JP2013034101A - Tcp session management method and tcp proxy device - Google Patents

Abstract

A TCP session management method capable of preventing occurrence of buffer overflow in a common memory area and improving memory utilization efficiency even when a window memory is shared among a plurality of sessions. provide.
A window for managing a ACK number and a window size of each session for each session, and a common buffer 31 which is a memory area set in units of contents in common for a plurality of sessions as a window for each session The management table 32 is used. When the remaining memory amount is calculated based on the difference between the maximum ACK number and the minimum ACK number in a plurality of sessions existing in the common buffer 31 with reference to the window management table 32 and falls below the threshold value Then, the session with the smallest ACK number is disconnected.
[Selection] Figure 2

Description

  The present invention relates to a session management method suitable for a one-to-many live data distribution service, and a proxy device that manages a session by such a session management method.

  Recently, a live distribution type or a live streaming type that uses an IP (Internet Protocol) network to distribute radio programs to a large number of users or to perform TV (television) live distribution such as sports broadcasts. IP data services are becoming popular. These services attempt to distribute the same content from a single data distribution server to a large number of user terminals almost simultaneously. These services use IP as a protocol in the network layer, and use TCP (Transmission Control Protocol) defined in RFC 793 (Non-Patent Document 1) as a protocol in the transport layer. . Therefore, in such an IP data service, a TCP session is established between the user terminal and the data distribution server, and an area for the maximum window size of the session is secured for each TCP session on the memory of the data distribution server. The packet retransmission control is performed while managing the sequence number and ACK (acknowledgement) number recorded in the TCP header. Assuming live data distribution to a large number of users, a TCP proxy device is provided between the user terminal and the data distribution server on the IP network, and data distribution to the user terminal is performed via the TCP proxy device. In many cases, in that case, a TCP session is established between the TCP proxy device and each user terminal, and an area for the maximum window size is secured for each session on the memory of the TCP proxy device in the same manner as described above. Packet retransmission control is performed.

  In terms of performing live data distribution by establishing sessions for a large number of user terminals, neither the data distribution server for live distribution nor the TCP proxy device is changed, and the TCP proxy device is further used for live data distribution. Since a data distribution server is provided with a function for processing data into a suitable form, a function that allows a user to select distribution contents, and a user account management function, a TCP used for live data distribution will be described below. The proxy device will be described.

  FIG. 1 is a block diagram showing a hardware configuration of a general TCP proxy device. The TCP proxy device 10 establishes a TCP session by connecting to a large number of user terminals 21 via a network 20 that is an IP network. The TCP proxy device 10 includes a high-speed and wide-band bus 11, a network interface 12 used for connection to the network 20, and a network that is provided between the bus 11 and the network interface 12 and controls communication with the network 20. A controller 13; a disk device 14 for storing programs and data; a disk controller 15 provided between the bus 11 and the disk device 14 for controlling access to the disk device 14; and a memory 16 connected to the bus 11. And a CPU (central processing unit) 17 connected to the bus 11. A window buffer for each TCP session is secured on the memory 16, and the CPU 17 performs TCP state management for each TCP session.

  For example, it is assumed that the bandwidth of the network interface 12 is 10 Gbps (gigabit / second) and the bandwidth necessary for content distribution is 100 kbps (kilobit / second) per user (ie, per session). Since 10 Gbps / 100 kbps = 100000, if the 10 Gbps network interface 12 is used, 100,000 users can simultaneously view content having a required bandwidth of 100 kbps. In this way, when 100,000 users simultaneously view the same content by live data distribution, if the required window size for each session is 64 KB (kilobytes), data for the window size for all sessions is stored. Is 64 KB × 100,000 = 6.4 GB (gigabytes), and the capacity of the memory 16 is required to be at least 6.4 GB. If each session applies window scaling, 10 GB or more of memory is required. When TCP state management is possible for 100,000 sessions by providing the high-speed CPU 17 and the high-speed bus 11, the size of the necessary memory becomes a problem.

  By the way, in the case of live-type data distribution, data that is not completely different for each user is transmitted, and although there is a difference in RTT (Round-Trip Time) difference in each TCP session, Each user is downloading at almost the same time. Therefore, instead of allocating a memory area for each session, a memory area is allocated for each content, and this common memory area is referred to by each session as a shared memory area used by multiple sessions. If the retransmission control is performed by managing the sequence number and the ACK number for each session, the problem that the required memory size becomes too large can be avoided.

  However, when the memory area for holding data is shared among a plurality of sessions in this way, there is a possibility that a buffer overflow occurs in the common memory area due to a difference in download speed or data transfer speed. For example, when session A having a slow download speed is viewing data 10 seconds ago, it is necessary to store data from 10 seconds ago to the present time in memory for session A. As a result, the secured memory A problem arises where the space is exhausted and new data cannot be provided to other sessions.

RFC 793 "Transmission Control Protocol", IETF (Internet Engineering Task Force), September 1981

  As described above, when live data distribution is performed using TCP as a transport layer protocol, the memory for a window is commonly used for a plurality of sessions. Although it is effective in suppressing the increase, there is a possibility that a buffer overflow in the common memory area may occur due to a difference in data transfer speed for each user terminal as a connection partner.

  Therefore, the object of the present invention is to prevent the occurrence of buffer overflow in the common memory area even when the window memory is shared among a plurality of sessions, and to improve the memory utilization efficiency. This provides a TCP session management method capable of increasing the number of accommodated users in the live data distribution service, and a TCP proxy device that executes such a TCP session management method.

  A first TCP session management method of the present invention is a TCP session management method for managing a plurality of sessions corresponding to contents to be distributed by TCP, and is a content common to a plurality of sessions for a window of each session. A common buffer, which is a memory area set in units, and a window management table that manages the ACK number and window size of each session for each session are stored, and exists in the common buffer by referring to the window management table The maximum ACK number in a plurality of sessions is Max_ACK, the minimum ACK number is Min_ACK, a predetermined number that is a multiple of the maximum segment length is α, the window size is W, and the difference between Max_ACK and Min_ACK is Use { When satisfying resize <(Max_ACK-Min_ACK) + W + α}, disconnects the session ACK number is smallest among the plurality of sessions are present in the common buffer.

  The second TCP session management method of the present invention is a TCP session management method for managing a plurality of sessions corresponding to content to be distributed by TCP, and is a content common to a plurality of sessions for a window of each session. A common buffer, which is a memory area set in units, and a window management table that manages the ACK number and window size of each session for each session are stored, and exists in the common buffer by referring to the window management table The round trip propagation delay time is measured for each session with respect to a plurality of sessions, and the difference between the round trip propagation delay time and the window between the session having the largest ACK number and the session having the smallest ACK number among the plurality of sessions. Find the size difference and round-trip propagation When the difference in total time is ΔRTT, the difference in window size is ΔW, and a predetermined threshold value for time is β, when {(remaining memory amount ÷ ΔW) × ΔRTT <β} is satisfied, The session having the smallest ACK number is disconnected from the plurality of existing sessions.

  A first TCP proxy device of the present invention is a TCP proxy device that connects to a network, manages a plurality of sessions corresponding to the content, and distributes the content to each terminal connected to the network by TCP, A common buffer that is a memory area that is set for each session in common for multiple sessions and a window management table that manages the ACK number and window size for each session. A TCP processing unit that performs protocol processing by TCP with reference to the window management table to transmit data in the buffer to each terminal, and a maximum in a plurality of sessions that exist in the common buffer with reference to the window management table Set the ACK number to Max_A Let K be the smallest ACK number, Min_ACK, α be a predetermined number that is a multiple of the maximum segment length, W be the window size, and use the difference between Max_ACK and Min_ACK to {reserve memory size <(Max_ACK− (Min_ACK) + W + α}, a session disconnection determination unit that instructs the TCP processing unit to disconnect a session having the smallest ACK number among a plurality of sessions existing in the common buffer.

  A second TCP proxy device of the present invention is a TCP proxy device that connects to a network, manages a plurality of sessions corresponding to the content, and distributes the content by TCP to each terminal connected to the network, A common buffer that is a memory area that is set for each session in common for multiple sessions and a window management table that manages the ACK number and window size for each session. A TCP processing unit that executes TCP protocol processing with reference to the window management table to transmit data in the buffer to each terminal, and a plurality of sessions existing in the common buffer for each session via the TCP processing unit R to measure round-trip propagation delay time Reciprocal propagation between a session having the largest ACK number and a session having the smallest ACK number among a plurality of sessions based on the measurement result of the RTT measurement unit with reference to the T measurement unit and the window management table The difference between the delay time and the window size is obtained, the difference between the round trip propagation delay times is ΔRTT, the window size difference is ΔW, and a predetermined threshold value for time is β, {(remaining memory amount ÷ ΔW) A session disconnection determination unit that instructs the TCP processing unit to disconnect the session with the smallest ACK number among a plurality of sessions existing in the common buffer when × ΔRTT <β} is satisfied.

  In the present invention, when a window memory is shared by a plurality of TCP sessions, a low-speed session is disconnected using a certain criterion. As a result, it becomes possible to delete old data from the common memory, and it becomes possible to prevent the buffer from overflowing, and the memory utilization efficiency in the TCP proxy device and the live data distribution server is improved. A session can be established again for the disconnected session.

It is a block diagram which shows the general hardware constitutions of a TCP proxy apparatus. It is a block diagram which shows the logical structure of the principal part of the TCP proxy apparatus of the 1st Embodiment of this invention. It is a figure explaining memory management, Comprising: (a) shows the memory management in the conventional TCP proxy apparatus, (b) is a figure which shows the memory management in the TCP proxy apparatus based on this invention. It is a block diagram which shows the logical structure of the principal part of the TCP proxy apparatus of the 2nd Embodiment of this invention. It is a figure explaining the outline | summary of operation | movement of a TCP proxy apparatus.

  Next, a preferred embodiment of the present invention will be described with reference to the drawings.

  The TCP session management method according to the present invention is suitable for a one-to-many live data distribution service that distributes content using TCP as a transport layer protocol. When TCP is used and the same content is distributed to a plurality of user terminals at almost the same timing, it is necessary to manage a plurality of TCP sessions corresponding to each user terminal. Therefore, in the TCP session management method according to the present invention, in order to prevent an increase in the memory size associated with setting a window buffer for each session, it is set for each session window in common for each session. This memory area is used as a common buffer. In order to manage a plurality of sessions corresponding to the content to be distributed, a window management table for managing the ACK number and window size of the session is used for each session, and buffer overflow in the common buffer is prevented. To prevent memory usage efficiency, use a certain criterion to disconnect a session with a low download speed (transfer speed) and release the area used only for the disconnected session in the common buffer. Allow new data to be written.

  Judgment criteria for session disconnection are in accordance with the reserved memory utilization rate. Specifically, for example, there are an ACK number threshold value setting method and a download speed difference threshold value setting method. In the ACK number threshold setting method, the ACK number of each section in the common buffer is checked by referring to the window management table, and the remaining memory amount is determined from the difference between the largest and smallest of these ACK numbers. Is compared with the threshold value, and when the remaining memory amount falls below the threshold value, the low speed section, that is, the section with the smallest ACK number is cut off. On the other hand, the download speed difference threshold setting method refers to the window management table, checks the round-trip propagation delay time (RTT) for each section, and the remaining memory amount becomes zero after how many seconds under the current data transmission status. The section with the smallest ACK number is cut when the time until it becomes zero falls below the threshold.

  The TCP proxy device of the present invention that executes such a TCP session management method will be described below. As described above, there is no change in the data distribution server for live distribution and the TCP proxy device in terms of establishing live sessions and distributing live data to a large number of user terminals. The device itself is also included in the category of the TCP proxy device of the present invention.

  FIG. 2 is a block diagram illustrating a logical configuration of a main part of the TCP proxy device according to the first embodiment of this invention. The TCP proxy device of the present embodiment has the same hardware configuration as that shown in FIG. 1, but is based on the present invention using an ACK number threshold setting method as a criterion for session disconnection. In order to execute the TCP session management method, a logical buffer includes a common buffer 31, a window management table 32, a session disconnection determination unit 33, a TCP processing unit 34, and an IP processing unit 35. The common buffer 31 and the window management table 32 are secured as areas on the memory 16 in the hardware configuration shown in FIG. 1, and the session disconnection determination unit 33, the TCP processing unit 34, and the IP processing unit 35 are stored in the CPU 17 by the software program. It is realized by executing. The session disconnection determination unit 33, the TCP processing unit 34, and the IP processing unit 35 can each be realized by a hardware configuration.

  The common buffer 31 is a buffer area that is set as a socket buffer in common for a plurality of sessions as a window for each session, and is supplied with content data from a data distribution server, for example. The window management table 32 is a table for managing the ACK number and window size of each session for each session.

  The TCP processing unit 34 refers to the window management table 32 to perform data processing in the TCP in order to transmit data in the common buffer 31 to each terminal, and sends the generated TCP segment to the IP processing unit 34. The IP processing unit 35 incorporates the TCP segment from the TCP processing unit 34 into an IP packet and sends it to the network interface, so that the content data is distributed to each user terminal.

  The session connection determination unit 33 refers to the window management table 32, sets the maximum ACK number in a plurality of sessions existing in the common buffer 31 to Max_ACK, sets the minimum ACK number to Min_ACK, and sets the maximum segment in TCP. When the predetermined number that is a multiple of the length (MSS) is α, the window size is W, and the difference between Max_ACK and Min_ACK is used to satisfy {reserved memory size <(Max_ACK−Min_ACK) + W + α}, the common buffer 31. Instruct the TCP processing unit 34 to disconnect the session with the smallest ACK number among the plurality of sessions existing in 31, and further release (clear) the memory area related only to the disconnected session. 31 is instructed.

  Here, α corresponds to a threshold value for disconnecting the low-speed session. Since α is a multiple of MSS, it can be said that α indicates how many TCP segments allow a low-speed session to be disconnected under the worst condition that the TCP segment is the longest. Although the window size may vary from session to session, for example, the window size of the session with the largest window size may be W.

  FIG. 3 shows a comparison between memory management in a conventional TCP proxy device that secures memory in session units and memory management in the TCP proxy device of the present invention.

  As shown in FIG. 3A, in the conventional TCP proxy device, it is necessary to secure a memory area for a window for each session, and roughly speaking, a memory area corresponding to the window size × the number of sessions is required. When the number is large, a very large amount of memory area is required. On the other hand, as shown in FIG. 3B, the proxy device according to the present invention secures a memory area for each content on the assumption that live distribution is performed. Therefore, if there is only one content to be distributed, the buffer size required in the TCP proxy device is compared with the conventional one, although it depends on the threshold used for the low-speed session disconnection, {(same The number of video viewing users-1) × TCP window size} can be reduced, and a reduction in initial cost and a reduction in power can be expected due to a reduction in memory size required per session.

  FIG. 3 also shows an example of the contents of the window management table 32. Here, assuming that a TCP session is established from the TCP proxy device for each user terminal, the current ACK number and window size of the session are stored in the window management table 32 for each user terminal, that is, for each session. It is shown. In FIG. 3B, a broken-line arrow denoted by reference numeral 51 indicates a memory portion between a maximum ACK number and a minimum ACK number among a plurality of sessions (sessions 1 to 3 in the illustrated example). In the first embodiment, the memory capacity in this memory portion is calculated as the remaining memory amount and used for determination for session disconnection.

  Next, a TCP proxy device according to the second embodiment of this invention will be described. FIG. 4 is a block diagram illustrating a logical configuration of a main part of the TCP proxy device according to the second embodiment of this invention. The TCP proxy device shown in FIG. 4 is the same as that shown in FIG. 2, but uses the download speed difference threshold value setting method as a criterion for session disconnection. 2 and differs from that shown in FIG. 2 in the operation of the session disconnection determination unit and the TCP processing unit. Also in the TCP proxy device shown in FIG. 4, the common buffer 31 and the window management table 32 are secured as areas on the memory 16 in the hardware configuration shown in FIG. 1, and a session disconnection determination unit 36, a TCP processing unit 37, The IP processing unit 35 and the RTT measurement unit 38 are realized, for example, by the CPU 17 executing a software program or by a hardware configuration. In the following, the TCP proxy device shown in FIG. 4 will be described while referring to differences from the one shown in FIG.

  The RTT measurement unit 38 measures the round-trip propagation delay time (RTT) via the TCP processing unit 37 for each session regarding a plurality of sessions existing in the common buffer 31. As an RTT measurement method, there is a method of executing using a three-way handshake packet. Alternatively, using the sequence number in the data packet to be transmitted and the time at which the data packet was transmitted, the ACK number in the ACK packet to be received corresponding to the data packet and the time at which the ACK packet arrived, the maximum segment length is set to MSS. As such, there is a method in which RTT is (reception time−transmission time) when {ACK number> sequence number + MSS} is satisfied.

  The TCP processing unit 37 refers to the window management table 32 in order to transmit the data in the common buffer 31 to each terminal, executes the protocol processing by TCP, sends the generated TCP segment to the IP processing unit 34, and When performing RTT measurement using three-way handshake packets, it is necessary to perform three-way handshake processing and to measure RTT according to the time of the ACK packet corresponding to the data packet. This information is transmitted to the RTT measurement unit 38.

  The session disconnection determination unit 36 refers to the window management table 32 and, based on the measurement result of the RTT measurement unit 38, between the session having the largest ACK number and the session having the smallest ACK number among the plurality of sessions. When the difference between the round-trip propagation delay time (ΔRTT) and the window size difference (ΔW) is calculated and a predetermined threshold value for time is β, and {(remaining memory amount / ΔW) × ΔRTT <β} is satisfied In addition, the TCP processing unit 37 is instructed to disconnect the session having the smallest ACK number among a plurality of sessions existing in the common buffer 31, and the memory area related only to the disconnected session is released (cleared). The common buffer 31 is instructed as follows.

  A broken arrow indicated by reference numeral 52 in FIG. 3B indicates a memory portion that is unused at the present time. In the second embodiment, the unused portion is used up after several seconds. In anticipation of this, it is used to judge for session disconnection.

  FIG. 5 shows an operation when the TCP proxy device according to each of the above-described embodiments is arranged between the data distribution server and a plurality of user terminals. Here, it is assumed that a plurality of video contents (for example, video 1 and video 2) are stored in the server. 2 and 4 only show the configuration related to the session to the user terminal side in the TCP proxy device, FIG. 5 shows both the TCP processing with the distribution server side and the TCP processing with the user terminal side. ing. Although not shown in the figure, it is assumed that a user management table is provided for user account management and the like.

  A socket buffer (common buffer) is set for both video 1 and video 2, and in processing with the distribution server, each content data is handled through IP processing, classifier processing for classifying headers, and TCP processing. Stored in the socket buffer. Content identification can be performed based on a URI (uniform resource identifier) that is extracted by extracting an HTTP Get request packet from a classifier and performing HTTP header processing. In the case of new content, a new session is established in the TCP process, and in the case of existing content, a so-called 5-tuple of TCP and content information are linked.

  In the process with the user terminal side, first, when the HTTP Get request packet arrives from the user terminal, the destination IP address, the source IP address and the URI are confirmed, and the address set in the user management table is When the corresponding video exists in the TCP proxy, the user terminal is allowed to participate in the session. Then, in order to perform live delivery to the user terminal from that point, the most known sequence number existing in the current socket buffer is described in the SYN / ACK packet and transmitted to the user terminal. As a result, the user can receive live distribution of the designated content.

  When the server delivers only a single video, when the SYN packet arrives from the user terminal, the destination IP address and the source IP address are confirmed, and the address set in the user management table If so, the user terminal is allowed to participate in the session. Then, in order to perform live delivery to the user terminal from that point, the most known sequence number existing in the current socket buffer is described in the SYN / ACK packet and transmitted to the user terminal. As a result, the user can receive live distribution of the content.

10 TCP Proxy Device 11 Bus 12 Network Interface 13 Network Controller 14 Disk Device 15 Disk Controller 16 Memory 17 CPU
20 Network 21 User Terminal 31 Common Buffer 32 Window Management Table 33, 36 Session Disconnection Determination Unit 34, 37 TCP Processing Unit 35 IP Processing Unit 38 RTT Measurement Unit

Claims (8)

A TCP session management method for managing a plurality of sessions corresponding to content to be distributed by TCP,
A common buffer that is a memory area set in units of contents in common for the plurality of sessions as a window for each session; a window management table that manages the ACK number and window size of the session for each session; And distributing data within a window size range from the ACK number stored in the memory area to each session.   Referring to the window management table, the maximum ACK number in a plurality of sessions existing in the common buffer is Max_ACK, the minimum ACK number is Min_ACK, and a predetermined number that is a multiple of the maximum segment length is α And the window size is W, and the difference between Max_ACK and Min_ACK is used, and when {reserved memory size <(Max_ACK−Min_ACK) + W + α} is satisfied, the ACK number of the plurality of sessions existing in the common buffer is The TCP session management method according to claim 1, wherein the session that is the minimum is disconnected.   Referring to the window management table, the round trip propagation delay time is measured for each of the plurality of sessions existing in the common buffer, and the session having the largest ACK number and the smallest ACK number among the plurality of sessions. A difference between the round-trip propagation delay time and the window size between the sessions having the same, and the difference between the round-trip propagation delay times is ΔRTT, the difference between the window sizes is ΔW, and a predetermined threshold for time 2, the session having the smallest ACK number is disconnected from the plurality of sessions existing in the common buffer when {(remaining memory amount / ΔW) × ΔRTT <β} is satisfied. TCP session management method.   Using the sequence number in the data packet to be transmitted, the time at which the data packet was transmitted, the ACK number in the ACK packet received corresponding to the data packet and the time at which the ACK packet arrived, the maximum segment length as MSS , {TCP number> sequence number + MSS} (reception time−transmission time) is set as the round-trip propagation delay time, the TCP session management method according to claim 3. A TCP proxy device that connects to a network, manages a plurality of sessions corresponding to the content, and distributes the content by TCP to each terminal connected to the network,
A common buffer that is a memory area set in units of contents in common for the plurality of sessions for a window of each session;
A window management table for managing the ACK number and window size of the session for each session;
A TCP processing unit that performs protocol processing by TCP with reference to the window management table to transmit data in the common buffer to each terminal;
A TCP proxy device.   Referring to the window management table, the maximum ACK number in a plurality of sessions existing in the common buffer is Max_ACK, the minimum ACK number is Min_ACK, and a predetermined number that is a multiple of the maximum segment length is α And the window size is W, and the difference between Max_ACK and Min_ACK is used, and when {reserved memory size <(Max_ACK−Min_ACK) + W + α} is satisfied, the ACK number of the plurality of sessions existing in the common buffer is The TCP proxy device according to claim 5, further comprising a session disconnection determination unit that instructs the TCP processing unit to disconnect a session that is the minimum. An RTT measuring unit that measures a round-trip propagation delay time for each of a plurality of sessions existing in the common buffer via the TCP processing unit;
The round-trip propagation delay time between the session having the largest ACK number and the session having the smallest ACK number among the plurality of sessions based on the measurement result of the RTT measurement unit with reference to the window management table And the difference between the window sizes, ΔRTT is the difference between the round-trip propagation delay times, ΔW is the difference between the window sizes, and β is a predetermined threshold for time {(remaining memory amount ÷ ΔW) A session disconnection determination unit that instructs the TCP processing unit to disconnect a session having the smallest ACK number among a plurality of sessions existing in the common buffer when satisfying × ΔRTT <β};
The TCP proxy device according to claim 5, comprising:   The RTT measurement unit uses a sequence number in a data packet to be transmitted and a time at which the data packet is transmitted, an ACK number in an ACK packet to be received corresponding to the data packet, and a time at which the ACK packet arrives. The TCP proxy device according to claim 7, wherein the maximum segment length is MSS, and (rounding time−transmission time) when {ACK number> sequence number + MSS} is satisfied is the round-trip propagation delay time.

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