WO2004064341A1 - Method for realizing uninterruptible transfer during line failure in ip network - Google Patents

Abstract

An uninterruptible transfer can be realized during a line failure in a transmission system performing a packet transmission between transmitting apparatuses connected via a plurality of lines. In a method for realizing the uninterruptible transfer, test packets including information of the number of packets received from the transmitting apparatus of a destination are periodically sent to the transmitting apparatus of a source. The transmitting apparatus of the source compares the received information of the number of packets included in the received test packets with the number of packets sent out to the transmitting apparatus of the destination via one line. When the comparison shows a disagreement between the number of the received packets and the number of the sent-out packets, packets corresponding to the disagreement are resent to the transmitting apparatus of the destination via another line. The packets, before being sent out to the transmitting apparatus of the destination, are stored in a buffer memory. When the comparison shows an agreement between the number of the received packets and the number of the sent-out packets, packets, which are stored in the buffer memory, corresponding to the agreement are released from the buffer memory.

Description

 Specification

Method of uninterrupted transfer in case of line failure in IP network

 The present invention relates to an uninterruptible transfer method in the event of a line failure in an IP network, which prevents a bucket loss at the moment when a failure occurs due to a line disconnection, etc., between devices accommodating a plurality of IP packet lines. . Background art

 FIG. 1 is a diagram illustrating a conventional example of packet transfer in a network.

 At normal time, an example is shown in which data is downloaded from the server 1 to the PC user terminal 2 on the route A through the network 3 via the routes R1, R2, and R3.

 In Fig. 1, if a disconnection fault occurs at point A-a during this download, the data is invalid because the download is not completed (packet loss). In such a case, when the user notices this and requests retransmission, route B through network R1, R2, R4, and R3 of network 3 is established, and the download from server 1 is executed again. Is done.

 In the above case, the user of the PC user terminal 2 feels stress due to a large delay in the download operation, and the protocol on the PC user terminal 2 protects retransmission and the like. However, there is no guarantee that accidents such as damage to important data will be completely prevented.

In other words, as shown in Fig. 1, when a line failure occurs on the network, retransmission occurs between the transmitting and receiving terminals (END-END) due to packet loss. This will give network users inconveniences such as “damage of data transfer” and “delay of response”. Disclosure of the invention

 Therefore, an object of the present invention is to prevent a packet loss in the event of a line failure, rescue the lost packet at the moment of the failure by resending it, and use the line transmission / reception terminal (END-END for packet communication). It is an object of the present invention to provide a hitless transfer method for preventing the influence of a failure and a packet transmission device to which the method is applied.

 In order to achieve the object of the present invention, the method of instantaneous interruption transfer in the event of a line failure in an IP network according to the present invention is intended for use in a transmission system that performs bucket transmission between transmission devices connected by a plurality of lines. The first aspect of the non-instantaneous transfer method according to the first aspect is that a test packet including information on the number of packets received from the transmission apparatus at the transmission destination is periodically transmitted to the transmission apparatus at the transmission source, and the transmission apparatus at the transmission source is transmitted. And comparing the number information of the received packets included in the received test packet with the number of packets transmitted to the transmission apparatus of the transmission destination through one line, and in the comparison, in the comparison, the received packet When the number of transmitted packets does not match the number of transmitted packets, a packet corresponding to the mismatch is retransmitted to the transmission destination (`to the transmission device ') through a line different from the one line.

 According to a second mode of the hitless transfer method according to the present invention for achieving the object of the present invention, in the first mode, a bucket transmitted to the transmission device at the transmission destination is stored in a buffer memory before transmission. In the comparison, when the number of received packets matches the number of transmitted packets, a packet stored in the buffer memory corresponding to the match is released from the buffer memory. And

 A third mode of the hitless transfer method according to the present invention that achieves the above object of the present invention is the second aspect, wherein in the second mode, one user packet transmitted to the transmission apparatus at the transmission destination is classified into a plurality of quality classes. O Classifying and storing only user packets of a predetermined quality class or higher in the buffer memory.

Fourth mode of the hitless transfer method according to the present invention that achieves the object of the present invention The first aspect is characterized in that, in the first aspect, a packet retransmitted by a line different from the one line is connected to a maximum length of transmittable and formed into one packet, and then retransmitted. .

 A fifth aspect of the hitless transfer method according to the present invention for achieving the object of the present invention is the first aspect, wherein in the first aspect, when retransmitting a packet through a line different from the one line, the It is characterized in that a transfer band and a transfer band of a packet transmitted by the different line are set equally.

 The features of the present invention will become more apparent from embodiments of the invention described with reference to the following drawings. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a diagram for explaining a conventional example of packet transfer in a network.

 FIG. 2 is a diagram for explaining a conceptual configuration of a method of instantaneous interruption transfer at the time of a line failure according to the present invention in an IP network corresponding to FIG.

 FIG. 3 is a diagram for explaining the flow of a packet between the devices R1 and R2 corresponding to the operation shown in FIG.

 FIG. 4 is a diagram for explaining the operation of the conventional packet buffer 100. FIG. 5 is a diagram for explaining the operation of the packet buffer 100 according to the present invention.

 FIG. 6 is a diagram illustrating a mechanism for detecting a line failure in the present invention.

 FIG. 7 is a diagram illustrating a mechanism for suppressing an increase in traffic by increasing the “test packet transmission cycle”.

 FIG. 8 is a diagram for explaining an embodiment for solving the problem of a large number of packets to be transmitted at the time of packet retransmission.

 FIG. 9 is a diagram for explaining the processing of the connection control unit 122.

Figure 10 shows a case where the load temporarily increases suddenly on the line to be switched to. FIG. 3 is a diagram for explaining an embodiment for preventing occurrence of indiscriminate packet discarding.

 An embodiment of the present invention will be described below with reference to the drawings.

 FIG. 2 is a diagram for explaining a conceptual configuration of a method of instantaneous interruption transfer at the time of a line failure according to the present invention in an IP network corresponding to FIG. FIG. 3 is a diagram illustrating a flow of a packet between the device R1 and the device R2 corresponding to the router in FIG.

 As shown in FIG. 3, the device R 1 and the device R 2 corresponding to the router and the buffer memory 100, respectively, and a plurality of line interface circuit 200 A 1, A 2-200 B 1, Β Has two.

 In the example shown in Fig. 2 and Fig. 3, the physical connection between the line interface 200A1 of port A1 of device R1 and the line interface 200B1 of port B1 of device R2. A physical link is formed between the link and the line interface 200A2 of port A2 of device R1 and the line interface 20 "ΌB2 of port B2 of device R-2. Have been.

 Here, consider a case where a line disconnection occurs at a failure point A—a of a physical link between ports A 1 and B 1.

 It connects the interface 200A1 of port A1 with the interface 200A1 of port 1 and the interface 200A2 of port A2 and the interface 200B2 of port B2. A user packet, which is a packet having overnight information, flows on the physical link, and a test packet carrying information on the number of received packets at each port is periodically transmitted.

As shown in FIG. 3, the test packet has information on the number of packets received by each device between the header a and the check code (FCS) b of the MAC / IP address. The two physical links 200A1—200B1 and 200A2—200B2 from device R1 to device R2 The information on the number of received packets includes the information on the number of received packets c 1 and c 2 in the two interface circuits 200 A 1 and 200 A 2 of the device R 1.

 Similarly, the two physical links 200 B1 to 200 A1 and 200 B2 to 200 A2 from the device R2 to the device R1 are used as information on the number of received packets. R2 has information d1 and d2 on the number of received packets in the two interface circuits 200B1 and 200B2.

 Before a failure occurs at the fault point A—a, the receiver connected to the interface circuit 200 B 1 on the device R 2 is connected to the interface circuit 200 A 1 on the device R 1 Receives test packets sent periodically from the transmitter. As a result, it is confirmed that the physical link from the interface circuit 200A1 to 200B1 is normal.

 Further, information about the number of received buckets d 1 sent from the interface circuit 200 B 1 to the interface circuit 20 OA 1 and included in the test bucket arriving at the interface circuit 20 OA 1 Thus, the number of user packets that have normally arrived from port A1 of device R1 to port B1 of device R2 is confirmed. · — — ·

 At this time, a packet corresponding to the number of reception packets confirmed to be received by the device R2 is cleared from the buffer memory 100 of the device R1, and the occupied memory space is released. .

 Further, the test packet between ports B2 and A2 includes the number of received packets of ports A1 and B1, and the test packet between ports B1 and A1 includes port A2. , B2, the number of received packets.

 When a failure occurs at the failure point A—a, a test is performed to the interface circuit 200 A1 of the port A1 of the device R1 and the interface circuit 200B1 of the port B1 of the device R2. Top packets will not arrive. As a result, it is detected that an error has occurred in the physical link between the ports A1 and B1.

At this point, the test packet from port B1 to port A1 has no information on the number of received packets at port B1, so the user packet on buffer memory 100 of device R1 is cleared. It is kept without being. After a failure occurs, the user packets held in the buffer memory 100 of the device R1 are cleared by the number of received packets at the port B1 mounted on the test packet in the direction from the port B2 to the port A2, and the remaining packets are cleared. Uses the normal physical link from port A 2 to port B 2 to perform retransmission by detouring. Therefore, double transmission is suppressed.

 By the above procedure, the bucket once lost at the moment of the failure is remedied by retransmission, and the effect of the line failure on the packet communication between the sending and receiving terminals (END-END) is prevented, and instantaneous uninterrupted protection is provided. Is achieved.

 Here, in the event of a line failure, the conventional method always causes a packet loss, and then requires retransmission processing between the sending and receiving terminals (END-END). And other inconveniences. On the other hand, in the above-described embodiment of the present invention, the above-described inconvenience does not occur because packet loss is prevented between devices when a line failure occurs.

 Here, in the above-described instantaneous interruption transfer method according to the present invention, the relationship between the “test packet transmission cycle” and the “transmission packet retransmission buffer capacity” is important.

 If the “test bucket transmission cycle” is short, the traffic of the test bucket itself increases and the line utilization efficiency deteriorates. Conversely, if the transmission cycle is long, it takes time to detect a line failure, so the required capacity of the retransmission buffer increases, and there is a difficulty in increasing the equipment cost and increasing the size.

 Therefore, in the embodiment of the present invention, only packets having a specific quality of service (QoS) or more are held in a buffer and complemented. As a result, it is possible to prevent an increase in the buffer capacity and to prolong the “test packet transmission period” to suppress an increase in traffic.

Furthermore, when performing retransmission, it is necessary to transmit a normal user's packet and a packet for the retransmission, and it is necessary to transmit a large number of packets in a short time. In this case, it is easy to edit the packet data to be retransmitted because the packet data to be retransmitted exists in the buffer 100 in a stationary state. Therefore, multiple short packets to be retransmitted are By linking (compositing) up to the maximum length and making one packet, it is possible to improve the line use efficiency.

 In addition, the bandwidth guarantee class of the switching source traffic guarantees the guaranteed bandwidth before the occurrence even after a line failure occurs, and the lowest bandwidth guarantee class of the switching source traffic that was used immediately before the line failure occurred To the guaranteed minimum bandwidth. In addition, non-guaranteed classes of the switching source traffic are discarded with priority.

 Similarly, in the physical link that is used in the detour in the retransmission process, there is naturally user traffic flowing before that point. Therefore, when a circuit is switched for detour, the bandwidth guarantee class of the traffic at the switching destination must guarantee the guaranteed bandwidth before the occurrence even after a line failure occurs. Of the above traffic, the non-guaranteed class is preferentially discarded. The minimum bandwidth guaranteed class suppresses the bandwidth used immediately before a line failure occurs to the minimum bandwidth guaranteed value, and discards the non-guaranteed class with priority.

 FIG. 4 is a diagram for explaining the operation of the conventional packet buffer 100. In FIG. 4, the packet PK input to the source transmission device R1 is temporarily stored in a buffer memory 100, and when a packet is transmitted, a buffer area for packet information transmitted from the port is set. Open. In FIG. 4, the packet information sent from port 2 is deleted from the corresponding area.

 On the other hand, FIG. 5 is a diagram for explaining the operation of the packet buffer 100 according to the present invention. The packet input to the source transmission device R1 is temporarily stored in the buffer memory 100. Then, as described with reference to FIG. 3, the source transmission device R1 receives the number-of-received-packets information from the transmission destination, and after confirming that the reception has been normally performed, releases the buffer area of the corresponding packet information. I do.

 Hereinafter, an embodiment in which the above-described conceptual configuration of the present invention is applied to prevent packet loss at the time of a line failure will be described.

 Network failure detection mechanism>

FIG. 6 is a diagram illustrating a mechanism for detecting a line failure in the present invention. You. Although FIG. 6 shows only the interface portion of the one-sided device R1, the same applies to the opposing device R2. For convenience, the device R1 will be referred to as a transmission source device, and the device R2 will be referred to as a transmission destination device, with reference to the one-way packet transmission direction. The same applies to the following _embodiments.

 In the present invention, first, as a function of detecting a line failure between the devices, a test bucket is mutually transmitted between the source transmission device R1 and the destination transmission device R2 at a constant cycle.

 The test packet sent from the source transmission device R1 to the destination transmission device R2 includes the number of packets per user received by the source transmission device R1 [PORT 1 is Al, Port (PORT) 1 is equipped with A2]. Conversely, the test packet sent from the destination transmission device R2 to the source transmission device R1 includes the number of packets per user received by the destination transmission device R2 [Port (PORT) 1 is Bl, Port (PORT) 1 is equipped with B 2].

 The format of such a test bucket is header as shown.

(H), a check section (FCS), and received bucket number information A1, A2, B1, and B2 inserted therebetween.

 In FIG. 6, each of the ports 1 and 2 in the interface section extracts a test packet generated by the test packet generator 201 that generates the test packet and a test packet transmitted from the transmission destination transmission device R2. And a test bucket extracting unit 202. Further, it has a transmission-side buffer memory (hereinafter simply referred to as a buffer) 100-1, a reception-side buffer memory (hereinafter simply referred to as a buffer) 100-2, a multiplexer 101, and a demultiplexer 102.

The test packet generation unit 201 is read from the transmission buffer 100-1 of the transmission source device R1 during a period from transmitting the test packet to transmitting the next test packet. The count of the number of packets transmitted per user [the number of packets C1 transmitted from port (PORT) 1 and the number of packets C2 transmitted from port (PORT) 2] is counted and monitored. This meter The number monitoring result is notified to the test packet extracting unit 202.

 Therefore, the test packet extraction unit 202 knows the number of packets to be received by the destination transmission device R 2 (the transmission packet counted in the count of the test packet generation unit 201). The numbers C 1 and C 2 are notified to the test packet extraction unit 202). Accordingly, the number of received packets (B1 for port 1 and B2 for port 2) mounted on the test packet sent from the destination transmission device R2 and the number of received packets from the source transmission device R1 to the destination transmission device R2 The number of the transmitted packets (port 1 compares C1 and port 2 compares C2. In this comparison, if they do not match, it is possible to detect a line failure.

 For example, the number of received packets (B 1) of port 1 of destination transmission device R 2 mounted on a test packet received by source transmission device R 1 from destination transmission device R 2 is equal to that of source transmission device R 2. If the number of packets (C 1) previously transmitted from port 1 of port 1 to port 1 of destination transmission apparatus R 2 is the same, port 1 of destination transmission apparatus R 2 normally operates It can be recognized that packet transmission / reception has been performed. · '

 At this time, it recognizes that the packet transmission / reception has been normally performed, and releases the information of the corresponding packet stored in the transmission buffer 100-1 in the transmission source transmission device R1.

 Conversely, the number of received packets (B 1) of port 1 of destination transmission device R 2 mounted on the test packet received by source transmission device R 1 is equal to port 1 of source transmission device R 1. Is smaller than the number of packets (C 1) sent to port 1 of destination transmission device R 2 (or cannot be received), port 1 of source transmission device R 1 and destination transmission device R 2 Recognize as a line failure between ports 1. At this time, the information of the corresponding packet stored in the buffer 100-1 is read out (120) and retransmitted by another line connected to the port 2 of the transmission source device R1.

 Mechanism for detecting the number of lost packets>

Here, if a line abnormality is detected as described above, The number of lost buckets is calculated. The calculation of the number of lost packets is based on the number of packets (C 1) transmitted from the source transmission device R 1 to the destination transmission device R 2 counted by the test packet generation unit 201 and the destination transmission device It is determined by the difference between the number of buckets to be received by R2.

 For example, if a line failure occurs between the source transmission device R1 and the destination transmission device R2, the test packet notifies that the number of received packets is (B1) from the destination transmission device R2. Then, the number of lost buckets is (C 1 _ B 1). At this time, the number of received packets (B 1) means that packet communication was normally performed, and corresponds to the number of relevant packets (B 1) held in buffer 100-1. Release the packet. For the remaining (C1—B1) packets, the information for the corresponding number of packets (C1−B1) held in the buffer .100-1—is stored in port 2 It is retransmitted by another line connected to. As a result, it is possible to prevent packet loss due to line failure.

 Here, in the above embodiment, the relationship between “the test packet transmission cycle” and “the transmission packet retransmission buffer capacity” is important.

 If the “test bucket transmission cycle” is short, the traffic of the test bucket itself increases and the line utilization efficiency deteriorates. On the other hand, if the transmission cycle is long, it takes time to detect a line failure, so the required capacity of the retransmission buffer increases, which leads to an increase in equipment cost and an increase in size.

 Therefore, only packets with a specific QoS or higher are held in the buffer 100-1 and complemented. This can prevent an increase in the capacity of the buffer 100-1. With reference to FIG. 7, a description will be given of a mechanism for suppressing the increase in traffic by lengthening the “test packet transmission cycle”.

 That is, the packet type input to the interface unit is Q1 # H (bandwidth guarantee class of port 1 of source transmission device R1), Q1 # M (minimum bandwidth of port 1 of source transmission device R1). Guaranteed class) and Q1 # L (non-guaranteed class for port 1 of source transmission device R1).

For this purpose, a QoS filter 110 is provided in front of the “1” You. With this filter 110, guarantee is allocated in the event of a line failure according to the above bucket type.

 At this time, the relationship of the following formula is set in advance so that the distribution ratio is equal to or less than the buffer capacity occupied by the non-guaranteed class Q1 # L. deep.

 Buffer holding (Q1 # H + Q1 # M) Buffer not holding (Q1 # L)

 By limiting the classes (Q1 # H and Q1 # M) that guarantee the bandwidth of the packets held in the buffer 100-1, the increase in the capacity of the buffer 100-1 is suppressed. Can be done.

 Further, in FIG. 7, for the packet of (J1 # L (non-guaranteed class of the port 1 of the transmission source transmission device R1)), the packet is read from the buffer 100-1, and the transmission source transmission device R After sending from 1, buffer 1 0 0—1 is released.

 On the other hand, for the bandwidth guarantee classes (Q1 # H and Q1 # M) only, the test packet extraction unit 202 normally receives data at the transmission destination transmission device R2 as described above with reference to FIG. Releases buffer 100-1 when notified of the changed packet information—:

 At this time, if the test packet extraction unit 202 receives the notification of the loss packet information due to the line failure, the packet information is held in the buffer 100-1, and the other line [Port (P0RT) 2] Switch to and send. As a result, it is possible to prevent an increase in the capacity of the router and to supplement a loss packet caused by a failure of the port 1 line.

 Here, when retransmitting a packet, the retransmitted packet must be transmitted together with a normal user packet, so that a large number of packets need to be transmitted. Therefore, it is necessary to transmit packets in a short time. FIG. 8 shows an embodiment corresponding to such a situation, which is characterized in that a connection control unit 121 is provided.

At the time of retransmission, short packets are combined (composite) up to the maximum transmittable bucket length (MTU) size in order to transmit a large number of packets in a short time. Normally, the packet structure to be transmitted consists of a header and a chain for each packet. Qubit FCS etc. are attached.

 In the connection control unit 121, as shown in FIG. 9, a plurality of short packets, for example, packets A, B, C, D, and E can be transmitted at the maximum packet length size, for example, 1522 bytes. To be connected. By transmitting the packet F thus combined (composite), it is possible to reduce the header and the bandwidth of the FCS and the like for the combined packet (5 packets in the example of FIG. 9). As a result, a large amount of packets can be retransmitted in a short time, and retransmission can be performed without packet loss in the event of a line failure.

 Here, when a line failure occurs, the buffer 100, which holds the difference between the number of transmitted packets and the number of received packets, is connected to port 2 to complement the packet lost due to the line failure. When re-transmitting from another line, the load may temporarily increase suddenly on the other line at the switching destination.

 Such a situation could lead to indiscriminate discarding of packets. An embodiment for preventing such inconvenience is shown in FIG.

 The embodiment shown in FIG. 10 has a bandwidth guaranteeing unit 130 having a priority processing unit 1331 and a round robin unit 132 in order to deal with such inconvenience.

 The packets input from the buffer 1 0 0—1 of port 1 as the transmission source to the priority processing unit 1 3 1—1 are the bandwidth guarantee class (Q1 # H) and the minimum bandwidth guarantee class (Q1 # M). ), Non-guaranteed class (Q1 # L).

 Packets input from the buffer 1 0 0-1 on the port 2 side to be switched to the priority processing unit 131-2 are also bandwidth guaranteed class (Q2 # H), minimum bandwidth guaranteed class (Q2 # M), Non-guaranteed class (Q2 # L).

Here, the priority processing units 131-1 and 131-2 are the bandwidth guarantee class (Q1 # H for port 1 and Q2 # H for port 2) and the minimum bandwidth guarantee class (Q1 # H for port 1). #M, port 2 Q2 # M) packet is sent preferentially, and if there is no bandwidth guarantee class or minimum bandwidth guarantee class packet, a non-guaranteed class outside the minimum bandwidth guarantee (Q1 #L, Q2 # L at port 2) Do.

 In the normal case, the packets processed by the priority processing sections 131-1-1 and 131-2 pass through the round robin (WRR) section 132 and are transmitted as they are. In the event of a line failure, the ratio of packets sent to each port can be changed by the round robin (WRR) unit 132.

 The round robin (WRR) unit 132 sets, for example, the maximum physical line speed from port 1 and port 2 to 1 Gbit / sec. Normally, 100% packet transmission settings are made for Port 1 and Port 2 respectively.

 Next, assuming that a line failure occurs in port 1, when the line fails, the packet transmitted from port 1 is retransmitted from port 2. That is, bucket 1 of 2 Gbit / sec of port 1 and port 2 flows into port 2. However, since the maximum physical line speed is 1 Gbit / sec, the remaining 1 Gbit / sec will be discarded, and there is a concern about discarding guaranteed packets. Therefore, the round robin section 132 sets 50% transmission to that of port 1 and port 2. As a result, the line speeds of port 1 and port 2 are set equally, and it is possible to prevent 'bandwidth guarantee packet' from being discarded.

 In FIG. 10, when a circuit failure notification is received from the test packet extraction unit 202, the packets processed by the priority processing unit 13 1 11 are passed through the connection control unit 12 1 and shown in FIG. As described above, the packets are combined and input to the round mouth bin unit 132.

 At this time, in the switching destination port 2, in addition to the packets Q2 # H, 赚, and Q2 # L that are originally supposed to be transmitted, the packets Q1 # H, Q1 # M, and Q1 # L of port 1 lost due to the line failure Will be sent. If left as it is, there is a possibility that retransmission packets from port 1 and original bandwidth guaranteed packets of port 2 will be discarded.o

Therefore, if the bandwidth ratio is set equally in the round robin section 132 as described above, the retransmission packet from port 1 and the original bandwidth guarantee packet from port 2 are sent to the line without discarding. It is possible. As described above, the quality of ports 1 and 2 is guaranteed without loss of the bandwidth guarantee class packet of the retransmission port 1 and the bandwidth guarantee class packet of the switching destination port 2, and if there is a line failure. It is possible to supplement the bucket of port 1 that has been lost once. Industrial potential

 According to the present invention, an increase in the buffer capacity required for the retransmission processing is suppressed, and an increase in traffic generated in the retransmission processing can be suppressed. Furthermore, it is possible to mitigate the sudden increase in traffic that occurs in the retransmission processing. This provides an instantaneous uninterrupted transfer method in the event of a line failure in an IP network that eliminates inconveniences such as delays and data corruption in the event of a line failure. Is provided.

Claims

The scope of the claims  1. A non-instantaneous interruption transfer method in the event of a line failure in a transmission system that performs bucket transmission between transmission devices connected by a plurality of lines,  A packet including information on the number of packets received from the source transmission device at the destination transmission device is periodically sent from the destination transmission device to the source transmission device, and  The transmission device of the transmission source compares the information on the number of received packets included in the received packet with the number of packets transmitted to the transmission device of the transmission destination via a certain line,  In the comparison, when the number of received packets and the number of transmitted packets do not match, a packet corresponding to the mismatch is retransmitted to the transmission apparatus at the transmission destination through a line different from the certain line.  A non-instantaneous transfer method.  2. In Claim 1,  The packet transmitted to the transmission device at the transmission destination is stored in a buffer memory before transmission.  In the comparison, when the number of received packets and the number of transmitted packets match, the packet stored in the buffer memory corresponding to the match is released from the buffer memory.  A non-instantaneous transfer method.  3. In Claim 2,  The user packets transmitted to the transmission device of the transmission destination are classified into a plurality of quality classes, and only the user buckets of a predetermined quality class or higher are stored in the memory.  A non-instantaneous transfer method.  4. In claim 1, A non-stop transmission method characterized in that packets retransmitted by a line different from the one line are connected up to the maximum length of transmission and formed into one packet and then retransmitted. 5. In claim 1,  When retransmitting a packet through a line different from the one line, a transfer band of the packet to be retransmitted and a packet transfer band transmitted by the different line are set equally. Instantaneous interruption transfer method. 6. A means for comparing the number of packets transmitted from one transmission line to the transmission device of the transmission destination with the number of reception packets in the test bucket periodically transmitted from the transmission device of the transmission destination,  According to the comparison, when there is a difference between the number of packets to be transmitted and the number of received packets in the test packet, the packet corresponding to the difference is transmitted to the destination by a line different from the one line. A packet transmission device having means for retransmitting to a device.  7. In Claim 6, further,  A buffer memory for storing a packet to be transmitted to the transmission device of the transmission destination before transmission;  The packet transmission device, wherein the packet stored in the buffer memory is released from the buffer memory when the number of received packets matches the number of transmitted packets in the comparison. .  8. In Claim 7,  The buffer memory stores only user packets of a predetermined quality class or higher among the user packets transmitted to the transmission device of the transmission destination.  A packet transmission device characterized by the above.  9. In Claim 6,  Further, the packet transmission apparatus further comprises means for linking a packet retransmitted by a line different from the one line to a maximum length that can be transmitted and forming the same into one packet.  10. In claim 6, Further, when retransmitting a packet through a line different from the one line, the packet is transmitted through the different line and the transfer band of the retransmitted packet. A packet transmission device having means for setting a transfer band of a packet to be equal.