Alcatel-Lucent 9500 User Manual page 177

A common reference clock is NOT available at both Ends.
The IWF system, at Rx side, generates the output clock based on data arrival rate: TDM
clock is slowly adjusted to maintain the average fill level of a jitter buffer at its midpoint.
3.10.15.1.3 — Node timing
The Node timing is timing from the network clock as defined in G.8261. When it is
selected the regenerated E1 at receiver side is synchronized to the network element clock
(NEC). This method can be selected for each E1 stream.
At MSS-1c level, all the "Node Timed" TDM flows:
• will egress the MSS-1c with the same clock (the MSS-1c NEC);
• MUST ingress the MSS-1c being synchronized by the same clock.
As for any synchronisation clock transmission, the user shall particularly take care to avoid
synchronisation loop and TDM traffic hits:
• or the MSS-1c is the master clock and the external equipment must recover its own
clock from one of the "node timed" TDM flows and use this recovered clock to
generate its TDM flows;
• or the external equipment is the master clock (i.e. it generates all its TDM flows by
using its internal clock) and the MSS-1c MUST use one of the "node timed"
ingressing TDM flows as clock source for its NEC;
• or both of the MSS-1c and external equipment MUST be synchronized by the same
clock if this clock comes from another equipment.
3.10.15.1.4 — Synchronization for MSS-1c
Each Network Element must have a reference clock (NEC), which will be distributed to
each circuit of the NE. Such clock is a 25 MHz generated in the MSS-1c in the Clock
Reference Unit (CRU) function.
The NEC is locked to a Synchronization Source.
The sources can be:
• Internal Local Oscillator. It is the clock provided by the Local Oscillator inside the
NE
• Any E1/T1 available at input traffic interfaces (the specific E1/T1 port has to be
chosen)
• The Symbol Rate of the Rx signal of the Radio direction
MPR-e and MSS-1c User Manual 3DB19901EFAA Edition 01
Functional description
177