Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1996-03-07
2003-03-18
Ton, Dang (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S401000
Reexamination Certificate
active
06535512
ABSTRACT:
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is in the field of communication apparatus and methods. Generally, the invention relates to processing and organizing digital information for communication from one location to another. More specifically, this invention relates to use of asynchronous transfer mode in a communication network to communicate information. The communicated information is processed and organized in apparatus and according to methods disclosed herein. Still more particularly, the present invention relates to an ATM communication system interconnect/termination unit (hereinafter, “ATMCSI/TU”).
2. Related Technology
Asynchronous Transfer Mode (ATM) is a network protocol which is highly advantageous because it allows high speed transmission of divergent types of data, including digital codes, video, and voice. This is accomplished by breaking down incoming digital data to be transmitted into units of constant size. These units are called cells, and include a 48-octet field containing the actual data; along with a header field, for a total of 53 octets in the cell. A Conversion Sublayer Protocol Data Unit (CS-PDU) may have both a header and a trailer of additional information, and may be as long as 64 K bits The process of communicating these cells involves taking digital data and segmenting it into cell-size units and assembling these units into CS-PDU's. At interconnections, the CS-PDU's are segmented and reassembled to route cells to their destinations in accord with the communication traffic load of the network, the class of service for the senders of the cells, and a variety of other parameters familiar to those skilled in the pertinent arts.
The header contains a virtual channel identifier and a virtual path identifier which identify the particular cell and its intended destination, and specify an optimal path through the network along which the cell should be routed to reach its destination. The header can also include numerous other information such as the type of data in the CS-PDU and attributes of the data, the sender and/or the destination. In combination, the virtual path identifier and virtual channel identifier define a virtual circuit within the network. This virtual circuit is unlike the old and well known actual hard-wired communication circuits of conventional telephone and data transmission systems, for example, because it does not actually provide a fixed or constant communication path (i.e., an electrical conductor, twisted-pair conductors, radio link, or fiber-optic light conductor, for example) continuously extending between the end points. A virtual circuit is continually reconfigured (i.e., possibly following a succession of several different alternative network paths) as the operating circumstances of the network change dynamically.
The ATM-protocol data may be transmitted along a digital electronic data network. A series of cells or packets communicated between endpoints of the network effectively provides a communication circuit between these endpoints. Such communication networks are becoming increasing widespread. These networks allow for the communication of divergent types of data including computer-coded text and graphics, voice, music, images, and video. Such networks enable the interconnection of large numbers of computer work stations, telephone, television systems, video teleconferencing systems, and other facilities over common data links or carriers.
Computer work stations are typically interconnected by local area networks (LAN) such as Ethernet, Token Ring, DECNet and RS-232, whereas metropolitan, national and international systems are interconnected by wide area networks (WAN) such as T1, V3.5 and FDDI.
LANs and WANs themselves can be interconnected by devices known as hubs, bridges and routers in an unlimited configuration. Although the distinction between these interconnection devices is becoming increasingly arbitrary, they are officially classified in accordance with the layer in the Open Systems Interconnection (OSI) model in which they operate.
Hubs interconnect devices using the Physical Layer, bridges utilize the Data Link layer, whereas routers operate using the Network layer. Hubs and bridges generally act merely as switches or funnels, whereas routers perform higher level functions including selecting optimal routes through the network for transmission of data packets or cells on an individual basis, and performing network management tasks such as forcing diagnostics operations and controlling other routers or nodes. Whereas hubs and bridges generally operate on data which is formatted in a single protocol such as those listed above (i.e., uni-protocol), routers can typically identify and process data which can be in any one of several protocols (multi-protocol).
Interconnect devices, especially the more sophisticated routers, have typically been large, bulky and expensive units which operate at relatively low speed. As such, they limit the data throughput speed in the network in which they are installed. The reasons why routers have been so slow is that they are generally multi-chip units which transfer data being processed to and from Content Addressable Memory (CAM) chips which are separate from the processor, input/output (I/O) and other functional chips of the unit. These data-transfer operations each require multiple system clock cycles which fundamentally limit the data transfer speed. In addition, multiple latencies are present in the various paths by which data moves through the unit. The degree by which such latencies can be reduced, as well as the degree by which the size and cost of a multi-chip system can be reduced, are also fundamentally limited.
It should be recalled that the digital communication connections (i.e., virtual circuits) maintained by an ATM system may belong to different classes of service. The reasons for these differing classes of service have to do with the differing types of digital data being communicated. Video connections, for example, do not require the same class of service as do file transfers. A file transfer is not sensitive to delay, while a video connection certainly is sensitive to transmission delay. Similarly, an audio connection is not sensitive to cell loss, while a file transfer is very sensitive to cell loss. With an audio connection, the loss of a cell in not noticeable to the recipient of the conversation because the human ear is not sensitive enough to detect the small gap in the conversation. The human ear takes meaning from context, so that a small gap in the sound of a word would probably not even be noticed. On the other hand, a file transfer is very sensitive to loss of a cell. A missing cell from a file transfer means that the received file is deficient and incomplete, and that the file data may be meaningless without the missing data.
Consequently, differing classes of service are provided to users of ATM systems. One class of service is constant-bit-rate (CBR) service, and is commonly used for audio communications and un-compressed video information. With constant-bit-rate service a cell is transmitted from a given connection on a regularly repeating time interval, perhaps one cell every couple of microseconds. Another class of service is variable-bit-rate (VBR) service, and is commonly used to transmit compressed video data. The cell rate in this instance is variable dependent on the video compression technique in use and the video image contents (i.e., rate of video image change or frames per second). Understandably, managing these variable-bit-rate services becomes a burdensome task when a multitude of connections (perhaps in t
Daniel Thomas
Nattkemper Dieter
Varma Subir
LSI Logic Corporation
Ton Dang
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