FI92358B - Hierarchical synchronization procedure and a data traffic system that uses message-based synchronization - Google Patents

Description

92358.

The invention relates to a hierarchical synchronization method according to the preamble of appended claim 1, which is used in a communication system using message-based synchronization. The invention also relates to a communication system according to the preamble of appended claim 5.

In this representation, the intersections of the transmission links of the system are referred to as a node. The node can be any device or hardware that is capable of interfering with the clock rate, e.g., a branch or cross-connect device.

15 The nodes of a system using message-based synchronization are interconnected by the transmission connections they use to transmit data. The connections used also forward the sender's clock frequency to the recipient. Each node selects either the frequency of a signal from one of the 20 neighboring nodes or the frequency of its own internal clock source as its own clock frequency source. In order to make all the nodes of the system work at the same clock frequency, the aim is usually to get the system to synchronize to one clock source, the so-called the master source. In this case, all nodes in the system directly connected to the selected main source are synchronized to this main source, and nodes connected to these but not directly connected to the main source are synchronized to these nodes adjacent to the main source. Correspondingly, nodes that are always farther away from the main source 30 are always synchronized to those nodes that are one connection distance closer to the main source.

In order to build a synchronization hierarchy as described above inside the system, the nodes of the system transmit synchronization messages to each other. These 35 messages contain information that allows individual 2 92658 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 highest priority level. At the same priority level, nor-5 has only one node in the system painted. Normally, the synchronization messages contain information on who the clock frequency of the node sending the message originates from, which is the node priority, and a value that describes the quality of the clock signal. This allows a single node to 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 speed.

In the system start-up phase, each node selects its own internal clock-15 source as its clock frequency 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. Once the system has reached a synchronization-stable state after all messages have spread to the system, the system is hierarchically synchronized to the clock frequency of the main source.

Figure 1 shows a system using message-based synchronization in a stabilized situation. The priorities assigned to the others of Sol-25 are marked with numbers inside the circles describing the nodes. The lower the number, the higher the priority of the node. The synchronization messages sent by node n (n = 1 ... 6) are marked with the reference number MSGn. The synchronization message sent by each node is usually different and depends on the message-based synchronization method used. The propagation of the clock frequency from the master clock (Node 1) to the other nodes of the system is shown by solid lines. Dashed connections between nodes are not used in the normal-35 lit situation for system synchronization, but they are> 1 92358 3 available in change situations.

The simple principle in message-based synchronization is that the user defines a node synchronization hierarchy, giving each node its own identifier indicating the node level in the hierarchy, and the system synchronizes to the defined master clock independently using all existing connections between nodes if necessary. ). If the connection to the master clock is lost and no alternate connection 10 exists, or the master clock fails, the system synchronizes to the next highest level node. Fig. 2 shows a situation when the main clock fails in the system according to Fig. 1. The response to the change in synchronization takes place by means of an inter-node messaging 15. When the incoming timer is interrupted, the synchronization hierarchy is rebuilt from the point of interruption onwards (away from the system master). This is done, for example, in such a way that the node that first notices the interruption first goes to the internal timing mode for a certain period of time and forwards 20 information about the change. When the next node notices the changed situation, it also goes to the internal timing mode for a period of time and sends information about the change, etc. When the deadlines of the individual nodes expire, the formation of a new synchronization hierarchy begins.

25 Usually, the end result is a hierarchical structure similar to the original, in which the failed connection is replaced by a functioning connection, while the rest of the structure remains almost unchanged.

A network using message-based synchronization is described, e.g., in U.S. Patents 2,986,723 and 4,837,850. The former illustrates a system in which nodes enter an internal timing state in fault situations as described above. The latter discloses a system in which post-fault resynchronization is based on a separate, master node search 92358 to be transmitted in the event of a fault.

4 keywords. These systems are described in more detail below.

In known systems, a fault situation such as that described above requires quite a long time before sync-5 resonance is found again, because finding a synchronization usually requires (depending on the network topology and fault location) several consecutive internal timing visits (and thus several synchronization tree changes) or alternatively sending separate paging messages. .

10 (Synchronization tree refers to the hierarchical tree-like structure that arises in submerged synchronization from the main node to the network.)

It is therefore an object of the present invention to provide a hierarchical synchronization method by which resynchronization can be accelerated after a node has lost its selected timing source. This is achieved by the method according to the invention, which is characterized by what is described in the characterizing part of the appended claim 1. The communication system according to the invention, in turn, is characterized by what is described in the characterizing part of the appended claim 5.

(When a node loses its timing source, it is either a loss of signal or deterioration of signal quality so that it can no longer / cannot be used for synchronization, or deterioration of 25 selected synchronization messages. A degraded synchronization identifier means that the corresponding synchronization message is still qualitatively acceptable, but The deterioration of the incoming synchronization identifier indicates a change / failure on the connection to the main source of the system.)

The idea of the invention is that if a node that has lost its timing has a neighboring node that is at the same level in the synchronization hierarchy at the time of the loss of timing, and which node is closer to the master node than the node that lost its timing, select that node. a neighboring node as a new source of thought. In this way, resynchronization to the main body of the system can be significantly accelerated.

The invention will now be described in more detail with reference to the examples of Figures 3 to 6 in the accompanying drawings, in which Figure 1 shows a message-based synchronization system in general form synchronized to the main source clock frequency, Figure 2 shows the network of Figure 1 when its main node has failed; a slave synchronization network (SOMS) in its initial state, Fig. 4 shows the network of Fig. 2 in a stable state, Fig. 5 shows a flow chart 20 principles according to the invention, Figs. 6 and 7 show a SOMS network applying the method according to the invention, and Fig. 8 shows node synchronization means by which the method according to the invention is carried out.

Figure 3 shows a system using Self-Organizing Master-Slave synchronization (SOMS), a message-based synchronization method known per se, in this case five nodes (or devices), denoted by reference numerals 1. .5 according to their hierarchical level. (The main node of the network has the smallest SOMS address.) The nodes forward messages containing the above SOMS addresses. This allows the nodes to identify each other with these address numbers and build a synchronization-35 hierarchy, allowing the entire network to synchronize to 92358 6 master nodes.

As mentioned above, the messages that are sent continuously on the network depend on the message-based synchronization method used. In addition, the messages are 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 visible to the sending node as the main node.

D2 is the distance to the node expressed by D1r. This distance is expressed as the number of nodes in between.

15 D3 is the SOMS address of the sending node.

Each node (or device) continuously compares incoming SOMS tags with each other and selects the smallest of these. In the identifier, the parts D1, D2 and D3 are directly connected into one number by putting them in succession 20 (D1D2D3) (for the sake of clarity, a dash will be written in the following to separate the different parts; Thus, the primary selection criterion for the smallest address becomes the SOMS address (D1) of the node visible to the previous nodes as the main node, i.e. the node tends to synchronize to a signal whose frequency is originally from the node whose address is as small as possible. In this case, in a stable situation, the entire network is synchronized to the same master node (because the master node of the entire network has the smallest SOMS address).

If two or more of the incoming signals are synchronized to the same master node, the one with the shortest path is selected (D2). 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 n 92358 7 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) is left intact, 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 incoming SOMS messages contains an identifier that is less than the internal identifier, the node uses its own internal oscillator or possibly a separate synchronization input as the source of its clock frequency. The outgoing SOMS message naturally uses 15 internal SOMS identifiers.

The nodes continuously send SOMS messages in each direction so that the changed information in the SOMS identifiers spreads as quickly as possible and the operational status of the neighboring nodes is constantly known. Before SOMS identifiers can be compared, 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, its SOMS identifier is immediately accepted for comparison if the message was error-free.

25 When an incoming transmission link has an accepted SOMS identifier and an error-free message with the same identifier arrives continuously, the situation remains unchanged. If an SOMS message is found to be invalid, the old SOMS identifier is retained until 30 consecutive SOMS messages are received as invalid. In that case, the SOMS tag for comparison. Waiting for three consecutive SOMS messages is intended to eliminate momentary interference.

If no SOMS message arrives from the connection, even if the connection 35 otherwise works, three consecutive 92358 8 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, 5 valid SOMS tags are not obtained for comparisons, the the SOMS identifier of the transport connection. In this case, the as a SOMS identifier of the incoming transmission link, a constant identifier in which all parts (D1, D2 and D3) get 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 does 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. If none of the incoming tags is smaller than the internal tag, the node to use 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-25 node within the node, because the others have not yet been processed. In Figure 3, the incoming SOMS tags are marked next to each node, and the selected tag is written inside the frame (in the initial situation of Figure 3, all nodes use their internal timing source). The connections in use in Synk-30 resonance are drawn on a solid line, the spare connections are in a broken line (in the initial situation according to Figure 3, all connections are spare).

When the nodes have time to process the incoming SOMS-sa-35 nominations, the node 1 remains in use of the internal timing, t

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92358 9 nodes 2 and 4 are synchronized to node 1 based on the identifier 1-0-1, node 3 is synchronized to node 2 (2-0-2) and node 5 is synchronized 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.

In the 10 synchronization methods disclosed in the aforementioned U.S. Patent 2,986,723, the node of the system that has lost its synchronization connection to use internal timing (its own oscillator) for a period of time and sends its own internal timing identifier X-O-X (where X is its own synchronization number) to neighboring nodes. When a neighboring node receives an internal timing identifier from the node through which it is synchronized, it itself switches to internal timing for a specified period of time and begins sending its own internal timing identifier Y-O-Y to neighboring nodes. When the forced time limit of a single node 20 has elapsed, it again freely selects its timing from the incoming signals of the source based on the incoming synchronization messages, whereby the structure of the synchronization hierarchy begins to re-form in the part of the system behind the fault point for synchronization.

Thus, when the synchronization structure breaks down as a result of a transmission link or node failure, some of the nodes in the system use their own clock for timing, which is almost never qualitatively as good as the main clock of the system 30.

In the synchronization method disclosed in the aforementioned U.S. Patent 4,837,850, a device (node) that has lost its synchronization connection sends a paging message searching for a master device and at the same time acts as a master clock for those devices that had synchronized through it before the failure. When 92358 10 other devices receive a paging message sent by the device that detected the fault, they forward it. If the keywords eventually reach the main unit of the system, the main unit sends back its own normal synchronization message. Upon receipt of this synchronization message, the device that detected the fault has a new synchronization connection to the main device along the established replacement route. The system operates in a similar manner if one device (node) fails, in which case the devices behind the 10 devices that failed the synchronization lose the connection they used to the main device of the system.

In a system using the synchronization method disclosed in U.S. Patent 4,837,850, failure of a device (node) in the middle of a synchronization connection or synchronization hierarchy structure will result in a break in the synchronization structure, whereby the system is divided into two parts for synchronization. In the second part, the clock frequency of the main device is used as the clock frequency, and in the second part, the clock frequency of the device that detected the fault. When a new route has been found to the main unit of the system by means of a paging message and the information about it has passed back to the device that detected the fault, the whole system receives its timing again from the main unit.

The solution according to the invention accelerates the synchronization of the system with the master clock in fault situations. Fig. 5 is a flow chart of the operation performed by a system node when it detects a weakening or interruption of a signal selected for synchronization or a deterioration of a selected synchronization identifier, which may be due to e.g. a failure of the connection used by the selected signal or the selected signal transmitting node. When the loss of the selected timing source is detected in step 51, the node examines if there is another identifier of the same level among the other synchronization identifiers coming to it (step 52). If such an identifier is found, it is examined whether the node sending that identifier is closer to the main node in the synchronization tree (step 53). If so, the signal of that identifier is immediately accepted as a new timing source for the node. If, on the other hand, the comparison carried out in either step 5 52 or 53 gives a negative result, a procedure known per se is immediately initiated in order to find an alternative connection to the master node. In the case of a SOMS network, this means that the node enters the internal timing mode for a fixed period of time.

10 Furthermore, since the synchronization identifier with the selected synchronization identifier is required to be closer to the master node in the synchronization tree than the fault-detecting node, depending on the synchronization method used, the synchronization message 15 may need to be appended to the synchronization message. If the network uses self-directed slave synchronization (SOMS) as described above, the information is automatically transmitted with the synchronization identifier (the second 20 digits of the identifier, i.e. D2). If, for example, the system disclosed in e.g. U.S. Patent 4,837,850 is used, the generation and transmission of said information must be added to the system. In practice, this is done in a similar way as in the SOMS network, i.e. by adding a distance-telling part to the message, the value of which is set to zero by the master node and whose value is increased by one by the other nodes when forwarding the message of the master node.

The transmitting node in the synchronization tree must be closer to the main node than the fault detecting node, because otherwise there is a risk that a synchronization will occur, i.e. the device is synchronized to a signal whose frequency has already passed through it itself.

Figures 6 and 7 show an implementation of the method according to the invention in a network using the self-directed submissive synchronization (SOMS) described above.

92358 12

The network comprises six nodes 1 ... 6. If the connection between Nodes 2 and 4 fails, Node 4 loses connection to Node 2. In this case, Node 4 does not force into the internal timing state, but immediately accepts the synchronization identifier (1-1-3) received from Node 3, which is at the same hierarchy level as previously selected. ID (1-1-2). In this case, the synchronization identifier sent by the node 4 does not change at all (cf. Fig. 7), and no other changes occur in the synchronization tree below it. This saves forced internal scheduling visits that slow down synchronization, which can be very numerous, depending on the situation and network topology. Thus, there are no unnecessary changes in the synchronization tree either, because the nodes do not switch to the internal timing mode one after the other.

Momentary interference is filtered out because the synchronization message must be invalid three times in a row before the incoming synchronization identifier is rejected.

Similarly, the method of the invention can be utilized in any system in which one node has at least two neighboring nodes that are equidistant from each other (and closer to the main node of the system).

25 Accepting a peer-to-peer synchronization tag in place of the selected tag is performed in the node synchronization decision section. Figure 8 shows the elements of the node that perform the timing source selection. The figure shows two signals from neighboring devices to the system device 30, A and B. Each signal comes from the system's own node and contains a synchronization message, which is separated by the signal receiving section 13a and 13b, respectively, and forwarded to the synchronized message receiving section 16a and 35, respectively. 16b. The receiving section of the synchronization message 92928 13 acknowledges the error-free nature of the message and forwards it to the central synchronization decision section 20 of the device, each input of which is connected to the output of the respective receiving section 16a, 16b. The signal receiving parts 5 also monitor the quality of the received signal and store information about them in the connection-specific fault databases 24a and 24b, respectively. The receiving section 16a of the synchronization message receives the fault information from the database 24a and the receiving section 16b from the fault database 24b, respectively. If the 10 incoming signals are not valid for synchronization, the receiving part of the synchronization message prohibits its use. This can be done separately by denying or setting the value of the incoming tag to the maximum possible, in which case in the latter case it is practically not used for synchronization in any case.

The decision section 20 compares the messages and stores them in the memory 21. When the selected synchronization identifier becomes worse or disappears completely, the decision section searches among the other identifiers in the synchronization hierarchy for an identifier of the same level. If such an identifier is found, the decision section 20 examines whether the node sending that identifier in the synchronization tree is closer to the master node than the node itself. If so, the decision section selects the signal corresponding to such an identifier as its new timing source. If an identifier that meets the above criteria is not found, the decision section initiates a normal, slower method to find the connection to the main node of the system. The messages may also be in the memory 21 in order of priority, so that at the highest level 30 there is an available clock source with the "best" synchronization identifier according to the current message-based synchronization method. When the selected synchronization identifier is lost, the next one in the list is selected immediately, if it is marked as meeting the above-mentioned criteria 35. Thus, the comparison (Fig. 5, steps 52 and 92358 14 53) does not need to be performed until after the loss of timing, but the comparison can be performed all the time, at the time of the loss of timing it is immediately known whether a new identifier can be selected immediately or started as such. a known, slower method for finding an alternative connection to a master node. The synchronization tags may also be in the memory 21 in different lists, so that the first list contains all the inbound synchronization tags and the second list has 10 first selected synchronization tags and below it, in order of priority, all those tags that meet the above criteria. When losing the selected synchronization identifier, the node can immediately select the next identifier from said second list.

After a neighbor node meeting the above criteria is found, the node may also have a certain short filtering time before selecting the synchronization identifier of that neighbor node. This is especially true in larger systems, as the loss of timing can also be due to a fault in the remote network. In this case, the fault can only be reflected a little later in another identifier of the same level. The purpose of the filtering time is to prevent the node from selecting the identifier to which the fault is just being reflected. In practice, the length of the filtering time is, for example, half of the time spent on one connection interval detecting and responding to the change.

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. The method according to the invention can, for example, be used in connection with various message-based synchronization methods, although it is best suited for the SOMS network, because the synchronization message used in the SOMS network 35 is as suitable as possible for the solution according to the invention.

Claims (6)

92358 15 A hierarchical synchronization method for a communication system using message-based synchronization, comprising a plurality of nodes (1 to 6) connected to each other by transmission links, the method comprising transmitting signals to each other containing synchronization messages comprising information about the priority of a corresponding signal in the system. 10 synchronization hierarchy, characterized in that when a node loses the timing source of its choice, it tends to select as a new synchronization source a neighbor node whose synchronization identifier is at the same level in the system synchronization hierarchy as the access timer source the node selects it as its new synchronization source, or if such a node is not found, the node 20 initiates a procedure known per se; to find a new connection to the master node. A method according to claim 1, characterized in that if a neighbor node meeting said criteria is found, the node accepts it as its new timing source immediately after the timing is lost and said new neighbor node is found. A method according to claim 1, characterized in that if a neighboring node meeting said criteria is found, the node accepts it as a new timing source after a certain filtering time and said new neighboring node is found if the synchronization identifier of said neighboring node has not changed during the filtering time. . A method according to claim 2, characterized in that the node continuously maintains a list 92358 16 of neighboring nodes meeting said criteria, wherein the replacement synchronization identifier is continuously known if the selected synchronization identifier is lost. A communication system using message-based synchronization, comprising a plurality of nodes (1 to 6) interconnected by transmission links through which the nodes send each other signals containing synchronization messages comprising information about the priority of the corresponding signal in the internal synchronization hierarchy. characterized in that the system node comprises means (20, 21) for storing in its own group of incoming synchronization identifiers which are in the system synchronization hierarchy at the same level as the synchronization identifier of the currently selected timing source and which the transmitting node is closer to the system master node than the node self. A system according to claim 5, characterized in that said synchronization identifiers are stored in order of priority. 17 2 ό 5 8