Optical communications – Fault recovery
Reexamination Certificate
2000-09-27
2004-03-16
Ngo, Hung N. (Department: 2633)
Optical communications
Fault recovery
C398S009000, C398S017000, C398S051000, C398S079000
Reexamination Certificate
active
06708000
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a photonic node, photonic nodes for transmission and reception, and a method of restoring traffic upon occurrence of link failure in optical path network, which are suitable for use in a technology for accommodating an IP packet in a wavelength division multiplexing optical signal and subjecting to a cross-connection for carrying out routing.
(2) Description of Related Art
Recently, owing to a rapid deployment of the internet, the size of traffic running through the transmission network using an IP (Internet Protocol) is progressively increased. For this reason, a technology of IP over WDM (Wavelength Division Multiplexing) system using the wavelength division multiplexing scheme comes to be introduced as a technology for effectively processing the traffic which requires an exchanger having a great amount of exchanging capability.
The IP over WDM system is a system for subjecting a packet to a cross-connection operation to carry out routing. When a packet is subjected to the cross-connection operation, an information of cross-connect is utilized. When an optical signal is subjected to transmission through an optical transmitting network in which a plurality of photonic IP nodes are connected to one another, the optical signal is transmitted depending on the information of cross-connect indicating a photonic IP node as a source and a photonic IP node as a destination. Therefore, the information of cross-connect also indicates whether or not the optical signal under transmission shall be dropped at a node or transmitted through the node without being dropped. The term “photonic IP node” means an optical transmission node in the following description.
In more concretely, when an IP packet is subjected to a routing between two photonic IP nodes of the optical transmission network, initially, one of the photonic IP nodes assigns the IP packet to be routed to a particular wavelength of a wavelength division multiplexing optical signal in accordance with the IP address (destination address). Thus, the IP packet is once converted into an optical signal. Then, the wavelength division multiplexing optical signal made up with a plurality of optical signals each of which is assigned to the IP packet depending on each IP address, is transmitted through an optical transmission path and received by another photonic IP node. In this photonic IP node, only the particular IP packet is extracted from the wavelength division multiplexing optical signal. Thus, the IP packet is routed.
When the technology of IP over WDM system is introduced, even if the IP packet has a variety of addresses, or alternatively, a number of IP packets to be transmitted are created in a burst fashion, each of the photonic IP nodes can cope with the IP packets independently. Thus, the optical transmission network can deal with a great traffic which requires an exchanger to have a large exchanging capability.
Further, in order to utilize the wavelengths for optical signals more effectively, there is proposed a system in which the IP packets are accommodated into an optical signal of the same wavelength depending on the IP address or QoS (Quality of Service). According to the system, each of the photonic IP nodes carries out not only simple routing operation but operation of switching on the transmission paths of an optical signal deriving from the IP packet or operation of switching on the wavelength of the optical signal deriving from the IP packet upon carrying out routing. In this case, the terms “to accommodate IP packet” means “to convert the IP packet into an optical signal”. The terms will be utilized as the same meaning in the following description. Also, the term “switching on IP packet” is sometimes referred to as “IP packet switching”. In addition, in the following description, a transmission path is sometimes referred to as an optical path.
When an optical signal is received by a photonic IP node, the photonic IP node examines the destination address of the received optical signal. If the optical signal is one that is to be dropped at the photonic IP node, the photonic IP node extracts the IP packet to be dropped from the optical signal. The rest of the optical signal is returned to an optical path switching which corresponds to the layer
1
and then subjected to an IP packet switching which corresponds to the layer
2
. In this manner, IP packet can undergo a routing operation with the aid of optical add/drop function.
FIG. 23
is a diagram schematically showing the optical add/drop function. A photonic IP node shown in
FIG. 23
has input ports
1
,
2
and output ports
3
,
4
. A wavelength division multiplexing optical signal composed of a plurality of optical signals having different wavelengths is supplied to the input port
1
whereas an IP packet of another node destination (destination of another photonic IP node) is supplied to the input port
2
. This IP packet is subjected to a photoelectric conversion and a resultant signal is generated from the output port
3
. In this case, of the plurality of optical signal which is supplied from the outside at the input port
1
and multiplexed in a wavelength division manner, an optical signal with a destination of this node is branched and dropped at the output port
4
. On the other hand, of the plurality of optical signals which is multiplexed in a wavelength division manner, an optical signal with a destination of another node is passed through the output port
3
and added together with the optical signal which is supplied at the input port
2
and photoelectric converted. The optical signal resulting from the add-operation is transmitted to another node.
FIG. 24
is a physical arrangement of the photonic IP node. The photonic IP node
81
shown in
FIG. 24
has input transmission paths
81
a,
81
b,
output transmission paths
81
d,
81
e,
an optical cross-connect apparatus
81
c,
an ATM exchanger
81
f,
routers (access router)
81
g,
81
h,
81
i.
IP packets are supplied to the node at the routers
81
g,
81
h,
81
i,
and each of the IP packets is assigned to an optical signal of a wavelength corresponding to the IP address. In this way, a plurality of optical signals are transmitted from the left side of
FIG. 24
to the right side of the same. The plurality of optical signals is supplied to the node at the input transmission paths
81
a,
81
b.
At the optical cross-connect apparatus
81
c,
of the plurality of optical signals which are multiplexed in a wavelength division manner, an optical signal with a destination of this node is dropped as a signal with a destination of this node. Rest of the optical signals are regarded as those with another node destination, and hence multiplexed together with the added IP packet and transmitted to other node from a desired one of the output transmission paths
81
d,
81
e
which is selected in accordance with the wavelength.
The ATM exchanger
81
f
is a unit for classifying the IP packets supplied from a plurality of photonic IP nodes and bundle the same depending on the IP address. Thus, the ATM exchanger
81
f
can be regarded as an electric switch for switching IP packets as an electric signal. The ATM exchanger
81
f
is provided, at the side of the optical cross-connect apparatus
81
c,
with switching elements for superimposing the assigned IP packet on an optical signal of a predetermined wavelength depending on the IP address and generate the same therefrom. When the ATM exchanger
81
f
functions with the switching element, the unit can serve as a packet switch unit.
The optical cross-connect apparatus
81
c
transfers IP packets contained in the optical signal with a destination of the own node to the ATM exchanger
81
f.
The optical cross-connect apparatus
81
c
also generates an optical signal supplied from the ATM exchanger
81
f
to another photonic node. Further, the optical cross-connect apparatus
81
c
transfers an optical signal of which address is not own node, to the adjacent node. Thus, the
Kuroyanagi Satoshi
Nishi Tetsuya
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Ngo Hung N.
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