CN107634813B - The complete trails method for synchronizing time of software definition in information centre's smart grid - Google Patents
The complete trails method for synchronizing time of software definition in information centre's smart grid Download PDFInfo
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Abstract
The present invention provides a kind of complete trails method for synchronizing time of software definition in information centre's smart grid, in the cache routing based on name, utilize two functional modules of interest table (PIT) and forwarding information table FIB undetermined in cache routing device, the same paths that data packet is reached from interest packet return, all nodes on the paths realize that one is subsynchronous, time synchronization process is managed by SDN controller simultaneously, thus balance efficiency and accuracy on catenet.The method of the present invention introduces the method for software definition to realize the flexibility in extensive smart grid, controllability and reliability.
Description
Technical field
The present invention relates to a kind of complete trails method for synchronizing time of software definition in information centre's smart grid.
Background technique
Smart grid is developed based on traditional power grid, generally according to power generation, transmission of electricity, distribution and this four portions of Electric control
Divide and is managed.Compared with traditional power grid, smart grid is created by two-way flow to break one-way flow and concentrate hair
The limitation of electricity, and since distributed energy smart grid also gradually develops to distributed network.With from centrally connected power supply system
It unites to more decentralized system transformation, it is contemplated that the demand in small distributed power plant, smart grid is changing, control
Complexity processed improves.The characteristics of infrastructure promising as future electrical energy power grid, smart grid is by mentioning
High efficiency, reliability and safety and automation control and modern communication technology, such as wireless network, ICN and SDN meet electricity
Net new requirement.
Each step in information centre's smart grid, such as generate electricity, distribution, consumption electric power be all it is interrelated, interact.
Because all there is information exchange in cache routing device and user side and grid side.Therefore in the information in heart smart grid, cache way
By device needs, there are also power grid entities all to keep synchronous with user's side gusset, the basic demand with complete trails time synchronization.In addition,
Smart grid abandons centralized control, and the decision in power grid and control are based on multiple path cache routing devices and grid equipment.Cause
This, the data delivery in smart grid entity and path between cache routing device results in the requirement of complete trails time synchronization.However,
Existing Time Synchronizing is all based on IP network, they are not directly applicable ICN, it is most important that they are not supported entirely
Path time is synchronous.Cache routing device in ICN can carry out content memory buffers and reusing data Bao Bingyu smart grid is real
Body interacts, different from IP network.On the other hand, existing Time Synchronizing is in large-scale flexible and dynamic and intelligent electricity
Lack comprehensive time synchronization Managed Solution on the net.SDN has been incorporated into dynamic and spirit to realize information centre's smart grid
Activity.
Because ICN (information centre's network) is using data are named rather than IP address, it directly can search and obtain base
In the information of package name, if the data of request are buffered and effective, user can obtain from neighbouring caching
Data packet.On the other hand, due to decoupling, software-defined network reality in large scale network of data plane and control plane
Show flexibly, dynamic control and management.Therefore, ICN provides efficient data transmission, while SDN increases the network architecture
Flexibility.As emerging network mode, ICN and SDN have been applied to smart grid, this is a research hotspot problem.
Firstly, the performance of smart grid can be improved using ICN in smart grid.The separation of information and position increases
The safety of smart grid, the cache routing device in information centre's smart grid provide efficient data transmission and energy distribution.
Information centre's smart grid communications framework, the communication between smart grid entity is supported using publish/subscribe normal form, to utilize
Advantage of the ICN in terms of flexibility.In addition, power grid abnormal conditions, this normal form can be by being simply reconfigured to effectively
Ground processing.
Secondly, SDN frame is possible to solve many challenges that smart grid is encountered in electric power and communication aspects.Use SDN
Frame makes to control plane and data planar separation, the simple forwarding device and Logical central control device of realization.It grinds at present
Study carefully the dynamic management for proposing the smart grid frame based on SDN to realize smart grid.In addition, also having there is document to propose
The design of ICN framework in SDN frame, the advantages of ICN and SDN can be combined.
Summary of the invention
The object of the present invention is to provide a kind of complete trails method for synchronizing time of software definition in information centre's smart grid,
It combines the specific feature of ICN and does customization design for large-scale intelligent power grid, introduce the method for software definition to realize
Flexibility in extensive smart grid, controllability and reliability.
The technical solution adopted in the present invention is as follows:
The complete trails method for synchronizing time of software definition in a kind of information centre's smart grid, in the cache way based on name
In, using two functional modules of interest table (PIT) and forwarding information table FIB undetermined in cache routing device, data packet is from interest
The same paths that packet reaches return, and all nodes on the paths realize that one is subsynchronous, while by SDN controller come pipe
Time synchronization process is managed, thus balance efficiency and accuracy on catenet.
Select a node synchronous as host node first, then host node is as the provider in time synchronization theme,
Other entities in smart grid are all consumers, and consumer uses subscriber's primitive from theme acquisition time data, and provides
Measurement data is published to theme using publication primitive by quotient, in time synchronization theme, the sheet of information consumer and path routing
Ground clock is adjusted according to the master clock of the local clock as provider.
Consumer's subscription step includes: to express its time synchronization request, the section by sending interest packet to its local DN
Point is ICN node, and the identifier of designated key, the content name name of interest Bao Youqi time synchronization, firstly, consumer sends out
It send interest packet and its sending time T1 is recorded according to the local clock of oneself, smart grid entity all passes through ICN node and is connected to
Network, DN and aggregation node RP also record its sending time according to the local clock of oneself while forwarding user's request,
Provider receives the interest packet from consumer and records its receiving time T2 according to local clock later.
Provider's issuing steps, which include: provider, is published to its local DN for data packet, and data packet covers two timestamps,
T2 and T3, T2 are the interest packet arrival times recorded according to provider's local zone time i.e. master clock, and T3 is according to offer
The time synchronization data packet sending time of quotient's local clock record, due to the PIT and FIB in ICN node, DN receives data
Packet, and forwards it to consumer by identical path, in addition, DN has recorded the receiving time of local clock, in path
All nodes all record the receiving time of its local clock while forwarding data packet, until consumer receives the data
Packet, consumer's received data packet record data packet arrival time according to local zone time T4, and therefore, each node in the path obtains
Four timestamps are obtained, they can calculate propagation delay and offset using formula (1) (2) according to this four timestamp informations,
And its local clock is modified according to master clock,
Data packet name supports flattening name and stratification to name two kinds of naming methods.
To reduce synchronization delay under the premise of meeting accuracy requirement, SDN controller carries out error estimation algorithm, judgement
Whether router in path can be considered as to synchronous master clock kth is subsynchronous, SDN controller include northbound interface equipment,
Southbound interface equipment and time synchronization service provide three parts, and northbound interface equipment connects application layer and controller, carries out simultaneously
Communication between time synchronization and controller, time synchronization service provide synchronous service, synchronous error estimation service and timestamp
More new demand servicing, be interested in packet and time synchronization data packet are sent to controller by flow table.
When intermediate node has synchronized, consumer is under conditions of synchronous error meets required precision, synchronized
Intermediate node as synchronous master clock, it is specific as follows to simplify the synchronizing process between consumer and master clock,
Step 0: consumer sends synchronous interest packet；
Step 1: nearest cache routing device CR1 extraction accuracy requirement from data packet, and upon receipt to when CS lookup
Between stab；
Step 2: compared with required precision, CR1 carries out estimation error；
Step 3: if error meets required precision, CR1 updates the time stamp T 2 and T3 of data packet in cache routing device, so
After forward it to consumer, if error is unsatisfactory for required precision, CR1 forwards interest packet, and CR2 repeats step 0-3, when there is packet
When time synchronization data packet containing the timestamp information for meeting required precision is returned by original path, CR1, which is forwarded it to, to disappear
Expense person and the local clock for synchronizing oneself.
The method of estimation error specifically includes: this since there are correlativities between synchronous error e and synchronizing cycle T
Correlativity indicates with formula (3), wherein e0It is small inevitable synchronous error, Δ f is master clock and local clock
Oscillation frequency is poor, they can be considered as constant in relatively long time, can be measured:
E=e0+Δf*T (3)
Error measure: node periodically sends interest packet, records local zone time ti, and then host node forwards main time stamp T i.
Master clock is indicated with formula (4):
Ti=e0+Δf*ti (4)
Node collects several groups timestamp information { t1, T2, T3, t4 }, and estimates synchronous error e and frequency with formula (5)
Poor Δ f,
During kth is subsynchronous, according to Δ T synchronizing cyclei, master clock Ti K, masterrIt is indicated with formula (6),
Ti k,master=Ti k-1,master+ΔTi (6)
Formula (7) expression of the master clock of estimation,
If Ti K, masterrWithDifference meet required precision, node i can be considered as main in synchronizing process
Clock.
Intermediate node all synchronizes its local clock in each data transmission procedure in information centre's smart grid,
So as to realize that high-frequency synchronous, cache routing device all play the part of the role of intermediate node, the sheet of intermediate node in each path
Ground clock keeps the high level of synchronization with master clock by high-frequency synchronous.
The smart grid topology includes link network or binary tree network.
Compared with prior art, the present invention have it is following the utility model has the advantages that
The present invention is to realize complete trails time synchronization in heart smart grid in the information for the first time, in the cache way based on name
In, using the advantage of PIT (interest table undetermined) and FIB (forwarding information table), data packet can be from the same of interest packet arrival
Path returns.Based on this feature, it is subsynchronous that all nodes on this paths may be implemented one.This will increase time synchronization effect
Rate.In addition, invention introduces SDN controllers to manage time synchronization process, thus balanced on catenet two because
The accuracy and efficiency of element.Finally, the present invention pays close attention to the performance of smart grid.In design time synchronization scheme, intelligence is emphasized
The reliability and safety of power grid, do not influence the performance of smart grid using this Time Synchronizing.
Detailed description of the invention
Upon reading the detailed description of non-limiting embodiments with reference to the following drawings, other feature of the invention,
Objects and advantages will become more apparent upon:
Fig. 1 is complete trails time synchronization framework proposed by the present invention；
Fig. 2 is SDN controller architecture；
Fig. 3 is simplified complete trails time synchronization working drawing；
Fig. 4 is the comparison of synchronizing relay in chain network；
Fig. 5 is the comparison of synchronizing relay in binary tree network.
Specific embodiment
The present invention is described in detail combined with specific embodiments below.Following embodiment will be helpful to the technology of this field
Personnel further understand the present invention, but the invention is not limited in any way.It should be pointed out that the ordinary skill of this field
For personnel, without departing from the inventive concept of the premise, several changes and improvements can also be made.These belong to the present invention
Protection scope.
Pub/sub normal form, in each theme, data publisher, i.e., in smart grid are used in the embodiment of the present invention
Its measurement data is traveled to theme using publication primitive by provider, such as phasor measurement unit (PMU), and information consumer
As phasor data concentrator (PDC) and active generator (APG) obtain them to the interested number of the theme using primitive is subscribed to
According to.
A. the path time based on name is synchronous
In order to realize the time synchronization for the smart grid for using ICN, the invention proposes between provider and consumer
The complete trails Time Synchronizing of software definition, as shown in Figure 1.Entire layout is divided into three bulks, including OF-ICN controls network
Refer to that information centre's smart grid controls plane, in openflow ICN (OF-ICN) network representation information centre smart grid
Simple Forwarding plane, final edge network coverage smart grid entity, such as PMU, PDC.Select a node as master first
Node is synchronous.Master clock answers with good stability, high-precision and high reliability.Then host node is in time synchronization theme
Provider, other entities in smart grid are all consumers.For example, consumer A is obtained using subscriber's primitive from theme
Time data, and supplier's (we select a node as host node, and this is the supplier in the theme) uses hair
Measurement data is published to theme by cloth primitive.In time synchronization theme, the local clock root of information consumer and path routing
It is adjusted according to the master clock of the local clock as provider.
Consumer expresses its time synchronization request by sending interest packet to its local DN (design node), which is
ICN node, and the identifier of designated key.The content name of interest Bao Youqi time synchronization is named.Firstly, consumer's transmission is emerging
Interest wraps and records its sending time T1 according to the local clock of oneself.PDC, PMU and other smart grid entities are all saved by ICN
Point DN is connected to network.DN and aggregation node RP is also recorded according to the local clock of oneself while forwarding user's request
Its sending time.Provider receives the interest packet from consumer and records its receiving time T2 according to local clock later.It orders
Read step completion.It is requested according to time synchronization, provider's issuing time data.Followed by issuing steps, provider is by data
Packet is published to its local DN.Data packet covers two timestamps, T2 and T3, T2 be according to provider's local zone time i.e. it is main when
The interest packet arrival time of clock record, T3 are the time synchronization data packet sending times recorded according to provider's local clock.By
PIT and FIB in ICN node, DN receives data packet, and forwards it to consumer by identical path.In addition, DN
Have recorded the receiving time of local clock.All nodes in path all record its local clock while forwarding data packet
Receiving time, until consumer receives the data packet.Therefore, each node in the path obtains four timestamps, they
Propagation delay and offset can be calculated using formula (1) (2) according to this four timestamp informations, and it is modified according to master clock
Local clock.
Construct information centre's smart grid, key component be using content name as Route Distinguisher rather than destination address
To realize that data are transmitted.In the present invention, data packet format is as shown in Figure 1, support flattening name and stratification to name two kinds
Nomenclature scheme.The format of interest packet is constant, and data packet format is by modification but does not change content name.For example, interior in DONA
Hold name to be made of { P:L }, wherein P indicates the keyed hash of the public key of information publisher, and L is the label of time synchronization, time
Synchronization packets add two timestamps in its next field.P and L self is tested with as before so P is still realized
Card, L is also that the whole network is unique.On the other hand, due to longest prefix matching principle, when two timestamps are added to stratification
It is not in aggregation problem in nomenclature scheme when next field of content name.
In order to realize Time Synchronizing, there are some synchronous requirements in need of consideration, such as efficiency, accuracy is expansible
Property, complexity, robustness and network flow expense etc..There is no the Time Synchronizings that can satisfy synchronous requirement.It is most important
, efficiency and accuracy are two factors to be balanced.The synthesis of time synchronization is realized in the present invention using SDN controller
Management.To reduce synchronization delay under the premise of meeting accuracy requirement, SDN controller carries out error estimation algorithm, judges
Whether kth is subsynchronous can be considered as synchronous master clock for the router in path.The design of SDN controller as shown in Fig. 2, comprising
Northbound interface equipment, southbound interface equipment and time synchronization service provide three parts.Firstly, northbound interface equipment connects application layer
And controller, while the equipment based on OpenFlow carries out the communication between time synchronization and controller.Time synchronization service mentions
For module synchronization service, synchronous error estimation service and update of time stamp service.In addition, OF-ICN gateway (OF-ICN-GW) is used
In the communication with SDN controller.Packet and the time synchronization data packet of being interested in are sent to controller by flow table.
Software definition complete trails Time Synchronizing proposed by the present invention significantly improves the efficiency of time synchronization, however,
If we can abandon accuracy to a certain extent, it is same that the time with more short delay may be implemented in the scheme proposed
Step.When intermediate node has synchronized, consumer can be under conditions of synchronous error meets required precision, synchronized
Intermediate node is as synchronous master clock.Synchronizing process between consumer and master clock can simplify.Simplified synchronization is such as
Under, as shown in Figure 3.
Step 0: consumer sends synchronous interest packet；Step 1: nearest cache routing device CR1 extracts essence from data packet
Degree requires, and searches timestamp to CS upon receipt；Step 2: compared with required precision, CR1 carries out evaluated error.Step 3: such as
Fruit error meets required precision, and CR1 updates the time stamp T 2 and T3 of data packet in cache routing device, is then forwarded to consumption
Person, if error is unsatisfactory for required precision, it includes to meet required precision when having that CR1, which forwards interest packet, and CR2 repeats step 0-3
When the time synchronization data packet of timestamp information is returned by original path, CR1 forwards it to consumer and synchronizes oneself
Local clock.
Estimation error: in order to estimate synchronous error, synchronous error is calculated using least square method.Error refers to master clock
Clock skew between synchronized cache routing device node, this is because oscillator frequency difference and one hyposynchronous intrinsic
Caused by error.When the synchronization interest packet containing specific required precision reaches, judge to be stored in CS using estimation error
In timestamp whether meet accuracy requirement.In view of there are correlativity, this methods between error e and synchronizing cycle T
It is reasonable.T referred to from the last time and was synchronized to the now time interval synchronizing cycle.This correlativity can use formula (3)
It indicates, wherein e0Small inevitable synchronous error, Δ f is that master clock and local clock oscillation frequency are poor, they
The constant that can be considered as in relatively long time can be measured:
E=e0+Δf*T (3)
Error measure: node periodically sends interest packet, records local zone time ti, and then host node forwards main time stamp T i.
Master clock can be indicated with formula (4):
Ti=e0+Δf*ti (4)
Node collects several groups timestamp information { t1, T2, T3, t4 }, and estimates synchronous error e and frequency with formula (5)
Poor Δ f,
During kth is subsynchronous, according to Δ T synchronizing cyclei, master clock Ti K, masterrIt can be indicated with formula (6),
Ti k,master=Ti k-1,master+ΔTi (6)
The master clock of estimation can use formula (7) expression,
If Ti K, masterrWithDifference meet required precision, node i can be considered as main in synchronizing process
Clock.
Error estimation algorithm is as follows:
B. the path time synchronization based on title and high-frequency synchronous
In the network centered on information, cache routing device (CR) is different from the router in IP network.Cache routing
There are three additional corn module, contents to store (CS) for device, interest table (PIT) to be processed and forwarding information storehouse
(FIB).When CR, which is obtained, does not have the interesting data packet of matched data packet in content storage area, it is notified that PIT record reached
Interface, and require to send ongoing interface to FIB.In addition, it can be according to the name in PIT when CR obtains data packet from provider
The arrival interface of word lookup interesting data packet.Because in the information in the heart network supplier return data packet can by with consumption
Person issues the identical path of interest packet, and therefore, in synchronizing, each node in the path can obtain four timestamps, with
Realize the synchronization of its local clock.
For example, A is (in Fig. 1 for interest packet passage path as shown in Figure 1, consumer A is synchronous with supplier in this theme
Consumer A-DNA-RP-DNB- provider) path include consumer A, ICN node DNA, DNB, cache routing device RP and offer
Quotient, then data packet also can passage path A return.Consumer's A and ICN node DNA, DNB and cache routing device RP all in accordance with
The clock information of provider modifies its local clock.Then, consumer B also wants, interest packet passage path B synchronous with provider
(the consumer B-DNC-RP-DNB- provider in Fig. 1) path includes consumer B, ICN node DNC, DNB, cache routing device RP
And provider, likewise, the time synchronization data packet that provider returns is returned also by path B.Therefore, all in the B of path
Node can modify its local clock according to master clock.DNB and RP is not only in the A of path, also in the B of path.That is, it
Will synchronous local clock twice.
In complicated information centre's smart grid, intermediate node will all synchronize it in each data transmission procedure
High-frequency synchronous may be implemented in local clock.Obviously, high-frequency synchronous leads to high-precise synchronization.Cache routing device is in each path
All play the part of the role of intermediate node.In addition, the local clock of intermediate node keeps same with the height of master clock by high-frequency synchronous
Step.
The invention proposes a kind of path time synchronization schemes of software definition.Due to data packet by with interesting data packet
Identical routed path is transmitted to the specific function of consumer, and it is synchronous that it realizes path time.In addition, cache routing device is realized
High-frequency synchronous.With the development of smart grid, network is added in many new nodes, and network size constantly expands, our invention
Gradually show the advantage of communication efficiency.In addition, the SDN controller in our motion maintains an error estimation algorithm,
It is made of error measure stage and judgement stage.Judge whether cache routing device can be according to the required precision of a synchronous point
As host node.SDN controller management time synchronization is comprehensive, balance quality and efficiency.It is proposed that software definition path
The characteristics of Time Synchronizing is the dynamic characteristic of high efficiency and enhancing, is two important indicators of information centre's smart grid.
Software definition complete trails Time Synchronizing in information centre's smart grid proposed by the present invention is better than traditional
Pair-wise synchronization scheme.In terms of communication efficiency, Time Synchronizing tool proposed by the present invention has great advantage.It proposes
The communication efficiency of Time Synchronizing meets the needs of smart grid scale enlargement.With traditional time synchronization side pair-wise
Case is compared, and the path time synchronization scheme of proposition improves a lot in terms of validity, especially when there are great deal of nodes.
Assuming that simulation topology is chain structure.Assuming that number of nodes is n, the delay of each link includes transmission delay d and processing
Postpone a.Complete trails Time Synchronizing proposed by the present invention and the synchronization delay of traditional pairing scheme are by formula (8) and (9) table
Show, formula (10) is the difference between them.
delayp=(n-1) d+ (n-1) a (8)
Complete trails Time Synchronizing proposed by the present invention is when number of nodes is huge with the advantage being more and more obvious.Figure
4 be the simulation result of ns-3 simulation software, demonstrates the theory analysis of front.In simulations, the every 10ms of consumer sends one
Interesting data packet, the data rate of each link are 1Mbps, and the comparison of the two schemes is as shown in Figure 4.The result shows that using
The delay time of the path time synchronization scheme of proposition is well below traditional pair wise Time Synchronizing.Most of all,
Complete trails Time Synchronizing proposed by the present invention improves communication efficiency.
However, in most cases, network topology is binary tree.In this case it is proposed path time it is synchronous
Scheme is still better than traditional pair wise Time Synchronizing.On the one hand, we still can see mentioning for communication efficiency
It rises.In this case, leaf node is communicated with root node, while leaf node and intermediate node are all synchronous with root node.So
And when using traditional pairwise Time Synchronizing, the second node layer is synchronous with root node first, then every layer with it is upper
Layer is synchronous.Propagation delay is identical, shorter using the processing delay of complete trails Time Synchronizing proposed by the present invention.When using biography
When the pairwise Time Synchronizing of system, upper layer node modifies its local clock, then to time synchronization packet before modification.Compare
The difference of both Time Synchronizings, delay time can pass through formula (11):
Δdelay=(n-1) a (11)
Wherein, n is the number of plies of y-bend tree topology, and a is processing delay.Ns-3 simulation result is as shown in Figure 5.On the other hand,
In traditional Time Synchronizing, node is with upper layer node rather than root node is synchronous, and error caused by algorithm can be from upper
Layer is accumulated to lower layer.In view of synchronization accuracy, it is not as good as the path time synchronization scheme proposed.
In conclusion no matter in link network or binary tree network, the path time synchronization scheme of proposition have compared with
High communication efficiency.
Specific embodiments of the present invention are described above.It is to be appreciated that the invention is not limited to above-mentioned
Particular implementation, those skilled in the art can make a variety of changes or modify within the scope of the claims, this not shadow
Ring substantive content of the invention.In the absence of conflict, the feature in embodiments herein and embodiment can any phase
Mutually combination.
Claims (9)
1. the complete trails method for synchronizing time of software definition in a kind of information centre's smart grid, which is characterized in that based on life
In the cache routing of name, two functional modules of interest table (PIT) and forwarding information table FIB undetermined in cache routing device, number are utilized
It is returned according to the same paths that packet is reached from interest packet, all nodes on the paths realize that one is subsynchronous, while passing through SDN
Controller manages time synchronization process, thus balance efficiency and accuracy on catenet；Specifically: selecting one first
Node is synchronous as host node, then other entities of host node as the provider in time synchronization theme, in smart grid
It is all consumer, consumer uses subscriber's primitive from theme acquisition time data, and provider will be measured using publication primitive
Data publication is to theme, and in time synchronization theme, the local clock of information consumer and path routing is according to as provider
The master clock of local clock be adjusted.
2. the complete trails method for synchronizing time of software definition in information centre's smart grid according to claim 1, special
Sign is that consumer's subscription step includes: to ask by sending interest packet to its local design node DN to express its time synchronization
It asks, which is information centre's network ICN node, and the identifier of designated key, the content name of interest Bao Youqi time synchronization
Claim name, consumer sends interest packet and records its sending time T1 according to the local clock of oneself, and smart grid entity is all logical
Cross ICN node be connected to network, DN and cache routing device RP forward user request while, also according to the local of oneself when
Clock records its sending time, and provider receives the interest packet from consumer and records its receiving time according to local clock later
T2。
3. the complete trails method for synchronizing time of software definition in information centre's smart grid according to claim 2, special
Sign is, provider's issuing steps include: that data packet is published to its local DN by provider, and data packet covers two timestamps,
T2 and T3, T2 are the interest packet arrival times recorded according to provider's local zone time i.e. master clock, and T3 is according to offer
The time synchronization data packet sending time of quotient's local clock record, due to the PIT and FIB in ICN node, DN receives data
Packet, and forwards it to consumer by identical path, in addition, DN has recorded the receiving time of local clock, in path
All nodes all record the receiving time of its local clock while forwarding data packet, until consumer receives the data
Packet, consumer's received data packet record data packet arrival time T4 according to local zone time, and consumer sends interest packet and according to certainly
Oneself local clock records its sending time T1, and therefore, each node in the path obtains four timestamps, they are ok
When calculating propagation delay and offset using formula (1) (2) according to this four timestamp informations, and modifying its local according to master clock
Clock,
4. the complete trails method for synchronizing time of software definition in information centre's smart grid according to claim 1, special
Sign is that data packet name supports flattening name and stratification to name two kinds of naming methods.
5. the complete trails method for synchronizing time of software definition in information centre's smart grid according to claim 1, special
Sign is, to reduce synchronization delay under the premise of meeting accuracy requirement, carries out error estimation algorithm by SDN controller,
Judge whether the router in path can be considered as to synchronous master clock kth is subsynchronous, SDN controller is set comprising northbound interface
Standby, southbound interface equipment and time synchronization service offer three parts, northbound interface equipment connection application layer and controller, while into
Communication between row time synchronization and controller, time synchronization service provide synchronous service, synchronous error estimation service and time
More new demand servicing is stabbed, be interested in packet and time synchronization data packet are sent to controller by flow table.
6. the complete trails method for synchronizing time of software definition in information centre's smart grid according to claim 1, special
Sign is, when intermediate node has synchronized, consumer is under conditions of synchronous error meets required precision, synchronized
Intermediate node is as synchronous master clock, thus simplify the synchronizing process between consumer and master clock, it is specific as follows,
Step 0: consumer sends synchronous interest packet；
Step 1: nearest cache routing device CR1 extraction accuracy requirement from data packet, and upon receipt to content memorizer CS
Search timestamp；
Step 2: compared with required precision, CR1 carries out estimation error；
Step 3: if error meets required precision, CR1 updates the time stamp T 2 and T3 of data packet in cache routing device, then will
It is transmitted to consumer, if error is unsatisfactory for required precision, CR1 forwards interest packet, and cache routing device CR2 repeats step 0-3,
When there is the time synchronization data packet comprising the timestamp information for meeting required precision by original path return, CR1 is by its turn
It issues consumer and synchronizes the local clock of oneself.
7. the complete trails method for synchronizing time of software definition in information centre's smart grid according to claim 6, special
Sign is that the method for estimation error specifically includes: since there are correlativity, this phases between synchronous error e and synchronizing cycle T
Pass relationship indicates with formula (3), wherein e0It is small inevitable synchronous error, Δ f is that master clock and local clock shake
Difference on the frequency is swung, they can be considered as constant in relatively long time, it can be measured:
E=e0+Δf*T (3)
Error measure: node periodically sends interest packet, records local zone time ti, and then host node forwards main time stamp T i, when main
Between stamp Ti with formula (4) indicate:
Ti=e0+Δf*ti (4)
Node collects several groups timestamp information { t1, T2, T3, t4 }, and estimates synchronous error e and frequency difference Δ with formula (5)
F,
During kth is subsynchronous, according to Δ T synchronizing cyclei, master clock Ti K, masterrIt is indicated with formula (6),
Ti k,master=Ti k-1,master+ΔTi (6)
Formula (7) expression of the master clock of estimation,
If Ti K, masterrWithDifference meet required precision, when node i can be considered as main in synchronizing process
Clock.
8. the complete trails method for synchronizing time of software definition in information centre's smart grid according to claim 6, special
Sign is that intermediate node all synchronizes its local clock in each data transmission procedure in information centre's smart grid,
So as to realize that high-frequency synchronous, cache routing device all play the part of the role of intermediate node, the sheet of intermediate node in each path
Ground clock keeps the high level of synchronization with master clock by high-frequency synchronous.
9. the complete trails method for synchronizing time of software definition in information centre's smart grid according to claim 1, special
Sign is that the smart grid includes link network or binary tree network.
Priority Applications (1)
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| CN105723666A (en) * | 2014-12-16 | 2016-06-29 | 北京大学深圳研究生院 | Content-based routing method and system |
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