
, the transmission equipment
201
and
202
perform bidirectional line switching and thereby heals a signal through the use of the protection line
211
. When failures occur in both the working line
221
and the protection line
211
, i.e., failures such as a cable cut, etc. occur, a diverse route characterized by the ring type network is utilized. Namely, the 4Fiber type BLSR system performs line switching by means of the transmission equipment
201
and
202
to thereby allow the healing of a signal through the use of the protection lines
212
through
214
. The method of healing the signal by the ring type in this way is characterized in that two clockwise and counterclockwise routes can be selected. The present 4Fiber BLSR system is provided by GR-1230-CORE.
SUMMARY OF THE INVENTION
The conventional survival network performs line switching to heal a traffic with a view toward healing failures such as a cable cut, cutting-off of an optical fiber and a breakdown in optical transmit-receive unit, etc.
However, the above-described 1:N NPS system needs an optical fiber according to the demand for traffics. However, when the number of optical fibers is insufficient, the system needs to additionally increase optical fibers between transmission equipment and thereby involves great installation cost.
The above-described BLSR system has the following drawbacks. Since the BLSR is of a 1:1 system, protection lines corresponding to transmission capacity of working lines must be installed. Accordingly, the capacity of the maximum traffic, which is necessary for an optical span, results in the total capacity of the ring. When only a traffic between the transmission equipment
201
and
202
takes the maximum capacitance value in the network in
FIG. 3
, for example, the entire ring must be set to the maximum capacitance value as well as to the maximum capacitance value of the working line
221
. Namely, as the traffic concentrates on a given span in the ring, a problem occurs in use efficiency and economy.
Since the survival network needs the optical fibers corresponding to the transmission capacity due to fueling of an additional demand as described above, the cost of increasing the optical fibers and the efficiency of use of each optical fiber turn into problems.
The invention of the present application has been made to solve the above-described various problems.
A first object of the invention of the present application is to provide an optical network capable of flexibly selecting protection optical paths upon the occurrence of a failure without depending on the form of installation of an optical transmission line, e.g., an optical fiber.
A second object of the invention of the present application is to improve the efficiency of use of an optical transmission line, e.g., an optical fiber employed in an optical network.
A summary of a basic form of the invention of the present application will be briefly described. Summaries of
Ikeda Hiroki
Kanetake Tatsuo
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Swarthout Brent A.
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