Network connection method

Abstract: One of the fundamental benefits of the 10BASE-T physical interface for 802-3/Ethernet is that the health of the communications link can be permanently monitored. When in the "link good" condition, the 10BASE-T transceiver is required to output a link status (LNKST) signal to this effect. Media Access Controller (MAC) 30, with an embedded 10BASE-T transceiver (37), uses the LNKST signal to provide power management to the MAC (30). By using the programmable AWAKE bit, the receive section of the 10BASE-T transceiver (37) can remain powered, even if the SLEEP input to the MAC (30) is activated. This allows the transceiver (37) to detect a link beat pulse (60) or receive packet activity. If either receive condition is encountered, the internal transceiver (37) will activate the LNKST output from the MAC (30). The system hardware and/or software can use the LNKST output to take appropriate action. For instance, if the LNKST output is active (low), then the computer is connected to an active network, and it is likely that the operating system will allow the MAC (30) to remain powered. However, if the LNKST becomes inactive (high) then the system can assume that the link is inactive, and the MAC can be powered down to save power. If at a later time the link is re-established, the MAC (30) can be powered back up to take advantage of the communications channel. In this way, the power consumption of the Ethernet connection can be managed by the operating software/hardware.

Description: The present invention relates generally to a method for automatic connection and disconnection of a node in a local area network (LAN) to manage power of a LAN controller, and particularly, it relates to such a method as implemented with an Ethernet network employing a transmitter/receiver (transceiver) which meets the ANSI/IEEE 802.3 10BASE-T international standard. Preferably, it relates to such a method implemented a media access controller (MAC) for 802.3/Ethernet, also known as MACE, implemented in an integrated circuit including the 10BASE-T transceiver. Ethernet is a commonly used local area network scheme in which multiple stations are connected to a single shared serial data path. Typically, only one station can transmit data onto the path at a time. A station connected to the path transmits data in the form of a packet that includes a destination address. The packet propagates throughout the network medium and is received by all other stations. The addressed station copies the entire packet as it goes by; the others reject the packet after determining that it is addressed to another station. A Media Access Controller (MAC) serves as an interface between a shared data path and the stations connected to that path. Each node connected to the network includes a MAC which performs a number of functions involved in the transmission and reception of data packets. For example, during the transmission of data, the MAC assembles the data to be transmitted into a packet with address and error detection fields. Conversely, during the reception of a packet, the MAC disassembles the packet and performs address checking and error detection. In addition, the MAC typically performs encoding/decoding of digital signals transmitted over the shared path and performs preamble generation/removal as well as bit transmission/reception. Traditional Ethernet is a coaxial wired system. The coaxial cable provides a linear bus to which all nodes are connected. Signalling is accomplished using a current sink technique with the center conductor used for signal, and the shield as a ground reference. Twisted pair Ethernet in accordance with IEEE Standard 802.3 IOBASE-T is able to use standard voice grade telephone cable employing separate transmit and receive pairs (4 wires). The system uses a star topology. At the center of the star is a "repeater". The repeater (or hub) performs signal amplitude and timing restoration. It takes an incoming bit stream and repeats it to all other ports connected to it (but not back to the originating port). In this sense, the repeater acts as "logical coax", so that any node connected to the network will see another's transmission. Differential signalling is employed with one pair acting as the transmit path, and the other as receive. Further details on IOBASE-T Ethernet networks, including a description of the state of the art for such networks, is provided by Crayford, "10BASE-T in the Office," Wescon, San Francisco, November 20, 1991. Transceivers as used in 10BASE-T Ethernet networks may incorporate a sleep mode, in which a node incorporating the transceiver powers down when there is no activity for it after a predetermined period of time. However, when the node is in the sleep mode, it will miss any transmissions intended for it. It would be desirable to provide the power saving advantages of the sleep mode without resulting in missed transmissions. Efficient network management also requires that nodes on a network be identified as present. With prior art sleep modes, a network controller of a node in sleep mode is treated as if it were disconnected from the network. According to the present invention there is provided a method for operating a local area network, which comprises connecting a data processing terminal to an Ethernet local area network through an Ethernet media access controller and an Ethernet 10 Base-T transceiver and comprising periodically signalling the presence of the network to the transceiver, the method being characterised by the steps of: allowing the media access controller to assume a power saving sleep mode while allowing a receive section of the transceiver to remain awake; signalling the presence of the network to said receive section of the transceiver when the media access controller is in the sleep mode; and awakening the media access controller from the sleep mode in response to said transceiver receiving from the network a packet transmission including a node address for the data processing terminal and an awakening instruction. Before proceeding to a detailed description of the present invention, three prior art documents cited in EP-A3-0,573,204 will be acknowledged as follows. US-A-4,996,706 discloses a data communication interface for exchanging data between a computer station and a telephone system. The interface comprises the computer station and a bidirectional modem with an associated data access means including a ringing detection circuit and a control unit. The interface provides for an energy saving "stand-by" mode in which the modem is powered down during times in which no data transmission or reception activity occurs. The ringing detection circuit detects a calling signal on the telephone line from a remote computer station and initiates powering up of the modem by the control unit. Similarly, the powering up of the modem can be triggered by a transmission request signal from the computer station. WO-A-92,03004 discloses a power controlled local computer connected to a telephone line, the power controlling being responsive to a carrier detect signal on the telephone line. EP-A-0,343,630 discloses a data communication system in which data processing terminals are linked via a transmission line to a master station which sends out commands using an address portion within a data frame to designate the destination terminal. The terminal can receive a reset signal in the same manner as normal data and, upon receipt of that reset signal, initiate a reset instruction. This indicates that the terminal must be awake and in normal receive operation in order to receive the reset signal which is sent and received in the same manner as a normal data signal. This disclosure does not involve a sleep mode. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram of a media access controller incorporating the invention for an Ethernet network. Figure 2 is a more detailed block diagram of a portion of the media access controller incorporating the invention, connected in a network. Figure 3 is a block diagram corresponding to Figure 2 of an alternative embodiment of the invention, connected in a network. Figure 4 is a diagram showing control bit assignments for practice of the invention. Figures 5A and 5B are a more detailed block diagram of a portion of the media access controller of Figure 1. DETAILED DESCRIPTION OF THE INVENTION Turning now to the drawings, more particularly to Figure 1, there is shown a media access controller (MAC) 30 used as an interface in an Ethernet data processing network. The MAC 30 controls the passage of information between a shared Ethernet serial data path 32 and a system bus 34. The MAC 30 includes a Manchester encoder/decoder 36 and a MAC core 38, which in the preferred embodiment, is implemented in accordance with the IEEE 802.3 standard. The MAC 30 also includes a receive FIFO 40, a transmit FIFO 42 and FIFO control logic 44 as well as command and control registers 46. A system bus interface unit 48 is logically disposed between the receive and transmit FIFOs 40 and 42 and the system bus 34. The MAC core 38 includes a station address detect (SAD) unit 50 which determines whether packets received by the MAC 30 in fact are addressed to it and should be captured in their entirety, or are addressed to a different MAC station (not shown) and should be rejected. The byte tracking system of this invention is incorporated in the system bus interface unit 48, transmit FIFO 42, MAC core 38 and Manchester encoder/decoder 36 of the MAC 30. The encoder/decoder 36 is connected to an Attachment Unit Interface (AUI) transceiver 35 and a 10BASE-T transceiver 37. Further background information on the Ethernet data processing network and the MAC 30 are provided in EP-A-0,558,234. Further details on the IOBASE-T transceiver 37, its connection to the MAC 30 and its connection to another IOBASE-T transceiver 37a are shown in Figure 2. In operation, the 10BASE-T transceiver 37 outputs a link beat pulse 60 every 8-24 milliseconds. Detection of the link beat pulses 60 produced by the transceiver 37 by the transceiver 37a is used to establish that a link in the network is in place. Figure 3 shows a portion of another embodiment of a network system in which 10BASE-T transceivers 37' and 37a' each output a link beat pulse 60 every 8-24 milliseconds. Detection of the link beat pulses 60 produced by the other transceiver to which the transceivers 37' and 37a' are connected is used to establish that a link in the network is in place. The "AUTO WAKE" (AWAKE) feature of the MAC 30 is specifically designed for use with mobile computing equipment, such as laptop or palmtop computers. The "REMOTE WAKE" (RWAKE) feature is intended for use in secure environments, providing a remote manager the capability of enabling or disabling a LAN station remotely, using a network command. One of the fundamental benefits of the 10BASE-T physical interface for 802.3/Ethernet of Figure 2 is that the health of the communications link can be permanently monitored. This is known as the Link Integrity Test. When in the "link good" condition, the 10BASE-T transceiver 37 is required to output a link status (LNKST) signal to this effect. The MAC 30, with the embedded 10BASE-T transceiver 37, uses the LNKST signal to provide power management to the MAC 30. A SLEEP pin (not shown) on the MAC 30 is an input that allows the MAC 30 to be placed in one of its power saving modes. When SLEEP is active, all outputs will be placed in an inactive or high impedance state, providing that both the AWAKE bit and the RWAKE bit functions in a PHY Configuration Control register (not shown) are not enabled. This is the optimal mode for power saving, allowing clock inputs to the MAC 30 to be suspended. If the AWAKE bit is set prior to the activation of SLEEP, the 10BASE-T receiver 37 and the LNKST output pin remain operational. If the RWAKE bit is set prior to SLEEP being asserted, the Manchester encoder/decoder 36, AUI cell and 10BASE-T cell 37 remain operational, as do the SRD, SRDCLK and SF/BD outputs. The input on XTALI must remain active for the AWAKE or RWAKE features to operate. By using the programmable AWAKE bit, the receive section of the 10-BASE T transceiver 37 can remain powered, even if the SLEEP input to the MAC 30 is activated. This allows the transceiver 37 to detect a link beat pulse 60 or receive packet activity. If either receive condition is encountered, the internal transceiver 37 will activate the LNKST output from the MAC 30. The system hardware and/or software can use the LNKST output to take appropriate action. For instance, if the LNKST output is active (low), then the computer is connected to an active network, and it is likely that the operating system will allow the MAC 30 to remain powered. However, if the LNKST becomes inactive (high) then the system can assume that the link is inactive, and the MAC can be powered down to save power. If at a later time the link is re-established, the MAC 3() can be powered back up to take advantage of the communications channel. In this way, the power consumption of the Ethernet connection can be managed by the operating software/hardware. By using the programmable RWAKE bit, the receive section of the 10BASE-T transceiver 37 and AUI port remain powered after the SLEEP input to the MAC 30 is activated. In addition, External Address Detection Interface (EADI) 52 is maintained operational. This allows data received on either the AUI or 10BASE-T receiver 37 to be passed to the EADI 52, via the Manchester decoder 36, and hence allows an external address or message detection circuit to observe the contents of the incoming packet. In this way, a system can be simply designed to provide a central manager station with the ability to control remotely the state of the MAC 30 and the associated computer station. External circuitry can be implemented to interface to pins of the EADI 52, and effectively wait for a match based on a specific receive frame contents, in addition to just address alone. By way of example, a serial to parallel converter 53 and a comparator 55 of a terminal to which the MAC 30 is connected are shown. The comparator 55 provides a remote wake signal in response to a command from the central manager to reawaken from a sleep mode. This mode of operation effectively allows the MAC 30 and associated external logic to respond to specific frames on the network and thereby facilitate remote controlled node operation. Some emerging network management protocols, such as the 3Com/lBM HLM Specification, already have the requirement to be able to control the node remotely. For applications requiring network controlled power or security management, the EADI 52 of the MAC 30 offers a unique solution. Not only can the station be remotely powered down, but with segregated power supply distribution, the MAC 30 and the associated EADI logic can remain active, and effectively wait for a command to reactivate the station. This function is referred to as the "Remote Wake" capability. Since the logic for "snooping" on the receive packet, and the power management distribution, is under the control of the system designer, the end station can implement security as simply as disabling the keyboard entry and/or display system, or a more sophisticated power down of all non-critical functions, such as the system CPU itself. The AWAKE and RWAKE bits are located in the PHY Configuration Control (PHYCC) register of the MAC 30. All bits within the PHY Configuration Control register are cleared by hardware or software reset. Bit assignments are as shown in Figure 4. Each bit has the function described in the following table: Bit 7 LNKFL LNKFL reports the link integrity of the IOBASE-T receiver. When the link test function is enabled (DLNKTST = 0), the absence of link beat pulses on the Receive Data (RXD)± pair will cause the integrated 10BASE-T transceiver 37 to go into the link fail state. In the link fail state, data transmission, data reception, data loopback and the collision detection functions are disabled, and remain disabled until valid data or >5 consecutive link pulses appear on the RXD± pair. During link fail, the LNKST pin is internally pulled HIGH. When the link is identified as functional, the LNKST pin is driven LOW, and is capable of directly driving a "Link OK" LED. In order to inter-operate with systems which do not implement Link Test, this function can be disabled by setting the DLNKTST biL With Link Test disabled (DLNKTST = 1), the data driver, receiver and loopback functions as well as collision detection remain enabled irrespective of the presence or absence of data or link pulses on the RXD± pair. The transmitter will continue to generate link beat pulses during periods of transmit data inactivity. Bit 6 DLNKTST Disable Link Test. When set, the integrated IOBASE-T transceiver 37 will be forced into the link pass state, regardless of receive link test pulses or receive packet activity. Bit 5 REVPOL Reversed Polarity. Indicates the receive polarity of the RXD± pair. When normal polarity is detected, the REVPOL bit will be cleared, and the RXPOL pin (capable of driving a "Polarity OK" LED) will be driven low. When reverse polarity is detected, the REVPOL bit will be set, and the RXPOL pin should be externally pulled high. Bit 4 DAPC Disable Auto Polarity Correction. When set, the automatic polarity correction will be disabled. Polarity detection and indication will still be possible via the RXPOL pin. Bit 3 LTS Low Threshold Select. When set, the threshold of the twisted pair receiver will be reduced by 4.5 dB, to allow extended distance operation. Bit 2 ASEL Auto Select. When set, the PORTSEL [1-0] bits are overridden, and the MAC 30 will automatically select the operating media interface port. When the 10BASE-T transceiver is in the link pass state (due to receiving valid packet data and/or Link Test pulses or the DLNKTST bit is set), the 10BASE-T port will be used. When the 10BASE-T port is in the link fail state, the AUI port will be used. Switching between the ports will not occur during transmission, to avoid any type of fragment generation. Bit 1 RWAKE Remote Wake. When set prior to the SLEEP pin being activated, the AUI and 10BASE-T receiver sections and the EADI 52 will continue to operate even during SLEEP. Incoming packet activity will be passed to the EADI 52 pins to allow detection of specific frame contents to be used to initiate removal of the SLEEP function. RWAKE must be programmed prior to SLEEP being asserted for this function to operate. RWAKE is not cleared by SLEEP, only by activation of the SWRST bit or RESET pin. Bit 0 AWAKE Auto Wake. When set prior to the SLEEP pin being activated, the 10BASE-T receiver section will continue to operate even during SLEEP, and will activate the LNKST pin if receive activity is detected. AWAKE must be programmed prior to SLEEP being asserted for this function to operate. AWAKE is not cleared by SLEEP, only by activation of the SWRST bit or RESET pin. Further details of the MAC 30 as shown in Figure 1 are provided in Figures 5A and 5B. These diagrams are useful for understanding operation of the AUI and 10BASE-T circuits 35 and 37, and their interaction with the SLEEP pin and AWAKE/RWAKE bits. The MAC core cell 38 performs all of the 802.3/Ethernet transmit and frame assembly and interfaces through the bus interface unit 48 to the host system bus 34. Port multiplexer 80 allows the MAC 30 to select between the AUI interface 35 and the 10BASE-T interface 37. The port selection process as such is not a part of the present invention and is therefore not described in detail, but it basically allows either manual selection (via programmable bits) or automatic selection (using the LNKST pin indication) of the media interface. Manchester encoder 82 and phase locked loop (PLL) and decoder 84 together form the Manchester encoder/decoder 36. Assuming normal (SLEEP inactive) operation, transmit data flow originates from the MAC 38, which is Manchester encoded at 82 and then passed to the appropriate AUI or 10BASE-T media driver 86 or 88 through transmit logic 87 or 89. Receive data flow may originate from either the AUI or the 10BASE-T receiver 90 or 92. The receivers 90 and 92 first perform pulse amplitude detection. If the received waveform passes the amplitude criteria, pulse width detection is then performed at 94 or 96. In the case of the AUI, if pulse amplitude and width criteria are met, the signal is effectively qualified and passed to receive multiplexer 98 as AUI receive data and AUI receive carrier sense signals. Similarly, the AUI waveform is also received and amplitude tested by collision detection receiver 91 and tested for pulse width at 95. If the AUI waveform meets the amplitude and width criteria, an AUI collision signal is supplied to the port multiplexer to block AUI transmissions while an AUI waveform is being received. For the 10BASE-T receive path, data is further qualified by "smart squelch" 100, which in essence looks for multiple pulses in a specific order, to ascertain that this receive waveform is packet data and not noise. If the waveform passes this criteria, it is qualified and passed to the receive multiplexer 98 as 10BASE-T data and 10BASE-T receive carrier sense. The receive multiplexer 98 is set up to select one of the receive data paths (either by programming or automatically as previously discussed), allowing the receive data to be decoded from Manchester to non-return to zero (NRZ) format by the PLL/decoder 84, and passed to the MAC 38 through the port multiplexer 80. In addition, for the 10BASE-T port, the transmission of link test pulses 60 (Figure 3) on line 101 is controlled by 10BASE-T transmit link state machine 102, so that pulses are transmitted during periods of data (packet) inactivity. 10BASE-T receive link state machine 104 monitors the presence of receive link beat pulses or packet data, and asserts the LNKST pin if the link is considered operable. SLEEP 1 and SLEEP 2 outputs from port multiplexer 80 are effectively set up by the condition of the AWAKE and RWAKE bits. If the SLEEP pin is activated, and AWAKE and RWAKE have not been programmed, SLEEP 1 and SLEEP 2 will be activated, shutting down the AUI and 10BASE-T transmit and receive functions. Note that 10BASE-T link test pulses will not be generated by the MAC 30 when the SLEEP pin is asserted, as an additional power saving feature. Note also that the entire MAC core portion 38 of the chip will be in a low power sleep mode, consuming minimal power. If AWAKE is set and the SLEEP pin activated, SLEEP 1 is asserted, but SLEEP 2 is not. This powers down the entire AUI transmit and receive paths, and the 10BASE-T transmit path. However, the 10BASE-T receiver 92 remains powered, and the receive chain remains operable, including the ability to detect link test pulses. If RWAKE is set and the SLEEP pin activated, SLEEP 1 and SLEEP 2 are " not asserted. Both the AUI and IOBASE-T receivers 90 and 92 remain operable, as does the PLL/decoder 84. Data received will be passed to the port multiplexer 80, which will allow the EADI 52 output pins Serial Receive Data (SRD), Serial Receive Data Clock (SRDCLK) and Start Frame/Byte Delimiter (SF/BD) to be driven. The transmit portions of the AUI and IOBASE-T interfaces will not be in their most optimal power conservation mode, but will be static (no data and/or link test pulses will be transmitted). The MAC core 38 will of course be in its power saving mode. Since this mode is intended for "security" applications, the power conservation issue is not deemed as important. Note that the LNKST pin output buffer is active when in the normal operating mode or when AWAKE is set before SLEEP is asserted (it is not active during RWAKE operation). The data processing network controller operates in a sleep mode to conserve power, but a portion of the controller remains active to monitor for transmissions. Power consumption of a network connection is managed by operating software/hardware. A data processing network controller can be used to power down a terminal on a network from a central network system, and the terminal can also be powered up from the central network system. A portion of the network controller remains active to signal its presence to the network during the sleep mode. It should further be apparent to those skilled in the art that various changes in form and details of the invention as shown and described may be made.

Claims: A method for operating a local area network, which comprises connecting a data processing terminal (34) to an Ethernet local area network through an Ethernet media access controller (MAC) (30) and an Ethernet 10 Base-T transceiver (37), and comprising periodically signalling the presence of the network to the transceiver, the method being characterised by the steps of: while the media access controller assumes a power saving sleep mode, a receive section of the transceiver remains awake; signalling the presence of the network to said receive section of the transceiver (37) when the media access controller is in the sleep mode; and awakening the media access controller from the sleep mode in response to said transceiver receiving from the network a packet transmission including a node address for the data processing terminal and an awakening instruction. The method of claim 1 additionally comprising the step of periodically signalling the network with the transceiver to signal presence of the transceiver on the network. The method of claim 1 or claim 2 comprising the step of monitoring the packet transmissions on the network by the transceiver.

Inventors: CRAYFORD IAN S, CRAYFORD, IAN S.
Applicants: ADVANCED MICRO DEVICES INC, ADVANCED MICRO DEVICES, INC.
Application year: 1993
Main classification: H04L12
IPC codes: G06F1, H04L12