Specifications

White Paper V800-Vodafone V802SE
18 August 2004
Handover/service continuity
The scope of this text includes service require-
ments for handover maintaining continuity of serv-
ice to a wireless terminal, as it moves between the
radio coverage area, or “cells”, associated with dif-
ferent base station sites. This functionality is called
“handover”. It is a key requirement to allow for dual
or multi-mode terminals to handover traffic from
UTRAN to other radio systems such as GERAN and
vice versa.
This part describes the general principles for serv-
ice continuity within UMTS Radio Access Network,
within GSM/GPRS and between UMTS Radio
Access Network and other radio systems such as
GSM/GPRS. As a principle, the requirements on
service continuity characteristics should be
according to the target network on which the serv-
ice is maintained.
Service continuity
Service continuity should support the following
scenarios:
• Continuity of active circuit switched services
when moving within UMTS Radio Access Net-
work, within GSM/GPRS and between UMTS
Radio Access Network and GSM/GPRS cover-
age areas.
• Continuity of active and packet switched ses-
sions when moving within UMTS Radio Access
Network, within GSM/GPRS and between
UMTS Radio Access Network and GSM/GPRS
coverage areas.
General operational considerations
Mechanisms defined to support service continuity
between different radio systems or radio access
modes should effectively cope with a number of
coverage scenarios:
• Limited coverage in a “sea” of coverage pro-
vided by another radio system or radio access
mode.
• Selective operation at a geographical boundary,
with extensive UMTS Radio Access Network
coverage on one side, and extensive coverage
from another radio system on the other side.
• Geographically co-located areas of UMTS
Radio Access Network coverage and another
radio system.
Performance requirements
Temporary degradation of service caused by
handover
During intra-UMTS Radio Access Network hando-
ver or handover from UMTS Radio Access Network
to GSM/GPRS, degradation of service should be
no greater than during intra-GSM/GPRS handover.
The duration of the discontinuity experienced by
packet switched and circuit switched real time
services should be shorter than that in the hando-
ver of voice calls over GSM/GPRS.
Requirements on multiple bearer
services handover from UMTS Radio
Access Network to GSM/GPRS
Consideration must be given to services that may
involve multiple bearer services (and simultaneous
sessions). The mapping between UMTS Radio
Access Network bearer services and GSM/GPRS
bearer services depends on many factors such as
data rate, delay constraints, error rate etc. In the
event that certain UMTS Radio Access Network
bearer services cannot be handed over to GSM/
GPRS, the handover of some of the bearers to
maintain the service should not be precluded.
In the case where a user equipped with a dual
mode terminal is in UMTS Radio Access Network
coverage, and has multiple PDP contexts activated
(for instance to support multimedia), then it is pref-
erable to handover one PDP context, rather than
dropping all of them.
As a first priority only the PDP contexts which have
an associated QoS that can be supported by the
GSM/GPRS should be candidates for handover.
If there are still multiple PDP contexts as “handover
candidates”, then the operator should choose
which PDP is maintained. When roaming, the serv-
ing network should make this decision. The opera-
tor may choose to either:
• Drop all of the PDP contexts.
• Choose one based upon criteria such as dura-
tion, amount of traffic transferred, etc.