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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] ABSTRACT

Handovers 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

requirements.

KEYWORDS

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 [1] [2] [3]. 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 [4].

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 [1].

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 [5]. Because handover

mechanisms aren’t 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 and

LTE/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

and UMTS?

4. Do the handover solutions comply with the

requirements 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

presented.

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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11th

Twente Student Conference on IT, Enschede, June 29th

, 2009 Copyright 2009, University of Twente, Faculty of Electrical Engineering,

Mathematics and Computer Science



point supported by another wireless technology. This process is

called a vertical handover. [5] [6]

The central goal of the handover mechanisms is to maximize

overall network utilization and allow each client to remain “best

connected” at all times [7]. 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,

see [8].

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 aren’t

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 [5].

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 [2] [9].

With today’s 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 [7].

3. REQUIREMENTS FOR AN EFFICIENT

HANDOVER 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 moment

One 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 isn’t chosen at the right point this might also lead to

unnecessary handovers. This leads to the next criterion, see

[10].

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

mechanism is.

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 [8] [11].

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 [5] [12].

The International Telecommunication Union (ITU) has

specified a handover delay QoS parameter for IP transport of

telecommunication applications in [13]. 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

ms.

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. [12] The ITU has also got a QoS parameter

for this and states that the probability for a packet loss shouldn’t

be more than 1 × 10 – 3, see [13].

3.5 Scalability: how scalable is a handover

solution?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

errors.

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 can’t use the

handover.

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

deployed.



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 called Node B’s. 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 [14].

RNS

RNC

RNS

RNC

Core Network

Node B Node B Node B Node B

Iu Iu

Iur

Iub IubIub Iub

UTRAN

Figure 1: UTRAN Architecture Intra Frequency handovers

(from [15])

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 [14].

4.1.2 Inter 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 [14].

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 [15]. 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 [16]. 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 aren’t needed

anymore which makes EUTRAN a flat network architecture, see

[14].

Figure 3 LTE/SAE Architecture (from [15])



4.2.1 LTE Intra EUTRAN Handover Because 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 [17].

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 [3] [14].

The LTE specification [18] 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 Handover To 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 [15]. 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 [19]. A graphicalrepresentation of the handover is given in Figure 5.

Figure 5: LTE to UMTS handover

4.3 Non UMTS or LTE standard handover

mechanismsThis 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 [20].

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 theMN’s COA and finally to the MN itself, this is also called



triangular routing [5]. 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 [20].

Figure 6: Mobile IP routing (from [20])

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 doesn’t need to be tunneled anymore

through the HA, see [21].

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[6])

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 [6]. 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 [22].

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 [23].

As stated in [23], SIP supports five facets of establishing and

terminating multimedia communications:

- User location: determination of the end system to be used

for communication;

- User availability: determination of the willingness of the

called party to engage in communications;

- User capabilities: determination of the media and media

parameters to be used;

-

Session setup: "ringing", establishment of sessionparameters at both called and calling party;

- Session management: including transfer and termination of

sessions, modifying session parameters, and invoking

services.

With these functionalities, clients can always be found after a

handover and connections can be re-established and maintained.

SIP doesn’t 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. [23] 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:user@domain”. 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 [24].

5. COMPARISON AND ANALYSIS OF

HANDOVER 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 Moment

o Good : handover on the perfect moment, without

service degradation;

o Fair : handover on the moment where both cells are

still in range, but with a little service degradation

(i.e. higher packet loss);

o Bad : handover too early or too late, with high

service degradation or even service loss;

o Fair*: the handover moment quality for the MIP

base 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 [25].

Unnecessary Handovers

o Good : no unnecessary handovers;

o Fair : some unnecessary handovers but without


o Bad : too much unnecessary handovers which causes


o Fair*: the unnecessary handovers quality for the

MIP 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

[25];

Handover Delay

o Good : handover delay is below 100 ms (class 0 of

ITU);

o Fair : handover delay is below 400 ms (class 1 of

ITU);

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

[25].

Packet Loss

o Good : no packets are lost during the handover;

o Fair: some packets may be lost during the transfer,

but below the threshold of 1 × 10 – 3;

o Bad: packet loss is higher than the threshold of

1× 10 – 3.

Scalability

o Good : very good usable in environments with both

high and low density of users;

o Fair : moderate usable in environments with both

high and low density of users;

o Bad : not usable in environments with both high and

low density of users.

Complexity

o 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 are

needed but can still be done by almost any device

and makes it moderate to implement;

o Bad : a lot of procedures and resources needed, hard

for most mobile devices and hard to implement.

Modifications to the protocol

o Good : very easy to implement without modifications

to the protocols used;

o Fair : moderate to implement, some changes have to

be made to the protocols used;

o Bad : hard to implement, a lot of changes have to be

made to the protocols used.



Handover

moment

Unnecessary

Handovers

Handover

delay

Packetloss

Scalability

Complexity

Modification

s

toprotocol

Inter

RAT

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 Fair

Figure 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

battery.

As stated in [18] the handover delay during a EUTRAN to

UTRAN handover doesn’t 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 [14].

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 [26]. MIP handovers can take up to seconds, see

[27]. 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 [26]. 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 [20].

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 [25].

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 of MIH 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 [6].

5.4 Session Initiation Protocol (SIP)According to [24], 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

loss.

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 [24]. 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 [3]. The most

important requirements where: handover moment, handover

delay, packet loss, scalability, complexity and protocol

modifications.

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

researched.

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 [24][26][28][29][30]. 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

my English.

REFERENCES[1] Banerjee, N.; Wei Wu; Das, S.K., “Mobility support in

wireless Internet,” Wireless Communications, IEEE ,

vol.10, no.5, pp. 54-61, Oct 2003[2] 3GPP TS 23.009 V8.0.1 (2009-01), “Handover

procedures,” January 2009

[3] Racz, A.; Temesvary, A.; Reider, N., “Handover

Performance in 3GPP Long Term Evolution (LTE)

Systems,” Mobile and Wireless Communications Summit,

2007. 16th IST , pp.1-5, July 2007

[4] Bachl, R., Gunreben, P., Das, S., & Tatesh, S., “The long

term evolution towards a new 3GPP* air interface

standard.” Bell Labs Technical Journal, vol.11, no.4, pp.

25-51, March 2007

[5] Taylor, L.; Titmuss, R.; Lebre, C., “The challenges of

seamless handover in future mobile multimedia networks,”

Personal Communications, IEEE , vol.6, no.2, pp.32-37,April 1999

[6] Wright, D.J., “Maintaining QoS During Handover Among

Multiple Wireless Access Technologies,” Management of

Mobile Business, 2007. ICMB 2007. International

Conference on the , pp.10-10, July 2007

[7] Hollos, D.; Poyhonen, P.; Strandberg, O.; Aguero, R.;

Pentikousis, K.; Blume, O., “A Study of Handover

Strategies for Mobile Multiaccess Ambient Networks,”

Mobile and Wireless Communications Summit, 2007. 16th

IST , pp.1-5, July 2007

[8] Anas, M.; Calabrese, F.D.; Ostling, P.-E.; Pedersen, K.I.;

Mogensen, P.E., “Performance Analysis of Handover

Measurements and Layer 3 Filtering for Utran LTE,” Personal, Indoor and Mobile Radio Communications,

2007. PIMRC 2007. IEEE 18th International Symposium

on , pp.1-5, September 2007

[9] 3GPP TS 48.008 V8.5.0 (2008-11), “Mobile Switching

Centre - Base Station System (MSC-BSS) interface; Layer

3 specification,” November 2008

[10] Christophorou C.; Pitsillides A., “MBMS Handover

control: A new approach for efficient handover in MBMSenabled 3G cellular networks”, Computer Networks, vol.

51, no. 18, pp. 4897-4918, December 2007

[11] Christophorou, C.; Pitsillides, A., “An Efficient Handover

Algorithm for MBMS Enabled 3G Mobile Cellular

Networks,” Computers and Communications, 2006. ISCC

'06. Proceedings. 11th IEEE Symposium on , pp. 187-193,

June 2006

[12] Kim H.; Yeom H., “An efficient multicast mechanism for

data loss prevention,” Advanced Communication

Technology, 2005, ICACT 2005. The 7th International

Conference on, vol.1, pp. 497-502, February 2005

[13] ITU-T Y.1541 “Network Performance Objectives for

IPBased Services,” May 2002

[14] Holma H.; Toskala A., “WCDMA for UMTS: HSPA

Evolution and LTE,” 4th edition, John Wiley & Sons,

2007.

[15] Hammer, M.; Salkintzis, A.; Tanaka, I.; Wong, C., “Voice

call handover mechanisms in next-generation 3GPP

systems,” Communications Magazine, IEEE , vol.47, no.2,

pp.46-56, February 2009

[16] 3GPP TS 36.300 V8.7.0 (2008-12) , “Evolved Universal

Terrestrial Radio Access (E-UTRA) and Evolved

Universal Terrestrial Radio Access Network (E-

UTRAN),” December 2008

[17] Amirijoo, M.; Frenger, P.; Gunnarsson, F.; Kallin, H.;

Moe, J.; Zetterberg, K., “Neighbor cell relation list and

measured cell identity management in LTE,” Network

Operations and Management Symposium, 2008. NOMS

2008. IEEE , pp.152-159, April 2008

[18] UTRA-UTRAN Long Term Evolution (LTE) and 3GPP

System Architecture Evolution (SAE)

ftp://ftp.3gpp.org/Inbox/2008_web_files/LTA_Paper.pdf ,

access date: 22 April 2009

[19] Salkintzis, A.; Hammer, M.; Tanaka, I.; Wong, C., "Voice

call handover mechanisms in next-generation 3GPP

systems," Communications Magazine, IEEE , vol.47, no.2,

pp.46-56, February 2009

[20] RFC3344, c. Perkins, “IP mobility support for IP4 nodes”,August 2002

[21] RFC3775, D Johnson, C. Perkins, J. Arkko, “Mobility

Support in IPv6”, June 2004

[22] Taniuchi, K.; Ohba, Y.; Fajardo, V.; Das, S.; Tauil, M.;

Yuu-Heng Cheng; Dutta, A.; Baker, D.; Yajnik, M.;

Famolari, D., “IEEE 802.21: Media independent handover:

Features, applicability, and realization,” Communications

Magazine, IEEE , vol.47, no.1, pp.112-120, January 2009

[23] RFC3261, J Rosenberg, et. Al., “Mobility SIP: Session

Initiation Protocol”, June 2002

[24] Jover, F.; Reid, G.; Jover, X., “A faster Handover

Mechanism using SIP,” Mobile and Wireless

Communications Summit, 2007. 16th IST , pp.1-5, July2007

ftp://ftp.3gpp.org/Inbox/2008_web_files/LTA_Paper.pdf





[25] RFC5268, R. Koodli, Ed. , “Mobile IPv6 Fast Handovers”,

June 2008

[26] Seta, N.; Miyajima, H.; Zhang, L.; Hayashi, H.; Fujii, T.,

“All-SIP Mobility: Session Continuity on Handover in

Heterogeneous Access Environment,” Vehicular

Technology Conference, 2007. VTC2007-Spring. IEEE

65th , pp.1121-1126, April 2007[27] F. Zhu and J. McNair, “Cross layer design for Mobile IP

handoff,” in Proc. IEEE Vehicular Technology Conference

(VTC 2005-Spring), vol. 4, pp. 2255 – 2259, March 2005

[28] Hwang Y.; Park A., “Vertical Handover Platform over

Applying the Open API for WLAN and 3G LTE Systems,”

Vehicular Technology Conference, 2008. VTC 2008-Fall.

IEEE 68th , pp.1-5, September 2008

[29] Kwon D.; Kim W.; Suh Y., “An efficient mobile multicast

mechanism for fast handovers: A study from design and

implementation in experimental networks,” Computer

Communications, vol. 31, no.10, pp. 2162-2177, June

2008[30] Yoo S.; Shin S., “Fast Handover Mechanism For Seamless

Multicasting Services in Mobile IPv6 Wireless Networks,”

Wireless Personal Communications, 2007 , vol. 42, no. 4,

pp. 509-526, September 2007

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