Abstract:
A method for reducing errors on an Ethernet network multi-speed link segment and thereby increasing network stability and performance. An error rate on the link segment is evaluated. When the error rate exceeds a threshold, the link segment is automatically reconfigured to operate at a lower speed Ethernet implementation. According to an embodiment of the present invention, the error rate may be evaluated by one or both of the network entities coupled to the link segment. For example, the network entity could be a switch or a hub. Also, when the network entity is part of a personal computer having an Ethernet interface card, the evaluation of the error rate may be performed by the card of Ethernet driver software.

Description:
FIELD OF THE INVENTION 
     The present invention relates to Ethernet networks, and in particular, to a method for reducing errors on dedicated multi-speed Ethernet link segments. 
     RELATED TECHNOLOGY 
     Ethernet local area networks are in wide use today. The term Ethernet is often used to refer to all carrier sense multiple access/collision detection (CSMA/CD) LANs that generally conform to Ethernet specifications, including IEEE (Institute of Electrical and Electronic Engineers) 802.3. IEEE 802.3, for example in the version published on Jul. 29, 1996, sets forth standards for Ethernet-type networks. Ethernet also forms the technological basis for ISO-IEC (International Organization for Standardization-International Engineering Consortium) 8802-3, as published in 1996. 
     Basic Ethernet, such as 10 Base-T, is capable of a data transmission rate of 10 Mbps (Megabits per second). The need for greater data rates has led to the development of “fast Ethernet”, such as 100 Base-TX. 100 Base-TX fast Ethernet runs well, i.e., with acceptable error rates, on EIA-TIA (Electronic Industries Alliance-Telecommunications Industry Association) 568 Category 5 unshielded twisted-pair cable, sometimes called UTP-5, or CAT 5. 100 Base-TX operates with lower signal levels, and therefore requires higher quality cable and is more sensitive to electromagnetic interference than 10 Base-T. While 100 Base-TX is capable of running on Category 3 unshielded twisted-pair cable, or CAT 3, the result is often a poor link segment with many errors. 
     Autonegotiation is a mechanism specified in IEEE 802.3 whereby the network entities at either end of a link segment automatically determine the data rate at which the link segment will operate. Using autonegotiation, each network entity compares what Ethernet implementation it supports to what implementation network entity at the other end supports. The network entities choose which implementation to use for that network link segment according to a predetermined priority ranking. For example, 100 Base-TX full duplex has a higher priority than 10 Base-T. Most current Ethernet network entities support autonegotiation. 
     As an Ethernet network is upgraded from 10 Mbps to 100 Mbps equipment, link segment cabling must be upgraded from CAT 3 to CAT 5 to properly support 100 Base-TX. Because such a cabling upgrade is costly, among other reasons, networks are often upgraded in a phased or piecemeal fashion. Thus, some network cable plants may include a mixture of CAT 5 cable and CAT 3 cable. There is a good chance that a 100 Base-TX link may be inadvertently established over a CAT 3 cable. The result of attempting to run 100 Base-TX over CAT 3 cable may be high error rates and an unstable network. An unacceptably high error rate may occur even when running a 100 Base-TX over a CAT 5 cable when the cable is subject to electromagnetic interference. Such electromagnetic interference may be caused by, for example, running the cable in a cable tray alongside power cables. Once a link segment is operating at 100 Base-TX, it may continue to do so even at unacceptably high error rates. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for controlling a data rate on a dedicated multi-speed link segment in an Ethernet network between two network entities, the link segment operating at a first data rate. The method comprises evaluating an error rate on the link segment, and, when the error rate on the link segment exceeds a threshold, automatically reconfiguring the link segment to operate at a second, lower data rate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the method according to the present invention are elucidated in the following description and depicted in the drawings, in which: 
     FIG. 1 shows a schematic representation of an Ethernet network in accordance with the present invention; and 
     FIG. 2 shows a flowchart of an exemplary embodiment of the method of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, link segment  10  interconnects personal computer (PC)  20  and switch  30 . As embodied herein, PC  20  and switch  30  are network entities in an Ethernet local area network. PC  20  and switch  30  are each capable of running multiple Ethernet implementations, such as 10 Base-T or 100 Base-TX, for example, using appropriate software and/or hardware. In other embodiments of the present invention, PC  20  and switch  30  could each be any of a variety of appropriate devices, such as a hub, a router, a printer, etc. PC  20  is preferably configured with an Ethernet interface card  25 . As embodied herein, PC  20  and switch  30  each support autonegotiation. 
     As embodied herein, link segment  10  interconnects PC  20  and network switch  30 . Link segment  10  is a Category 3 unshielded twisted-pair (CAT 3) cable. In other embodiments, however, link segment  10  may be a Category  5  unshielded twisted-pair (CAT 5) cable, or other type of cable. As embodied herein, link segment  10  is capable of multiple data rates, such as 10 Mbps and 100 Mbps. 
     PC  20  and switch  30 , along with link segment  10 , form part of an Ethernet, e.g., an IEEE 802.3, local area network. The network topology may be Ring, Star, or other configuration in which link segment  10  is a dedicated, multi-speed link between PC  20  and switch  30 . As embodied herein, switch  30  is an Ethernet switch forming the center of a Star topology network. Link segments  10 ,  12  and  14  radiate from switch  30 . As embodied herein, link segments  12  and  14  are connected to other network entities (not shown), although link segments  12  and  14  are not required for the present invention. 
     Referring now to FIG. 2, in an exemplary embodiment of the method of the present invention, an error rate on link segment  10  is evaluated, represented by step  102 . As embodied herein, the error rate evaluated is the symbol error rate in transmission between PC  20  and switch  30 . In other embodiments of the present invention, the error rate can be a cyclic redundancy check (CRC) error, a sum of both symbol error and CRC, or another suitable error measure. 
     As embodied herein, the error rate on link segment  10  is measured by an Ethernet controller (not shown) in PC  20  and an Ethernet controller (not shown) in switch  30 . An Ethernet controller in PC  20  is preferably part of Ethernet interface card  25 . In other embodiments, the error rate on link segment  10  may be determined in only one network entity or by other suitable means. The error rate on link segment  10  may be due to a variety of causes, such as cable errors due to cable type, length, location and quality, electromagnetic interference noise, and physical interface problems. 
     As shown in block  104 , the error rate is compared to a given, or predetermined, threshold. When the error rate on link segment  10  exceeds the threshold, according to the present invention the link is automatically reconfigured to a second, lower speed (data rate) Ethernet implementation, as shown in block  106 . For example, a link running at 100 Base-TX would be reconfigured to operate at 10 Base-T. As embodied herein, the reconfiguration of link segment  10  to run at a lower speed is effected using instructions coded in software. The software may reside on any network entity, such as either PC  20  or switch  30 , or both. The software may be run by a processor in any network entity, such as either PC  20  or switch  30 , or both, or by any external processor. For PC  20 , the software is preferably part of the Ethernet driver software. For switch  30 , or for a hub or a router, the software of the present invention is preferably part of the loaded software of the device. 
     Preferably, the software of the present invention is loaded in, and runs on, both PC  20  and switch  30 . In this way, errors in both receive and transmit wire 
     pairs of the link segment  10  cable are used in implementing the method of the present invention. In other embodiments, the software of the present invention is loaded only on switch  30  so that no modification to connected network entities, such as PC  20 , are required. It is advantageous from a network administration standpoint to modify or load software in a switch at the factory or on an operational network by a network manager. Likewise, the method of the present invention may be overridden or disabled by a network manager. In other embodiments of the present invention, the software of the present invention could reside in/or be run on any suitable device connected to a network entity, for example, the software could be run on a managed hub central processor module connected to a simple hardware hub. Alternatively, in other embodiments, the method of the present invention may be implemented in hardware. Implementing hardware may be built into an ASIC (Application-Specific Integrated Circuit) or other hardware on Ethernet interface card  25 , for example. In other embodiments of the present invention, implementing hardware could be located in switch  30 , or in any other suitable platform. 
     The method of the present invention works in conjunction with the autonegotiation feature of a network entity to reconfigure the network entity to a lower speed Ethernet configuration when a predetermined error rate threshold is reached. As long as both PC  20  and switch  30  support autonegotiation, only one of these network entities need perform the method of the present invention. When the network entity is reconfigured to a lower speed Ethernet implementation, a connected network entity will automatically reconfigure to the same speed Ethernet implementation through autonegotiation. As embodied here, the link segment remains at the lower speed Ethernet implementation until the link segment is deactivated or otherwise goes down such as when the network is powered off, etc. In other embodiments of the present invention, the link segment is returned to the original, higher speed Ethernet implementation once certain conditions, e.g., error thresholds, are met. For example, in decision block  108  it is determined whether the error rate has fallen below a given reset level. If it has then in block  110 , the link is automatically reconfigured to operate at the first data rate. 
     The method of the present invention works in conjunction with the autonegotiation feature of a network entity to reconfigure the network entity to a lower speed Ethernet configuration when a predetermined error rate threshold is reached. As long as both PC  20  and switch  30  support autonegotiation, only one of these network entities need perform the method of the present invention. When the network entity is reconfigured to a lower speed Ethernet implementation, a connected network entity will automatically reconfigure to the same speed Ethernet implementation through autonegotiation. As embodied herein, the link segment remains at the lower speed Ethernet implementation until the link segment is deactivated or otherwise goes down, such as when the network is powered off, etc. In other embodiments of the present invention, the link segment is returned to the original, higher speed Ethernet implementation once certain conditions, e.g., error thresholds, are met. 
     The predetermined error rate threshold at which the method of the present invention reconfigures a network entity to a lower speed Ethernet implementation may be set in a variety of ways. Preferably, the error rate threshold is set by a network manager at switch  30 , as this is administratively convenient and requires no changes to PC  20 . In other embodiments of the present invention, the error rate threshold may be preloaded at the given network entity, may be set as a function of network traffic conditions, or set in other suitable ways. 
     The method of the present invention may be implemented in any suitable software language. In one example embodied herein, the method of the present invention may be implemented in PASCAL code as follows: 
     If PORTTYPE=10/100 Base-TX and AUTO NEG=TRUE and 
     LINKTYPE=100 and LINK=UP and PARTNER=10/100 Base-TX then 
     {use this feature if both ends of the link segment support 10 Base-T, 
     100 Base-TX and auto negotiation} 
     Begin 
     LINK_ERRORS:=0; 
     {start by setting link error to 0} 
     While LINK_ERRORS&lt;MAX_ERRORS and LINK=UP do 
     {Check for too many symbol errors once a minute} 
     Begin 
     LINK_ERRORS:=0; 
     {reset error counter each minute} 
     Wait(60 sec); 
     End; 
     If LINK_ERRORS &gt;MAX_ERRORS and LINK=UP then 
     {If there are too many symbol errors set mode to 10 Base-T only and 
     restart 
     autonegotiation} 
     Begin 
     AN-ADVERTISMENT:=10 Base-T; 
     {advertise only 10 Base-T} 
     RESTART-AN:=TRUE; 
     {AN (autonegotiation) will give a 10 Base-T link} 
     Wait(5 sec); 
     {wait for link to come up} 
     While LINK=UP do NOP; {wait for the link to go down} 
     AN-ADVERTISMENT:=10/100 Base-TX; 
     {set back to default after link down} 
     End; 
     End; 
     Variations may be made in the method steps and physical implementations that are within the scope of the present invention. For example, the method of the present invention may be applied to reconfigure a multi-speed Ethernet link from 1000 Base-TX, as in a future gigabit Ethernet, to 100 Base-TX, or any other lower speed. The present invention can be used in general to reconfigure a multi-speed Ethernet link segment operating at any given speed to a lower speed Ethernet implementation when the error rate on the link segment reaches a predetermined configurable threshold. The present invention is applicable to Ethernet variations and speed implementations which may be developed in the future. The present invention may be implemented in either software or hardware residing on any of a variety of platforms and being run by any of a variety of platforms. These and other variations within the scope of the claims are contemplated parts of the present invention.