Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-05-18
2001-05-15
Pascal, Leslie (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06233074
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data communications networks and more particularly relates to a ring network that utilizes wave division multiplexing (WDM) to increase the capacity of the network.
BACKGROUND OF THE INVENTION
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
ATM originated as a telecommunication concept defined by the Comite Consulatif International Telegraphique et Telephonique (CCITT), now known as the 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). 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 uses 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 in 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.
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 above disadvantage, the resulting network may be limited in bandwidth. When attempting to establish large numbers of connection 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 to the ATM core farm which typically is located in the basement. Wherever the switch core farm or server firm 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 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 and on Switched fathered 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 networked software applications. Each user is given network connectivity to the local switched hub, e.g., 100 Mbps for a Fast Ethernet network interface card (NIC). In typical office building environments, each floor is provided with one or more switched hubs that users are directly connected to. If the switched hub has sixteen 10 Mbps ports it may potentially be forced to handle a 1,600 Mbps data rate from all the connected users.
Currently available conventional technology, using electrical processing, forces the switched hub to analyze every bit of information and to determine its destination. Even in the event where most of the data is not switched between the local ports on the switch but rather is passed up to higher levels of switching, all the information must be still analyzed by the switched hub. This bottleneck for data that is not switched locally leads to high data rates within the switch. The high internal data rates result in a more complicated design in terms of both hardware and software, thus increasing the cost of the switch.
A diagram illustrating a prior art example network having multiple levels is shown in FIG.
1
. The network, generally referenced
10
, is a typical Ethernet network comprising a switched hub
12
labeled C connected to two switched hubs
14
labeled A and B. The switched hubs
14
comprise a first level of processing and the switching hub
12
comprises a second level of processing. Switching hubs
14
are connected to a plurality of end users
16
labeled end user #1 through end user #6.
Connections between end users in the network can be established on the same switched hub or may be established between different switched hubs. For example, a connection between end user #1 and end user #2 requires only one level of processing on switched hub A. On the other hand, a connection between end user #1 and end user #4 requires the operation of three different processing engines: (1) the processing engine in switched hub A (2) the processing engine in switched hub C and (3) the processing engine in switched hub B. It is important to note that switch hub C processes data even though it did not require the data for purposes other than to tra
Lahat Amir
Sfadya Yakov
3Com Corporation
Pascal Leslie
Weitz David J.
Wilson Sonsini Goodrich & Rosati
Zaretsky Howard
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