Arrangement for transmitting data packets from a media access controller across multiple physical links

[0002] 1. Technical Field

[0003] The present invention relates to transmitting packet data on a high speed network, more specifically to methods and systems for transmitting data from a media access controller (MAC) layer onto a physical layer of a full-duplex network operating at data rates of at least one gigabit per second.

[0004] 2. Background Art

[0005] Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) that sends data packets to a physical layer transceiver for transmission on the network media.

[0006] The Ethernet protocol ISO/IEC 8802-3 (ANSI/IEEE standard 802.3, 1993 edition) defines a half-duplex media access mechanism that permits all stations to access the network channel with equality. The half-duplex mechanism typically operates at either 10 MB/s, or 100 MB/s. A full-duplex environment has also been proposed for Ethernet networks, referred to as IEEE 802.3x, Full-Duplex with Flow Control—Working Draft (0.3). The full-duplex environment provides a two-way, point-to-point communication link between two networks stations using the switched hub, for example at 100 MB/s, so that two stations can simultaneously transmit and receive Ethernet data packets between each other without collision.

[0007] The IEEE 802.3z Task Force is currently defining standards for the operation of a shared (i.e., half-duplex) and full-duplex gigabit Ethernet. The standard will describe a media access control (MAC) layer, a reconciliation layer, a gigabit-media independent interface (GMII), and physical media dependent sublayers that will implement the physical layer (PHY) of the proposed networks. The proposed networks will enable users to implement Ethernet links capable of operating at a data rate of 1 gigabit per second in half-duplex mode and 2 gigabits per second in full-duplex mode.

[0008] Currently, the Fast Ethernet standard describes a media independent interface (MII) that is used to connect Fast Ethernet MAC layer devices to the Fast Ethernet devices, enabling users to implement Ethernet links operating at 100 MB/s half-duplex, and 200 MB/s full-duplex.

[0009] There currently is no means for users to implement Ethernet links that operate in the range of data rates that exceed 200 MB/s and are lower than 1 gigabit per second. In addition, efforts at implementing a physical data link at gigabit transmission rates is very expensive, since the current state of technology does not permit use of copper links for gigabit data rate transmissions. Hence, only fiber optics can be used to transmit data at gigabit data rates.

[0010] One arrangement for implementing physical layer data links that provide gigabit transmission rates is disclosed in commonly assigned, co-pending application Ser. No. 08/912,235, filed Aug. 15, 1997, entitled “ARRANGEMENT FOR TRANSMITTING HIGH SPEED PACKET DATA FROM A MEDIA ACCESS CONTROLLER ACROSS MULTIPLE PHYSICAL LINKS” now U.S. Pat. No.6,094,439. The disclosed arrangement uses a modified reconciliation layer between the media access controller and the physical layer to transmit at least a portion of the packet data from the media access controller onto multiple media interface links. Use of multiple media interface links provides higher data transmission rates in a cost effective manner by simultaneously transmitting different serial data streams on multiple media interface links, effectively increasing the data rate.

[0011] There is a need for an economic arrangement that specifically identifies implementation functions necessary to enable load allocation of high speed data frames across multiple lower-speed physical links.

[0012] There is also a need for an arrangement that specifies an architecture necessary to implement allocation of high speed data frames across multiple transmission links based on the respective priority of the data frames and the availability of the transmission links.

[0013] These and other needs are attained by the present invention, where data frames received by a media interface from a high speed media access controller are transmitted on selected media interface links based on path selection arbitration logic in the media interface.

[0014] According to one aspect of the present invention, a method of transferring a data frame output from a media access controller of an originating network node to a destination network node, comprises establishing a plurality of first media interface links each configured for transmitting data at a first data rate to respective physical layer links in communication with the destination network node, receiving the data frame in a media interface from the media access controller via a second media interface link at a second data rate higher than the first data rate, and transmitting the received data frame from the media interface for transmission on a selected one of the first media interface links according to a path selection arbitration logic in the media interface. Transmission of data frames received from a media access controller onto media interface links at a lower data rate enables transmission of data from a high speed media access controller in an economic manner by distributing the data frames along multiple lower-rate transmission paths. Moreover, transmission based on the path selection arbitration logic provides a virtual switch fabric below the media access control layer that manages the high speed data frame traffic across multiple lower-speed transmission links.

[0015] Another aspect of the present invention provides an apparatus for transmitting a data frame received from a media access controller via a first media interface link at a first transmission rate, comprising a plurality of transmit buffers configured for storing data to be output to a respective plurality of second media interface links, the second media interface links each configured for sending and receiving data at a second data rate less than the first data rate, a first media interface controller having path selection arbitration logic for selectively storing the received data frame in a selected one of the transmit buffers, and a second media interface controller configured for outputting the data stored in each of the transmit buffers based on a corresponding number of stored bytes exceeding a prescribed threshold and an availability of the corresponding second media interface link.

[0016] Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

[0017] Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent like elements throughout and wherein:

[0018] FIG. 1 is a block diagram illustrating an arrangement for transmitting packet data across a high speed data network according to an embodiment of the present invention.

[0019] FIG. 2 is a block diagram illustrating in detail the virtual gigabit layer for transferring data frames from a media access controller to multiple media interface links according to a first embodiment of the present invention.

[0020] FIG. 3 is a block diagram illustrating the virtual gigabit layer for transmitting high priority frames and low priority frames across multiple physical layer links according to a second embodiment of the present invention.

[0021] FIG. 4 is a block diagram illustrating the path selection arbitration logic of FIGS. 2 and 3.

[0022] FIG. 5 is a diagram illustrating a data frame structure that may include priority information for transmission on high priority links.

[0023] The disclosed embodiment enables a media implementation of gigabit networks using multiple 100 MB/s PHY technology. Since 100 MB/s PHY technology is readily available and cost effective, the 100 MB/s links provide an inexpensive and transparent solution for applications needing higher bandwidth and quality of service options. Moreover, the scaleable link is transparent to the user's application, system and device drivers, enabling a user to seamlessly migrate to full gigabit speeds by simply replacing the disclosed media interface and corresponding physical layer with a gigabit compliant implementation, once available in the technology.

[0024] The disclosed arrangements are directed to implementation of an Ethernet link having scaleable speeds from 200 MB/s to gigabit rates in 200 MB/s steps, using existing 100 MB/s physical layer (PHY) technology. Use of multiple links enables parallel transmissions of different data frames (i.e., data packets) to increase the effective data rate, for example using ten (10) 100 MB/s physical links to produce one virtual GB/s link.

[0025] FIG. 1 is a block diagram illustrating the use of multiple layer links in order to provide gigabit transmission rates using 100 MB/s data links according to an embodiment of the present invention. Each network node 12 includes a protocol layer and a device driver (not shown), and a gigabit media access controller (GMAC) layer 14 having a gigabit MAC (GMAC) core 16 compliant with the gigabit Ethernet standards proposed by the IEEE 802.3z Working Group. Each network node 12 also includes a special reconciliation layer 18, also referred to as a generic media interface, which interfaces with media interface link 19 to the gigabit MAC 18 and provides service functions required to distribute, multiplex, demultiplex, and aggregate traffic via a plurality of 100 MB/s media interface links 21 to and from at least one 100 MB/s physical layer (PHY) device 20 providing a plurality of 100 MB/s media interface links 22₀, 22₁, 22₂, to 22_n. As shown in FIG. 1, the special reconciliation layer 18 and the GMAC layer 14 include gigabit speed media independent interfaces (GMII) 24 for sending and receiving IEEE 802.3 compliant data packets, shown in FIG. 5, for example on a per-byte basis at 125 MB/s via the media interface link 19.

[0026] The GMAC 16 generates a data packet, also referred to as a data frame, according to IEEE 802.3 protocol. The GMAC 16 then outputs the data packet of FIG. 5 including preamble, header (including source and destination addresses 102 and 104, optional VLAN tag 106, packet type/length field 108), payload data field 110, and cyclic redundancy check (CRC) or frame check sequence (FCS) field 112 to the reconciliation layer 18 (i.e., the media interface) via the GMII interface 24. The reconciliation layer 18 includes a virtual gigabit layer 26 configured for receiving the data packet from the GMII interface 24 at the gigabit data rate, and configured for transmitting the received data frame for transmission on a selected one of the media interface links 22₀-22_n. Specifically, the virtual gigabit layer outputs each data frame to a selected one of a plurality of media independent interfaces (MII), shown collectively in FIG. 1 as nMII 28. As recognized in the art, each of the MIIs 28 provides a 100 MB/s full duplex connection via a corresponding media interface link 21 to the physical layer device 20 for transmission and reception across a corresponding physical layer link 22. The physical layer devices 20 may be of type 100BASE-TX, 100BASE-T4, or 100BASE-FX, as desired.

[0027] FIG. 2 is a block diagram illustrating in detail one of the virtual gigabit layers 26aof FIG. 1 according to a first embodiment of the present invention. As shown in FIG. 2, the VGL 26aincludes a preamble detection circuit 30 configured for detecting a preamble from the GMAC 16avia the GMII 24 indicating a start of packet data at a gigabit data rate. The VGL 26aalso includes a GMII control circuit 32 having a path selection, arbitration logic 33, a plurality of MII transmit buffers 34, an MII control 36, a plurality of 100 MB/s preamble detection circuits 38, and management convergence logic 42 configured for supplying a management data clock (MDC) and management data (MDIO) between the GMII 24 and the multiple 100 MB/s MII links 28. The VGL 26 also includes a plurality of MII receive buffers 44 for data received from the MIIs 28 to be output to the GMII 24.

[0028] As shown in FIG. 2, a data frame output by the GMAC 16ais received by the VGL 26avia the GMII 24 across the gigabit media interface link 19a.The preamble detection circuit 30 detects a preamble on the gigabit packet on the GMII interface 24, enabling the VGL 26ato synchronize with the GMAC 16aand to begin reception of the packet data packet. In response to detection of the preamble, the GMII control 32 forwards the packet data (including preamble, header, payload data, and CRC field) to a selected one of the MII transmit buffers 34_i. As described below, the GMII control 32, also referred to as a GMII media interface controller, includes arbitration logic 33 for selecting the transmit buffer 34_ifor a corresponding 100 MB/s transmit path.

[0029] The MII control 36, also referred to as an MII media interface controller, outputs a data frame in response to the stored data in the transmit buffer 34_iexceeding a prescribed threshold, shown as a dotted line in FIGS. 2 and 3. The MII control 36 also controls storing a received data frame from an MII 28_iin the corresponding MII receive buffer 44_i. Once a predetermined minimum number of bytes are stored in a receive buffer 44_i, as indicated by the dotted line, the GMII controller 32 outputs the data frame from the appropriate receive buffer 34_ito the GMAC 16 via the GMII 24.

[0030] The GMII control 32 controls transmission of a data frame received from the GMII 24 using the path selection arbitration logic 33 to select one of the transmit buffers 34_i. Specifically, FIG. 4 is a block diagram illustrating different arbitration logic schemes that may be used by the GMII control 32 in routing an incoming data frame from the GMII 24 to a selected one of the transmit buffers 34_i. The path selection arbitration logic 33 includes a least recently used arbitration portion such as a round-robin portion 33a,a statistical arbitration portion 33b, and a priority arbitration portion 33c. Typically, one of these arbitration logic portions will be selected during initial configuration of the network, depending upon the application. The round-robin arbitration logic 33ais configured to forward a received packet to the next successive transmit buffer 34_iin a prescribed sequence. Alternatively, the arbitration logic 33amay be configured in a more general manner to supply the data frame to the least recently used transmit buffer 34_i, independent of the ordering of the transmit buffers or the respective MII links. The statistical arbitration logic 33bmay be used to provide a more even distribution of data packets from a traffic management standpoint in the event that data packets have substantially different lengths. In this case, high level processing above the MAC layer (e.g., Transmission Control Protocol (TCP)) may be used to monitor the ordering of packets at a destination station. Finally, the priority arbitration logic 33cis used in the arrangement of FIG. 3 to determine a priority of a data frame received from the GMII 24. In this case, the priority arbitration 33cmay determine the priority of the received data frame by different methods, including detecting a prescribed value in the header of the received data frame (e.g., from one of the fields 102, 104, 106, or 108 of FIG. 5), or by detecting a prescribed data pattern in the data field 110 shown in FIG. 5.

[0031] FIG. 3 is a block diagram illustrating the virtual gigabit layer 26aconfigured for transmitting high priority frames and low priority frames across multiple physical layer links according to an embodiment of the present invention. As shown in FIG. 3, the virtual gigabit layer 26′ includes a plurality of transmit buffers 34 configured for storing data frames to be output to respective 100 MB media interface links 28, and a plurality of receive buffers 44 configured for storing data frames received from the respective 100 MB media interface links 28. As such, the receive path of FIG. 3 is identical to the receive path of FIG. 2.

[0032] FIG. 3 also includes a high priority transmit buffer 60 configured for storing data frames from the GMAC 16 via the GMII 24 that are identified by the priority arbitration logic 33cin the GMII controller 32′ as having a high priority. The virtual gigabit layer 26′ also includes a low priority transmit buffer 62 configured for storing data frames from the GMAC 16 via the GMII 24 identified by the priority arbitration logic 33cof the GMII control 32′ as having a low priority.

[0033] The path selection arbitration logic 33 selects one of the transmit buffers 34_ifor transmission of data on the corresponding 100 MB media interface links 28 by first checking if the high priority transmit buffer 60 stores any data. If the high priority transmit buffer 60 has any stored data frames, or if the number of stored data bytes exceeds a prescribed minimum threshold, the GMII control 32′ first outputs the contents of the high priority transmit buffer 60 into a selected one of the transmit buffers 34_i. For example, if the high priority transmit buffer 60 stores two data frames, the GMII control 32′ may transfer the first high priority data packet from buffer 60 to transmit buffer 34₀, and transmit the second high priority data frame from buffer 60 to transmit buffer 34₁. Once the amount of stored data in the high priority buffer 60 falls below a certain prescribed threshold, the GMII control 32′ will then transfer any data frames stored in the low priority buffer 62 to a selected one of the transmit buffers 34_iusing the least recently used arbitration, or statistical arbitration.

[0034] According to the disclosed embodiment, data frames can be transmitted between a high speed media interface link and selected lower-speed media interface links according to a path selection arbitration logic in a media interface to manage transmission and reception of the multiple data packets across the multiple lower-speed media interface links. Timing and synchronization is maintained by storing the data frames in respective buffers associated with the respective lower-speed media interface links, where a first media interface controller controls transmission and reception of data frames associated with the high speed media interface link, and a second media interface controller controls the transmission and reception of data frames across the multiple media interface links.

[0035] Although the disclosed embodiment has been described using a GMII-compliant PHY interface, IEEE 802.3z specifies that the GMAC may be connected to either the GMII-compliant PHY or an 8B/10B-compliant PHY, where 8B/10B encoding is done in the MAC. The disclosed VGL 26 may be modified for 8B/10B protocol by performing 8B/10B decoding of encoded transmit data from the GMAC 16 prior to storage in the Tx buffer 34, performing 8B/10B encoding of receive data prior to output from the Tx buffer 44 to the GMAC 16, and substituting the GMII interfaces 24 with the appropriate 8B/10B interfaces. Hence, the present invention encompasses the use of the alternative 8B/10B protocol.

[0036] While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.