Abstract:
A method for communicating network data of varying speeds comprises establishing a plurality of signal interconnections; storing a first mapping of XGMII signals onto the plurality of signal interconnections; storing a second mapping of GMII signals onto the plurality of signal interconnections; and storing a third mapping of MII signals onto the plurality of signal interconnections. Ones of the plurality of signal interconnections are mapped by each of the first, second, and third mappings. The method further comprises selecting one of the first, second, and third mappings and transmitting the network data over the plurality of signal interconnections using the selected one of the first, second, and third mappings.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 11/114,842, filed Apr. 26, 2005 claims the benefit of U.S. Provisional Application No. 60/640,529, filed on Dec. 30, 2004. The disclosure of the above application is incorporated herein by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to transmitting network data. 
   BACKGROUND OF THE INVENTION 
   Referring now to  FIG. 1 , a block diagram of a system  100  employing a 10 Gbps media independent interface (XGMII) according to the prior art is depicted. A switch  102  contains a media access controller (MAC)  104 . The MAC  104  communicates with a 10 Gbps physical layer device (PHY)  106  within a PHY module  108  via an XGMII connection  110 . The terms MAC, PHY, and many others are explained in IEEE Standard 802.3ae (30 Aug. 2002), which is incorporated herein by reference in its entirety. The XGMII is a simple and easy to implement interconnection between the switch  102  and the PHY module  108 , but it only supports a very limited connection distance between the switch  102  and PHY module  108 . As such, a repeater layer that can extend the reach of XGMII was developed. 
   Referring now to  FIG. 2 , a system  130  according to the prior art contains a switch  132  and a PHY module  134 . Within the switch  132 , a MAC  136  communicates with a first XGMII extender sublayer (XGXS) module  138  via an XGMII link  140 . The first XGXS module  138  communicates with a second XGXS module  142  via a 10 Gbps attachment unit interface (XAUI). The second XGXS module  142  communicates with a 10 Gbps PHY  146  via a second XGMII link  148 . XAUI allows the switch  132  and PHY  134  to have a connection distance in the tens of inches, as compared to a limit of approximately 3 inches for an XGMII link (as in  FIG. 1 ). The XGXS modules,  138  and  142 , translate between XGMII and XAUI. This allows the design of the MAC  136  and the PHY  146  to remain unchanged while still achieving the extended reach of XAUI. 
   SUMMARY OF THE INVENTION 
   A rate adaptation layer (RAL) module for converting from a first interface operating at a first rate to a second interface operating at a second rate comprises first and second input/output (I/O) modules that communicate with the first and second interfaces, respectively. A repeater module receives symbols from the first I/O module and transmits the symbols n times to the second I/O module, where n is determined by the first and second rates. A pull-down module receives symbols from the second I/O module and selectively extracts symbols to be communicated to the first I/O module. 
   In other features, the second rate is greater than or equal to the first rate. The first rate is one of 10 Mbps, 100 Mbps, 1 Gbps, and 10 Gbps. The second rate is 10 Gbps. The repeater module stripes repeated symbols across four lanes. The repeater module begins striping symbols in one of the four lanes. A delimiter injection module communicates a start symbol to the second I/O module to indicate a packet beginning and a terminate symbol to the second I/O module to indicate a packet ending. The second I/O module communicates data symbols and the start and terminate symbols to the second interface. The delimiter injection module replaces a data symbol communicated from the repeater module to the second I/O module with the start symbol. The repeater module stripes repeated symbols across four lanes. At least one of the four lanes are selectively deactivated. Three of the four lanes are selectively deactivated. 
   In other features, the at least one of the four lanes are deactivated when the first rate is less than the second rate. The delimiter injection module selectively inserts idle symbols before the terminate symbol to align the terminate and start symbols on the same one of the four lanes. A carrier extend substitution module selectively replaces symbols received from the first I/O module before they are passed to the repeater module. The carrier extend substitution module replaces a carrier extend symbol with an idle symbol and a carrier extend/error symbol with a symbol error. n is equal to the second rate divided by the first rate. 
   In other features, a nibble replicator module selectively replaces each four-bit nibble received from the first I/O module with a byte comprising two copies of the nibble, before passing the byte to the repeater module. The nibble replicator module is enabled when the first rate is equal to one of 10 Mbps and 100 Mbps. n is equal to the second rate divided by twice the first rate when the nibble replicator module is enabled, and equal to the second rate divided by the first rate otherwise. The pull-down module extracts one of x symbols, then one of y symbols, in alternating succession. x is equal to a rounded up division of n by four, and wherein y is equal to a rounded down division of n by four. The first I/O module inserts and removes idle symbols to retain clock synchronization with the first interface. 
   In other features, a media and speed independent device comprises the RAL module and further comprises a media access controller (MAC) that communicates with the RAL module. A physical extension module communicates with the RAL module and with the external device using a physical extension interface. The physical extension interface includes a 10 Gbps attachment unit interface (XAUI) and the physical extension module includes a 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) module. The physical extension interface is bidirectional serial and the physical extension module includes a 10 Gbps BASE-R (10GBASE-R) module. The MAC communicates with the RAL module using extended XGMII (EXGMII). 
   In still other features, a media and speed independent device comprises the RAL module and further comprises a physical layer device (PHY) that communicates with the RAL module. A physical extension module communicates with the RAL module and with the external device using a physical extension interface. The physical extension interface includes a 10 Gbps attachment unit interface (XAUI) and the physical extension module includes a 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) module. The physical extension interface is bidirectional serial and the physical extension module includes a 10 Gbps BASE-R (10GBASE-R) module. The PHY communicates with the RAL module using EXGMII. 
   A method for operating a rate adaptation layer (RAL) module comprises providing a first interface operating at a first rate and a second interface operating at a second rate; providing first and second input/output (I/O) modules that communicate with the first and second interfaces, respectively; receiving symbols from the first I/O module; transmitting the symbols n times to the second I/O module, where n is determined by the first and second rates; and selectively extracting symbols to be communicated to the first I/O module. 
   In other features, the second rate is greater than or equal to the first rate. The first rate is one of 10 Mbps, 100 Mbps, 1 Gbps, and 10 Gbps. The second rate is 10 Gbps. The method includes striping repeated symbols across four lanes. The method includes beginning striping symbols in one of the four lanes. The method includes communicating a start symbol to the second I/O module to indicate a packet beginning; and communicating a terminate symbol to the second I/O module to indicate a packet ending. In other features, the method includes communicating data symbols and the start and terminate symbols to the second interface. The method includes replacing a data symbol communicated from the repeater module to the second I/O module with the start symbol. The method includes striping repeated symbols across four lanes. The method includes selectively deactivating at least one of the four lanes to save power. The method includes selectively deactivating three of the four lanes. The method includes selectively deactivating the at least one of the four lanes when the first rate is less than the second rate. 
   In other features, the method includes selectively inserting idle symbols before the terminate symbol to align the terminate and start symbols on the same one of the four lanes. The method includes selectively replacing symbols received from the first I/O module before they are passed to the repeater module. The method includes replacing a carrier extend symbol with an idle symbol; and replacing a carrier extend/error symbol with a symbol error. n is equal to the second rate divided by the first rate. The method includes selectively replacing each four-bit nibble received from the first I/O module with a byte comprising two copies of the nibble before passing the byte to the repeater module. The method includes extracting one of x symbols, then one of y symbols, in alternating succession. x is equal to a rounded up division of n by four, and wherein y is equal to a rounded down division of n by four. The method includes inserting and removing idle symbols to retain clock synchronization with the first interface. 
   A rate adaptation layer (RAL) module for converting from a first interface operating at a first rate to a second interface operating at a second rate comprises first and second input/output (I/O) means for communicating with the first and second interfaces, respectively. Repeater means receives symbols from the first I/O means and transmits the symbols n times to the second I/O means, where n is determined by the first and second rates. Pull-down means receives symbols from the second I/O means and selectively extracts symbols to be communicated to the first I/O means. 
   In other features, the second rate is greater than or equal to the first rate. The first rate is one of 10 Mbps, 100 Mbps, 1 Gbps, and 10 Gbps. The second rate is 10 Gbps. The repeater means stripes repeated symbols across four lanes. The repeater means begins striping symbols in one of the four lanes. Delimiter injection means communicates a start symbol to the second I/O means to indicate a packet beginning, and communicates a terminate symbol to the second I/O means to indicate a packet ending. The second I/O means communicates data symbols and the start and terminate symbols to the second interface. The delimiter injection means replaces a data symbol communicated from the repeater means to the second I/O means with the start symbol. 
   In other features, the repeater means stripes repeated symbols across four lanes. At least one of the four lanes are selectively deactivated to save power. Three of the four lanes are selectively deactivated. The at least one of the four lanes are deactivated when the first rate is less than the second rate. The delimiter injection means selectively inserts idle symbols before the terminate symbol to align the terminate and start symbols on the same one of the four lanes. Carrier extend substitution means selectively replaces symbols received from the first I/O means before they are passed to the repeater means. The carrier extend substitution means replaces a carrier extend symbol with an idle symbol, and replaces a carrier extend/error symbol with a symbol error. n is equal to the second rate divided by the first rate. 
   In other features, nibble replicating means for selectively replacing each four-bit nibble received from the first I/O means with a byte comprising two copies of the nibble, before passing the byte to the repeater means. The nibble replicator means is enabled when the first rate is equal to one of 10 Mbps and 100 Mbps. n is equal to the second rate divided by twice the first rate when the nibble replicator means is enabled, and equal to the second rate divided by the first rate otherwise. The pull-down means extracts one of x symbols, then one of y symbols, in alternating succession. x is equal to a rounded up division of n by four, and wherein y is equal to a rounded down division of n by four. The first I/O means inserts and removes idle symbols to retain clock synchronization with the first interface. 
   In other features, a media and speed independent device comprising the RAL module of and further comprises media access controller (MAC) means for communicating with the RAL means. Physical extension means communicates with the RAL means and the external device using a physical extension interface. The physical extension interface includes a 10 Gbps attachment unit interface (XAUI) and the physical extension means includes a 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) module. The physical extension interface is bidirectional serial and the physical extension means includes a 10 Gbps BASE-R (10GBASE-R) module. The MAC means communicates with the RAL means using extended XGMII (EXGMII). 
   In still other features, a media and speed independent device comprising the RAL module and further comprises physical layer (PHY) means for communicating with the RAL module. Physical extension means communicates with the RAL module and with the external device using a physical extension interface. 
   In other features, the physical extension interface includes a 10 Gbps attachment unit interface (XAUI) and the physical extension means includes a 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) module. The physical extension interface is bidirectional serial and the physical extension means includes a 10 Gbps BASE-R (10GBASE-R) module. The PHY means communicates with the RAL means using EXGMII. 
   A media and speed independent system for transmitting Ethernet data comprises a media access controller (MAC) and a first rate adaptation layer (RAL) module that communicates with the MAC. A first physical extension module communicates with the first RAL module. A second physical extension module communicates with the first physical extension module using a physical extension interface. A second RAL module communicates with the second physical extension module. A physical layer device (PHY) communicates with the second RAL module. 
   In other features, the physical extension interface includes a 10 Gbps attachment unit interface (XAUI) and the first and second physical extension modules include 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) modules. The physical extension interface includes bidirectional serial and the first and second physical extension modules include 10 Gbps BASE-R (10GBASE-R) modules. The MAC communicates with the first RAL module using extended XGMII (EXGMII), and the PHY communicates with the second RAL module using EXGMII. 
   A media and speed independent device for transmitting Ethernet data to an external device comprises a media access controller (MAC) and a rate adaptation layer (RAL) module that communicates with the MAC. A physical extension module communicates with the RAL module and with the external device using a physical extension interface. 
   In other features, the physical extension interface includes a 10 Gbps attachment unit interface (XAUI) and the physical extension module includes a 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) module. The physical extension interface includes bidirectional serial and the physical extension module includes a 10 Gbps BASE-R (10GBASE-R) module. The MAC communicates with the RAL module using extended XGMII (EXGMII). 
   A media and speed independent system for transmitting Ethernet data comprises media access controller (MAC) means for providing a first interface. First rate adaptation layer (RAL) means communicates with the MAC means. First physical extension means communicates with the first RAL means. Second physical extension means communicates with the first physical extension means using a physical extension interface. Second RAL means communicates with the second physical extension means. Physical layer (PHY) means communicates with the second RAL means and a medium. 
   In other features, the physical extension interface includes a 10 Gbps attachment unit interface (XAUI) and the first and second physical extension means include 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) modules. The physical extension interface includes bidirectional serial and the first and second physical extension means include 10 Gbps BASE-R (10GBASE-R) modules. The MAC means communicates with the first RAL means using extended XGMII (EXGMII), and the PHY means communicates with the second RAL means using EXGMII. 
   A media and speed independent device for transmitting Ethernet data to an external device comprises media access controller (MAC) means for providing an interface. Rate adaptation layer (RAL) means communicates with the MAC means. Physical extension means communicates with the RAL means and with the external device using a physical extension interface. 
   In other features, the physical extension interface includes a 10 Gbps attachment unit interface (XAUI) and the physical extension means includes a 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) module. The physical extension interface includes bidirectional serial and the physical extension means includes a 10 Gbps BASE-R (10GBASE-R) module. The MAC means communicates with the RAL means using extended XGMII (EXGMII). 
   A method for operating a media and speed independent system for transmitting Ethernet data comprises providing a media access controller (MAC); providing a first rate adaptation layer (RAL) module that communicates with the MAC; providing a first physical extension module that communicates with the first RAL module; providing a second physical extension module that communicates with the first physical extension module using a physical extension interface; providing a second RAL module that communicates with the second physical extension module; and providing a physical layer device (PHY) that communicates with the second RAL module. 
   In other features, the physical extension interface includes a 10 Gbps attachment unit interface (XAUI) and the first and second physical extension modules include 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) modules. The physical extension interface is bidirectional serial and the first and second physical extension modules include 10 Gbps BASE-R (10GBASE-R) modules. The method includes using extended XGMII (EXGMII) for communication between the MAC and the first RAL module; and using EXGMII for communication between the PHY and the second RAL module. 
   A method for operating a media and speed independent device for transmitting Ethernet data to an external device comprises providing a media access controller (MAC); providing a rate adaptation layer (RAL) module that communicates with the MAC; and providing a physical extension module that communicates with the RAL module and that communicates with the external device using a physical extension interface. 
   In other features, the physical extension interface is a 10 Gbps attachment unit interface (XAUI) and the physical extension module is a 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) module. The physical extension interface is bidirectional serial and the physical extension module includes a 10 Gbps BASE-R (10GBASE-R) module. The method includes using extended XGMII (EXGMII) for communication between the MAC and the RAL module. 
   A media and speed independent device for transmitting Ethernet data to an external device comprises a physical layer device (PHY) and a rate adaptation layer (RAL) module that communicates with the PHY. A physical extension module communicates with the RAL module and with the external device using a physical extension interface. 
   In other features, the physical extension interface is a 10 Gbps attachment unit interface (XAUI) and the physical extension module is a 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) module. The physical extension interface is bidirectional serial and the physical extension module is a 10 Gbps BASE-R (10GBASE-R) module. The PHY communicates with the RAL module using EXGMII. 
   A media and speed independent means for transmitting Ethernet data to an external device comprises physical layer (PHY) means for providing an interface to a medium. Rate adaptation layer (RAL) means communicates with the PHY means. Physical extension means communicates with the RAL means and with the external device using a physical extension interface. 
   In other features, the physical extension interface includes a 10 Gbps attachment unit interface (XAUI) and the physical extension means includes a 10 Gbps media independent interface (XGMII) extender sublayer (XGXS) module. The physical extension interface includes bidirectional serial and the physical extension means includes a 10 Gbps BASE-R (10GBASE-R) module. The PHY communicates with the RAL means using EXGMII. 
   A method for communicating network data of varying speeds comprises establishing a plurality of signal interconnections; defining a first mapping of XGMII signals onto the plurality of signal interconnections; defining a second mapping of GMII signals onto the plurality of signal interconnections; and defining a third mapping of MII signals onto the plurality of signal interconnections. 
   In other features, the first mapping is a one to one mapping. The plurality of signal interconnections includes a transmit set of signal interconnections and a receive set of signal interconnections. The first, second, and third mappings include mapping transmit data signals to a set of the data signal interconnections of the transmit set. The first, second, and third mappings include mapping receive data signals to a set of the data signal interconnections of the receive set. The first, second and third mappings include mapping transmit control signals to a set of control signal interconnections of the transmit set. The first, second and third mappings include mapping receive control signals to a set of control signal interconnections of the receive set. The first, second and third mappings include mapping a receive clock signal to a clock signal interconnection of the receive set. The first and second mappings involve mapping a transmit clock signal to a clock signal interconnection of the transmit set. The third mapping involves mapping a transmit clock signal to the clock signal interconnection of the transmit set. The third mapping involves mapping a transmit clock signal to one of the data signal interconnections of the receive set. 
   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 block diagram of system employing a 10 Gbps media independent interface (XGMII) according to the prior art; 
       FIG. 2  is a block diagram of a system according to the prior art contains a switch and a PHY module; 
       FIG. 3  is a block diagram of a system using a serial link to connect a switch and PHY; 
       FIG. 4  is a mapping table of MII, GMII, and XGMII signals onto EXGMII pins; 
       FIG. 5  is a block diagram of a system having an exemplary speed and media independent interface; 
       FIG. 6  is a block diagram of an alternative system using another exemplary interconnection according to the principals of the present invention; 
       FIG. 7  is a block diagram of an exemplary implementation of a rate adaptation layer (RAL) module; 
       FIG. 8  is a graphical depiction of exemplary byte striping across XGMII lanes; 
       FIG. 9  is a table depicting byte striping on XGMII at the end of a packet; and 
       FIG. 10  is a table depicting byte striping across XGMII at the end of an alternate packet. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module, controller and/or device refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
   Referring now to  FIG. 3 , a system  160  according to the present invention that uses a serial link to connect a switch and PHY is illustrated. A MAC  162  within a switch  164  communicates with a 10 Gbps base R (10GBASE-R) module  166  via first XGMII link  168 . The 10GBASE-R module  166  communicates with a second 10GBASE-R module  170  via a serial link  172 . The second 10GBASE-R module  170  is located within a PHY module  174  and communicates with a 10 Gbps PHY  176  via a second XGMII link  178 . This system  160  essentially uses a 10 Gbps serial Ethernet connection between the switch  164  and the PHY module  174 . Although the serial link does not afford much greater distance than an XGMII link, the PHY module  174  can be used to convert between electrical and optical media. 
   Because many MACs and PHYs are capable of supporting different speeds, it would be advantageous for the media independent interface (MII) to also be speed independent so that the same MII could be used regardless of the speed of the MAC or of the PHY. Additionally, it would be beneficial for the design of the XGXS and the XAUI to remain unchanged and yet still transmit data at any speed supported by the MAC and the PHY. 
   A media independent interface (MII) is defined for transmitting 10 Mbps data and 100 Mbps data. A 1 Gbps MII (GMII) is defined to transmit 1 Gbps Ethernet data, and a 10 Gbps MII (XGMII) is defined to transmit 10 Gbps Ethernet data. Using three separate MIIs to support transmission of the four speeds of Ethernet data is redundant. To reduce this waste, an extended XGMII (EXGMII) has been developed. In some implementations, the EXGMII uses the same number of signal interconnections (pins, traces, etc.) as XGMII, and accommodates XGMII, GMII, and MII. 
   Referring now to  FIG. 4 , a mapping of MII, GMII, and XGMII signals onto EXGMII pins is shown. A mapping table  200  contains six columns. A first column  202  lists EXGMII pin names. A second column  204  specifies the transmission direction with respect to the PHY. A third column  206  specifies the XGMII signals that map to the corresponding EXGMII pin, which is indicated in the first column  202 . A fourth column  208  specifies the GMII signals that map to the corresponding EXGMII pin, which is indicated in the first column  202 . A fifth column  210  specifies the MII signals that map to the corresponding EXGMII pin, which is indicated in the first column  202 . A sixth column  212  specifies an alternative mapping of MII signals to EXGMII pins. The alternative mapping in the sixth column  212  allows the transmit direction to be source-synchronous by making TX_CLK an input to the PHY (providing the clock for the input TXD data signals). 
   Referring now to  FIG. 5 , a system  300  having an exemplary speed and media independent interface is depicted. A switch  302  includes a media access controller (MAC)  304 , a MAC rate adaptation layer (RAL)  306 , and a first XGMII extender sublayer (XGXS) module  308 . The MAC  304  communicates with the MAC RAL  306  via an EXGMII link  310 . The MAC RAL  306  communicates with the first XGXS module  308  via an XGMII link  312 . A physical layer device (PHY)  320  module contains a multispeed PHY  322 , a PHY rate adaptation layer (RAL)  324 , and a second XGXS module  326 . The PHY  322  communicates with the PHY RAL  324  via an EXGMII link  328 . The PHY RAL  324  communicates with the second XGXS module  326  via an XGMII link  330 . 
   The first and second XGXS modules,  308  and  326 , communicate via a 10 Gbps Attachment Unit Interface (XAUI)  332 . While the PHY  322  and the MAC  304  can operate at a number of speeds (including 10 Mbps, 100 Mbps, 1 Gbps, and 10 Gbps), the XGXS modules,  308  and  326 , and the XAUI link  332  operate at 10 Gbps. The RALs  306  and  324  convert from the line speed to 10 Gbps. In this way the XGXS modules and the XAUI protocol can be used without redesign. 
   Referring now to  FIG. 6 , a block diagram of an alternative system  350  using another exemplary interconnection according to the principals of the present invention is depicted. The alternative system  350  is the same as the system  300  of  FIG. 5 , except that the XGXS modules,  308  and  326 , have been replaced with 10 Gbps BASE-R (10GBASE-R) modules,  352  and  354 , which communicate via a serial link  356 . The 10 GBASE-R modules,  352  and  354 , essentially form a 10 Gbps Ethernet link between the switch  302  and PHY module  320 . 
   Referring now to  FIG. 7 , a block diagram of an exemplary implementation of a rate adaptation layer (RAL) module is depicted. A system  400  includes a RAL module  402  that communicates on one side with EXGMII and on the other with XGMII. A first input module  404  and a first output module  406  communicate with EXGMII. A second input module  408  and a second output module  410  communicate with XGMII. The first input module  404  communicates with a carrier extend substitution module  412 . The carrier extend substitution module  412  communicates an output to a nibble replicator  416 . The nibble replicator  416  communicates an output to a repeater module  418 . The repeater module  418  communicates an output to a delimiter injection module  420 . The delimiter injection module  420  communicates an output to the second output module  410 . 
   The second input module  408  communicates with a pull-down module  422 . The pull-down module  422  communicates an output to the first output module  406 . A data rate value  424  is communicated to the carrier extend substitution module  412 , the nibble replicator  416 , the repeater module  418 , the delimiter injection module  420 , and the pull-down module  422 . 
   The carrier extend substitution module  412  operates when the rate  424  is 1 Gbps. When operating, the carrier extend substitution module  412  replaces a carrier extend symbol received from the first input module  404  with an idle symbol, and replaces a carrier extend/error symbol with a symbol error. Otherwise, the carrier extend substitution module  412  passes symbols unchanged. The nibble replicator  416  is enabled when the rate  424  is either 10 Mbps or 100 Mbps. When enabled, the nibble replicator  416  takes each received 4-bit nibble and duplicates it to form a byte. For example, a nibble 1011 will become the byte 10111011. 
   The repeater module  418  is inactive (pass-through) when the rate  424  is 10 Gbps. When the rate  424  is 1 Gbps, the repeater module  418  will repeat each received 8-bit data symbol ten times. The way in which these repeated symbols are transmitted to the delimiter injection module  420  is discussed below in conjunction with  FIGS. 8 through 10 . When the rate  424  is 100 Mbps, the repeater module  418  repeats each byte fifty times. When the rate  424  is 10 Mbps, the repeater module  418  repeats each byte five hundred times. The repeated symbols that the repeater module  418  produces are striped across four lanes as XGMII specifies. As with the repeater module  418 , the delimiter injection module  420  operates when the rate  424  is not 10 Gbps. The delimiter injection module  420  places a /S/ start symbol on lane zero at the beginning of a packet, and a /T/ terminate symbol on lane zero immediately after the end of a packet. Any bytes between the end of the packet and the concluding /T/ symbol are filled with a pad byte. 
   The first and second input modules,  404  and  408 , and first and second output modules,  406  and  410 , can be responsible for inserting and removing idle symbols to match internal clock rates with that of the XGMII and EXGMII links. FIFO (first-in first-out) buffers used for inserting and removing idle symbols can be made smaller when only the first input module  404  and the first output module  406  are responsible for idle insertion and removal. The pull-down module  422  operates when the rate  424  is not 10 Gbps. The operation of the pull-down module  422  will become more clear after  FIGS. 8 through 10  are discussed. 
   Referring now to  FIG. 8 , a graphical depiction  500  of exemplary byte striping across XGMII lanes is presented. Four XGMII lanes are numbered  0  through  3 . Idles  502  appear before the beginning of a packet. This example is for an EXGMII link operating at 1 Gbps, and so bytes are repeated ten times. Bytes are striped, beginning with lane  0  and progressing through lane  3 . For example, byte  0  (denoted B 0 ) starts in column  504 , and continues through column  506  and half of column  508 , where the next ten replicated bytes (B 1 ) begin. The first instance of B 0  (the start of a packet) is replaced with the /S/ start symbol  510  (shown shaded). Striping for a packet begins on lane  0 , and so the /S/ symbol will always occur on lane  0 . Inspecting lane  0  by itself, it can be seen that bytes are presented in a 3-2-3-2 order. This is because four divides into ten 2.5 times. In order to decode the byte striping, only lane  0  need be inspected, and 1 byte selected from each of the 3- or 2-byte groups. 
     FIG. 9  is a table  530  depicting byte striping on XGMII at the end of a packet. The example of table  530  is also for a 1 Gbps EXGMII rate, and in this table the number of bytes in the packet is even. This means that a /T/ terminate symbol  532  placed after the last byte of the packet will naturally fall on lane  0 . The remaining three lanes are filled with idle symbols. 
   Referring now to  FIG. 10 , a table  560  depicts byte striping across XGMII at the end of an alternative packet. Here, the EXGMII rate is still 1 Gbps, but the number of bytes in the packet is odd. With an odd number of packets, a /T/ terminate symbol placed at the end of the data bytes will naturally fall in lane  2 . For ease of recovery, however, the /T/ terminate symbol should be placed on lane  0 . To this end, two pad symbols  562  are inserted on lanes  2  and  3 , which then causes the /T/ terminate symbol  564  to fall on lane  0 . As can be seen, the bytes of a packet can be decoded by looking only at lane  0 . This means that lanes  1  through  3  may be turned off to save power when not operating at 10 Gbps. 
   Returning now to  FIG. 7 , operation of the pull-down module  422  is more clear. The pull-down module  422  simply passes data through when the rate  424  is 10 Gbps. When the rate  424  is 1 Gbps, the pull-down module  422  extracts from XGMII lane  0  one of three bytes, one of two bytes, one of three bytes, one of two bytes, and so on. When the rate  424  is 100 Mbps, recall that bytes were replicated fifty times. Four divides into fifty 12.5 times, and therefore the pull-down module  422  will extract one of thirteen bytes, one of twelve bytes, one of thirteen bytes, one of twelve bytes, and so on. In 10 Mbps mode, recall that bytes were replicated five hundred times. Four divides evenly into five hundred 125 times, and therefore the pull-down module  422  extracts one byte out of every 125 bytes received. 
   Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.