Synchronous digital hierarchy network

 

(57) Abstract:

The invention relates to a synchronous digital hierarchy network (SDH networks). The technical result - the prevention of closed circuit synchronization. The technical result is achieved by labeling each node of a clock signal passing through the specified node identification data. In one embodiment, each node in its functioning parametervalue any identification data for the previous node and indicates that the clock signal should not be used for the purpose of synchronization, if the node to which it should be transferred, will cause a closed circuit synchronization. In the second embodiment, the identification information of the node is entered in the list, and if any node considers its own identity from this list, he decides that you should not use this signal to synchronize. By counting the number of nodes through which the signal has passed, may be provided with means to prevent the reference sequence synchronization excessive length. 2 S. and 6 C.p. f-crystals, 6 ill., table 2.

The present invention relates to si connection with the use of optical networks and to a lesser extent radio network, are becoming more common to use digital formats of communication. The European system of CCITT standardized on the basis of SDH networks, while American systems use synchronous optical network (SONET - synchronous optical networks), hereinafter defined as SONET network operating in accordance with the ANSI standard. The SDH system uses an interface of a network node and is compatible with the SONET system. For a system of a network node needs to obtain information about the network using a synchronizing pulse that is usually derived from an external synchronization source. The invention is applicable to any such system.

For such systems it is important that the synchronizing pulse used in the node for synchronization purposes, had the highest possible quality, i.e. it should not be distorted to such an extent, which could lead to uncertainty of its value. One of the problems associated with the emergence of such distortion may occur when a loop synchronization is formed in such a way that the same synchronization signal is transmitted by repetition in a chain, and distortion occurs in the signal synchronization whenever it passes through the network node. The invention rlando, US, vol.1-2-3,6.12.1992, Institute Of Electrical And Electronics Engineers, pp. 821-828, J. A. Crossett et al: "the SONET/SDH Network Synchronisation And Synchronisation Sources described the reference synchronization signals to synchronize the networks SDH and SONET, as well as the distribution of these reference signals in a synchronous optical network. These signals provide synchronization of data transmission equipment and control centers. In this work discusses the levels of the quality of synchronization provided in the network. Synchronizing the network is presented with the position of the SONET network, and made a comparison with the SDH network. In the international application WO-A-94-11966 described a hierarchical synchronization method for a telecommunications network that uses a synchronization message-based and contains many nodes interconnected by transmission lines. In this way, the nodes communicate signals containing synchronization messages with information about the priority of the corresponding signal in the form of the characteristics of the site, and within the internal hierarchy of synchronization in the system. In addition, the transmission line between two nodes is monitored to check if it is bidirectional, and as soon as the bi-directionality of the line cannot be confirmed, the use of this line for synchronization is prohibited.

As soon as the next node learns which hosts passed the synchronization signal can be decided whether to arise closed circuit synchronization.

In one of the embodiments, each node includes means for replacing any data that identifies the node from the previous node, through which the signal has passed.

This solution provides an effective means, in particular, to prevent the occurrence of closed circuits synchronization between neighboring nodes.

Preferably, in this case, each node includes means for reading identification data of the node from which it received the incoming clock signal, and for transmitting, in case the signal should not be used for synchronization.

In SDH networks, information is transmitted in frames, consisting of 270 bytes. They ordered columns and nine rows. The first nine columns are used to create the service information (overhead), known as the service information section. Display the synchronization status is included as part of this service information. Bytes-related information in the service information section for synchronization, denoted as S1 and is used to indicate the quality of the timing source that supports traffic with which it is associated. In the present embodiment, it is the byte S1 of the status of synchronization is designed for data transmission signal indicating that the clock signal should not be used.

An implementation option, described above, is used, in particular, to prevent chain synchronization between neighboring nodes in the network. To prevent the possibility of large closed circuits with a large number of nodes in an alternative embodiment, each node includes means for adding identification data of the node to the list transmitted together with a clock signal, and this re the treatment, if this list contains the identification information of the corresponding node, use the corresponding node of the clock signal for synchronization.

If the node finds its own identification data in this list, it means that the corresponding node has detected a loop synchronization.

In addition, it is desirable that, regardless of the presence of synchronization circuits a clock signal is not passed through too many nodes before it is discarded. To do this, in the above embodiment, each node preferably includes means for counting the number of nodes, which passed through the clock signal, and to prevent, if the number of nodes has exceeded the set value, use the corresponding node of the clock signal for synchronization.

Embodiments of the invention will be described by example with reference to illustrate his drawings showing the following:

Fig. 1 - schematic representation of SDH network in the form of a ring;

Fig. 2 is a view of the network in Fig. 1 after the occurrence of the failure mode;

Fig. 3 is a view of a pair of neighboring nodes in the composition of the alternative options, the aspect of the invention;

Fig. 5 - representation of the more complex multi-mode network, corresponding to the invention;

Fig. 6 - representation of the network in Fig. 5, uses another aspect of the invention.

In accordance with Fig. 1 SDH network contains four nodes 1, 2, 3, 4, arranged in an annular configuration, and the neighboring nodes are connected by bidirectional communication channel 5. In a typical case, each node contains a "network element" consisting of a multiplexer/demultiplexer designed for routing traffic and other signals to the other switching elements through additional inputs and outputs, which are not shown in Fig. 1 for reasons of clarity of the drawing. Because SDH network is a synchronized network, it is important that high-quality synchronization signal provided at all nodes in the network. As shown in the drawing, the external synchronization source 6 is connected to the first input node 1 of the network. External synchronization source indicated on the drawing G. 811 that means in terms of SDH network that is the source of the highest quality. This signal is then distributed over the data transmission channel 5 so that do not form a closed chain synchronization, i.e., in each channel 5A or 5B signal sin is hildren will fail synchronization source, as shown in Fig. 2 at the point X, the chain synchronization is established, because the channel 5V to receive timing information from the corresponding available for this channel, i.e. channel 5A from node 4. In this case, the display of synchronization status should be entered into as part of a multiplexed service signal area in the part of the service S1 signal segment. It should be borne in mind that the discovery "cycled" synchronization is not easy to implement, as shown in the drawing. Since each node can be connected through many areas and, consequently, the loop synchronization can occur if the sync signal from one of these sources would return to the same site, but in another area, as shown in Fig. Z

The examples shown in Fig. 1, 2, 3, illustrate a very simple set of directions, conventionally referred to as "North-South", to determine where the synchronization signal is looped. When using devices with cross-connections or elements included in the "grid" network, determining where the synchronization signal is returned back to its source, becomes less certain, and therefore Nicotiana be provided for each node.

In accordance with the invention in one of its aspects, each node during its operation enters identification data signal associated with a clock signal, such as signal SSMB (indicating synchronization status) in a hierarchical network SDH.

Byte S1 contains four backup bits (1-4), and these bits are used. ID requires allocation of a fairly large scale, and therefore is allocated 16 bits per MP basis, as shown in the table. 1.

Designation FAW refers to the code word alignment frame. In Fig. 4 shows the case when two nodes 10, 11 are connected to two separate bi-directional channels 5. The synchronization source 6 with level of quality G. 811 is used to synchronize each of the sites traffic from the first node 10 to the second node 11. Display the synchronization status (SSMB) used for each of the sections of the site, indicates that the quality level corresponds G. 811, and sets the source ID to indicate that it refers to the first node 10. The second node 11 uses the recovered clock signal with one of the mentioned sites for synchronization of traffic back to the first node 10. However poznati, both channel 5A15V1connected with the first node 10 and, therefore, synchronization would be reversed. The S1 byte is set to the state "1111" for status indication "do not use" signal.

In Fig. 5 shows an example of a more complex network in which each node 21, 22, 23, 24 is connected to two bidirectional sections 51, 52and the third node 23 is connected to two other nodes 24 and 25. In each case, the loop synchronization indication "not use" is passed to indicate the status of the synchronization SSMB. Each node is able to determine from any other node in the network adopted the synchronization signal, and then determine whether to reverse the synchronization signal.

As described above, the claimed device eliminates the need to load in the network control center information indicating potential loop synchronization. In addition, the network requires minor changes or does not require configuration changes in the data link synchronization. The system has a high reliability, because the necessary configuration is reduced simply to provide the ID of the synchronization source or node ID for each

An implementation option, described above, can be used, in particular, to prevent the occurrence of closed circuits synchronization (loops) between neighboring nodes in the network. The second variant of the invention, which will be described below, provides identification of closed circuits multimode synchronization, can also provide a means to identify the number of nodes passed to the synchronization signal. This can be important due to the fact that the distortion of the clock signal occurs whenever it is used for synchronization purposes. For example, the SDH standards currently specify that not more than twenty-synchronized clock signals must form part of the so-called synchronized reference sequence due to distortion of the quality of synchronization. In the second embodiment, the identification information of the node is included in the list whenever the clock signal passes through the corresponding node. The identification information is added to indicate the status of the synchronization SSMB, as described below. As mentioned earlier, the S1 byte contains four backup bits (1-4). Each identifier requires a relatively large range, with whom ecna, and also provides an indication of the number of IDs available currently in this list. This structure is formed on a MP based and shown in the table. 2.

Whenever the synchronization source is used by the node identification data is added to the list of nodes available in the display of synchronization status SSMB, and the number of identifiers of the source is incremented. This new display of synchronization status SSMB is then passed to each site that uses this source for synchronization.

Fig. 6 corresponds to Fig. 5 except that you use an alternative method. Each node can detect potential closed chain synchronization, if its identity is present in the received indication of the status of the synchronization SSMB. For example, the third node 23 knows that he can't synchronize with nodes 25 and 26, as its own identification information is present in the display of synchronization status SSMB adopted from these nodes. Each node may also determine the length of the reference sequence synchronization and, thus, can be reduced if the quality of synchronization to ATI nodes, was evaluated as unacceptable, then sync from the sixth node 26 will indicate in its display of synchronization status SSMB quality corresponding to state "do not use".

1. Synchronous digital hierarchy network (SDH-network) that contains many nodes, interconnected bidirectional communication channels, the external clock signal applied to the input of one of the mentioned nodes that are configured to pass the clock signal from node to node in the synchronization process, wherein each node includes means for marking the clock signal passing through the corresponding node, data that identifies this node as part of the means to prevent the occurrence of closed circuits synchronization.

2. Synchronous digital hierarchy network p. 1, wherein each node includes means for replacing any data identifying the node from the previous node, through which the signal has passed.

3. Synchronous digital hierarchy network under item 2, wherein each node includes means for reading identification data of the node that originated the incoming clock signal, and for transmitting, in slocal should not be used for synchronization.

4. Synchronous digital hierarchy network under item 3, wherein the indication of the status of the synchronization is designed to transmit a signal indicating that the clock signal should not be used.

5. Synchronous digital hierarchy network p. 4, characterized in that the specified signal is byte S1 indicate the status of the synchronization.

6. Synchronous digital hierarchy network p. 1, wherein each node includes means for adding identification data to a node in the list that is passed with a clock signal, and this list identifies many of the previous nodes, which passed through the clock signal, and means for preventing, in the case where the list contains data that identifies the appropriate node, use the corresponding node of the clock signal for synchronization.

7. Synchronous digital hierarchy network p. 6, wherein each node includes means for counting the number of nodes, which passed through the clock signal, and to prevent, if the specified number exceeded a predetermined value, use the corresponding node of the clock in a synchronous digital hierarchy network (SDH networks), contains many nodes, interconnected bidirectional communication channels and made with the possibility of transmission of the external clock signal from node to node in the synchronization process, wherein the labeled clock signal passing through the node, the identifying data of the mentioned site.

 

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