Computer Communications 33 (2010) 1030-1048
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Computer Communications
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / c o m c o m
Design of the multicast service for mobile users in the 802.16 network environment
Chun-Shian Tsai a,*, Chun-Chuan Yang b
a Department of Computer Science and Information Engineering, Chung Chou Institute of Technology, 6, Lane 2, Sec. 3, Shanjiao Rd.,Yuanlin Changhua 51003, Taiwan, ROC
b Department of Computer Science and Information Engineering, National Chi Nan University, #1, University Road, PULI, Nantao 545, Taiwan, ROC
a r t i c l e
i n f o
a b s t r a c t
Article history:
Middle-domain mobility management provides an efficient routing, low registration cost and handoff
Received 29 October 2008
latency for layer 3 (IP layer) 802.16-based mobile network environment. In the middle-domain, the
Received in revised form 11 January 2010
802.16 base station (BS) acts as an agent or proxy to manage mobile networks to achieve this goal.
Accepted 12 January 2010
The BS could only address external traffic but without internal case management. In order to complement
Available online 18 January 2010
this defect, an enhanced version for the middle-domain mobility management is designed in this paper.
Moreover, we research and design the multicast extension for the middle-domain by applying the idea of
Keywords:
the enhancement, which is called HMP (Hierarchical Multicast Protocol). Associated handoff scheme is
802.16
also proposed in this paper. Since it is a complicated case for designing the multicast service in 802.16
Mobility management
Mobile IP
network environment, we need a characteristic method to address this case. In order to fulfill this
Multicast
achievement of designing HMP scheme, we introduce a reduction process (RP) in this paper. By using
Tunnel convergence problem
the RP, a complicated 802.16-based network environment can be actually reduced to a simpler network
environment. The mathematical analysis and simulation study are presented for performance evaluation.
Simulation results have demonstrated that the enhanced middle-domain mobility management has the
better network performance in terms of registration cost, handoff latency and routing cost in comparing
with conventional mobility management schemes. Moreover, the proposed multicast extension for HMP
scheme is simple and has scalability and network performance advantages over other approaches in
mobile multicasting.
O 2010 Elsevier B.V. All rights reserved.
This work was supported in part by the National Science Coun-
Recently, a new wireless technology called 802.16 (or WiMAX)
cil, Taiwan, ROC, under Grant No. NSC96-2218-E-235-002.
[19-28] is emerging. In our previous work [29], we have discussed
that it is not suitable to fit macro- or micro-mobility technologies
into 802.16-based network environment, because of frequent reg-
1. Introduction
istration and increased handoff latency in Mobile IP, and lengthy
internal data path with gateway in Cellular IP. Thus, middle-domain
Mobility management [1-10] is an essential component in en-
mobility management is proposed in [29] to insert in between
abling mobility of hosts while maintaining the packet routing effi-
macro-domain and micro-domain. The middle-domain mobility
ciency between the hosts. Mobile IP (MIP) [11-14] has been
management for layer 3 (L3) 802.16 mobile network environment
designed to serve the needs of the burgeoning population of mo-
is designed to be able to accommodate different micro-mobility
bile computer users who wish to connect to the Internet and main-
protocols and is transparent to macro-mobility and micro-mobility
tain communications as they move from place to place. The
protocols. Moreover, it has significantly reduced the registration
proposed standard for Mobile IP (mobility management referred
cost and handoff latency since localized registration is designed
to as macro-mobility), however, has several drawbacks ranging
in the middle-domain. For the middle-domain, the 802.16 devices
from triangle routing and its effect on network overhead and
en route create the location cache for the corresponding mobile
end-to-end delays, to poor performance during handover due to
host. The registering procedure for Mobile IP in the middle-domain
communication overhead with the home agent (HA), and instead,
can be terminated at the crossover node (i.e. a shared node on the
Cellular IP (CIP) [15-18] (mobility management referred to as mi-
rooted path) because each 802.16 device en route intercepts the
cro-mobility) was proposed. CIP provides local mobility and hand-
Mobile IP registration message for the location cache at crossover.
off support for frequently moving hosts, which means that
Therefore, efficient mobility management can be addressed within
mobile hosts can migrate inside a CIP network with little distur-
the middle-domain.
bance to active data flow.
Different from HMIPv6 [30] technology, middle-domain adopts
* Corresponding author. Tel.: +886 04 8311498x2413; fax: +886 04 8394147.
an efficient direct routing through referring to these location ca-
E-mail address: cstsai@dragon.ccut.edu.tw (C.-S. Tsai).
0140-3664/$ - see front matter O 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.comcom.2010.01.008

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C.-S. Tsai, C.-C. Yang / Computer Communications 33 (2010) 1030-1048
1031
ches for packet delivery but not tunneling. The idea of improving
The rest of the paper is organized as follows. First of all, we
handoff and communication performance for mobile nodes
make a brief of survey of (1) conventional mobility management
through using location cache is useful, particularly for the consid-
(2) middle-domain mobility management (3) multicast extension
ered wireless mobile network environment. On the contrary, the
for Mobile IP, and (4) hierarchical mobile multicast in Section 2.
tunneling is an inefficient routing for 802.16 network performance
An enhanced version for middle-domain mobility management is
because of the IP-in-IP encapsulated packets and Tunnel Conver-
presented in Section 3. In Section 4, multicast extension associated
gence Problem[31]. Though middle-domain provides low cost for
with idea of middle-domain enhancement in the 802.16 network
home registration and less time for handoff, it does not still solve
environment called Hierarchical Multicast Protocol (HMP) is pro-
the problem of tunnel-based protocols. While acting in case of
posed. Simulation environment and results for performance evalu-
internal traffic, middle-domain mobility management does not
ation for mobility management (unicast version) and multicast
be mentioned. To complement this defect, we consider supporting
case are mentioned in Sections 3.5 and 4.5, respectively. Theoreti-
an enhancement for the middle-domain.
cal analysis and characteristic for the middle-domain are re-
Moreover, demand for applications has recently risen such as
searched in Section 5. Finally, Section 6 concludes this paper.
(1) teleconferencing in which part of or all of the participants are
mobile users in distributed networks, (2) live video, and (3) multi-
2. Related work
player online games, where mobile users located in different parts
of the world participate via Internet. Multicasting could prove to be
2.1. Conventional mobility management: MIP, FMIPv6, HMIPv6
a more efficient way of providing necessary services for these
applications. However, no efficient research into multicasting for
For conventional mobility management, Mobile IP (MIP[11-14]),
WiMAX applications has been performed yet. Therefore, in this pa-
Fast Handover for Mobile IPv6 (FMIPv6[46]), and Hierarchical Mobile
per, we mainly aim to design the multicast extension by inheriting
IPv6 (HMIPv6 [30]) are all famous schemes which will be detailed
the idea of enhanced middle-domain mobility management, which
as follows.
is denoted by HMP (Hierarchical Multicast Protocol). On the design
In Mobile IP, a mobile host (MH) uses two IP addresses: a fixed
of the HMP scheme, we find that the traditional tunnel-based mul-
home address and a care-of-address (CoA) that changes at each
ticast routing protocols such as BT[31,32], MoM [33] fitted into the
new point of attachment (subnet). A router called Home Agent
802.16 network environment are not appropriate and difficult
(HA) on an MH's home network is responsible for maintaining
since inefficient multicast routing problems such as triangular rout-
the mapping (binding) of the home address to the CoA. When a
ing, duplicate of tunnels, tunnel convergence problem and frequent
mobile host moves to a foreign network, it obtains a new CoA from
DMSP [33,34] handoff problem would occur. These problems would
the Foreign Agent (FA) and registers the CoA with its HA. In this
be mentioned and discussed in Section 4.1.
way, whenever a mobile host is not attached to its home network,
For simplifying the complicated case, a Reduction Process (RP)
home agent gets all packets destined for mobile host and arranges
needs to be addressed in this paper. With the concept for RP, the
to deliver to the MH's current point of attachment by tunneling the
HMP scheme can be easily designed based on the associated idea
packets to the MH's CoA.
of the enhanced version for the middle-domain mobility manage-
FMIPv6 provides seamless handover by minimizing handover
ment with the MoM-applied scheme to do the multicast service.
latency, associated with anticipative movement detection to re-
Lastly, simulation study and theoretical analysis have demonstrated
duce handover latency and packet loss. After discovering one or
that proposed enhanced version for middle-domain mobility man-
more nearby access points, mobile host performs the layer 3 hand-
agement and HMP scheme for multicasting can achieve better net-
over when it is connected to a PAR (previous access router), and in
work performance in 802.16-based network environment.
this case, the PAR must have known information about an NAR
MH
PAR
Handoff trigger is
NAR
HA
data flow(buffering)
beginning

(1-1) Router solicitation
(1-2) Router advertisement
(2-1) HI
(1-3) Fast binding update
(2-2) HAck
e
m
Ti
data forwarding
data
buffering
(3) Fast binding acknowledgment
(4-1) F-NA
Handoff trigger is
N
completing

(4-2) NAAck
O
SESSI
data flow
(5-1) Registration request message
(5-2) Registration reply message
data flow
Fig. 1. Flow sequence chart for FMIPv6.

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C.-S. Tsai, C.-C. Yang / Computer Communications 33 (2010) 1030-1048
(next/neighbor access router). Through a router solicitation for proxy
CN
(RtSolPr) and a proxy router advertisement (PrRtAdv) messages, the
mobile host obtain information of NAR. The mobile host requests
tunneling sending a fast binding update (FBU) message with PAR.
The PAR establishes a tunnel between itself and the NAR, and then
Internet
verifies the MH's new CoA by exchanging a handover initiate (HI)
Home
HA
message and a handover acknowledge (HAck) message. Packets that
Macro-domain
network
arrive at previous care-of address (PCoA) are forwarded to the NAR
through an established tunnel during the handover, and the NAR
buffers the packets. When the mobile host arrives at new location,
BS SFA
the Fast Neighbor Advertisement (F-NA) message is used to inform
Device
the NAR. In latter, the NAR replies a Neighbor Advertisement
Functionality
omain
Acknowledgment (NAACK) to mobile host, and the buffered packets
SS
R
SS
R
are forwarded to it. Fig. 1 shows the flow of FMIPv6.
le-d
HMIPv6 has been proposed to provide a method for efficient
mobility management in a network where MHs frequently change
Midd
their points of attachment. The manageability of traditional Mobile
GR FA
GR FA
GR FA
GR FA
IP can be enhanced by using a Mobility Anchor Point (MAP). A MAP
Micro-
Micro-
acts as a local Home Agent (HA) for MHs in the foreign domain, and
Micro-
Micro-
a multilevel hierarchy of MAPs in HMIPv6 is recommended. The
domain
domain
domain
domain
operations of the MAP in HMIPv6 scheme are presented in the fol-
lowing. When an MH attaches to a new link, it receives a router
Fig. 2. Deployment of layer 3 802.16 network environment for the middle-domain.
advertisement, including a MAP option. The MAP option informs
the mobile node of the MAP's IP address. The MH generates a regio-
nal care-of address (RCoA) based on the MAP's prefix and another
M-CoA: Middle-domain CoA, MH:Mobile host
address for the on-link care-of address (LCoA; address derived from
the foreign link's prefix). The MH then sends a binding update to
BS:
MH's ID
Next Hop
M-CoA
Micro-domain CoA
the MAP, using its RCoA as a home address and its LCoA as the
care-of address. Moreover, the MH also sends a binding update
to the home agent, it binds its RCoA to its home address. Hence,
SS:
MH's ID
Next Hop
Micro-domain CoA
whenever the home agent receives packets destined to the MH's
home address, it will intercept them and forward them to the
Fig. 3. Cache structure in the middle-domain.
RCoA. Since the MAP is also acting as a local home agent for the
MH's RCoA, it will intercept those packets and forward them to
the MH's current location (the LCoA stored in the MAP's binding
main care-of-address (denoted by M-CoA) for the mobile host. The
cache). Through using this concept of localized registration in the
M-CoA is usually the address of the BS and is used in Mobile IP reg-
MAP, there is no required to do binding update if MH is always
istration. Moreover, the BS issues a Mobile IP registration request
moving under the MAP domain.
including the M-CoA to the HA of mobile host on behalf of the for-
eign agent GR. Meanwhile, the BS also sends a Mobile IP reply mes-
2.2. Middle-domain mobility management: SFA
sage back to the GR instead of the HA. In this way, there is no need
to perform Mobile IP home registration with HA as mobile host
In our previous work [29] for the middle-domain, we investi-
handoffs within the middle-domain. This is also the basic idea of
gate the characteristics of IEEE 802.16 and conclude that it is better
SFA for the middle-domain.
to equip base station (BS) and subscriber station (SS) with Layer 3
In order to support middle-domain operations, the cache struc-
(L3) functionality. Therefore, an 802.16 network can act as the
tures in BS and SS for a mobile host are displayed respectively in
backbone network of different subnets for better deployment. As
Fig. 3, in which MH's ID is the home address of the mobile host,
illustrated in Fig. 2, a basic L3 802.16 network consists of a BS
the Next Hop for a mobile host in BS is the address of the next
and a couple of SS that connects to BS via a high-speed wireless
SS, the next hop for a mobile host in SS is the address of the next
link. The BS acts as a gateway to the Internet. The complex subnet
GR, the M-CoA is used in Mobile IP home registration, and the Mi-
systems in micro-domain can connect to the 802.16 network via
cro-domain CoA is used in Mobile IP reply to the GR.
SS. Note that for each frame in Fig. 2, it presents ``Device" and
``Functionality", respectively. For instance, the BS device could
2.3. Multicast extension for Mobile IP: RS, BT, MoM
equip with SFA functionality, SS device is equipped with regular
router (R) functionality, and GR device could equip with MIP FA
Mobile IP proposes two approaches to support mobile multi-
functionality. For Fig. 2, the micro-domain gateway router (GR) un-
cast, which is called Foreign Agent-based multicast (referred to as
der each SS is required to equip with FA functions of Mobile IP and
Remote Subscription, RS [35]) and Home Agent-based multicast (re-
is responsible for MIP home registration.
ferred to as Bi-Directional tunneling, BT [31,32]). Afterwards, Harri-
The operation for middle-domain is summarized as follows. If a
son et al. proposed a home agent-based protocol called MoM
mobile host enters the middle-domain the first time, the GR acts as
(Mobile Multicast) [33] to enhance performance of BT scheme. For
FA for performing the registered procedure of Mobile IP. But the
the Mobile IP multicast protocols, we make a brief survey in the
registration requests issued by the GR are intercepted by SS or BS
following.
in order to maintain proper location (downlink) cache information
In RS scheme, a mobile host must have the responsibility to
of the mobile hosts. When this request message is relayed and ar-
resubscribe to its desired multicast groups each time it enters a
rived at the BS, the BS would act as a super foreign agent (SFA) to
foreign network. RS has better performance if mobile host stays
perform home registration of Mobile IP on behalf of FA. The SFA,
for a long time within a network, otherwise multicast delivery tree
which is a new defined term in this paper, allocates a middle-do-
will be updated frequently. More specifically, RS offers a shortest

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C.-S. Tsai, C.-C. Yang / Computer Communications 33 (2010) 1030-1048
1033
the multicast packet, a foreign agent deliveries it to mobile hosts
Multicast Delivery Tree
using link-level multicast (see Fig. 4(a)). Moreover, MoM uses the
IPinIP Tunnel
DMSP (Designated Multicast Service Provider) to solve tunnel con-
Mobile
Mobile
Mobile
vergence problem. As illustrated in Fig. 4(b), the foreign agent per-
Host1
Host2
Host3
forms a selection to appoint one of multiple home agents (i.e. home
agent1) as the DMSP. The DMSP forwards only one datagram into
Home Agent
the tunnel, while other home agents that are not the DMSP do
not forward the datagram. Though MoM scheme provides a better
One copy datagram
network performance in a distributed system, it is not suitable to
CN
be fitted in a hierarchical-based network environment. Once a
Tunnel
high-level hierarchical network is deployed, the tunnel conver-
Internet
gence problem including with duplicated tunnels becomes more
IPinIP
and more aggravation so that network performance is to go down.
2.4. Hierarchical mobile multicast: HMoM
Foreign Agent
In Mobile IPv6 networks, HMIPv6 [30] introduces hierarchical
mobility management to allow for local mobility handling. Acting
Mobile
Mobile
Mobile
as a local home agent at a visited network, a Mobility Anchor Point
Host1
Host2
Host3
(MAP) will receive all packets on behalf of the mobile host it is
serving and will encapsulate and forward them directly to the cur-
(a) One copy of tunnel for mobile multicast
rent address of mobile host by tunnel. When a mobile host moves
Mobile
Mobile
within the same MAP domain, it only needs to register its new CoA
Mobile
Mobile
Host3
Host2
Host4
with the MAP. Using this feature, Wang et al. [36] proposed a
Host1
Home
speed-based idea for a hierarchical multicast protocol in Mobile
Home
Agent3
DMSP
Home
Agent2
IPv6 networks (HMoM), which utilizes the advantages of hierarchi-
Agent1
cal mobility management in handling unicast routing. For HMoM
scheme, if a mobile host is expected to stay at a new visited
CN
network for a relatively long period of time, it will register to
Internet
the MAP with the smallest distance and the selected MAP joins
the multicast group on behalf of the mobile host. Otherwise, the
MAP with the furthest distance is selected as a multicast agent in
order to avoid frequent tree reconstruction. The multicast agent
is selected dynamically and can be located at any level in a hierar-
Foreign Agent
chical network of routers according to the handoff frequency of
mobile hosts. However, it remains tunnel-based defects in hierar-
Mobile
Mobile
Mobile
Mobile
chical networks. For example, as these mobile hosts with various
Host1
Host2
Host3
Host4
speeds handoff to a same access network, the multiple MAPs with
different distances would be selected. The data delivery firstly
(b) Tunnel convergence problem
aggregate at their MAPs. These MAPs would tunnel them to mobile
Fig. 4. Home agent-based multicast extension for MoM.
hosts by multiple unicast. The technology for HMoM degenerates
to be as a unicast scheme and it wastes the network bandwidth.
Besides, the dwelling time based on history data is adopted in
HMoM. It is not transparent for the mobile host because the mobile
routing path for delivery of multicast datagrams to the mobile
host always needs to evaluate their speed based on the history
host, and the overhead is the cost of reconstructing the delivery
dwelling time. Also, this rule is not precise and objective for a com-
tree while a handoff occurs.
plicated hierarchical network environment, especially for mobile
In BT scheme, the mobile host receives all multicast datagrams
multicasting. Therefore, in this paper, a better network perfor-
by its home agent using unicast Mobile IP tunnels. This approach
mance for multicasting is researched in Section 4 and tunnel-based
handles source mobility as well as recipient mobility, and in fact
problems would be resolved within the middle-domain. Moreover,
hides host mobility from all other members of the group. However,
our scheme is transparent to micro-mobility and macro-mobility
there are three main drawbacks for this approach. First, tunnel for
protocols.
delivery path may be in triangle routing, which can be far from
optimal. Second, the home agent has to replicate and delivery tun-
nel multicast datagrams to each mobile host, regardless of at which
3. Enhanced middle-domain mobility management
foreign networks they reside. Third, if multiple mobile hosts that
belong to the different home networks visit the same foreign net-
For the conventional Mobile IP-based mobility management
work, duplicated copies (tunnels) of multicast packets will arrive at
schemes such as HMIPv6 and FMIPv6 fitted into 802.16 network
the common foreign network, which is denoted by Tunnel Conver-
environment, the tunnel-based problems would happen. These
gence Problem [31-33]. Thus, the network resources will be wasted.
problems would be tunnel convergence,1 triangle routing and IP-in
A home agent-based multicast extension namely mobile multi-
IP Encapsulation problems. As shown in Fig. 5(a), the HMIPv6 scheme
cast (MoM) scheme is to use the home agent functionality of Mo-
presents that data delivery designated for the mobile host is inter-
bile IP to effect delivery of multicast datagrams to mobile host.
cepted by HA and then MAP, the repetitions for tunnels are between
There is only one copy of the multicast datagrams tunneled from
1 In most of papers, the term for ``tunnel convergence" is for multicast issue, not for
home agent to a foreign agent in the event that the home agent
mobility management case (Unicast). But, we think that the similar concept for the
has multiple mobile hosts ever presented there. Upon receiving
repeated tunnels can also be applied in mobility management case for this paper.

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C.-S. Tsai, C.-C. Yang / Computer Communications 33 (2010) 1030-1048
Routing
Routing
CN
CN
Tunnel
Tunnel
Internet
Internet
MAP
HA
FA
HA
FA
Domain 1
Domain 2 Domain 3 Domain 4
Domain 1
Domain 2 Domain 3 Domain 4
MH
MH
(a) Tunnel convergence in between HA
(b) Lengthy tunnels in between HA
and MAP for HMIPv6 scheme
and MH for FMIPv6 scheme
Fig. 5. Tunnel-based problems for conventional Mobile IP-based schemes fitted into 802.16 network environment.
them. Another case for FMIPv6 scheme, as displayed in Fig. 5 (b),
Fig. 6(a), an efficient routing is presented as home agent (HA) lo-
whenever a high speed MH passes along the different access routers,
cated outside the 802.16 network. Corresponding node (CN) is
this technology would be failing. These repetitions for 802.16 net-
indicated as a source node. External traffic for data packet is sent
work resources would be wasting by applied these conventional Mo-
from CN to HA, the HA intercepts them and tunnels packet to FA
bile IP-based mobility management schemes. Therefore, we would
of mobile host (MH). Meanwhile, the BS en route intercepts the tun-
need to try designing more suitable mobility management technol-
nel packet on behalf of MH's FA since the BS acts as a Super Foreign
ogy for 802.16-based network environment. In the previous work
Agent (SFA) to perform MIP FA operations for managing MIP FA in
[29] for the middle-domain concept fitted in 802.16-based network
the middle-domain.
environment, it has already improved the 802.16 network perfor-
On the other hand, the middle-domain can not address the case
mance. But, some issues still remain in previous work. In this paper,
of HA located within the 802.16 access network since the BS was
we would complement these drawbacks and detail them in latter.
merely designed for managing a set of foreign agents but not home
agents, an inefficient routing emerges. For example in Fig. 6(b), the
3.1. Basic idea
Triangular Routing Problem [31,33] happens since the BS lacks the
ability of managing home agents. Therefore, our basic idea for
From the concept of the middle-domain as mentioned in related
the enhanced middle-domain mobility management in this paper
work, the BS can be regarded as a super node to be an agent or
is: besides the idea of SFA-applied, we think that the BS should
proxy of MIP FAs (Foreign Agents of Mobile IP). As illustrated in
be also equipped with MIP HA (Home Agent of Mobile IP) function-
Routing
HA
Tunnel

CN




CN


Internet
Internet
BS

SFA
BS

SFA


SS
R
SS
SS

R
R
SS R
GR
GR
GR
GR
GR HA



FA



FA



FA



FA



GR
FA
GR
FA
GR
FA
Domain 1 Domain 2 Domain 3 Domain 4
Domain 1 Domain 2 Domain 3 Domain 4
MH
MH
(a) An efficient routing as HA located
(b) Routing inefficiency with HA located
outside the 802.16 network
inside the 802.16 network
Fig. 6. Mobility management in middle-domain.

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C.-S. Tsai, C.-C. Yang / Computer Communications 33 (2010) 1030-1048
1035
Fig. 7. Location management for SHA/SFA.
ality to be an agent or proxy for managing HAs of mobile hosts. The
types of handoff an MH can make as follows: (a) Intra-BS handoff
newly defined term for the BS is called Super Home Agent (SHA) in
(b) Inter-BS handoff. For case (a), Mobile IP registration can be ad-
this paper.
dressed at a crossover node since en route the downlink cache can
In order to solve inefficient routing problem for the middle do-
be recorded at a shared node on the rooted path. It could reduce
main, it is not suitable for only applied either SFA or SHA. We rec-
the cost for the registration and handoff latency. As shown in
ommend it is better included with both idea of SFA and SHA.
Fig. 7(a), MH handoffs from GR1 to GR2 within home 802.16 net-
Therefore, an enhancement of the middle-domain mobility man-
work, the Mobile IP registration request is only arrived at crossover
agement associated with SFA and SHA is proposed in this paper.
nodes SS1. Through the operation of Mobile IP, en route the cross-
Moreover, we also propose a multicast extension based on SFA-
over SS1 updates downlink cache to GR2. Similarly, when the mo-
and SHA-applied concepts which will be mentioned in Section 4.
bile host continuously handoffs from GR2 to GR3, BS1 creates
Before the present of the multicast service, location management
downlink cache to SS2 and the SS2 creates its downlink cache to
and handoff scheme for mobile host needs to be addressed firstly
GR3 since the crossover node is at the BS1. Note that for an
in next subsection.
802.16 home network in middle-domain, data packets perform a
tree-based routing along recorded downlink cache to micro-do-
3.2. Location management
main gateway router GR. Once the GR received data packets, it
could adopt one of these existed micro-mobility protocols for data
For the enhanced middle-domain mobility management, SHA
delivery to mobile host and it is transparent to micro-domain for
manages multiple home agents in home 802.16 network and SFA
each mobile host. On the other hand, for case (b), if a mobile host
manages multiple foreign agents in foreign 802.16 network,
enters a foreign 802.16 network the first time as shown in Fig. 7(b),
respectively. As each mobile host stays at home 802.16 network,
the following actions are taken on the intercepted Mobile IP regis-
as illustrated in Fig. 7(a), the micro domain gateway router (i.e.
tration request:
GR1) equipped with home agent (i.e. HA1) functionality is required
to perform an local home 802.16 registration (new defined packet)
(1) Downlink cache creation: The mobile host issues a Mobile IP
with its super node BS (i.e. BS1). Meanwhile, SS and BS en route
registration request message to its home agent. The BS and
intercept this registration request in order to perform downlink ac-
SS en route create the downlink location cache for the
tions of middle-domain. The BS is regarded as super home agent on
mobile host.
behalf of the HA (i.e. HA1) to perform Mobile IP operation. Thus, all
(2) SFA actions: The BS in the foreign 802.16 network allocates a
data packets sent from CN are first intercepted by the super home
middle-domain CoA (denoted by M-CoA) for the mobile host.
agent and it has responsibility to forward these packets along with
The M-CoA is usually the address of the BS and is used in
the downlink cache of the middle domain to MH.
Mobile IP registration. When the BS received the Mobile IP
The handoff of an active mobile host results in the change of
registration request in the foreign 802.16 network, the BS
location for any possible data transmission. Therefore, in order
(with functionality of SFA) issues a Mobile IP registration
not to let obsolete cache data (i.e. wrong downlink) lead to wrong
request which including with the M-CoA to the home agent
redirection, the handoff scheme must be mentioned. There are two
of the mobile host on behalf of the micro-domain gateway

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C.-S. Tsai, C.-C. Yang / Computer Communications 33 (2010) 1030-1048
router GR (with functionality of FA). Meanwhile, the BS
latency can be further reduced. For example, as a source node CN
sends a Mobile IP reply message back to the GR on behalf
initially located at an MH's HA inside the home 802.16 network
of the home agent.
can act as a mobile host and both must have the local home
(3) SHA actions: The BS (with functionality of SHA) in home
802.16 registrations with a super node BS. Meanwhile, SS and BS
802.16 network en route intercepts Mobile IP registration
intercept the registration request issued from the both CN and
request issued from SFA, and updates location information
MH in order to cache the downlink information and perform the
of the mobile host into SHA-cache so that a redirection can
proper actions of the middle-domain. As the MH stay away from
be established on between SHA and SFA. The super home
its HA, Mobile IP registration procedure can be terminated at a
agent for SHA has responsibility to reply Mobile IP message
crossover node since previously intercepted downlink cache infor-
back to the SFA on behalf of home agent of the mobile host,
mation. Thus, the routing can be redirected at crossover node
and simultaneously it should also forward the Mobile IP reg-
either SS or BS. The handoff scheme for Intra-SS and Inter-SS as
istration request message with its home agent for complet-
CN located inside a home 802.16 network is illustrated in
ing a Mobile IP procedure.
Fig. 10(a) and (b), respectively.
Signaling flow for a mobile host entering a foreign 802.16 net-
3.4. Data delivery
work the first time for Inter-BS handoff is illustrated in Fig. 7(b).
Location cache and message sequence chart of Fig. 7 are displayed
Data delivery from the CN to an MH is explained as follows. As
in Figs. 8 and 9, respectively. Moreover, as a case for the CN located
illustrated in Fig. 11, data packets destined to an MH's home ad-
inside a home 802.16 network, the routing scheme requires to be
dress are first intercepted by the SHA. Since the care-of-address
mentioned in next subsection.
of middle domain registered for mobile host is the M-CoA, the
SHA tunnels packets to the SFA by using an allocated M-CoA ad-
dress. The SFA decapsulates the received packets and forwards
3.3. Dealing with CN inside the home 802.16 network
them to the correct GR according to the location cache maintained
by the BS and SS. Lastly, forwarding of the packets within a micro-
As CN is located inside the home 802.16 network, the routing
domain is based on one of these micro-mobility protocols, which
scheme requires all data packets to be routed to the BS first. Mean-
can be either tunneling-based (e.g. MIP-RR[37]) or routing-based
while, if downlink cache in crossover node provides with destina-
(e.g. CIP [15-18]).
tion information, the data packet will be intercepted and redirect
Similar to CIP, data packets transmitted by mobile host in
the route to the destination. Thus, all data packets should not go
802.16-middle domain are first forwarded toward the gateway
beyond the crossover node so that registration cost and handoff
BS. However, the handling of the internal data flow is more effi-
cient in the middle-domain as explained in the following. Since
BS and SS maintain the location cache for each mobile host and if
(*) presents a crossover node
the data packets are destined to the other mobile hosts in the same
802.16-middle domain, the crossover node between micro do-
micro-domain
MH's ID
Next Hop
M-CoA
mains will identify the corresponding location cache for the desti-
CoA
nation MH and relay data packets to correct downlink location.
BS1
MH
SS1
SHA
HA1
3.5. Simulation study
SS1
MH
GR1
HA1
One 802.16 network is created in the simulation as illustrated in
Fig. 12. One base station (BS) connects to Internet, four subscriber
(a) When MH staying in home network HA1
stations (SS) and four micro-domains (i.e HA or FA) are connected
to the BS and SS, respectively. There are mobile hosts from range 5
to 100 assigned in the network. In the beginning of the simulation,
BS1
MH
SS1
SHA
HA1
these initial mobile hosts are uniform distributed in the micro-do-
mains which include one HA and fifteen FAs. Time is slotted in the
*SS1
MH
GR2
FA2
simulation and each mobile host leaves its current micro-domain
and moves to one of the neighboring micro-domains with proba-
(b) When MH handoffs to micro-domain 2
bility 50% for every time slot. The total number of samples for
the simulation is about 50,000 simulated topologies, and each sam-
ple performs 100 time slots. The total run time is 5,000,000 time
*BS1
MH
SS2
SHA
FA3
slots. Details of the simulation parameters are displayed in Table 1.
Three performance criteria are defined for comparing our pro-
SS2
MH
GR3
FA3
posed scheme and the conventional MIP-applied contrasts: (1)
(c) When MH handoffs to micro-domain 3
the average binding cost, (2) the average handoff latency and (3)
the average routing cost. The average binding cost is total accumu-
lated registration cost for MHs' handoffs per time slot, and the
*BS1
MH
BS2
SHA
FA4
average handoff latency is defined as the total accumulated time
to complete binding update after handoffs for each time slot. The
BS2
MH
SS3
SFA
FA4
average routing cost indicates that the routing path is from the
source CN to delivery data to the MH.
Fig. 13 shows the average number of control packets for accu-
SS3
MH
GR4
FA4
mulated binding update of MHs per time slot in comparing with
enhanced middle-domain mobility management (i.e. SHA + SFA
(d) When MH handoffs to micro-domain 4
scheme) and conventional MIP-applied contrast schemes for IEEE
Fig. 8. Location Cache of Fig. 7.
802.16. Fig. 13 has demonstrated that the proposed enhancement

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C.-S. Tsai, C.-C. Yang / Computer Communications 33 (2010) 1030-1048
1037

GR1
GR2
GR3
GR4
GR5
GR6
BS2
BS1
SS1
SS2
SS3
SS4
(HA1) (FA2)
(FA3)
(FA4)
(FA5)
(FA6)
(SFA)
(SHA)
(1)
MH
(1-1) 802.16 registration request
(1-2) 802.16 registration request
(1-3) 802.16 registration reply
(1-4) 802.16 registration reply
(2)
handoff
MH
(2-1) MIP registration request
(2-2) MIP registration reply
(3)
handoff
MH
(3-1) MIP registration request
(3-2) MIP registration request
(3-3) MIP registration reply
e
m
(3-4) MIP registration reply
Ti
(4)
handoff
MH
(4-1) MIP registration request
(4-2) MIP registration request
(4-3) MIP registration request
(4-3) MIP registration reply
(4-5) MIP registration request forwarding
(4-4) MIP registration reply
GR1
(4-5) MIP registration reply
(HA1)
(4-6) MIP registration reply
Fig. 9. Message sequence chart for Fig. 7.
Routing
R: Regular Router
BS1 SHA
BS1 SHA
SS1 R
SS2 R
SS1 R
SS2 R
GR1 HA
GR2 FA
GR3 FA
GR1 HA
GR2 FA
GR3 FA
Domain1
Domain2
Domain3
Domain1
Domain2
Domain3
CN
MH
CN
MH
(a) Intra-SS handoff
(b) Inter-SS handoff
Fig. 10. Location management as CN located inside a home 802.16 network.
with idea of SHA and SFA-applied has significantly reduced binding
over actions so that handoff latency is very small, we merely
cost in comparing with the contrast schemes, because of localized
consider in three cases for SHA/SFA, HMIPv6 and Mobile IP in
registration. Performance of the average handoff latency is dis-
Fig. 14. The relation of Figs. 13 and 14 is presented in the following
played in Fig. 14. Because FMIPv6 scheme can perform pre-hand-
as they have the same trend in the results. For each MH's handoff

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1038
C.-S. Tsai, C.-C. Yang / Computer Communications 33 (2010) 1030-1048
Src
Dest
CN
MH
Payload
BS SHA
CN
Macro-domain
Encapsulated datagram
Src
Dest
Src
Dest
SHA M-CoA CN
MH
Payload
BS SFA
Src
Dest
SS
R Middle-domain
CN
MH
Payload
GR
Tunneling
Routing
Micro-
domain
Tunneling or Routing
AP
R: Regular Router
MH
Fig. 11. Data delivery by using the idea of SHA and SFA.
in MIP scheme, the signaling control packets including with home
home binding cost, the pre-handover cost for significant number
registration request and reply message need to be addressed in be-
of binding updates also needs to be mentioned. For HMIPv6
tween MH and HA. For FMIPv6 scheme, besides of the MIP-applied
scheme, the binding update messages are always delivered to
its highest MAP location (i.e. BS) per handoff for each MH, regard-
less of the neighboring location for MHs. However, with SHA and
SFA-applied idea, MIP registered procedure should not go beyond
CN
the crossover node. The registration cost and handoff latency are
Internet
1500
SHA/SFA
1200
ets)
HMIPv6
MobileIP
BS
900
FMIPv6
600
SS1
SS2
SS3
SS4
vg. Binding Cost
A
300
(signal control pack
0
5
10
20
40
60
80
100
HA
FA
FA FA
FA FA
FA FA
FA FA FA
FA
FA
FA
FA FA
MH#
MH
Fig. 13. Average binding cost for each time slot.
Fig. 12. Simulation environment.
1200
Table 1
SHA/SFA
Simulation parameters.
y
1000
HMIPv6
MH# = 5, 10, 20, 40, 60, 80, 100
MobileIP
Samples = 50,000
800
Per sample performs 100 time slots
f Latenc
Handoff probability = 0.5
600
Horizontal move
400
Signal cost unit
S
(time cost unit)
MH-FA, SMH-HA, SFA-SS,
vg. Handof
SHA-SS, SSS-BS(1 cost unit each)
A
Delay time
L
200
MH-FA = 1 Time Unit
LMH-HA = 1 Time Unit
L
0
FA-SS = 2 Time Unit
5
10
20
40
60
80
100
LHA-SS = 2 Time Unit
L
MH#
SS-BS = 3 Time Unit
Routing path
PCN-BS = 100 hops
Fig. 14. Average handoff latency for each time slot.

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C.-S. Tsai, C.-C. Yang / Computer Communications 33 (2010) 1030-1048
1039
12000
passed twice for data delivery. Thus, the transmission time is
SHA/SFA
delayed.
10000
HMIPv6
(2) Duplicate tunnels: As an HA tunnels the multicast packets to
MobileIP
a group of FAs, the number of tunnels is related to the num-
8000
FMIPv6
ber of FAs in which MH's current point of attachment. For
6000
example in Fig. 16(b), there are two duplicate packets sent
separately from HA to two FAs by tunneling. This wastes
4000
the network bandwidth.
vg. Routing Cost (hops)
A
2000
(3) Tunnel convergence problem: The multiple tunnels result
from different HAs to go through a common BS, and termi-
0
5
10
20
40
60
80
100
nate at MHs' FAs. In Fig. 16(c), it shows a tunnel convergence
MH#
problem for 802.16-based network environment as the BS
has not the ability to appoint a DMSP from one of multiple
Fig. 15. Average routing cost for each time slot.
HAs. The BS is passed three times and it results in higher
traffic load in the BS.
(4) Frequent DMSP handoff: For MoM, if there are multiple visi-
only terminated at a crossover to show the same trend in less
tors from their different HAs to arrive at the common foreign
cost evaluation.
network, any mobile host handoff may make DMSP handoff
The average routing cost in different number of MHs for com-
occurs. For example in Fig. 16(d), the mobile hosts M1 and
paring with our scheme and conventional MIP-applied schemes
M2 are far from their home agents HA1 and HA2, respec-
is displayed in Fig. 15. Fig. 15 shows that the proposed SHA/SFA
tively, and the tunnels are quite long. Assume that the com-
mobility management scheme outperforms conventional MIP-ap-
mon foreign agent FA designates HA1 to be a DMSP (not
plied mobility management schemes (without idea SHA/SFA) in
HA2) for serving the mobile hosts M1 and M2. Once the
terms of average transmission cost. In order to achieve seamless
DMSP member M1 handoff, the DMSP handoff should also
handoff, FMIPv6 uses pre-handover technology to build a forward-
occur. Moreover, as a mobile host handoff occurs, its home
ing tunnel path so that the routing cost becomes increasing. If a
agent can learn the mobile host's new FA immediately by
high-speed MH moves along different wireless areas, the routing
using Mobile IP registration procedure. But the previous FA
make the 802.16 network performance degenerate. To avoid the
can not know the handoff until timeout. Thus, before the
routing cost increases too fast so that the simulation graph can
new DMSP is selected, none will serve the mobile hosts
be well displayed, we limit the lengthy routing from FMIPv6 in
within the previous network. Multicast packets for mobile
the simulation. That is whenever an MH passes twice in between
hosts will be lost during this period.
wireless areas, the binding update should be addressed by its HA
to shorten the routing path. The routing cost is thus reduced, but
In summary, once one of these problems happen as mentioned
it still keeps a worst case in comparing with the other schemes.
above, we call the multicast meeting a Hierarchical-based Tunnel
Please note that this simulation for mobility management is
Convergence Problem (H-TCP) in this paper. If the BS could also
mainly focused within a home 802.16 network, but not in case
act as Mobile IP HA or FA to manage multicast, the H-TCP problem
for HA outside of the 802.16 network. Moreover, for the simplicity,
can be solved well. Therefore, we consider adopting the idea of SFA
in case of route optimization (RO) for the simulation would be ig-
and SHA of middle-domain mobility management to enhance the
nored since the proposed SHA/SFA mobility management scheme
802.16-based multicast service. This is also the basic idea of
can also apply the RO easily. The considering is simple, fair and
designing the HMP scheme. Moreover, in order to simplify the de-
acceptable.
sign of the HMP scheme, the multicast solution can be researched
in two parts: (1) multicast within the middle-domain and, (2) multi-
4. Hierarchical multicast protocol (HMP)
cast outside the middle-domain. Two cases are detailed in Subsec-
tions 4.2 and 4.3, respectively.
4.1. Inefficient routing problems
4.2. Multicast within the middle-domain
As mentioned in the related work, HA-based multicast exten-
sion, i.e. MoM over BT2, has enhanced the performance of BT. The
In HMP, the BS is responsible for group membership manage-
MoM scheme maintains scalability through the use of a designated
ment. As illustrated in Fig. 17, data traffic is first intercepted by
multicast service provider (DMSP) optimization per multicast group
the BS and multicasting among group members requires related
for each foreign network, and the use of dynamic multicast tunnels
nodes in the multicast tree to maintain proper membership infor-
to foreign networks for solving inefficient tunnel of BT scheme. How-
mation for the group. Therefore, we design a simple cache struc-
ever, for MoM applied in 802.16 network environment, if the BS is
ture for the middle-domain to achieve this goal. Group downlink
merely regarded as a regular router without adopting the idea of
cache records members' ID of a group that a downlink can lead
SHA and SFA, some inefficient multicast routing problems emerge
to and helps in transmitting multicast packets to proper down-
as explained in the following:
links. The group downlink includes the following fields: (1) Group
ID, (2) Downlink ID, (3) ID of the group members this downlink can
(1) Triangular routing: As illustrated in Fig. 16(a), two-fold rout-
lead to. Manipulation of the group downlink is presented in the
ing happens within the 802.16 network. Multicast data-
following.
grams destinated to MH are firstly intercepted by HA, and
When a mobile host wants to join a group, it sends out an IGMP-
HA tunnels the data to FA in which MH's current point of
Join (Internet Group Management Protocol) message to its micro do-
attachment. Meanwhile, the path between HA and BS is
main gateway router GR. The IGMP-Join message is then forwarded
along the uplink path to the BS. Each en route node that relays the
2 In BT (Bi-directional Tunneling) technology, an inefficient multiple unicast is
IGMP-Join message establishes group downlink cache for the new-
adopted for data delivery. The new term ``MoM over BT" presents a multicast
ly member. For example, in Fig. 18(a), mobile host M1 is the first
extension of BT, which means that the design of the MoM scheme is also based upon
the BT technology or environment.
member to join/create group G1. When the BS has received the

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Document Outline

• Design of the multicast service for mobile users in the 802.16 network environment
  • Introduction
  • Related work
    • Conventional mobility management: MIP, FMIPv6, HMIPv6
    • Middle-domain mobility management: SFA
    • Multicast extension for Mobile IP: RS, BT, MoM
    • Hierarchical mobile multicast: HMoM
  • Enhanced middle-domain mobility management
    • Basic idea
    • Location management
    • Dealing with CN inside the home 802.16 network
    • Data delivery
    • Simulation study
  • Hierarchical multicast protocol (HMP)
    • Inefficient routing problems
    • Multicast within the middle-domain
    • Multicast outside the middle-domain
    • Designated multicast service provider (DMSP)
    • Simulation study
      • Simulation environment and performance criteria
      • Simulation results
  • Theoretical analysis
    • Theoretical environment and parameters setup
    • Calculation of the multicast cost
    • Numerical results
    • Characteristic in middle-domain
  • Conclusion
  • References

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