Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-02-08
2003-05-06
Negash, Kinfe-Michael (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S108000, C370S392000
Reexamination Certificate
active
06559989
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to an optical packet header, and more particularly to an apparatus for processing an optical packet header in an optical manner in an optical communication switching field.
BACKGROUND OF THE INVENTION
Communication techniques may generally be classified into a transmission field and a switching field. Up to the present, the transmission field has made startling progress on the basis of the developments of a wavelength division multiple accessing (WDMA) technique and an electrical time division multiplexing (ETDM) technique to meet a rapid increase in demand for communication resulting from the influence of the Internet. With the developments of various optical techniques based on the advent of fiber optics, the transmission field has made another technical development that can advance an optical signal from an ingress node to an egress node with no optical/electric conversion.
The transmission field has been developed centering around an optical signal according to the spread of fiber-optic techniques as mentioned above, but the switching field is not so. In other words, the switching field has still employed such a conventional technique that converts an optical signal into an electrical signal to be switched and reconverts the switched electrical signal into the optical signal, resulting in a bottleneck degrading the overall communication rate.
Hence, an optical transparency must be secured in the switching field so that an electrical signal can be converted into an optical signal and the converted optical signal can be switched directly with no optical/electric conversion. On the other hand, the optical transparency can be secured on the basis of an optical packet switching technology, which has been studied in various ways for practical use. An optical packet header processing technique is one of several problems to be solved for the implementation of the optical packet switching technology.
However, although a variety of optical packet header processing techniques have been proposed up to now, they have not been put to practical use because they involve many problems in spite of their respective advantages.
Conventional optical switching techniques will hereinafter be described briefly.
FIG. 1
shows the construction of a conventional optical switch
10
, which is operated in response to an electrical signal. Optical signals are inputted to respective input ports and then converted into electrical signals by respective optical/electric converters
11
. Each of the electrical signals is stored in a packet unit into an electrical signal storage unit
12
in an appropriate manner. A head processor
13
decodes information in a header of each packet in an electric/electronic manner. A switch
14
analyzes a path of each packet using the header information and determines an output port of each packet in accordance with the analyzed result. Upon determining the output port, the switch
14
switches the corresponding packet to an output memory stack associated with the determined output port. Each output memory stack is implemented in a first in first out (FIFO) manner. As a result, each output memory stack outputs an earlier input signal, which is then converted into an optical signal by an associated electric/optical (E/O) converter
15
.
FIG. 2
is a view illustrating the concept of a conventional optical packet switch
20
. Each optical signal is inputted to an input port and then optically split into two optical signals by a beam splitter
21
. The split optical signals are stored into an optical signal storage unit
22
and further transferred to a header processor
23
, which decodes information in a header of each packet. Upon determining an output port of an optical packet as a result of the analysis, the header processor
23
operates an optical switch
24
to output the optical packet through the determined output port. At this time, the output optical packet is continuously maintained in an optical signal form through the entire construction of the optical packet switch
20
without being subjected to either optical/electric conversion or electric/optical conversion.
In such an optical packet switching field, the header processing is one of important technical elements and has been proposed in various manners. In
FIG. 2
, the header processor
23
is compelled to perform optical/electric conversion because the optical switch
24
processes an optical signal under an electrical control.
Such optical header processing techniques may greatly be classified into two methods, or the former performing optical/electric conversion and electrically processing the resultant signal and the latter optically processing a given signal and performing the optical/electric conversion with respect to the resultant signal. These methods have their respective merits and demerits, but such a common feature that they should store an optical packet in the form of an optical signal while processing its header. An optical path with a predetermined length, based on the uniformity in light velocity, is used for the storage of the optical signal, and the optical header must be processed rapidly within a given time.
An approach to the former method, or the optical header processing method which first performs the optical/electric conversion and then the electrical process, has been proposed by KEOPS [see: Guillemot, C., et al., “Transparent Optical Packet Switching: The European ACTS KEOPS Project Approach”, IEEE J. Lightwave Technology, vol. 16, No. 12, December 1998]. The overall length of an optical packet is 1646 nsec, which corresponds to 128 bytes at 622 Mbps. In the optical packet, a payload has a length of 1350 nsec and a header has a length of 14 bytes. The payload is subjected in rate to no particular restriction from several hundred Mbps up to 10 Gbps, but the header is fixed in rate to 155 Mbps. A synchronization pattern is appended to a head of the header for the processing of the header. A transmitted optical packet is optically radiated by a 1×2 coupler and then subjected to optical/electric conversion. Subsequently, a clock is recovered from a header of the optical packet according to a synchronization pattern of the header and the contents of the header are decoded synchronously with the recovered clock. An address and other information can be written in the header as in a typical electrical method and thus be electrically restored. As a result, a sufficiently large amount of information can be secured, thereby enabling the general optical switch to be operated as shown in FIG.
2
.
On the other hand, there have been proposed various methods of processing optical packet headers in an optical manner, as will hereinafter be mentioned. One method is a keyword method [see: Cotter, D., et al., “Self-routing of 100 Gbps packets using 6 bit ‘keyword’ address recognition”, IEEE Electronics Letters, vol. 31, No. 25, Dec. 7, 1995]. Each node in this keyword method is an add-drop node
30
as shown in FIG.
3
. An n-bit header is created on the basis of n/2−n codes. A unique address is assigned to each node, which comprises a 2×2 optical switch
34
for decoding a header of each input packet and determining whether to pass or drop each packet.
A header processor
33
acts to perform the header decoding operation, and an optical AND operation is used for the header decoding of the header processor
33
. Namely, if one optical packet arrives at a specific node, then this node optically produces a complement address to a self address synchronized with a header of the optical packet. Thereafter, the specific node performs an optical AND operation for the optical packet header and the produced complement address, sequentially one bit by one bit.
At this time, provided that the header of the arrived optical packet has the same destination address as the self address of the specific node, the header address and the complement address of the node will have respective bit values opposite to each other. I
Chung Hee Sang
Kim Kwang Joon
Lee Jong Hyun
Lee Sung Un
Youn Ji Wook
Electronics and Telecommunications Research Institute
Negash Kinfe-Michael
SEED IP Law Group PLLC
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