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Handover Latency Reduction Using Integrated Solution
Scheme for Proxy Mobile IPv6
Md. Mahedi Hassan, Poo Kuan Hoong
Faculty of Information Technology,
Multimedia University, 63100, Cyberjaya, Malaysia.
{md.mahedi.hassan08, khpoo} @mmu.edu.my
Abstract. Recent trends are showing rapid developments and fast convergence
of mobile and wireless communication networks with internet services to
provide the quality of ubiquitous access to network users. It is expected that the
next-generation mobile and wireless communications will be supported by an
all-IP based infrastructure and also need for an effective mobility management
protocol to support ubiquitous network access by providing seamless handover.
This is especially true with invention of portable mobile and laptop devices that
can be connected almost everywhere at any time. However, the recent
explosion on the usage of mobile and laptop devices has also generated several
issues in terms of performance and quality of service. Nowadays, mobile users
demand high quality performance, best quality of services and seamless
connections that support real-time application such as audio and video
streaming. The goal of this paper is to observe the impact and evaluate the
mobility management protocols under micro mobility domain on link layer and
network layer handover performance. Therefore, this paper proposes an
integration solution of network-based mobility management framework, based
on Proxy Mobile IPv6, to reduce handover latency when mobile host moves to
new network during handover on high speed mobility. Simulations are
conducted to analyze the relationship between the network performances with
the moving speed of mobile host over mobility protocols. Based on simulation
results, we presented and analyzed the results of mobility protocols under intra-
domain traffics in micro mobility domain.
Keywords: Seamless handover; Handover latency; Mobility protocols; Intra-
domain; Proxy MIPv6; NS-2.
1 Introduction
In recent years, mobile and wireless communications have undergone tremendous
changes due to the rapid development in wireless and communication technologies as
well as the ever increasing demands by users. Nowadays, mobile end-users are
constantly on the go and moving from one place to another in fast pace. As a result,
connected mobile devices are also constantly changing their points of attachment to
the communication networks, such as Mobile Cellular Networks (MCN), Wireless
Local Area Networks (WLAN), Wireless Personal Access Networks (WPAN), and so
on. These days, most of the wireless and mobile communication networks are moving
towards all IP based. These communication networks are either connected together
through the Internet or through private IP core networks. In order to maintain
connection, one of the main challenges faced by Mobile Host (MH) is the ability to
obtain a new IP address and update its communication partners, while moving
amongst these different wireless and mobile networks.
In order to meet the above challenge, Internet Engineering Task Force (IETF) [1]
designed a new standard solution for Internet mobility officially called – IPv6
mobility support and popularly named as Mobile IPv6 (MIPv6) [2][3]. MIPv6 is the
modified version of MIPv4, that has great practicality and able to provide seamless
connectivity to allow a mobile device to maintain established communication sessions
whilst roaming in different parts of the Internet.
When a MH is handed over from one network to another network, it changes the
point of attachment from one access router (AR) to another. This is commonly known
as handover which allows MH to establish a new connection with a new subnet.
Handover is also defined as the process of changing between two ARs and when ARs’
point of attachment in the network changes. The point of attachment is a BS for
cellular network, or an AR for WLAN. Commonly, handover can be handled in the
link layer, if both the ARs are involved in the same network domain. Otherwise, a
route change in the IP layer possibly will be needed the so-called network layer
handover. In this case, Mobile IPv6 is a standard protocol for handling network layer
handover.
One of the most important issues in IP-mobility protocols design is the IP handover
performance. IP handover occurs when a MH changes its network point of attachment
from one base station (BS) to another. Some of the major problems that may occur
during handover are handover latency and packet loss which can degrade the
performance and reduce quality of service. In a nutshell, handover latency is the time
interval between the last data segment received through the previous access point (AP)
and first data segment received through the next access point. [4][5] The major
problem arises with handovers is the blackout period when a MH is not able to receive
packets, which causes a high number of packet loss and communication disruption.
Such long handover latency might disrupt ongoing communication session and some
interruptions. If that change is not performed efficiently, end-to-end transmission
delay, jitters and packet loss will occur and this will directly impact and disrupt
applications perceived quality of services. For example, handovers that might reach
hundreds of milliseconds would not be acceptable for delay-sensitive applications like
video streaming and network gaming [5].
Currently, there are several mobility protocols which have been proposed in order
to alleviate such performance limitations. One of which is the enhanced version of
terminal independent Mobile IP (eTIMIP) [6][7], which is a kind of mobility
management protocol. eTIMIP enhances the terminal independent Mobile IP (TIMIP)
by reducing the amount of latency in IP layer mobility management messages
exchanged between an MH and its peer entities, and the amount of signaling over the
global Internet when an MH traverses within a defined local domain. TIMIP [6] is a
micro-mobility protocol that is optimized to provide local access to a Mobile-IP-
enabled Internet in support of fast-moving wireless hosts. The protocol is specifically
designed to support seamless mobility, passive connectivity, and paging.
Compared to the above mobility protocols, Proxy Mobile IPv6 (PMIPv6) [8][9]
defines a domain in which the MH can roam without being aware of any layer 3
movement since it will always receive the same network prefix in the Router
Advertisement (RA). The PMIPv6 specification defines a protocol to support Network-
based Localized Mobility Management (NETLMM) [8] where the MH is not involved
in the signaling. This new approach is motivated by the cost to modify the protocol
stack of all devices to support MIP (and potentially its extensions) and to support
handover mechanisms similar to the ones used in 3GPP/3GPP2 cellular networks
In this paper, we make use of Network Simulator, ns-2 [16] to simulate, examine
and compare the performance of eTIMIP, TIMIP, PMIPv6 as well as our proposed
integration solution of PMIPv6 with MIH (PMIPv6-MIH) in intra-domain traffic with
high speed MH. We compare the handover latency and packet delivery throughput of
transmission control protocol (TCP) and user datagram protocol (UDP) for eTIMIP,
TIMIP, PMIPv6 and our proposed integrated solution of PMIPv6-MIH in intra-domain
traffic.
The rest of this paper is organized as follows: Section II briefly explain related
research works on the mobility protocols. Section III explains overview of media
independent handover. Section IV briefly describes the propose solution scheme.
Section V shows simulation results of UDP and TCP flow under intra-domain traffic.
Finally, Section VI we conclude the paper and provide possible future works.
2 Existing Mobility Protocols
For mobility protocols, there are several protocols to reduce handover latency and
packet loss, such as the Session Initiation Protocol (SIP) [10] and the Stream Control
Transmission Protocol (SCTP) [11]. Both protocols focus on mobility management on
an end-to-end basis but they do not have the potential to achieve short handover
latency in network layer. The communication sessions in these protocols are initiated
and maintained through servers. The behavior of these protocols is similar to the
standard Mobile IP scheme during handovers. However, there are some enhanced
Mobile IP schemes that able to reduce the handover latency such as PMIPv6 and
CIMS, (Columbia IP Micro-Mobility Suite) [12].
2.1 Micro Mobility Protocols
Micro mobility protocols work within an administrative domain which is to ensure
that packets arriving from the internet and addressed to the MHs are forwarded to the
appropriate wireless access point in an efficient manner. It is also called intra-domain
traffic [13][14]. Under the CIMS (Columbia IP Micro-Mobility Suite) project,
several micro mobility protocols have been proposed such as –Handoff-Aware
Wireless Access Internet Infrastructure (Hawaii) and Cellular IP (CIP) [12].
The CIMS is an extension that offers micro-mobility support. CIMS implements
HMIP (Hierarchical Mobile IP) and two micro-mobility protocols for CIP and
Hawaii. The CIMS project is mainly focused on intra-domain handover and uses the
basic idea of Mobile IP for inter-domain handover.
Subsequently, the CIMS project was upgraded by Pedro, Teresa and Mário [6][7]
which included the original implementation of TIMIP (terminal independent Mobile
IP) protocol, and the extended version of TIMIP protocol such as eTIMIP (enhanced
version of terminal independent Mobile IP) as well as the implementation of CIP,
HAWAII, and HMIP protocols. The proposed eTIMIP protocol which is a mobility
solution protocol that provides both network and terminal independent mobile
architectures based on the usage of overlay micro-mobility architecture.
2.2 Enhanced version of Terminal Independent Mobile IP (eTIMIP)
Figure 1: Architecture of eTIMIP
As shown in figure 1, the physical network and overlay network are two
complementary networks that are organized in the architecture of eTIMIP. Both
networks are separated in the mobile routing from the traditional intra-domain routing
which also known as fixed routing. Generally, the physical network can have any
possible topology, where it is managed by any specialized fixed routing protocol. The
overlay network is used to perform the mobile routing, where it selects routers which
support the eTIMIP agents, in which will be organized in a logical tree that supports
multiple points of attachment to the external of the domain.
2.3 Proxy Mobile IPv6 (PMIPv6)
PMIPv6 is designed to provide an effective network-based mobility management
protocol for next generation wireless networks that main provides support to a MH in
a topologically localized domain. In general terms, PMIPv6 extends MIPv6 signaling
messages and reuse the functionality of HA to support mobility for MH without host
involvement. In the network, mobility entities are introduced to track the movement
of MH, initiate mobility signaling on behalf of MH and setup the routing state
required. The core functional entities in PMIPv6 are the Mobile Access Gateway
(MAG) and Local Mobility Anchor (LMA). Typically, MAG runs on the AR. The
main role of the MAG is to perform the detection of the MH’s movements and initiate
mobility-related signaling with the MH’s LMA on behalf of the MH. In addition, the
MAG establishes a tunnel with the LMA for forwarding the data packets destined to
MH and emulates the MH’s home network on the access network for each MH. On
the other hand, LMA is similar to the HA in MIPv6 but it is the HA of a MH in a
PMIPv6 domain. The main role of the LMA is to manage the location of a MH while
it moves around within a PMIPv6 domain, and it also includes a binding cache entry
for each currently registered MH and also allocates a Home Network Prefix (HNP) to
a MH. An overview of PMIPv6 architecture is shown in figure 2.
Figure 2: Architecture of PMIPv6
Since the PMIPv6 was only designed to provide local mobility management, it still
suffers from a lengthy handover latency and packet loss during the handover process
when MH moves to a new network or different technology with a very high speed.
Even more, since detecting MHs' detachment and attachment events remains difficult
in many wireless networks, increase handover latency and in-fly packets will certainly
be dropped at new MAG (n-MAG).
3 Overview of Media Independent Handover
The working group of IEEE 802.21 [15] developed a standard specification, called
Media Independent Handover (MIH), which defines extensible media access
independent mechanisms that facilitates handover optimization between
heterogeneous IEEE 802 systems such as handover of IP sessions from one layer 2
access technology to another. The purpose of the IEEE 802.21 MIH standard is to
develop a specification that enables the optimization of handovers between
heterogeneous access networks by providing link layer intelligence and other related
network information to upper layers.
The MIH services introduce various signaling, particularly for handover initiation
and preparation and to help enhance the handover performance. Figure 3 shows the
overall framework of MIH.
Figure 3: The framework of MIH services
Basically, IEEE 802.21 introduces three different types of communications with
different associated semantics, the so-called MIH services: Media Independent Event
Service (MIES), Media Independent Command Service (MICS) and Media
Independent Information Service (MIIS).
3.1 Media Independent Event Service (MIES)
MIES introduces event services that provide event classification, event filtering
and event reporting corresponding to dynamic changes in link characteristics, links
status, and link quality. It also helps to notify the MIH users (MIHU) such as PMIPv6
about events happening at the lower layers like link down, link up, link going down,
link parameters report and link detected etc and essentially work as layer 2 triggers.
3.1 Media Independent Command Service (MICS)
MICS provides the command services that enable the MIH users to manage and
control link behavior relevant to handovers and mobility, such as force change or
handover of an interface. The commands generally carry the upper layers like layer 3
decisions to the lower layers like layer 2 on the local device entity or at the remote
entity. There are several examples of MICS commands, such as MIH scan, MIH
configure, MIH handover initiate, MIH Handover prepare and MIH handover
complete.
3.1 Media Independent Information Service (MIIS)
MIH provides the information services through a MIIS, which enables effective
system access and effective handover decisions based on the information about all
networks in a geographical area from any single layer 2 networks. MIIS provides
registered MIH users with the knowledgebase of the network and information
elements and corresponding query-response mechanisms for the transfer of
information. By utilizing these services, the MIH users are able to enhance handover
performance such as through informed early decisions and signaling. MIIS are
classified into three groups, namely general or access network specific information,
Point of Attachment specific information and vendor specific information.
4 Proposed Solution Scheme
In response to the PMIPv6 problems mentioned in Section 2, we proposed solution
scheme that provides an integration solution with integrate the analysis of handover
latency introduced by PMIPv6 with the seamless handover solution used by MIH as
well as the Neighbor Discovery message of IPv6 to reduce handover latency and
packet loss on network layer at n-MAG to avoid the on-the-fly packet loss during the
handover process. Figure 4 represents the proposed integration solution of PMIPv6
with MIH.
Figure 4: Proposed Integration Solution
Figure 5: Integration solution architecture of PMIPv6
The key functionality is provided by Media Independent Handover (MIH) which is
communication among the various wireless layers and the IP layer. The working
group of IEEE 802.21 introduces a Media Independent Handover Function (MIHF)
that is located in the protocol stack between the lower layer wireless access
technologies and IP at upper layer. It also provides the services to the layer 3 and
layer 2 through well defined Service Access Points (SAPs) [15].
4.1 Neighbor Discovery
Neighbor Discovery (ND) enables the network discovery and selection process by
sending network information to the neighbor MAG before handover that can helps to
eliminate the need for MAG to acquire the MH-profile from the policy server/AAA
whenever a MH performs handover between two networks in micro mobility domain.
It avoids the packet loss of on-the-fly packet which is routed between the LMA and
previous MAG (p-MAG). This network information could include information about
router discovery, parameter discovery, MH-profile which contains the MH-Identifier,
MH home network prefix, LMA address (LMAA), MIH handover messages etc., of
nearby network links.
4.2 Analysis of Handover Latency and Assumptions
The overall handover latency consists of the layer 2 (L2) and layer 3 (L3)
operations. The handover latency is consequent on the processing time involved in
each step of handover procedure on each layer.
The handover latency can be expressed as:
………………………………..… (1)
where
represents the network layer as example switching latency and
represents link layer as example switching time.
On L3, the handover latency is affected by IP connectivity latency. The IP
connectivity latency results from the time for movement detection (MD), configure a
new CoA (care-of-address), Duplicate Address Detection (DAD) and binding
registration. Therefore, L3 can be denoted as follows:
…………………..… (2)
where Tmove represents the time required for the MH to receive beacons from n-
MAG, after disconnecting from the p-MAG. In order to estimate the movement
detection delay, based on the assumptions of mobility management protocols that the
times taken for MD are RS and RA messages as follows:
…………………………………..…..… (3)
represents the time that taken for new CoA configuration.
represents
the time elapsed between the sending of the BU from the MH/MAG to the
MAP/LMA and the arrival/transmission of the first packet through the n-MAG.
Binding registration is the sum of the round trip time between MH/MAG and
MAP/LMA and the processing time as follows:
…………………………………..…..… (4)
represents the time required to recognize the uniqueness of an IPv6 address.
Once the MH discovers a new router and creates a new CoA it tries to find out if the
particular address is unique. This process is called DAD and it is a significant part of
the whole IPv6 process.
As simplification of (2), (3) and (4) equations, it can be expressed as:
…………………(5)
On L2, MH has to perform three operations during the IEEE 802.11 handover
procedure such as scanning (
), authentication (
) and re-association
(
). Handover latency at L2 can be denoted as follows:
…………………………….(6)
represents the time that taken the MH performs a channel scanning to find the
potential APs to associate with. When MH detects link deterioration, it starts scanning
on each channel finding the best channel based on the Received Signal Strength
Indicator (RSSI) value.
represents the time taken for authentication procedure that depends on the
type of authentication in use. The authentication time is round trip time between MH
and AP. While
represents the time needed for re-association consists of re-
association request and reply message exchange between MH and AP if
authentication operation is successful.
Figure 6: An Analytical Model of Integration solution of PMIPv6 with MIH
The following notations are depicted in Figure 6 for integration solution of
PMIPv6 with MIH.
The delay between the MH and AP is
, which is the time required for a
packet to be sent between the MH and AP through a wireless link.
The delay between the AP and n-MAG is
, which is the time between
the AP and the n-MAG connected to the AP.
The delay between the n-MAG and LMA is tag.
The delay between the LMA and Corresponding Node (CN) is tca.
The delay between the n-MAG and CN is tcm, which is the time required for
a packet to be sent between the n-MAG and the CN.
The delay between the mobility agents and AAA is ta.
As shown in figure 6, we proposed integration solution of PMIPv6 with MIH to
reduce handover latency as the time taken for scanning by informing the MH about
the channel information of next APs and use ND message of IPv6 to reduce handover
delay and packet loss on network layer at n-MAG to avoid the on-the-fly packet loss
during the handover process.
During the IEEE802.11 handover procedure the MH performs scanning on the
certain number of channels to find the potential APs to associate with. By informing
the MH about the channel information of next APs can significantly reduce the
scanning time.
However, the scanning time also depends on the type of scanning is used. There
are two types of scanning which are defined as active and passive. In active scan
mode, MH sends probe request and receives probe response if any AP is available on
certain channel. While in passive scan mode, each MHs listens the channel for
possible beacon messages which are periodically generated by APs. The handover
delay in active scan mode is usually less than in passive scan mode. The operation of
passive scan mode depends on the period of beacon generation interval. Therefore,
this can provide better battery saving than active scan mode of operation.
As in L2 trigger, the p-MAG has already authenticated the MH and sends the MH's
profile which contains MH-Identifier to the n-MAG through the ND message since
the MH is already in the PMIPv6 domain and receiving as well as sending
information to CN before the handover. Hence, the authentication delay is eliminated
during actual handover. Thus, the L2 handover delay can be expressed as:
……………………..…… (7)
As the parts of L3 handover delay that should be taken into consideration in
PMIPv6. Since we proposed the integration solution of PMIPv6 with MIH services
and ND, the number of handover operations should not be considered for overall
handover latency. As a result, L3 handover delay is considered only two things in
integration solution of PMIPv6 with MIH in a micro mobility domain.
o When MH attaches to the n-MAG and delivers event notification of
MIH_Link_up indication, n-MAG sends a PBU message to the LMA for
updating the lifetime entry in the binding cache table of the LMA and
triggering transmission of buffer data for the MH
o RA message
Therefore, the overall handover delay at L3 can be expressed as:
Based on Analytical model:
……………………...… (8)
Seamless Handover Latency of integration solution of PMIPv6 with MIH can be
expressed as:
5 Simulation Experiment and Results
In order to evaluate the impact on intra-domain handover performance, simulations
were performed to evaluate micro mobility protocols by using the ns-2 [16]. For the
simulations, two important performance indicators are measured which are the
throughput for packet delivery and handover latency. In order to obtain reasonable
results, we measure the performance for micro mobility protocol in intra-domain
traffic for both TCP and UDP packet flow.
5.1 Simulation Setup
The simulation scenario setup is implemented as a network-based mobility
management protocol in the simulation of mobility across overlapping wireless access
networks in micro mobility domain. The proposed integration solution scenario setup
is the same as the PMIPv6 but further incorporates MIH functionality in the MH and
the MAGs. Thus, the simulation setup scenario is as shown in figure 7 below:
Figure 7: Simulation Scenario Setup of proposed Integration solution of
PMIPv6-MIH
In the above simulation scenario, the p-MAG and n-MAG are in separate subnets.
The two MAGs have both L2 and L3 capabilities that handles handovers. The router
is interconnected to the LMA by a series of agents that are organized in a hierarchical
tree structure of point-to-point wired links.
The packet flow of CBR and FTP are simulated and transmitted from the CN to the
MH using UDP and TCP. The link delay between the CN and the LMA is set at 10ms
while the bandwidth is set at 100Mb. The link delay between the LMA and the
respective MAGs is set at 1ms. The CBR and FTP packet size is set at 1000 and 1040
bytes while the interval between successive packets is fixed at 0.001 seconds.
5.2 Simulation Results
Simulation results for intra-domain traffics are obtained as follows:
Figure 8: Handover Latency of UDP Flow in micro
mobility domain
Figure 9: Handover Latency of TCP Flow in micro
mobility domain
From the above results, it is observed that UDP and TCP performance of eTIMIP
and TIMIP increased the handover latency during the MH moves to new network in
micro mobility domain. It also noted from the simulation results that performance of
throughput also shown degradation. This is due to the fact that, when MH moves
away from one network to another in micro mobility domain with high speed
mobility, there are lots of operations to perform between the changes of network, such
as configuring new CoA, DAD operation, binding registration and MD.
In comparison to PMIPv6, it does not require CoA and DAD as MH is already
roaming in the PMIPv6 domain. Once the MH has entered and is roaming inside the
PMIPv6 domain, CoA is not relevant since according to the PMIPv6 specification, the
MH continues to use the same address configuration. A DAD operation is required for
a link-local address since address collision is possible between MH, MAG and all
MH’s attached to the same MAG. The DAD operation may significantly increase
handover latency and is a very time consuming procedure. As DAD requires around
one second (or even much than one sec.), PMIPv6 introduce a per-MH prefix model
in which every MH is assigned a unique HNP. This approach may guarantee address
uniqueness. But still PMIPv6 suffers from a lengthy handover latency and packet loss
during the handover process when MH speed is high. To overcome these problems,
we proposed integration solution scheme for PMIPv6 that can send the MH-profile to
the n-MAG through ND message before handover on L3 and also reduce the time on
L2 scanning by informing the MH about the channel information of next APs using
MIH services.
Based on the proposed solution scheme, the result of handover latency and
throughput are better than other mobility protocols. The reason of reduce handover
latency and improve throughput in micro mobility domain as below:
The time required to obtain MH profile information can be omitted since n-
MAG performs this information retrieval prior to MH’s actual attachment.
Figure 9: Handover Latency of TCP Flow in micro
mobility domain
Figure 10: Throughput (Mbps) of UDP Flow in micro
mobility domain
Figure 11: Throughput (Mbps) of TCP Flow in micro
mobility domain
As the specification of PMIPv6, the time needed to obtain the DAD
operation and configure new CoA can also be non-appreciable since n-MAG
performs a pre-DAD procedure like assigning a unique HNP during
available resource negotiation with p-MAG and the MH continues to use the
same address configuration.
The time required to obtain mobility-related signaling massage exchange
during pre-registration may not be considered since this negotiation is
established before MH attachment. Since the MH is already pre-registered
and there is no need to confirm at the n-MAG, therefore the last Proxy
Binding Acknowledgement (PBA) message send from the LMA may not be
considered.
6 Conclusion
In this paper, we conducted simulations to evaluate, compare and examine the
mobility protocols under intra-domain approaches. As for performance, we compared
performance indicators such as handover latency and throughput for mobility
protocols to the proposed integration solution. Based on our simulation results
obtained, the integration solution of PMIPv6-MIH demonstrates better performance
as compared to other mobility protocols. As for the future work, we would like to
improve the handover latency, and evaluate the performance of the proposed
PMIPv6-MIH on real-time applications e.g. video streaming.
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