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A Network-based Seamless Handover Scheme for
Multi-homed Devices
Md. Shohrab Hossain and Mohammed Atiquzzaman
School of Computer Science, University of Oklahoma, Norman, OK 73019
Email: {shohrab, atiq}@ou.edu
Abstract—Terminal-based mobility protocols require mobile
devices to participate in mobility signaling that consumes lots
of processing power and memory. Network-based mobility pro-
tocol solves this problem by excluding low-end mobile devices
from signaling requirement. We earlier proposed SEMO6, a
terminal-based mobility protocol which exploits multiple network
interfaces to achieve seamless handover. In this paper, we have
proposed a network-based mobility solution for SEMO6. We have
performed a thorough cost analysis of its major mobility entities
that participate in mobility management and also obtained their
efficiency based on signaling overhead. Results show interesting
relationships among various network parameters. Our signaling
analysis can be used by network engineers to estimate the
resource requirements of its entities in actual deployment.
Index Terms—Mobility management, Proxy Mobile IPv6, mul-
tihoming, seamless handover.
I. INTRODUCTION
Proliferation in mobile computing has drawn signifi-
cant attention of the research community and Mobile IPv6
(MIPv6) [1] was standardized to facilitate Internet connec-
tivity to mobile devices. However, as a host-based mobility
solution, Mobile IPv6 requires low-end mobile devices to
perform all mobility related signaling to maintain connectivity.
Therefore, Internet Engineering Task Force (IETF) proposed
Proxy Mobile IPv6 (PMIPv6) [2], a Network-based Localized
Mobility Management (NetLMM) solution which provides
Internet connectivity to low power mobile devices without
requiring them to get involved in mobility signaling.
With the convergence of next generation wireless access
technologies, such as 802.11, WiMAX, GPRS, 3G, etc, mo-
bile devices are now getting equipped with multiple network
interfaces that can facilitate increased availability, fault toler-
ance. This capability of communicating through multiple net-
work interfaces is sometimes termed as multihoming. Though
PMIPv6 supports multihoming, it has not been specified
clearly how to achieve seamless handover in multihoming
scenario.
Multi-homed mobile devices can maintain seamless con-
nectivity with multiple wireless access networks, thereby ben-
efitting the ongoing sessions with its peers. We, therefore,
proposed SEamless MObility using Shim6 (SEMO6) [3], [4],
a network-layer based solution that provides seamless con-
nectivity to multi-homed mobile devices. However, SEMO6
is a terminal-based protocol and it requires involvement of the
low-power mobile devices for mobility management.
A few works on PMIPv6 and related protocols have been
reported in the literature. Iapichino et al. [5] propose a
multi-homing solution combining Host Identity Protocol with
PMIPv6. Lee et al. [6] compares HMIPv6 and PMIPv6. Kim
et al. [7] performed handover analysis of PMIPv6. Iapichino et
al. [8] performed experimental evaluation of PMIPv6. How-
ever, none of the exiting works [6]–[8] exploited the multi-
homing feature of mobile devices to improve the performance
of PMIPv6. Although there exists a few entity-wise cost
evaluation of mobility protocols [9], [10] in the literature,
no such evaluation for PMIPv6 has been attempted. Such an
entity-wise evaluation is very crucial as mobility management
entities are very resource restricted and overloading of these
entities may result in complete outage for the whole system.
Our objective of this work is to propose a network-based
mobility architecture that ensures seamless handover of mobile
devices through its multihoming feature. We have proposed
a novel mobility architecture combining the idea of PMIPv6
and SEMO6 [4] and named it Proxy-SEMO6 that exploits
make-before-break strategy to achieve seamless handover in
localized mobility domain. In addition, we have performed
entity-wise cost evaluation of the proposed scheme.
The contributions of this work are: (i) proposing a network-
based seamless mobility solution for SEMO6, (ii) developing
an analytical model to perform signaling analysis of its key
entities, and presenting numerical results.
Our results show the impact of various network parameters
on the total overhead and performance of the mobility man-
agement entities of Proxy-SEMO6. Our proposed scheme can
guide design engineers to improve the handoff performance
of network-based mobility protocols that have received signif-
icant attention with the convergence of next generation all-IP
networks.
The rest of the paper is organized as follows. Section II
explains basic SEMO6 [3] architecture in brief. In Section III,
the proposed Proxy-SEMO6 architecture is explained along
with its protocol operation and timing diagram. Section IV
presents a cost analysis of all the entities of Proxy-SEMO6,
followed by the numerical results in Section V. Finally, we
conclude the paper in Section VI.
II. SEMO6 ARCHITECTURE
To achieve seamless handover of multihomed mobile de-
vices, we earlier proposed SEMO6 [3], a terminal-based
GC'12 Workshop: The 4th IEEE International Workshop on Mobility Management in the Networks of the Future World
978-1-4673-4941-3/12/$31.00 ©2012 IEEE 1042
Fig. 1. Proxy-SEMO6 architecture.
mobility solution in network layer. SEMO6 is based on
Shim6 [11] and it decouples upper layer session identifier
from locator, thereby tries to reduce the impact of mobility on
upper layer protocols, e.g., transport and application layers.
SEMO6 focuses on providing a single platform for mobility
and multihoming. Moreover, it exploits multi-homing feature
of Mobile Host (MH) to minimize handover latency which is
a very crucial factor for any handover protocol. However, as
a terminal-based mobility solution, the MH is responsible for
all the mobility-related signaling in SEMO6; thus, it consumes
significant amount of power – a major concern for any mobile
device. Therefore, it is essential to design a network-based
mobility solution that relieves MH from mobility related
signaling in addition to achieving seamless handover for multi-
homed mobile devices.
III. PROXY-SEMO6 ARCHITECTURE
Fig. 1 shows the Proxy-SEMO6 architecture which is sim-
ilar to Proxy MIPv6. The main difference is the support of
seamless mobility for the multi-homed MH. Location Mobil-
ity Anchor (LMA) keeps track of the MH in the localized
mobility domain and all traffic destined to the MH from any
Correspondent Node (CN) are routed through the LMA. The
Mobility Anchor Gateway (MAG), usually the access router
of the MH, performs all mobility related signaling on behalf
of the MH, thereby saving MH’s resources. In our proposed
scheme, we assumed that LMA will allocate separate binding
cache entry per interface of the MH.
A. Timing diagram
The timing diagram for the proposed Proxy-SEMO signal-
ing is shown in Fig. 2. When any multihomed MH enters
the Proxy-SEMO6 domain, it attempts to attach to the access
network (L2 attachment) through one of its interfaces (e.g.,
IF1) and sends router solicitation to the access router (e.g.,
MAG1). Upon receiving the solicitation, the MAG uses MH’s
identification (e.g., MAC address) to determine whether the
MH is authorized to use the localized mobility support. The
MAG then registers the MH’s one interface (IF1) with the
Fig. 2. Timing diagram of Proxy-SEMO6 signaling.
LMA through Proxy Binding Update (PBU) which associates
MAG1’s addre ss wi th MH’s I F1. The LMA adds a Bind-
ing Cache Entry (BCE) into its table and establishes a bi-
directional tunnel with the MAG1if one does not already exist.
The LMA also sends Proxy Binding Acknowledgement (PBA)
to the MAG1along with the assigned prefix. Upon receiving
the PBA, the MAG1sends the MH Router Advertisement (that
includes the allocated prefix), allowing MH to configure its IF1
address through stateless auto-configuration.
When the MH moves in a region that is covered by two
access networks, it attempts to acquire another IP address
from the MAG2for its second interface (IF2) in a similar way
mentioned above (see Fig. 2). Thus, when the LMA receives
the PBU from the MAG2, the LMA inserts another BCE into
its table corresponding to the MH’s IF2and establishes similar
bi-directional tunnel with the MAG2. In addition, the LMA
sends MH’s CN a SEMO6 Update Request (UR) message to
add this new IP address into CN’s peer locator list.
Thus, during the handoff, when the MH moves away from
the MAG1link, the (L2 detachment) event is detected by the
MAG1(for example, through IPv6 neighbor unreachability
detection event). The MAG1then informs the LMA about
this event through the deregistration PBU which results in
possible tunnel deletion (if not needed for any other MH). At
this point, the LMA sends CN UR message so that CN can
modify its peer locator list by removing the MH’s unreachable
IP address. The CN can still continue the session using the
unique ULID (through the other locator corresponding to IF2),
thereby reducing handoff latency and packet loss.
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B. Proxy-SEMO6 vs. PMIPv6
Proxy-SEMO6 attempts to reduce handover latency of
PMIPv6 by exploiting the following strategies:
•Proxy-SEMO6 exploits the make-before-break strategy,
that is, attempts to connect through new MAG before
disconnecting with the old MAG.
•It decouples the upper layer session identifier from the
location-based IP address, thereby ensuring session con-
tinuity, even though the MH’s IP address varies due to
the change of attachment point.
However, Proxy-SEMO6 reduces handover latency of
PMIPv6 at the cost of some additional signaling (e.g., sending
URmessagetoCNbytheLMA).
IV. SIGNALING COST ANALYSIS
In this section, we perform entity-wise cost analysis of
Proxy-SEMO6.
A. Assumptions and Notations
To make the model analytically tractable, the following
assumptions have been made:
•Session arrival at each MH is equal.
•All session lengths are of equal size.
•Searching an entry in binding cache is assumed to use
binary search.
•Our cost analysis ignores standard IP switching costs.
The notations used in the analysis are listed below.
NmNumber of MHs in the LMA-domain,
NcAverage number of CNs per MH,
mNumber of MAGs in the LMA-domain,
βMUnit transmission cost for message type M={PBU,
PBA, UR, UA, ... }
σProportionality constant of wireless link over wired
link,
ωLinear coefficient for lookup cost,
TrSubnet residence time,
λsAverage session arrival rate,
κMaximum transmission unit,
αAverage session size,
δXProcessing cost at entity X.
B. Local Mobility Anchor
In Proxy-SEMO6, the major costs for LMA are 1) initial
registration cost, 2) binding update cost, 3) context establish-
ment cost, 4) CN update cost, and 5) data delivery cost.
1) Initial registration cost: We assume that fraction of
MHs enters into the LMA-domain from outside at a rate of
θd. Thus, a total of NmθdMHs enters into the LMA-domain
per second. When a MH enters the LMA-domain, the MAG
tracks it and sends PBU to the LMA. The LMA processes the
PBU, allocates prefix for the MH, updates the binding cache
and sends back PBA to the MAG. This incurs transmission
costs (βPBU and βPBA) and processing cost (δLM A)onthe
LMA. Thus, the cost incurred at the LMA is,
ΛReg
LMA =NmθdβPBU +βPBA +δLM A (1)
2) Binding update cost: When the MH moves within the
LMA-domain and crosses subnets (in every Trseconds), the
concerned (new) MAG detects it and sends the PBU to the
LMA. In addition, MAGs send periodic refreshing updates
to the LMA for extending the binding lifetime so that the
entries are not removed from the cache. Let the binding
lifetime be Tl. Hence, frequency of sending periodic refreshing
updates are ηr=Tr
Tl/Tr, and total frequency of sending
LU and refreshing PBU is ηt=1+Tr
Tl/Tr,This
incurs transmission cost (βPBU and βPBA) and lookup cost
(ωlog2Nm) at the LMA. Hence,
ΛPBU
LMA =ηtNmβPBU +βPBA +ωlog2Nm(2)
3) Context establishment cost: The LMA establishes Shim6
context with the MH so that LMA can subsequently send
update to CN about the locator change (when MH moves to
a new MAG-region). During the context establishment phase,
the LMA is informed about the ULID, locator list and current
locator used by the MH. Thus, it incurs transmission cost for
Shim6 Context (βSC) and processing by the LMA. Hence,
ΛSC
LMA =λsNm2βSC +δLM A (3)
4) CN update cost: In order to modify the CN’s peer locator
list, LMA sends UR message to CN whenever any new binding
entry is inserted corresponding to MH’s second interface.
Furthermore, when MAG sends deregistration message to
the LMA, the LMA deletes corresponding binding entry and
informs CN through UR message. Thus, the cost on LMA
regarding UR message is as follows:
ΛUR
LMA =NmNc
TrβUR +βUA(4)
5) Data delivery cost: In a session between the CN and
MH, an average of α
κdata packets (and corresponding ACK)
are transmitted. The total data packet arrival rate to the LMA
is λp=NmNcλsα
κ. Data packets received by the LMA are
tunneled through the respective MAG to the destination MH.
This incurs transmission cost for data and Ack packet (βDP
and βDA ) including extra IP-header (βIP ), and lookup cost.
Therefore, data delivery cost for the LMA is given by,
ΛDD
LMA =λpβDP +βDA +βIP +ωlog2Nm(5)
6) Total Cost on LMA: Thus, the total cost on the LMA
can be obtained by adding Eqns. (1), (2), (3), (4) and (5):
ΛLMA =Λ
Reg
LMA +Λ
PBU
LMA +Λ
UR
LMA +Λ
SC
LMA +Λ
DD
LMA (6)
C. Mobility Anchor Gateway
The major costs for each MAG are 1) MH authentication
cost, 2) binding update cost, and 3) data delivery cost.
1) MH authentication cost: For every registration request
from an incoming MH, the MAG is responsible for authentica-
tion. Based on the credentials (AAA information) of the MH,
the MAG either accepts or rejects the registration request. As a
total of NmθdMHs enters into the LMA-domain per second
and if there are mMAGs in the LMA-domain, therefore each
MAG processes Nmθd/m authentication requests. Hence,
ΛAAA
MAG =Nmθd
m×δMAG (7)
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2) Binding update cost: Assuming MHs are uniformly
distributed in the LMA-domain, each MAG sends PBU and
refreshing PBU messages (receives corresponding PBA) on
behalf of Nm/m MHs. Moreover, the MAG has to detect the
movement of the MH inside its domain in to sense its arrival or
departure, thereby requiring processing cost at MAG (δMAG).
Hence, cost incurred at each MAG for binding updates can be
obtained as follows:
ΛPBU
MAG =ηtNm
mβPBU +βPBA +δMAG(8)
3) Data delivery cost: Each MAG receives data packets
tunneled from the LMA and decapsulate them and sends them
to the corresponding MH. So the data delivery cost at each
MAG is given by,
ΛDD
MAG =NmNc
mα
κλsβDP +βDA +βIP (9)
4) Total Cost on MAG: Thus, the total cost on each MAG
can be obtained by adding Eqns. (7), (8) and (9):
ΛMAG =Λ
AAA
MAG +Λ
PBU
MAG +Λ
DD
MAG (10)
D. Mobile Host
As a network-based mobility solution, Proxy-SEMO6 incurs
least cost at the MH. As all the encapsulation and decapsula-
tion are performed by the MAG (for the packets to and from
the MH), the wireless access network is not affected by the
extra IP headers. Other than packet delivery, the only task a
MH is required to do is to establish Shim6 context with the
LMA after registers with the LMA-domain. Thus, the total
cost for each MH is as follows:
ΛMH =σNcα
κλsβDP +βDA+2λsβSC (11)
E. Efficiency
We define a new metric called efficiency to measure the
performance of Proxy-SEMO6. It is defined as the ratio of net
data delivery cost (excluding all overheads) to the total cost
(that includes signaling and data delivery costs).
The net data delivery cost of LMA can be expressed as
follows:
ΛNet−DD
LMA =λpβDP +βDA(12)
Hence, the efficiency of LMA is given by,
ξLMA =ΛNet−DD
LMA
ΛLMA
(13)
The net data delivery cost of MAG can be expressed as
follows: ΛNet−DD
MAG =NmNc
mα
κλsβDP +βDA(14)
Hence, the efficiency of MAG is given by,
ξMAG =ΛNet−DD
MAG
ΛMAG
(15)
The net data delivery cost of the MH can be expressed as
follows:
ΛNet−DD
MH =σNcα
κλsβDP +βDA(16)
Hence, the efficiency of MH is given by,
ξMH =ΛNet−DD
MH
ΛMH
(17)
V. N UMERICAL RESULTS
In this section, we present numerical results showing impact
of various system parameters on Proxy-SEMO6 entities. The
parameter values used in numerical analysis are derived using
similar approaches used in [9], [10]; each cost metric is a
relative quantity and is based on the specific packet size (unit
cost for 100 bytes [9]). For example, βPBU = 0.76, since
the size of PBU packet is 76. Therefore, we have set the
parameters as follows: βPBA = 0.76, βIP = 0.40, βDP = 5.72,
βDA = 0.60, = 20%,θ
d=0.10,σ= 10, η=0.3,η=0.3,
λs= 0.01, δLM A =0.3,δMAG =0.3,κ= 512 bit/sec, α=
10240 bits. The default values of other parameters are m=
10, Tr= 70 sec, Nm= 4000, Nc= 1. It can be noted that
while computing the total overhead of the LMA and MAG, we
have considered all the factors considered including tunneling
overhead, except payload delivery cost.
A. LMA
Fig. 3 shows the impact of Session to Mobility Ratio (SMR)
on the total overhead of LMA for different number of MHs in
the LMA-domain. SMR is the product of subnet residence time
(Tr) and session arrival rate (λs). We kept λs=0.01(fixed)
while varying Trvalue. Again higher number of MHs under
the LMA-domain increases the data delivery overhead on the
LMA, resulting in higher overhead on the LMA. However,
with respect to SMR, the total overhead on LMA decreases
very slowly. This is due to the fact that higher SMR (less
mobility rate) causes reduction in PBU cost, which is very
small compared to the data tunneling overhead. Hence the
graphs are almost flat in nature. This is an interesting finding
phenomena obtained from our analysis.
Fig. 4 shows the impact of number of CNs (per MH) on
the total overhead of LMA. Total overhead increases for both
increased number of CNs and higher session arrival rates.
Higher session arrival affects data tunneling overhead since
more data packets are required to be tunneled through LMA.
Fig. 5 shows the impact of SMR on the efficiency of LMA.
We find that efficiency increases for higher session lengths,
having more payload traffic compared to mobility signaling
traffic. In addition, the efficiency of LMA increases slowly
with the increase of SMR since higher SMR (less mobility)
causes reduced signaling traffic for the LMA. However, effi-
ciency falls a little bit when the value of Tris 120 sec (SMR
= 1.2) and again in SMR = 2.4 due to rise in signaling traffic
caused by refreshing updates.
B. MAG
Fig. 6 shows the impact of subnet residence times on the
total overhead of each MAG, for different number of MHs
in the PMIPv6-domain. The total overhead on each MAG
decreases for higher values of Tr, producing less PBUs.
However, there are some additional refreshing PBU sent to
the LMA by the MAG, to keep the binding entry valid and
those refreshing PBUs causes the overhead on MAG to rise
in 120 sec and then 240 sec, which are multiple of binding
entry lifetime.
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1 2 3 4
1000
2000
3000
4000
5000
6000
7000
Total overhead on LMA
Session to Mobility Ratio
Nm = 1000
Nm = 3000
Nm = 5000
Fig. 3. Impact of SMR on the total overhead
of LMA for different number of MHs.
2 4 6 8 10
0
1
2
3
4
5
x 105
Total overhead on LMA
Number of CNs
λs = 0.01
λs = 0.04
λs = 0.16
Fig. 4. Impact of number of CNs on total cost
of LMA for different session arrival rates.
0.5 1 1.5 2 2.5 3 3.5 4
50
52
54
56
58
60
Efficiency of LMA (%)
Session to Mobility Ratio
α = 5k
α = 10k
α = 20k
Fig. 5. Impact of SMR on the efficiency of
LMA for different session lengths.
50 100 150 200 250 300
0
20
40
60
80
100
Total Overhead on MAG
Subnet Residence Time (sec)
Nm = 1000
Nm = 3000
Nm = 5000
Fig. 6. Impact of subnet residence times
on total overhead of each MAG for different
number of MHs in the PMIPv6-domain.
2 4 6 8 10
x 1
0
4
59
59.5
60
60.5
61
61.5
Efficiency of MAG (%)
Session length (bits)
Nc = 1
Nc = 5
Nc = 10
Fig. 7. Impact of session lengths on the
efficiency of each MAG for different number
of CNs.
2 4 6 8 10
0
0.05
0.1
0.15
0.2
Signaling Overhed on MH (%)
Number of Correspondent Nodes
α = 5kb
α = 10kb
α = 20kb
Fig. 8. Signaling overhead on the MH vs.
number of CNs.
Fig. 7 shows the impact of session lengths on the efficiency
of each MAG. Efficiency increases for larger sessions as net
data delivery through the MAG increases. In addition, higher
number of CNs also results in more data traffic to the CNs,
resulting in improved efficiency.
C. MH
The percentage of signaling overhead on each MH is shown
in Fig. 8. The only signaling responsibility of MH (other than
data transmission cost) is to establish Shim6 context with
the LMA after its registration with it. Results show that the
overhead is very small (<0.25%) for the MH; the higher the
session length is, the lower the percentage overhead is, having
more payload traffic compared to signaling traffic.
VI. CONCLUSION
In this paper, we have proposed a novel seamless mobility
solution for network-based mobility management that requires
least involvement of the low-power mobile devices. We have
developed analytical model to derive the total overhead on
the mobility management entities of the proposed scheme.
Results show interesting relationships among various network
parameters, such as, network size, mobility rate, traffic rate.
Our proposed scheme can guide design engineers to improve
the handoff performance of network-based mobility protocols
that have received significant attention with the convergence
of next generation all-IP networks.
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