Modernization of the site zonal networks Stepnogorsk-Kokshetau based fiber-optic line

- T2 power - PDH, 2048 kbit / s (G.703 / 704);

- T3, the source - clock 2048 MHz or 2048 kbit / s (G.703 / 704);

- clock outputs:

a) T4, external synchronization signal 2048 MHz (G.703);

b) T4, 2048 kbit / s (G.703 / 704).

- own accuracy: ± 4,6 • minimal 10E-6.

SETS Block diagram shown in Figure 1.

Figure 1 - Synchronization SDH equipment

For transporting the synchronization signal in the SDH network typically used payload signals (traffic). To meet the quality standards of international digital connections (G.822) the primary clock source must comply with PRC standard (G.822).

For secure synchronization, SDH multiplexers network should have multiple redundant clock sources:

- PRC or the source of the signal quality is not lower than PRC;

- Secondary clock (SSU);

- Your own timing source (SETS).

The maximum allowable number of network elements of the network (NE) between the two SSU is 20, the maximum number of SSU in the chain synchronization - 10. Total number of consecutive sync items (NE and SSU) shall not exceed 60.

Self-healing SDH network structure in a crash on the network perform automatic reconfiguration of the synchronization, which is controlled by a time-marker and priority switching of SDH equipment. The criterion for switching sources in synchronization network elements are the following events:

- LOS (loss of signal);

- LOF (loss cycle);

- AIS (Alarm Indication Signal);

- TMA (alarm synchronization marker);

- Exc.BER (10 bit error rate).

Information about the quality of the timing source is transmitted in bits 5-8 S1 byte header MSOH STM-1 frame. Table 2 contains the information contained in the byte synchronization marker SSM.

Table 2 - The information in byte synchronization marker SSM

Note: Notes to Table 2:

The PRC, SSM when receiving the value of bits 5-8, 0010, each network element is synchronized with this reference oscillator Q1 quality.

SSU-A, when receiving SSM bits 5-8 the value 0100 indicates the use of a timing source, respectively G.812T ITU-T with a level of quality Q2.

SSU-B, Q3 quality is almost an order of magnitude lower than for transit SSU.

SEC, SSM source clock multiplexer synchronization marker byte is sent when the priority list are no other sources of clock signals.

Quality is not known: the SSM byte is transmitted by the network element in the STM output as long as the internal crystal oscillator is not synchronized with the incoming clock signal sources.

To synchronize the unused byte synchronization marker with a value of 5-8 bits 1111 (Q6) is transferred automatically in the case of SDH-sync port in the opposite direction. This prevents the formation of the loop synchronization.

The basic requirement when planning the synchronization network is the availability of primary and backup synchronization signal pathways, in compliance with the required hierarchy, as well as the lack of opportunities for a closed loop synchronization.

Signal distribution network with land-Kokshetau Stepnogorsk shown in Figure 1

Figure 1 - Distribution of SDH network synchronization with the site-Kokshetau - Stepnogorsk.

The network element located in the city of Kokshetau appointed master (master node). On it sync signal from an external reference source PRC (Q1) at a frequency of 2048 kHz from the INSM. He is the first priority of the planned network. A highly accurate time generator is a strategic object, and therefore his whereabouts secret.

An alternative source for the synchronization master node SDH network is designed AMTS in Kokshetau. Summary Q1 synchronization is distributed in the STM-1 signal successively to the nodes Shchuchinsk, Stepnogorsk Saul and with first priority for these sites (Table 3).

Table 3 - Distribution synchronization sources

Functional timing circuit designed SDH network is shown in Figure 3.

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