National Semiconductor Corporation

Debra J Worsley

Brian C Edem

Michael Steward Evans

Richard Win Thaik

Geetha N Rangan

Michael T Werstlein

Support for a mixed network environment is provided which can contain multiple isochronous and/or non-isochronous LAN protocols such as isochronous-ethernet, ethernet, isochronous-token ring, token ring, other isochronous-LAN or other LAN systems. Support for a mixed environment includes a protocol detection mechanism which is embodied in a handshaking scheme. This handshaking scheme determines the signalling capability at the end points of the link and implements the correct protocol. This enables isochronous nodes and hubs to automatically detect the presence of ethernet, token ring, or other LAN equipment at the other end of the network cable. If this detection occurs, the isochronous LAN equipment will fall-back to a LAN compliant mode of operation. Typically, only the hub will have the capability of operating in different networking modes, such as ethernet, Token Ring isochronous modes. The hub will listen for some form of identification from the attached nodes as to the type of service to provide--isochronous or non-isochronous; ethernet, token ring or other LAN service.

Network link endpoint capability detection

A data communication system, such as a local area network, is provided with a capability of transmitting isochronous data. Preferably the system conveys both isochronous data and non-isochronous data by time-multiplexing the data into a recurring frame structure on a four-bit nibble basis. An efficient encoding scheme permits transmission of both isochronous and non-isochronous data over existing media, such as twisted pair, without degrading bandwidth previously achieved for non-isochronous data over the same media, such as using an ethernet system. Bandwidth available for a particular isochronous source/sink is selectable and sustainable with a predefined granularity. The arriving data is de-multiplexed at the hub into separate channels for handling the separate streams by appropriate hardware. Preferably, the present invention can be implemented in a fashion that is transparent to already-installed media access controllers. Preferably, some components of the system can detect the frame-transmission capability of other components and, if such capability is lacking, can fall back to a mode compliant with existing capabilities.

Method of maintaining frame synchronization in a communication network

A data communication system, such as a local area network, is provided with a capability of transmitting isochronous data. Preferably the system conveys both isochronous data and non-isochronous data by time-multiplexing the data into a recurring frame structure on a four-bit nibble basis. Switching of data is handled using switching tables. The tables can be updated by a processor. Updates can be performed asynchronously so that the processor does not have to wait until the switch tables are in an unused updatable state before outputting the update information. An efficient encoding scheme permits transmission of both isochronous and non-isochronous data over existing media, such as twisted pair, without degrading bandwidth previously achieved for non-isochronous data over the same media, such as using an Ethernet system. The arriving data is de-multiplexed at the hub into separate channels for handling the separate streams by appropriate hardware.

Asynchronous processor access to a switch table in a network with

Data communication network with transfer port, cascade port and/or frame

A network for transferring packet data in a frame structure, preferably mixed with isochronous data. The frame structure is a continuously repeating structure, with each frame having a number of time slots. Certain ones of the time slots are available for transmitting packet data. The packet data is re-timed, e.g., by using a FIFO to output the data nibble-wise as required by the frame structure. Information about variability in delays at the transmitting end is sent to the receiving end. The receiving end uses the information to eliminate the variability, such as by a variable delay FIFO, thus restoring/recreating the original packet and IFG timing. Preferably, the frame structure is translated to and from a packet structure to permit the present invention to be used with previously available packet circuitry such as a media access controller and a hub repeater circuit.

Delay control for frame-based transmission of data

The present invention provides for communication of data to and from isochronous data sources and sinks. Preferably, a portion of bandwidth on the link is also dedicated to convey data to and from non-isochronous sources and sinks, as well as to permit conveying housekeeping information (such as information relating to data sources and destinations) and status and control maintenance information. A management port is included in the isochronous switching devices to allow monitoring or diagnostic access to the serial isochronous data stream to and from all physical layer portion connections. Accessing one connection's data stream does not affect normal operation of the other connections.

Data communication network with management port for isochronous switch

A data communication system, such as a local area network, is provided with a capability of transmitting isochronous data. Preferably the system conveys both isochronous data and non-isochronous data by time-multiplexing the data into a recurring frame structure on a four-bit nibble basis. Bandwidth available for a particular isochronous source/sink is selectable and sustainable with a predefined granularity. Data rates can be adjusted by using 'rate adjustment' time slots which can transmit data in some frames and 'no data' in other frames. A particular time frame or template is provided which accommodates isochronous data, non-isochronous data, D channel data, maintenance data and frame synchronization signals. Non-isochronous operation and bandwidth allocation is independent and transparent to the isochronous data activity. Frame timing can be coordinated with one or more reference clock signals, e.g., from a public telephone or wide area network. A buffer can convert between the source/sink or hub circuitry data rates and the data rates for transmission over the physical media which, for a given type of data, is discontinuous on a small time scale.

Network for transmitting isochronous-source data using a frame structure

An apparatus and method for transferring data between two entities in a time slot interchange fashion. The apparatus and method includes a buffer memory comprised of three sections to accommodate up to one cycle of skew between the two independently operating entities. Cycle start detection logic coupled to the two entities controls or, as implemented in the preferred embodiment, designates a physical location within the buffer memory for each of the three sections upon receipt of cycle start reference signals from the two entities.

Time slot exchanger mechanism in a network for data communication having

A data communication system such as a local area network or a wide area network capable of transmitting isochronous data. The system conveys both isochronous data and non-isochronous data by time multiplexing data into a recurring frame structure on a 4-bit nibble basis. The arriving data is de-multiplexed at a hub into separate channels which are forwarded to separate hardware appropriate for handling the particular data stream. The data is passed hierarchically from a source, through a node, and to a hub. The hub places the data into an internal connection memory for switching onto a high bandwidth bus for distribution to other destination hubs, nodes, or sinks, except, where the source node and destination node are attached to the same hub, the hub provides a local loopback to the destination node, thus avoiding the need to place the transmitted data onto the bus. This system conserves room on the bus for other isochronous and non-isochronous data.

Local loopback of isochronous data in a switching mechanism

A data communication system, such as a local area network, is provided with a capability of transmitting isochronous data. The system conveys both isochronous data and non-isochronous data by time-multiplexing the data into a recurring frame structure on a four-bit nibble basis. The arriving data is de-multiplexed at the hub into separate channels for handling the separate streams by appropriate hardware. When no calls are in progress, a low power mode enables two ends of a network link to reduce power consumption by transmitting a single pulse once every 125 microseconds in lieu of transmitting an entire cycle template. Synchronization while in low power mode allows circuitry at both ends of a network link to remain synchronized to a single reference clock.

Low power isochronous networking mode

A data transfer delay compensation system for a data communications system having a first transceiver and a second transceiver wherein the first transceiver includes circuitry for transferring an external cycle reference signal and a cycle delay signal to the second transceiver. The second transceiver includes circuitry for transmitting the received cycle reference back to the first transceiver a given time period after receipt of the cycle reference. The first transceiver receives the cycle reference transmitted from the second transceiver and measures a phase difference between the received cycle reference and the external cycle reference signal in order to update the cycle delay signal.

Isochronous link protocol

A network for transferring packet data in a frame structure, preferably mixed with isochronous data is provided. The frame structure is a continuously repeating structure, with each frame having a number of time slots. Certain ones of the time slots are available for transmitting packet data. The packet data is re-timed, e.g., by using a FIFO to output the data nibble-wise as required by the frame structure. Similar re-timing can be used for isochronous data so that the frame structure defines time-division multiplexing of the packet data and isochronous data. A four/five encoding scheme provides sufficient encoding efficiency that both the packet data and other data can be accommodated without degrading the data rate of the packet data. The encoding scheme provides extra symbols which can be used for transferring 'no carrier' information, or 'frame alignment' messages. Preferably, the frame structure is translated to and from a packet structure to permit the present invention to be used with previously available packet circuitry such as a media access controller and a hub repeater circuit. Latency of the FIFO can be reduced by pre-filling with packet preambles, and/or sub-latency propagation of preamble bytes, or providing special MACs which do not output preambles, and using the buffer circuitry to output preambles.

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Vista, CA, United States of America

Debra J Worsley