Abstract:
A method and apparatus for selecting a media for communication in a network. The method includes (i) using a first autonegotiation circuit to attempt to establish a link over a first media of a first type, and (ii) simultaneously using a second autonegotiation circuit to attempt to establish a link over a second media of a second type, the second type being different from the first type. In response to establishing the link over the first media prior to establishing the link over the second media, the second autonegotiation circuit is powered down. In response to establishing the link over the second media prior to establishing the link over the first media, the first autonegotiation circuit is powered down.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/400,457, filed Apr. 7, 2006, which is a continuation of U.S. patent application Ser. No. 09/991,046 filed Nov. 21, 2001. The disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to computer networks, and more particularly to an automatic media selector for Ethernet networks. 
     BACKGROUND OF THE INVENTION 
     Referring now to  FIG. 1 , a data link layer  10  of the open systems interconnection (OSI) model includes a logical link control (LLC) layer  12  and a media access control (MAC) layer  14 . The LLC layer  12  addresses and exchanges data with a network layer  16 . The MAC layer  14  provides an interface between the LLC layer  12  and a physical layer  18 . 
     The MAC layer  14  frames data for transmission over the network and then passes the frame to the physical layer  18  for transmission as a stream of bits. In other words, the MAC layer  14  frames data into distinct units or packets that are transmitted one at a time over the network. 
     The physical layer  18  typically includes a physical coding sublayer (PCS)  20 , a physical medium attachment (PMA) sublayer  22 , and an autonegotiation sublayer  24 . A medium dependent interface (MDI)  26  such as an RJ-45 connector connects the physical layer  18  to media  28  such as twisted pair wires, optical fiber or other media. The IEEE 802.3 specification, which is hereby incorporated by reference, further defines how physical network interfaces operate with different types of media such as coaxial cable, twisted-pair cable and optical fiber. 
     To improve flexibility, the physical layer  18  of some network devices has been designed to be connected to different types of media. The manufacturer and/or the user may not know the type of media that will be used at the time of manufacturing or purchase. The type of media that is used may also change over time. 
     For example, the physical layer  18  is selectively connectable to copper or optical fiber. Currently, the PCS sublayer  20  of the physical layer  18  is programmed to handle the specific type of media that will be used. For example when optical fiber is used, the operating mode of the PCS  20  is programmed to provide an optical interface. If the user later decides to use a different type of media such as copper, the operating mode of the PCS  20  is programmed to provide a copper interface. The reprogramming process increases the cost of operating the network. 
     The autonegotiation sublayer  24  initiates the exchange of information between two connected network devices and automatically configures the devices to take maximum advantage of their respective abilities. The autonegotiation sublayer  24  advertises the abilities of the network device, acknowledges receipt, identifies common modes of operation, and rejects the use of operational modes that are not shared or supported by both devices. When more than one common mode of operation exists between the devices, an arbitration function of the autonegotiation layer  24  identifies and selects a single mode of operation. After autonegotiation is complete, the devices establish a link and exchange data. 
     SUMMARY OF THE INVENTION 
     A network device and method of operating a network device according to the invention includes a media access controller (MAC) and a physical layer. The physical layer includes an interface that communicates with the MAC. A first autonegotiation circuit attempts to establish a first link using a first transceiver over a first media. A second autonegotiation circuit attempts to establish a second link using a second transceiver over a second media. A media selector communicates with the interface and the first and second autonegotiation circuits. The media selector enables data flow from the first media to the MAC using the interface when the link over the first media is established first. 
     In other features of the invention, the media selector powers down the second autonegotiation circuit and/or the second transceiver when the first link over the first media is established first. The media selector powers up the second autonegotiation circuit and/or the second transceiver when the first link is lost. 
     In still other features, the media selector enables data flow from the second media to the MAC using the interface when the second link over the second media is established first. The media selector powers down the first autonegotiation circuit and/or the first transceiver when the second link over the second media is established first. The media selector powers up the first autonegotiation circuit and/or the first transceiver when the second link is lost. 
     In still other features, the media selector enables data flow from the first media to the MAC using the interface when the first and second links over the first and second media are established at the same time. The media selector powers down the second autonegotiation circuit and/or the second transceiver when the first and second links over the first and second media are established at the same time. The media selector powers up the second autonegotiation circuit and/or the second transceiver when the first link over the first media is lost. 
     In yet other features, the first media is copper and the second media is optical fiber. The interface is a physical coding sublayer (PCS) circuit. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a partial OSI network model for communication between network devices according to the prior art; 
         FIG. 2  is a functional block diagram of a network device including a media access control (MAC) layer and a physical layer with an automatic media selector according to the present invention; 
         FIG. 3  is a more detailed functional block diagram of the first exemplary physical layer including the automatic media selector of  FIG. 2 ; 
         FIG. 4  is a more detailed functional block diagram of the second exemplary physical layer including the automatic media selector of  FIG. 2 ; and 
         FIG. 5  illustrates steps performed by the automatic media selector of  FIGS. 3 and 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     Referring now to  FIG. 2 , a media access control (MAC) layer  50  communicates with a physical layer  52  of a network device. The physical layer  52  includes analog circuits  54  and digital circuits  56 . In the exemplary embodiment, the analog circuits  54  are physically connected to copper media  60  and/or fiber media  64  using media dependent interfaces (MDI) (not shown in  FIG. 2 ) such as an RJ-45 connector or a fiber connector. Skilled artisans can appreciate that the present invention applies to other types of media such as radio frequency as well. 
     In use, the digital circuits  56  of the physical layer  52  include a physical coding sublayer (PCS) interface. Both the copper and fiber autonegotiation sublayers attempt to initiate a link over the copper and fiber media  60  and  64 , respectively. If autonegotiation is completed over the fiber media, the PCS interface is configured for fiber. The copper autonegotiation sublayer and the copper transceiver are preferably powered down. Data flow from the fiber media  64  to the MAC layer  50  is enabled. When the link over the fiber media  64  goes down, the copper autonegotiation layer and/or the copper transceiver are powered back up. 
     Alternately, if autonegotiation and a link are completed over the copper media before or at the same time as the fiber media, the PCS interface is configured for copper. The fiber autonegotiation sublayer and the fiber transceiver are preferably powered down. Data flow from the copper media  60  to the MAC layer  50  is enabled. When the link over the copper media  60  goes down, the fiber autonegotiation sublayer and the fiber transceiver are powered up. As a result, the physical layer  52  automatically configures itself without requiring the physical layer  52  (and/or the PCS thereof) to be reprogrammed. 
     Skilled artisans can appreciate that a standard interface may be provided between the MAC layer  50  and the physical layer  52 . For example, the standard interface can be TBI, GMII, SGMI, RGI, RTBI, MII, RMII, SMII or other suitable interfaces. 
     Referring now to  FIG. 3 , the analog circuits  54  of a first exemplary physical layer  52 - 1  are shown in further detail and include a copper transceiver  70  and a fiber transceiver  72 . The digital circuits  56  of the physical layer  52 - 1  are also shown in further detail and include a copper autonegotiation circuit  76  and a fiber autonegotiation/link circuit  78  that are connected to the copper transceiver  70  and fiber transceiver  72 , respectively. A physical coding sublayer (PCS) interface  90  communicates with the copper transceiver  70 , the copper autonegotiation circuit  76 , the fiber autonegotiation/link circuit  78  and/or the fiber transceiver  72 . The PCS interface  90  has first and second modes of operation for copper and optical fiber, respectively, that can be selected by an automatic media selector  110  as will be described more fully below. 
     During copper autonegotiation, the copper transceiver  70  transmits Fast Link Pulse (FLP) bursts over the copper  60 . The FLP pulse bursts contain configuration parameters that the first network device wishes to advertise. If the copper transceiver  70  receives FLP bursts, negotiation of the configuration parameters occurs and a link over the copper  60  is established and data is exchanged. 
     During fiber autonegotiation, code groups are initially transmitted by the fiber transceiver  72 . For example code groups such as KDKD . . . are transmitted where each symbol represents multiple bits. When autonegotiation occurs, code groups such as KDCCKDCC . . . are transmitted. The link circuit  78  monitors the code groups and identifies sync status. When autonegotiation completes, a link over fiber  64  is established and data is exchanged. 
     The media selector  110  communicates with the copper autonegotiation circuit  76 , the link circuit  78 , and/or the PCS interface  90 . The media selector  110  monitors the status of the copper autonegotiation circuit  76  and the link circuit  78  to identify the media that establishes a link first. Once the link is established over one media, the autonegotiation circuit and/or the transceiver associated with the other media are powered down until the link goes down. When this occurs, the autonegotiation circuit and/or the transceiver that is associated with the other media is powered back up. 
     Referring now to  FIG. 4 , reference numbers from  FIG. 3  are used in  FIG. 4  where appropriate to identify the same elements. A second exemplary physical layer  52 - 2  is shown. The PCS interface  90  may include a copper interface  114  and an optical fiber interface  116 . As described above, the automatic media selector  110  selects one of the interfaces  114  and  116  depending upon which media completes a link first. The other interface is preferably disabled and/or powered down until the link goes down. Otherwise, the operation for the physical layer  52 - 2  is similar to the physical layer  52 - 1 . 
     Referring now to  FIG. 5 , steps for performing automatic media selection according to the present invention are shown generally at  150 . Control begins with step  152  and proceeds to step  154 . In step  154 , both copper and fiber autonegotiation are initiated. In step  156 , the media selector  110  determines whether a fiber link has completed. If the fiber link has completed, the media selector  110  powers down the copper interface  114 , the copper autonegotiation circuit  76  and/or the copper transceiver  70  in step  160 . In step  162 , the media selector  110  enables data flow over fiber to the MAC layer  50 . In step  164 , the media selector  110  determines whether the fiber link is down. If not, control loops back to step  164 . Otherwise, control continues with step  168  where the circuits that were powered down in step  160  are powered back up. Control continues from step  168  back to step  154 . 
     If the fiber link does not complete first as determined in step  156 , control continues with step  172 . In step  172 , control determines whether a copper link is established. If the copper link occurs, the media selector  110  powers down the fiber PCS interface  116 , the link circuit  80 , the fiber autonegotiation/link circuit  78  and/or the fiber transceiver  72  in step  174 . In step  176 , the media selector  110  enables data flow over copper to the MAC layer  50 . In step  178 , the media selector  110  determines whether the copper link is down. If not, control loops back to step  178 . Otherwise, control continues with step  180  where the circuits that were powered down in step  174  are powered back up. Control continues from step  180  to step  154 . 
     The copper interface is employed as a default when both copper and fiber complete the link at the same time. Alternatively, skilled artisans can appreciate that fiber can be selected as a default when both copper and fiber complete the link at the same time. However, both copper and fiber will rarely complete the link at the same time. As can be appreciated, the physical layer can be implemented in a variety of ways such as analog and/or digital circuits, software executed by a processor and memory, application specific integrated circuits, or in any other suitable manner. 
     Thus it will be appreciated from the above, the present invention discloses an automatic media selector and method for selecting the media for Ethernet transceivers. It will be equally apparent and is contemplated that modification and/or changes may be made in the illustrated embodiment without departure from the invention. Accordingly, it is expressly intended that the foregoing description and accompanying drawings are illustrative of preferred embodiments only, not limiting, and that the true spirit and scope of the present invention will be determined by reference to the appended claims and their legal equivalent.