establishment of the radio access bearer in more
detail.
3.5.1 Overall Procedure
Figure 3-5 shows how the bearer is established
in UMTS. The user establishes a UMTS bearer
(PDP context activation) by specifying the QoS
requested. The SGSN authorises the QoS given
the subscription of the user and does admission
control given its available resources. It then
requests the establishment of a radio access
bearer (RAB). To do so it derives the adequate
QoS profile for the RAB given the QoS profile
of the UMTS bearer. As an example the transfer
delay might be set to 80 ms if the UMTS bearer
QoS profile indicates 100 ms. This mapping is
implementation dependent.
Once the Radio Access Bearer has been set-up
the SGSN forwards the request to the GGSN.
The GGSN will perform admission control and
replies to the SGSN that in turn replies to the
Terminal. Additionally, the SGSN will take the
initiative to configure the Core network bearer.
The QoS proposed by the network may be lower
than that requested by the terminal. The terminal
might reject the establishment of the UMTS
bearer, renegotiate the QoS or accept the QoS.
3.5.2 QoS across IP Transport Networks
The UMTS architecture for the PS domain
deploys IP transport networks for the Iu inter-
face (RNC – SGSN) and for the Gn interface
(SGSN-GGSN). Across these interfaces Diff-
Serv is used as the IP transport layer QoS mech-
anism. Hence, at the RNC, SGSN and GGSN the
QoS mechanisms at the UMTS bearer service
layer are mapped to DiffServ Code Points to pre-
serve the QoS relationship between the protocol
Table 3 Values for the UMTS
bearer service attributes
Figure 3-5 UMTS Bearer
establishment
Traffic Conversational Streaming Interactive Background
class class class class class
Maximum bitrate (kb/s) < 2 048 < 2 048 < 2 048 - < 2 048 -
overhead overhead
Delivery order Yes/No Yes/No Yes/No Yes/No
Maximum SDU size <= 1 500 or 1 502 <= 1 500 or 1 502 <= 1 500 or 1 502 <= 1 500 or 1 502
(octets)
SDU format information
Delivery of erroneous Yes/No/ - Yes/No/ - Yes/No/ - Yes/No/ -
SDUs
SDU 5*10-2, 10-2, 5*10-3, 5*10-2, 10-2, 5*10-3, 4*10-3, 10-5, 4*10-3, 10-5,
Residual BER 10 -3, 10-4, 10-6 10 -3, 10-4, 10-5, 6*10-8 6*10-8
10 -6
SDU error ratio 10 -2, 7*10-3, 10-3,10-1, 10-2, 7*10-3,10-3, 10-4, 10-6 10 -3, 10-4, 10-6
10 -4, 10-5 10 -3, 10-4, 10-5
Transfer delay 100 -> maximum 250 -> maximum
(ms) value FFS value
Guaranteed bit rate (kb/s) < 2 048 < 2 048
Traffic handling priority 1, 2, 3
Allocation/Retention priority 1, 2, 3 1, 2, 3 1, 2, 3 1, 2, 3
QoS Mapping
PDP Cont. Act. (QoS)
RAB set-up (QoS ́)
procedure
Create PDP Cont. Req. (QoS)
Activate PDP Context Accept (QoS) Create PDP Cont. Acc. (QoS)
MS RNC SGSN GGSN
SM SM GTP-c GTP-c
Admission Control