<s>
Mobile	O
cellular	O
service	O
providers	O
may	O
offer	O
mobile	B-General_Concept
QoS	I-General_Concept
to	O
customers	O
just	O
as	O
the	O
fixed	O
line	O
PSTN	O
services	O
providers	O
and	O
Internet	O
service	O
providers	O
may	O
offer	O
QoS	O
.	O
</s>
<s>
QoS	O
mechanisms	O
are	O
always	O
provided	O
for	O
circuit	B-Protocol
switched	I-Protocol
services	O
,	O
and	O
are	O
essential	O
for	O
non-elastic	O
services	O
,	O
for	O
example	O
streaming	O
multimedia	O
.	O
</s>
<s>
A	O
phone	O
call	O
or	O
other	O
session	O
may	O
be	O
interrupted	O
after	O
a	O
handover	B-Protocol
,	O
if	O
the	O
new	O
base	O
station	O
is	O
overloaded	O
.	O
</s>
<s>
Unpredictable	O
handovers	B-Protocol
make	O
it	O
impossible	O
to	O
give	O
an	O
absolute	O
QoS	O
guarantee	O
during	O
a	O
session	O
initiation	O
phase	O
.	O
</s>
<s>
crosstalk	O
)	O
blocking	O
probability	O
(	O
the	O
probability	O
that	O
the	O
required	O
level	O
of	O
QoS	O
can	O
not	O
be	O
offered	O
)	O
and	O
scheduling	B-Operating_System
starvation	I-Operating_System
.	O
</s>
<s>
These	O
performance	O
measures	O
are	O
affected	O
by	O
mechanisms	O
such	O
as	O
mobility	O
management	O
,	O
radio	B-Protocol
resource	I-Protocol
management	I-Protocol
,	O
admission	O
control	O
,	O
fair	B-Algorithm
scheduling	I-Algorithm
,	O
channel-dependent	B-Protocol
scheduling	I-Protocol
etc	O
.	O
</s>
