George Metaxas, David Hutchison and Nicholas J.P. Race
Computing Department, InfoLab21
Lancaster University, Lancaster LA1 4WA, UK
Address Autoconfiguration, Nomadic Ad hoc Networks, Wireless Networking, IPv6.
Densely populated urban environments provide unique nomadic movement patterns. People tend to move in
groups across predefined paths, with low intra-group movement, giving rise to Nomadic Ad hoc Networks
(NANETs). NANETs, which are a constrained subset of Mobile Ad hoc Networks (MANETs) in terms of
mobility, concentrate on civilian-style usage and are sufficiently dynamic in nature to present significant chal-
lenges in the design of even the most common tasks such as packet routing or name resolution. An intriguing
issue relates to the automatic configuration of IP addresses to constituent nodes that will allow data exchange.
The underlying physical group structure can be utilised in the network layer as a basis for an address autocon-
figuration mechanism, which would yield low and localised signalling traffic overhead coupled with a subnet
optimisation. This paper proposes and discusses the AALM IPv6 address autoconfiguration mechanism, which
has been developed to provide the aforementioned characteristics.
Nomadic Ad hoc Networks (NANETs), first ex-
plored in (Prince, 2005), provide a relatively fresh
view to the generic field of Mobile Ad hoc Networks
(MANETs). The inherent nomadic nature constrains
the movement patterns of constituent nodes to a tacit
model found in densely populated urban environ-
ments. People tend to move in groups across pre-
determined paths, pausing at places of interest for an
undetermined amount of time. Intra-group mobility
is considered low, whereas group mobility in respect
to the environment may be high. NANETs present an
environment found in crowded city centres, univer-
sity campuses and shopping centres, which are typ-
ical civilian-style rather than military or emergency
response scenarios.
Although constrained in relation to MANETs,
NANETs are still highly dynamic ad hoc networks
and exhibit several MANET traits, such as lack of a
centralised infrastructure. Consequently, basic tasks
such as packet routing, name resolution and automatic
address configuration require cooperative approaches.
The most widely researched subject is associated with
packet routing. Several experimental standards have
been produced by the IETF MANET Working Group,
which is responsible for engineering such solutions.
Aside from packet routing, address autoconfigura-
tion provides an area of significant challenges. In
wired and wireless infrastructure networks, this is
supported by infrastructure means, such as address
pool servers. In a MANET, it is impossible and un-
wise to presume the presence of infrastructure sup-
port. Therefore, address autoconfiguration requires
node cooperation and the design of distributed algo-
rithms capable of rapidly adapting to environmental
conditions. The constrained and specialised nature of
mobility in NANETs, can be exploited to provide bet-
ter solutions and reveal issues, otherwise hidden due
to unconstrained and unnatural movement patterns.
This paper proposes an address autoconfiguration
mechanism for NANETs, which has been fundamen-
tally designed to operate in partitioned networks, by
localising signalling traffic, through the use of cluster-
ing concepts. The added advantage of this approach
is the subnet optimisation which minimises routing
table size. The remainder of this paper is organ-
ised as follows. Section 2 discusses related work in
the field of address autoconfiguration mechanisms for
MANETs and details various physical layer issues.
Section 3 presents the design of the proposed mecha-
nism. Section 4 provides an evaluation of the mecha-
Metaxas G., Hutchison D. and J.P. Race N. (2006).
In Proceedings of the International Conference on Wireless Information Networks and Systems, pages 121-128
nism through extensive simulations. Finally, Section
5 concludes the paper and discusses future work.
Address autoconfiguration mechanisms became a re-
quirement in wired networks as a result of the growth
and popularity of the Internet. They are classified in
two categories, statefull and stateless. The former
requires the presence of a centralised server for dis-
tributing addresses, as in DHCP (Droms, 1997). The
latter achieves address configuration per node atom-
ically, without contacting a centralised server. The
IPv6 Stateless Address Autoconfiguration (SAA),
defined in (Thomson and Narten, 1998), is such a
mechanism. Nodes are equipped with link local and
global addresses. SAA requires a router advertising
a unique subnet prefix in every subnet. A link lo-
cal address is formed by converting the MAC address
of a network interface to a 64-bit identifier and ap-
pending it to the link local prefix (FE80::). Address
uniqueness on the link is verified through a broadcast
message, which initiates the Duplicate Address De-
tection (DAD) process. A reply signals duplication
causing the repetition of the procedure. Otherwise,
the address is considered unique and a global address
is formed by appending the unique interface identifier
to the subnet prefix.
Pure ad hoc networks require stateless approaches,
which are classified in three categories, conflict avoid-
ance, conflict detection and hybrid. In conflict avoid-
ance mechanisms, addresses are acquired through a
configured neighbour which possesses an unallocated
address pool. In contrast, nodes atomically acquire
addresses in conflict detection mechanisms and at-
tempt to detect and resolve possible duplications.
Hybrid solutions provide a fusion of the above ap-
proaches. Several ad hoc address autoconfiguration
mechanisms are presented in Section 2.1.
At present, software solutions developed for use
in ad hoc networks are impeded by various physical
layer issues. These issues are mainly concerned with
scalability and partition formation. They are inher-
ent in two of the most popular wireless technologies
used for constructing ad hoc networks, IEEE 802.11
and Bluetooth. Section 2.2 discusses some of these
2.1 Address Autoconfiguration In
Ad Hoc Networks
An initial attempt to provide a MANET address auto-
configuration mechanism, similar to the IPv6 SAA is
described in (Perkins et al., 2000). An unconfigured
node selects a random IPv4 address from a specific
range, broadcasts a message requesting a route to the
generated address and sets a timer. If the timer expires
and no replies are received, the process is repeated up
to a pre-specified number of times. Further lack of
replies, is assumed to reveal that the address is unal-
located and can be assigned to the node. Otherwise
the address is in use and the process is repeated.
(Vaidya, 2002) terms the above idea as Strong
DAD and argues that it fails if message delay between
any pair of nodes is unbounded. The proposed Weak
DAD technique allows routing protocols to correctly
deliver packets even in the presence of duplicate ad-
dresses. This is achieved by associating a predefined
unique key with each node, such as an IMEI
, dis-
tributed and stored alongside IP addresses to enable
unique node identification when required.
(Zhou et al., 2003) uses a common address pool
which is drawn from the results of a carefully chosen
function that generates sequences with a low proba-
bility of producing the same numbers. The first ini-
tialised node chooses the function and the seed to be
used. It is called a prophet as a result of its ability to
predict all generated addresses. Unconfigured nodes
request the help of their closest configured neighbour,
which creates an address using the selected function
and returns it, along with the seed and the function in
use, to the requester.
Another technique called Passive Duplicate Ad-
dress Detection (PDAD) is discussed in (Weniger,
2003) and (Weniger, 2005). It is a passive approach,
involving no explicit signalling traffic transmission,
deriving its decisions from routing protocol traffic in-
vestigation. Nodes are configured with addresses that
are unlikely to be duplicate, deriving their decisions
through a probabilistic algorithm, which is aided by
an Address Allocation table maintained per node.
A common issue in MANETs is the occurrence
of partitions, which are collections of nodes separat-
ing from or merging into the network. Address au-
toconfiguration mechanisms handle partitions by as-
sociating them with identifiers and providing dupli-
cate address resolution in case of partition merge,
as in (Sun and Belding-Royer, 2003), (Nesargi and
Prakash, 2002), (Zhou et al., 2003) and (Toner and
O’Mahony, 2003). A node is chosen to create, dis-
tribute, maintain and advertise the partition identi-
fier. Partition splits and mergers are identified by the
lack of partition identifier advertisements or the re-
ception of multiple different advertisements respec-
tively. This approach is cumbersome, generates ex-
cessive signalling traffic and does not resolve address
duplications across multi-hop partitions. Moreover,
partition identifiers are unrelated to the network oper-
ation and introduce additional bandwidth and routing
A pre-configured unique 15-digit number used in GSM
table size overheads.
2.2 Physical Layer Issues
One of the major issues inhibiting the wide deploy-
ment of MANETs are the inherent physical layer is-
sues in the most popular underlying networking tech-
nologies. These issues result in the creation of parti-
tions and impact the scalability of the resulting net-
works. Partitions are mainly manifested when several
nodes become separated from the rest of the network,
as a result of physical movement or due to wireless
channel conditions. The existence of partitions pro-
hibits proper operation of distributed algorithms due
to the lack of routing paths. Even though partitions
can be treated as separate networks, the presence of
mobility and freedom of movement leads to partition
merging and splitting.
Wireless channel conditions are the most impor-
tant contributer to partitioning, apart from physical
node movement. This is especially evident in the
IEEE 802.11 protocol. (Lundgren et al., 2002) reports
the problem of gray zones, which are areas where
nodes are able to exchange routing information but no
data. The problem of unidirectional links discussed
in (Prakash, 1999), can also lead to partitions, espe-
cially if such a link exists between key routing paths
in the network. Even the number of people impacts
the channel quality as discussed in (Mathur et al.,
Ad hoc networks are also plagued by scalability
problems impeding their multihop ability, as a re-
sult of various physical layer issues. (Tschudin et al.,
2003) and (Tschudin et al., 2004) discuss the Ad hoc
Horizon problem which exists in IEEE 802.11. It dic-
tates that beyond two to three hops, routing informa-
tion becomes useless, route maintenance and discov-
ery inhibit network operation and TCP performance
becomes unacceptable. Bluetooth is known for its
difficulty in scaling due to oversights in its specifi-
cation, as discussed in (Guerin et al., 2002), regard-
ing the scatternet formation procedure used for creat-
ing larger Bluetooth networks. A number of research
studies propose different algorithms for this purpose,
such as for example (Zaruba et al., 2001) and (Law
and Siu, 2001). However, it is doubtful whether Blue-
tooth is scalable, due to the increased overhead re-
quired for scatternet creation, as discussed in (Mikl
et al., 2000) and (Vergetis et al., 2005).
Partitioning is a natural tendency of MANETs and
NANETs due to physical movement and wireless
channel conditions. Especially in the case of
NANETs, the existence of partitions is a highly likely
occurrence due to the underlying nomadic behav-
iour. However, current address autoconfiguration pro-
posals treat partitioning as a special case and con-
sider generic MANET movement scenarios, which
are mostly unrealistic and do not reflect civilian-style
scenarios. The Ad hoc Address autoconfiguration
Localisation Mechanism (AALM) is a novel ap-
proach in the field. It has been designed around IPv6,
reuses the ICMPv6 signalling mechanisms and at-
tempts to tailor the SAA procedure for use in parti-
tioned NANETs.
Partitioning is fundamental to the design of
AALM, which combats this issue and provides a scal-
able, low overhead solution. This is achieved through
the use of Network layer clusters, or groups as they
are referred to in this paper, which are at most two
hops in diameter. This technique also achieves in-
creased scalability by reducing the required routing
table size, as groups are considered to be small scale
subnets. Address uniqueness is highly localised in
small regions, up to a maximum of six hops. Con-
sequently, the impact of address duplications and par-
tition creations is localised to a very small network
part, thereby minimising the signalling traffic over-
head. This localisation of signalling traffic governs
all aspects of address generation and maintenance.
All packets are transmitted with a hop count of one
unless otherwise stated.
3.1 Assumptions
Several assumptions are required in the design of the
AALM mechanism. The underlying environment is
assumed to be constrained in terms of mobility and
node movement, following the nomadic model, where
nodes move in groups and intra-group mobility is
considered low. NANETs concentrate on civilian-
style scenarios found in settings such as city centres.
Therefore, it is assumed that group movement with
respect to the environment and other groups is con-
sidered low. Low mobility is similar to the walking
speed of people. Constituent devices are considered
to be small mobile devices, such as mobile phones,
PDAs or laptops.
Each device must be equipped with one wireless
ad hoc interface and one wireless infrastructure inter-
. The interface operating in infrastructure mode
is assumed to be assigned a globally unique IPv6 ad-
dress which remains unchanged. Furthermore, each
ad hoc interface is associated with a unique MAC
address. For the remainder of this paper, the abbre-
viations NSOL, NAD, RAD and RSOL specify the
ICMPv6 Neighbour Solicitation, Neighbour Adver-
For example IEEE 802.11 and GPRS, found in some
mobile phone models
Figure 1: The link and extended link concepts.
tisement, Router Advertisement and Router Solicita-
tion messages respectively.
3.2 Founding Concepts of AALM
AALM defines two neighbour sets, the link and the
extended link. A link is: the set of all one hop neigh-
bours of a node, whereas an extended link is: the
set of all one hop neighbours of a node plus their
one hop neighbours. The link definition resembles
the corresponding definition used in wired networks.
An extended link represents a node’s two hop neigh-
bourhood. Nodes acquire unique link local addresses
that are cooperatively maintained in their extended
link. Precise knowledge of the extended link is not
required, but provides a safety zone for link local ad-
dress uniqueness. Figure 1 shows the difference be-
tween the two constructs.
The SAA specification requires nodes to defend
themselves in case of address duplication in their link.
Reception of a message on a specific multicast ad-
dress, after the completion of the SAA procedure, per-
mits the receiver to defend its address by transmitting
an appropriate NAD. Nodes using the AALM mecha-
nism are also required to respond to any potential du-
plications, but also defend their link neighbours. This
is necessary due to a node’s partial perception of the
network topology. Maintaining address uniqueness in
a node’s link requires neighbour cooperation, as their
link is part of the defended node’s extended link. All
address defence messages are transmitted to the All
Nodes in Link Multicast (FF02::1) address.
There are two address types assigned by the AALM
mechanism, link local and site local. Link local ad-
dresses are of limited scope, valid for one hop com-
munications only. Their uniqueness is maintained in
a node’s extended link through regular beaconing and
neighbour cooperation. This cooperation is enforced
by transmitting all beaconing, address acquisition and
maintenance related messages to the IPv6 broadcast
address, for inspection by all neighbours. All such
messages are transmitted with a hop count of one.
Upon acquiring link local addresses, group forma-
tion is initiated to equip nodes with site local ad-
dresses. AALM uses the term group rather than clus-
ter to differentiate from clustering algorithms, which
are usually implemented at the MAC layer. Each
group is associated with a 32-bit Group Identifier
(GID) that is embedded in the site local addresses of
group members. GID uniqueness is maintained across
neighbouring groups. There are three group member
types, a leader, gateways and ordinary nodes. Groups
are centred around a leader and all group members are
one hop neighbours of a leader. Therefore, all group
members are at most two hops away. Nodes record
neighbour information in their Neighbour Cache and
group information in their Prefix and Router Caches.
3.3 Link Local Address Acquisition
The link local address acquisition procedure, is simi-
lar to the DAD procedure of SAA, although there are
several distinct features associated with the AALM
mechanism. The 64-bit interface identifier is ran-
domly generated, rather than being associated with
the MAC address, for enhancing privacy. The NSOL
carrying the generated address is transmitted to the
All Nodes in Link Multicast address (FF02::1) to
promote cooperation among neighbours in the con-
figuration procedure. Receiving nodes must record
this information in their Neighbour Cache, unless a
duplication is detected. The initial NSOL is transmit-
ted exactly once and the node must also set a timer
to signal the end of the DAD procedure. This event
is followed by the initialisation of a pseudo-periodic
beaconing service to advertise a node’s link local ad-
dress, which in AALM terms has been acquired by
the node that is now considered to be configured.
MAC address comparison is used for resolving du-
plications, with the lowest one favoured. The pre-
ferred node is also determined by whether either of
the offending nodes has acquired the address. If both
or none have acquired the address, only MAC address
comparison is performed. Otherwise, the node which
is configured or presumed to be configured is allowed
to maintain ownership of the address, irrespective of
MAC address comparison. Furthermore, if address
duplication occurs after group formation, involving a
leader and a non leader node, the leader is favoured.
All signalling and data traffic containing link local ad-
dresses are searched in the Neighbour Cache for du-
The favoured node is not defended immediately,
unless it is also the one detecting the duplication. In
all other cases an appropriate reply packet is created
and queued for future transmission. The queueing in-
terval is random for each node, but does not exceed
one hundred milliseconds. Reception of a similar re-
ply packet, causes the receiving node to cancel its
queued transmission if it is in agreement with the pro-
vided information. Otherwise, it re-evaluates its deci-
sion and proceeds to update the contents of its queued
packet, but not the scheduled transmission time. This
procedure minimises the number of defence packets
transmitted and reduces wireless channel contention
and the number of dropped packets. Assuming two
conflicting nodes, only one packet is necessary to re-
solve a duplication.
3.4 Group Formation and Site Local
Address Acquisition
The group formation procedure is based on the
Lowest-ID and Least Cluster Change (LCC) clus-
tering algorithms, discussed in (Ephremides, 1988)
and (Chiang, 1997) respectively. Lowest-ID is used
in leader election, whereas LCC is used as a means
to increase group stability by not destroying groups
whenever a member with a lowest identifier from the
leader becomes a group member. As previously men-
tioned, the Prefix and Router Caches record informa-
tion about groups. The former stores prefixes adver-
tised by group leaders or gateways, whereas the latter
stores leaders addresses. Prior to the group formation
procedure, nodes investigate their Prefix and Router
Caches to identify groups in the vicinity, in which
case they associate themselves with such a group, be-
coming members. Otherwise, group formation is ini-
tiated by investigating the contents of the Neighbour
Cache for identifying the node possessing the low-
est MAC address, which is designated as a potential
leader. All other nodes set a timer and await for a
leader to make its presence known. This is required
in case a potential leader does not claim its leader-
ship due to the existence of a node with an even lower
MAC address in its link.
The potential leader picks a random GID, by first
investigating the contents of the Prefix Cache, and
generates its leader specific site local address as:
. To verify the
GID uniqueness, the newly introduced Duplicate
GroupIdentifier Detection (DGID) procedure is ini-
tiated. A NSOL sourced from the leader’s link lo-
cal address is transmitted to the All Nodes In Link
Multicast address, containing the leader specific site
local address. The hop count of the message is set
to one and an option specifying the leader’s wireless
infrastructure address, which uniquely distinguishes
every node in the network, is included. A timer is set
to signal the end of the DGID procedure.
Neighbouring nodes receiving the NSOL investi-
gate their Prefix Caches for the included prefix. If
HIGH-GID and LOW-GID represent the high and low
order 16 bits of the GID respectively
one is found, a duplicate GID may have been de-
tected which is resolved by comparing the associated
wireless infrastructure addresses, with the lowest be-
ing favoured. In GID duplications it is also important
to check if they involve established groups. If both
groups are established or are not established, then
comparison of the leaders wireless infrastructure ad-
dresses resolves the duplication. Otherwise, the es-
tablished group is favoured. The result of the resolu-
tion is transmitted by either RADs or NADs, depend-
ing on whether the detecting node is a leader or not.
Only leaders are allowed to immediately transmit a re-
ply. All other nodes are required to queue their packet
for a random time interval of up to one hundred mil-
liseconds and follow a similar procedure to link local
address defence, to transmit or cancel the packet ac-
If a potential leader receives a NAD signifying du-
plication, it picks a new GID and restarts the DGID
procedure. However, if a RAD is received, an es-
tablished leader is in the link of the potential leader
which must stop the group formation procedure and
join the existing group. If no messages are received by
the potential leader and its timer expires, the GID is
assumed unique, no other leaders are found in the link
and the group can be established. Its NAD beaconing
service is replaced by pseudo-periodically transmit-
ted RADs. All such packets are transmitted from the
leader’s link local address and contain options signi-
fying the prefix advertised, the leader’s link layer ad-
dress and its wireless infrastructure address.
All nodes receiving the group creation NSOL mes-
sage insert appropriate entries in their Prefix and
Router Caches and generate a site local address. This
is achieved by appending the interface identifier from
their link local address to the prefix included. The
resulting address is associated with a tentative status,
as the group is not yet established. Permanent status
is only assigned after reception of a valid RAD from
the same leader which advertised the address prefix.
Nodes receiving RADs from multiple leaders become
gateways and create site local addresses per group.
One group is selected as the primary group of each
AALM attempts to maintain GID uniqueness
among neighbouring groups. There are two types of
neighbouring groups, direct and indirect. Two groups
are direct neighbours of each other when there exists
a gateway node, in other words a one hop neighbour
of both leaders. In contrast, two groups are indirect
neighbours when they have no gateways among them,
but there are member nodes in each group which
are one hop neighbours of each other. Neighbour-
ing groups of a group are responsible for maintain-
ing GID uniqueness by prohibiting any of their neigh-
bours to use the same GID. This process guarantees
site local address uniqueness across a maximum of
Figure 2: Average lifetime of link local addresses.
six hops. It is augmented by the newly introduced
Group Multicast Information Exchange Mecha-
nism (GMIEM) which uses a Group Multicast Ad-
dress (GMA), as well as a newly defined ICMPv6
Group Information option. Each group leader main-
tains knowledge about neighbouring groups proac-
tively and is able to resolve possible GID duplica-
The Group Information option is a new ICMPv6
option for the exchange of group information. It con-
tains a GID and the associated wireless infrastructure
address of the leader, together with a flag signify-
ing whether the information belongs to the transmit-
ter’s primary group. These options are inserted by
all group members in their beacons. Each leader in-
cludes the complete contents of its Prefix Cache in
all transmitted RADs. This provides group members
with an up-to-date view of all known neighbouring
groups and are qualified for resolving possible GID
Member nodes passively register to the GMA of
each group they are members of. The GMA is a
multicast address of the form: FF02:FF02:HIGH-
GID:LOW-GID::1. All traffic transmitted to the
GMA is received by some of the members of the as-
sociated group. It is provided as a means to filter out
certain nodes from receiving packets. Only a leader
may be able to reach all group members. The GMA
is used in the GMIEM, to assist member nodes in in-
forming their group neighbours and especially their
respective leaders about newly discovered groups and
propagate this information through the packet queue-
ing mechanism.
Nodes regularly monitor GMA traffic to identify
information identical to their queued packets, result-
ing in the cancellation of their own packets. Dupli-
cations are resolved through wireless infrastructure
address comparison of the conflicting group leaders,
Figure 3: Average lifetime of primary site local addresses.
Table 1: Summary of Simulation Scenarios.
No of Groups Total Nodes
7 7 to 70 increments of 7
11 11 to 110 increments of 11
15 15 to 150 increments of 15
with the lowest one being favoured. A reply is imme-
diately transmitted, if the transmitter is a leader, and
forwarded to the affected group as a NAD.
The AALM mechanism has been evaluated through
extensive simulations using the ns-2 simulator. The
characteristics investigated are the amount of sig-
nalling traffic generated, the lifetime of addresses and
the impact of increasing numbers of physical groups
and nodes in the simulation. The simulated scenarios
are produced by the rpgm tool, kindly provided by the
authors of (Camp et al., 2002), which implements the
Reference Point Group Mobility Model. The exact
node and group configuration parameters of the simu-
lations are shown in Table 1. For each node and group
increment, twenty scenarios are generated and simu-
lated with 100 different seeds. The simulator has been
configured with the standard IEEE 802.11 implemen-
tation, using the Two Ray Ground propagation model.
There exists no other traffic in the network apart from
AALM signalling traffic. The simulated area is 300
metres wide by 300 metres long and the transmission
range is set to 60 metres. The simulated scenario time
is fixed at 300 seconds. The allowed address space
used, is constrained. The interface identifier values
are restricted from 0 to 4 times the number of nodes
in the simulation, which is also applied to GIDs. Fi-
Figure 4: Average total number of packets transmitted per
nally, the beaconing interval for all nodes is set to
2 seconds, apart from leaders which advertise their
presence every 1.5 seconds.
The results acquired regarding the lifetime of link
local addresses are highly positive. As shown in Fig-
ure 2 the average lifetime is high, with a lowest value
of about 282 seconds. The graph demonstrates a min-
imal decrease in the link local address lifetime as
the number of nodes per group increases. Increased
numbers of physical groups in the simulation result
in slightly decreased lifetime values. The decreased
trends observed are mainly related with the number of
physical groups, rather than nodes per group. Insert-
ing more groups in the network increases the number
of nodes in the simulation which are beyond a node’s
extended link. Therefore, the existence of a duplicate
address somewhere in the simulation area, which is
not resolved, is more probable.
Figure 3 shows the results obtained regarding the
average lifetime of primary site local addresses, in
other words the address associated with a node’s pri-
mary group. It is evident that increased numbers of
nodes per group results in decreased address lifetime
values. The same applies to increased numbers of
physical groups. Another important observation is
that as the number of physical groups increases, the
differences in the results obtained for increased num-
bers of nodes per group are decreased. For example,
for 15 physical groups, the average primary site lo-
cal address lifetime for 1 node per group is about 30
seconds, whereas it is 20 seconds for 10 nodes per
group, a difference of 10 seconds. On the other hand,
for 7 groups the corresponding values are 60 and 36,
which is a difference of 24 seconds. The obtained
values are suitable for HTTP-type traffic, where the
amount of data exchanged is relatively low. They
are unsuitable for multimedia-type traffic and large
Figure 5: Average number of packets transmitted per node.
data exchanges, due to the requirement for a mech-
anism capable of maintaining connections after ad-
dress changes. Although such mechanisms exist in
wired networks (MIPv6), which have been somewhat
adapted to operate in an ad hoc context, there exists
no mechanism at present to operate in a pure ad hoc
networking environment. The lifetime of primary site
local addresses is dependent on group and link local
address lifetime. Whenever a link local address is
removed, for any reason, all site local addresses are
also removed. Furthermore, upon group destruction,
nodes must pick a new primary site local address, if
another group is present, or initiate the group forma-
tion process. The achieved results point to reduced
group lifetimes. This is one aspect of the proposed
mechanism which requires further investigation and
The graphs shown in Figure 4 show the signalling
traffic footprint of the mechanism. Clearly as the
number of nodes and nodes per group increases, so
does the number of transmitted packets. This increase
is almost linear in nature. It is observed that increas-
ing the total number of nodes in the simulation by 40
results in about 7000 extra packets. Figure 5 shows
the average number of packets transmitted per node.
In this figure, it is interesting to note that for the most
part, increasing the number of nodes per group, re-
sults in an increased average number of packets trans-
mitted per node. The only exception is for 1 node
per group. The initial high values are attributed to
the greater number of leaders in respect to ordinary
nodes per group, which transmit packets at a lower
interval (1.5 seconds for leaders versus 2 seconds for
ordinary nodes). Furthermore, increasing the number
of groups results in slightly increased values. The av-
erage number of packets transmitted per node and the
one hop nature of these packets indicates the scalabil-
ity of the mechanism.
This paper has presented a novel address autoconfig-
uration mechanism for NANETs, which are a sub-
set of MANETs and are associated with civilian-style
scenarios. The mechanism has been fundamentally
designed to address the problem of partitioning, util-
ising underlying environmental characteristics to im-
pose a Network layer subnet structure. Furthermore,
the structure is maintained through signalling traffic
localisation, thereby reducing the effects of partition-
ing and probable address duplications.
The evaluation of the proposed AALM mechanism,
through extensive simulations, has demonstrated its
effectiveness to facilitate short lived HTTP-type traf-
fic, in regards to signalling traffic overhead and link
local addresses lifetime. It is an efficient approach
for assigning addresses usable for one hop data ex-
change, although requires further improvement re-
garding long-lived connectivity in respect to the life-
time of site local addresses. Future work should also
concentrate on improving the design of AALM in or-
der to provide a more generic solution applicable to a
wider range of MANETs.
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