Nortel Networks DCT1900 User Manual

Page 30

Technical Product Manual - DCT1900

System Description, System Overview

2-8

System-DCT1900/R8/mw

De–registration
De–registration is the process where the authorization at registration is removed. Once the user is
de-registered, he can no longer be reached. A user can de–register from the RE by switching the
Portable Telephone off, or by roaming to another system.

Whenever the RE is not able to inform the MS (e.g. congestion in the MS) about the de-
registration, the RE will repeat it every time there is an incoming call for that specific Portable
Telephone.

Authentication
The authentication of a Portable Telephone is done during registration and at incoming or outgoing
call establishment. It will be executed according to the PWT Standard Authentication Algorithm
(PSAA). The algorithm uses the authentication key that is downloaded over the programming
cable into the Portable Telephone during initialization.

In a DCT1900 Mobility Server configuration for performance reasons, a session key (temporary
key, reissued at registration time) will be stored locally in the RE as the result of a registration, to
allow authentication without consulting the MS during call establishment.

Inter System Handover (DCT1900 Mobility Configuration Only)
Inter system handover is the capability in a mobility configuration of a Portable Telephone that is
handed over automatically to another RE when leaving the coverage area of one RE and moving
into a coverage area of another RE. When a user moves to a new RE (refer to Figure 2–2), on
request of the MS the old RE will remove the relation between the moved Portable Telephone and
the old RE (de–registration) while the new RE adds the relation between it and the Portable
Telephone (registration). Handovers from one RE to another can only be achieved when all of the
following conditions apply:

Base Stations of different RE’s meet the PWT specifications.

The REs involved are synchronized.

Both REs have system numbers that fall within the Portable Telephone system range.

The Portable Telephone detects a stronger signal from the new RE than the old RE.

If these conditions are not met, the inter system handover will not be seamless or the call can even
be lost when the Portable Telephone tries to move to the new RE.

If two REs operate in overlapping areas, a Portable Telephone may need to choose between an
intra system (to another Base Station of the same RE) and an inter system handover. In these
situations, the Portable Telephone will prefer an intra system handover. In general, a 6dB signal
strength improvement is required for an intra system handover while a 12dB improvement is
required for an inter system handover.

Roaming (DCT1900 Mobility Configuration Only)
Roaming is a feature whereby a Portable Telephone moves between two geographically separate
but electronically connected MSs with the attendant REs. When turned on in its home coverage
area, the Portable Telephones’ connectivity and functionality is normal. When turned on in the
other MS coverage area, the Portable Telephone registers itself as a visitor and this MS
communicates with the other MS to let it know that the Portable Telephone is now active on the
other RE. Any calls to the Portable’s PUN will then be routed to the new MS to be passed on to the
Portable Telephone.