Full duplex flow control for Ethernet networks

Abstract

CSMA / CD is used to implement flow control in a full-duplex Ethernet network in a lossless fashion. Uniquely identifiable flow control transmit on / off ("XON / XOFF") messages are transmitted, preferably during IPG, by a receiving station about to be congested to the transmitting station whose data output is to be controlled. The transmitting station physical layer receives and decodes these messages. If XOFF is recognized, the transmitting station continuously asserts CRS to its MAC layer at the MII, regardless of the prior CRS current state. CRS is continuously asserted until the receiving station transmits an XON flow control signal, indicating its ability to accept further data. During CRS assertion, the transmitting station defers transmission, e.g., is flow controlled. The MAC layer is slightly modified (but is still backward compatible with half-duplex networks) to provide separate transmit deferral receive data frame mechanisms using separate and independent input status signals, namely CRS and RX_DV. CRS provides a carrierSense signal used for deferral within the MAC transmit process, and RX_DV provides a receive_carrierSense signal that frames data within the MAC receive process. As long as CRS remains asserted, the transmitting station defers transmission, thereby implementing flow control. In addition to slight MAC layer modification, the present invention slightly modified the physical layer, MII interface and reconciliation sublayer.

Description

FIELD OF THE INVENTIONThis invention relates to networks in general including Ethernet networks, and more specifically to implementing an Ethernet network having full duplex flow control.BACKGROUND OF THE INVENTIONA network is a communications facility that permits a number of workstations, computers or other equipment (hereinafter collectively "computer(s)") to communicate with each other. Portions of a network involve hardware and software, for example, the computers or stations (which individually may comprise one or more central processing units, random access and persistent memory), the interface components, the cable or fiber optics used to connect them, as well as software that governs the access to and flow of information over the network. In networks in which data flow is 100 Mbits / sec. ("Mbps") or higher, the transmission medium is often fiber optics. In networks in which a slower data rate is acceptable, e.g., 10 Mbps, the transmission medium may be coaxial cable or, as i...

AI Technical Summary

Problems solved by technology

The result is a collision and garbled messages.

Unfortunately, in going to a full-duplex environment, the IEEE 802.3 CSMA / CD MAC half-duplex mechanisms for collision avoidance and for transmission deferral must be abandoned.

Further, since a station desiring to transmit over a full-duplex network does not monitor the medium, half-duplex deferral and backpressure flow control procedures are also useless.

Thus, the various half-duplex CSMA / CD data pacing mechanisms cannot be used in full-duplex to control or limit access to the network.

While such devices can temporarily store rapidly arriving data during a slower read-out, device memories can readily fill and congest unless some mechanism can halt or slow the entry of new data into the network, or at least the link including the congested device.

(While half-duplex networks can also have links with different data rates, the problem is aggravated in full-duplex networks in which considerably more data flows, especially at 100 Mbps.)

Unfortunately, in the prior art there is no flow control mechanism for full-duplex Ethernet networks that avoid such data congestion and resultant data loss, without sacrificing data throughput.

Flow control devices implemented in full-duplex networks at the transport layer are slow and inefficient.

Unfortunately, data throughput will be slower than the rate associated with the congested device using such flow control mechanisms.

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