KR100594077B1 - How to provide interframe gap period - Google Patents

Abstract

The present invention provides a method for providing an interframe gap period in a medium access control block employing a CSMA / CD (CSMA / CD) access method, wherein the interframe gap period in a half-duplex transmission mode is defined by a first interval. When the medium access control block receives a signal indicating that the frame has been successfully transmitted or a signal indicating that the frame is not being transmitted in the half-duplex mode, the first interval is counted and traffic from the network is divided into a second section. If it occurs, counting again from the beginning, and if the first section is counted, the second section is counted exclusively, and when the count is completed, the period consisting of the first section and the second section is provided as the interframe gap period. The process is done.

Interframe Gap Period, MAC

Description

How to provide interframe gap period {METHOD FOR PROVIDING INTER-FRAME GAP TIME}             

1 is an example configuration diagram of a MAC block of CSMA / CD access method;

2 is a MAC frame configuration diagram,

3 is a state diagram of an interframe gap timer according to the prior art;

4 is a state diagram of an interframe gap timer according to an embodiment of the present invention;

5 is a diagram to help explain the operation of an interframe gap timer;

TECHNICAL FIELD The present invention relates to a network, and more particularly, to a method for providing an interframe gap period in a MAC block of a local access network (hereinafter referred to as "LAN").

Local Access Networks (hereinafter referred to as "LANs") can build computers, peripherals, and computer-related devices distributed within a certain area, such as buildings, factories, and school premises, as independent communication networks. Further developments are being made by the development, office automation, and LAN standardization.

The LAN layer model uses the layering concept adopted by the Open Systems Interconnection (OSI) reference model, but targets only the lower two layers (data link layer, physical layer) among the seven layers that the OSI reference model targets. The upper tiers inherited the concept of the OSI seven-tier model. The physical layer of the LAN plays a role of signal transmission through the medium, and also performs signaling, encoding and handling of the medium. The data link layer of a LAN consists of two layers: Logical Link Control (hereinafter referred to as "LLC") and Media Access Control (hereinafter referred to as "MAC"). The LLC layer is a data link control service commonly applied to each medium access method, and its purpose is to perform data transmission. The MAC layer serves as an interface between the LLC layer and the physical layer, and connects logical and physical functions. . In more detail, the MAC layer performs a function of generating a frame of data and a medium access management. Carrier access management can use the Carrier Sense Multiple Access with Collision Detection (CSMA / CD) access method. The CSMA / CD access method is the media access control method most commonly used in a bus or tree type LAN. The MAC layer uses the algorithm of the CSMA / CD access method to avoid collisions, transmit MAC frames, and perform processing when a collision occurs.

FIG. 1 is a diagram illustrating a configuration of a MAC block of a CSMA / CD access method as an example, and FIG. 2 is a diagram illustrating a configuration of a MAC frame used in a MAC procedure of a CSMA / CD.

As shown in FIG. 2, the MAC frame of the CSMA / CD includes a preamble, a start frame delimiter (SFD) area, a destination address (DA) area, a source address (SA) area, a length area, and a data area. It consists of FCS (Frame Check, Sequence) area. The information SFD in the SFD area indicates the head of the valid frame, the information DA in the DA area indicates a reception address, and the information SA in the SA area indicates a transmission address. When the information in the length area indicates the number of octets of data in the data area, the information in the data area is transmission data, and the PAD in the PAD area does not satisfy the minimum frame length necessary to correctly perform protocol processing of CSMA / CD. Added as extra bits. In the FCS of the FCS area located at the rear of the PAD area, the CRC code that is the target range from the address area DA to the PAD is recorded.

Referring to Figure 1 will be described in the frame transmission and reception operation in the MAC block. The transmitting unit 4 of the MAC block assembles the MAC frame as shown in FIG. 2 and transmits it to the physical layer unit through the MII 8 in response to a host request received through the MIU (MAC Interface Unit) 2. More specifically, the MAC transmitter 4 checks the state of the carrier sensing signal Crs received through the MII 8 when the host transmits a request, and the state of the carrier sensing signal Crs is idle. ), I.e., if no carrier is detected, the preamble, SFD, and jam generator 22 generate the preamble and SFD under the control of the MAC controller 16, and output the preamble and SFD to the multiplexer 6, and the MAC transmission buffer 20 The DA, SA and data stored in the data are output to the multiplexer 6. At this time, when the data bit string from the DA area to the FCS area does not satisfy the prescribed minimum frame length, the PAD bit generated by the PAD and FCS generation unit 24 under the control of the MAC controller 16 generates a multiplexer (5). ) The multiplexer 6 multiplexes the input signals according to the MAC frame format as shown in FIG. 2, and then uses the MMI 8 to transmit the MAC frame, for example, the 4-bit unit transmission bit sequence Tx_D [3: 0]. Transmit to physical layer. Upon completion of the transmission, the PAD and FCS generator 24 of the transmitter 4 generates an FCS for the target range from the address region SA to the PAD of the transmitted MAC frame to generate the multiplexer 6 and the MII 8. Transmit to physical layer through

If a collision is detected while transmitting the MAC frame, the MAC transmitter 4 stops the intra-frame bit string transmission and transmits a jam signal jam to the physical layer by using the PAD and FCS generator 24. After transmitting the jam signal jam, the MAC frame is retransmitted after the back off period is delayed by using the back off timer of the back off and inter frame period timers 30. If the transmission for the MAC frame is successful, wait for the predetermined inter-frame gap time (or inter-frame spacing time) by using the inter-frame period timer of the backoff and inter-frame period timers 30, and then the other MAC. Send a frame. The interframe gap period is 9.6 GHz at 10 Mbps and 0.96 GHz at 100 Mbps.

When the MAC receiver 12 detects the SFD portion of the bit string Rx_D [3: 0] of the frame received through the MII 8 and the demultiplexer 10, the MAC receiver 12 starts receiving and whether the length of the frame is larger than the minimum frame length. It determines whether it is a local address, whether the FCS is normal, etc., and when they satisfy all, it is regarded as normally received and stores the received frame in the MAC reception buffer 32. The presence or absence of normal FCS is performed by the FCS check unit 34. Then, necessary data in the frame is transmitted to the host through the MIU (2).

On the other hand, in the MAC block, the flow controller 14 controls the flow for frame transmission and reception in order to reduce the frame loss rate, and the MAC controller 16 includes a status register and the like and performs overall control of the MAC block.

The interframe duration timer of the backoff and interframe duration timer 30 operates differently depending on whether the current data transmission scheme is a full duplex mode or a half duplex mode.

The operation of the interframe period timer will be described in more detail below with reference to FIGS. 3 and 5. FIG. 3 is a state diagram of an interframe gap timer according to the related art, and FIG. 5 is a diagram to help explain the operation of the interframe gap timer.

In Fig. 3, st_rst is in a reset state. st_cnt96 is a state of counting 96-bit time, st_fullok is a state indicating successful interframe gap formation in full-duplex mode, and st_fnotok is a state indicating that interframe gap can not be formed in full-duplex mode. st_cnt64 is a state of counting 64-bit time, st_halfok is a state of successful interframe gap formation in half duplex mode, and st_hnotok is a state of inability to form interframe gap in half duplex mode. On the other hand, in Figure 5, the done signal is a signal used only in the half-duplex communication mode is set to the binary logic "high" state when the frame is successfully transmitted. Tx_EN is enabled in binary logic "high" state when the frame is transmitting and disabled (ie binary logic "low" state) when no frame transmission is taking place. The gap_ok signal is enabled by the interframe gap timer (outputting a "high" state pulse) when the formation of the interframe gap period is successful.

In full-duplex mode, the interframe timer counts 96-bit times, an inter-frame gap, and counts the gap_ok signal after completion of counting 96-bit time, regardless of network traffic. Let it be. The 96-bit time, which is the frame gap period, becomes 9.6 ms at a transmission rate of 10 Mbps. The reason is as follows.

96 bit time = 4 bit * 24 = 24 * 40 ns = 960 ns = 9.6 ms

Here, "4 bits" is the number of bits that can be transmitted per one clock of the transmission clock according to the embodiment of Figure 1, "24" is the number of transmission clock in the 96-bit time count. 40 ns is the transmission clock cycle (2.5 MHz) at a transmission rate of 10 Mbps. The 96-bit time, the frame gap period, is 0.96 ms at 100 Mbps.

When the full duplex mode is entered, the interframe gap timer transitions from the reset state st_rst of FIG. 3 to the st_cnt96 state. In the st_cnt96 state, when the Tx_EN signal is disabled (Tx_EN = "0"), a 96-bit time (96 bit times) is counted. When the state of Tx_EN = "0" continues and the 96-bit time is counted, the interframe gap timer transitions to the st_fullok state. The st_fullok indicates a successful interframe gap formation in the full-duplex mode. In this case, the interframe gap timer enables the gap_ok signal as shown in FIG. 5. After the Tx_EN signal is enabled (Tx_EN = "0"), the interframe gap timer transitions to the st_fnotok state indicating that the interframe gap cannot be formed in the full duplex mode.

In the half-duplex mode, on the other hand, as shown in FIG. 5, the 96-bit time, which is the interframe gap period, is divided into a first 64-bit time and a last 32-bit time. So, if the network has traffic during the initial 64-bit time, it starts counting again from the beginning.If the network has traffic during the last 32-bit time, it ignores it and continues counting to complete the total 96-bit time, the interframe gap period. After that, enable the gap_ok signal.

Referring to FIG. 3, in the half duplex mode, the interframe gap timer transitions from the reset state st_rst to the st_cnt64 state. In the st_cnt64 state, the Tx_EN signal is disabled (Tx_EN = "0"), and the carrier detection signal Crs received from the MAC transmitter is idle, that is, if no carrier is detected (not Crs), the initial 64 bit times (64 bit times) are counted. Perform If the state of Tx_EN = "0" is maintained and the carrier detection signal Crs is kept in the idle state to complete the counting of the initial 64-bit time, the interframe gap timer transitions to st_cnt32 state, ignoring any traffic occurring during the later 32-bit time. The count completes and transitions to st_halfok state. The st_halfok state indicates a successful inter-frame gap formation in the half-duplex mode. The inter-frame gap timer enables the gap_ok signal as shown in FIG. 5. Then, when the Tx_EN signal is enabled (Tx_EN = "0") or the carrier detection signal Crs becomes active, the interframe gap timer transitions to the st_hnotok state indicating that the interframe gap cannot be formed in the half duplex mode.

Also, in the half duplex mode, the inter-frame gap timer receives a flag "flag =" as shown in FIG. 3 when a done signal indicating that the frame has been successfully transmitted is received with a logic "high" pulse as shown in FIG. Set to 1 "and transition from the reset state st_rst to st_cnt64 state. The frame gap timer immediately transitions to the st_cnt32 state without counting the 64-bit time in the st_cnt64 state when the flag is "flag = 1". In the st_cnt32 state, the flag is reset to " flag = 0 " and counting for the 96-bit time which is the interframe gap period is performed. At this time, even if network traffic occurs, this is ignored and the count for the 96-bit time, which is the interframe gap period, is completed and the state transitions to the st_halfok state. The st_halfok state indicates the success of interframe gap formation in the half-duplex communication mode. At this time, the interframe gap timer enables the gap_ok signal as shown in FIG.

As described above, in the half-duplex mode, once the frame transmission is successfully completed, the 96-bit time, which is the interframe gap period, is counted regardless of network traffic. That is, in the half-duplex mode of the prior art, frame transmission is given priority over frame reception. Therefore, the MAC cannot participate in reception during the interframe gap period. This means that channel exclusive phenomenon occurs in half duplex mode.

It is therefore an object of the present invention to provide a method for stably providing an interframe gap period in a medium access control block.                         

Another object of the present invention is to provide a method for eliminating channel monopoly caused by channel occupancy at the transmitting end of a media access control block.

In accordance with the above object, the present invention provides a method for providing an interframe gap period in a medium access control block employing a CSMA / CD access method, wherein the interframe gap in a half-duplex transmission mode. The period is divided into a first section and a second section, and when the medium access control block receives a signal indicating that the frame has been successfully transmitted or a signal indicating that the frame is not being transmitted in the half duplex mode, the first section is divided. Counting and counting again from the beginning when traffic is generated from the network; and counting the second section exclusively when the first section is counted, and when the count is completed, the period consisting of the first section and the second section. Characterized in that the process to provide a gap period between frames.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same elements in the figures are represented by the same numerals wherever possible. In addition, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

4 is a state diagram of an interframe gap timer according to an embodiment of the present invention.

In the half-duplex mode according to the embodiment of the present invention, as in the prior art, a channel monopoly phenomenon in the half-duplex mode is prevented from occurring by not giving priority to frame transmission rather than frame reception. To this end, an embodiment of the present invention does not operate a flag even if a done signal is received as in the prior art. That is, even if the done signal is received, the flag is not set to "flag = 1". In the state transition diagram of FIG. 4, it can be seen that no flag is operated.

Hereinafter, an operation of an interframe gap timer for forming an interframe gap period according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 1, 3, and 5.

In the embodiment of the present invention, the operation of the interframe period timer in the full duplex mode is the same as the operation according to the prior art. In full-duplex mode, the interframe timer counts 96-bit times, an inter-frame gap, and counts the gap_ok signal after completion of counting 96-bit time, regardless of network traffic. Let it be.

When the full duplex mode is entered, the interframe gap timer transitions from the reset state st_rst of FIG. 4 to the st_cnt96 state. In the st_cnt96 state, when the Tx_EN signal is disabled (Tx_EN = "0"), a 96-bit time (96 bit times) is counted. When the state of Tx_EN = "0" continues and the 96-bit time is counted, the interframe gap timer transitions to the st_fullok state. The st_fullok indicates a successful interframe gap formation in the full-duplex mode. In this case, the interframe gap timer enables the gap_ok signal as shown in FIG. 5. After the Tx_EN signal is enabled (Tx_EN = "0"), the interframe gap timer transitions to the st_fnotok state indicating that the interframe gap cannot be formed in the full duplex mode.

In the half-duplex mode, on the other hand, as shown in FIG. 5, the 96-bit time, which is the interframe gap period, is divided into a first 64-bit time and a last 32-bit time. In the half-duplex mode, when the done signal or Tx_EN = "0" indicating that the frame has been successfully transmitted is received, the initial 64-bit time is counted and the initial 64-bit time is counted. When traffic occurs from the network, counting starts again from the beginning. Even if traffic comes from the network during the last 32-bit time, the count is ignored and the count is continued. After counting the total 96-bit time between frames, the gap_ok signal is checked. Enable it.

Referring to FIG. 4, when the half-duplex communication mode is entered, the inter-frame gap timer transitions from the reset state st_rst to the st_cnt64 state. In the st_cnt64 state, the Tx_EN signal is disabled (Tx_EN = "0"), and the carrier detection signal Crs received from the MAC transmitter is idle, that is, if no carrier is detected (not Crs), the initial 64 bit times (64 bit times) are counted. Perform In addition, the inter-frame gap timer according to an embodiment of the present invention is a st_cnt64 in the reset state st_rst even if a done signal indicating that the frame has been successfully transmitted in the half-duplex communication mode is received from the network with a logic "high" pulse as shown in FIG. Transition to state. In the st_cnt64 state, the Tx_EN signal is disabled (Tx_EN = "0"), and the carrier detection signal Crs received from the MAC transmitter is idle, that is, if no carrier is detected (not Crs), the initial 64 bit times (64 bit times) are counted. Perform

If the state of Tx_EN = "0" is maintained and the carrier detection signal Crs is kept in the idle state to complete counting the initial 64-bit time, the interframe gap timer transitions to st_cnt32 state, even if traffic from the network occurs during the later 32-bit time. Ignore it and complete the count and go to st_halfok state. The st_halfok state indicates a successful inter-frame gap formation in the half-duplex mode. The inter-frame gap timer enables the gap_ok signal as shown in FIG. 5. Then, when the Tx_EN signal is enabled (Tx_EN = "0") or the carrier detection signal Crs becomes active, the interframe gap timer transitions to the st_hnotok state indicating that the interframe gap cannot be formed in the half duplex mode.

In the above description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be defined by the described embodiments, but should be determined by the equivalent of claims and claims.

As described above, the present invention can provide a stable interframe gap period by eliminating the occurrence of channel monopoly occurring in the half-duplex communication as the interframe gap timer of the MAC block transmitter gives priority to packet transmission. This allows the same packet to be sent to multiple ports without channel monopoly.

Claims (1)

A method for providing an interframe gap period in a media access control block employing a CSMA / CD access method, In the half duplex mode, the interframe gap period is divided into a first section and a second section, and a signal indicating that a frame has been successfully transmitted in the half duplex mode or a signal indicating that a frame is not being transmitted is transmitted. Counting the first section when the control block receives and counting again from the beginning when traffic is generated from the network; And when the counting is completed, the second section is counted exclusively, and when the counting is completed, a period consisting of the first section and the second section is provided as the interframe gap period. How to provide a gap period.

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