Abstract:
Ethernet collision control systems and methods for an ethernet network are provided which utilize a media access controller (MAC) which inserts a counter code in the inter-frame gap (IFG) between frame units when transmitting data of a data size which exceeds the capacity of a single frame of the ethernet protocol. The counter code provides a clock signal which may be received by other hosts on the network when they monitor the network to determine whether they are able to make transmissions. First, by recognizing the counter code between frames as distinguished from an idle period signal, the hosts seeking to transmit are notified that additional frames are expected in the next time window from the currently transmitting host. In addition, a counter is provided on each host which generates a count value from the received counter code received during inter-frame gaps and generates a retransmission criterion for controlling transmissions based on the received counter code. Accordingly, a counter code may be used to prioritize access to the network based upon the sequence with which additional hosts wishing to transmit data access the network responsive to an internally generated transmission request.

Description:
FIELD OF THE INVENTION 
     The present invention relates to ethernet networks. More specifically, the present invention relates to collision protocols for ethernet networks. 
     BACKGROUND OF THE INVENTION 
     Communication networks such as computer networks are increasingly used in interconnecting a plurality of computers each of which independently executes tasks while communicating information over the network for shared use. The volume of information which may be transferred over such networks has increasingly become more demanding on the structure of the networks themselves. Various network devices are known to allow the connection of a greater number of computers to a single network and further to allow more free communication of information between computers or other devices on the network or on other interconnected networks. As the number of devices on networks increases, the demands for high performance repeaters and other devices to meet the challenge of managing the information flow so that the data does not create a bottleneck effect on the network are increasingly required. Furthermore, the protocol supporting communications over such networks are typically evolving to support higher data rates and larger volumes of information transmittal over the communication networks. 
     One example of such a communication protocol is known as the ethernet protocol as defined by the Institute of Electrical and Electronic Engineers (IEEE) 802.3 standard. The ethernet protocol is one of the most widely implemented local area network (LAN) standards. An updated version of the ethernet protocol, fast ethernet, is specified to support data transfer rates of 100 megabits per second (Mb/s). A further version, gigabit ethernet, is specified as supporting data rates of 1,000 Mb/s. The developments in the standard related to such technical progress in general have been based on the physical layer, i.e., on the lowest or first layer of an open system interconnection (OSI). While developments and commercialization of faster physical layers has progressed, the protocols for the media access controllers (MAC) currently used in ethernet networks have seen relatively little change. 
     One problem encountered with ethernet as a result of the increasing performance of personal computers and the number of hosts using a single network, thereby creating increased volumes of traffic on the network, is that difficulties may occur using carrier sense multiple access/collision detection (CSMA/CD) methods such as those provided by ethernet for conventional MAC protocols. A CSMA/CD type host (terminal/computer) generally checks carriers on a transmission path of the network before transmitting frames. The host then transmits a frame during what appears to the host to be an idle period on the transmission path. However, such networks allow collisions to occur when two different connected hosts both attempt to transmit frames on the network at the same time. When the collision is detected, the ethernet protocol provides for collision recovery steps including stopping transmission of any remaining parts of a frame currently being transmitted and initiating retransmission of transmission frames which encounter the collision after some time interval which is typically specified by the collision detection recovery protocol in use on the network. 
     More particularly, when two transmissions of data collide, collision signals with predetermined bits indicating a collision may be transmitted to each host involved in the transmissions which collided. On receiving the collision signals, the host terminals may retransmit the data. The timing of retransmission is typically controlled using a retransmitting algorithm such as a binary exponential backoff (BEB) algorithm. The BEB algorithm generally specifies “2” as a common small constant factor by which the time between making retransmission attempts is increased for each subsequent attempt. 
     For example, when a host A transmits data on the network and a first collision occurs, a retransmission may be attempted after a single minute. If, during the first retransmission attempt by host A, a second collision occurs, another retransmission is attempted after two minutes. If a third collision occurs at this point, another retransmission is attempted after four minutes and so on. 
     One problem with this type of BEB algorithm is fairness to competing hosts attempting to access the communication channel. For example, assuming that host A attempts a retransmission after four minutes delay when a third subsequent collision occurs, a separate host, host B may transmit data while host A is delayed waiting a specified time period for a subsequent retransmission attempt. If no collision is encountered by host B during its transmission, it will have transmitted its data prior to host A even though “fairness” would dictate that host A be allowed to transmit data prior to host B as host A sought to transmit such data in advance of the request by host B. In other words, when the BEB algorithm is used, it is possible for a host which attempted to transmit data later than another host to transmit data first. This problem is generally referred to as a capture effect and reduces network performance. The capture effect is generally an intrinsic problem when utilizing the CSMA/CD method and may worsen when the number of hosts in a network is sharply increased or when a larger amount of data is transmitted over a network. 
     In an attempt to solve this problem various algorithms have been developed as modifications over the BEB algorithm. One such algorithm is the capture avoidance binary exponential backoff (CABEB) algorithm. Another is the binary logarithmic arbitration method (BLAM) algorithm. These algorithms are based on the BEB algorithm and may allow for improved methods for calculating the delay times while still facilitating prevention of collisions. However, the CABEB and BLAM algorithms are still subject to the problem of a lack of fairness in access to the network resource. 
     In a further aspect of operation of ethernet networks, when signal collisions occur in hubs or repeaters in the network, a collision truncation method which detects collisions and transmits collision signals to a host can be used. This method may reduce the delay time required for collision signals to be transmitted to the respective host so that there is less reduction in the performance of the network. Although this method may improve network performance, the problems of collision and unfairness may still exist. 
     Accordingly, conventional methods for collision detection and recovery create problems in fairness and may often times result in the reduction of the performance of a network. Furthermore, when the traffic load on a network is sharply increased, the data to be transmitted may surpass a maximum transmission time such that information is not successfully transmitted and is lost. Typically, such problems can only be solved in upper layers of the communication hierarchy which may adversely impact the total performance of the communications over the network. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide systems and methods for collision control on an ethernet network which may decrease the likelihood of collisions. 
     It is a further object of the present invention to provide systems and methods for collision control on an ethernet network which may reduce capture effect and provide for improved fairness in access to the network. 
     In order to provide for the foregoing and other objectives, ethernet collision control systems and methods for an ethernet network are provided which utilize a media access controller (MAC) which inserts a counter code in the inter-frame gap (IFG) between frame units when transmitting data of a data size which exceeds the capacity of a single frame of the ethernet protocol. The counter code provides a clock signal which may be received by other hosts on the network when they monitor the network to determine whether they are able to make transmissions. First, by recognizing the counter code between frames as distinguished from an idle period signal, the hosts seeking to transmit are notified that additional frames are expected in the next time window from the currently transmitting host. In addition, a counter is provided on each host which generates a count value from the received counter code received during inter-frame gaps and generates a retransmission criterion for controlling transmissions based on the received counter code. Accordingly, a counter code may be used to prioritize access to the network based upon the sequence with which additional hosts wishing to transmit data access the network responsive to an internally generated transmission request. 
     In one embodiment of the present invention, A collision control system for an ethernet network is provided including a media access controller (MAC) circuit that provides data for transmission in frame units. The MAC circuit further includes a code generator that generates a counter code that is transmitted in an inter-frame gap (IFG) between frame units. The counter code is distinct from an idle period code specified by the ethernet network. Also included in the collision control system is a transmitter coupling the MAC circuit to the ethernet network that transmits the frame units and the counter code on the ethernet network. 
     In another embodiment of the present invention, the collision control system further includes a receiver coupling the MAC circuit to the ethernet network that receives transmissions from the ethernet network including frame units and counter codes transmitted by other collision control systems coupled to the ethernet network. In this embodiment, the MAC circuit further includes a counter for generating a transmission criterion responsive to the received counter codes. The counter code may include a start-period, a clock period. The counter may generate a transmission criterion responsive to the clock period. In one embodiment, the clock period includes a plurality of clock signals and the counter generates a counter value responsive to the plurality of clock signals, the counter value specifying a priority for use as the transmission criterion. In addition, the counter code may further include an end period and the counter may be initialized by the start period and count the plurality of clock signals until the end period is received. The MAC circuit may be configured to use the counter value as a coefficient of a binary exponential backoff (BEB) algorithm to control transmission by the transmitter. 
     In a further aspect of the present invention, a collision control system for an ethernet network is provided including a receiver coupled to the ethernet network that receives transmissions from the ethernet network including frame units and a counter code transmitted by other collision control systems coupled to the ethernet network and a media access controller (MAC) that receives data in frame units and counter codes from the receiver. The MAC circuit includes a counter for generating a transmission criterion responsive to the received counter code. 
     In yet another aspect of the present invention, methods are provided for collision control for an ethernet network. Frames of data and a received counter code are received from the ethernet network. The received counter code is received between a first and a second of the frames of data. The received counter code is analyzed to determine a transmission criterion and frames of data are transmitted responsive to the transmission criterion. In one embodiment, transmitting operations include generating a plurality of frames of data for transmission, generating a transmit counter code and transmitting the plurality of frames of data on the ethernet network with the transmit counter code inserted in an inter-frame gap (IFG) between each of the plurality of frames responsive to the transmission criterion. 
     In one embodiment of the method aspects of the present invention, the received counter code comprise a start period and a clock period including a plurality of clock signals and the analyzing operations include generating a counter value responsive to the plurality of clock signals, the counter value specifying a priority for use as the transmission criterion. The plurality of frames of data may be transmitted at a time determined using the counter value as a coefficient of a binary exponential backoff (BEB) algorithm. In one embodiment, the received counter code further includes an end period and a counter value is generated by initializing the counter responsive to the start period, counting the plurality of clock signals and stopping the counting step and setting the counter value responsive to the end period. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic illustration of ethernet frame transmissions in a high speed (fast) ethernet network; 
     FIG. 2 is a schematic illustration of an inter-frame gap according to an embodiment of the present invention; 
     FIG. 3 is a schematic illustration of frame transmissions in a high speed ethernet network according to an embodiment of the present invention; 
     FIG. 4 is a block diagram of a collision control system according to an embodiment of the present invention; 
     FIG. 5 is a flow chart illustrating frame transmission according to an embodiment of the present invention; and 
     FIG. 6 is a flow chart illustrating receiving operations according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. As will be appreciated by one of skill in the art, the present invention may be embodied as methods or devices. Accordingly, the present invention may take the form of a hardware embodiment, a software embodiment or an embodiment combining software and hardware aspects. 
     Referring to the schematic illustration of FIG. 1, framed transmissions in a fast ethernet network will now be described. Such networks have idle periods, frames and inter-frame gaps (IFG) occurring between frames. In the idle periods, no data is transmitted over the network. In the illustrated schematic of FIG. 1, data to be transmitted over the network is divided up across three frames, frame 1 , frame 2  and frame 3 , which are transmitted over the network. The IFGs are located between frame 1  and frame 2  and between frame 2  and frame 3 . With the frame structure illustrated in FIG. 1, the codes representing the idle periods are generally identical with those representing the IFGs. Accordingly, a host seeking to make a transmission on the network detects what it recognizes as idle available period indicators in the idle periods or the IFGs and then subsequently attempts to transmit data. 
     In order to control and potentially prevent data collisions, the apparatus and methods of the present invention provide for specific codes (counter codes) during the IFGs which allow idle periods to be distinguished from the IFGs. Furthermore, improved BEB algorithms for retransmission are provided which beneficially utilize the counter codes provided during the IFGs. Referring now to FIG. 2, an embodiment of the present invention will be further described with reference to the schematic illustration of an IFG providing a counter code. As shown in FIG. 2, the length of the IFG is 96 bits. The corresponding counter code includes a 10 bit IFG start period in the first 10 bits (shown as 00001 0001). The following 80 bits provide a clock period which represents clock signals (shown as a repeating pattern of “0011 0011”). Finally, a 6 bit duration IFG end period is appended at the end of the counter clock period. In the illustrated embodiment of FIG. 2, the clock signals and the clock period are set to repeat a “0011 0011” pattern which, within the 80 bit clock period, provides an actual maximum clock cycle count of 20. This clock cycle amount (20) is sufficient to satisfy the requirements of the maximum retransmission trial amount count of 16 for the BEB algorithm generally recommended by the IEEE 802.3 standard. 
     FIG. 3 is a schematic illustration of frame transmissions in a fast ethernet network according to an embodiment of the present invention. As shown in FIG. 3, three hosts, A, B, and C are coupled to the network and, at various times, attempt data transmission over the network. Host A checks the status of the transmission path of the network at time t 1 . Because the status of the transmission path is detected as idle by host A, host A starts to transmit data during period t 2 . In the illustrated example of FIG. 3, the total data to be transmitted by host A exceeds the capacity of a single frame and is, therefore, divided into two frames, frame 1  and frame 2 . Frame 1  is transmitted during period t 2  and the IFG counter code is transmitted during the time period t 3  between frame 1  and frame 2 . Frame 2  is then transmitted during the subsequent period t 4 . Host A, after completing transmission of the data, may repeatedly transmit during period t 5  the code “101010. . . ” representing an idle period. 
     As shown in FIG. 3, during time period t 3  host B and then, shortly there after, host C, check the transmission path to determine if they are able to transmit data during period t 3 . As noted previously in reference to FIG. 1, for the conventional method of FIG. 1, host B and C would both read the idle period code “101010. . . ” during their check of the transmission path and, accordingly, would simultaneously attempt to transmit data during period t 4 , thereby causing a collision to occur. However, pursuant to the apparatus and methods of the present invention, both hosts B and C receive the counter code corresponding to the IFG period when checking the status of the transmission path during period t 3 . Accordingly, they receive the clock signals provided during the counter clock period which are used by both host B and host C to operate internal counters for use in generating a transmission criterion for the respective hosts. As will be described further herein, because host B checked the transmission path and detected the counter code during the IFG some time period prior to host C, host B&#39;s counter will generate a counter value greater than that generated by the counter of host C. This greater count will generate respective transmission criteria causing host B to transmit its frame of data during time period t 5  while host C waits for time period t 6 . 
     For example, a counter value may be used to generate a coefficient for use in a BEB algorithm that varies depending upon the counter value. More particularly, the counter of host B may provide a coefficient resulting in a shorter delay for transmission than that provided by host C based on the greater value of the count calculated by host B during reading of the counter code during period t 3 . Alternatively, a delay period within time period t 5  immediately following completion of frame transmission by host A may be inversely related to the count generated during time period t 3  and each of host B and host C may be required to check transmission path status before beginning transmissions. Accordingly, host B will begin transmission of its frame thereby resulting in a non-idle period indication on the transmission path when host C subsequently checks the transmission path at its designated delay after the end of time period t 4 . Accordingly, host C will need to wait an additional time period after the transmission of a frame by host B before it encounters, during time period t 6 , an idle period indication at its check time before transmission of its frame. Accordingly, multi-framed transmissions may be successfully provided without collisions from the individual host and the sequencing of competing additional hosts accessing the network following completion of transmissions by a first host may be provided while avoiding the occurrence of collisions on the network. 
     The BEB algorithm for collision control as provided by the IEEE 802.3 standard is as follows: 
     
       
         0 ≦r &lt;2 k   
       
     
     where k=min (n, 10), and, according to the IEEE 802.3 standard, the value of n is “1” for both hosts B and C. Accordingly, host B and C, having identical n values, may use their counter value to determine which host has the transmission priority. As in the illustrated example of FIG. 3 host B has a greater counter value than host C, host B has the higher priority and, after host A completes data transmission, host B starts to transmit data during time period t 5 . Host C subsequently transmit data during time period t 6 . 
     An embodiment of a collision control system for an ethernet network will now be further described with reference to the block diagram of FIG.  4 . As shown in the embodiment of FIG. 4, the collision control system includes a media access controller (MAC)  100 , a transmission data path unit  200 , a code generator  300 , a transmitter  400 , a receiver  500 , a receiving data path unit  600  and a counter  700 . The MAC  100 , the transmission data path unit  200 , the code generator  300 , the receiving data path unit  600  and the counter  700  comprise a MAC circuit  101 . 
     The MAC  100  illustrated in the embodiment of FIG. 4 generates data and manages communications with the ethernet network pursuant to the IEEE 802.3 standard including generating data for transmission in frame units and receiving transmissions from the ethernet network in frame units. The transmitter  400  is a physical layer coupling unit which converts transmission data into electrical signals in a suitable form for transmitting the electrical signals over the transmission path of the network. Accordingly, the transmitter  400  couples the MAC circuit  101  to the ethernet network and transmits frame units on the ethernet network. Similarly, the receiver  500  provides a physical layer coupling unit which receives electrical signals from the transmission path and transforms the signals into a data format suitable for providing to the MAC circuit  101 . 
     The transmission data path unit  200  located between the MAC  100  and the transmitter  400  provides the data from the MAC  100  to the transmitter  400 . The code generator  300  generates the specific counter codes, such as those illustrated in the embodiment of FIG. 2, for insertion into the IFG between data frames for transmission over the network. Accordingly, the transmission data path unit  200  provides an appropriate data stream including frames containing data for transmission as well as counter codes in the IFG period between frames of a multiple frame transmission of data. 
     The receiving data path unit  600  which is coupled between the receiver  500  and the MAC  100  provides data received by the receiver  500  via the transmission path of the ethernet network to the MAC  100 . In addition, the counter  700  is configured to detect the start period of the counter code in the IFG and perform counter operations on the clock signals contained in the counter clock. More particularly, the counter may be initialized responsive to detection of the start period and then count a plurality of clock signals received until the end period signal is received by the counter  700  from the receiver  500 . The counter value so generated may then be provided to the MAC  100  for use in establishing a transmission criterion controlling subsequent transmissions. 
     Operations according to an embodiment of the present invention will now be further described with reference to the flow chart illustration of FIG.  5 . FIG. 5 illustrates operations related to frame transmission. Operations begin at block  800  when the MAC  100  generates data to be transmitted and analyzes the data length to determine whether the data may be transmitted as a single frame or must be transmitted as multiple frames. Where more than a single frame are required to support transmission of the data (block  805 ), the code generator  300  is activated (block  810 ). Subsequently, a first frame is transmitted containing a portion of the data which has been divided across a plurality of frames (block  820 ). The code generator  300  then provides a counter code to the transmission data path unit  200  for transmission by the transmitter  400  during the IFG (block  830 ). Operations of block  820  and  830  repeat for the remainder of the plurality of frames containing the data for transmission. 
     Where only a single frame is required for the data transmission (block  805 ), the code generator  300  is maintained in a standby mode (block  840 ). The data from the MAC  100  is then transmitted in a single frame by the transmitter  400  as the data is received from the data transmission path unit  200  (block  850 ). 
     Referring now to FIG. 6 operations according to an embodiment of the present invention will now be further described with reference to the flow chart illustration of receiving operations. As shown on FIG. 6 operations begin with a host computer (collision control system for an ethernet network) monitoring the transmission path of the ethernet network to determine whether the host may transmit data (block  900 ). If the host receives an IFG associated counter code such as that illustrated in FIG. 2 (block  905 ), the counter  700  is initialized and activated (block  910 ). The counter  700  then performs counting operations responsive to the clock signals contained in the counter code clock period (block  920 ). On receipt by the counter of the end period of the IFG counter code, counter operations are stopped and the respective counter value is provided to the MAC  100  by the counter  700  (block  930 ). The MAC  100  then determines transmission priorities using the counter value as a transmission criterion. Each respective host monitoring the network accordingly retransmits (or transmits) data responsive to the determined priorities. 
     As described above, the present invention provides for the use of a counter code which is generated during the IFG and which is received and counted by a counter operating responsive to clock signals contained in a clock period of the counter code. Resulting counter values determined during checking of the transmission path prior to transmissions are transmitted to the MAC  100  which may thereby provide for reduction or prevention of delays in utilization of the network by MAC attempts to retransmit data and may further reduce the potential for overwhelming of the network by data from a particular transmitting host. Furthermore, fairness between transmission opportunities by various hosts which occupy the transmission path after a collision and hosts which did not occupy the transmission path may also be maintained. 
     As will be appreciated by those of skill in this art, the above-described aspects of the present invention in FIGS. 4-6 may be provided by hardware, software, or a combination of the above. While various components of the MAC circuit  101  have been illustrated in FIG. 4, in part, as discrete elements, they may, in practice, be implemented by a processor, such as a microcontroller, including input and output ports and running software code, by custom or hybrid chips, by discrete components or by a combination of the above. For example, the code generator  300  may be contained within a processor (not shown) supporting other functions of the MAC  100 . 
     Operations of the present invention have been described above with reference to the flow chart and schematic block diagrams of FIGS. 4-6. It will be understood that each block of the flowchart illustrations and/or block diagrams and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These program instructions may be provided to a processor to produce a machine, such that the instructions which execute on the processor create means for implementing the functions specified in the flowchart and/or block diagram block or blocks. The computer program instructions may be executed by a processor to cause a series of operational steps to be performed by the processor to produce a computer implemented process such that the instructions which execute on the processor provide steps for implementing the functions specified in the flowchart and/or block diagram block or blocks. 
     Accordingly, blocks of the flowchart illustrations and block diagrams support combinations of means for performing the specified functions, combinations of steps for performing the specified functions and program instruction means for performing the specified functions. It will also be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by special purpose hardware-based systems which perform the specified functions or steps, or combinations of special purpose hardware and computer instructions. 
     In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.