KR20080033074A - Method and apparatus for estimating one-way delay - Google Patents

Abstract

A one-way delay time estimation method and a device thereof are provided to exactly estimate one-way delay time between a client and a server even though the client and the server cannot receive the same timing information, thereby accurately synchronizing a clock of the client with a clock of the server. A time measurer(210) measures transmission time of an ICMP(Internet Control Message Protocol) packet. An operator(216) operates a time difference between transmission time measured in a server and transmission time measured in a client, and operates one-way delay time between the server and the client in case a clock of the client is synchronized with a clock of the server. A comparator(218) compares the operated time difference with the operated one-way delay time. A delay time estimator(220) determines one of values which are less than the operated one-way delay time as one-way delay time between the server and the client, by responding to the compared results.

Description

One-way delay estimation method and apparatus {Method and apparatus for estimating one-way delay}

The present invention relates to a method for estimating a one-way delay time between two hosts, and more particularly, to a method for estimating a one-way delay time between a client and a server, which is information necessary for synchronizing a clock of a client with a clock of a server. will be.

Clocks of hosts that are spaced apart from each other may be synchronized to each other or may not be synchronized.

As a way to synchronize the clocks of unsynchronized hosts with each other, they all receive the same timing information from the base station of the satellite or cellular phone, There is a way to synchronize the received timing information. However, this method has a problem in that the utilization is low in that each host must have expensive receiving equipment such as an antenna.

On the other hand, as another method for synchronizing the clocks of unsynchronized hosts with each other, the client returns the packet from the server when the client, one of the hosts, transmits the packet to the server, the other of the hosts. It measures the round trip delay time, which is the time until the received point, estimates the median value of the round trip delay time as the one-way delay time between the server and the client, and synchronizes the client clock with the server clock using the estimated one-way delay time. There is a way to make it. Another alternative is to synchronize the clock of the client with the clock of the server even if the client and server are not in an environment in which timing information such as satellite or base station is provided. However, this alternative approach assumes that the one-way delay between the server and the client is always the median of the round trip delay between the server and the client, and uses the estimated one-way delay to synchronize the client's clock with the server's clock. There is no limit to accurately estimating the actual time difference between the clock of the server and the clock of the server. Accordingly, the other approach has a problem in that the clock of the client is accurately synchronized with the clock of the server.

The technical problem to be solved by the present invention is that the unidirectional delay time for accurately synchronizing the clock of the client with the clock of the server by accurately estimating the unidirectional delay time between the client and the server even if the client and the server cannot be provided with the same timing information. To provide an estimation method.

Another technical problem to be solved by the present invention is unidirectional for accurately synchronizing the clock of the client with the clock of the server by accurately estimating the unidirectional delay time between the client and the server even if the client and server cannot be provided with the same timing information. The present invention provides a delay estimation apparatus.

In order to achieve the above object, the present invention provides a method for estimating a unidirectional delay time, the method comprising: measuring a transmission time of the ICMP packet at a client and a server that sends and receives an ICMP packet according to a standard IP protocol; Calculating a time difference between a transmission time measured by the server and a transmission time measured by the client, and calculating a one-way delay time between the server and the client when the clock of the client is synchronized with the clock of the server; Determining whether the calculated time difference coincides with the calculated one-way delay time; And if it is determined that the calculated time difference coincides with the calculated one-way delay time, determining one of values below the calculated one-way delay time as a one-way delay time between the server and the client. Do.

In order to achieve the above object, the apparatus for estimating a unidirectional delay time according to the present invention includes a time measuring unit for measuring a transmission time of the ICMP packet in a client and a server that transmits and receives an ICMP packet to and from the client according to a standard IP protocol. ; A calculation unit calculating a time difference between a transmission time measured by the server and a transmission time measured by the client, and calculating a one-way delay time between the server and the client when the clock of the client is synchronized with the clock of the server; A comparison unit comparing the calculated time difference with the calculated one-way delay time; And a delay time estimator for determining, as a one-way delay time between the server and the client, one of values calculated below the calculated one-way delay time in response to the comparison result.

The method and apparatus for estimating a unidirectional delay time according to the present invention measure the transmission time of the ICMP packet in the client and the server that exchanges the ICMP packet with the client according to the standard IP protocol, and then measure the transmission time and the client measured in the server. Calculates the time difference between the transmission time points measured at, and calculates the one-way delay time between the server and the client when the clock of the client is synchronized with the clock of the server, and if the calculated time difference coincides with the calculated one-way delay time. Since one of the values below the calculated one-way delay time is determined as the one-way delay time between the server and the client, according to an embodiment of the present invention, even if the client and the server cannot be provided with the same timing information, One-way latency can be estimated accurately, and thus The clock can be synchronized exactly to the server's clock.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings that illustrate preferred embodiments of the present invention and the accompanying drawings.

Hereinafter, a method and apparatus for estimating a unidirectional delay time according to the present invention will be described with reference to the accompanying drawings.

1 is a diagram illustrating a server and a client connected to a network. As shown, a server 110 and a client 120 are connected to the network 130.

Server 110 and client 120 communicate according to standard Internet Protocol (IP) protocol. A personal computer (PC) in which an Internet environment such as the World Wide Web (WWW) is implemented is an example of each of the server 110 and the client 120.

The server 110 and the client 120 exchange predetermined data with each other. In detail, the server 110 and the client 120 exchange Internet Control Message Protocol (ICMP) packets with each other. Here, ICMP packets are defined in RFC (Request For Comments) documents 792, 1122, 1812 and the like.

More specifically, when the client 120 transmits an ICMP packet to the server 110 in the type 13 format defined in the RFC document, the server 110 sends a one-way delay from the point at which the ICMP packet is transmitted from the client 120. When the time elapses, the ICMP packet is transmitted. Thereafter, as soon as the server 110 receives the ICMP packet from the client 120, the server 110 transmits the ICMP packet to the client 120 in the format of Type 14 defined in the RFC document. In this case, the client 120 receives the ICMP packet from the server 110 when the one-way delay time elapses from the time when the ICMP packet is transmitted. In this way, the server 110 and the client 120 exchange ICMP packets with each other.

This exchange may be performed multiple times. That is, as soon as the client 120 receives the ICMP packet from the server 110, the client 120 transmits the ICMP packet to the server 110 in the type 13 format defined in the RFC document. In this case, the server 110 receives the ICMP packet from the client 120 when the one-way delay time elapses from the time when the ICMP packet is transmitted. Thereafter, as soon as the server 110 receives the ICMP packet from the client 120, the server 110 transmits the ICMP packet to the client 120 in the format of Type 14 defined in the RFC document. In this case, the client 120 receives the ICMP packet from the server 110 when the one-way delay time elapses from the time when the ICMP packet is transmitted.

In the present specification, the one-way delay is a time from a time when a packet transmitted by the client 120 to the server 110 leaves the client 120 to a time when the packet arrives at the server 110. It may also mean time, or may mean the time from when the packet transmitted by the server 110 to the client 120 leaves the server 110 to when it arrives at the client 120.

The server 110 and the client 120 may be symmetrically connected or may be asymmetrically connected. Here, the asymmetrical connection means that the time required for data transmission from the server 110 to the client 120 and the time required for data transmission from the client 120 to the server 110 are different from each other. do.

The network 130 may be a wired network or a wireless network.

One or more hosts may be connected to the network 130, and the present invention provides a method of estimating a one-way delay time between the server 110, which is one of the hosts, and the client 120, which is the other of the hosts. It is suggested as follows.

2 is a block diagram for explaining an example of the unidirectional delay time estimation apparatus according to the present invention. The time measurement unit 210, the error detection and correction unit 212, the offset setting unit 214, and the operation unit 216 are described. , A comparator 218, a delay time estimator 220, and a clock adjuster 222.

The time measuring unit 210 measures k (where k is a natural number), k + 1 and k + 2th transmission time points at the server 110, and measures k and k + 1th transmission time points at the client 120. do. Here, the measurement by the server 110 means the measurement by the clock provided in the server 110, and the measurement by the client 120 means the measurement by the clock provided by the client 120. In addition, the term 'transmit' may mean only 'transmit' in context, may mean only 'receive', or may mean both 'transmit' and 'receive'.

That is, the time measurement unit 210 is the time when the server 110 transmits the k-th ICMP packet, when the client 120 receives the k-th ICMP packet, and the client 120 receives the k-th ICMP packet. When the server 110 receives the ICMP packet k + 1 times, when the server 110 transmits the ICMP packet k + 1 times, the client 120 sends the ICMP packet k + 1 times The second time point is received, the client 120 transmits the ICMP packet by the k + 1th time, and the server 110 receives the ICMP packet by the k + 2th time. Here, transmitting means transmitting, and receiving means receiving.

The error detection and correction unit 212 checks whether there is an error, that is, a lost part, in the ICMP packet, and if so, restores the lost part.

The offset setting unit 214 intentionally sets a positive offset or a negative offset between the time indicated by the clock of the server 110 and the time indicated by the clock of the client 120. At this time, whether to set a positive offset or a negative offset may be specified by the user. In detail, the offset setting unit 214 intentionally reflects the offset α or β at the transmission time measured by the client 120.

If the user wants to set a negative offset, the offset setting unit 214, the m (where m is one of k, k + 1, k + 2) measured at the client 120, the transmission time, It may be changed as a result of adding a predetermined value α to the mth transmission time measured by the server 110.

This operation of the offset setting unit 214 can be expressed by the following equation.

[Equation 1]

t_B_ (m) = t_A_ (m) + α

Hereinafter, A means server 110, B means client 120, t_B_ (m) means the mth transmission time point measured by server 110, and t_A_ (m) indicates client 120. Means the mth transmission time point measured in

On the other hand, α is preferably set to satisfy the following equation.

[Equation 2]

t_A_ (k) <t_B_ (k) <t_A_ (k + 1) and

t_A_ (k + 1) <t_B_ (k + 1) <t_A_ (k + 2)

On the contrary, if the user wants to set a positive offset, the offset setting unit 214 may refer to the k + 1th transmission time point measured by the client 120 as' the k + 1th transmission time point measured by the server 110. It may be changed to the result of subtracting the predetermined amount value β from the result of adding the 'k th round-trip delay time calculated by the client 120 to'. In the present specification, a round-trip time (RTT) calculated at the server 110 is defined as a packet transmitted from the server 110 to the client 120 when the packet is returned to the server 110 again. It means the time taken from the server 110 to reach the server 110 again. Similarly, the round trip delay time calculated by the client 120 indicates that when a packet transmitted from the client 120 to the server 110 returns back to the client 120, the packet leaves the client 120 and the client ( The time it takes to reach 120 again.

This operation of the offset setting unit 214 can be expressed by the following equation.

[Equation 3]

t_B_ (k + 1) = t_A_ (k + 1) + R_B_ (k)-β

Here, R_B_ (k) means the k-th round trip delay time calculated by the client.

On the other hand, β is preferably set to satisfy the above equation (2).

In this way, if the user wants to set a positive offset, the offset setting unit 214 transmits the k-th transmission time measured by the client 120 to the k + 1th transmission from the client 120 changed according to Equation (3). It is possible to change the result of subtracting the k-th round trip delay time calculated by the client 120 from the viewpoint '. This can be expressed by the following equation.

[Equation 4]

t_B_ (k) = t_B_ (k + 1)-R_B_ (k)

Since the round trip delay time used in Equations 3 and 4 described above is a value calculated by the calculation unit 216 to be described later, the offset setting unit 214 to set the offset as a positive value calculates the numerical value of the calculated round trip delay time. Provided at 216 is preferred.

On the other hand, the meaning of the offset amount and sound, and the reason for intentionally setting the offset amount and sound in advance will be described in the description of FIGS. 3 and 4 to be described later.

The calculator 216 calculates a time difference between the m th transmission time measured by the server 110 and the m th transmission time measured by the client 120. Strictly, the operation unit 216 is the 'mth transmission time measured by the server 110' and 'the time when the offset set by the offset setting unit 214 is reflected in the mth transmission time measured by the client 120' Calculates the time difference of.

In addition, the calculation unit 216 assumes that the clock of the client 120 is synchronized with the clock of the server 110, and calculates the m-th one-way delay time using one or more transmission points measured by the time measurement unit 210. do. In this case, each of the transmission time points measured by the client 120 among the transmission time points used is a time point at which an offset set by the offset setting unit 214 is reflected.

More specifically, the calculation unit 216 assumes that the clock of the client 120 is synchronized with the clock of the server 110, calculates k and k + 1st round trip delay times in the server 110, and the client 120. Compute the k-th round trip delay time At this time, the round trip delay time can be expressed by the following equation.

[Equation 5]

R_A_ (k) = t_A_ (k + 1)-t_A_ (k)

R_B_ (k) = t_B_ (k + 1)-t_B_ (k)

R_A_ (k + 1) = t_A_ (k + 2)-t_A_ (k + 1)

Here, R_A_ (k) means the k-th round trip delay time calculated in the server 110, R_B_ (k) means the k-th round trip delay time calculated in the client 120, R_A_ (k + 1) Denotes the k + 1st round trip delay time calculated by the server 110. Meanwhile, in Equation 5, R_A_ (k) should be strictly expressed as Equation 9, but since the difference between t_A_ (k) and t_A_ (k + 1) is very small, R_A_ (k) is also Equation 5 Can be expressed as

[Equation 6]

R_A_ (k) = t_A_ (k + 1)-(The result of integrating S_A_ (t) from t = t_A_ (k) to t = t_A_ (k + 1))-t_A_ (k)

Here, S_A_ (t) means 'difference between the clock frequency of the server 110 and the clock frequency of the client 120' generated over time.

Thereafter, the calculation unit 216 calculates the m-th one-way delay time when the clock of the client 120 is synchronized with the clock of the server 110 using these round trip delay times. This is expressed as the following equation (7).

[Equation 7]

b = [(R_B_ (k)-R_A_ (k)) / (R_A_ (k + 1)-R_A_ (k))] * R_A_ (k)

a = [(R_A_ (k + 1)-R_B_ (k)) / (R_A_ (k + 1)-R_A_ (k))] * R_A_ (k)

b '= [(R_B_ (k)-R_A_ (k)) / (R_A_ (k + 1)-R_A_ (k))] * R_A_ (k + 1)

a '= [(R_A_ (k + 1)-R_B_ (k)) / (R_A_ (k + 1)-R_A_ (k))] * R_A_ (k + 1)

Here, a means the k-th one-way delay time calculated in the server 110, a 'means k + 1st one-way delay time calculated in the server 110, b is calculated in the client 120 The k-th one-way delay time, b 'refers to the k + 1st one-way delay time calculated by the client 120.

Equation 7 described above is derived through Equations 8 to 11 below.

[Equation 8]

J_A_ (k) / J_B_ (k) = a / b = a '/ b'

where,

J_A_ (k) ≡ a '-a

J_B_ (k) ≡ b '-b

Here, J_A_ (k) is called jitter calculated at the server 110 and J_B_ (k) is called jitter calculated at the client 120.

Equation 8 is derived on the assumption that Equation 9 below holds.

[Equation 9]

a / a '= b / b' i.e. a / b = a '/ b'

Meanwhile, the round trip delay time when the clock of the client 120 is synchronized with the clock of the server 110 may be expressed as follows.

[Equation 10]

R_A_ (k) = a + b

R_A_ (k + 1) = a '+ b'

R_B_ (k) = a + b '

This equation (10) is substantially the same as the above equation (5).

Using Equations 9 and 10, the following Equation 11 is derived.

[Equation 11]

a / a '= b / b' = R_A_ (k) / R_A_ (k + 1)

Using the above Equation 11 and the above Equation 10, the above Equation 7 is derived.

As described above, Equation 7 is derived based on the assumption that the clock of the client 120 is synchronized with the clock of the server 110. On the other hand, if the clock of the client 120 is synchronized with the clock of the server 110, the time difference between the m-th transmission time measured by the client 120 and the m-th transmission time measured by the server 110, the operation unit 216 ) Must match the m-th one-way delay time calculated in This is expressed as the following equation (12).

[Equation 12]

b = t_B_ (k)-t_A_ (k)

a = t_A_ (k + 1)-t_B_ (k)

b '= t_B_ (k + 1)-t_A_ (k + 1)

a '= t_A_ (k + 2)-t_B_ (k + 1)

The comparison unit 218 checks whether at least one of the four equations described in Equation 12 is satisfied. In detail, the comparing unit 218 compares the time difference calculated by the calculating unit 216 with the one-way delay time calculated by the calculating unit 216. More specifically, the inspecting unit 218 may check whether the time difference calculated by the calculating unit 216 and the unidirectional delay time calculated by the calculating unit 216 match.

Accordingly, when the time difference calculated by the calculation unit 216 and the one-way delay time calculated by the operation unit 216 are compared, the calculated one-way delay time is' the clock of the client 120 is compared to the clock of the server 110. It is 100% reliable as the one-way delay time between the server 110 and the client 120 when synchronized.

However, even when the time difference calculated in the calculator 216 and the one-way delay time calculated in the calculator 216 match, the calculated one-way delay time is synchronized with the clock of the server 110. Since it is calculated under the assumption that the value is calculated, the one-way delay time between the server 110 and the client 120 that is not actually synchronized with the clock of the server 110 is referred to as the calculated one-way delay time. It cannot be concluded.

However, the one-way delay time between the server 110 and the client 120 whose clock of the client 120 is not actually synchronized with the clock of the server 110 is calculated by the calculation unit 216 and the time difference calculated by the calculation unit 216. It can be estimated that the calculated one-way delay time is equal to or less than the calculated one-way delay time. A detailed description thereof is also disclosed in the description of FIGS. 3 and 4.

Accordingly, in response to the result compared by the comparison unit 218, the delay time estimator 220 may select one of the values equal to or smaller than the one-way delay time calculated by the calculator 216, such that the server 110 and the client ( Unidirectional delay time between &quot; 120 &quot; For example, in response to the result compared by the comparison unit 218, the delay time estimator 220 calculates a medium value of the one-way delay time calculated by the calculator 216 as the server 110 and the client 120. Unidirectional delay time between

Specifically, when the delay time estimator 220 compares that the time difference calculated by the calculator 216 and the one-way delay time calculated by the calculator 216 coincide with each other, the calculator 216. One of the values below the one-way delay time calculated in may be determined as 'one-way delay time between the server 110 and the client 120'. At this time, one of the values less than or equal to the one-way delay time calculated by the operation unit 216 may be sufficient as one of the values less than or equal to, and is not necessarily limited to any particular value of the values less than or equal to.

That is, when "b = t_B_ (k)-t_A_ (k)" is compared in the comparing unit 218, the delay time estimator 220 transmits "one of the values of b or less" to the server 110. Determine as one-way delay time between clients 120. Similarly, when "a = t_A_ (k + 1)-t_B_ (k)" is compared in the comparing unit 218, the delay time estimator 220 returns "any one of the values below a". ) And the one-way delay time between the client 120. Similarly, when "b '= t_B_ (k + 1)-t_A_ (k + 1)" is compared in the comparing unit 218, the delay time estimator 220 determines the value of any one of values below "b'. Is determined as the one-way delay time between the server 110 and the client 120. In the same principle, when "a '= t_A_ (k + 2)-t_B_ (k + 1)" is compared in the comparison unit 218, the delay time estimator 220 may determine any one of values below "a'. Value "is determined as the one-way delay time between the server 110 and the client 120.

However, as a result of the comparison in the comparison unit 218, the k-th one-way delay times (a, b) calculated by the operation unit 216 and the k + 1th one-way delay times (a ', calculated by the operation unit 216). If there are a plurality of one-way delay times satisfying Equation 12 in b '), the comparison unit 218 compares the plurality of one-way delay times with each other to find a minimum value among the plurality of one-way delay times, and adds delay time. The government 220 preferably operates only for the minimum value found. For example, if (i) b, a, b ', and a' all satisfy Equation 12, the comparison unit 218 compares, and (ii) if b among b, a, b ', and a' is the minimum value, the comparison is performed. The unit 218 compares b, a, b ', and a' with each other to find b, the minimum value of b, a, b ', and a', and delays that the minimum value of b, a, b ', and a' is b. The estimator 220 recognizes the delay time, and the delay time estimator 220 determines one of the following values as 'one-way delay time between the server 110 and the client 120'.

Meanwhile, the delay time estimator 220 may estimate the actual offset existing between the clock of the server 110 and the clock of the client 120 that are not synchronized with each other by using the estimated one-way delay time.

The clock adjuster 222 uses the 'unidirectional delay time' estimated by the delay time estimator 220, and more specifically, uses the 'actual offset' estimated using the estimated one-way delay time. The clock of 120 is synchronized with the clock of the server 110.

3 is a diagram illustrating a case in which a clock of the client 120 is synchronized with a clock of the server 110, and illustrates a case in which an offset does not exist between the clock of the server 110 and the clock of the client 120. See also for reference. In FIG. 3, A means server 110, B means client 120, and the meanings of other symbols are already described in the description of FIG. 2.

4 is a diagram illustrating a case where a clock of the client 120 is not synchronized with a clock of the server 110, and illustrates a case where an offset exists between the clock of the server 110 and the clock of the client 120. See also for reference. 4, A means server 110, B means client 120, Ofs (m) means the actual offset included in the m-th transmission time, and other symbols Meaning has already been described in the description of FIG.

As shown in FIG. 4, each of the transmission time points t_BC (k) and t_BC (k + 1) measured at the client 120 exists between the clock of the client 120 and the clock of the server 110. The actual offset Ofs is reflected.

As described above, in the present invention, the actual one-way delay time A, B, A 'between the server 110 and the client 120 when the clock of the client 120 is not synchronized with the clock of the server 110. , B ') is disclosed, and according to the present invention, t_BE_ (k) and t_BE_ (k + 1) can be accurately estimated. Meanwhile, for convenience of description, in the present specification, a positive offset means an offset when t_BC_ (k) is larger than t_BE_ (k) as shown in FIG. 4, and a negative offset is different from that shown in FIG. 4. It means an offset when t_BC_ (k) is smaller than t_BE_ (k).

Specifically, the comparison unit 218 checks that Equation 12 is satisfied for a and b. If the actual offset Ofs (k) is a positive offset, the delay time estimation unit 220 determines that B is smaller than b. We can assume that we have some value and A has some value greater than a.

Similarly, the comparator 218 checks that Equation 12 is satisfied with respect to a 'and b', and if the actual offset Ofs (k + 1) is a positive offset, the delay time estimator 220 is B '. Can be assumed to have some value less than b 'and A' to have some value greater than a '.

That is, since the delay estimator 220 estimates the one-way delay time between the server 110 and the client 120 to be less than or equal to the one-way delay time calculated by the calculator 216, the estimated one-way delay time is 'server'. The time required for the ICMP packet to be transmitted from the client 110 to the client 120 may be used, or the time required to transmit the ICMP packet from the client 120 to the server 110 may be used. Specifically, as shown in FIG. 4, if the actual offset is positive, the estimated one-way delay time may mean an estimated time of 'time taken for the ICMP packet to be transmitted from the server 110 to the client 120'. Unlike in FIG. 4, if the actual offset is negative, the estimated one-way delay time means an estimated time of 'time taken for the ICMP packet to be transmitted from the client 120 to the server 110'.

On the other hand, as shown in FIG. 4, if the actual offset is positive, the delay time estimator 220 may estimate that a value smaller than b (or b ') is B (or B'). In this case, the delay time estimator 220 estimates the actual offset as follows.

[Equation 13]

ofs_estim = min [b, b '] / 2 where Ofs> 0

ofs_estim =-min [a, a '] / 2 where Ofs <0

Here, Ofs means an actual offset, and ofs_estim means an estimated offset.

As a result, the error E_ofs that the estimated offset ofs_estim may have may be obtained by subtracting the estimated offset ofs_estim from the actual offset Ofs. This is expressed as the following equation (14).

[Equation 14]

| E_ofs | ≤ min [b, b '] / 2 where Ofs> 0

| E_ofs | ≤ min [a, a '] / 2 where Ofs <0

As such, the one-way delay time estimated by the delay time estimator 220 may vary depending on whether the actual offset is positive or negative. However, since there is no method of checking whether the actual offset (Ofs) is positive or negative, the offset setting unit 214 intentionally sets the offset (α, or β) at the transmission time measured by the client 120 To reflect.

5 is a reference diagram for explaining the ICMP packet 500 exchanged between the server 110 and the client 120 according to the present invention. The ICMP packet 500 shown in FIG. 5 is an ICMP packet of Type 13 or 14 defined in the RFC document. Specifically, the packet exchanged between the server 110 and the client 120 is an ICMP packet defined in the RFC document, the ICMP packet according to Type 13 is transmitted from the client 120 to the server 110, the server 110 In the client 120, an ICMP packet according to Type 14 is transmitted.

6 is a flowchart for explaining a one-way delay estimation method according to the present invention. Even if a client and a server cannot be provided with the same timing information, FIG. Steps 610 to 624 to accurately synchronize to the clock of FIG.

The time measuring unit 210 measures t_A_ (k), t_B_ (k), t_A_ (k + 1), t_B_ (k + 1), and t_A_ (k + 2) (step 610), error detection and The correction unit 212 determines whether there is a missing part in the ICMP packet exchanged between the server 110 and the client 120 (step 612), and if it is determined that the missing part exists, restores the lost part. (Step 614).

After step 614 or after it is determined in step 612 that no part is lost in the ICMP packet, the offset setting unit 214 determines the time indicated by the clock of the server 110 and the time indicated by the clock of the client 120. A positive offset or a negative offset is intentionally set in the liver (step 616). At this time, whether to set a positive offset or a negative offset may be specified by the user.

After operation 616, the operation unit 216 calculates a time difference between t_A_ (m) and t_B_ (m), and the server 110 and the client when the clock of the client 120 is synchronized with the clock of the server 110. The m-th one-way delay time is calculated as one-way delay time between steps 120 (step 618).

After operation 618, the comparator 218 determines whether the time difference calculated in operation 618 matches the one-way delay time calculated in operation 618 (operation 620).

If it is determined in step 620 that the match time, the delay time estimator 220 is a one-way delay time between the server 110 and the client 120 when the clock of the client 120 is not synchronized with the clock of the server 110 Is determined as one of values less than or equal to the one-way delay time calculated in operation 618 (operation 622).

After operation 622, the clock adjuster 222 synchronizes the clock of the client 120 with the clock of the server 110 using the unidirectional delay time determined in operation 622 (operation 624).

The program for executing the above-mentioned one-way delay time estimation method according to the present invention on a computer may be stored in a computer-readable recording medium. Here, the computer-readable recording medium may be a magnetic storage medium (for example, a ROM, a floppy disk, a hard disk, etc.), and an optical reading medium (for example, a CD-ROM, a DVD). : Digital Versatile Disc).

So far, the present invention has been described with reference to the preferred embodiments. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

1 is a diagram illustrating a server and a client connected to a network.

2 is a block diagram illustrating a one-way delay time estimation apparatus according to the present invention.

3 is a reference diagram for describing a case where a clock of a client is synchronized with a clock of a server.

4 is a reference diagram for explaining a case where a clock of a client is not synchronized with a clock of a server.

5 is a reference diagram for explaining an example of an ICMP packet exchanged between a server and a client according to the present invention.

6 is a flowchart for explaining a one-way delay time estimation method according to the present invention.

Claims (5)

Measuring a transmission time of the ICMP packet at a client and a server which transmits and receives an ICMP packet to and from the client according to a standard IP protocol; Calculating a time difference between a transmission time measured by the server and a transmission time measured by the client, and calculating a one-way delay time between the server and the client when the clock of the client is synchronized with the clock of the server; Determining whether the calculated time difference coincides with the calculated one-way delay time; And If it is determined that the calculated time difference coincides with the calculated one-way delay time, determining one of the values below the calculated one-way delay time as a one-way delay time between the server and the client. Estimation method. The method of claim 1, wherein the determining comprises: determining the median value of the calculated one-way delay time as a one-way delay time between the server and the client when it is determined that the calculated time difference coincides with the calculated one-way delay time. One-way delay time estimation method. The method of claim 1, wherein the unidirectional delay time estimation method And synchronizing a clock of the client to a clock of the server by using the determined one-way delay time. The method of claim 1, wherein the server and the client exchanges the ICMP packet a plurality of times, The measuring may include measuring k (where k is a natural number), k + 1 and k + 2th transmission time points of the ICMP packet at the server, and k and k + 1th transmission of the ICMP packet at the client. To measure the view point, The calculating may include calculating a time difference between the mth transmission time measured by the server (where m is one of k to k + 2) and the mth transmission time measured by the client, and the clock of the client is Calculate an m-th one-way delay time between the server and the client when synchronized to the server's clock, The determining may include determining whether the calculated time difference coincides with the calculated m-th one-way delay time. The determining may include determining whether the calculated time difference coincides with the calculated m-th one-way delay time, and converting one of the values below the calculated m-th one-way delay time to the one-way delay time between the server and the client. One-way delay time estimation method to determine. A time measuring unit for measuring a transmission point of the ICMP packet at a client and a server receiving and receiving an ICMP packet according to a standard IP protocol; A calculation unit calculating a time difference between a transmission time measured by the server and a transmission time measured by the client, and calculating a one-way delay time between the server and the client when the clock of the client is synchronized with the clock of the server; A comparison unit comparing the calculated time difference with the calculated one-way delay time; And And a delay time estimator configured to determine, as a unidirectional delay time between the server and the client, one of values calculated below the calculated one-way delay time in response to the comparison result.

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