JPH0832615A - Repeater - Google Patents

Abstract

PURPOSE:To provide a repeater which can prevent an under-run error at the time of repeating data and which needs only to change the units of a terminal and a repeater to high speed ones at the time of changing low speed LAN to high speed LAN by deciding the timing of the transmission start of a frame from a frame length and the value of a byte number counter so as to transmit data. CONSTITUTION:The transmission-side of a port for high speed LAN is provided with a frame length detection circuit 42 extracting information of a length field included in data of the frame and detecting the frame length of data to be transmitted and the byte number counter 41 counting the number of the bytes of frame data to be transferred. Furthermore, a transmission control circuit 43 deciding the timing of the transmission start of the frame from the frame length and the value of the byte number counter 41 and starting transmission is provided. Thus, delay time until the frame is transmitted by the port for high speed LAN from time when the frame is received by the low speed LAN can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an LA having a high transmission speed.
The present invention relates to a relay device that relays a frame between N and a LAN having a low transmission speed.

[0002]

2. Description of the Related Art As the processing speed of personal computers, workstations and the like has increased, so has the speed of networks. As one of the flows, standardization for increasing the transmission rate of Ethernet to 100 Mbps is being discussed by the IEEE committee. As a device to which the 100 Mbps Ethernet is applied, there is a relay device that connects the conventional Ethernet having a transmission speed of 10 Mbps and the 100 Mbps Ethernet.

FIG. 10 shows a conventional example of a relay device. In the figure, the transmission speed is high, for example, CS of 100 Mbps
MA / CD (Carrier Sence Multiple Access with Col)
LIsion Detection) LAN port has one port and low transmission speed, for example, 10 Mbps CSMA / C
A configuration example of a network using a relay device for relaying a frame in which the port for the D system LAN is 8 ports is shown. Below, CSM with transmission speed of 100 Mbps
A / CD type LAN is 100 Mbps LAN and CSMA / CD type LAN is 10 Mbps and transmission rate is 10 Mbps.
It is called an Mbps LAN. In the frame relay device 10,
LAN station 11 of 100 Mbps and LA of 10 Mbps
N stations 12a-12h are connected.

FIG. 11 shows the internal structure of the frame relay device 10. The frame relay device 10 is a 100 Mbps LA
N receiver 21, reception buffer 2 for temporarily accumulating frames received from a 100 Mbps LAN port
2. A data transfer control circuit 23, which controls transfer of the frame data accumulated in the reception buffer 22, a relay control circuit 24, a relay 25, and a transmission buffer 26, 100 Mbps for temporarily accumulating frame data to be transmitted from a LAN port of 100 Mbps. LAN transmitters 27, 10
It is composed of a transmitter 29 for Mbps LAN.

The frame relay device 10 relays a frame received from one of the ports 0 to 8 to all ports except the receiving port.
When a frame is received from port 1, the receiver 28a
Detects the reception of a frame and outputs a frame data transfer request signal to the relay control circuit 24. Upon detecting the transfer request signal from the receiver 28a, the relay control circuit 24 switches the relay 25 to the port 1 side. Receiver 28
The frame data output from a is transferred to all ports via the relay 25. On the output side of port 0,
The transmission buffer 26 temporarily stores the data transferred via the relay 25. After the data transfer is completed, the data once stored in the transmission buffer 26 is transmitted via the transmitter 27 at a transmission rate of 100 Mbps. On the output side of the ports 2 to 8, the transmitter 29 directly transmits the data transferred via the relay 25 at a data transfer rate of 10 Mbp.
Send with s. In the transmitter 29a on the output side of port 1,
Since the transfer request signal is output from the receiver 28a, the receiver 28a which has detected this signal does not execute the transmission of the data transferred via the relay 25.

When a frame is received from port 0, which is a LAN port of 100 Mbps, received data is temporarily stored in the reception buffer 22 via the receiver 21.
When the receiver 21 detects frame reception, it outputs a carrier detection signal to the data transfer control circuit 23. When the data transfer control circuit 23 detects the carrier detection signal from the receiver 21, the data transfer control circuit 23 outputs a data transfer request signal to the relay control circuit 24 and the transmission buffer 26. Relay control circuit 24
When detecting the data transfer request signal from the data transfer control circuit 23, switches the relay 25 to the port 0 side.

Next, the data transfer control circuit 23 reads the frame data from the reception buffer 22 and 10 Mbps.
Starts data transfer at the transfer rate of. The transferred data is transmitted to the ports 1 to 8 via the transmitter 29. The transmission buffer 26 that has detected the transfer request signal from the data transfer control circuit 23 does not store the data even if the data is transferred via the relay 25.

When transfer request signals are output from a plurality of ports to the relay control circuit 24, in order to notify all stations connected to the frame relay device 11 that a collision has occurred, The relay control circuit 24 outputs a jam signal output request signal to the transmitters of all the ports. When the transmitters 27 and 29 detect the jam signal output request signal from the relay control circuit 24, they start outputting the jam signal and notify the station connected to the port that a collision has occurred.

FIG. 13 shows a frame format of a CSMA / CD system LAN. CSMA / CD type LA
The N frame includes a preamble 61, an SFD (Start Fr
ameDelimiter, start frame delimiter) 62, DA
(Destination Address, 6)
3, Length 65, FCS (FrameChec
k Sequence, frame check sequence) 67. The number of bytes of the data 66 is stored in the length 65.

FIG. 14 is a diagram showing a conventional example of another relay device.

This relay device comprises Ethernet interfaces 41 and 42 and a memory 4 for storing transmission / reception data.
3, a CPU 44, and a bus 45. Ethernet is the most popular network at present, and the transmission speed is 10 Mbps, and data is transmitted in units of a set of data called a frame.

FIG. 15 is a diagram showing the frame structure of the Ethernet used in the relay device shown in FIG.

The frame 46 is composed of a destination address 46a, a source address 46b, a data length 46c, data 46d and an FCS 46e. The maximum frame length of the frame 46 is specified as 1518 bytes.

FIG. 16 is a diagram showing a temporal relationship of frame transmission / reception at each port in a bridge connecting Ethernets.

The relay device uses the frame 46 from port 1.
After the reception of 01, the destination address is analyzed, and if it is determined that the frame 4601 should be relayed, the frame 4602 is transferred to the port 2. The relay device stores the addresses of all terminals connected to the network, compares the destination address in the received frame with the stored terminal address, and determines whether to relay the frame 4601. decide.

By the way, in the case of the method shown in the figure, since the relay processing is performed after the frame is received, there is a problem that the delay becomes large especially when the frame length of the frame 4601 is long. An Ethernet switch solves this problem.

FIG. 17 is a diagram showing a time relationship of frame transmission / reception at each port in the Ethernet switch. Destination address 4601a at the beginning of frame 4601
Data is received, it is analyzed immediately, and if it is determined that the frame 4601 should be relayed, port 1
The transfer of the frame 4602 to the port 2 is started even before the reception of the frame from the. In this case, there are advantages that the data delay in the device is small and the data delay is constant regardless of the frame length.

FIG. 19 is a diagram showing another conventional example of the relay device.

The relay device shown in the figure has a high speed, for example, 1
It is an Ethernet LAN terminal 110 of 00 Mbps,
100 Mbps Ethernet LAN physical layer processing unit 11
6, internal bus 111, reception path 112, transmission path 11
3, Ethernet LAN data link layer processing unit 118,
It is composed of a CPU 117 and an internal circuit 119. The terminal 110 is a 100 Mbps Ethernet repeater, 11
4 is a 100 Mbps Ethernet repeater 115 and a terminal 110
It is a twisted pair wire transmission line of two pairs or four pairs that connect with. 1
In the 00 Mbps Ethernet LAN, the terminal 110
In the signal exchange between the Ethernet repeater 115 and the Ethernet repeater 115, one pair in the twisted pair transmission line 114 of two or four pairs is used for reception from the 100 Mbps Ethernet repeater 115, and the 100 Mbps Ethernet repeater 1
One of the two or four twisted pair transmission lines 114 is used for transmission to 15.

FIG. 20 is a diagram showing a frame structure used in the relay apparatus shown in FIG.

The frame structure of the 100 Mbps Ethernet LAN and the maximum frame length and the minimum frame length are 1
This is exactly the same as the frame structure and maximum frame length of the 0 Mbps Ethernet LAN.

A frame 30 of a 100 Mbps Ethernet LAN includes a 56-bit preamble 31, an 8-bit start delimiter 32, a 16-bit or 48-bit destination address 33, a 16-bit or 48-bit source address 34, and a 16-bit frame length. 35, data 3
The frame check sequence 37 consists of 6 and 32 bits. The minimum frame length is 512 bits and the maximum frame length is 12144 bits.

FIG. 21 is a diagram showing the maximum wiring configuration when the 100 Mbps Ethernet terminal shown in FIG. 19 is used. 115a and 115b are 100 Mbps ether repeaters, 114a to 114c are two or four twisted pair transmission lines, and 110a and 110b are conventional 100 Mbps.
s Ethernet terminal, the number of repeaters between two terminals is 2 or less, and the maximum length of 114a and 114c is 1
The maximum length of 00m and 114b is limited to 10m. The reason why such a limitation is added is shown below.

In the Ethernet LAN, the CSMA / CD method is used as a medium access method. C
In the SMA / CD system, a Collision is performed between a certain terminal starting transmission of a frame and its end.
If the signal (hereinafter referred to as “collision”) is not detected, it is recognized that the frame has reached the destination correctly. Therefore, it is important to detect the "collision" accurately.

A state in which another terminal starts frame transmission from the start of frame transmission to the end thereof is called "collision". The maximum wiring configuration that can correctly detect a "collision" is determined by the minimum frame transmission time. The reason for this is shown below.

In FIG. 22, the frame 30 sent from the terminal 110a installed at one end of the maximum wiring configuration.
(See FIG. 20) is the terminal 110b installed at the other end.
When it arrives, a "collision" occurs when the terminal 110b starts transmitting the frame 30. Terminal 1 that detected a "collision"
10b interrupts the transmission of the frame 30 and sends a jam signal (collision detection signal) to notify the other terminal 110a that a "collision" has occurred. At this time, the terminal 110a cannot correctly detect the occurrence of the "collision" unless it continues to transmit the frame 30 until the jam signal arrives.

Therefore, the round-trip wiring propagation delay time when the frame 30 reaches the terminal 110b from the terminal 110a having the maximum wiring configuration and the frame 30 returns to the original terminal 110a must be less than the minimum frame transmission time.

Incidentally, FIG. 22 shows 100 Mbp shown in FIG.
It is a figure which shows the relationship of the minimum frame transmission time, the maximum wiring structure, and wiring propagation delay time when using an s Ethernet terminal. In the figure, the vertical axis represents each position of the wiring system in FIG. 21, and the horizontal axis represents time. 140 is the terminal 110
a is a propagation delay time required for the frame 30 to reach the terminal 110b, 141 is a time required for the terminal 110b to detect a "collision", and 142 is a propagation delay time required for the frame 30 to return to the original terminal 110a. , 143 is the minimum frame transmission time. In a 100 Mbps Ethernet LAN, the speed at which the frame 30 travels in the twisted pair transmission line is 177 × 10 ⁶ m / s, the repeater internal delay time is 530 ns, and the “collision” detection time is 490 ns. Therefore, the propagation delay times 140 and 142 are Twisted pair transmission line 21
1.19 μs (= time required for the frame to advance 0 m (=
210 / (177 × 10 ⁶ )) and the repeater delay time of 1.06 μs (= 530 ns × 2), which is 2.25 μs, and the “collision” detection time 141 is 0.49 μs.
The minimum frame transmission time 143 is 1 bit transmission time is 1
0 ns (= 1/100 Mbps), minimum frame length is 5
Since it is 12 bits, 5.12 μs (512 × 10n)
s), and the sum of time 140, time 141, and time 142 is 4.99 μs (= 2 × 2.25 μs + 0.49 μs).
Is less than 5.12 μs which is the minimum frame transmission time 143.

[0029]

FIG. 12 shows the timing of relaying a frame from a 10 Mbps LAN station to a 100 Mbps LAN station in the conventional frame relay apparatus shown in FIG. When a frame received from a 10 Mbps LAN port is relayed to a 100 Mbps LAN port, the received frame data is temporarily stored in the transmission buffer 26 and is set to 1 after frame reception is completed.
In order to start the frame transmission to the station of 00 Mbps LAN, there is a problem that the delay time from the reception of the frame at the 10 Mbps LAN port to the transmission of the frame at the 100 Mbps LAN port becomes long. It was Further, when a collision occurs during frame transmission from the 100 Mbps LAN port, even if the frame relay device outputs a jam signal to the frame transmission station, the frame transmission station has already completed frame transmission. Therefore, even if a jam signal from the frame relay device is detected, it is not possible to recognize that the relay of the frame has failed.

Further, in the relay device for connecting networks having different transmission speeds, as shown in FIG. 17, when the transfer is started to the other port while receiving the data from the one port, the following will be shown. There is such a problem.

FIG. 18 shows 100 from a 10 Mbps port.
It is a figure which shows the time relationship of frame transmission / reception in each port at the time of carrying out frame relay to the port of Mbps. FIG. 17
Similarly, when the relay device starts relaying to the 100 Mbps port immediately after receiving the destination address 4603a of the frame 4603, it receives 1 port of 10 Mbps.
00 Mbps port transmission overtakes (frame 460
3 transmission time> frame 4604 transmission time), underrun error (frame 4 while data cannot be prepared)
There is a problem that the transmission / reception processing of 604) occurs (the hatched portion 4604f in FIG. 18 is transmitted before the reception).

When it is desired to carry out reliable transmission without error, as shown in FIG. 16, the method is to carry out the relay processing after the reception of the frame is completed. There is a problem that the delay becomes large.

Further, in the 100 Mbps Ethernet terminal 110 shown in FIG. 19, since the frame structure and the maximum frame length and the minimum frame length are exactly the same as the frame structure, the maximum frame length and the minimum frame length of the 10 Mbps Ethernet LAN, the transmission speed is 10 Mbps.
From 100 Mbps to 10 times, the minimum frame transmission time is 1/1 of the case when the transmission rate is 10 Mbps
0, and the twisted pair transmission line with the maximum wiring configuration has a transmission speed of 1
It is shorter than 0 Mbps, and the number of repeaters 115 that can be placed between two terminals is 10 M
Less than for bps.

FIG. 23 shows the maximum wiring configuration of the 10 Mbps Ethernet LAN.

In the figure, 51a to 51d are 10 Mb.
ps ether repeater, 52a to 52e are two or four pairs of twisted wire transmission lines, 53a and 53b are 10 Mbps Ethernet terminals, and a repeater 51a between the two terminals.
˜51d is 4 or less, and the length of the twisted wire transmission lines 52a to 52e is 100 m at maximum.

Conventional 100 Mbps Ethernet terminal 1
When changing a 10 Mbps Ethernet LAN system to a 100 Mbps Ethernet LAN system using 10, since the maximum wiring configuration is different, simply 10 Mbps
s Ethernet terminal is replaced with 100 Mbps Ethernet terminal, and 10 Mbps Ethernet repeater is replaced with 100
It is not possible to correctly detect that a collision has occurred by simply replacing the Mbps Ether Repeater with CSMA /
It is not possible to transfer frames based on the CD system. As a result, when a 10 Mbps Ethernet LAN system is changed to a 100 Mbps Ethernet LAN system, not only devices such as terminals and repeaters are changed to those at 100 Mbps, but also wiring system rearrangement work and internetwork devices such as bridges and routers are required. Become.

Therefore, an object of the present invention is to solve the above-mentioned problems and to reduce the delay time in relaying a frame from a low-speed LAN port to a high-speed LAN port, causing a collision during frame transmission from the high-speed LAN port. In this case, the frame transmission station can be recognized and an underrun error at the time of data relay can be prevented.
In the case of changing to AN, a relay device is provided in which only devices such as terminals and repeaters need to be changed to high-speed ones.

[0038]

To achieve the above object, a first invention is a relay device for relaying a frame between a LAN having a high transmission speed and a LAN having a low transmission speed. A frame length detection circuit that detects the frame length of the data to be transmitted by extracting the information of the length field included in the frame data on the transmission side of the port for counting, and the number of bytes of the transferred frame data is counted. And a transmission control circuit for deciding the transmission start timing of the frame based on the frame length and the value of the byte number counter and for starting the transmission.

A second aspect of the present invention is a relay device for relaying a frame between a LAN having a high transmission rate and a LAN having a low transmission rate, which is a high speed when data is relayed from a high speed LAN to a low speed LAN. Receives frames from LAN,
If the relay device determines that the frame is to be transferred to the low-speed LAN, the frame transmission to the low-speed LAN is started before the frame reception from the high-speed LAN is completed, and the data is transferred from the low-speed LAN to the high-speed LAN. When relaying a frame, even if the relay device determines that the frame is to be transferred to a high-speed LAN, it does not immediately transmit a frame to the high-speed LAN, Of the high-speed L at the timing of either waiting for the time guaranteed that the underrun of the data during the transmission does not occur or completing the frame reception from the low-speed LAN.
It starts frame transmission to the AN.

A third aspect of the invention is a relay device for relaying a frame between a LAN having a high transmission rate and a LAN having a low transmission rate, in which the round trip propagation time and the collision detection time of the maximum wiring configuration of the low speed LAN are When transmitting a frame that has a transmission time shorter than the sum, a preamble is added to the beginning of the frame.

In addition to the structure of the third invention, a high-speed LA
An Ethernet physical layer processing unit and a preamble addition circuit may be provided in the N and low-speed LAN.

[0042]

According to the first aspect of the present invention, when a frame is relayed from a low-speed LAN port to a high-speed LAN port, frame transmission must be performed before frame reception is completely completed, as shown in FIG. By starting, it is possible to reduce the delay time from the reception of the frame at the low speed LAN port to the transmission of the frame at the high speed LAN port. 2 is a diagram showing the timing when a frame is relayed from a port for low speed LAN to a port for high speed LAN in the relay device shown in FIG. 1 which will be described later.

Even if a collision occurs at a high-speed LAN port during frame transmission, a jam signal is output before the frame transmission station finishes frame transmission as shown in FIG. Can detect when a collision occurs.

According to the second invention, in relaying from a high-speed LAN to a low-speed LAN, the relay operation is started before the frame reception is completed, so that the internal delay is considerably larger than that of a conventional bridge or the like. It becomes smaller, and its value is equivalent to that of an Ethernet switch. On the contrary, in the relay from the low-speed LAN to the high-speed LAN, the relay operation is waited for the time guaranteed that the data underrun error does not occur, so that the reliable transmission is performed. Regarding the delay in the device in that case, the relay operation can be started before the completion of reception for a frame with a long frame length.
The average delay time can be reduced as compared with a conventional device such as a bridge.

According to the third invention, as shown in FIG. 7, a 100 Mbps Ethernet terminal 6 as a high speed LAN.
When a frame is transmitted from 0 (S-1), low speed L
It is determined whether or not the frame transmission time is shorter than the sum of the round-trip propagation delay time and the collision detection time of the maximum wiring configuration of the 10 Mbps Ethernet LAN as the AN (S-2), and when the frame transmission time is short (YES. ), A preamble is added to the beginning of the frame (S-3) to increase the frame length and transmit the frame (S-4).
When the frame transmission time is not short (NO), the frame is transmitted as it is without adding the preamble (S-5). This allows high-speed L instead of low-speed LAN.
AN can be used. 7. FIG. 7 is an explanatory diagram for explaining the operation of the relay device shown in FIG.

[0046]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing an embodiment of the relay apparatus of the present invention.

As shown in FIG.
The frame received from the port (port 1) for the Mbps LAN is 100 Mbps L as a high-speed LAN.
The case of transferring to the AN port (port 0) will be described as an example. The same reference numerals are used for the same members as in the conventional example shown in FIG.

The relay device has a port 0 for high-speed transmission and reception,
It has low-speed transmission / reception ports 1 to 8, the receiver 21 and the transmitter 27 are connected to the port 0, and the receivers 28a to 28b and the transmitters 29a to 29b are connected to the ports 1 to 8. There is.

The output line of the receiver 21 is connected to the reception buffer 22, and the output of the reception buffer 22 is connected to the data transfer control circuit 23. The output lines of the data transfer control circuit 23 and the receivers 28a to 28b are connected to the relay control circuit 2
4 and the input side of the relay 25 whose connection state is controlled by the relay control circuit 24. The output line of the data transfer control circuit 23 is connected to the transmission control circuit 43, and the output lines of the receivers 28a and 28b are connected to the low speed side transmitters 29a to 29b.

The output line of the relay 25 is connected to the frame length detection circuit 42, the byte number counter 41, the buffer 26, and the input side of each of the low speed side transmitters 29a-29b. Byte counter 41 and frame length detection circuit 4
The output line of 2 is connected to the input side of the transmission control circuit 43, and the output line of the transmission control circuit 43 is connected to the input side of the transmitter 27 on the high speed side to form a relay device.

Next, the operation of the embodiment will be described.

In FIG. 1 and FIG. 2, when the frame data received from port 1 is transferred, the transmitting side of port 0 temporarily stores the transferred frame data in the transmission buffer 26, and at the same time, the byte number counter 41
Counts the number of bytes of frame data transferred. The frame length detection circuit 42 extracts frame data length information from the length field of the transferred frame data, and notifies the transmission control circuit 43 of the value. The transmission control circuit 43 calculates the time required to transfer the frame data from the frame data length and the time required to transmit the frame data at a transmission rate of 100 Mbps, and starts the frame transmission at the byte data of the frame data transfer. Then, it is determined whether the frame data transfer and the frame transmission can be ended at the same time.

Then, the transmission control circuit 43 starts the transmission of the frame when the value of the byte number counter 41 becomes equal to the above value, and the frame is transmitted to the station connected to the port 0 via the transmitter 27. It

When a frame is received from the receiving side of port 0 during frame transmission, the receiver 21 and the receiving buffer 2
The data transfer control circuit 23 to which the frame data is input via 2 outputs a frame data transfer request signal to the relay control circuit 24. At this time, the relay control circuit 24
Since the frame data transfer request signal is also output from the receiver 28a, the relay control circuit 24 is
A jam signal output request signal is output to 7 and 29.
This causes the transmitters 27 and 29 to output a jam signal.

In the above, according to the present embodiment, by starting the transmission of the frame before the frame reception is completely completed, the frame is received by the low speed LAN port and then the high speed LAN port is received. It is possible to reduce the delay time until the frame is transmitted. Further, even if a collision occurs at the high-speed LAN port during frame transmission, the frame transmission station outputs a jam signal before the frame transmission is completed. Can be detected.

FIG. 3 is a diagram showing another embodiment of the relay apparatus of the present invention. The same reference numerals are used for the same members as in the conventional example shown in FIG.

As shown in the figure, the memory 4 is connected to the bus 45.
3, a low speed Ethernet interface 41, a high speed Ethernet interface 42 and a CPU 44a are connected, and a timer 46 is connected to the CPU 44a.

FIG. 4 shows the time relation of frame transmission / reception at each port when the frame 4604 is relayed from port 2 to port 1, that is, from the faster transmission speed to the slower speed in the relay device shown in FIG. It is the figure shown.

As in the case of FIG. 17, frame 4604
When the destination address 4604a at the beginning of the frame is received and it is determined that this frame 4604 is a frame to be relayed,
Immediately start the relay operation. In this case, the reception speed is faster than the transmission speed (transmission time of frame 4604 <
(Transmission time of frame 4605), underrun error does not occur, and the processing of frames 4604 and 4605 may be the same as the processing in the conventional Ethernet switch.

FIG. 5 shows each port when relaying a frame having the maximum length defined by the standard from port 1 to port 2, that is, from the one having a slower transmission speed to the one having a faster transmission speed in the relay device shown in FIG. FIG. 3 is a diagram showing a temporal relationship of frame transmission / reception of FIG.

The CPU 44a (FIG. 3) uses the frame 460.
When the destination address 4606a at the head of 6 is received and it is determined that this frame 4606 is a frame to be relayed, the relay operation is not started immediately and the timer 46 is started.
Then, after the timer 46 has passed a certain fixed time,
Notify the CPU 44a that the timer time has expired, and
Upon receiving this notification, the PU 44a starts the transmission operation to the port 2. A frame 4607 is transmitted from port 2.

The time waited by the timer 46 is set such that when the frame of the maximum length defined by the standard is relayed, the port 2 is received before the last data of the frame 4606 is received from the port 1.
Is a time guaranteed not to transmit the last data of the frame 4607, and is represented by 1.09 ms (difference between maximum frame lengths of two Ethernets)-(time required for relay determination).

In this case, since the transmission operation to the port 2 can be performed before the reception from the port 1 is completed,
In-device delay can be minimized. However, when the received frame length is shorter than 1.09 ms, the reception of the frame 4606 is completed before the expiration of the timer time.
In such a case, waiting by the timer 46 will increase the delay time. Therefore, C
It is assumed that the PU 44a starts the transmission operation when either the expiration of the timer time or the completion of reception of the frame 4606 is satisfied.

FIG. 6 is a diagram showing a temporal relationship of frame transmission / reception at each port when a frame having a short frame length is relayed from port 1 to port 2 in the relay device shown in FIG.

In this case, since the transmission time of the frame 4609 is shorter than the transmission time of the frame 4608, an underrun error does not occur, and after the reception of the frame 4608 at the port 1 is completed, the frame 2609 from the port 2 is transmitted.
Will be sent.

As described above, according to this embodiment, the high speed L
When relaying from the AN to the low-speed LAN, the relay operation is started before the frame reception is completed, so that the internal delay is considerably smaller than that of a conventional device such as a bridge, and its value is equivalent to that of an Ethernet switch. Become. On the contrary, in the relay from the low-speed LAN to the high-speed LAN, the relay operation is waited for the time guaranteed that the data underrun error does not occur, so that the reliable transmission is performed. Regarding the delay in the device in that case, the relay operation can be started before the completion of the reception of a frame having a long frame length, and the average delay time can be reduced as compared with the conventional device such as a bridge.

Although the relay device having two network interfaces having different transmission rates has been described in the present embodiment, the same frame as described above between any two interfaces having three or more interfaces is described. It can also be applied to a device that performs the relay processing of.

FIG. 8 is a diagram showing another embodiment of the relay apparatus of the present invention.

In the figure, the relay device 60 includes a high-speed Ethernet LAN physical layer processing unit 116 and an internal bus 111.
A reception path 112, a transmission path 113, an Ethernet LAN data link layer processing section 116, and a CPU 117.
And an internal circuit 119 and a preamble addition circuit 170.

Reference numeral 115 is a 100 Mbps ether repeater, and 114 is two or four twisted pair transmission lines connecting the high speed ether repeater 115 and the terminal 60.

FIG. 9 is a block diagram of a preamble addition circuit used in the relay device shown in FIG.

In the figure, 81 is a frame length writing register, 82 is a minimum transmission frame length holding register, and 8 is a minimum transmission frame length holding register.
3 is a subtracter, 84 is a temporary storage first-in first-out memory for transmission frames, 85 is a preamble generation circuit, 91 and 92 are gate circuits, 88 is an enable signal for the gate circuit 92,
87 is an enable signal for the gate circuit 91, and 86 is an enable signal for the preamble generation circuit 85.

Prior to frame transmission, the minimum transmission frame length holding register 82 is set in the low-speed Ethernet L shown in FIG.
The sum of the round-trip propagation delay time and the collision detection time of the maximum wiring configuration of the AN is written in advance, and at the time of frame transmission, the CPU writes the frame length in the frame length writing register 81, and the subtractor 83 sets the minimum in the frame length writing register 81. The difference between the transmission frame length holding registers 82 is calculated, and when the value of the frame length writing register 81 is larger than the value of the minimum transmission frame length holding register 82, the enable signal 87 of the gate circuit 91 is output to output the minimum transmission frame length. When the value of the frame length writing register 81 is smaller than the value of the holding register 82, the value obtained by adding the length of the preamble generated by the preamble generation circuit 85 and the transmission frame length exceeds the value of the minimum transmission frame length holding register 82. Thus, the enable signals 86 and 87 are output.

The round-trip propagation delay time of the maximum wiring configuration of the low speed Ethernet LAN shown in FIG. 23 is 5.65 μs (= 1000 / (177 × 10 ⁶ )) of the propagation delay time of the twisted pair wire.
And repeater delay time 4.24 μs (= 530 ns ×
8) and the collision detection time are 10.38 μs.

As described above, according to this embodiment, the high speed L
When a frame is transmitted from the AN, it is first determined whether or not the frame transmission time is shorter than the sum of the round-trip propagation delay time and the collision detection time of the maximum wiring configuration of the low-speed LAN, and if it is shorter, the preamble is added to the beginning of the frame. By adding the frame, the frame length is lengthened and the frame is transmitted. If it is not short, the frame is transmitted without adding the preamble.

[0077]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) From a low speed LAN port to a high speed L
When frame data is transferred to the AN port, the high-speed LAN port does not store all frames in the buffer and starts frame transmission, so that the low-speed LAN port receives the frame It is possible to shorten the delay time until the frame is transmitted from the high-speed LAN port. Further, even if a collision occurs at a high-speed LAN port during frame transmission, the frame transmission station can output a jam signal before the frame transmission ends, so that the frame transmission station has a collision. Can be detected.

(2) When the data is relayed from the higher transmission speed to the lower transmission speed, the relay processing can be started before the data reception is completed, so that the delay in the apparatus can be minimized. Also, when relaying data from the slowest to the slowest, the data underrun error does not occur. Furthermore, for the relay of a frame whose frame length is long to some extent, it is possible to start the relay processing before the frame reception is completed, so compared to the method of starting the relay processing after receiving all the frames. The delay time in the device can be reduced.

(3) A high-speed Ethernet terminal is newly provided with a preamble addition circuit, and a low-speed Ethernet LAN
When transmitting a frame that has a transmission time shorter than the sum of the round-trip propagation delay time and the collision detection time of the maximum wiring configuration of, the low-speed Ethernet LAN system is added to the high-speed Ethernet LA to add a preamble to the beginning of the frame.
When changing to the N system, it suffices to change devices such as terminals and repeaters.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a relay device of the present invention.

FIG. 2 is a diagram showing a timing when a frame is relayed from a port for low speed LAN to a port for high speed LAN in the relay device shown in FIG.

FIG. 3 is a diagram showing another embodiment of the relay device of the present invention.

FIG. 4 is a diagram showing a temporal relationship of frame transmission / reception at each port when a frame is relayed from port 2 to port 1, that is, from a faster transmission speed to a slower speed in the relay apparatus shown in FIG. is there.

FIG. 5 is a frame transmission / reception at each port when relaying a frame having a maximum length defined by a standard from port 1 to port 2, that is, from a slower transmission speed to a faster transmission speed in the relay device shown in FIG. It is a figure showing the time relation of.

6 is a diagram showing a temporal relationship of frame transmission / reception at each port when a frame having a short frame length is relayed from port 1 to port 2 in the relay device shown in FIG.

FIG. 7 is an explanatory diagram for explaining the operation of the relay device shown in FIG.

FIG. 8 is a diagram showing another embodiment of the relay device of the present invention.

9 is a block diagram of a preamble addition circuit used in the relay device shown in FIG.

FIG. 10 is a diagram showing a conventional example of a relay device.

11 is a diagram showing an internal configuration of the relay device shown in FIG.

FIG. 12 is 10 Mbp in the relay device shown in FIG.
It is a figure which shows the timing at the time of frame relay from the LAN station of s, to a LAN station of 100 Mbps.

FIG. 13 is a diagram showing a frame format of a CSMA / CD system LAN.

FIG. 14 is a diagram showing a conventional example of another relay device.

15 is a diagram showing a frame structure of Ethernet used in the relay device shown in FIG.

FIG. 16 is a diagram showing a temporal relationship of frame transmission / reception at each port in a bridge connecting Ethernets.

FIG. 17 is a diagram showing a time relationship of frame transmission / reception at each port in the Ethernet switch.

FIG. 18 is a diagram showing a temporal relationship of frame transmission / reception at each port when a frame is relayed from a 10 Mbps port to a 100 Mbps port.

FIG. 19 is a diagram showing another conventional example of a relay device.

20 is a diagram showing a frame configuration used in the relay apparatus shown in FIG.

FIG. 21 is a diagram showing a maximum wiring configuration when the 100 Mbps Ethernet terminal shown in FIG. 19 is used.

22 is a diagram showing the relationship between the minimum frame transmission time, the maximum wiring configuration, and the wiring propagation delay time when the 100 Mbps Ethernet terminal shown in FIG. 19 is used.

FIG. 23 is a diagram showing the maximum wiring configuration of a 10 Mbps Ethernet LAN.

[Explanation of symbols]

 21 (for High Speed) 22 Receive Buffer 23 Data Transfer Control Circuit 24 Relay Control Circuit 25 Relay 26 Transmit Buffer 27 (For High Speed) Transmitter 28a-28b (For Low Speed) Receiver 29a-29b (For High Speed) Transmitter 40 Repeater 41 Byte counter 42 Frame length detector 43 Transmission control circuit

Claims (4)

[Claims] 1. A relay device for relaying a frame between a LAN having a high transmission speed and a LAN having a low transmission speed, wherein a frame included in frame data is transmitted to a transmission side of the high speed LAN port. Frame length detection circuit that detects the frame length of the data to be transmitted by extracting the information in the field, the byte number counter that counts the number of bytes of the transferred frame data, and the value of the frame length and the byte number counter. A relay apparatus, comprising: a transmission control circuit that determines a timing of starting transmission of a frame and starts transmission. 2. A relay device for relaying a frame between a LAN having a high transmission speed and a LAN having a low transmission speed, when receiving data from a high speed LAN to a low speed LAN, the frame is received from the high speed LAN. If the relay device determines that the frame is to be transferred to the low-speed LAN, the frame transmission to the low-speed LAN is started before the frame reception from the high-speed LAN is completed, and the low-speed LAN transfers the high-speed LAN. When relaying data to the high speed LAN, even if the relay device determines that the frame is to be transferred to the high speed LAN, the frame is not transmitted to the high speed LAN immediately, and even if the frame of the maximum data length is relayed, the high speed Either waiting for a time guaranteed that no underruns of data during transmission to the LAN will occur or frame reception from the slow LAN will be completed A relay device, which starts frame transmission to a high-speed LAN at a timing. 3. A relay device for relaying a frame between a LAN having a high transmission speed and a LAN having a low transmission speed, which is shorter than the sum of the round trip propagation time and the collision detection time of the maximum wiring configuration of the low speed LAN. A relay device characterized in that, when a frame having only a transmission time is transmitted, a preamble is added to the beginning of the frame. 4. The high-speed LAN and the low-speed LAN,
The relay device according to claim 3, further comprising an Ethernet physical layer processing unit and a preamble addition circuit.