Page 280 - From GMS to LTE

266 From GSM to LTE-Advanced Pro and 5G

4.6.4 Default and Dedicated Bearers
Despite the similarities in the processes between GSM, UMTS and LTE, there is never-
theless one major difference between LTE and earlier technologies. As mentioned
above, the attach process already includes the assignment of an IP address. This is
unlike in GSM and UMTS where the device could attach to the packet‐switched net-
work and only later request the assignment of an IP address with a separate procedure.
This second procedure was often also referred to as a ‘packet call’ to compare the estab-
lishment of an Internet session with the establishment of a voice call. In LTE, this com-
parison no longer fits, as LTE devices get an IP address straight away, similar to a
computer that immediately attaches to a Wi‐Fi network or a cabled Local Area Network
(LAN) once it is detected and configured.
The IP connection that is automatically established during the attach procedure uses
a default bearer. For network operator‐based applications such as VoLTE, special QoS
requirements such as a constant delay and minimum bandwidth can be ensured for a
particular traffic flow by establishing a dedicated bearer. IP packets flowing over a dedi-
cated bearer use the same source IP address as packets flowing through the default
bearer.
In practice, a mobile device can also be assigned several IP addresses. This can be
useful, for example, to separate services offered by the mobile network operator from
general Internet access. For each IP address assigned to the mobile device, a new default
bearer is established. A device can hence have more than one default bearer. For each
default bearer, it is possible to establish one or more dedicated bearers in addition if
they are required for some time for data streams with stringent QoS requirements. The
establishment of dedicated bearers is controlled by the application itself, which is why
only network operator‐deployed applications can make use of them at this time.
It is also theoretically possible to allow Internet‐based applications to request the
establishment of a dedicated bearer or for the network to detect multimedia streams
automatically by analyzing IP addresses, port numbers, etc., and to act accordingly. This
is not standardized, however, and also not widely used.

4.7 Mobility Management and Power Optimization

Now that the major LTE procedures have been introduced in the previous sections, the
following sections take a look at the general mobility management and power consump-
tion optimization functionality. LTE knows two general activity states for mobile
devices. These are the RRC (Radio Resource Control) connected state and the RRC idle
state. This state model is much simpler than the one used in UMTS, which has many
more states such as Cell‐DCH, Cell‐FACH, Cell‐PCH, URA‐PCH and idle.

4.7.1 Mobility Management in RRC Connected State
While the mobile device is in RRC connected state, it is usually fully synchronized
with the network in the uplink and the downlink directions and can hence transmit
and receive data at any time. While the mobile device is in this state, a user data tunnel
is established on the S1 interface between the eNode‐B and the Serving‐GW and