JP2004135076A - Reassembling and reordering device for fragment packet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occupation of a resource by a buffer memory and packet delay due to meaningless congestion in a reassembling and reordering process of a fragment packet. <P>SOLUTION: A call is identified from a first fragment of a packet supplied to a fragment packet buffer part (MEM-F) 38 reassembling the fragment packet (52). A GTP layer termination part (GTPLT) 44 is informed that the fragment packet on the call is received. If the reception of the fragment packet on the call is informed when passing of the packet is detected in a reordering memory (MEM-R)56 of GTPLT 44, reordering is performed by accumulating the passing packet in a buffer. When it is not informed, the packet is not accumulated and forwarding is immediately performed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reassembling and reordering device for restoring a packet before fragmentation from a fragmented packet and reversing the reversal of the packet arrival order, in particular, a GPRS (General Packet Radio Service) GTP (GPRS Tunneling). (Protocol) The present invention relates to a reassembling and reordering apparatus for restoring an unfragmented packet from a fragmented packet in a tunnel and reversing the reversal of the packet arrival order caused by fragmentation and reassembly.
[0002]
[Prior art]
In GPRS that provides IP network services to users of mobile devices such as mobile phones, GTP is employed as a protocol for maintaining communication with mobile devices moving within the network. That is, a tunnel is established between an RNC (Radio Network Controller) connected to a base station in an area to which the mobile device belongs and an SGSN (Serving GPRS Support Node). When the mobile station moves and performs handover to an adjacent area, communication is maintained by switching tunnels with the RNC in the new area. Furthermore, a tunnel is established between a GGSN (Gateway GPRS Support Node), which is a connection point with the Internet or an intranet, and the SGSN. When a mobile station relocates to an area under the control of another SGSN, a tunnel is renewed not only between the RNC and the SGSN but also between the SGSN and the GGSN.
[0003]
In this GTP protocol, a new header is added to a user packet, so that the packet becomes longer in the tunnel by that amount. When a packet having a length obtained by adding this increment to the MTU (Maximum Transmission Unit) of the user packet cannot be transmitted between GSNs (GPRS Service Node) (for example, when the MTU given to the user and the MTU of the network between the GSNs are equal). The packet is fragmented by the bottleneck GSN or the relay router. The GSN host reconstructs (reassembles) these fragmented packets to restore the packets before fragmentation. At the time of reassembling, since the fragmented packets wait until all the fragments are completed, the unfragmented packets may be overtaken and the order of the packets may be reversed. For packets belonging to a service that must maintain the order of arrival of packets, refer to the sequence numbers assigned to the packets after reassembly to buffer packets that arrived ahead of fragmented packets. It is necessary to temporarily store the order and reverse the order inversion (reordering).
[0004]
[Patent Document 1]
JP-A-5-103016
[Problems to be solved by the invention]
However, after the reassembly process, it is determined whether the unarrived packet has not arrived due to the reversal of the order due to the reassembly, or has not arrived because the packet has been lost somewhere in the middle. In each case, a buffer is used for packet storage. In a node handling a large amount of traffic, this becomes a huge amount as a whole, and the processing time increases due to unnecessary buffering. Therefore, conventionally, this problem has been avoided by restricting the MTU of the user to a predetermined value (for example, the MTU-increment of the network).
[0006]
Accordingly, an object of the present invention is to provide a fragment packet reassembling and reordering apparatus capable of maintaining the order of packets by using minimum necessary resources without limiting the MTU of a user. It is in.
[0007]
[Means for Solving the Problems]
According to the present invention, the reception of a fragment packet is detected, the original packet is reconstructed from the detected fragment packet, the reassembly unit, and the first fragment detection for detecting and notifying the reception of the first fragment of the packet are performed. And detecting the overtake packet from the packet from the reassembly unit, and when the overtake packet is detected, forwards the overtake packet without storing it in the buffer unless the first fragment detection unit notifies the first fragment reception unit of the reception. An apparatus for reassembling and reordering fragmented packets, comprising: a reordering unit that reorders packets by accumulating an overtake packet in a buffer when notified of the reception of the first fragment.
[0008]
The first fragment detection unit extracts information necessary for identifying a user from the first fragment, and the reordering unit determines whether or not there is a notification of reception of the first fragment of a packet belonging to the same user as the overtake packet. Is preferably stored in a buffer.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a diagram illustrating an increase in overhead due to the GTP protocol and fragmentation of packets caused by the increase. In FIG. 1, a GTP header 12, a UDP header 14, and a network IP header 16 are added to a user packet 10. If the value of the MTU value 11 given to the user plus the length of the newly added header is greater than the MTU 13 of the network, the first fragment 18 and It is fragmented into second fragments 20. Here, the first fragment 18 contains all the header information of the packet before fragmentation such as the GTP header 12 and the UDP header 14, whereas the second fragment 20 contains the user packet contained in the first fragment. It is noted that only the remaining 10-2 of 10-1 is included.
[0010]
FIG. 2 is a block diagram showing a configuration of a GSN node device to which the present invention has been applied. The present invention will be described by taking the GSN node device in GPRS as an example, but the present invention is not limited to this, and it goes without saying that the present invention can be similarly applied to any device that performs reassembly and reordering of fragmented packets. No.
[0011]
In FIG. 2, an L1 / L2 termination unit (SAR) 32 terminates the physical layer (L1) and the data link layer (L2), and an IP layer termination unit (IPLT) terminates the IP layer. A fragment packet detector (FRGC) 36 is provided between the SAR 32 and the IPLT 34. When the fragment packet is detected, the FRGC 36 drops the fragment packet into the fragment packet buffer unit (MEM-F) 38 and inserts the reconstructed packet from the MEM-F 38. The MEM-F 38 has a remaining fragment management unit 40 and a buffer memory 42. The remaining fragment management unit 40 temporarily stores the fragment packets in the buffer memory 42 for each fragment ID based on parameters such as the fragment ID extracted from the network IP header 16 (FIG. 1) of the fragment packet, Reassemble the packet when the required fragments are available. The GTP layer terminator 44 terminates the GTP layer, from which a new GTP tunnel starts via the IP layer terminator 46 and the L1 / L2 terminator 48.
[0012]
The GTPLT 44 refers to the version number included in the header (52), and to which the packet belongs based on the destination IP address (and, if necessary, the source IP address) and the TEID (see FIG. 3) included in the GTP header. A call (user) is identified (54), and for a packet belonging to a call that needs to maintain the order of the packets, the order of the packets is reversed for each call with reference to the sequence number (FIG. 3) included in the GTP header. If necessary, the order of the packets is restored by storing the packets in the reordering memory (MEM-R) 56 for each call (user). Details of this will be described later.
[0013]
In the present invention, in addition to reassembling the fragment packet in the MEM-F 38, the call identification information extracting unit 52 extracts the first fragment of the packet (54), and refers to the version number in the same manner as the GTPLT 44 (56). ), And identifies the call (user) to which the packet belongs from TEID or the like (58) and notifies the MEM-R 56 of the GTPLT 44 that the first fragment of the packet belonging to the call is detected. Note that the call identification information extraction unit 52 may extract only necessary parameters, and the GTPLT 44 may identify a call (user) based on those parameters. In the MEM-R 56, the overtaking of the packet is detected by monitoring the packet sequence number of the packet belonging to the call in which the order of the packet must be maintained. The reassembled packet arrives and the order can be recovered only when it is notified that the first fragment has been detected for a packet belonging to the same call as the packet when the overtaking of the packet is detected. The overtake packets are stored in the buffer until the time is over or until a predetermined time considering the time until the reassembled packet arrives elapses.
[0014]
The above processing will be specifically described with reference to FIGS. FIG. 4 shows a state where packets of sequence numbers 18 and 19 have arrived and have been output without being stored in the buffer. At this time, the expected sequence number of the packet arriving next changes from 19 to 20. In the case shown in FIG. 4, the sequence number of the packet arriving next is 20, which matches the expected value and is output immediately without being stored in the buffer. The same applies to the packet of sequence number 21. In the case shown in FIG. 5, while the expected value of the next sequence number is 20, the MEM-F reports that the packet of sequence number 22 has arrived and that the fragmented packet for this call has been received. You have been notified. In this case, the subsequent packets with sequence numbers 22, 23, 24,... Continue to be stored in the buffer until the packet with sequence number 20 and the packet with sequence number 21 arrive at the MEM-R or until the timer expires. . When the packet with the sequence number 20 and the packet with the sequence number 21 are received, the packet and the packet stored in the buffer are forwarded in a correct order. When the timer expires without receiving the packet with the sequence number 20 or the packet with the sequence number 21 (in the illustrated example, when 14 packets are accumulated in the buffer), the packet in the buffer is forwarded without waiting any longer. As shown in FIG. 6, when the MEM-F has not notified that the fragmented packet has been received, the subsequent packet is immediately output without being stored in the buffer. When the overtaking of the packet is detected, the subsequent packet is stored in the buffer until a certain time elapses, and after the elapse of the certain time, the presence or absence of the first fragment detection notification is checked. If the notification is received, the packet accumulation is continued. If the notification has not been received, the packet in the buffer may be immediately forwarded. As a result, it is possible to prevent the occupation of the resources of the MEM-R and the delay of the packet due to the meaningless stay, and to efficiently use the reordering buffer.
[0015]
In the MEM-F 38, if the received fragment is not the first fragment and does not match the fragment currently staying in the buffer 42, it is determined that a failure in the IP relay network or a change in the routing table has occurred. Only the information necessary for the reassembly management (source IP address on the IP layer, ID, offset, flag, total length of the packet, and, if necessary, the checksum port number on the UDP layer) are held until the timer expires, It is desirable to collectively discard other fragments including the first fragment that arrived before the expiration of the timer. That is, when other fragments arrive before the first fragment from the same packet, it is determined that a failure or the like has occurred, and that fragment and all fragments from the same packet are discarded without being stored in the buffer. . As a result, unnecessary buffer stagnation can be suppressed, and the influence of disturbance in the IP relay network can be suppressed.
[0016]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent resource occupation of the buffer memory and packet delay due to meaningless stay.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an increase in overhead due to a GTP protocol and fragmentation of a packet caused by the increase.
FIG. 2 is a block diagram illustrating a configuration of a GSN node device to which the present invention has been applied.
FIG. 3 is a diagram showing details of a GTP header.
FIG. 4 is a diagram illustrating a normal operation of the MEM-R.
FIG. 5 is a diagram illustrating an operation of the MEM-R at the time of receiving fragmented packets.
FIG. 6 is a diagram illustrating an operation of the MEM-R when a packet is lost.

Claims (4)

A reassembly unit that detects reception of fragment packets and reconstructs an original packet from the detected fragment packets;
A first fragment detector for detecting and notifying the reception of the first fragment of the packet;
The overtaking packet is detected from the packets from the reassembly unit. When the overtaking packet is detected, if the first fragment detecting unit does not notify the reception of the first fragment, the overtaking packet is forwarded without being stored in the buffer. A reassembling and reordering apparatus for fragmented packets, comprising: a reordering unit that reorders packets by accumulating overtake packets in a buffer when a notification of reception is received. The first fragment detection unit extracts information necessary for identifying a user from the first fragment,
The apparatus according to claim 1, wherein the reordering unit stores the overtake packet in a buffer when there is a notification of reception of a first fragment of a packet belonging to the same user as the overtake packet. The apparatus according to claim 1, wherein the reordering unit checks whether or not notification of reception of the first fragment has been received after a predetermined time has elapsed from detection of the overtake packet. The apparatus according to any one of claims 1 to 3, wherein the reassembly unit discards all fragments from the same packet when another fragment is received before a first fragment from the same packet.

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