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Mobile IPv6 Extensions to support Nested Mobile Networks
ZhiJun Gu
LGE
[email protected]
Dongmin Yang
POSTECH
[email protected]
Abstract
Unlike host mobility support, network mobility is
concerned with situations where an entire network
changes its point of attachment to the Internet.
Furthermore, we should consider the situation of
several mobile networks recursively attached together.
The goal of network mobility support is to provide
continuous and optimal Internet access to all nodes
located in the mobile network.
In this paper we present a solution to support
nested network mobility by extending MIPv6. Note that
the IETF MIPv6[2] protocol is for mobile nodes and
not for mobile networks. The main idea is to register a
prefix binding in HA and CN with a chain of
intermediate mobile router’s (MR’s) care-of-addresses
(CoAs). To the main idea, we introduce new option;
The Nested Care-of-Address Option (NCO) is used to
carry a sequence of MR’s CoAs in the header. The
Router Alert Option (RAO) is used to indicate that
NCO is set. When RAO is set, it is not necessary to
encapsulate an outgoing packet. The HA and CN can
use the addresses in its binding cache to construct a
Type 2 Routing Header to send packets into the mobile
network. This extension allows our scheme to give an
optimal routing path, avoid the tunnel-in-tunnel
problem, save the bandwidth resource and reduce the
computation overhead in the home network.
1. Introduction
In the last ten years, the computer industry has
faced a huge evolution. The geographical mobility of
people is increasing, which in turn, generates a need
for more mobility. However, the Internet can hardly
support perfectly this mobility request, because
protocols used in the Internet are not conceived for
devices that frequently change their point of
attachment to the Internet. The aim of mobility support
is to make mobile nodes keep connectivity without
Cheeha Kim
POSTECH
[email protected]
modification when roaming. The most important
improvement in Mobile IPv6 (MIPv6) [2] is to provide
a powerful and flexible optimization mechanism
between a mobile node and a correspondent node by
establishing a binding between a mobile node’s home
address and its current CoA, which allows the
correspondent node directly to send a packet to the
new location of the mobile node.
But MIPv6 cannot scale to handle the mobility of a
network. Indeed, mobility support should be concerned
with mobile hosts as well as the mobile networks.
There are situations where an entire network moves
and attaches to different places in the Internet. An
airline or a train company may want to provide
permanent on-board Internet access. In this case,
airplane or train may be an example of mobile network.
Some solutions were proposed in [3,4,5,6,7] to
support network mobility. In the case of Nested
Mobile Network (Mobile Network), these solutions
suffer from the tunnel-in-tunnel and non-optimal
routing problem. This can decrease the performance of
the router and, consume more bandwidth and generate
more traffic overhead.
The IETF Network Mobility Work Group (NEMO)
briefly proposes two approaches for supporting
network mobility: Prefix Scope Binding Update
(PSBU) [6], and Reverse Routing Header approach
(RRH) [7]. The PSBU only can support single mobile
network. In the Nested Mobile Network, this scheme
cannot work well because the communication between
CN and Nested MoNET will suffer from the tunnel in
tunnel problem. On the other hand, RRH is dedicated
to supporting Nested Mobile Network. The RRH is
specified to reduce the encapsulation overhead which
can be generated in the Nested MoNET. This scheme
is based on the bi-direction tunnel between HA and
MR. RRH can support Nested MoNET without
suffering from the tunnel in tunnel problem. However,
since every packet goes through the bi-direction tunnel
between MR and HA, an optimal routing path does not
exist, and the traffic congestion will be increased in the
home link.
Proceedings of the 18th International Conference on Advanced Information Networking and Application (AINA’04)
0-7695-2051-0/04 $ 20.00 © 2004 IEEE
In this paper we present a solution to support
nested network mobility by extending MIPv6. Note
that the IETF MIPv6[2] protocol is for mobile nodes
and not for mobile networks. The main idea is to
register a prefix binding in HA and CN with a chain of
intermediate mobile router’s (MR’s) care-of-addresses
(CoAs). To the main idea, we introduce new option;
The Nested Care-of-Address Option (NCO) is used to
carry a sequence of MR’s CoAs in the header. The
Router Alert Option (RAO), is used to indicate that
NCO is set. When RAO is set, it is not necessary to
encapsulate an outgoing packet. The HA and CN can
use the addresses in its binding cache to construct a
Type 2 Routing Header to send packets into the mobile
network.
The remainder is structured as follows. We present
the proposed idea in section 2 to support Nested
MoNET. In section 3, we evaluate the proposed
protocol. Section 4 concludes the paper.
When HA and CN send packets to MoNET, using a
binding cache, those packets are routed through an
optimal routing path. Also, when packets are sent out
of the Nested MoNET, using a RAO, we obtain an
optimal routing.
2.1. Extensions
Router Advertisement: We define a new bit “N” in
the router advertisement to indicate that it can support
Network Mobility. When a MR attaches to a new link
and finds that its upper router supports network
mobility, it should solicit its upper mobile router for a
sequence of upper mobile router’s CoAs. Also if a MR
receives this kind of solicitation, it should send back a
chain of CoAs.
Nested Care-of-Address Option (NCO): This is a
Mobility Sub-Option added to the PSBU message in
order to carry mobile router’s CoAs.
2. Proposed Protocol
As mentioned in the previous section, PSBU and
RRH protocols have some problems in supporting
Nested MoNET. The first approach will suffer from
the tunnel-in-tunnel problem and the second protocol
has a non-optimal routing path. Before going any
further, we should specify some constraints. First, the
routing path between CN and MNN (nodes located in
mobile network) should be optimal with a minimal
signaling overhead. Second, the movement of mobile
network should be transparent to MNN. Finally, the
scheme should be scalable to the number of mobile
networks.
This proposed protocol is designed to solve
problems with the previous two approaches. We want
to find a solution to support Nested MoNET during the
BU registration process. We propose to extend the
PSBU message to carry sufficient topology
information about the Nested MoNET to HA. The
binding associates the Network Prefix with the mobile
router’s CoA and a sequence of intermediated mobile
router’s CoAs. The MoNET prefix identifies the home
link within the Internet topology. All MNNs share the
same IP prefix. All the mobile router’s CoAs are the
intermediated hops when a packet routing into the
MoNET. MR will send a PSBU message with a chain
of CoAs when registering with HA and CN. After HA
and CN receive this BU message, they can build a
binding entry like this in their binding cache: MoNET
prefix Æ a chain of intermediated MR’s CoA, MR’s
CoA.
Router Alert Option (RAO): This option is used
when MR encapsulates data out of the MoNET. It
indicates that the mobile router need not to encapsulate
it again and merely needs to replace the source address
with its CoA. If there is no RAO in the IPv6 header, an
MR must encapsulate the packet to avoid ingress
filtering. Since the RAO has been defined already in
[8], we can apply new values used in our scheme.
Type 2 Routing Header (RH2): We extend this
routing header in MIPv6 to carry multiple hops. HA
and CN should use a binding cache to construct it, to
route packets into the Nested MoNET.
Mobile IPv6 Extension: The MIPv6 protocol has to
be extended to operate those two new options specified
previously. We also need to extend CN’s capability of
de-capsulation.
2.2. Protocol Operation
A. Initialization. When a MR moves into a new link,
it constructs a new CoA and, it solicits its upper mobile
router for the upper mobile router’s CoAs (a chain of
CoAs).
When the MR sends a PSBU datagram to its HA, the
datagram contains an option with MoNET’s prefix, an
NCO including CoAs, a RAO, and a Home Address
Option with MR’s home address (Figure 1). MR2
replaces the source address with MR2.CoA and
forwards to MR1.HA instead of encapsulation because
of RAO in the header. Then, HA replaces the source
Proceedings of the 18th International Conference on Advanced Information Networking and Application (AINA’04)
0-7695-2051-0/04 $ 20.00 © 2004 IEEE
address using the address in HAO and checks a
security. If success, HA builds a PSBU with two
addresses: MR1’s Prefix -> MR2.CoA, MR1.CoA.
HA2
CN
HA1
Internet
IPv6 Hdr (src=MR1.CoA, dst=MR1.HA)
Hop-by-Hop Opt:
Router Alert Option
Dst Opt:
HAO(MR1.HoA)
AH/ESP
Mobility Hdr:
BU option(MR1’s Network prefix)
Nested CoA option(MR2.CoA, MR1.CoA)
Prefix1 -> MR2 coa
MR1.coa
MR2 coa
AP
MoNET2
MR1 coa
MoNET1
LFN
Figure 1. BU from MR1 to HA1
B. MR Operation. Receiving an incoming packet
with a type 2 routing header, MR operates like a
normal router, and switches the destination to next hop.
If the packet is tunneled from its HA, MR should send
a PSBU to the original source node, including the
NCO.
Receiving an outgoing packet with RAO in the
header, MR merely overwrites the source address with
its CoA and forwards it to the next router. If the packet
has no RAO, MR must encapsulate it, set the source
address to its CoA and, insert a RAO into the outer
header. After this process, MR continues to forward
this packet to the next router (Figure 2). Since the data
from LFN must be encapsulated to avoid the ingress
filtering, CN must have the capability to decapsulate.
Figure 3. First Datagram transits via HA into
MoNET1.
C. CN Operation. If CN wants to communication
with LFN, the first datagram will be intercepted by
HA1 and tunneled to MR1 using RH2. MR1
decapsulates it and forwards the inner data to LFN
(Figure 3). Since this packet is tunneled from HA1,
MR1 should register its prefix to CN, the same as with
HA1. Sending other packets to LFN, CN checks its
binding cache and understands that this address
belongs to MoNET’s prefix. Those packets should be
routed via several CoAs. So, those subsequent packets
are sent to LFN via MR2.coa, MR1.coa using RH2
(Figure 4).
HA2
CN
HA2
CN
HA1
Internet
MR2
HA1
Internet
Prefix1 -> MR2 coa
MR1.coa
MR2 coa
Prefix1 -> MR2 coa
MR1.coa
MR2 coa
AP
MoNET2
MR1 coa
AP
MoNET2
MoNET1
LFN
MR1 coa
MoNET1
LFN
Figure 2. MR1 encapsulates outgoing Data, and
inserts RAO in the header. MR2 replaces the source
address with its own CoA.
Figure 4. Optimal Routing Between CN and LFN
3. Evaluation
According to those operations, we believe that our
solution is well adapted in supporting Nested MoNET.
Proceedings of the 18th International Conference on Advanced Information Networking and Application (AINA’04)
0-7695-2051-0/04 $ 20.00 © 2004 IEEE
The sequence of mobile router’s CoAs ensures an
optimal routing between CN and MoNET.
So we can say our solution can support Nested
MoNET well if the mobility frequency of a mobile
network is low.
3.1. Advantages
First, we allow an MR to register a chain of CoAs
with its HA and CN in the registration process. This
can save on registration time compared with RRH,
since it needs another scheme to finish registration
process first.
Second, we can obtain the optimal routing in the
outgoing direction through the RAO, obtain optimal
routing in the incoming direction through RH2. In our
protocol, there is no tunnel in tunnel problem.
Third, communication between CN and MoNET can
have an optimal routing without passing through home
link. This can alleviate the failure affection of home
link to MoNET, reduce the computation overhead in
HA side.
3.2. Drawbacks
Our solution requires extensions at CN. CN must
have the capability of de-capsulation. Also, we add
two new options, Nested Care-of-Address Option and
Router Alert Option, for our scheme. These options
will add some signaling overhead to the registration
process. Sine the MIPv6 protocol is still under
researched, these drawbacks should be limited.
A most important drawback is if the number of CN
is great the signaling overhead will be too large for a
rapid moving network. Our scheme only can be used in
a slow mobility situation.
4. Conclusions
References
[1] Cizault, “IPv6”, Editions O’Reilly, 2nd edition, 1999.
[2] David B.Johnson, Charles E.Perkins, Jari Arkko,
“Mobility Support in IPv6”, IETF Internet Draft, draft-ietfmobileip-ipv6-19.txt, 29 Oct 2002, Work in progress.
[3] Thierry ERNST, “Network Mobility Support in IPv6”,
Doctor Thesis, University Joseph Fourier, Department of
Mathematics and Computer Science, France, 29th,
October,2001.
[4] Raihan Al-Ekram, “A Mobile IPv6 Extension to Suport
Total Mobility in the Internet”, 5th, December, 2001.
[5] Thierry Ernst, “Extending Mobile IPv6 with Multicast to
support Mobile Networks in IPv6”, In IP based Celluar
Network conference (IPCN), Paris La Defense, France, May
2000.
[6] Thierry Ernst, Ludovic Bellier, Alexis Olivereau,
Claude Castelluccia and Hong-Yon Lach, “Mobile Networks
Support in Mobile IPv6 (Prefix Scope Binding Updates)”,
IETF Internet Draft, draft-ernst-mobileip-v6-network-03.txt,
March 2002, Work in progress.
[7] P.Thubert, M.Molteni, “IPv6 Reverse Routing Header
and its application to Mobile Networks”, IETF Draft, draftthubert-nemo-reverse-routing-header-01.txt, October, 2002.
[8] Hidetoshi Yokota, Akira Idoue, Toru Hasegawa,
Toshihiko Kato, “Link Layer Assisted Mobile IP Fast
Handoff Method over Wireless LAN Networks”,
MOBICOM’02, September, 2002.
In this paper, we have discussed the MIPv6 ability
in supporting mobile networks. We describe PSBU
and RRH two approaches. PSBU can support a single
mobile network well but, in the Nested MoNET case,
there is a tunnel in tunnel problem. In RRH, there is a
non-optimal routing problem. RRH only can be used
after MR finishing the registration process.
Finally, we propose our solution in supporting
Nested MoNET. The key idea is to register a chain of
intermediated mobile router’s CoA with HA and CN
when sending a PSBU message. HA and CN can
obtain a map of the topology in the Nested MoNET.
So they can construct a routing header to route packet
into Nested MoNET in an optimal way. The second
idea is to use a Router Alert Option. With this option,
we can obtain an optimal routing in the outgoing
direction. MR will not encapsulate the outgoing packet
if a RAO existed in the IPv6 header.
Proceedings of the 18th International Conference on Advanced Information Networking and Application (AINA’04)
0-7695-2051-0/04 $ 20.00 © 2004 IEEE