User's Manual

ALFOplus 24GHz (North America) - Release 01.05.0x - MN.00395.E - 004 57
7.11 SOURCES OF SYNCHRONISM
SIAE equipment is able to select among different sources of synchronization. A priority has to be assigned
to enable each source, with a value ranging from 1 to 9 included. The priority 1 corresponds to the maxi-
mum value, while the priority 9 corresponds to the minimum value. The priority shall be used to select in
which order the different synch sources must be used. In case the Priority is set as “Disabled” the corre-
spondent interface is not used as a synchronization source.
Fig.23 - Sources of synchronisation
The selectable sources of synchronisation are listed below. For each source it is also listed in square brack-
ets the correspondent acronym used by the SETS:
• Radio Interface: it is possible to have 1 radio interfaces (1+0).
• GE Interface [TE]: to identify which LANs are the sources of synchronization they have to be chosen
under “TE LAN A” and “TE LAN B”. This implies that a maximum of 2 LAN interfaces can be set as
source of synchronization. In order to receive the synchronization signal (and regardless of the SSM
status) the GE interface has to be set as “Slave”. The configuration choices and other details are
explained in “SSM on Ethernet Interfaces”.
• Internal Clock [T0]: with the Synchronization not enabled the equipment is locked into its internal
clock
In case SSM is not enabled, the equipment switches from one source of synchronization to another follow-
ing the priority scale, starting from the source set to priority 1 and scaling to the sources with higher values
of priority (i.e. lower priority level). The synch source switch occurs when the present source suffers one
of the following events:
• The source of synchronization is not physically available
• The clock deviation is bigger than 4.6 ppm (maximum deviation that the internal clock can follow).
In other words, if the LAN1 is selected as first source (priority 1) of synchronization, and the LAN2 is se-
lected as the second source (priority 2) of synchronization, the SIAE equipment will be synchronized on
the LAN1 until the cable will be physically unplugged or the LAN1 frequency and phase will be out of their
specified ranges. Once one of these events occurs, the SIAE equipment will switch the source of synchro-
nization to the second source listed. If the second source listed is unplugged or out of maximum range then
the SIAE equipment will switch to the third source and so on.
In case no other synch sources are available the SIAE equipment will go on “Internal Source”, i.e. the in-
ternal clock present in SIAE equipment. In this condition the internal clock will be kept in hold status, trying
to keep the last synchronization reference received. In these conditions, the internal clock of SIAE equip-
ment has a reliability of 0.3 ppm over 24 h. When the SIAE equipment switches to internal clock, it prop-
agates a quality of SEC – SDH Equipment Clock.