Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2002-04-16
2003-05-27
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C370S528000, C370S366000, C370S433000, C370S468000
Reexamination Certificate
active
06570687
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a packet exchange apparatus. More particularly, it relates to a broad-band optical packet exchange apparatus employing an inexpensive optical/electrical converter.
BACKGROUND OF THE INVENTION
In a packet exchange apparatus employing an optical switch in an exchange stage and also employing an electrical/optical converter and an optical/electrical converter in an input/output unit, the optical/electrical converter is usually of an ac coupling circuit configuration. In this case, there is presented a problem that, if there is any time period during which the 1 or 0 level continues for a longer time than a pre-set time period or during which there is no packet to be received, data dropout occurs in the packet or in the directly following packet.
As a method for overcoming this problem, there is proposed in, for example, JP Patent Kokai JP-A-4-72939 a packet exchange apparatus employing an optical switch in which a dummy data appending circuit is provided on the transmission side so that dummy data is transmitted during a domain (length of time) in which there is no transmission data while the appended dummy data is removed by a dummy data removing circuit provided on the reception side, so that it is attempted to eliminate occurrence of no time devoid of transmission data on the transmission route there is no continuation of 0 or 1 for a longer time than a pre-set time, thus eliminating the malfunction of data dropout in the optical/electrical converter. This method consists in sending a dummy packet in the absence of packets for transmission on the input side.
This dummy packet is a pattern which is made up of at least one bit of 0 and the same number of bit of 1, with 0 or 1 not continuing for longer than a pre-set time, and to which is appended a particular code by which the packet can be judged to be a dummy packet. An output unit includes a dummy packet eliminating circuit which discriminates a dummy packet based on the possible presence of the particular code specifying a dummy packet to eliminate the discriminated dummy packet in order to receive only the necessary packets.
In case where, in this configuration, there are packets to be transmitted to the same output unit on plural input units, a contention resolution circuit is used in order to inhibit packet interference due to arrival of plural packets at the same output unit, which would lead to reception of erroneous data.
If a connection request is received from the input unit before the input unit sends a transmission packet and connection requests are made to the sole output unit from plural input units, the contention resolution circuit selects a sole input unit from the plural input units to give the input unit a permission for connection. The remaining input units are inhibited from connection. Since the input units inhibited as to connection are equivalent to the input units devoid of the packets for transmission, these input units send dummy packets. The contention resolution circuit has to detect an input unit devoid of the packets for transmission and an output unit devoid of packets for reception and to find out a connection pattern to interconnect these input and output units.
FIG. 37
shows a configuration of a conventional optical switch used in an exchange stage. Referring to
FIG. 37
, this optical switch is a 4-input 4-output splitter/combiner type optical switch having four light splitters
10
,
16
optical gates
11
and four light combiners
12
. For controlling this switch,
42
or
16
control lines are required to control the
16
optical gates.
SUMMARY OF THE DISCLOSURE
During the course of investigations toward the present invention, the following problems have been encountered.
In sending packets from a sending station to the exchange apparatus, the sending station transmits, along with a packet(s), a destination address specifying the receiving station to receive the packet(s), to the exchange apparatus. In the absence of packets to be transmitted in the input unit, no designation of the destination address is made from the transmitting station to the input unit.
In transmitting a dummy packet by the above-described conventional packet exchange apparatus, a contention resolution circuit searches an input unit devoid of a packet(s) to be transmitted and an output unit devoid of a packet(s) to be received and controls the optical switch driving circuit for interconnecting these input and output units.
Unless this search is expedited or it is constructed so as to unnecessitate the search, the exchange apparatus is increased in the circuit scale. If the network speed is increased, it becomes impossible to control the exchange apparatus at a high speed.
Meanwhile, since the dummy packet is deemed in the receiving station as being unnecessary or erroneous data, it is necessary to provide a dummy packet eliminating system in order to prevent the dummy packet from being output from the exchange apparatus to the receiving station.
In the dummy packet eliminating system of the conventional packet exchange apparatus, described above, the special code specifying a dummy packet appended to the dummy packet is detected for eliminating the dummy packet. That is, in case where a packet other than the dummy packet is received as a substitute for the dummy packet in order to avoid malfunction of an O/E converter of an output unit inherently having no packet to be received, the dummy packet eliminating system cannot eliminate this packet as an invalid packet and erroneously sends this packet to the reception station.
Therefore, in the above-described conventional packet exchange apparatus, an output unit devoid of the packet to be received has to be connected to an input unit transmitting a dummy packet, that is to an input unit devoid of the packet to be transmitted, such that it becomes necessary to search and connect input and output units sending and receiving the dummy packet expeditiously.
Another problem is the interconnection for control signals for the optical switch. That is, if the optical switch is increased in scale, the control signal lines between the optical switch and the control circuits are increased in volume and structure thus causing congestion of the control signal lines.
For example, if, in the case of a 128 by 128 line full-cross bus switch, a bit map of the switch connection pattern is formulated in the control circuit and a control signal is sent to the optical switch, 128
2
or 16384 control lines are required. Since these numerous control signal lines affect mounting of the exchange apparatus or optical switches, it is incumbent to reduce the number of the control signal lines.
In view of the above-described problems, it is a primary object of the present invention to eliminate any of the aforementioned problems. Particularly, it is an object of the present invention to provide an optical packet exchange apparatus and an optical switch in which searching for connection patterns between input units devoid of packet(s) for transmission and output units devoid of packet(s) for reception is reduced and can be performed speedily. It is another object to provide an optical packet exchange apparatus and an optical switch in which, if the number of channels of the exchange apparatus is increased or the network speed is higher, switch control can be made quickly to suppress or reduce the hardware scale.
Still further objects of the present invention will become apparent in the entire disclosure including the claims.
For accomplishing the above object, the first aspect of the present invention resides in the following features: An optical packet exchange apparatus includes (a) a plurality of input devices having input buffer means (units), parallel/serial conversion means (units), electrical/optical conversion means (units), and dummy packet insertion means (units) for sending a dummy packet if there is no packet to be transmitted. The apparatus further includes (b) exchange counterpart contention resolution means (units) for control
Araki Soichiro
Henmi Naoya
Maeno Yoshiharu
Suemura Yoshihiko
Tajima Akio
NEC Corporation
Pascal Leslie
Phan Hanh
Scully Scott Murphy & Presser
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