FI91691C - Hierarchical synchronization method - Google Patents

Description

91691

Hierarchical synchronization method

The invention relates to a hierarchical synchronization according to the preambles of the appended claims 5 1 and 4 in a method used in a communication system using message-based synchronization.

In this presentation, the system uses the node referred to as the junction of the transmission links. The node may be any device or apparatus capable of interfering with the clock rate, e.g. a branch or cross-connect device.

The nodes of a system using message-based synchronization are interconnected by the transmission links they use to communicate. The connections used also forward 15 to the senders of the sender's clock frequency. Each node selects either the frequency of a signal from a neighboring node or the frequency of its own internal clock source as the source of its own clock frequency. In order to make all the nodes of the system operate at the same clock frequency, 20 efforts are usually made to cause the system to synchronize to one clock source, the so-called påålahteeseen. In this case, all nodes in the system directly connected to the selected main source are synchronized with the nodes connected to this main source and these, but without a direct connection to the main source 25, are synchronized with these nodes next to the main source. Correspondingly, nodes that are always farther away from the bale are always synchronized to those nodes that are one connection closer to the bale.

In order to build a synchronization hierarchy 30 as described above within the system, the nodes of the system select synchronization messages to each other. These messages contain information that allows individual nodes to select the timing source. The nodes in the system are prioritized and the system tends to synchronize to the clock frequency of the node that is at the 91691 2 priority level. At the same priority level, there is normally only one node in the system. Normally, the synchronization messages contain information on who the clock frequency of the node sending the message is from, which is.

5 node priority, and a value describing the quality of the clock signal. Thus, a single node can select the clock frequency of the neighboring node that originates from the desired node and is of the best quality as the source of its own clock frequency.

10 During the system start-up phase, each node selects its clock frequency as its own internal clock source because no incoming synchronization message has been processed. When the first incoming synchronization messages have been processed, the clock frequency of the neighbor with the highest priority is selected as the source of its own clock frequency. When the system has reached a stable state in terms of synchronization after all the messages have been spread in the system, the system is hierarchically synchronized to the clock frequency of the source.

Figure 1 shows a system using message-based synchronization in a stabilized situation. The priorities defined for the sol are marked with numbers inside the circles describing the nodes. The lower the number, the higher the node's priority. The synchronization messages sent by node n (n = 25 1 ... 6) are marked with the reference number MSGn. The synchronization message sent by each node is generally different and depends on the message-based synchronization method used. The propagation of the clock frequency from the main clock (node 1) to the other nodes of the system to the other nodes is shown by solid lines. Connections between nodes drawn with a dashed line are not used in a normal-situation to synchronize the system, but they are available in a change situation.

A simple principle in message-based synchronization is that the user defines the sync of the nodes.

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3,91691 roning hierarchy, giving each node its own identifier indicating the level of the node in the hierarchy, and the system synchronizes to the defined main clock independently, using all existing connections between the nodes (5) as needed. If the connection to the main clock is lost, there is no alternative connection, or the main clock fails, it is synchronized to the next highest level node in the system. Fig. 2 shows a situation when the main clock fails in the system 10 according to Fig. 1. The response to the change in synchronization is through inter-node messaging. When the incoming timer is interrupted, the synchronization hierarchy is rebuilt forward from the point of interruption (away from the system master). This happens e.g.

15 so that the node that first notices the interruption first goes to the state of the internal timing as a determinant and forwards the change of information, at which point the formation of a new synchronization hierarchy begins. Usually, the end result is a hierarchical structure similar to the original one, in which the faulty-20 connection is replaced by a functional connection, while the rest of the structure remains almost unchanged.

A network using message-based synchronization is described, for example, in U.S. Patents 2,986,723 and 4,837,850. Both patents disclose methods in which, in the event of a system failure in this system, time limits depending on the size and shape of the system, during which the nodes are forced to enter a predetermined constant state in order to prevent failure. In the event of a fault, information about the fault-30 is transmitted as described above via system messages. When information about the changed situation has spread throughout the system or over a sufficiently large area, the synchronization is rebuilt at the point of change and possibly further afield, if necessary. With the help of the deadlines, it will be ensured that information about the change will spread to a wide area of 4,91631. Upon detecting a change / failure, the node forwards this information forward, starts its own timer and enters a predefined state. When the time expires, the node restarts its normal operations to obtain the timing, and the system begins to resynchronize for those parts affected by the change / failure. The solution according to the present invention is specifically intended for systems such as that described in the aforementioned U.S. Patent 2,986,723, in which a change in the system appears as a change in the synchronization identifier entering the node. In the system disclosed in U.S. Patent 2,986,723, said constant state is an internal timing state in which a node uses its own internal clock as the source of its timing. The method according to the method disclosed in this U.S. Patent 15 is hereinafter referred to as Self-Organizing Master-Slave Synchronization (SOMS) and will be used hereinafter as an example in the more detailed description of the invention.

It should be further clarified that when we refer to a deadline in this connection, it means the predetermined time by which the system is intended to prevent the selection of erroneous / outdated synchronization messages.

In the system used in the SOMS synchronization method, the failure of the synchronization connection or the failure of the node in the middle of the hierarchical structure in the part of the synchronization structure decomposition in the system. After the synchronization structure is broken, some of the nodes in the system use their own internal clock for scheduling until 30, when the synchronization structure is rebuilt.

However, the internal clock of a node is usually never as good in quality as the main clock of the system. As a result, it is difficult to maintain the required 35 quality levels in synchronization, especially in the synchronization of larger systems.

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5,91691

It is an object of the present invention to provide a method in which the disadvantages described above are reduced and in which resynchronization can be accelerated. This is achieved by a method according to the invention, characterized in its first embodiment by what is described in the characterizing part of the appended claim 1, and in its second embodiment by what is described in the characterizing part of the appended claim 4.

The idea of the invention is, instead of automatically going into the state of internal timing, e.g., to select a new synchronization identifier for the old bay indiscriminately, when the incoming synchronization identifier currently selected deteriorates. The selection is performed at least 15 whenever said degraded identifier has a higher priority level than the intra-node synchronization identifier. A degraded synchronization identifier means that the corresponding synchronization message is still qualitatively acceptable, but the identifier within it has become lower in priority. Deterioration of the incoming synchronization identifier indicates a change / failure of the system on the connection to the bale source.

Thanks to the solution according to the invention, unnecessary visits (or corresponding transitions to the constant state) are avoided in the internal timing, and the synchronization tree of the system is better preserved in resynchronization, whereby the interruption in the frequency transmission of the main node is shorter. In the case of interruptions, it is resolved by resynchronizing one or a few nodes 10 instead of all the nodes in the synchronization tree below the interruption point creeping in internal timing, as is the case in the known SOMS method. The total time required for synchronization is thus even shorter. Thanks to the solution 15, the significance of the location of the breakpoint 6 91691 in the synchronization time is also reduced, which makes it possible to better define in advance the use of synchronization in the system in different situations. (A synchronization tree refers to that hierarchical tree-like structure that, in submissive 5 synchronization, is created in a network from a main node to a bay.)

In the following, the invention and its preferred embodiments will be described in more detail with reference to the examples of Figs. 3-8 in the accompanying drawings, in which Fig. 1 shows a message-based synchronization system in general form synchronized with the bale clock frequency, Fig. 2 shows when its main node has failed, Fig. 3 shows the network using self-directed slave synchronization (SOMS) in its initial state, Fig. 4 shows the network of Fig. 3 in a stable state, Fig. 5 shows the resynchronization of the network of Fig. 4 after its main node has failed, Fig. 6 shows the resynchronization of the network of Fig. 4 after the disconnection of a two-node silent connection, Figs. 7a-7g show the application of the method according to the invention in a SOMS system, and Fig. 8 shows the elements of a single node in which the method according to the invention is implemented.

Figure 3 shows a system using Self-Organizing Master-Slave synchronization (SOMS) according to the aforementioned U.S. Patent 2,986,723, which in this case encounters five 30 nodes (or devices) denoted by reference numerals 1 to 5 thereof. according to the level of the hierarchy. (The main node of the network has the smallest SOMS address.) The nodes complain to each other of messages that contain the above SOMS addresses. Thus, the nodes are able to identify each other using these address numbers and 35 to build a synchronization hierarchy, so that the entire network

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7 91691 can synchronize to the main node.

As mentioned above, the messages to be sent continuously in the network depend on the message-based synchronization method used. The messages are additionally 5 unique for each sending node. In a SOMS network, a synchronization message comprises three different parts: a frame structure, an identifier, and a checksum. The SOMS identifier is the most important part of the SOMS message. It consists of three consecutive numbers D1 ... D3: 10 D1 is the origin of the synchronization frequency of the sending node of the SOMS message, i.e. the SOMS address of the node that appears as the main node for the sending node.

D2 is the distance to the node indicated by D1. This distance is expressed as the number of nodes in between.

15 D3 is the SOMS address of the node to be sent.

Each node (or device) constantly compares the incoming SOMS tags with each other and selects the smallest one. In the identifier, the parts D1, D2 and D3 are directly connected into one number by placing them in sequence (D1D2D3) 20 (for the sake of clarity, a dash will be written in the future to separate the different parts; Thus, the primary selection criterion for the smallest address becomes the SOMS address (D1) of the node appearing as a pa-node for the previous nodes, i.e. the node tends to synchronize to a signal whose frequency is initially 25 from the node whose address is as small as possible. In such a stable situation, the whole network is synchronized to the same pSSsol (because the main node of the whole network has the smallest SOMS address).

If two or more of the incoming signals are synchronized to the same main node, the one that comes from the shortest path (D2) is selected. the last selection criterion remains the SOMS address (D3) of the node sending the SOMS message, on the basis of which a selection is made, if no difference is otherwise obtained between the incoming signals.

35 Once a node has accepted one of the neighboring nodes 8 91691 as its new synchronization source based on the incoming SOMS identifier, the node has to re-establish its own SOMS identifier. The new SOMS identifier can be derived from the selected smallest SOMS identifier as follows: the first part (D1) of the en-5 is left untouched, the second part (D2) is incremented by one and the third part (D3) is replaced by the node's own SOMS address.

Each node also has its own internal SOMS identifier X-O-X, where X is the one in question. the SOMS address of the node. If none of the 10 incoming SOMS messages contain an identifier that is smaller than the internal identifier, the node uses its own clock frequency as its source for its own internal oscillator or possibly a separate synchronization input. The outgoing SOMS message naturally then uses 15 internal SOMS identifiers.

The nodes continuously send SOMS messages in each direction so that the changed information in the SOMS identifiers can be spread as quickly as possible and the operational status of the neighboring nodes is constantly clear. Before SOMS identifiers can be compared with each other, incoming SOMS messages must be accepted and SOMS identifiers must be separated from them.

When a SOMS message is first received from a particular transmission link, the SOMS identifier it contains is immediately accepted for comparison, provided the message was error-free.

25 When an SOMS identifier has been accepted for an incoming transmission connection and an error-free message containing the same identifier is continuously received, the situation remains unchanged. If the SOMS message is found to be invalid, the old SOMS identifier is still retained until three consecutive SOMS messages are received as invalid. In that case, the SOMS tag for comparison. By waiting for three consecutive SOMS messages, the aim is to eliminate momentary disturbances.

If no SOMS message arrives from the connection, even if the 35 connection otherwise works, three consecutive li 916 * 1 9 SOMS messages are waited until the current SOMS identifier is discarded. If the connection is completely lost, the SOMS identifier is rejected immediately. If, due to interference in the incoming signal, comparisons for 5 valid SOMS tags are not obtained, the the SOMS identifier of the transport connection. In this case, the comparison uses the as a SOMS identifier of the inbound transmission link, a standard identifier in which all parts (D1, D2 and D3) receive their maximum value (MAX-MAX-MAX).

10 When a new changed SOMS identifier is detected in an incoming SOMS message, it is immediately accepted for comparison if the message was error-free. This will not cause unnecessary delays for network changes.

In the initial situation, each node uses its own internal synchronization source, in which case it sends its own internal SOMS identifier X-O-X to the other nodes. This tag is also compared to incoming SOMS tags. WHY the incoming tags are not smaller than the internal tags, continues. node use of its own internal timing-20.

In Figure 3, the SOMS network is shown in the initial state, in which no node (or device) has had time to process incoming SOMS messages. For all nodes, the highest priority is given to the SOMS tun-75 node within the node, because the others have not yet been processed. In Figure 3, each node is marked with the incoming SOMS identifiers, and the selected identifier is written inside the frame (in the initial situation according to Figure 3, all nodes use their internal timing source). The connections in use of the Synk-30 resonance are drawn on a solid line, the spare connections on the dashed line (in the initial situation according to Figure 3, all connections are on the spare line).

When the nodes have time to process the incoming SOMS-sa-35 names, the node 1 remains in use of the internal timing, the nodes 2 and 4 are synchronized to the node 1 based on the identifier 1-0-1, the node 3 is synchronized to the node 2 (2-0-2) and the node 5 to node 3 (3-0-3). At the same time, the nodes form their own new SOMS identifiers as described above and exchange the new identifier in their outgoing SOMS message. The state of the network after its stabilization is shown in Figure 4. All nodes are synchronized to the main node 1 by the shortest possible route.

If the smallest of the incoming SOMS identifiers entering the node changes or disappears completely when the connection is lost, the node selects a new synchronization direction according to the second smallest SOMS identifier. However, before this, the node is forced into internal scheduling, where it lingers for a predetermined length of mSM to allow the invalid SOMS identifiers to "kill" off the network. For example, if, in the situation of Figure 4, node 1 went out of order, nodes 2 and 4 would no longer receive the identifier 1-0-1, according to which they were synchronized. If, in this situation, they inevitably accepted the next smallest SOMS identifier, the network would no longer be synchronized to one main node, but the synchronization would circulate in the loop. When Node 1 fails, Node 2 still receives tags 1-1-4 and 1-2-3 and Node 4 again tags 1-1-2 and 1-2-5, because Nodes 3 and 5 have not yet had time to react to the 25 changed situation. . If the second smallest tags were accepted vSlittom: node 2 would be synchronized according to node 4 and node 4 according to node 2. This situation is prevented by the aforementioned forced internal timing mode, in which case the the nodes switch to using their own 30 internal timing sources and begin to shout out their own internal SOMS identifier (Χ-0-Χ). Those nodes in the store that * synchronized to the node that moved to the internal timing will notice that a change has occurred in the network and that the old SOMS-35 message on which the synchronization was based is no longer valid because it has become an internal SOMS message for neighbor 11 91691. . In this case, the mentioned nodes themselves enter the state of forced internal timing as a determinant.

If, in the case of Figure 4, the master node fails, the nodes 2 and 4 immediately forcibly enter the internal timing state after losing the incoming SOMS identifier 1-0-1. When nodes 3 and 5 detect a change in nodes 2 and 4, they are also forced to enter the internal timing. When the node 2 returns to the normal state, it 10 receives from the nodes 3 and 4 their internal SOMS tags (3-0-3 and 4-0-4) and stays in the internal timing, because the external pressure does not become a smaller SOMS tag than its own internal tag (2 -0-2). Node 4 in turn synchronizes with Node 2. After stabilizing, the network is in the state 15 shown in Figure 5, where Node 2 has become the new main node of the network.

If, for example, only the connection between nodes 1 and 2 is lost (Fig. 6), only node 2 is forced to enter the internal timing state. When it returns to normal, it synchronizes with node 4, which is connected to the main node of the network. Once the entire network 20 has stabilized, synchronization will still come from Node 1 despite a single outage. This situation is shown in Figure 6.

When there is an interruption or other change in the upper parts of the synchronization tree (closer to the system baler) as a result of which the synchronization identifier of the currently selected timing source in the node deteriorates because there is no longer an old connection, the system is no longer connected. according to, the new, degraded synchronization identifier of the selected timing source 30 is immediately converted to a new synchronization identifier. (Thus, the node does not go into the internal timing state, as happens in the known solution described above).

Figures 7a-7g show a sequence of events from the use of the method according to the invention in a part of the SOMS system, 12 91691, comprising nodes 15, 17, 18, 19, 27 and 30. connections are still marked with solid 5 lines. In the first step shown in Figure 7a, the connection of the node 15 to the main node of the system is lost. In the next step (Fig. 7b), the node 15 forcibly enters the internal timing state and starts transmitting its internal synchronization identifier. In this case, the synchronization identifier entering the nodes 18 and 19 10, which is currently selected in them, deteriorates, whereby they immediately select the changed identifier as their new synchronization identifier and on this basis form a new own outgoing identifier (Fig. 7c). Nodes 18 and 19 are forced to stop at a new, changed identifier with a predetermined identifier before they are free to choose the smallest (best) of all incoming synchronization identifiers. This forced automatic selection of the changed identifier according to the invention ηδη spreads down in the synchronization tree without changing it. In the step shown in Fig. 7d, it has reached the nodes 27 and 30. In the next step (Fig. 7e), the timeout of the node 15 has expired and it is free to choose its timing from among the synchronization identifiers 25 entering the source. However, since there is no better synchronization identifier elsewhere, the node 15 voluntarily remains in the internal timing. In the step shown in Figure 7f, the delimiters of nodes 18 and 19 also expire. Node 18 receives 30 synchronizations from node 17 from the system source and synchronizes based on them, but node 19 remains in the old state because it does not receive a better identifier elsewhere than the identifier from node 15. In the step shown in Figure 7g, the nodes 15 and 19 have had time to process the new identifier sent by the node 18, which has changed due to changes in the previous step. Nodes 15 and

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13 91691 19 are then synchronized to the main source of the system via sol-roun 18. The determinants of nodes 27 and 30 have expired, but they do not need to change their timing sources because there will be no better synchronization identifier elsewhere. As can be seen from the sequence of images (e.g., Figure 7d), node-to-node connections are used for synchronization even when the node is forcibly at the limit.

The minimum length of said determiner preferably corresponds to the time that elapses after the node's neighbor nodes have been informed of the node's transition to said constant state, reacted to the change, and the node itself has received information from neighboring nodes about their response. This time can be calculated using the following formula: (1) K = 2 x (S + H + V), where S is the maximum duration for generating the synchronization message and its transmission between the two nodes, H is the maximum duration for accepting the synchronization message at the node and V is the incoming sync the maximum duration of the comparison at the node. By using the length of the timeout according to the formula (1) 20, the synchronization can be further accelerated and the timeout is made constant regardless of the size of the system. The use of said time limit and the advantages to be obtained therefrom are described in more detail in the co-pending FI patent application FI-92xxxx, to which reference is made in more detail.

Figure 8 shows the elements of the node in which the method according to the invention is implemented. The figure shows two connections to the node of the system from neighboring nodes, A and B. The transmission line of each connection is connected to the signal transmission and reception section 13a and 13b, respectively, which perform the physical signal processing. The section 13a (and 13b, respectively) forwards the synchronization message to the synchronization message transmission and reception section 16a (and 16b, respectively) connected to it. The transmitting and receiving parts 16a and 16b are suitable for num. checking the correctness of the message and forwarding the message to a cell-centered synchronization decision section 23, said input being connected to the output of the respective transmission and reception section 16a or 5 16b. The signal transmitting and receiving sections 13a and 13b also monitor the quality of the received signal and store the woman in the data connection-specific fault databases 24a and 24b, respectively. The sending and receiving section 16a of the synchronization message receives the fault information from the database 10a and the sending and receiving section 16b from the fault database 24b, respectively. The detection of a related fault / change in the signal transmission and reception parts takes place as is known per se.

The decision section 23 compares the messages and 15 stores them in the memory 21, e.g. in order of priority, so that the synchronization identifier is always selected at the top. The decision section also receives the error information of the corresponding signal from the connection-specific transmission and reception block 11a or 11b, either in the form of a synchronization message or 20 as separate error information. When the decision-making part detects from the information received that the node has to go to a constant state determined as a determinant, it selects its timing in the synchronization method used by the source in the manner specified by the receiver, giving out the memory 22 (to which it 25 forms the user). to parts 16a and 16b and starts its timer member 25. With the new identifier, the node indicates the change that has taken place to its neighboring nodes.

30 When the timer elements 25 have given the information of the timer K

the decision section 23 may again select the timing source according to the normal procedure.

When the decision section receives a degraded synchronization from the transmission and reception part of the message corresponding to the selected synchronization identifier.

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15 91691 message message, it starts its timer element 25, selects the degraded identifier and on the basis of it forms its new own synchronization identifier, which it feeds from the memory 22 to all synchronization message transmission units.

According to a preferred embodiment of the invention, the node, after selecting the degraded identifier as a new identifier, can select a new identifier for it, provided that it still obtains an even better identifier from the selected connection as the time lasts. However, identifiers from other connections cannot be accepted as newly selected identifiers until the deadline has elapsed. The aforementioned additional feature further speeds up the synchronization of the system.

In the embodiment described above, the degraded synchronization identifier was selected either for the entire time period or at least for part of that time period. According to another embodiment of the invention, the node first compares the degraded synchronization identifier with its own internal identifier and selects nSistS as a better option. The comparison is performed in decision making section 23. If the internal identifier is better, the node enters the internal timing in a known manner, and if the degraded identifier is better, the node selects it as its new identifier as described above, either as a whole delimiter or until 25 connections provide an even better identifier.

Although the invention has been described above with reference to the examples according to the accompanying drawings, it is clear that the invention is not limited thereto, but can be modified within the scope of the inventive idea set forth above and in the appended claims. Thus, although the SOMS system has been used as an example above, the solution according to the invention is applicable to all similar types of systems in which the change in the system appears as a change in the synchronization message entering the node.

Claims (6)

1. Hierarchical synchronization method for a data communication system using message-based synchronization, said data communication system comprising a plurality of nodes interconnected with connections (A, B), in which the method nodes transmit signals containing synchronization messages in the system, including information of prior synchronization messages, internal synchronization hierarchy, and in which a node as a result of a change situation, such as a failure situation, forcibly switches to a predetermined default state to prevent the selection of incorrect synchronization messages, then signed by one when each selected at a time synchronization identifier is changed to the same, the node immediately changes this changed identifier to its new synchronization identifier and compulsively adheres to this maximum for a predetermined period of time. 2. The method of claim 1, characterized in that, if said assembled identifier is changed to the later one during said fixed time period, the node immediately turns the improved identifier to its new synchronization identifier. 3. A method according to claim 1, characterized in that, as a minimum value for the determined time period, the time (K) is used to allow the node's neighbor nodes to receive information that the node has switched to said standard state, reacted to the change and the node is clean from the neighbor nodes received. information on their reaction. 4. Hierarchical synchronization method for a data communication system using message-based synchronization, which system comprises a plurality of nodes interconnected with connections (A, B), in which the nodes transmit signals which contain synchronization messages, includes information about a corresponding signal's priority in the system's internal synchronization hierarchy, and in which a node-like procedure, such as a failure situation, compulsively switches to a predetermined default state to prevent the selection of incorrect synchronized states, that when a selected synchronization identifier located on a single occasion in a node is changed to the second, the node compares this deteriorated synchronization identifier with an internal synchronization identifier in the node, and of these the immediate one immediately selects the newer to its new synchronizer. and if a new synchronization identifier is chosen, the said defaulted identifier, the node adheres to this maximum for a predetermined time period, and if a new synchronization identifier is selected, the second internal time identifier adheres to the second, the entire node adheres to the second. 5. A method as claimed in claim 4, characterized in that, if said aforesaid identifier is selected, and it is changed to the better one for said predetermined time period, the node immediately selects the enhanced identifier for its new synchronizer identifier. 6. A method according to claim 4, characterized in that as the minimum length for said determined period of time, the time (K) is used to allow the node's neighbor nodes to receive information that the node has switched to said standard state, reacted to the change and the node itself from the neighbor nodes. received information on their reaction.