synchronization of telecom network

7/30/2019 Synchronization of Telecom network

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E4-E5 (E&WS)-Synchronization of Telecom NW Rev. Date 16.03.11

For internal circulation of BSNL only

Chapter 3

Synchronization of Telecom Network





Synchronization Planning: while extending PRC clock from one node to other

node through transmission network of SDH and DWDM few guidelines are required to

be kept in mind. This is essential as the clock quality keeps on getting deteriorated as and

when it crosses number of nodes. Following is the salient planning rules:

• From one PRC maximum 10 numbers of SSUs can be supported.

• Between two SSUs maximum 20 NE can be placed.

• In total maximum 60 numbers of NEs can be supported in one PRC chain.

PRC: Primary Resource Clock

SEC: SDH Equipment Clock





However, the above figures are theoretical figures and as such they may be adjusted as

per the quality of transmission network, so that the quality of clock in the network always

remains comparable to PRC clock i.e. better than 10exp-12 accuracy.

BSNL Synchronization Plan:

It is proposed to have 21 numbers of PRCs with two caesium tubes (mostly at all Level-1

TAX locations) for geographical diversity and for ensuring the minimum nodes slippage.

However, in view of the requirement for the orderly distribution of the PRC clock

throughout the transmission network, it is proposed to locate the SSUs at the convergent

nodes of the existing DWDM backbone rings. Overlapping with DWDM network

enables to transport the clock on a number of SDH rings to as many district head

quarters, where SSUs are proposed to be located. Most of these nodes are co-located with

SS

K=1

PRS

SSU

SSU

Rule 1

K < 10 SSUs

SEC (NE with SONET/SDH Equipment Clock)

Rule 2

N < 20 SECs

K=2

K=3

SSU

Co-located PRS & TSG

SSUK=1

1

201 2

PRS

1

2

SSU K=1

1

2

1

20

201

21

1

20

SSU K=2

PRS





the Level –I TAX stations. Thus these 21 PRCs are expected to supply clock for all the

Transmission, Switching and Access elements in the transmission geographic area, also

called as the PRC timing Island. The SSU at the PRC location depends on the PRC itself

for the first master clock input. In case of failure or deterioration of the PRC, the SSU

depends on the other three PRC clock inputs received from the nearest three PRCs. In the

event of complete failure of the PRC inputs or in the event of the deterioration of clock

quality all the PRCs below the GPS standard, the SSU draws the clock from the GPS

clock, which shall be in-built in SSU. It is proposed to place at least one SSU at each of

the SSA Headquarter. Thus at least 322 SSUs shall be required for distributing the clock.

In the cities, where more than 3 lakh DELs are available, there will be at least 3 SSUs in

the same city for distributing the clock across the city network. Similarly in all the cities

with more than one Lakh DELs but less than 3 Lakh DELs two SSUs are proposed in the

same city for distributing the clock.

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synchronization of telecom network

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