Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-01-14
2001-09-25
Pascal, Leslie (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C370S222000, C370S223000, C370S224000
Reexamination Certificate
active
06295146
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical ring networks.
2. Related Art
A self-healing optical ring network has three or more ring elements (also called nodes) connected in a logical loop. Each ring element is connected to two other ring elements by working fiber and spare fibers (also called channels). When wavelength division multiplexing (WDM) is used a working channel and a spare channel can be carried on one or more fibers. A working channel carries traffic between ring elements during a normal mode of operation. A spare channel also carries traffic between ring elements, but a spare channel only does so when one of the working channels in the ring experiences a failure.
Ring elements can include an add/drop multiplexer (ADM). An ADM can pass traffic between the ring network and other equipment such as an electrical broadband digital crossconnect switch (DXC) and line terminal equipment.
In a typical opto-electronic Synchronous Optical Network (SONET) ring network, an ADM includes a failure detection unit that detects when a channel failure has occurred. For example, an ADM detection unit will detect a channel failure if it senses a loss of signal condition. In response to detecting a failure, the ADM sends a failure indication (also known as an alarm indication) to a central network management system, and the ADM switches traffic onto a spare channel using loopback to provide ring restoration.
FIG. 1A
illustrates an example self-healing optical ring network having four ring elements
102
,
104
,
106
, and
108
. In normal mode, the working channels
110
,
112
,
114
, and
116
carry data around the ring in a single direction and the spare channels
118
,
120
,
122
, and
124
are idle. When a failure occurs in a ring configuration, the spare channels not affected by the failure are activated and route the traffic around the fault in the opposite direction.
FIG. 1B
illustrates the operation of a self-healing optical ring when working channel
110
, which is designed to carry traffic between ring element A and ring element B, experiences a failure. After ring element A detects a failure in working channel
110
, ring element A switches traffic arriving on working channel
116
onto spare channel
124
in the opposite direction of the traffic flow on working channel
116
. Similarly, after ring element B detects a failure in working channel
110
, ring element B switches traffic arriving on spare channel
120
onto working channel
112
in the opposite direction of the traffic flow on spare channel
120
. In this manner, the ring self-heals upon sensing a break in the ring.
While a present-day opto-electronic SONET ring design has the advantages of simplicity and fast switching speed, it has the drawback of an inefficient spare to working capacity ratio. The spare to working capacity ratio is the ratio of the number of spare channels to the number of working channels. In opto-electronic SONET ring networks the spare to working capacity ratio is 1:1. That is, for each working channel there must be a corresponding spare channel.
A self-healing optical network is needed that retains the speed and simplicity of a self-healing SONET ring network while providing more efficient use of spare channels.
SUMMARY OF THE INVENTION
The present invention provides a self-healing optical network that retains the speed and simplicity of a self-healing optical ring network while providing more efficient use of spare channels by having two or more optical ring networks share a spare channel, thereby decreasing the spare to working capacity ratio.
According to the present invention a first optical switching unit (OSU) is optically coupled to a first ring element of a first optical ring network, and is optically coupled to a first ring element of a second optical ring network. A second OSU is optically coupled to a second ring element of the first optical ring network, and is optically coupled to a second ring element of the second optical ring network. The first OSU and second OSU are optically coupled by a spare channel that is to be shared by the first and second optical ring networks. The first OSU optically couples either the first ring element of the first optical ring network or the first ring element of the second optical ring network to the spare channel. The second OSU optically couples either the second ring element of the first optical ring network or the second ring element of the second optical ring network to the spare channel. In this manner the spare channel can be shared among two or more optical ring networks.
Additionally, according to the present invention, the first ring element of the first optical ring network and the first ring element of the second optical ring network each send messages to the first OSU. The second ring element of the first optical ring network and the second ring element of the second optical ring network each send messages to the second OSU.
In a first embodiment of the present invention, the first ring element and second ring element of the first optical ring network, upon sensing a failure within the first optical ring network, send a data message indicating the failure to the first OSU and second OSU, respectively. Similarly, the first ring element and second ring element of the second optical ring network, upon sensing a failure within the second optical ring network, send a data message indicating the failure to the first OSU and second OSU, respectively. Upon receiving a failure indication from a ring element, the first OSU optically couples that ring element to the spare channel if that ring element is not using the spare channel as a result of a failure event. Similarly, the second OSU, upon receiving a failure indication from a ring element, optically couples that ring element to the spare channel. Consequently, when a failure occurs in the first optical ring network, the spare channel will be available to the first ring, and when a failure occurs in the second optical ring network, the spare channel will be available to the second ring.
In an alternative embodiment of the present invention, the first OSU transmits a status message to each ring element optically coupled to the first OSU. The second OSU transmits a status message to each ring element optically coupled to the second OSU. A ring element optically coupled to the first OSU will transmit a data message containing a switch command to the first OSU if the ring element is not using the spare channel and the ring element senses a failure. Similarly, a ring element optically coupled to the second OSU will transmit a data message containing a switch command to the second OSU if the ring element is not optically coupled to the spare channel and the ring element senses a failure. Upon receiving a switch command, the first and second OSU optically couple the ring element that sent the switch command to the spare channel.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
REFERENCES:
patent: 5406401 (1995-04-01), Kremer
patent: 5442623 (1995-08-01), Wu
patent: 5717796 (1998-02-01), Clendening
patent: 5731867 (1998-03-01), Fee
patent: 5870212 (1999-02-01), Nathan et al.
Fee John A.
Nathan Sridhar
MCI Communications Corporation
Pascal Leslie
Sedighian M. R.
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