Conflict Free Address Allocation Mechanism for Mobile
Ad Hoc Networks
Sudath Indrasinghe, Rubem Pereira, John Haggerty
School of Computing and Mathematical Sciences
Liverpool John Moores University
M.P.Indrasinghe@2004.ljmu.ac.uk, {R.Pereira, J.Haggerty} @ljmu.ac.uk
Abstract
A Mobile Ad-hoc Network (MANET) can be
implemented anywhere where there is little or no
communication infrastructure, or the existing infrastructure
is inconvenient to use. A number of people with mobile
devices may connect together to form one large group.
Later on, they may split into smaller separate groups and
partitions may merge if necessary. Network partitions and
merges are potentially frequent occurrences in MANETs,
hence address auto-configuration is an important
requirement. In this paper we present a mechanism for
address auto-configuration in MANETs, which is capable
of assigning conflict-free addresses in a dynamic and
distributed manner. Also we propose novel mechanisms to
address MANET partition and merging.
1. Introduction
A Mobile Ad-hoc Network (MANET) consists of a set
of mobile hosts communicating with each other via wireless
links. Such a network may operate in a stand-alone fashion.
Dynamic address assignment is a desirable feature for
deploying MANETs due to host mobility, with hosts
joining and departing the network at will. This ad-hoc
nature is used to address important typical scenarios and
some MANETs applications are listed below:
Military Field Activities: Originally these ad-hoc
techniques came from battlefield-related scenarios. Much
military equipment nowadays relies on communications
and MANETs are vital where there is no networking
infrastructure, thus facilitating military communication, for
instance to maintain information between field personnel,
field vehicles, aircraft and transferring and sharing
information with different locations, for example,
headquarters to forward troops [13] [9].
Crisis Service Management: MANET can be used in
non-existing or damaged communications infrastructure
situations or humanitarian crises such as fire, flood, and
earthquakes, to name a few. This technology could be used
to exchange information from one rescue team member to
another over small handheld devices [13].
Local and Educational Requirements: MANET can
provide a temporary multimedia network. Local level
applications include taxicabs, sports stadium environment,
etc. Educational-level applications could utilise notebook or
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palmtop computers to share information among participants
at a conference or classroom [9].
Mobile Wireless Sensor Network: Sensor networks are a
form of wireless networks with mobile, possibly multifunctional hosts. This can be used in many application
environments such as scientific studies, domestic purposes,
environmental observations etc. These hosts could be
placed anywhere as required. For example, sensor hosts can
even be placed inside the body of a patient for monitoring
purposes.
Address Auto-configuration Approaches - The
approach we consider for address configuration is autoconfiguration, which automatically assigns IP addresses. IP
address auto-configuration can broadly be classified into
stateless and stateful approaches. In the stateless approach,
an unconfigured host must obtain its own IP address by
self-assignment. This stateless approach adapts random
address assignment and is followed by duplicate address
detection mechanism to achieve address uniqueness.
Stateless approaches do not keep any allocation table. C
Perkins et al [15] protocol is based on the newly-joining
host selecting an address from the address space and
informing all configured hosts of this new address. If an
existing host already has the same address, then a new one
is tried, and so on, until a conflict-free address is selected.
In the stateful approach, an unconfigured host asks its
neighbouring MANET hosts to work as proxies to obtain an
IP address. Assignments of addresses to new hosts are
based on a proxy’s knowledge. Stateful approaches can be
classified as follows:
Centralized maintenance of the allocation table [6] only one host in the MANET is permitted to select
addresses for unconfigured hosts. Every host in the
MANET must have the possibility to reach it all the time.
This centrally-operated host is also a member of the
MANET, causing the following drawbacks: unnecessary
address changes and a high-level overhead when the central
host departs the MANET.
Distributed maintenance of a common allocation table
[4][7] - every host in the MANET can allocate addresses
for unconfigured hosts as they request them. Many address
auto-configuration protocols use this mechanism in
conjunction with Duplicate Address Detection (DAD),
which is necessary to resolve any address conflicts.
Distributed
maintenance
of
multiple
disjointed
http://folk.uio.no/paalee
allocation tables [10] – This is really a hybrid approach.
The new host does not need to ask permission from other
hosts to assign a specific address as it can select one
randomly from an assigned address space. This mechanism
is efficient and reliable. Synchronization is required to
detect the address conflicts. High bandwidth usage and the
requirement for frequent flooding are the main drawbacks
of this mechanism.
The mechanism we propose is based on allocating a
conflict free address to all newly arrived nodes, by using
multiple disjointed address spaces, whereby each host in the
MANET is responsible for allocating a range of addresses,
disjoint from the ranges of all other hosts.
This paper is organized as follows. Section 2 discusses
related work and previous attempts to solve the automatic
address configuration problems. The conflict-free address
auto-configuration mechanism is provided in Section 3. In
Section 4 we discuss details of MANET partitioning
including the proposed address re-use mechanisms and in
Section 5 we discuss novel mechanisms to address
MANETs merging with same MANET ID. Finally
conclusions and future works are in section 6.
2. Related Issues
Previous research in the area of MANET address autoconfiguration primarily focuses on three problems: address
generation, network merges and partitions, and duplicate
address detection. Current research is summarized below.
Problematic Issues in Address Auto-Configuration:
Significant research on MANETs has been focused on the
design of efficient routing protocols to meet the
requirements of mobile ad-hoc networks. This includes
limited power, mobility and limited transmission range. The
majority of routing protocols assume that mobile hosts in
ad-hoc networks are configured a priori with IP addresses
before they begin communications in the network [14].
However, not all hosts have pre-assigned static or dynamic
IP addresses, especially if they usually obtain their address
through a dynamic mechanism on the wired network.
Unavailability of a central server and hosts’ mobility in
a MANET requires a reliable host identifier for
communication. Frequent topology changes occurring in
MANET due to hosts’ mobility make it difficult to allocate
unique identifiers manually. Also hardware-based MAC
addresses are neither reliable nor suitable for MANET
communications due to the following:
1. These addresses can be duplicated.
2. Some network adapters do not have an IEEE MAC
address at all.
3. MANET hosts are not restricted by IEEE MAC
addresses.
4. In some instances, multiple Network Interface Cards
maintaining the same MAC address.
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5. Hardware-based addressing exploits the identity and
privacy of the host [4][8].
However, IP addresses provide the uniqueness to form
the basis of an addressing scheme. Some protocols require
higher-level control packets, which are power consuming
for hosts joining the network, detecting partitioning and
merging, resolving address conflict as well as leading to
complicated computations. This is at the cost of reliable and
efficient MANET communications. These issues form the
basis for the rest of the section.
Address Allocation for New Hosts: When a new host
comes to join the network, it is necessary for the host to
acquire an address from the MANET. According to some
protocols, new the host broadcasts an address request
message and receives a reply from its neighbours. After
selecting one neighbour as an initiator (or address allocator,
attachment agent, buddy [4][7][12], etc.), it performs a
defined procedure with that host based on duplicate address
detection, using allocation tables or pending allocation
table. If the initiator receives a negative reply from the
network hosts, a conflict has been detected and the initiator
has to allocate another address and repeat the procedure
until it receives positive reply from all hosts.
The Prophet Address Allocation protocol [7] uses a
mathematical function and state values to generate a
sequence of addresses resulting in fairly complex
computations. However, this mechanism also generates
some duplicate addresses and requires performing DAD to
resolve these address conflicts. In the Efficient Network
Layer Addressing (ENLA) protocol [12], when a new host
joins the MANET, the initiator floods address requests.
However, the initiator cannot find out if all hosts have
responded to its request.
MANET Partitioning and Merging: The MANETConf
protocol [4] creates a partition identity (ID) for the MANET
and it periodically floods the entire network. If a host does
not receive the partition ID control packets within a certain
time (periodical flooding), it assumes that this network is
partitioned. In addition, such a periodical flooding increases
network disruption. Higher overhead and network resource
consumption are present with the above mentioned
mechanisms. Also, the ENLA protocol adds parameters
such as the highest address in use and address length to the
header of every transmitted packet. Comparing the
parameters, significant differences in received packets aid
detection of network merges. The use of very large
addresses, such as IPv6 128-bit addresses with only a few
hundred participants will consume network resources
unnecessarily. Also, this kind of address scheme creates
unnecessary overheads, and increased workload by using
limited resources.
3. Conflict Free Address Allocation
Here we consider stand-alone Mobile Ad Hoc
Networks. We assume that a block of IPv4 private
addresses is used for addressing the hosts within a
MANET. The blocks provided for private addressing are:
0
1
10.0.0.0 - 10.255.255.255 (10/8 prefix)
172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
2
We consider, for the sake of illustration, the first block,
which provides 24 bits for addressing. We considered the
following issues: generation of conflict free addresses for
each MANET, but also we need to bear in mind that as
hosts from different MANETs may come into contact with
each other, they should be able to identify, by the address
used, that they are from different MANETs. However, as
will be discussed below, it is possible for 2 distinct
MANETs to have the same MANET ID, and if two such
MANETs come into contact with each other, we need a
separate mechanism to distinguish between them. For this
purpose, MANETs should also have a name, distinct from
their IP addresses (MANET naming is discussed in section
5). By structuring the address space into MANET ID and
Host ID, both objectives can be achieved, at least
statistically.
If 8 bits of the 24 bits available are used for the
MANET ID, then clearly the probability of 2 MANETs
with same ID is 1/256. This leaves 16 bit for host ID,
allowing up to 64K hosts in the MANET. The mechanism
presented here provides a distributed algorithm for
allocating the remaining address space (in this example 16
bit address space) to the hosts.
Our mechanism [2] posits that every mobile host in the
network is capable of generating a range of addresses, and
the ranges of addresses of any two hosts in the MANET are
disjointed. In other words, each host generates numbers that
are unique for that host, and the number of unique
addresses generated by each hosts depends on a selected
Base Value. Each host is numbered according to the order
of arrival on the MANET. When a host departs from the
MANET the number is reused, in which case it will not
represent the order of arrival of the new host. Any given
host, whose number is n, can generate the following
numbers:
Base Value – 1
∑
n x Base Value + i
(1)
i=0
Where
Base Value
= 2, 3, 4, ..…..
Host Number n = 0, 1, 2, 3, ……
i
= 0, 1, 2, 3,………(Base Value – 1)
The values obtained in Eq. (1) are then added to the
first address in the host range to generate a new address.
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3
4
8
5
9
6
10
11
12
7
13
14
15
Figure 1. Addresses allocation tree with base value of 2.
Table 1. Number generation for base value 2
Host
Number
0
1
2
3
4
5
6
7
i
value
Generated
value
0
0
1
1
0
2
1
3
0
4
1
5
0
6
1
7
0
8
1
9
0
10
1
11
0
12
1
13
0
14
1
15
This algorithm leads to a tree structure in the way the
addresses are generated, as illustrated in Figure 1 for the
base value of 2. The higher the base value, the wider the
tree and the higher the number of leaves with free addresses
to allocate. However, situations like address reuse in a host
departing a network abruptly or network partitioning, will
create busy network environments. In other words, one
parent host has to deal with many address re-allocations.
The sequence of addresses generation with the base value
and the host number are depicted in table 1 and figure. 1.
4. MANET Partitioning
MANET partitioning is a more general case of hosts
departing the network and it could frequently occur as
shown in Figure 2. A single MANET will split into two or
more MANET partitions in either a graceful or abrupt
manner. A group of hosts abruptly departing network can
have a severe effect to MANET communication and it is
necessary to resolve it efficiently.
First, we considered the graceful partitioning in
MANET. For example, one or a few groups of hosts can
depart the MANET to participate in some other session
separately. This means that a network may split into
multiple partitions gracefully. Partitioned networks know
their partition and need to update reachable host tables in
the new network. For this purpose, new network hosts are
required to perform addresses clean up through entire
parent network according to the new topology changes for
correct and efficient network communication. When a
MANET splits into a few partitions, the MANET ID of
these partitions will initially be the same. These partitions
may merge if they wish to participate for a different
session. Therefore, partitions need to act as an independent
network. To achieve this requirement each partitioned
network has to change their MANET ID. In our proposed
address scheme 8 bits are allocated for MANET ID and
there are 256 possibilities to have a unique MANET ID.
The host holding the lowest address in each partition
randomly selects a new MANET ID within the available
range.
Partition B
Parent
Network
Group B
Group A
Partition A
Figure 2. MANET Partitioning.
More challenging is abrupt network partitioning. When
a network is partitioned abruptly, hosts in partitions initially
are not aware of the partition. Before initiating
communication among existing hosts, partitioned networks
have to clarify about reachable hosts in the new network
environment. To approach this task, they need to clean up
unreachable host addresses belonging to other networks.
This address clean up would normally happen only when a
new host joins the network. Upon arriving, a new host is
configured with a new address as explained in section 3.
The newly configured host broadcasts its new address to the
network. The new host, upon receiving the
acknowledgement of each existing host, will detect a
missing host address in the tree structure and inform the
missing host’s parent, in case the missing host may have
departed abruptly. Address cleanup, therefore is not
performed until a new host joins the network. With a
partition, when many nodes leave the parent network
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simultaneously, one alternative is for hosts to use the
routing table information in order to detect missing hosts.
Proactive Routing Protocols: Hosts maintain routing
information to every other host in the network in tables
(The Global State Routing Protocol [3] maintains 3 tables
and a list of all available neighbours). When these protocols
initiate a periodical query flood through partitioned child
networks, the routing table information is updated with
each existing host according to network topology changes.
With regard to this propagating update information, hosts in
partitioned networks can realize hosts in the parent network
that are no longer reachable. Then a clean up for the
addresses of all unreachable hosts could be initiated with
periodical query flooding. This results in hosts in the child
partition acquiring new MANET ID randomly. This can be
achieved by detecting the node with the lowest IP address
of the child partition, which generates the new MANET ID
and communicates it to all hosts in the new network.
Reactive Routing Protocols: In this type of routing
protocol, routes are determined and maintained for hosts
only when they need to send data to a particular destination.
Just after the network is partitioned, hosts in each partition
do not know exactly which hosts are in the MANET. When
a source wishing to transmit to a destination does not have
the route to the destination in its current routing table (due
to topology changes), it broadcasts a route discovery packet
throughout the MANET to find the route between itself and
destination. With this route discovery, existing hosts in the
child partition realize that it may not be possible to reach
some hosts who used to be in the MANET prior to the
partition. As mentioned above, the host with the lowest IP
address in the partition can allocate a new network identity
to form new network.
All hosts in a new network know their existing network
members. Some addresses may not be present in some
partitions and would remain un-assignable, as shown in
figure 3. For example, if host No 3 is not present, all its
potential children addresses would not be assignable. These
are numbers 6, 7, 12, 13, 14, 15, and so on according to the
address tree as depicted in fig.3. To address this issue, we
develop a new mechanism presented below.
The lowest address host is authorised to generate a root
address (or lowest) if it is not present in the child network.
This root host can generate addresses according to a
relevant base value (in this case base value equals two).
This is then given the task of allocating addresses with the
restriction that this host must not allocate child addresses
already in use. For example, if the lowest existing host
number is 2 and it can allocate the root address “0” to a
newly joining host with the restriction that when address 1
host is generated, this can only generate address 3, as
address already exists. This can be achieved as follow:
When allocating a root address, the root informs every
host in the network and they confirm their acceptance of
this address by sending an acknowledgement. With these
communications, a root host knows all existing hosts and
their immediate parents. The root host’s addresses
allocation will proceed according to a base value and the
restrictions with existing child host addresses.
Continuing un-assignable
addresses
0
1
2
3
4
8
5
9
10
6
11
12
7
13
14
future endeavour in this research.
Consider the case when two merging MANETs have the
same MANET ID. Even though this unlikely, there is
nevertheless a probability that this may occur. When they
merge, routing protocols are likely to fail, due to repeated
IP addresses. The source to destination route may not be
established and routes are misdirected to different
destinations specifically due to the presence of repeated IP
addresses. This is illustrated in figure 4. For example, when
host A from M1 network needs to send a message to B in
the same network. The message reaches its destination B
through hosts C, G or may be it reaches host B from M2
network. Likewise host G’s (from M2) message will be
delivered to either E (from M1 or M2) and hosts E’s
message could be received by either F, and so on.
15
Figure 3. Part of a tree that would not be assignable due
to a missing host.
5. MANET Merging
Merging frequently happens in MANET environments.
This merging may involve previously partitioned or
independent networks. Prior to merging, each partition will
have independently configured addresses. After merging,
two hosts in the merged network may have the same
address, thereby creating an address conflict. It is necessary
to resolve this situation immediately and efficiently for
correct MANET communications. Our research has
identified the importance of an alternative approach to
redress this situation.
When two networks merge with different MANET IDs,
we can address this issue as follows: When two distant
hosts’ X and Y from different networks come within
communication range of each other, they exchange their
MANETs identities. As the received and sent MANETs
identities are different, X detects the merger with Y’s
network and Y also detects the merger with X’s network.
After detecting the merger, both X and Y exchange their
respective addresses in use. Although the MANET’s ID
should be different, the hosts IDs are likely to be repeated
in both MANETs. Therefore the merged network starts
allocating new addresses for the MANET, with the larger
MANET adopting the smaller one. Then both merged
MANETs will have the same MANET ID of the larger
network. The smaller network will have its address
regenerated to be part of the same tree as the larger
network. However, as nodes in the smaller networks are
likely to have been within a communication session with
other nodes, a protocol needs to be developed so that the
new IP addresses can be assigned without disrupting
ongoing communications. This protocol is an issue for
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Figure 4. Misleading routes to destination.
To address this situation, we have developed the
following a mechanism: Each MANET should be named
with, say, eight random characters. This would ensure, with
probability close to 1, that two merging MANETs would
not have the same name. The purpose of naming MANETs
is that the hosts from one merging network can be
differentiated from hosts belonging to different networks in
the case of merger when the networks happen to have the
same MANET ID. When two networks merge, duplicate
addresses are detected (including MANET ID). The case
then is clear to the hosts in both networks that a merger
took place in which both MANETs had, originally, the
same MANET ID. To recover from this situation, the first
node to detect a neighbour with the same IP address as
itself broadcasts a message for all nodes. This special
message contains the name of the MANET to which the
broadcasting node originally belonged: All nodes belonging
to the same original MANET will act on this message, and
will change their MANET ID’s to the new ID contained in
the message. After this, the two merging MANETs will
have different MANET IDs, which can be solved as was
described in the beginning of this section.
6. Conclusion
This paper proposes a novel mechanism for conflict free
address generation and re-use in MANETs. We consider
the problems of MANET partition and MANETs merging.
To perform allocation of reusable addresses, the mechanism
uses the existing address space with regard to hosts’ childparent relationships. Even when the root host is
unavailable, this mechanism is capable of re-using
addresses by re-allocating root address. Also, we presented
a novel solution for MANET merging and in particular the
more difficult case when the MANET ID part of the IP
address is the same for the merging MANETs. Giving a
unique name for each MANET can identify its own group
members among other hosts from different networks,
therefore circumventing the difficulty imposed by possible,
albeit unlikely, IP address duplication after a merger of
MANETs that originally had the same MANET ID part of
the IP address. Future work will include simulation to
evaluate the message traffic required for updating the
address tree during network partitioning and merging, and
an evaluation of the relative merits of different base values,
with regards to the efficiency of the mechanism, and the
related performance implications, for instance the delay
associated with address clean up after partition and with
address changes following mergers.
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