CN109756391B - Time delay information measuring method of switching network - Google Patents
Time delay information measuring method of switching network Download PDFInfo
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- CN109756391B CN109756391B CN201811526623.7A CN201811526623A CN109756391B CN 109756391 B CN109756391 B CN 109756391B CN 201811526623 A CN201811526623 A CN 201811526623A CN 109756391 B CN109756391 B CN 109756391B
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Abstract
The invention belongs to the technical field of vehicle-mounted information networks, and particularly relates to a method for measuring delay information in an exchange type vehicle-mounted data network. The method is divided into an initialization process, a delay estimation process, a measurement process and a calculation and storage process. The scheme is based on a switched network, data packets and time-containing information data packets are interacted between the tested devices by using the measuring equipment, the receiving and sending time information is recorded, and the delay time of data transmission between the tested devices and the synchronous difference between the tested devices are calculated. The invention has the advantages that the data transmission delay time between two tested devices can be monitored in the switched network, the transmission jitter time is further calculated, the synchronous state between the tested devices is monitored, and the network and time level support is provided for developing, debugging and measuring the vehicle-mounted information network.
Description
Technical Field
The invention belongs to the technical field of vehicle-mounted information networks, and particularly relates to a method for measuring delay information in an exchange type vehicle-mounted data network.
Background
At present, in the development, debugging and testing stages of software and hardware of vehicle-mounted equipment, because vehicle-mounted nodes need to continuously transmit and receive information through a network, data measurement and monitoring are necessary to be carried out on a network level. The current common delay information measurement mode based on the bus is as follows: and (3) accessing the vehicle-mounted bus by using special equipment, monitoring and recording all data passing through the bus, and analyzing and calculating the recorded data by using secondary developed software and the like.
Data transmission of a switching network such as an ethernet network cannot simply record data of all networks because of the need of passing through a switch, and a measurement mode of delay data is generally completed by a time synchronization protocol or an algorithm (such as NTP, PTP, etc.) therein, for example: after all network nodes are synchronized to a reference clock by using the NTP or PTP protocol, a delay value can be obtained through the difference between the sending time and the receiving time, or the delay of information transmission among 2 nodes in the system is calculated through a delay estimation algorithm in the NTP, PTP and other clock synchronization protocols.
The disadvantages of these methods are: firstly, establishing clock synchronization of nodes of the whole network is technically complex, and software and hardware equipment with higher cost are required to be used; secondly, if the clock synchronization technology of the nodes of the whole network is not used, the test between every two test nodes needs to be carried out in the test mode, and normal network communication cannot be carried out in the test process.
Therefore, how to overcome the defect that the switch of the existing switching network cannot completely measure the information, the transmitting and receiving time and the synchronization state of the whole network becomes a direction of important attention of the vehicle-mounted switching network.
Disclosure of Invention
Technical problem to be solved
The technical problem to be solved by the invention is as follows: how to provide a delay information measuring method of a switching network without establishing full network node synchronization in advance is required to measure the time when a sending end sends information and the time when a receiving end receives information in a vehicle-mounted network under a normal working mode, the transmission delay of the information and the synchronization state (clock difference between nodes) of concerned nodes in the network can be effectively measured.
(II) technical scheme
In order to solve the above technical problem, the present invention provides a method for measuring delay information in an exchange type synchronous vehicle-mounted data network, comprising the following steps:
step S1: initializing the process;
accessing a measuring device into the switched synchronous vehicle-mounted data network, and obtaining a set of tested devices to be measured through information interaction;
step S2: a delay estimation process;
the measuring equipment sends a time-containing information request data packet to the tested equipment, then receives the time-containing information data packet returned by the tested equipment, and records: the method comprises the following steps that a first sending moment when a measuring device sends a time-containing information request data packet to a tested device, a first receiving moment when the tested device receives the time-containing information request data packet sent by the measuring device, a second sending moment when the tested device sends the time-containing information data packet to the measuring device, and a second receiving moment when the measuring device receives the time-containing information data packet sent by the tested device; estimating the transmission delay time according to the recorded moments;
step S3: applying a packet transmission delay measurement process;
this stage determines 2 devices under test, respectively a first device under test and a second device under test, the measured amount of time comprising: the first tested device sends the third sending moment of the application data packet to the second tested device; the second tested device receives a third receiving moment of the application data packet; the first time-containing data packet sending time sent to the measuring equipment by the first tested equipment; the second time-containing data packet sending time sent to the measuring equipment by the second tested equipment; the measuring equipment receives a first time-containing data packet receiving moment of a time-containing data packet sent by first measured equipment; the measuring equipment receives a second time-containing data packet receiving moment of the time-containing data packet sent by the second measured equipment;
step S4: a calculation and storage process;
and calculating the transmission delay time between the network nodes by using each time measured in the delay estimation process and each time measured in the application data packet transmission delay measurement process, calculating the clock difference between the first tested equipment and the second tested equipment by using each time obtained in the delay estimation process of the first tested equipment and the second tested equipment, and storing the calculation result and the measurement data.
In the initialization process of step S1, the measurement device is an additional device that is accessed to the vehicle switched network.
In the initialization process of step S1, the measuring device is an existing end node or switch in the switched network.
In the delay estimation process of step S2, the estimation method of the transmission delay time is: the measuring equipment sends a time-containing information request data packet to the measured equipment and records a first sending moment; the tested device returns the data packet to the measuring device after receiving the data packet, wherein the time-containing information data packet comprises a first receiving time when the tested device receives the time-containing information request data packet and a second sending time when the tested device sends the time-containing information data packet; and recording the second receiving time of the time-containing information data packet by the measuring equipment, and subtracting the difference between the second receiving time and the first receiving time contained in the time-containing information data packet by the measuring equipment to obtain the double of the estimated value of the transmission delay time.
Wherein, in the calculation and storage process of step S4, the transmission delay time is obtained by repeating the delay estimation process of step S2.
In the calculation and storage process of step S4, the clock difference between the devices under test is obtained by making a difference between the reference times of the two devices under test.
Wherein, the reference time of the device under test refers to: after the delay estimation process in step S2, in the time-containing information data packet obtained by the measurement device, the local time of the device under test that receives the time-containing information request data packet by the device under test subtracts the transmission delay time between the measurement device and the device under test to obtain the time.
(III) advantageous effects
The technical scheme of the invention comprises an initialization process, a delay estimation process, a measurement process and a calculation and storage process. The scheme is based on a switched network, data packets and time-containing information data packets are interacted between the tested devices by using the measuring equipment, the receiving and sending time information is recorded, and the delay time of data transmission between the tested devices and the synchronous difference between the tested devices are calculated.
The invention has the advantages that the data transmission delay time between the tested devices can be monitored in the switched network, the transmission jitter time is further calculated, the synchronous state between the tested devices is monitored, and the network and time level support is provided for developing, debugging and measuring the vehicle-mounted information network.
Drawings
FIG. 1 is a flow chart of a method according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of an embodiment of the present invention.
Fig. 3 is a schematic diagram of the delay estimation process of the present invention.
FIG. 4 is a schematic diagram of measuring and calculating propagation delay time according to the present invention.
FIG. 5 is a schematic diagram of the clock difference between the measured and calculated devices of the present invention.
In the figure: 1. a device under test A; 2. a switch; 3. a measuring device B; 4. a device under test C;
5. a device under test C;
6. time T of sending data packet by measuring equipment BB0；
7. Time T when the tested device A receives the data packetA0；
8. Time T when tested device A sends data packetA1；
9. Time T when measuring equipment B receives data packetB1；
10. Time T when tested device A sends data packetAC；
11. Time T when tested device A sends data packetAB；
12. Time T when measuring equipment B receives data packetBA；
13. Moment T of receiving data packet by tested device CCA；
14. Time T when tested device C sends data packetCB；
15. Time T when measuring equipment B receives data packetBC；
16. Reference time T of tested equipment AA(ii) a 17. Reference time T of tested device CC；
18. Number of transmissions from measuring device BTime T of packetB1；
19. Moment T of receiving data packet by tested device CC0；
20. Time T when tested device C sends data packetC1；
21. Time T when measuring equipment B receives data packetBC1。
Detailed Description
In order to make the objects, contents, and advantages of the present invention clearer, the following detailed description of the embodiments of the present invention will be made in conjunction with the accompanying drawings and examples.
In order to solve the problems of the prior art, the invention provides a method for measuring delay information in an exchange type synchronous vehicle-mounted data network, which comprises the following steps:
step S1: initializing the process;
accessing a measuring device into the switched synchronous vehicle-mounted data network, and obtaining a set of tested devices to be measured through information interaction;
step S2: a delay estimation process;
the measuring equipment sends a time-containing information request data packet to the tested equipment, then receives the time-containing information data packet returned by the tested equipment, and records: the method comprises the following steps that a first sending moment when a measuring device sends a time-containing information request data packet to a tested device, a first receiving moment when the tested device receives the time-containing information request data packet sent by the measuring device, a second sending moment when the tested device sends the time-containing information data packet to the measuring device, and a second receiving moment when the measuring device receives the time-containing information data packet sent by the tested device; estimating the transmission delay time according to the recorded moments;
step S3: applying a packet transmission delay measurement process;
this stage determines 2 devices under test, respectively a first device under test and a second device under test, the measured amount of time comprising: the first tested device sends the third sending moment of the application data packet to the second tested device; the second tested device receives a third receiving moment of the application data packet; the first time-containing data packet sending time sent to the measuring equipment by the first tested equipment; the second time-containing data packet sending time sent to the measuring equipment by the second tested equipment; the measuring equipment receives a first time-containing data packet receiving moment of a time-containing data packet sent by first measured equipment; the measuring equipment receives a second time-containing data packet receiving moment of the time-containing data packet sent by the second measured equipment;
step S4: a calculation and storage process;
and calculating the transmission delay time between the network nodes by using each time measured in the delay estimation process and each time measured in the application data packet transmission delay measurement process, calculating the clock difference between the first tested equipment and the second tested equipment by using each time obtained in the delay estimation process of the first tested equipment and the second tested equipment, and storing the calculation result and the measurement data.
In the initialization process of step S1, the measurement device is an additional device that is accessed to the vehicle switched network.
In the initialization process of step S1, the measuring device is an existing end node or switch in the switched network.
In the delay estimation process of step S2, the estimation method of the transmission delay time is: the measuring equipment sends a time-containing information request data packet to the measured equipment and records a first sending moment; the tested device returns the data packet to the measuring device after receiving the data packet, wherein the time-containing information data packet comprises a first receiving time when the tested device receives the time-containing information request data packet and a second sending time when the tested device sends the time-containing information data packet; and recording the second receiving time of the time-containing information data packet by the measuring equipment, and subtracting the difference between the second receiving time and the first receiving time contained in the time-containing information data packet by the measuring equipment to obtain the double of the estimated value of the transmission delay time.
Wherein, in the calculation and storage process of step S4, the transmission delay time is obtained by repeating the delay estimation process of step S2.
In the calculation and storage process of step S4, the clock difference between the devices under test is obtained by making a difference between the reference times of the two devices under test.
Wherein, the reference time of the device under test refers to: after the delay estimation process in step S2, in the time-containing information data packet obtained by the measurement device, the local time of the device under test that receives the time-containing information request data packet by the device under test subtracts the transmission delay time between the measurement device and the device under test to obtain the time.
Example 1
In this embodiment, as shown in fig. 1, in a switched network including three nodes, 2 switches and A, C, D, it is determined through an initialization process S1 that B is a measurement device, A, C is 2 devices under test, and a node D does not participate in the measurement process, and the content of the test includes the delay time for a to send a packet to a node C and the clock difference between the node a and the node C.
As shown in fig. 2, the delay estimation process S2 consists of the following 5 steps:
1. and the measuring equipment in the measuring equipment sends a time-containing information request data packet to the tested equipment. T in FIG. 2B0Representing the sending time of the time-containing information request data packet sent by the measuring equipment to the tested equipment;
2. the tested device receives the time-containing information request data packet sent by the measuring device. T in FIG. 2A0Representing the time when the time-containing information request data packet sent by the measuring equipment is received by the measuring equipment;
3. and the tested device sends a time-containing information data packet to the measuring device. T in FIG. 2A1Representing the time when the measured equipment sends the time-containing information data packet to the measuring equipment;
4. the measuring equipment receives a time-containing information data packet sent by the tested equipment to the measuring equipment. T in FIG. 2BA1Representing the time when the measuring equipment receives the time-containing information data packet sent by the tested equipment;
5. the measuring device estimates the transmission delay t between the measuring device and the device under test according to the following equation (1)AB(or t)BA)；
tAB＝(TBA1-TA1+TB0-TA0)/2 (1)
Wherein the device under test A will TA0And TA1And sending the time-containing information data packet to the measuring equipment B. Wherein equation (1) is also used to estimate the transmission delay between other devices under test and the measurement device, e.g. the delay t between the measurement device B and the device under test CBC(or t)CB)。
It is worth pointing out that the estimation of the transmission delay between the measurement device and the device under test by the measurement device can be obtained by performing the above 1-5 steps once, or by repeating the above 1-5 steps for multiple times to obtain tABAnd averaged to obtain the average value.
As shown in fig. 3, the time when the device under test itself sends a packet to the network in the packet transmission delay measurement process S3 is applied, and the time when the device under test receives a packet from the network is determined by the following method:
1. when the source device under test sends a data packet to the destination device under test in the network (a sends a data packet to C in fig. 3), the source device under test sends a data packet of the transmitting/receiving state to the measuring device. The information contained in the receiving and sending state data packet is as follows: the source tested device A sends a data packet to the device C, the network address of the destination C of the data packet, and the sending time of the data packet, and also comprises the sending time of a transmitting and receiving state data packet sent by the source tested device to the measuring device. T in FIG. 3ACTime, T, representing the moment at which device A sends a data packet to device CABRepresenting the time when the measured device A sends a data packet to the measured device B;
2. the measuring equipment receives a transceiving state data packet sent by the source tested equipment to the measuring equipment. T in FIG. 3BARepresenting the moment when the measuring equipment B receives the data packet of the tested equipment A;
3. and the target tested device receives the data packet sent by the source tested device. T in FIG. 3CARepresenting the moment when the tested device C receives the data packet of the tested device A;
4. and the target tested equipment sends a data packet of the transmitting and receiving state to the measuring equipment. In which transceiving is performedThe status packet contains information such as: the destination tested device C receives a data packet from a, the source network address of the data packet, the time when the destination tested device C receives the data packet, and the time when the destination tested device C transmits the transmit-receive state data packet. T in FIG. 3CBRepresenting the time when the measured device C sends a data packet to the measured device B;
5. and the measuring equipment receives the time-containing information data packet sent to the measuring equipment by the target tested equipment C. T in FIG. 3BCRepresenting the moment when the measuring equipment B receives the data packet sent by the tested equipment C;
after the above 5 steps of the application packet transmission delay measurement process S3, the data obtained in the measurement device includes: t isAC、TAB、TBA、TCA、TCB、TBC。
The calculation process S4 calculates the delay of a to C transmission of a packet according to the following equation (2):
tAC＝TBC-[TBA-tAB-(TAB-TAC)]-tBC-(TCB-TCA) (2)
t in formula (2)BCDenotes the data transmission delay between the device under test C and the measuring device B, tBCAnd tABMay be obtained by the delay estimation process S2.
As shown in fig. 4, the clock difference between the devices under test in the application packet transmission delay measurement process S3 is determined by the following method:
1. the measuring equipment sends a time-containing information request data packet to all the tested equipment. T in FIG. 4B0、TB1Representing the sending time of the time-containing information request data packet sent by the measuring equipment to the 2 tested equipment;
2. the tested device receives the time-containing information request data packet sent by the measuring device. T in FIG. 4A0Time, T, representing the time at which the device A receives the time-containing information request packetC0Representing the time when the time-containing information request data packet is received by the tested device C;
3. the tested device sends a time-containing information data packet to the measuring device. T in FIG. 4A1Time, T, representing the moment at which the device A sends a packet containing time information to the device BC1Representing the time when the time-containing information data packet is sent to the measuring equipment B by the measuring equipment C;
4. the measuring equipment receives a time-containing information data packet sent by the tested equipment to the measuring equipment. T in FIG. 4BA1Representing the moment T at which the measuring device B receives the time-containing information packet sent by the device A to be testedBC1Representing the time when the measuring equipment B receives the time-containing information data packet sent by the tested equipment C;
and the target tested equipment sends a data packet of the transmitting and receiving state to the measuring equipment. The information contained in the receiving and sending state data packet is as follows: the target tested device receives a data packet, the source network address of the data packet, the time when the target tested device receives the data packet, and the time when the target tested device sends the receiving and sending state data packet. T in FIG. 4CSRepresenting the time when the measured device C sends a data packet to the measured device B;
after the application packet transmission delay measurement process S3 goes through the above 4 steps, the data obtained in the measurement device includes: t isB0、TB1、TA0、TC0、TA1、TC1、TBA1、TBC1。
The calculation process S4 calculates the reference time T of the device under test a according to the following expression (3)A：
TA＝TA0-tAB (3)
T in formula (3)ABCalculated by the formula (1). Wherein, tABMay be obtained by the delay estimation process S2 or may be obtained by the calculation process S4 using T after the above 4 stepsB0、TA0、TA1、TBA1Recalculated by the formula (1).
The calculation process S4 calculates the reference time T of the device under test C according to the following expression (4)C：
TC＝TC0-tBC-|TB1-TB0| (4)
T in formula (4)BCCalculated by the formula (1)And (4) obtaining. Wherein, tBCMay be obtained by the delay estimation process S2 or may be obtained by the calculation process S4 using T after the above 4 stepsB1、TC0、TC1、TBC1Recalculated by the formula (1).
The calculation process S4 calculates the clock difference Δ t between the device under test a and the device under test C according to the following expression (5)AC：
ΔtAC＝TA-TC (5)
The real-time example provided herein only calculates the clock difference value between two tested devices, and when the clock difference values between a plurality of different tested devices need to be calculated, the reference times of the plurality of tested devices can be calculated for comparison, or the clock difference values between each device can be calculated after pairwise comparison.
The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (7)
1. A method for measuring delay information in a switched synchronous vehicle-mounted data network is characterized by comprising the following steps:
step S1: initializing the process;
accessing a measuring device into the switched synchronous vehicle-mounted data network, and obtaining a set of tested devices to be measured through information interaction;
step S2: a delay estimation process;
the measuring equipment sends a time-containing information request data packet to the tested equipment, then receives the time-containing information data packet returned by the tested equipment, and records: the method comprises the following steps that a first sending moment when a measuring device sends a time-containing information request data packet to a tested device, a first receiving moment when the tested device receives the time-containing information request data packet sent by the measuring device, a second sending moment when the tested device sends the time-containing information data packet to the measuring device, and a second receiving moment when the measuring device receives the time-containing information data packet sent by the tested device; estimating the transmission delay time according to the recorded moments;
the measurement device B estimates the transmission delay t between the measurement device B and the device under test according to the following formula (1)ABOr tBA；
tAB＝(TBA1-TA1+TB0-TA0)/2 (1)
Wherein, TB0The sending time of the time-containing information request data packet, namely the first sending time, is sent to the tested device by the representative measuring device B; t isA0Representing the moment when the time-containing information request data packet is received by the tested device, namely the first receiving moment; t isA1Representing the time when the measured equipment sends the time-containing information data packet to the measuring equipment B, namely the second sending time; t isBA1Representing the time when the measuring equipment B receives the time-containing information data packet sent by the tested equipment, namely the second receiving time;
wherein the device under test will TA0And TA1Sending the time-containing information data packet to a measuring device B; wherein, the formula (1) is also used for estimating the transmission delay t between other tested devices and the measuring device BBCOr tCB(ii) a Wherein A and C are both tested equipment;
step S3: applying a packet transmission delay measurement process;
this stage determines 2 devices under test, respectively a first device under test and a second device under test, the measured amount of time comprising: the first tested device sends the third sending moment of the application data packet to the second tested device; the second tested device receives a third receiving moment of the application data packet; the first time-containing data packet sending time sent to the measuring equipment by the first tested equipment; the second time-containing data packet sending time sent to the measuring equipment by the second tested equipment; the measuring equipment receives a first time-containing data packet receiving moment of a time-containing data packet sent by first measured equipment; the measuring equipment receives a second time-containing data packet receiving moment of the time-containing data packet sent by the second measured equipment;
step S4: a calculation and storage process;
calculating the transmission delay time between the network nodes by using each time measured in the delay estimation process and each time measured in the application data packet transmission delay measurement process, calculating the clock difference between the first tested device and the second tested device by using each time obtained in the delay estimation process of the first tested device and the second tested device respectively, and storing the calculation result and the measurement data;
in the application packet transmission delay measurement process S3, the time when the device under test itself sends a packet to the network is determined by the following method:
firstly, when source tested equipment sends a data packet to target tested equipment in a network, sending the data packet in a receiving and sending state to the measuring equipment; the information contained in the receiving and sending state data packet is as follows: the source tested device A sends a data packet to the source tested device C, the network address of the destination C of the data packet, the sending time of the data packet and the sending time of a receiving and sending state data packet sent to the measuring device by the source tested device;
receiving a receiving and sending state data packet sent to the measuring equipment by the source measured equipment by the measuring equipment;
receiving a data packet sent by source tested equipment by destination tested equipment;
transmitting a data packet of a receiving and sending state to the measuring equipment by the target equipment to be measured; the information contained in the receiving and sending state data packet is as follows: the target tested device C receives a data packet from the A, the source network address of the data packet, the moment when the target tested device C receives the data packet and the moment when the target tested device C sends a receiving and sending state data packet;
the measuring equipment receives a time-containing information data packet sent by the target tested equipment C to the measuring equipment;
after the above 5 steps of the application packet transmission delay measurement process S3, the data obtained in the measurement device includes: t isAC、TAB、TBA、TCA、TCB、TBC(ii) a Wherein, TACTime, T, representing the moment at which device A sends a data packet to device CABIs represented byThe moment when the measurement equipment A sends the data packet to the measurement equipment B; t isBARepresenting the moment when the measuring equipment B receives the data packet of the tested equipment A; t isCARepresenting the moment when the tested device C receives the data packet of the tested device A; t isCBRepresenting the time when the measured device C sends a data packet to the measured device B; t isBCRepresenting the moment when the measuring equipment B receives the data packet sent by the tested equipment C;
the calculation and storage procedure S4 calculates the delay of a sending a packet to C according to the following equation (2):
tAC＝TBC-[TBA-tAB-(TAB-TAC)]-tBC-(TCB-TCA) (2)
t in formula (2)BCRepresenting the data transmission delay between the device under test C and the measuring device B; wherein, tABRepresenting the transmission delay between the measuring device B and the device under test a;
the clock difference between the devices under test in the application packet transmission delay measurement process S3 is determined by the following method:
firstly, the measuring equipment sends a time-containing information request data packet to all the tested equipment;
receiving a time-containing information request data packet sent by the measuring equipment by the tested equipment;
thirdly, the tested equipment sends a time-containing information data packet to the measuring equipment;
receiving a time-containing information data packet sent to the measuring equipment by the measuring equipment;
the target tested equipment sends a data packet of a receiving and sending state to the measuring equipment; the information contained in the receiving and sending state data packet is as follows: the target tested equipment receives a data packet, the source network address of the data packet, the moment when the target tested equipment receives the data packet and the moment when the target tested equipment sends a receiving and sending state data packet;
after the application packet transmission delay measurement process S3 goes through the above 4 steps, the data obtained in the measurement device includes: t isB0、TB1、TA0、TC0、TA1、TC1、TBA1、TBC1(ii) a Wherein, TB0、TB1The sending time of the time-containing information request data packet is sent to 2 tested devices A and C by the representative measuring device B; t isA0Time, T, representing the time at which the device A receives the time-containing information request packetC0Representing the time when the time-containing information request data packet is received by the tested device C; t isA1Time, T, representing the moment at which the device A sends a packet containing time information to the device BC1Representing the time when the time-containing information data packet is sent to the measuring equipment B by the measuring equipment C; t isBA1Representing the moment T at which the measuring device B receives the time-containing information packet sent by the device A to be testedBC1Representing the time when the measuring equipment B receives the time-containing information data packet sent by the tested equipment C;
the calculation and storage process S4 calculates the reference time T of the device under test a according to the following expression (3)A：
TA＝TA0-tAB (3)
T in formula (3)ABCalculated by formula (1);
the calculation and storage process S4 calculates the reference time T of the device under test C according to the following expression (4)C：
TC＝TC0-tBC-|TB1-TB0| (4)
T in formula (4)BCCalculated by formula (1);
the calculation and storage process S4 calculates the clock difference Δ t between the device under test a and the device under test C according to the following expression (5)AC：
ΔtAC＝TA-TC (5)。
2. The method for measuring delay information in the switched synchronous vehicular data network as claimed in claim 1, wherein in the initialization process of step S1, the measuring device is an additional device accessed to the vehicular switched network.
3. The method for measuring delay information in the switched synchronous vehicular data network as claimed in claim 1, wherein in the initialization process of step S1, the measuring device is an existing terminal node or switch in the switched synchronous vehicular data network.
4. The method for measuring delay information in a switched synchronous vehicle-mounted data network as claimed in claim 1, wherein in the delay estimation process of step S2, the estimation method for the transmission delay time is: the measuring equipment sends a time-containing information request data packet to the measured equipment and records a first sending moment; the tested device returns the data packet to the measuring device after receiving the data packet, wherein the time-containing information data packet comprises a first receiving time when the tested device receives the time-containing information request data packet and a second sending time when the tested device sends the time-containing information data packet; and recording the second receiving time of the time-containing information data packet by the measuring equipment, and subtracting the difference between the second receiving time and the first receiving time contained in the time-containing information data packet by the measuring equipment to obtain the double of the estimated value of the transmission delay time.
5. The method for measuring delay information in a switched synchronous vehicular data network as claimed in claim 1, wherein in the calculating and storing of step S4, the transmission delay time is obtained by repeating the delay estimation process of step S2.
6. The method for measuring delay information in switched synchronous vehicle-mounted data network according to claim 1, wherein in the calculating and storing process of step S4, the clock difference between the devices under test is obtained by making difference between the reference time of two devices under test.
7. The method for measuring delay information in the switched synchronous vehicle-mounted data network according to claim 6, wherein the reference time of the device under test is: after the delay estimation process in step S2, in the time-containing information data packet obtained by the measurement device, the local time of the device under test that receives the time-containing information request data packet by the device under test subtracts the transmission delay time between the measurement device and the device under test to obtain the time.
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