Method for synchronizing transport ring network built around synchronous digital hierarchy system

FIELD: communications engineering; digital data transfer and synchronization systems; communication network synchronization systems.

SUBSTANCE: proposed method is characterized in that additional links are organized in network and provision is made for transferring sync signals in backup driving network component, output signals of the latter being generated bypassing internal generator from sync signals arriving from last first-priority component nn and from last second-priority component mm. Sync signal arriving from main sync signal supply is conveyed in series over network through backup driving network component bypassing internal generator; variation (reduction) in quality level of sync signals being used is entered in status message of STM-N heading. As a result, using backup path running to main driving component through m components does not cause closed-circuit synchronization. Hence, network will be always synchronized from one sync signal supply upon occurrence of any single accident.

EFFECT: enhanced quality of rendered communication services.

1 cl, 4 dwg

 

The proposed method relates to techniques for communications, more specifically to the transmission of digital signals and synchronization systems, and can be used to build synchronization systems of communication networks.

The traditional method of building a reliable system synchronization is to provide a synchronization signal to each network element in the main and standby paths. This ensures the continuity of synchronization in the accident.

If built properly, the network synchronization must meet the following basic requirements:

- the distribution of signals on the network using primary and backup transmission should not have closed-loop synchronization;

- each element of the network must be synchronized from the source, providing at the moment the highest quality of synchronization signals;

when the generator (any network element) enters the hold, it should not be a source of synchronization signals for another source to provide a higher quality of synchronization signals;

- the number of switches should be as minimal as possible (this implies that it is necessary to prevent "unnecessary" the number of times of synchronization signals and the variability in the direction of transmission of synchronization signals).

To perform p the listed above requirements in practice uses the following mechanisms:

- prioritize the inputs of the synchronization signals;

- send status messages about the quality of the synchronization signals in the stream header, STM-N or signals E1 (2048 kbps).

One way synchronization ring transport network currently in use and listed in the European standard ETSI EG 201 793 V.I. 1.1 (2000-10), in the guideline document industry RD 45.230-2001 and in the book "network Clock synchronization " (authors Davydkin P.N., Koltunov M.N., Ryzhkov, A.V., ECO-TRENDS, Moscow, 2004, p.35-38), selected as a prototype.

The option of constructing synchronization ring transport network in accordance with the known method is shown in figure 1. In figure 1 the following notation:

VZG 1 - the slave oscillator, which is in this scheme, the main source of synchronization signals;

VZG 2 - the slave oscillator, which is considered redundant source of synchronization signals;

No. 1 is the Leading primary network element of the transmission system SDH;

No. 2 - Leading backup network element of the transmission system SDH;

n1the first network element of n elements;

nnthe last network element of n elements;

m1the first network element of m elements;

mmthe last network element of m elements;

- the priority of the inputs of the network element;

(4), (8), (15) - the quality levels of the transmitted synchronization signals;

T3 input clock 2,048 MHz network element DDS;

T4 - signal output external synchronization network element DDS;

Q4, Q8 - assigning a quality level to the sync signal input T3 network element DDS;

Q≤4 - condition signal synchronization on the output of T4 network element DDS (if the value of the quality level of the clock signal is less than or equal to 4, then the signal at the output T4 not disabled);

- the main way of transmission of synchronization signals;

→ - back transmission of synchronization signals.

A significant feature of this method is the lack of a backup path to the primary and backup sources of synchronization signals that, as indicated in the above-mentioned documents, prevents the appearance of closed loops.

The known method synchronization ring transport network is based on a system of transmission of synchronous digital hierarchy (SDH) and consisting of a main and a backup source of synchronization signals, main and backup of the leading network elements n network elements, m network elements, designed for transmission of synchronization signals is that

- from the main East is cnica synchronization signal (SS) the synchronization signal with the first priority are served through the main leading network element and a sequential chain of n network elements and output the last n nth network element of the chain is passed on back leading network element from which synchronize redundant synchronization signal (SS), and the synchronization signal from the main source SS has a higher level of quality than the synchronization signal from the secondary source SS, the synchronization signal with the second priority from the backup source SS is passed back through leading network element and a sequential chain of n network elements, and the output of the first network element m is served on the main leading network element;

- the synchronization signal with the first priority from the main source SS is fed through a main leading network element and through a sequential chain of mmnetwork elements until the last mmnetwork element, the synchronization signal with the second priority from the backup source SS is passed back through leading network element and a sequential chain of m network elements to the first m1network element.

Thus, in the diagram shown in figure 1, there is no transmission of the synchronization signal from the first network element m1to the top of the main element, and mmth network element back to the master element.

Currently in use on the network synchronization method is insufficient is OK consisting in the fact that in case of any single accident in the chain of transmission of synchronization signals from the primary source to the backup network synchronization splits into two independent parts.

For example, when the accident in the area between the main leading network element and the first network element of n1(2) the synchronization signal coming from the last network element nnon the back leading the network element that has a quality level lower than the threshold signal at the output of T4 backup host network element. As a consequence, the signal at the output of the backup host network element is turned off, the backup source of synchronization signals goes on hold and the right part of the network to the accident synchronized from the secondary source: USG - back leading network element - nnelement and further to the first (n1element.

In the left part of the network is stored synchronization from the primary source the primary path synchronization: VSG - main leading network element to the first network element m1and next to the last mmelement.

Between parts of the network appears plesiochronous interaction.

Plesiochronous interaction leads to a decrease in the quality of the transmission of information signals, a reduced quality of communication services and the mind is neseniyu bandwidth.

To improve the quality of communication services in a known way synchronization ring transport network is based on a system of transmission of synchronous digital hierarchy (SDH) and consisting of a main and a backup source of synchronization signals, main and backup of the leading network elements, n of network elements and m network elements, designed for transmission of synchronization signals, features:

- from the main source of synchronization signals (SS) the synchronization signal with the first priority are served through the main leading network element and a sequential chain of n network elements and output the last nnth network element of the chain is passed on back leading network element from which synchronize redundant synchronization signal (SS), and the synchronization signal from the main source SS has a higher level of quality than the synchronization signal from the secondary source SS, the synchronization signal with the second priority from the backup source SS is passed back through leading network element and a sequential chain of n network elements, and output the first network element of n1served on the main leading network element;

- the synchronization signal with the first priority from the main source SS served through VI is th leading network element and through a sequential chain of m mnetwork elements until the last mmnetwork element, the synchronization signal with the second priority from the backup source SS is passed back through leading network element and a sequential chain of m network elements to the first m1network element,

- additional backing leading network element serves the synchronization signal with the second priority with the last mmth network element,

- advanced backup master network element external trigger signal network element SDH, formed in bypassing the internal oscillator is fed to the input of the same backup host network element, and make the change (decrease) the value of the quality level of the transmitted signal synchronization;

additionally, with the release of the first m1th network element backup path serves on entrance leading basic element of the synchronization signal with the third priority.

Figure 1 shows a diagram of the ring transport network, which uses the known synchronization method (prototype).

Figure 2 shows a variant of construction of the synchronizing ring transport network by a known method in the accident in the area between the main leading network element and the first network element of n1.

Figure 3 shows a scheme for constructing synchronize the ring transport network proposed in the application method.

Figure 4 shows a variant of construction of the synchronizing ring transportation network for the proposed method in the accident.

Thus, the difference of the proposed method from the one used at the present time is that in the network organises some additional links (backup path to network elements) and provides for the transmission of the synchronization signal in the backup master network element from the output of T4 to the input of T3 (figure 3).

Output signals T4 backup host network element are formed to bypass the internal generator of signals coming from two directions: from the nnelement with first priority and mmelement with the second priority.

The synchronization signal from the primary source of synchronization signals transmitted sequentially via the back leading network element bypassing the internal generator, and in the header of the stream STM-N in the status message is a change (decrease) the level of quality of the synchronization signal.

As a consequence, the use of a backup path to the primary master element m of elements does not lead to closed loop synchronization.

In case of any single accident, the network will always be synchronized from a single source of synchronization signals (figure 4), which will ensure high the e quality of communication services.

To get the same quality with plesiochronous interaction is possible only by increasing the accuracy of the frequency of the primary and backup sources of synchronization signals.

For example, the quality of the synchronous operation can be achieved in plesiochronous mode of operation, if the use of nuclear generators (for example, cesium or high quality rubidium). This inevitably leads to high equipment costs.

The method of synchronization ring transport network is based on a system of transmission of synchronous digital hierarchy (SDH) and consisting of a main and a backup source of synchronization signals, main and backup of the leading network elements n network elements, m network elements, designed for transmission of synchronization signals, namely, that from the primary source of synchronization signals (SS) the synchronization signal with the first priority are served through the main leading network element and a sequential chain of n network elements, and output the last nnth network element of this chain is passed on back leading network element from which synchronize redundant synchronization signal (SS), and the synchronization signal from the main source SS has a higher level of quality than the synchronization signal from the backup IP the student SS, the synchronization signal with the second priority from the backup source SS is passed back through leading network element and a sequential chain of n network elements, and output the first network element of n1served on the main leading network element; a synchronization signal with the first priority from the main source SS is fed through a main leading network element and through a sequential chain of mmnetwork elements until the last mmnetwork element, the synchronization signal with the second priority from the backup source SS transmits a leading network element and a sequential chain of m network elements to the first m1network element, characterized in that on the back leading network element serves the synchronization signal with the second priority with the last mmth network element in the backup master network element external trigger signal network element SDH, formed in bypassing the internal oscillator is fed to the input of the same backup host network element, and make the change (decrease) the value of the quality level of the transmitted synchronization signal, from the output of the first m1th network element backup path serves on entrance leading basic element of the synchronization signal with the third priority.



 

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