User's Manual

3.5.1 Redundant main control channel (MCCH)
By redundant main control channels (MCCH) the operation of a base station is guaran-
teed even if the carrier with the MCCH drops out or should be disturbed.
If the carrier that provided the main control channel last drops out, an alternative carrier
will take on this task. The MCCH is thus transferred. This transfer is made as often as the
number of carriers that are available on the base station. In this case, the replacement
carriers for the MCCH keep on sending on their original frequency, not on the frequency
of the failed carrier. This frequency change is useful especially when interfering carriers
affect the MCCH frequency that was being used up to that point such that the MCCH
does not suffer further interference after the frequency change.
Irrespective of the number of carriers, each radio cell has only one MCCH, via which the
terminals receive information, e.g. on adjacent radio cells. As a rule, the first channel of
the first carrier of a base station is used as the MCCH, the three remaining channels of
that carrier and all the channels of all the other carriers are used as voice channels or the
Packet Data service. Redundant MCCH are enabled by default and apply to all the base
stations with more than one carrier.
3.5.2
Carrier redundancy
To increase the reliability of carriers or to ensure the Base Station Function (BSF), redun-
dant carriers can be used within a base station. These spare carrier ensure the radio cov-
erage on the frequency of the failed carrier if a carrier drops out. Carrier redundancy is
mostly used in cases, in which only a few frequencies are available.
3.5.3
Controller redundancy
The controller required for operating a base station can be of redundant design. For this
purpose two BSCUs (Base Station Controller Units, BSCU) are used, where one BSCU is
in operation and the other is on standby. In the case of a failure of the active BSCU, the
standby BSCU is automatically activated and takes on its function. In this way, the opera-
tion of the base station is always ensured.
3.5.4
Fallback operation
The radio coverage of base stations is also ensured if the base station loses the connec-
tion to an IP Node (IPN) with Switching Controller Function (SCF). In this case, the base
station changes to fallback operation. In fallback operation, the base station in its radio
cell still maintains the Base Station Function (BSF). Even in fallback operation, authenti-
cation and authorization validation are ensured since the corresponding subscriber data
are stored in the base station.
The connection to other network constituents is not possible in fallback operation, the fol-
lowing services and features, however, are available locally:
n Group calls
n Individual calls (semi-duplex and duplex calls)
n Transmission of SDS and status messages
Product description
Redundancy options > Fallback operation
DIB-R5 flexibleTx
59Operation Manual 90DIBR5flexibleTxOM02 - 1.2