JP3855011B2 - Communication device and mobile communication terminal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a communication device and a mobile communication terminal that communicate via the Internet, and more particularly to a communication device and a mobile communication terminal that have improved a communication protocol of a transport layer.
[0002]
[Prior art]
TCP (Transmission Control Protocol) is a communication protocol for the transport layer in the Internet. TCP is standardized by the IETF (The Internet Engineering Task Force) as a transport layer protocol, and is widely used in Internet applications such as Web browsing (HTTP) and electronic mail (SMTP). On the other hand, it is known from the traffic analysis in the backbone by MAWI-WG of WIDE project that more than 80% of communication on the Internet uses TCP, and even though TCP supports today's Internet. It's not too much to say. TCP has flow control, retransmission control, and congestion control, and adjusts the data transmission rate, retransmits lost data, and avoids congestion. In TCP, flow control is performed using an advertised window, and congestion control is performed using a congestion window. What is important here is congestion control, which avoids congestion collapse and supports communication on the Internet today. In TCP congestion control, if a segment, which is an information transmission unit, is lost, it is determined that the network is overloaded and is congested, and the congestion window is halved (data transmission speed is halved). To reduce the amount of data transferred and avoid congestion collapse.
[0003]
As described above, most of current Internet communications use TCP. On the other hand, in recent years, with the downsizing of computers and the enhancement of the performance of wireless networks, it is becoming common for users to carry their own computers and move while connected to the network via a wireless LAN or mobile phone network. . As a result, it has become possible to enjoy Web browsing while moving, send and receive mail, transfer files, and the like, and it can be said that TCP communication via wireless lines is increasing.
[0004]
[Problems to be solved by the invention]
However, unlike a wired line, a wireless line causes a segment loss due to a high bit error rate due to noise, interference, and the like. Unlike the wired line, such a segment loss on the wireless line occurs regardless of the congestion, so there is no need to perform congestion control. However, the conventional TCP determines that the segment loss is congestion, and therefore, the amount of data transferred is suppressed by uniformly controlling congestion, resulting in a significant decrease in throughput in a wireless network environment. Arise.
[0005]
In order to solve this problem, a method for improving throughput by dividing a TCP connection at a radio base station and a method for detecting a segment loss and retransmitting at a radio base station have been proposed. These methods are based on the premise of monitoring the TCP header at the radio base station, and the system becomes complicated and IPsec (S. Kent, R. Atkinson, “Security Architecture for the Internet Protocol”, IETF, 1998, RFC2401 ) Cannot be applied. Therefore, the end-to-end solution is currently the mainstream, and SACK (Selective Acknowledgment) (M. Mathis, S. Floyd, A. Romanow, “TCP Selective Acknowledgment Options”, IETF 1996) , RFC2018), TCP-westwood (S. Mascolo, C. Casetti, M. Gerla, SS Lee, M. Sanadini, “TCP Westwood: Bandwidth Estimation for Enhanced Transport over Wireless Links”, The seventh annual international conference on Mobile computing and networking, 2001), but SACK has the problem that congestion control is the same as conventional TCP, and TCP-westwood has a problem that processing is complicated.
[0006]
MIPv6 (C. Perkins, J. David, “Mobility Support in IPv6”, Proceedings of the MobiCom, 1996), LIN6 (M. Kunishi, M, Ishiyama, H, Esaki, F. Teraoka, “LIN6: A New Approach to Mobility Support in IPv6 ”, Proceedings of the third International Symposium on Wireless Personal Multimedia Communications, 2000), movement transparency is realized in the IP layer, but conventional TCP does not consider the movement of terminals. Even if the network changes before and after the movement, there is a problem that the same congestion control as before the movement is performed.
[0007]
An object of the present invention is to improve throughput when using a wireless network and to implement congestion control in accordance with network changes due to movement in a communication apparatus and a mobile communication terminal using TCP.
[0010]
[Means for Solving the Problems]
The communication apparatus of the present invention has a receiving means for receiving information from the mobile communication terminal whether the upstream routers of the old and new base stations are common at the time of handoff of the mobile communication terminal, and the upstream router is common to the receiving means. when receiving the information that is used as result of ABE (Available bandwidth Estimation) mechanism the value of the bandwidth of the radio section of the new base station covers received from the mobile communication terminal, the congestion window and the slow start threshold When the information is determined and the information that the upstream router is not common is received by the receiving means, the information is provided with a congestion control means for performing a slow start using the value of the notification window as a slow start threshold.
[0013]
Further, the mobile communication terminal of the present invention receives an upstream router notification from a base station and determines whether the upstream routers of the old and new base stations are common at the time of handoff, Transmitting means for transmitting information on whether or not the upstream routers of the old and new base stations are common at the time of handoff determined by the router determining means to the counterpart communication device.
[0015]
In addition, the mobile communication terminal of the present invention includes an upstream router determination unit that receives a notification of an upstream router of the base station from a base station and determines whether the upstream routers of the old and new base stations are common at the time of handoff, and a wireless section Information on whether or not the upstream routers of the old and new base stations are common at the time of handoff determined by the upstream router determination unit, and the wireless section band determined by the bandwidth determination unit Transmitting means for transmitting the width to the counterpart communication device.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0017]
FIG. 1 is a functional block diagram showing the main part of the communication device according to the first embodiment of the present invention. The communication apparatus according to the present embodiment mainly includes a bandwidth calculation unit 11, a smoothing unit 12, and a congestion control unit 13. In the present embodiment, the currently effective bandwidth is estimated by an ABE (Available Bandwidth Estimation) mechanism, and a congestion window (cwnd) and a slow start threshold (ssth), which are variables used for TCP congestion control, are determined. The bandwidth calculation means 11 first calculates a sample of bandwidth by the equation (1) by the ABE mechanism.
[0018]
bk = dk / (tk-tk-1) (1)
here,
bk: Bandwidth sample dk: Data size (data size used for bandwidth estimation)
tk: ACK (Acknowledgement) arrival time formula (1) bandwidth sample includes fluctuations due to delayed ACKs that send several ACKs together and fluctuations due to random segment loss by the wireless network. Yes. For this reason, the smoothing means 12 smoothes the bandwidth sample obtained here by the following equation (2).
[0019]
BWk = [alpha] * BWk-1 + (1- [alpha]) * (bk + bk-1) / 2 (2)
here,
α: Smoothing constant BWk: Estimated bandwidth by ABE mechanism In the above-mentioned TCP-westwood, this smoothing formula is
BWk = {2T / (tk-tk-1) -1} / {2T / (tk-tk-1) +1} * BWk-1 + (bk + bk-1) / {2T / (tk-tk-1 + 1)}
It has become.
[0020]
The congestion control means 13 determines the congestion window cwnd and the slow start threshold ssth using the bandwidth value obtained by the smoothing according to the equation (2) as a result of the ABE mechanism. The decision method is as follows. RTTmin indicates the minimum value of RTT (round trip time), and ssize indicates the size of the segment (the maximum length of data transmitted by TCP at one time, which is determined when a TCP connection is established).
(1) Operation after retransmission due to segment loss detection due to duplicate ACK reception
(1) During congestion avoidance phase ssth = BW × RTTmin / ssize
cwnd = ssth
(2) During slow start phase ssth = BW x RTTmin / ssize
cwnd = (holds the latest value)
(2) Operation after retransmission due to segment loss detection due to timeout ssth = BW × RTTmin / ssize
cwnd = 1
Thus, by determining the congestion window cwnd and the slow start threshold ssth from the currently effective bandwidth obtained by the ABE mechanism, when the segment loss occurs, the data transmission speed is simply halved as in the conventional TCP. It is possible to avoid congestion without making it. As a result, it is possible to improve the TCP throughput in the wireless line.
[0021]
As a result of simulation by NS-2 (http://www.isi.edu/nsnam/ns), when the bit error rate in the radio section is 4 × 10 ⁻⁶ , this embodiment is 191 when NewReno is used as a reference. %, A throughput improvement of 35% was recognized based on TCP-westwood.
[0022]
FIG. 2 is a diagram showing a typical topology when a mobile node and a partner communication node are communicating. In this case, the counterpart communication node (CN) 21 sequentially passes from the root router (RR) 22 of each domain via the Internet to the lower node router (R) 23 and the mobile node (MN) 25 via the access router (AR) 24. Connected to. When attention is paid to changes in network resources (bandwidth), the types of movement can be classified into the following three types.
[0023]
Movement A: Movement within a domain when upstream routers are common. An extended router advertisement (RA) is used to determine whether the upstream router is common. The extended router notification here is obtained by adding upstream router information to the router notification (for example, including the address of the upstream router). When the upstream router is common, it is considered that the wired section is common, so congestion control is performed according to the wireless section of the movement destination.
(1) If the upstream router of the radio base station is common if (newRadioBW <BW) BW = newRadioBW
ssth = BW × RTTmin / ssize
cwnd = ssth
Here, newRadioBW: Bandwidth of the destination radio section When this destination is the bottleneck of the destination radio section due to this congestion control, the newRadioBW and BW are replaced to replace the newRadioBW and BW so that the bandwidth of the destination network is considered. Is possible.
[0024]
Movement B: Movement in the domain when the upstream router is not common. In this case, since it is considered that the wired sections are not common, the slow start threshold value ssth is set as the value of the notification window (Advertised Window), and the slow start is explicitly performed.
[0025]
Movement C: Movement between domains. In the movement between domains, like the movement B, it is considered that the wired section is not common. Therefore, even in the case of the movement C, the slow start threshold value ssth is set as the value of the notification window, and the slow start is explicitly performed.
(2) If the upstream router of the radio base station is not common, reset the ABE mechanism ssth = Win
cwnd = 1
Here, Win: Notification Window FIG. 3 is a functional block diagram showing the main parts of a communication apparatus, a base station, and a mobile communication terminal according to the second embodiment of the present invention. The partner communication node 30 which is a communication device according to the present embodiment mainly includes a receiving unit 31 and a congestion control unit 32. The base station 40 mainly includes an upstream router detecting unit 41, an upstream router notifying unit 42, a bandwidth measuring unit 43, and a bandwidth notifying unit 44. The mobile node 50 that is a mobile communication terminal mainly includes an upstream router determination unit 51, a bandwidth determination unit 52, and a transmission unit 53.
[0026]
The upstream router detection unit 41 creates a router notification including the address of the upstream router using a routing table, for example, that is, an expanded router notification, and sends the router notification to the upstream router notification unit 42. The upstream router notification unit 42 transmits the extended router notification to the upstream router determination unit 51. The bandwidth measuring unit 43 measures the bandwidth of the radio section covered by the base station 40 and sends it to the bandwidth notifying unit 44. The bandwidth notification unit 44 transmits the wireless section bandwidth to the bandwidth determination unit 52.
[0027]
The upstream router determination unit 51 determines whether the upstream routers of the old and new base stations are common at the time of handoff using the extended router notification received from the upstream router notification unit 42, and sends the determination result to the transmission unit 53. send. The bandwidth determination unit 52 sends the wireless section bandwidth received from the bandwidth notification unit 44 to the transmission unit 53. The transmission unit 53 transmits the information indicating whether or not the upstream routers transmitted from the upstream router determination unit 51 are common, and the wireless section bandwidth transmitted from the bandwidth determination unit 52 to the reception unit 31.
[0028]
The receiving unit 31 receives information about whether or not the upstream routers of the old and new base stations 40 are common and the wireless section bandwidth from the transmitting unit 53 when the mobile node 50 is handed off. The congestion control means 32 performs congestion control based on the information indicating whether the above upstream routers are common and the wireless section bandwidth.
[0029]
In addition, although it described so that information could be transmitted directly from the transmission means 53 to the reception means 31, this shows the relationship between the sender and receiver of information, and actually transmitted via the base station 40. Is done.
[0030]
The present invention is not limited to the above embodiment.
[0031]
For example, in the second embodiment, the radio section bandwidth is received from the base station, but the mobile node itself may be configured to measure the radio section bandwidth.
[0032]
In addition, the partner communication device is usually a personal computer or the like as a communication partner, but when the communication partner is a home fixed telephone, such as when the communication partner is not a communication partner by TCP / IP communication, A communication device at the end of communication.
[0033]
【The invention's effect】
As described above, according to the present invention, as a result of the simulation by NS-2, when the bit error rate in the radio section is 4 × 10 ⁻⁶ , it is 191% based on NewReno and 35 based on TCP-westwood. % Throughput improvement was observed. Also, pay attention to changes in network resources (bandwidth) due to movement of mobile nodes between networks (handoff), and adapt to destination network resources (bandwidth) by detecting movement and changing congestion control. Congestion control can be performed, and fairness between other TCP streams can be improved.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a main part of a communication device according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a typical topology when a mobile node and a counterpart communication node are communicating with each other.
FIG. 3 is a functional block diagram showing main parts of a communication device, a base station, and a mobile communication terminal according to a second embodiment of the present invention.
[Explanation of symbols]
21 Partner communication node (CN)
22 Route router (RR)
23 router (R)
24 Access router (AR)
25 Mobile node (MN)

Claims (3)

Receiving means for receiving information from the mobile communication terminal whether or not the upstream routers of the old and new base stations are common at the time of handoff of the mobile communication terminal;
When the information that the upstream router is common is received by the receiving means, the value of the bandwidth of the radio section covered by the new base station is received from the mobile communication terminal, and the result by the ABE (Available Bandwidth Estimation) mechanism And a congestion control means for determining a congestion window and a slow start threshold, and when receiving information that the upstream router is not common by the receiving means, using the value of the notification window as a slow start threshold. A communication device characterized by the above. An upstream router determination means that receives a notification of the upstream router of the base station from the base station and determines whether the upstream routers of the old and new base stations are common at the time of handoff,
A mobile communication terminal comprising: transmission means for transmitting information on whether or not the upstream routers of the old and new base stations are common at the time of handoff determined by the upstream router determination means to the counterpart communication device. An upstream router determination means that receives a notification of the upstream router of the base station from the base station and determines whether the upstream routers of the old and new base stations are common at the time of handoff,
A bandwidth determination means for determining a wireless section bandwidth;
Information on whether or not the upstream routers of the old and new base stations are common at the time of handoff determined by the upstream router determination means, and a transmission means for transmitting the wireless section bandwidth determined by the bandwidth determination means to the counterpart communication device; A mobile communication terminal comprising:

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