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UMTS and LTE/SAE handover solutions and their comparisonT.F.M. Hendrixen
Faculty of Management and Governance
University of Twente, the Netherlands
[email protected] are procedures used to keep one or more
communicating connection(s) of a mobile user alive, even when
the user roams from one network access point to another access
point. Handovers are therefore, very important for mobility
support in wireless networks. This paper focuses on the
efficiency of handovers between UMTS and the new 3GPP
network technology LTE. The paper first explains the important
requirements for efficient handovers. Once the requirements are
clear, five possible handover solutions are explained. To verify
if all solutions are efficient they are compared to the
LTE/SAE, UMTS, handover, efficiency
1. INTRODUCTIONThe demand for mobile internet increases every day. To keep up
with user preferences, several types of networks are available
and implemented. All these different networks have their own
properties such as bandwidth, response time and coverage area.
But due to developments in applications and services, larger
bandwidths, lower latency, always alive connections, etc., are
needed. To accommodate these needs, new better networks are
being specified and developed.Nowadays to provide mobile internet Universal Mobile
Telecommunications System (UMTS) / High-Speed Downlink
Packet Access (HSPDA) technologies are used. At the same
time the 3rd Generation Partnership Project (3GPP) is
developing a new technology called 3GPP Long Term
Evolution (LTE). 3GPP LTE aims to improve third generation
(UMTS) technology to meet requirements in a time perspective
of 2010 and beyond, see   . Some of the agreed
requirements/targets of LTE are a significant increase in peak
data rates (100 Mbps down and 50 Mbps up); a scalable
bandwidth and a reduced latency for the user .
Examples of applications that are used by mobile users are
video conferencing, email, messaging and even live TV. For
most of these applications mobile users desire that their
connections are maintained as their devices move from one
access point to another. To provide this service handover
mechanisms are used between access points .
To integrate a new technology like 3GPP LTE with the already
available networks, vertical handover mechanisms have to be
used. These mechanisms maintain network (internet)
connectivity for the mobile user and switch to the best suitable
technology available at that moment, see . Because handover
mechanisms arent a new way of keeping connections alive,
several mechanisms have already been researched and
developed. Some of these mechanisms are also used between
UMTS and LTE, but are these proposed handovers efficient? Is
there a better way to provide handovers between UMTS and
LTE? This brings us to the main research question of this paper:
- Are the handover solutions supported in UMTS andLTE/SAE efficient?
To answer this main research question, sub questions arederived:
1. How do handover mechanisms work?2. What are requirements for an efficient handover?3. What handover solutions are used between LTE/SAE
4. Do the handover solutions comply with therequirements for handover efficiency?
A literature study and a qualitative comparison analysis is used
in order to answer these research questions.
The paper is divided into sections, where each section answers a
research question. In section 2 available handover concepts are
explained. In section 3 the requirements for efficient handovers
are discussed. Section 4 treats the solutions that might be or are
used between UMTS and LTE. In section 5 the solutions are
compared with the derived requirements. Finally, the
conclusions and the possible future work activities are
2. HANDOVER MECHANISMSAs explained earlier, handovers are used to keep mobile clients
connected to their service network, even when these clientsroam from a network access point to another network access
point. To supply this service there are two types of handovers,
horizontal and vertical. For example: a mobile user is having a
video phone call, which uses UMTS, while traveling by train.
During the trip, the train moves out of the range of the currently
used UMTS network access point, i.e., UMTS cell coverage
area. To maintain the phone call, the phone switches from one
UMTS network access point to another UMTS network access
point, with a better signal quality. The type of handover used in
this case is called a horizontal handover, since the handover
occurs and is supported by the same wireless technology, i.e.,
UMTS. When the train reaches the next train station, the phone
picks up a WLAN (Wireless Local Access Network) access
point. The WLAN access point supports a much greaterbandwidth which might provide a much better quality video
call. At this point the mobile client switches to a network access
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Twente Student Conference on IT, Enschede, June 29th
, 2009Copyright 2009, University of Twente, Faculty of Electrical Engineering,
Mathematics and Computer Science
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point supported by another wireless technology. This process is
called a vertical handover.  
The central goal of the handover mechanisms is to maximize
overall network utilization and allow each client to remain best
connected at all times . Best connected is specified as
having the optimal connection for the service the client is using.
A handover process can typically be divided into five parts:measurements, processing, reporting, decision and execution. A
general description of the handover procedure is given below,
To make sure that the connection stays maintained, a handover
mechanism constantly scans the air for other access points and
monitors the active connection. Once the service criteria arent
fully supported anymore, or when a better suitable network is
found, then a handover procedure is started. The next section of
this paper explains this decision in detail, see .
To give a more detailed view of a handover, a high level GSM
handover example is given: In the first step of the handover
procedure the client connects and registers with the new access
point. Then the connection specific information is transmitted
(reference id, status, etc). Only when the connection is
successfully taken over, the client disconnects from the old
access point, see  .
With todays new technologies, vertical handovers become
more popular. For example, a few years ago tri-band mobile
phones were far from mainstream; nowadays quad-band phones
with personal area network interfaces are common, and phones
are even equipped with wireless LAN interfaces. With all these
types of networks deciding which network(s) to attach to are not
easy problems when considering all parameters involved: Radio
resource sharing, multi-operator environment, security, end-to-
end path optimality and energy efficiency.
Making the right decisions involves several constraints and
has to meet several objectives. Failing to satisfy the constraintscauses service interruptions for the mobile node; not meeting
the objectives leads to, for example, inefficient use of battery
power and network resources, see .
3. REQUIREMENTS FOR AN EFFICIENTHANDOVER SOLUTIONTo provide an efficient handover there are several requirements
and criteria. During the literature research many requirements
and criteria for an efficient handover were found. Some of these
requirements are listed below.
3.1 Handover momentOne of the most important criteria for an efficient handover isthe handover moment or handover location. To provide a
handover without degrading the quality of service (QoS) the
location of the handover moment should be carefully planned.
The optimal point for a handover is at a spot where the old and
the new access point have an overlap in coverage area. Outside
this area there might be a lot of noise which degrades the
connection and slows the handover down. When a handover
moment isnt chosen at the right point this might also lead to
unnecessary handovers. This leads to the next criterion, see
3.2 Unnecessary handoversAn important requirement for an efficient handover mechanism
is the amount of unnecessary handovers. The lower the numberof unnecessary handovers the more efficient the handover
To decide the handover moment, handover mechanisms use
signal strength algorithms to determine the distance to the
access point. Once the client comes near the border of the
coverage area the algorithm starts determining the handover
point. Measurement errors in this process can lead to
unnecessary handovers, which can lead to higher energy
consumption and possible degradation of the supported QoS,
see  .
3.3 Handover delayThe duration of the handover procedure is an important
criterion of the efficiency of a handover mechanism. When a
handover takes too long, service disruption can be experienced
or connections can timeout and will be lost. For example, a real
time video call could experience a temporary disruption when a
handover takes longer than 400 ms. If the delay is even longer,
the call could be terminated entirely.
To provide a seamless and efficient handover, this delay should
be as short as possible. The delay is measured from the
execution of the handover algorithm until the algorithm
completes the handover procedure and the client is successfullyconnected to the other access point, see  .
The International Telecommunication Union (ITU) has
specified a handover delay QoS parameter for IP transport of
telecommunication applications in . The value of the
required handover delay parameter changes for different
application classes. This paper focuses on seamless handovers
and for that reason only classes for real-time applications are
used. The classes used are 0 and 1. Class 0 requires a delay of
less than 100 ms and class 1 requires a delay of less than 400
3.4 Packet lossAn optimal handover mechanism provides handover without
packet losses. No packet or/-data loss is almost impossible sothe less packet loss a mechanism generates, the more efficient
the mechanism is.  The ITU has also got a QoS parameter
for this and states that the probability for a packet loss shouldnt
be more than 1 103, see .
3.5 Scalability: how scalable is a handoversolution?The scalability of a handover solution is an important factor
when implementing it into wireless network technologies with a
high density of mobile users. When the number of supported
users significantly increases will the handover mechanism still
be efficient? Often a high density of mobile users generates
3.6 Complexity of the solutionThe complexity of a handover procedure is very important when
talking about mobile devices. These devices are often battery
powered and have limited resources. If the handover mechanism
takes too many resources, smaller mobile devices cant use the
3.7 Modifications of the protocol standardsA solution which can be placed in the already available network
architecture without changing the standard (signaling)
procedures and protocols makes the solution easier to be
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4. HANDOVER SOLUTIONSTo make a comparison of handovers between UMTS and LTE,
the handovers used in the standards for both technologies are
explained in the first two sections. After that three other
possible solutions are explained.
4.1 UMTS HandoversAt this moment UMTS uses the Universal Terrestrial Radio
Access Network (UTRAN) for handovers. The architecture of
UTRAN can be seen in Figure 1. The main component in
UTRAN is the Radio Network Controller (RNC) which is
connected to several base stations calledNode Bs. Every Node
B can support several cells with clients connected. Within
UTRAN, UMTS uses Wideband Code Division Multiple
Access technology (WCDMA) to carry radio transmissions.
WCDMA is emerged as the most widely adopted third
generation air interface. Its specification has been created in the
3rd Generation Partnership Project (3GPP) WCDMA provides
three different types of handovers which will be explained
below, see .
Node B Node B Node B Node B
Iub IubIub Iub
Figure 1: UTRAN Architecture Intra Frequency handovers
4.1.1 Intra Frequency handoversIntra Frequency handovers are horizontal handovers between
two access points on the same frequency. The handover
initiation is started by an algorithm which measures the signal
strength continuously. When the algorithm finds a stronger cell,
the cell is added to its active set, or else into the neighbor list.
First, the RNC queries the client for its active set. After the
RNC receives the set, it chooses the best cell to switch to and
orders the client to handover. These handovers are the most
common ones and are performed to provide roaming and
mobility support to the users, see .
4.1.2Inter Frequency Handovers within WCDMAInter Frequency handovers within WCDMA are handovers
between different frequencies in the same network. These
handovers are used to provide a higher capacity on the cell.
The RNC triggers the client to start measuring and identify cells
and put them on the neighbor list. During the measurements and
identification the client finds cells with a shared channel. The
client indentifies the cells as separate single channel cells for
compatibility and reports the measurements to the RNC. The
RNC sends the command to connect to the cell with the lowest
load or best signal, see .
4.1.3 Inter System or Inter RAT HandoversInter System or Inter RAT handovers are vertical handovers
between different network types i.e. UMTS to LTE. At the start
of the UMTS deployment, this mechanism was mostly used to
provide continuous coverage. A graphical representation of the
handover is given in Figure 2.
Figure 2: UMTS to LTE Handover
The handover mechanism is triggered by the RNC. First the
RNC sends a command to measure and report the signal
strength from the cells in the vicinity. Between UMTS andLTE, the client performs E-UTRAN measurements which will
be explained in the next sub section. Once those measurements
are received by the RNC, it evaluates the measurement and
decides if and which cell to switch to. Once the decision has
been made, the RNC sends the command to perform the
handover, see . If the connection to the LTE network is
successful, the Serving GPRS support node (SGSN) will
forward packets from existing connections through the Serving
GateWay (S-GW) towards the client and vice versa.
4.2 LTE HandoversLTE uses Evolved UMTS Terrestrial Radio Access network
(EUTRAN) for handovers, see . EUTRAN is the
evolvement of UTRAN which was developed as a multipleaccess method with a functional split between the radio access
and core network in the network architecture, see Figure 3. Due
to this split all radio functionality (RLC/MAC) is placed in the
base station, also called eNodeB (an evolved UTRAN Node B).
This means that the eNodeB is responsible for decisions of
horizontal handovers. Due to the use of eNodeB with RNC
capabilities there is no need for a separate RNC and thus
handovers between two cells on the same RNC arent needed
anymore which makes EUTRAN a flat network architecture, see
Figure 3 LTE/SAE Architecture (from )
4.2.1 LTE Intra EUTRAN HandoverBecause of the flat architecture, LTE has only one horizontal
handover type called the intra EUTRAN handover. This
handover is triggered by the eNodeB. The eNodeB makes the
handover decision on signal measurements made by the client.
Once the source eNodeB decides to initiate the execution of the
handover, it requests a preparation on the target eNodeB. The
target eNodeB can perform admission control to check whether
the established QoS bearers of the client can be accommodated
in the target cell, see .
Next, the source eNodeB sends the handover command to the
client, this command includes all information that is necessary
for the client to access the target cell. At the same time the
source eNodeB closes the connection with the client and starts
to forward the data that has not yet been successfully send to the
client toward the target eNodeB.
Meanwhile, the client starts to execute the handover and tries to
connect at the target eNodeB. To perform this connection, the
client needs approximately 30 ms. This time is needed to
synchronize with the eNodeB to be able to commence data
transmission.Once connected, the client sends the handover complete
message through the target cell towards the target eNodeB. This
message is used by the target eNodeB to check that the client is
connected to the right cell. At this point the data connection is
completed. The target eNodeB reports the successful switch to
the source eNodeB to release the client, see  .
The LTE specification  states that due this fast handover
this mechanism supports seamless mobility support across the
cellular network speeds up to 500km/h are supported
(depending on the frequency).
4.2.2 LTE Inter RAT HandoverTo provide handover compatibility with other 3GPP network
types i.e. UMTS, LTE uses a component of the SystemArchitecture Evolution (SAE) called Evolved Packet Core
(EPC). A subcomponent in the EPC called S-GW provides
mobility for inter eNodeB handovers like EUTRAN to UTRAN.
Figure 4: LTE to UMTS Handover sequence
A LTE client constantly reports signal measurements to the
connected eNodeB. When the eNodeB determines the necessity
to initiate a handover, the handover preparation procedure is
initiated. This is done by sending the HANDOVER
REQUIRED message to the Mobility Management Entity
(MME) located in the EPC, see Figure 4. When the message is
received, the MME starts preparation by starting the Resource
allocation procedure. This procedure is responsible for getting
resource information from the access points in the vicinity.
With this information the handover decision is made and the
MME sends the HANDOVER command with the neededinformation to the eNodeB which sends it towards the client. At
this point the client disconnects from the source eNodeB and
connects to the other access point. This other access point, in
turn will report to the source eNodeB that the handover was
successful, see . Once connected the connection is
redirected via the SGSN to the S-GW which is connected to the
packet data network via the packet data network gateway (P-
GW). No network connections are lost due to the routing and
forwarding mechanism in the S-GW, see . A graphicalrepresentation of the handover is given in Figure 5.
Figure 5: LTE to UMTS handover
4.3 Non UMTS or LTE standard handovermechanismsThis section provides an overview of other possible solutions
that could be used to provide a vertical handover between the
UMTS and LTE wireless technologies.
4.3.1 Mobile IP (MIP)Mobile IP has two versions, version 4 and version 6, both willbe explained.
IP version 4 (IPv4) assumes that a node's IP address uniquely
identifies the node's point of attachment to the Internet. To
support this, a node must be located on the network indicated
by its IP address in order to receive data destined to it;
otherwise, data to the node would be undeliverable. If a node
wants to change its point of attachment in IPv4 it always loses
its connection (i.e.by IP address change). To support this
handover mobile IP defines such a mechanism, which enables
nodes to change their point of attachment to the Internet
without changing their permanent IP address, see .
However, when the mobile node changes its network point of
attachment, then this node gets via Mobile IP a temporarily IP
address called Care of Address (COA). In Mobile IP thepermanent IP address is called Home Address. During the
period in which the mobile node remains attached to the
network via the same network point of attachment, a binding
between the COA and the Home Address is maintained by the
Mobile IP functionality.
Mobile IP uses three basic functional entities: the mobile node
(MN), the Home Agent (HA) and the Foreign Agent (FA) , see
Figure 6. When a MN detects that it has moved to a foreign
network, it obtains a care-of address (COA) on the foreign
network. This address identifies the MN in the other network.
Once the MN has its COA, the MN registers it with its HA
trough the currently connected FA. At this point, the COA and
the home address are bound together. When now data is sent
towards the HA of the MN, the data is tunneled towards theMNs COA and finally to the MN itself, this is also called
triangular routing . The MN itself sends packets directly to
the host. In this way the permanent IP address, i.e., Home
Address, of the MN stays the same, so TCP connections can be
kept alive, see .
Figure 6: Mobile IP routing (from )
In IP version 6 (IPv6) mobility support shares many features
with mobility support in IPv4. But IPv6 benefits from the
experiences gained from IPv4 and so IPv6 has some major
improvements. One of the most important and relevant
improvement is the route optimization. Mobility support inIPv6 sends its COA towards the host to inform its IP address
change. This action optimizes the route of the data flow,
because now the data doesnt need to be tunneled anymore
through the HA, see .
4.3.2 Media Independent Handover (MIH)MIH is a handover mechanism that is standardized by IEEE and
is specified in IEEE 802.21. MIH is a handover mechanism that
focuses on service continuity and provides interworking
between any wireless network access technology, i.e. IEEE 802
systems (e.g., IEEE 802.11 and IEEE 802.16e), but also
between IEEE 802 and non-IEEE 802 systems (e.g., cellular
networks like 3G).
Figure 7: MIH layer (from)
MIH is a framework which is positioned between the IP layer
and the network specific link layer. As you can see in Figure 7
the layer has three communication lines to relay information
between the two layers, see . To explain this in more detail
the following scenario is described, see Figure 8.
Figure 8: MIH Scenario
In the scenario presented in Figure 8, the 3G operator and the
LTE operator have a roaming relationship and both core
networks contain MIH entities. While a mobile node is within
the UMTS network, it can query the information server to
obtain available LTE network information. This can be done
without activating and scanning through the LTE interface. Not
scanning can save battery power significantly. Using the
information provided by the information server, the mobile
node can activate its LTE interface and have the guarantee that
there is an available network. Then, the node can connect to the
LTE network while the session is still active through the UMTS
interface. When successfully connected, the node can use MIH
commands to handover. The use of the MIH services allows
much of the time-consuming preparation work to be done
before the handover takes place which significantly reduces
handover latency and packet losses, see .
4.3.3 Session Initiation Protocol (SIP)SIP is an application-layer control protocol that can establish,
modify, and terminate multimedia sessions. SIP can also invite
participants to already existing sessions, such as multicast
conferences. It transparently supports name mapping andredirection services, which supports personal mobility. This
means that users can maintain a single externally visible
identifier regardless of their network location, see .
As stated in , SIP supports five facets of establishing and
terminating multimedia communications:
- User location: determination of the end system to be usedfor communication;
- User availability: determination of the willingness of thecalled party to engage in communications;
- User capabilities: determination of the media and mediaparameters to be used;
Session setup: "ringing", establishment of sessionparameters at both called and calling party;
- Session management: including transfer and termination ofsessions, modifying session parameters, and invoking
With these functionalities, clients can always be found after a
handover and connections can be re-established and maintained.
SIP doesnt provide services, but provides primitives that can
be used to implement services. In particular, SIP can locate a
client and send a data object to it, the data object can contain
everything e.g. service related data.  also states that IPv4
and IPv6 are supported.
Figure 9: SIP Handover
A SIP session, see Figure 9, is started with SIP INVITE
message to the universal resource indicator (URI) which is
associated with the user device. This URI has a fixed address in
the format sip:[email protected] The message is sent trough a
SIP proxy server that registers the IP address of the user devices
and forwards the message. After that, the communication can
take place via the Real Time Protocol (RTP). When a client
changes from network architecture, the client has to re-INVITE
to the corresponding node and register at the proxy server. Once
this is done, both nodes can communicate again because the
proxy server knows where to find them, see .
5. COMPARISON AND ANALYSIS OFHANDOVER SOLUTIONSIn this section the vertical handover solutions explained earlier
will be compared with the requirements found in section 3.
Every solution is explained separately except the Inter RAT
Handovers from UMTS and LTE, which are treated together.
The reason why they are treated together is because both
handovers principles are very similar. First a table, see Figure
10, which summarizes the solutions compared to the
requirements is shown. The properties good, fair and bad are
interpreted for each requirement in the following way:
Handover Momento Good: handover on the perfect moment, without
o Fair: handover on the moment where both cells arestill in range, but with a little service degradation
(i.e. higher packet loss);
o Bad: handover too early or too late, with highservice degradation or even service loss;
o Fair*: the handover moment quality for the MIPbase protocol could not be easily defined, but it is
important to emphasize that the Internet Engineering
Task Force (IETF) has specified and is currently
specifying several handover enhancements that can
be applied in combination with the MIP baseprotocol, such as .
Unnecessary Handoverso Good: no unnecessary handovers;o Fair: some unnecessary handovers but without
o Bad: too much unnecessary handovers which causesservice degradation;
o Fair*: the unnecessary handovers quality for theMIP base protocol could not be easily defined, but it
is important to emphasize that the IETF has
specified and is currently specifying several
handover enhancements that can be applied in
combination with the MIP base protocol, such as
Handover Delayo Good: handover delay is below 100 ms (class 0 of
o Fair: handover delay is below 400 ms (class 1 ofITU);
o Bad: handover delay is over 400 ms (class 1 of ITU);o Fair*: the handover delay for the MIP base protocol,
is Bad, but it is important to emphasize that the
IETF has specified and is currently specifying
several handover enhancements that can be applied
in combination with the MIP base protocol, such as
Packet Losso Good: no packets are lost during the handover;o Fair: some packets may be lost during the transfer,
but below the threshold of 1 103;
o Bad: packet loss is higher than the threshold of1 103.
Scalabilityo Good: very good usable in environments with both
high and low density of users;
o Fair: moderate usable in environments with bothhigh and low density of users;
o Bad: not usable in environments with both high andlow density of users.
Complexityo Good: Just a couple of simple procedures and
resources needed which can be done by any device
and makes it easy to implement;
o Fair: Some more procedures and resources areneeded but can still be done by almost any device
and makes it moderate to implement;
o Bad: a lot of procedures and resources needed, hardfor most mobile devices and hard to implement.
Modifications to the protocolo Good: very easy to implement without modifications
to the protocols used;
o Fair: moderate to implement, some changes have tobe made to the protocols used;
o Bad: hard to implement, a lot of changes have to bemade to the protocols used.
Good Good Fair Good Good Fair Good
MIP Fair* Fair* Fair* Fair Fair Fair Fair
MIH Good Good Fair Fair Fair Bad Fair
SIP - - Fair Fair Fair Good FairFigure 10: Comparison of Handovers
5.1 Inter RAT HandoverDue to the fact that the handover moment of an inter RAT
handover is decided by measurements done by the client which
reports them to the source NodeB or eNodeB, the handovermoment can be chosen at the ideal time and location. This also
means that if the decisions made on the measurements are done
right, there is almost no chance of unnecessary handovers. This
method has also a disadvantage, using the client to measure
signal strength will take some processing power and consumes
As stated in  the handover delay during a EUTRAN to
UTRAN handover doesnt take longer than 300 ms for real-time
quality services. This is below the ITU threshold parameter for
real time services and thus will go unnoticed by the user. LTE
and UMTS support specific features to increase reliability and
packet loss. Therefore, it could be assumed that the packet
loss criterion can be graded with Good.
The provided handover solution needs sophisticated procedures,
but compared to the large number of features and procedures
supported by LTE and UMTS, this complexity can be
considered as non-significant. The flat architecture provided
due the split has also got its advantages. The biggest advantage
is that it makes the solution highly scalable, see .
5.2 Mobile IP (MIP)Due to the use of triangular routing, the QoS of real-time
communications can be degraded. This is because the routing
adds extra hops which can increase packet delay. In addition the
redundant routing in MIP results in traffic increase on the home
agent, see . MIP handovers can take up to seconds, see
. Due to these high handover delays, there is a high chance
that the handover will be noticed by the user. Long packet
routes and high packet delays create a bigger probability of
packet losses, see . Due to the fact that each home domain
can be managed by a different home agent, makes the MIP
solution fairly scalable. A scalability drawback however, is that
the capacity of a home agent can limit the number of mobile
users that can be supported in a home domain. Servers could
easily be placed in the core network to support MIP.
In order to use MIP for UMTS LTE handovers, some minor
modifications on the standards might be needed.
A MIP handover between UMTS and LTE is initiated when the
MN detects that it has moved to a foreign network, see .
Because of this, MIP cannot control the handover moment
which means it is not responsible for unnecessary handovers.
Note however, that the Internet Engineering Task Force (IETF)
has specified and is currently specifying several handover
enhancements that can be applied in combination with the MIP
base protocol, such as .
5.3 Media Independent Handover (MIH)MIH is dependent on an extra layer in the network stack. The
use of an extra layer between the link layer and the IP layer
makes the MIH solution a complex solution. The use of an
extra layer has also, a significant advantage: The scalability ofMIH depends on how it will be integrated within the LTE and
UMTS network. Moreover, this also depends on the way of
how the MIHF entities, see Figure 8, are distributed and used.
Due to the use of an additional protocol layer, between the IP
layer and the different Link layers, modifications on the
available standards might be needed.
Due to the fact that MIH uses a make-before-break handover
procedure, the information about the target network can be
gathered before the original connection is lost. This
significantly improves the calculation accuracy of the handover
moment and decreases the number of unnecessary handovers.
The delay of MIH handovers is dependent on the used protocol
in the IP layer. When implemented with Mobile IP, MIH
decreases the delay to approximately 200ms which also results
in low packet losses, see .
5.4 Session Initiation Protocol (SIP)According to , a SIP based handover performed will take
approximately 227 ms, in average. This time, depends of course
on the used network scenario, and is mainly consumed by the
reconnection, re-invite and termination + setup of the RTP.
With this procedure, the proxy SIP server already knows the
ends of the connection and with this information the connection
can be re-established quickly, which shortens the handover
delay significantly. A short handover delay means a low packet
Deployment of a SIP based handover solution is not complex.Due to the fact that SIP is an application layer handover
mechanism, it is easy to implement it on different platforms.
SIP is using a client server based architecture. This means that
the number of users that will be supported by the SIP based
handover solution will depend on the capacity and on the way
of how the SIP servers are distributed within the network.
A SIP handover between UMTS and LTE is initiated when the
client changes from subnet, see . SIP is an application layer
protocol and therefore, it is not able to accurately calculate the
handover moment and to prevent unnecessary handovers.
6. CONCLUSION AND FUTURE WORKIn this paper the efficiency of vertical handover mechanismssupported between UMTS and LTE have been researched. Due
to the fact that handover mechanisms maintain network
connections over different wireless technologies and network
architectures they are one of the most important mechanisms for
the support of the mobility of a user.
In this paper several handover solutions where compared with
the requirements for handover efficiency. These handover
efficiency requirements were found in the papers that studied
and analyzed handover mechanisms such as . The most
important requirements where: handover moment, handover
delay, packet loss, scalability, complexity and protocol
The research of this paper first focused on the already usedhandover mechanisms between UMTS and LTE. After that,
other possible solutions where used to make a comparison and
to analyze if there were other mechanisms that might
outperform the standardized Inter-RAT vertical handover.
These additional handover solutions are mobile IP, media
independent handover and session initiation protocol. These
solutions were chosen because they are often used and
Finally the solutions found were compared to the requirementsfor handover efficiency found earlier. This comparison gave
some interesting results. As can be seen in Figure 10, for some
of the criteria, the inter-RAT handover mechanism is
outperforming other handover mechanisms. None of the studied
handover mechanisms was found to be more efficient than the
standard Inter-RAT handover solution. During the research
several other solutions where identified. Most of these solutions
were combinations or improved copies of the basic solutions
described in other papers, see . These
handovers solutions might be very interesting for further
research. Finally, to test the handover efficiency of the different
handover solutions in a more accurate way, quantitative
experiments and analysis maybe needed, which can be
performed using, for all handover solutions, the same testenvironment and workload parameters.
ACKNOWLEDGMENTSI would like to thank my supervisor dr. ir. Georgios
Karagiannis. He helped me with the structure of my research
and always reviewed my work. I would also like to thank my
reviewers. They provided useful comments and helped me with
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