Apparatus for and method of measuring communication performance

• US 6,757,255 B1
• Filed: 07/27/1999
• Issued: 06/29/2004
• Est. Priority Date: 07/28/1998
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Aoki, Takeshi, Kikuchi, Shinji, Takahashi, Eiichi, Yokoyama, Ken, Katsuyama, Tsuneo, Okano, Tetsuya
• Primary Examiner(s): Ton, Dang
• Assistant Examiner(s): HOM, SHICK C
• Application Number:
  US09/361,249
• Time in Patent Office: 1,799 Days
• Field of Search: 370/232, 370/233, 370/234, 370/252, 370/389, 370/395.2, 370/395.21, 370/395.41, 370/395.52, 370/395.6, 370/395.61, 370/395.64, 370/395.65, 370/401, 370/402, 370/410, 370/229, 370/249, 709/102, 709/104, 709/203, 709/220, 709/221
• US Class Current: 370/252
• CPC Class Codes: H04L 1/187 Details of sliding window management
• CPC Class Codes: H04L 1/24 Testing correct operation
• 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 69/163 In-band adaptation of TCP data exchange; In-band control procedures
• CPC Class Codes: H04L 69/165 Combined use of TCP and UDP protocols; selection criteria therefor
• CPC Class Codes: H04L 9/40 Network security protocols

Abstract

A TCP communications performance measuring device 2 obtains an effective bandwidth (a transfer speed) representing performance in TCP communications, wherein performance indexes or both of a round trip time and a maximum segment size which are obtained based on TCP communications variable-length packets transmitted and received pursuant to a TCP (Transmission Control Protocol) defined as protocol of a transport layer of the OSI Reference model, and any one of an average congestion window size, a packet discard rate and a packet discard event rate. The measuring device 2 therefore includes a packet monitoring unit, a performance index detecting unit 22, a session management unit 23, a session management table 24 and a performance calculating unit 25. The measuring device 2 is capable of measuring the performance in the TCP communications on a communications route of a network without specially transmitting the multiplicity of measurement-oriented packets to the network.

Claims

1. An apparatus for measuring communications performance, comprising:

packet monitoring means for monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnect OSI Reference model, and obtaining, per session, log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

session managing means for managing a flow of the packets per session;

performance index detecting means for obtaining, as performance indexes, a round trip time, a maximum segment size and an average congestion window size on the basis of the log information;

storing means for recording values of the performance indexes detected by said performance index detecting means per session designated by said session managing means; and

performance calculating means for obtaining an effective bandwidth representing performance in the TCP communications by calculating the values of these performance indexes which are recorded in said storing means.

2. The apparatus for measuring communications performance according to claim 1, wherein said performance index detecting means detects as the performance index a packet discard rate instead of the average congestion window size, and

said performance calculating means obtains the effective bandwidth representing the performance in the TCP communications, with the packet discard rate, the round trip time and the maximum segment size being used as values of the performances indexes.

3. The apparatus for measuring communications performance according to claim 1 wherein said performance index detecting means detects as the performance index a packet discard event rate instead of the average congestion window size, and

said performance calculating means obtains the effective bandwidth representing the performance in the TCP communications, with the packet discard event rate, the round trip time and the maximum segment size being used as values of the performance indexes.

4. The apparatus for measuring communications performance according to claim 1, wherein the round trip is obtained from a difference between a transmission timing and a receipt timing of the packet transmitted and received in handshaking between said transmitting-side communications device and said receiving-side communications device when establishing a TCP connection.

5. The apparatus for measuring communications performance according to claim 1 wherein the maximum segment size is obtained from the packet size of the packets.

6. The apparatus for measuring communications performance according to claim 2, wherein the round trip time is obtained from a difference between a transmission timing and a receipt timing of the packet transmitted and received in handshaking between said transmitting-side communications device and said receiving-side communications device when establishing a TCP connection,

the maximum segment size is obtained from a packet size of the packets,

the packet discard rate is obtained by dividing, by the total number of packets, the number of discarded packets which is the number of the packets re-transmitted after a sequence number of the packet has been reversed, and

the effective bandwidth BW is obtained by the formula:

BW=C×

MSS/RTT/{square root over (p)}, where RTT is the round trip time, MSS is the maximum segment size, p is the packet discard rate, and C is the constant minutely adjusted within the range of 1±

0.3.

7. The apparatus for measuring communications performance according to claim 3, wherein the round trip time is obtained from a difference between a transmission timing and a receipt of the packet transmitted and received in handshaking between said transmitting-side communications device and said receiving-side communications device when establishing a TCP connection,

the maximum segment size is obtained from a packet size of the packets,

the packet discard event rate is, if an occurrence of reverse of a sequence number is conceived as one single packet discard event, obtained by dividing the number of the packet discard events by the total number of packets, and

the effective bandwidth BW is obtained by the formula:

BW=C×

MSS/RTT/{square root over (q)}, where RTT is the round trip time, MSS is the maximum segment size, q is the packet discard event rate, and C is the constant minutely adjusted within the range of 1±

0.3.

8. The apparatus as in claim 1 wherein the average congestion window size is obtained by counting the number of the packets transmitted or received within one single window cycle and by obtaining an average value of the number of the packets during a period for which the window size is adjusted by a congestion avoidance algorithm.

9. The apparatus as in claim 2, wherein the packet discard rate is obtained by dividing, by the total number of packets, the number of discarded packets which is the number of the packets re-transmitted after a sequence number of the packet has been reversed.

10. The apparatus as in claim 3, wherein the packet discard event rate is, if an occurrence of reverse of a sequence number is connected as one single packet discard event, obtained by dividing the number of the packet discard events by the total number of packets.

11. The apparatus as in claim 1, wherein the effective bandwidth BW is obtained by a formula:

BW=<

W>

×

MSS/RTT, where RTT is the round trip time, MSS is the maximum segment size, and <

W>

is the average congestion window size.

12. The apparatus as in claim 2, wherein the effective bandwidth BW is obtained by a formula:

BW=C×

MSS/RTT/{square root over (p)}, where RTT is the round trip time, MSS is the maximum segment size, p is the packet discard rate, and C is the constant minutely adjusted within a range of 1±

0.3.

13. The apparatus as in claim 3, wherein the effective bandwidth BW is obtained by a formula:

BW=C×

MSS/RTT/{square root over (q)}, where RTT is the round trip time, MSS is the maximum segment size, q is the packet discard event rate, and C is the constant minutely adjusted within the range of 1+0.3.

14. An apparatus for measuring communications performance, comprising:

packet monitoring means for monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnection OSI Reference model, and obtaining log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

performance index detecting means for obtaining, as performance indexes, both of a round trip time and a maximum segment size, and any one of an average congestion window size, a packet discard rate and a packet discard event rate on the basis of the log information; and

performance calculating means for obtaining an effective bandwidth representing performance in the TCP communications by calculating values of these performance indexes, wherein the average congestion window size is obtained by counting the number of the packets transmitted or received within one single window cycle and by obtaining an average value of the number of the packets during a period for which the window size is adjusted by a congestion avoidance algorithm.

15. An apparatus for measuring communications performance, comprising:

packet monitoring means for monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnection OSI Reference model, and obtaining log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

performance index detecting means for obtaining, as performance indexes, both of a round trip time and a maximum segment size, and any one of an average congestion window size, a packet discard rate and a packet discard event rate on the basis of the log information; and

performance calculating means for obtaining an effective bandwidth representing performance in the TCP communications by calculating the values of these performance indexes, wherein the packet discard rate is obtained by dividing, by the total number of packets, the number of discarded packets which is the number of the packets re-transmitted after a sequence number of the packet has been reversed.

16. An apparatus for measuring communications performance, comprising:

packet monitoring means for monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnection OSI Reference model, and obtaining log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

performance index detecting means for obtaining, as performance indexes, both of a round trip time and a maximum segment size, and any one of an average congestion window size, a packet discard rate and a packet discard event rate on the basis of the log information; and

performance calculating means for obtaining an effective bandwidth representing performance in the TCP communications by calculating values of these performance indexes, wherein the packet discard event rate is, if in occurrence of reverse of a sequence number is conceived as one single packet discard event, obtained by dividing the number of the packet discard events by the total number of packets.

17. An apparatus for measuring communications performance, comprising:

packet monitoring means for monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnection OSI Reference model, and obtaining log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

performance index detecting means for obtaining, as performance indexes, both of a round trip time and a maximum segment size, and any one of an average congestion window size, a packet discard rate and a packet discard event rate on the basis of the log information; and

performance calculating means for obtaining an effective bandwidth representing performance in the TCP communications by calculating values of these performance indexes, wherein the effective bandwidth BW is obtained by a formula;

BW=<

W>

×

MSS/RTT, where RTT is the round trip time, MSS is the maximum segment size, and <

W>

is the average congestion window size.

18. An apparatus for measuring communications performance, comprising:

packet monitoring means for monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnection OSI Reference model, and obtaining log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

performance index detecting means for obtaining, as performance indexes, both of a round trip time and a maximum segment size, and any one of an average congestion window size, a packet discard rate and a packet discard event rate on the basis of the log information; and

performance calculating means for obtaining an effective bandwidth representing performance in the TCP communications by calculating values of these performance indexes, wherein the effective bandwidth BW is obtained by a formula;

BW=C×

MSS/RTT/{square root over (p)}, where RTT is the round trip time, MSS is the maximum segment size, p is the packet discard rate, and C is the constant minutely adjusted within a range of 1±

0.3.

19. An apparatus for measuring communications performance, comprising:

packet monitoring means for monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnection OSI Reference model, and obtaining log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

performance index detecting means for obtaining, as performance indexes, both of a round trip time and a maximum segment size, and any one of an average congestion window size, a packet discard rate and a packet discard event rate on the basis of the log information; and

performance calculating means for obtaining an effective bandwidth representing performance in the TCP communications by calculating values of these performance indexes, wherein the effective bandwidth BW is obtained by formula;

BW=C×

MSS/RTT/{square root over (q)}, where RTT is the round trip time, MSS is the maximum segment size, q is the packet discard event rate, and G is the constant minutely adjusted within the range of 1+0.3.

20. An apparatus for measuring communications performance, comprising:

packet monitoring means for monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnection OSI Reference model, and obtaining log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

performance index detecting means for obtaining, as performance indexes, both of a round trip time and a maximum segment size, and any one of an average congestion window size, a packet discard rate and a packet discard event rate on the basis of the log information; and

performance calculating means for obtaining an effective bandwidth representing performance in the TCP communications by calculating values of these performances indexes, wherein the round trip time is obtained from a difference between a transmission timing and a receipt timing of each of the packets transmitted and received in handshaking between said transmitting-side communications device and said receiving-side communications device when establishing a TCP connection,

the maximum segment size is obtained from a packet size of the packets,

the average congestion window size is obtained by counting the number of the packets transmitted or received within one single window cycle and by obtaining an average value of the number of the packets during a period for which the window size is adjusted by a congestion avoidance algorithm,

the packet discard rate is obtained by dividing, by the total number of packets, the number of discarded packets which is the number of packets re-transmitted after a sequence number of the packet has been reversed,

the packet discard event rate is, if an occurrence of reverse of the sequence number is conceived as one single packet discard event, obtained by dividing the number of packet discard events by the total number of packets, and

the effective bandwidth BW is obtained by any one of the formulae;

BW=<

W>

×

MSS/RTT, BW=C×

MSS/RTT/{square root over (p)}, and BW=C×

MSS/RTT/{square root over (q)}, where RTT is the round trip time, MSS is the maximum segment size, <

W>

is the average congestion window size, p is the packet discard rate, q is the packet discard event rate, and C is the constant minutely adjusted within the range of 1±

0.3.

21. An apparatus for measuring communications performance, comprising:

packet monitoring means for monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnection OSI Reference model, and obtaining log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

performance index detecting means for obtaining, as performance indexes, both of a round trip and a maximum segment size, and any one of an average congestion window size, a packet discard rate and a packet discard event rate on the basis of the log information; and

performance calculating means for obtaining an effective bandwidth representing performance in the TCP communications by calculating values of these performance indexes, wherein the round trip time is obtained from a difference between a transmission timing and a receipt timing of the packet transmitted and received in handshaking between said transmitting-side communications device and said receiving-side communications device when establishing a TCP connection,

the maximum segment size is obtained from a packet size of the packets,

the average congestion window size is obtained by counting the number of the packets transmitted or received within one single window cycle and by obtaining an average value of the number of the packets during a period for which the window size is adjusted by a congestion avoidance algorithm, and

the effective bandwidth BW is obtained by the formula;

BW=<

W>

×

MSS/RTT, where RTT is the round trip time, MSS is the maximum segment size, and <

W>

is the average congestion window size.

22. An apparatus for measuring communications performance, comprising:

measuring means for measuring respectively a maximum segment size and a round trip time by transmitting and receiving a small number of measurement-oriented packets at an interval of a fixed time;

performance index detecting means for obtaining an average value or an intermediate value of the round trip times, and estimating a maximum congestion window size from a time change in the round trip time; and

performance calculating means for obtaining an effective bandwidth representing performance in Transmission Control Protocol TCP communications on the basis of the maximum segment size, the average value or the intermediate value of the round trip times, and the maximum congestion window size, wherein the round trip time and the maximum segment size are measured by transmitting and receiving as one of the measured-oriented packets an echo packet of an Internet Control Message Protocol ICMP defined as a network layer protocol of the OSI Reference model, and an echo packet of a TCP and a User Datagram Protocol UDP which are defined as protocols of a transport layer of the OSI Reference model.

23. An apparatus for measuring communications performance, comprising:

measuring means for measuring respectively a maximum segment size and a round trip time by transmitting and receiving a small number of measurement-oriented packets at an interval of a fixed time;

performance index detecting means for obtaining an average value or an intermediate value of the round trip times, and estimating a maximum congestion window size from a time change in the round trip time; and

performance calculating means for obtaining an effective bandwidth representing performance in Transmission Control Protocol TCP communications on the basis of the maximum segment size, the average value or the intermediate value of the round trip times, and the maximum congestion window size, wherein the maximum congestion window size is given by obtaining the average value or the intermediate value of cycles of a packet discard event from the time change in the round trip time, multiplying this value by 2, and dividing the multiplied value by the average value or the intermediate value of the round trip time.

24. An apparatus for measuring communications performance, comprising:

measuring means for measuring respectively a maximum segment size and a round trip time by transmitting and receiving a small number of measurement-oriented packets at an interval of a fixed time;

performance index detecting means for obtaining an average value or an intermediate value of the round trip times, and estimating a maximum congestion window size from a time change in the round trip time; and

performance calculating means for obtaining an effective bandwidth representing performance in Transmission Control Protocol TCP communications on the basis of the maximum segment size, the average value or the intermediate value of the round trip times, and the maximum congestion window size, wherein the effective bandwidth BW is obtained by the formula;

BW=(3/4)×

W×

MSS/<

RTT>

, where <

RTT>

is the average value or the intermediate value of the round trip times, MSS is the maximum segment size, and W is the maximum congestion window size.

25. An apparatus for measuring communications performance, comprising:

measuring means for measuring respectively a maximum segment size and a round trip time by transmitting and receiving a small number of measurement-oriented packets at an interval of a fixed time;

performance index detecting means for obtaining an average value or an intermediate value of the round trip times, and estimating a maximum congestion window size from a time change in the round trip time; and

performance calculating means for obtaining an effective bandwidth representing performance in Transmission Control Protocol TCP communications on the basis of the maximum segment size, the average value or the intermediate value of the round trip times, and the maximum congestion window size, wherein the round trip time and the maximum segment size are measured by transmitting and receiving as one of the measured-oriented packets an echo packet of an Internet Control Message Protocol ICMP defined as the network layer protocol of the Open Systems Interconnect OSI Reference model, and the echo packet of the TCP and a User Datagram Protocol UDP which are defined as the protocols of the transport layer of the OSI Reference model,

the maximum congestion window size is obtained by detecting a maximal point of the round trip time from the time change in the round trip, multiplying by 2 a time interval till the round trip time becomes maximal next since it has become maximal, and dividing the multiplied time interval by the average value or the intermediate value of the round trip times, and

the effective bandwidth BW is obtained by the formula;

BW=(3/4)×

W×

MSS/<

RTT>

, where <

RTT>

is the average value or the intermediate value of the round trip times, MSS is the maximum segment size, and W is the maximum congestion window size.

26. A method of measuring communications performance, comprising:

measuring a round trip time by transmitting and receiving a small number of measurement-oriented packets at a variable interval of a fixed time;

determining a rate at which the round trip time of one of the measurement-oriented packets is longer than the round trip time of another of the measurement-oriented packets just anterior thereto; and

checking whether or not the rate is over a predetermined threshold value, then, if over, judging that a transfer speed of one of the measurement-oriented packets exceeds an available bandwidth of a network route, and thereby judging that the available bandwidth of the network route in any one of a case where the communications are performed by use of a protocol of a transport layer of the Open Systems Interconnection OSI Reference model in which the protocol itself such as a User Datagram Protocol UDP does not control the transfer speed and a case where the communications are performed by use of a Transmission Control Protocol TCP defined as the protocol of the transport layer of the OSI Reference model, exceeds a certain predetermined value.

27. An apparatus for measuring communications performance, comprising:

measuring means for measuring a round trip time by transmitting and receiving a small number of measurement-oriented packets at a variable interval of a fixed time;

rate determining means for determining a rate at which the round trip time of one of the measurement-oriented packets is longer than the round trip time of another of the measurement-oriented packets just anterior thereto; and

performance determining means for checking whether or not the rate is over a predetermined threshold value, then, if over, judging that a transfer speed of the one of the measurement-oriented packets exceeds an available bandwidth of a network route, and thereby judging that the available bandwidth of the network route in a case where the communications are performed by use of a protocol of a transport layer of the Open Systems Interconnection OSI Reference model in which the protocol itself such as a User Datagram Protocol UDP does not control the transfer speed, exceeds a certain predetermined value.

28. The apparatus for measuring communications performance according to claim 27, wherein a process of judging whether or not the rate exceeds the threshold value while changing a value of the transfer speed of the one of the measurement-oriented packets by a split-half method, is repeated a predetermined number of times, and

there is estimated the available bandwidth of the network route in any one of the case where the communications are performed by use of the UDP that the protocol itself does not control the transfer speed, and the case where the communications are performed by use of the TCP.

29. The apparatus for measuring communications performance according to claim 27, wherein the process of judging whether or not the rate exceeds the threshold value while changing the value of the transfer speed of the one of the measurement-oriented packets by a regula falsi method, is repeated a predetermined number of times, and

there is estimated the available bandwidth of the network route in any one of the case where the communications are performed by use of the UDP that the protocol itself does not control the transfer speed, and the case where the communications are performed by use of the TCP.

30. The apparatus for measuring communications performance according to claim 27, wherein the process of judging whether or not the rate exceeds the threshold value while changing the value of the transfer speed of the one of the measurement-oriented packets by a monotone increasing method, is repeated a predetermined number of times, and

there is estimated the available bandwidth of the network route in any one of the case where the communications are performed by use of the UDP that the protocol itself does not control the transfer speed, and the case where the communications are performed by use of the TCP.

31. The apparatus for measuring communications performance according to claim 27, wherein the process of judging whether or not the rate exceeds the threshold value while changing a value of the transfer speed of the one of the measurement-oriented packets by a monotone decreasing method, is repeated a predetermined number of times, and

there is estimated the available bandwidth of the network route in any one of the case where the communications are performed by use of the UDP that the protocol itself does not control the transfer speed, and the case where the communications are performed by use of the TCP.

32. An apparatus for measuring communications performance, comprising:

measuring means for measuring a round trip time by transmitting and receiving a small number of measurement-oriented packets at a variable interval of a fixed time;

rate determining means for determining a rate at which the round trip time of one of the measurement-oriented packets is longer than the round trip time of another of the measurement-oriented packets just anterior thereto; and

performance determining means for checking whether or not the rate is over a predetermined threshold value, then, if over, judging that a transfer speed of the one of the measurement-oriented packets exceeds an available bandwidth of a network route, and thereby judging that the available bandwidth of the network route in a case where the communications are performed by use of a Transmission Control Protocol TCP defined as a protocol of the transport layer of the Open Systems Interconnection OSI Reference model, exceeds a certain predetermined value.

36. The apparatus for measuring communications performance according to claim 32, wherein a process of judging whether or not the rate exceeds the threshold value while changing a value of the transfer speed of the one of the measurement-oriented packets by a split-half method, is repeated a predetermined number of time, and

there is estimated the available bandwidth of the network route in any one of the case where the communications are performed by use of the UDP that the protocol itself does not control the transfer speed, and the case where the communications are performed by use of the TCP.

37. The apparatus for measuring communications performance according to claim 32, wherein the process of judging whether or not the rate exceeds the threshold value while changing the value of the transfer speed of the one of the measurement-oriented packets by a regula falsi method, is repeated a predetermined number of times, and

there is estimated the available bandwidth of the network route in any one of the case where the communications are performed by use of the UDP that the protocol itself does not control the transfer speed, and the case where the communications are performed by use of the TCP.

38. The apparatus for measuring communications performance according to claim 32, wherein the process of judging whether or not the rate exceeds the threshold value while changing the value of the transfer speed of the one of the measurement-oriented packets by a monotone increasing method, is repeated a predetermined number of times, and

there is estimated the available bandwidth of the network route in any one of the case where the communications are performed by use of the UDP that the protocol itself does not control the transfer speed, and the case where the communications are performed by use of the TCP.

39. The apparatus for measuring communications performance according to claim 32, wherein the process of judging whether or not the rate exceeds the threshold value while changing a value of the transfer speed of the one of the measurement-oriented packets by a monotone decreasing method, is repeated a predetermined number of times, and

there is estimated the available bandwidth of the network route in any one of the case where the communications are performed by use of the UDP that the protocol itself does not control the transfer speed, and the case where the communications are performed by use of the TCP.

33. A method for measuring communications performance, comprising:

monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnection OSI Reference model, and obtaining log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

obtaining, as performance indexes, both of a round trip time and a maximum segment size, and any one of an average congestion window size, a packet discard rate and a packet discard event rate on the basis of the log information; and

obtaining an effective bandwidth representing performance in the TCP communications by calculating values of these performance indexes, wherein;

obtaining the round trip time from a difference between a transmission timing and a receipt timing of each of the packets transmitted and received in handshaking between said transmitting-side communications device and said receiving-side communications device when establishing a TCP connection,

obtaining the maximum segment size from a packet size of the packets,

obtaining the average congestion window size by counting the number of the packets transmitted or received within one single window cycle and by obtaining an average value of the number of the packets during a period for which the window size is adjusted by a congestion avoidance algorithm,

obtaining the packet discard rate by dividing, by the total number of packets, the number of discarded packets which is the number of packets re-transmitted after a sequence number of the packet has been reversed,

obtaining the packet discard event rate, if an occurrence of reverse of the sequence number is conceived as one single packet discard event, by dividing the number of packet discard events by the total number of packets, and

obtaining the effective bandwidth BW by any one of the formulae;

BW=<

W>

×

MSS/RTT, BW=C×

MSS/RTT/{square root over (p)}, and BW=C×

MSS/RTT/{square root over (q)}, where RTT is the round trip time, MSS is the maximum segment size, <

W>

is the average congestion window size, p is the packet discard rate, q is the packet discard event rate, and C is the constant minutely adjusted within the range of 1±

0.3.

34. A method for measuring communications performance, comprising:

monitoring a variable length packet in Transmission Control Protocol TCP communications through which packets are transmitted and received based on a TCP defined as a protocol of a transport layer of the Open Systems Interconnection OSI Reference model, and obtaining log information containing address information of a transmitting-side communications device and a receiving-side communications device, a packet category and a packet size from the packets;

obtaining, as performance indexes, both of a round trip time and a maximum segment size, and any one of an average congestion window size, a packet discard rate and a packet discard event rate on the basis of the log information; and

obtaining an effective bandwidth representing performance in the TCP communications by calculating values of these performance indexes, wherein;

obtaining the round trip time from a difference between a transmission timing and a receipt timing of the packets transmitted and received in handshaking between said transmitting-side communications device and said receiving-side communications device when establishing a TCP connection,

obtaining the maximum segment size from a packet size of the packets,

obtaining the average congestion window size by counting the number of the packets transmitted or received within one single window cycle and by obtaining an average value of the number of the packets during a period for which the window size is adjusted by a congestion avoidance algorithm, and

obtaining the effective bandwidth BW by the formula;

BW=<

W>

×

MSS/RTT, where RTT is the round trip time, MSS is the maximum segment size, and <

W>

is the average congestion window size.

35. A method for measuring communications performance, comprising:

measuring respectively a maximum segment size and a round trip time by transmitting and receiving a small number of measurement-oriented packets at an interval of a fixed time;

obtaining an average value or an intermediate value of the round trip times, and estimating a maximum congestion window size from a time change in the round trip time; and

obtaining an effective bandwidth representing performance in Transmission Control Protocol TCP communications on the basis of the maximum segment size, the average value or the intermediate value of the round trip times, and the maximum congestion window size, wherein the round trip time and the maximum segment size are measured by transmitting and receiving as one of the measured-oriented packets an echo packet of an Internet Control Message Protocol ICMP defined as the network layer protocol of the Open Systems Interconnection OSI Reference model, and the echo packet of the TCP and a User Datagram Protocol UDP which are defined as the protocols of the transport layer of the OSI Reference model,

obtaining the maximum congestion window size by detecting a maximal point of the round trip time from the time change in the round trip, multiplying by 2 a time interval till the round trip time becomes maximal next since it has become maximal, and dividing the multiplied time interval by the average value or the intermediate value of the round trip times, and

obtaining the effective bandwidth BW by the formula;

BW=(3/4)×

W×

MSS/<

RTT>

, where <

RTT>

is the average value or the intermediate value of the round trip times, MSS is the maximum segment size, and W is the maximum congestion window size.