Inter-radio access technology is the ability to support the mobility of a
user device between differing radio access network types, also known as
vertical handovers. Inter-radio access between heterogeneous networks is
important to be executed properly for seamless communication with minimum delay
and packet loss to disassociate from the current serving BS to associate to the
new BS.
Inter-technology access can be supported using different techniques. The
most primitive one is the mobility from one technology to another without the
intervention of the network. In this case the device is equipped with different
technology interfaces. The user or the device selects which technology to access
and associate to the corresponding network. Once this network becomes
unavailable, the user or the device selects another technology and associate
with. This type of inter-technology handover is acceptable for delay-tolerant
and low QoS requirementapplications such as http and e-mail. However,
delay-intolerant or session based applications cannot tolerate the service
interruption and may require reinitiation of the session including the
re-authentication process. A more efficient inter-technology mobility for
session based applications is one that supports the data session continuity
across multiple technologies. In this type of mobility, session continuity is
preserved while the user moves across different technologies. Association to a
new technology and disassociation from a serving one is accomplished with no
user actions and it is transparent to the applications. Hence,
re-authentication by users or data interruption has no impact in this type of
mobility.
Different approaches are used to provide inter-technology mobility with
session continuity and these include;
Single Transmit
Device..........................:
Mobile IP (MIP) is standardized by the IETF to support for the session
continuity at the IP layer. Hence, cannot support user authentication and login
while moving across the different technologies. Single transmit device- MIP
based approach makes use of the MIP service and hence it is a single transmit
device, the device is only capable to associate with one technology at a time.
In other words, it needs to disassociate from the serving technology before
associating to the target technology. Despite the simplicity of this type, it
suffers from a large delay associated with the signaling needed to associate
and authenticate with the target technology. The type of inter-technology
handover is known as non-optimized inter-technology handover. 3GPP standard use
this approach to support inter technology mobility between WiMAX and LTE and
between EVDO and LTE. Optimized inter technology handover is defined in LTE as
the inter-technology handover which allows/requires the serving technology
exchanging control data and signaling messages with the target technology as
described in the following approach. The optimized handover is expected to
support delay-stringent applications such as VoIP.
Access Network Interconnect:.................................
This approach is used mainly in networks managed by single operator and
employ technology with different generations but similar origin (newer
technology that supports backward compatibility with older generations) such as
CDMA2000 and EVDO or UMTS and GSM. The access network interconnect requires the
serving and the target networks to be physically connected to facilitate the
handover process and exchange the signaling messages (optimized handover).
Access network interconnect is limited to the technologies produced by the same
standardization body, however, 3GPP with collaboration with 3GPP2 defined
procedures to extend this approach to EVDO. 3GPP and IEEE 802.16 working group
are in the process of investigating optimized handover between LTE and WiMAX.
Dual-Transmit Devices (DTD) based inter-technology handover:...........
This type of mobility does not require the serving technology to be
connected to the target technology, since the user device is involved in the
initiation and termination of the connection to the technology. It is realized
by two types of services, Mobile IP (MIP) and Session Initiation Protocol (SIP).
· MIP: In this type, since the device is equipped with dual transmitters, the
device during handover employs make-before-brake handover. The device while it
is connected to its serving technology uses its second transmitter to connect
to the target technology, hence maintaining its data session and preventing
data loss. Once the association process is completed with the target
technology, the device uses the MIP service to move the data session to the
target network. Examples are the inter-technology handover between LTE and WiFi
and EVDO and WiMAX.
· SIP: This solution is suitable for inter-device inter-technology mobility
where a data session is required to be moved not only between technologies but
also between devices. This is the only solution to support inter-device
mobility. However, it is only applicable for SIP based applications. An example
of this type of mobility is the standardization of LTE-Advanced which is
expected to support inter-device and inter-technology mobility based on SIP and
IMS.
