Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-12-07
2003-01-21
Ton, Dang (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S392000
Reexamination Certificate
active
06510156
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ATM data communications switches and switching protocols and more specifically to optimization techniques that may be used in ATM data communications switches and protocols to reduce cell size and thereby increase overall communication bandwidth.
BACKGROUND OF THE INVENTION
In digital communications networks, data, packed in frames, packets or cells, is routinely transmitted over links between many nodes. The data itself is stored and communicated as a series of binary digits (bits) represented by zeros and ones. During data communications, the manner in which the bits of data are specifically arranged and the order in which they are exchanged between devices is called a protocol. Protocols are usually established by industry standards (e.g., TCP/IP, ATM, ADSL). There are many different types of protocols serving different purposes, but each typically involves sending data arranged in one specific manner, and receiving data arranged in that same manner. For example, blocks of data can be reduced in size by compression protocols that utilize standard compression algorithms before transmission from a sending node in order to conserve bandwidth. Upon reception, the blocks are decompressed to obtain the data in a useable state.
Two popular data communications protocols that have been developed to transmit data over networks are Asynchronous Transfer Mode (“ATM”) and Asymmetric Digital Subscriber Line (“ADSL”).
Asynchronous Transfer Mode technology is based on the efforts of the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Study Group XVIII to develop Broadband Integrated Services Digital Network (BISDN) for the high-speed transfer of voice, video, and data through public networks. ATM is capable of transferring voice, video, and data through private networks and across public networks. ATM uses very large-scale integration (VLSI) technology to segment data (for example, frames from the data link layer of the OSI reference model) at high speeds into units called cells. In a standard ATM system, each cell consists of 5 octets of header information and 48 octets of payload data. Cells transit ATM networks by passing through devices known as ATM switches, which analyze information in the header of each cell to switch that cell to the output interface that connects the switch to the next appropriate switch as the cell works its way through the network to its destination.
ATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching (constant transmission delay and guaranteed capacity) with those of packet switching (flexibility and efficiency for intermittent traffic). Like X.25 and Frame Relay, ATM defines the interface between the user equipment (such as workstations and routers) and the network (referred to as the User-Network Interface, or UNI). This definition supports the use of ATM switches (and ATM switching techniques) within both public and private networks.
ADSL is a modem technology for use over twisted-pair telephone lines. ADSL can transmit more than 6 million bits per second (“Mbps”) to a subscriber and as much as 640 thousand bits per second (“Kbps”) bi-directionally. A conversation between two ADSL modems creates three information channels: a high speed downstream channel, a medium speed duplex channel and a Plain Old Telephone Service (“POTS”) channel. Data rates depend upon a number of factors, including the length of the copper line, the wire gauge, the use of bridges taps and cross-coupled interference. Signal attenuation increases with line length and frequency, and decreases as wire diameter increases. The American National Standards Institute (“ANSI”) working group T1E1.4 has approved an ASDL standard at rates up to 6.1 Mbps (ANSI Standard T1.413).
In either ATM or ADSL, connections are established between a sender and a receiver. A typical data transmission may involve the transmission of hundreds, or even thousands of cells from the sender to the receiver. A connection is basically a dedicated path through the network upon which these cells of data travel during the transmission of data from the sender to the receiver. A connection based networking scheme such as ATM thus sets-up or pre-defines a specific path between two machines within each ATM switch along the link between the two machines.
By way of example, if there are a series of ATM switches that create a network path between a sending and receiving host, as the first cell of a stream of data enters the network, the first ATM switch will determine the most appropriate “next switch” to which that cell should be switched. The first switch then creates a connection within itself (i.e., using software to configure the switches switching hardware) for future cells destined for the receiver. As the first cell makes its way to each successive ATM switch, each switch sets-up its own connection for cells between the sender and receiver. Once the first cell has made it to the receiver, subsequent cells may be quickly switched using the pre-established connections which remain configured until the sender and receiver no longer need to communicate. To switch each cell, the header portion of the cell is used to determine which connection is associated with the cell and therefore which port the cell should be switched to. When the connection (i.e., the communication session) is over and there are no more cells to be transmitted, each ATM switch can take-down its connections.
Though ATM cells are only 53 bytes in length, prior art systems have been developed to decrease the transmitted cell size to increase overall network bandwidth. U.S. Pat. No. 5,414,701, entitled “Method and data structure for performing address compression in an asynchronous transfer mode (ATM) system”, discloses a system which uses address compression in an ATM cell. In this system, before transmission of the cell, the address is compressed and replaced by a virtual path identifier referred to as a link. The link is computed based on the address and header information and is shorter in length than the overall header. Once the cell is transmitted and as it traverses the network, each switch that encounters the cell looks up the link appended to the cell in a link table maintained at the switch. The link table indicates the eventual destination for that cell, based on the cells unique link. As such, the switch can direct the cell in the appropriate direction. Essentially, before transmission, a link is appended to each cell based on a computation derived form the original cell header information. There may be a number of different links in use within a network, each signifying a specific connection (i.e., source and destination communication session).
SUMMARY OF THE INVENTION
Various problems are inherent in systems for reducing header information within cells transmitted on a network, such as those systems noted above. Existing systems and devices for processing ATM cells must transmit header information (including addressing and/or link information) with every ATM cell sent. In normal ATM systems, this header information creates significant overhead. Specifically, five bytes of header are sent for every 48 bytes of data sent in a standard ATM cell, and at least a link must be appended to each cell in the address compression mode noted above. Moreover, using the link mechanism for address compression requires a complex calculation to be made for each cell. The cell header must be matched to any one of a number of existing links, and then the header must be replaced by the matching link. If a link does not yet exist for the header of a current cell, a new link must be created and propagated throughout the switching network. Each switch must also maintain up-to-date link tables in order for throughput to remain efficient.
In all cases of prior art cell switching systems, cell header overhead reduces the bandwidth available over a given link thus reducing the amount of data and/or number of users that can avail th
Brock J. Christopher
Franzen R. Lee
Nguyen Brian
Ton Dang
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