SESSION RELAY DEVICE AND SESSION RELAY METHOD

• US 20090268742A1
• Filed: 11/02/2006
• Published: 10/29/2009
• Est. Priority Date: 11/07/2005
• Status: Active Grant

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Hama, Takayuki
• Granted Patent: US 8,085,669 B2
• Time in Patent Office: Days
• US Class Current: 370/400
• CPC Class Codes: H04L 47/10 Flow control; Congestion control
• CPC Class Codes: H04L 47/193 at the transport layer, e.g. TCP related
• CPC Class Codes: H04L 47/34 ensuring sequence integrity, e.g. using sequence numbers
• CPC Class Codes: H04L 47/36 by determining packet size, e.g. maximum transfer unit [MTU]
• CPC Class Codes: H04L 47/40 using split connections
• CPC Class Codes: H04L 47/43 Assembling or disassembling of packets, e.g. segmentation and reassembly [SAR]
• CPC Class Codes: H04L 67/14 Session management for real-time applications in data packet communications networks H04L65/1066
• CPC Class Codes: H04L 69/16 Implementation or adaptation of Internet protocol [IP], of transmission control protocol [TCP] or of user datagram protocol [UDP]
• CPC Class Codes: H04L 69/166 IP fragmentation; TCP segmentation

Abstract

A session relay device which can reliably send a data packet resent from a source to a destination without the need for reconfiguring and dividing a segment is supplied. Session relay device 110, adapted to be disposed between terminals for transmitting and receiving data as packets to which sequence numbers representative of the order of segments to be transmitted are assigned, includes session relay section 110-3 that relays data transmitted as packets between a first session opened between session relay device 110 and a terminal on a transmission side and a second session opened between session relay device 110 and a terminal on a reception side. Session relay section 110-3 receives the retransmitted segment from a terminal on the transmission side, updates a maximum segment size of the second session with the segment size of the retransmitted segment, and transmits the retransmitted segment to a terminal on the reception side.

Claims

1. A session relay device adapted to be disposed between terminals for transmitting and receiving data as packets to which sequence numbers representative of an order of segments to be transmitted are assigned, for relaying data transmitted as packets between a first session opened between the session relay device and a terminal on a transmission side and a second session opened between the session relay device and a terminal on a reception side, said session relay device comprising:

a session status holder for holding information of the first and second sessions;

a segment retransmission determining section for, when a packet is received through the first session, determining whether the segment of the received packet is a retransmitted segment having a sequence number identical to, and a segment size different from, the segment of a packet already received through said first segment, by referring to session information held by said session status holder; and

a segment retransmitter for, if it is determined by said segment retransmission determining section that the segment of the received packet is the retransmitted segment, transmitting said retransmitted segment through said second session.

2. A session relay device according to claim 1, further comprising:

a session maximum segment size updater for, if it is determined by said segment retransmission determining section that the segment of the received packet is the retransmitted segment, updating a maximum segment size of said second session with the segment size of the retransmitted segment.

3. A session relay device according to claim 1, further comprising:

a fragmentation request message transfer section for, when a fragmentation request message indicating that the segment of the data of said packet relayed toward the terminal on the reception side is to be divided is received through said second session, transmitting the received fragmentation request message through said first session toward the terminal on the transmission side, and reading the maximum transfer unit of a next hop which is included in the received fragmentation request message;

a maximum transfer unit storing section for storing the maximum transfer unit of a next hop which is read by said fragmentation request message transfer section; and

a maximum transfer unit checking section for, when the maximum transfer unit stored in said maximum transfer unit storing section is updated into a maximum transfer unit smaller than said maximum transfer unit, updating the maximum segment size of said second session based on the updated maximum transfer unit.

4. A session relay device according to claim 1, further comprising:

a fragmentation request message transfer section for, when a fragmentation request message indicating that the segment of the data of said packet relayed toward the terminal on the reception side is to be divided is received through said second session, transmitting the received fragmentation request message through said first session toward the terminal on the transmission side, reading the maximum transfer unit of a next hop which is included in the received fragmentation request message, and updating the maximum segment size of said second session based on the read maximum transfer unit.

5. A session relay device according to claim 1, further comprising:

a transmission acknowledgement receiver for receiving, through said second session, a transmission acknowledgement packet which is a response to a start packet of said first session which is relayed toward the terminal on the reception side;

a transmission acknowledgement packet transfer/termination determining section for determining whether it is to transfer or terminate the transmission acknowledgement packet received by said transmission acknowledgement receiver; and

a transmission acknowledgement transmitter for generating a new transmission acknowledgement packet for said start packet and transmitting the new transmission acknowledgement packet to the terminal on the transmission side if said transmission acknowledgement packet transfer/termination determining section determines that it is to terminate the transmission acknowledgement packet;

wherein said session status holder holds, as said session status information, a transmission sequence number of said start packet and a transmission acknowledgement sequence number of a transmission acknowledgement packet received from terminal on the transmission side; and

if a maximum segment size acknowledged for transmission which is represented by the difference between said transmission sequence number and said transmission acknowledgement sequence number is smaller than a preset value given as a multiple of the maximum segment size of said second session, then said transmission acknowledgement packet transfer/termination determining section transfers said transmission acknowledgement packet through said first session toward the terminal on the transmission side, and if said difference between said sequence numbers has reached said preset value, then said transmission acknowledgement packet transfer/termination determining section terminates said transmission acknowledgement packet.

6. A session relay device according to claim 1, further comprising:

a transmission acknowledgement receiver for receiving, through said second session, a transmission acknowledgement packet which is a response to a start packet of said first session which is relayed toward the terminal on the reception side;

a transmission acknowledgement packet transfer/termination determining section for determining whether it is to transfer or terminate the transmission acknowledgement packet received by said transmission acknowledgement receiver;

a transmission acknowledgement transmitter for generating a new transmission acknowledgement packet for said start packet and transmitting the new transmission acknowledgement packet to the terminal on the transmission side if said transmission acknowledgement packet transfer/termination determining section determines that it is to terminate the transmission acknowledgement packet; and

a minimum sequence number calculator for calculating a sequence number when a delivery segment size of a packet relayed toward the terminal on the reception side has reached the maximum segment size of said second session;

wherein said session status holder holds, as said session status information, a transmission sequence number of said start packet and a transmission acknowledgement sequence number of a transmission acknowledgement packet received from terminal on the transmission side; and

if a maximum segment size acknowledged for transmission which is represented by the difference between said transmission sequence number and said transmission acknowledgement sequence number is smaller than the sequence number calculated by said minimum sequence number calculator, then said transmission acknowledgement packet transfer/termination determining section transfers said transmission acknowledgement packet through said first session toward the terminal on the transmission side, and if the maximum segment size acknowledged for transmission has reached the calculated sequence number, then said transmission acknowledgement packet transfer/termination determining section terminates said transmission acknowledgement packet.

7. A session relay device according to claim 1, wherein said first and second sessions are in accordance with TCP.

8. A session relay device according to claim 3, wherein said fragmentation request message comprises an ICMP message for indicating an error.

9. A session relay device according to claim 5, wherein said transmission acknowledgement packet comprises an ACK packet in accordance with TCP.

15. A session relay device according to claim 4, wherein said fragmentation request message comprises an ICMP message for indicating an error.

16. A session relay device according to claim 6, wherein said transmission acknowledgement packet comprises an ACK packet in accordance with TCP.

10. A session relay method to be carried out by a session relay device adapted to be disposed between terminals for transmitting and receiving data as packets to which sequence numbers representative of an order of segments to be transmitted are assigned, for relaying data transmitted as packets between a first session opened between the session relay device and a terminal on a transmission side and a second session opened between the session relay device and a terminal on a reception side, said session relay method comprising:

of holding information of the first and second sessions in a session status holder;

when a packet is received through the first session, determining whether the segment of the received packet is a retransmitted segment having a sequence number identical to, and a segment size different from, the segment of a packet already received through said first segment, by referring to session information held by said session status holder; and

if the segment of the received packet is the retransmitted segment, transmitting said retransmitted segment through said second session.

11. A session relay method according to claim 10, further comprising:

if the segment of the received packet is the retransmitted segment, updating a maximum segment size of said second session with the segment size of the retransmitted segment.

12. A session relay method according to claim 10, further comprising:

when a fragmentation request message indicating that the segment of the data of said packet relayed toward the terminal on the reception side is to be divided is received through said second session, reading the maximum transfer unit of a next hop which is included in the received fragmentation request message, and updating the maximum segment size of said second session based on the read maximum transfer unit.

13. A session relay method according to claim 10, further comprising:

receiving, through said second session, a transmission acknowledgement packet which is a response to a start packet of said first session which is relayed toward the terminal on the reception side;

acquiring a transmission sequence number of said start packet and a transmission acknowledgement sequence number of a transmission acknowledgement packet received from terminal on the transmission side, from the session status information held by said session status holder, and determining the difference between the acquired sequence numbers; and

if a maximum segment size acknowledged for transmission which is represented by the difference between said sequence numbers is smaller than a preset value given as a multiple of the maximum segment size of said second session, transferring the received transmission acknowledgement packet toward the terminal on the transmission side, and if the maximum segment size acknowledged for transmission is equal to or greater than said preset value, terminating the received transmission acknowledgement packet generating a new transmission acknowledgement packet for said start packet, and transmitting the new transmission acknowledgement packet to the terminal on the transmission side.

14. A session relay method according to claim 10, further comprising;

receiving, through said second session, a transmission acknowledgement packet which is a response to a start packet of said first session which is relayed toward the terminal on the reception side;

acquiring a transmission sequence number of said start packet and a transmission acknowledgement sequence number of a transmission acknowledgement packet received from terminal on the transmission side, from the session status information held by said session status holder, and determining the difference between the acquired sequence numbers;

calculating a sequence number when a delivery segment size of a packet relayed toward the terminal on the reception side has reached the maximum segment size of said second session; and

if a maximum segment size acknowledged for transmission which is represented by the difference between said sequence numbers is smaller than the calculated sequence number transferring the received transmission acknowledgement packet toward the terminal on the transmission side, and if the maximum segment size acknowledged for transmission is equal to or greater than the calculated sequence number, terminating the received transmission acknowledgement packet, generating a new transmission acknowledgement packet for said start packet, and transmitting the new transmission acknowledgement packet to the terminal on the transmission side.