Nortel Networks DCT1900 - Manual (Page 32)

Technical Product Manual - DCT1900
System Description, System Overview
2-10 System-DCT1900/R8/mw
© 2000-2005
System Status
A Portable Telephone contains a list of the current RE status. For each system, the status may be:
NOT_ALLOWED:
The Portable Telephone is not allowed to access this RE.
TEMP_NOT_ALLOWED: The Portable Telephone is currently not allowed to access this
RE, but may be allowed to access this RE in the future.
ALLOWED: The Portable Telephone is allowed to access this RE.
Roaming
If the Portable Telephone is locked to a certain Base Station, two types of roaming are supported:
voluntary roaming, when a better bearer is available, or forced roaming, when the current bearer is
no longer valid. If the Portable Telephone is locked to a RE, it regularly scans its environment.
During the environment scan alternative REs are investigated and a bearer set–up may be
attempted.
Voluntary Intra System Roaming
Voluntary intra system roaming takes place if the Portable Telephone detects a Base Station of
which the signal strength is at least 6dB stronger than the current bearer, and remains at least this
amount stronger during a number of consecutive frames.
Voluntary Inter System Roaming
Voluntary inter system roaming takes place when:
z The RE status of the other RE is higher than the system status of the current RE. If the RE
status of the other RE is higher than the RE status of the current RE during a number of
consecutive frames, a location update will be started.
z The RE status of the other RE is equal to the RE status of the current RE. If the RE status of
the other RE is equal to the RE status of the current RE and the RSSI is at least 12dB stronger
than the current bearer RSSI during a number of consecutive frames, a location update will be
started.
z The RE status of the other RE is lower than the RE status of the current RE. If, during a
number of consecutive frames, the RE status of the other RE is lower than the RE status of the
current RE and the RSSI of the best bearer of a Base Station of the other RE is at least 12dB
stronger and the Portable Telephone does not see any other Base Stations of this RE and the
current Base Station has no further bearers available, the Portable Telephone will start a
location update.
Forced Intra System Roaming
If the current bearer cannot be used any more, the Portable Telephone will immediately try to
switch to the best bearer on the current RE.
Forced Inter System Roaming
If the bearers of the current RE cannot be used any more, the Portable Telephone will immediately
try to switch to the best bearer of alternative REs.
Handover
During a call, two types of handover are supported again: voluntary handover and forced
handover. If there are no problems with the current bearer, the Portable Telephone will investigate
alternative bearers during a call. Handling of the forced handover is critical because in this case
the speech service is disrupted.