Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-05-28
2002-07-09
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06417944
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data communications networks and more particularly relates to an ATM switch incorporating optical switching.
BACKGROUND OF THE INVENTION
Recently, more and more reliance is being placed on data communication networks to carry increasing amounts of data. In a data communications network, data is transmitted from end to end in groups of bits which are called packets, frames, cells, messages, etc. depending on the type of data communication network. For example, Ethernet networks transport frames, X.25 and TCP/IP networks transport packets and ATM networks transport cells. Regardless of what the data unit is called, each data unit is defined as part of the complete message that the higher level software application desires to send from a source to a destination. Alternatively, the application may wish to send the data unit to multiple destinations.
Asynchronous Transfer Mode
Asynchronous Transfer Mode (ATM) originated as a telecommunication concept defined by the Comite Consulatif International Telegraphique et Telephonique (CCITT), now known as the International Telecommunications Union (ITU), and the American National Standards Institute (ANSI) for carrying user traffic on any User to Network Interface (UNI) and to facilitate multimedia networking between high speed devices at multi-megabit data rates. ATM is a method for transferring network traffic, including voice, video and data, at high speed. Using this connection oriented switched networking technology centered around a switch, a great number of virtual connections can be supported by multiple applications through the same physical connection. The switching technology enables bandwidth to be dedicated for each application, overcoming the problems that exist in a shared media networking technology, like Ethernet, Token Ring and Fiber Distributed Data Interface (FDDI). In addition, ATM allows different types of physical layer technology to share the same higher layer—the ATM layer.
More information on ATM networks can be found in the book “ATM: The New Paradigm for Internet, Intranet and Residential Broadband Services and Applications,” Timothy Kwok, Prentice Hall, 1998.
ATM used very short, fixed length packets called cells. The first five bytes, called the header, of each cell contain the information necessary to deliver the cell to its destination. The cell header also provides the network with the ability to implement congestion control and traffic management mechanisms. The fixed length cells offer smaller and more predictable switching delays as cell switching is less complex than variable length packet switching and can be accomplished in hardware for many cells in parallel. The cell format also allows for multi-protocol transmissions. Since ATM is protocol transparent, the various protocols can be transported at the same time. With ATM, phone, fax, video, data and other information can be transported simultaneously.
ATM is a connection oriented transport service. To access the ATM network, a station requests a virtual circuit between itself and other end stations, using the signaling protocol to the ATM switch. ATM provides the User Network Interface (UNI) which is typically used to interconnect an ATM user with an ATM switch that is managed as part of the same network.
ATM is the enabling network technology for the high speed transmission of voice, data, video and multimedia information over communication links. Local Area Networks (LANs) based on ATM technology are becoming more and more popular due to the high speed and flexibility of ATM switching. ATM networks are typically configured in the shape of a star configuration with all the stations connected to a central switch or group of switches forming the network backbone. Currently, high speed electronic switches are used to route the ATM cells over the appropriate links. Although ATM is typically transmitted using optical communication links, the switches themselves are currently electronic based.
The benefits of optical communications are not utilized in current systems due to the frequent signal transformations from the optical domain to the electrical domain in order to provide the switching and routing functions.
In addition, the typical architecture of an ATM central switch includes a central ATM switch fabric and one or more interface (I/F) cards (modules). The interface modules incorporate the ATM cell processing, buffering and connection to the user interface which may be copper or optical fiber based. The central switch fabric includes the switch matrix and associated control functions thereof. The connection between the switch fabric and the interface modules is carried over a backplane printed circuit board (PCB). The connection is usually copper based and can be either parallel or serial.
There are numerous commercial vendors today that offer off the shelf building blocks for constructing such a switch. The main limitation, however, of this type of architecture is the throughput of the switch fabric which is currently limited to approximately 30 to 50 Gbps. The limitation is due to the limitations of current electronic switching technology. Another limitation is the connection over the backplane where the maximum bandwidth achievable today is limited to about 2.5 Gbps for each serial connection. Parallel connections can achieve much higher data rates but require large numbers of high speed serial connections aggregated together over the backplane PCB.
Current LAN Topology
Using ATM network technology as an example, the current topology of high performance ATM local area networks (LANs) includes ATM core switches at the backbone and an edge device having an ATM downlink to the one or more core switches. When a connection is established between two edge devices, the traffic must pass through the ATM switches in the core. Therefore, in order to support all potential connections between all edge devices, the ATM switches at the core need to be non blocking. Non blocking ATM switches are difficult to develop and thus are much more expensive.
In addition to the disadvantage described above, the resulting network may be limited in bandwidth. When attempting to establish large numbers of connections from the edge device, there may be a need for faster downlink data rates. Depending on the number of connections and the throughput required for each connection, the downlink capacity may not be sufficient to meet the needs of users.
An additional disadvantage is the amount of physical wiring required to implement such a network. In practice, each edge device must be connected to the ATM core via physical wires (i.e., cables). When considering a typical office building there may be many wires installed in parallel. A separate cable from each edge device on each floor must be run down to the ATM core farm which typically is located in the basement. Wherever the switch core farm or server is located, cables must be run from the switch core farm to each edge device. The total length of the required cabling can be relatively very high and thus have an associated very high cost.
The cost may be even higher depending on the type and length of cabling used. For example, in ATM networks, it is common to run high speed fiber optic cable from the ATM switch core to all the edge devices in the network. Data rates may range from OC-3 155 Mbps to OC-12 622 Mbps on the optical fiber, for example. Note that each optical fiber used in the network carries only a single communication channel using a single wavelength of light. If it is desired to maintain several communications channels at one time, more than one optical fiber is required. Using prior art transmission techniques, each communication channel requires a separate optical fiber.
Today, most legacy local area networks utilize ATM technology in combination with Switched Ethernet or Token Ring network topologies. The existing switching technology enables each user on the network to have their own dedicated bandwidth, e.g., 10 Mbps or 100 Mbps, for their
Lahat Amir
Sfadya Yackov
3Com Corporation
Chan Jason
Payne David C.
Zaretsky Howard
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