SONET/SDH network configurations
Overview
The following pages detail the two different network configuration types: free running and line timing for Alcatel-Lucent 1850 TSS-5 shelves equipped with VLNC2 and VLNC50/52/55 circuit packs.
Free running configuration
The free running/line timing network can operate without an external clock source. This configuration may be useful for initial access transport and customer location applications, and also meets the needs of an end-office trunk facility. This configuration cannot be used to provide OC-n/STM-n timing distribution or where SONET/SDH interconnections to other SONET/SDH networks are needed.
One Alcatel-Lucent 1850 TSS-5 synchronizes its transmitted OC-n/STM-n signals from the internal ±20 ppm timing generator. The other Alcatel-Lucent 1850 TSS-5 systems recover timing from the incoming OC-n/STM-n signal and use this timing for their transmitted signals.
Because the free running/line timed Alcatel-Lucent 1850 TSS-5 network is asynchronous, additional jitter may be experienced on de-multiplexed DS1/E1 or DS3/E3 signals. Certain interconnected equipment may be sensitive to such jitter and this configuration should not be used in cases where it would cause a problem for that equipment.
Important!
If the network is self-contained and the DS1/E1 or DS3/E3 synchronizer/desynchronizers are using the same reference (derived from the free running SMC/SEC ±20 ppm timing generator) then there is no additional jitter due to pointer adjustments because there will be no timing adjustments.
The following figure shows a free running configuration in a ring network.
Figure 6-3: Free running - ring network
Line timing configuration
The external/line timing configuration integrates access transport and customer location networks into the digital synchronization network. This application is ideal for networks where only one location has a building integrated timing supply (BITS) clock. The network is synchronized to a local central office clock via DS1/E1 references.
Important!
It is either the Alcatel-Lucent 1665 Data Multiplexer or Alcatel-Lucent 1665 DMXtend system that is externally timed in the following description, NOT the Alcatel-Lucent 1850 TSS-5.
The Alcatel-Lucent 1850 TSS-5 can be line timed from a SONET NE, such as the Alcatel-Lucent 1665 Data Multiplexer or Alcatel-Lucent 1665 DMXtend system. The local office clock from which the Alcatel-Lucent 1665 Data Multiplexer or Alcatel-Lucent 1665 DMXtend is timed should be Stratum 3 or better, with timing traceable to a primary reference source. The Alcatel-Lucent 1665 Data Multiplexer/Alcatel-Lucent 1665 DMXtend times its transmitted OC-n signals from the internal oscillator that is locked on the external reference. The remote Alcatel-Lucent 1850 TSS-5 recovers timing from the incoming OC-n signal and uses this timing for its transmitted signals.
A remote Alcatel-Lucent 1850 TSS-5 can also recover timing from an STM-n signal received from an NE that supports external timing from an SDH Equipment Clock (SEC). The Alcatel-Lucent 1850 TSS-5 is not externally timed.
In a ring topology, synchronization messaging allows automatic synchronization reconfiguration in the event of a fiber or equipment failure.
The following figure shows line timing in a ring configuration.
Figure 6-4: Line timing - ring network
