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					        Fault-tolerant Dynamic Host Auto-configuration
             Protocol for Heterogeneous MANETs
                              M. Nazeeruddin, G. Parr, Member, IEEE and B. Scotney, Member, IEEE


                                                                                 MANETs [5]. On the other hand, the protocols using stateless
   Abstract— Host auto-configuration of mobile hosts is a key                    approaches do not maintain any table and nodes select
issue in the mobile ad hoc networks (MANETs) as hosts cannot                     tentative addresses by themselves and verify address
participate in unicast routing without unique addresses. A                       uniqueness by a procedure known as Duplicate Address
distributed agent based dynamic host auto-configuration protocol
for heterogeneous MANET nodes is presented in this paper. In
                                                                                 Detection (DAD). The Internet Engineering Task Force
this approach, every address agent has a disjoint set of IP                      (IETF) Zeroconf and IPv6 address auto-configuration
addresses which it can assign to the new node without consulting                 mechanism [8] uses the stateless approach. However, these
any other address agents in the network. The proposed protocol is                protocols cannot be used in MANETs due to the multihop
robust and efficient. It also has the ability to handle node failures            topology of MANETs [1].
and message losses.                                                                 In this paper, a distributed agent based Dynamic Host Auto-
                                                                                 configuration Protocol for MANETs (DHAPM) is proposed.
  Index Terms— Host Auto-configuration, Ad Hoc Networks,
Stateful approach, IP Address.                                                   The proposed protocol uses a distributed table which is
                                                                                 maintained by the dynamically selected address agents. Each
                         I. INTRODUCTION                                         Address Agent (AA) has a disjoint set of IP addresses which it
                                                                                 can assign to a new node without consulting any other AA in
M      OBILE Ad hoc Networks (MANETs) are self-
       organizing infrastructure-less networks formed by a
group of mobile wireless nodes. MANETs eliminate the cost
                                                                                 the network.

                                                                                                      II. RELATED WORK
and time of infrastructure deployment, setup and
administration. However, setup and administration tasks                           The proposed solutions for MANETs in the literature can be
should be carried out by the participating nodes in order to                     classified into the following three categories [1] [3].
share the network resources efficiently. The MANETs have                           A. Stateful or Conflict free allocation
numerous applications especially in the military and                                The address allocation in stateful approaches is usually
emergency services.                                                              conflict free as these approaches maintain an allocation table.
   The key problem in MANETs is to allow efficient                               The allocation table can be maintained centrally by the only
communication between nodes and hence most research is                           elected address agent (AA) [5] or distributed across all the
concentrated on routing [14]. However, for proper data                           nodes [2] [3] [9]. In the centralized approach, AA becomes a
communication (for proper routing of data), all network nodes                    bottleneck and AA failure results in unnecessary address
must be configured with uniform & unique addresses. Due to                       changes. In contrast, distributed allocation table approaches
lack of central administration, prior address configuration of                   are robust to node failures. However, the reliable
nodes is not possible. Consequently, a host auto-configuration                   synchronization of all nodes is necessary to avoid duplicate
protocol is needed to dynamically allocate and de-allocate                       address assignment. Even though the problem of duplicate
addresses to the joining and departing nodes respectively.                       address assignment can be relieved by maintaining a disjointed
   The existing host auto-configuration protocols are using                      allocation table [4] [15], the disjointedness should be
either stateful or stateless approaches [1]. The protocols using                 guaranteed.
stateful approaches need a central address allocation table to
maintain the state information of already configured nodes and                     B. Stateless or Conflict detection allocation
their addresses. DHCP [6] is a popular example of stateful                          Protocols using stateless approaches, instead of maintaining
approach. DHCP is designed for wired networks and it is not                      an allocation table, let the un-configured node select an
suitable for MANETs due to the highly dynamic topology of                        address by itself and verify address uniqueness by a Duplicate
                                                                                 Address Detection (DAD) process. One simple way of
   This work is supported by the University of Ulster vice chancellor research   performing DAD is by querying all nodes in the network [7].
scholarship.                                                                     Some protocols are based on integrating DAD in the routing
   M. Nazeeruddin is a PhD student in the School of Computing and
Information Engineering, University of Ulster, Coleraine, UK. Prof. G. Parr      protocols [10] [11]. In general the reliability of the stateless
and Prof. B. Scotney are professors of telecommunication and informatics         approaches depends on the reliability of DAD. In addition, the
respectively in the same school. (Contact E-mail: nazeer@infc.ulst.ac.uk).       stateless approaches have a problem to support network
merge. In case of merging, either DAD needs to be repeated or       timer expires, the requester repeats the same process for a
permanently performed resulting in increased protocol               certain predefined number (NbReqThreshold) of times waiting
overhead [1].                                                       for a response. If all the attempts fail, the requester concludes
                                                                    that it is the first node in the network. Hence, it initializes the
  C. Hybrid
                                                                    MANET by selecting a random IP address block and Partition
  Hybrid approaches [12] [13] may offer robust protocols by         ID. It assigns itself with the first IP address of the selected IP
combining the principle of both stateful and stateless              block and elects itself as AA to maintain the allocation table.
approaches. Nonetheless, they may result in higher protocol
complexity and overhead [1].                                          C. New Node Joining the Network
                                                                       Lets assume that the MANET is already configured and a
                     III. PROPOSED SYSTEM                           new node (say node i) wants to join the network. It broadcasts
                                                                    the NbReq message and waits for the NbRes message. In this
  A. System Description                                             case, it receives at least one NbRes message from one of the
   In this paper, an autonomous MANET is considered which           neighbours which are already part of the MANET. If there are
is formed by a group of nodes coming together. The nodes are        any address agents reachable by node i, they will also respond
mobile and can join or leave the MANET at any time.                 with NbRes and node i selects the first responding AA as the
Therefore, the size and topology of the network is variable and     initiator. If it receives no replies from address agents, then it
cannot be predicted.                                                selects the first responding node as its initiator.
   The proposed system is based on multiple dynamically                Node i then sends a NewAddrReq message to the chosen
selected Address Agents (AAs). Each AA has a disjoint set of        initiator (say node j). If node j is an AA, then it allocates an IP
sequential IP addresses which it can assign to a new node           address to node i, updates its table and responds back with
without consulting any other AA in the network. Each AA             NewAddrRes message embedding the assigned IP address. If
maintains two tables. First table keeps the record of all AAs in    node j is not an AA, it forwards NewAddrReq message to its
the network and their IP address blocks. This table also keeps      AA and returns the received response to node i. Each node
a note about the state of the AA. This table is called Agent        requesting new address informs the AA whether it can serve as
Table. The Agent Table is small and sorted with respect to the      AA or not. This information is maintained by the AA and will
IP addresses. The Agent Table can be implemented as a binary        be used at the time of selecting a new AA.
tree and a certain block of IP addresses can be searched in the              AA       IP Address                         AA       IP Address
table in order of log r time, where r is number rows in the table                        Block                                       Block
[4]. The second table (Address Table) keeps record of all the                 1          1-254                            1          1-127
                                                                                                                         128       128-254
assigned IP addresses and the details of node to which they are
assigned. Node details include hardware address (usually                     AA       IP Address
Medium Access Control (MAC) address) and a Boolean bit.                                  Block
The Boolean indicates whether the node is capable of                          1          1-15                             AA       IP Address
                                                                             16          16-31                                        Block
becoming an AA or not. If the bit is set true, then it means that
                                                                              .            .                              1           1-127
corresponding node has ability to act as an address agent. By                 .            .                             128        128-191
default, the bit is true.                                                     .            .                             192        192-254
              TABLE I                         TABLE II                       240       240-254
           AGENT TABLE                      ADDRESS TABLE
                                                                    Fig. 1: Transition of agent table as network size grows (only for illustration 1-
   AA     IP Address   State          IP      MAC      Suitable                                 254 is selected as range)
             Block                                     for AA
     1       1-15       Stable         1      Mac1       True         D. Node Departure
    16      16-31      Alarming        2      Mac2       False         If a node wishes to leave the network, it sends an
    32      32-63      Unstable        3      Mac3       True
   …..       …..                       …       …          ….
                                                                    AddrRelReq message to its AA and waits for its response. The
   240     240-254       Stable       254    Mac254      True       corresponding AA will update its table and send a
                                                                    confirmation message (AddrRelRes) to the departing node. The
  B. MANET Initialization                                           node departs the network and sends AddrRelDone message to
   This process is similar to MANETconf [2]. The first node         AA. After receiving the confirmation message the AA reuses
(say requestor) that wishes to join the network starts the          the departing node’s IP address.
neighbourhood detection process by sending a broadcast                 It should be noted that even if a node leaves abruptly
message (NbReq message) and commences NbReqTime timer.              without informing its AA, the network can eventually detect its
The requester expects to hear a response (NbRes) message            departure. However, if a node follows the above procedure,
from at least one MANET node which can act as the initiator         the network and address agent resources will be saved
for assigning an IP address to the requester. Since the               E. Selection of Auto Address configuration nodes
requester is the very first node in the MANET it will not             In this approach, the selection of nodes which maintain the
receive any response from other nodes. After NbReqTime              address allocation table is important. As explained in the
subsection III.B, the first node which wants to join the network              changes in its part of address table to the other address agents
initializes the MANET by selecting itself as an AA. All other                 at least one time in every AASyncTime seconds using
address agents will be selected only in one of the following                  UpdateTable message. Some times an AA may send multiple
cases:                                                                        UpdateTable messages if there are significant changes in its
   1. When an AA is getting many NewAddrReq messages                          part of address table.
        from a certain node or from the nodes which a certain                  In addition to synchronization among address agents, the
        initiator has helped in getting addresses.                            MANET address agents check periodically all the nodes they
   2. When one of the existing AA is experiencing severe                      assigned address by sending a multicast message (Alive) and
        shortage of resources (processor, memory, network,                    nodes reply back with a confirmation message (Ack). If no
        etc) and wants to share addressing protocol load.                     response is received from a certain node during multiple
   3. When the ratio number of nodes/number of AAs in the                     consecutive synchronization periods then the AA concludes
        network is greater than AAThreshold. (The optimum                     that the node has abruptly left the network.
        value of AAThreshold should be determined through
        simulations.)                                                                           IV. EXCEPTION HANDLING
In the first case, the node which has acted as initiator for many                In the previous section, it was assumed that are no node
nodes will be selected as new AA. In the second & third cases,                failures and message losses. However, in reality MANETs are
the existing AA (say AAi) selects a new AA as follows:
                                                                              more susceptible to node failures and message losses than
     1. Selects the new address requesting node after
                                                                              wired networks and this may result in IP address conflicts and
          assigning it an address.
                                                                              leaks. Hence, this section discusses how the proposed protocol
     2. If the new node does not have the ability to manage
          allocation table then, it announces to all the nodes                handles the situations that may arise due to message losses and
          under its group which have Suitable for AA bit as                   node failures. We use the situations enumerated by [2] as
          TRUE to nominate for the new AA position. All                       basis and added more possibilities to them. Most of the
          nodes which are ready to serve will respond with                    situations can be handled with help of timers and message
          AAReqRes message. From the responded nodes, the                     retries.
          node which has recently joined the network will be                    A. Initiator Crash
          selected as new AA.
     3. If no response is received from any of the nodes even                   Sometimes the neighbour which is acting as initiator may
          after a number of retries then it stops assigning new               crash before it assigns new address to the requesting node.
          addresses until one of the existing node leaves the                 This situation can be handled by using a timer. The requesting
          network and a new node with willingness to serve as                 node starts a timer (NewAddrTime) after sending NewAddrReq
          AA requests an address.                                             message and waits for response. If the timer expires and no
  Once new AA selection process is finished, the AAi starts the               response is received from initiator, then it retries by resending
new AA initialization process by dividing its IP address block                the same message and resetting the timer. Even after retries, if
into two parts1 and assigns the second part to the selected AA.               no response is received then it selects the second neighbour
It sends the updated allocation table and agent table to the new              which responded to NbReq as new initiator and sends
selected AA node using NewAASetup message. After the                          NewAddrReq message to it.
successful completion of the setup, the new AA sends a                          B. Requesting Node Crash
multicast message to all the other AAs with NewAADone                           There is a possibility that the new address requesting node
message.                                                                      may crash after requesting a new address. In such situation, the
   Sometimes, it may happen that an AA (say AAi) wants                        AA and initiator will not receive NewAddrDone message as
relinquish its duties and it may not have time to go through the              confirmation from the requesting node. Hence, the AA will
above procedure. In this case, the AA will simply send a                      reuse this address.
AARelReq message to nearest neighbour AA (say AAx) which
responds back with AARelRes. On receiving an                                    C. Abrupt Departure of Address Agent (AA)
acknowledgement from another AA, the requesting AA                              As explained in subsection III.F, each AA sends a multicast
releases its job. If AAx has enough resources then it announces               message to other address agents with its part of updates. If an
itself as AA for the AAi IP block. Otherwise AAx selects new                  AA (say AAi) did not receive a message from the address
AA on behalf of AAi.                                                          agent AAx, then it marks state of AAx as Unstable and waits
                                                                              for two synchronization periods. If AAi still doesn’t receive
  F. Synchronization of Address Agents                                        any responses from AAx, it marks AAx state as Alarming and
  The synchronization of MANET address agents is essential                    sends a multicast message to the other address agents. In the
to maintain updated address allocation table. This is process is              next synchronization period, if any AA has updated
also useful in detecting any missing address agents. The                      information of AAx then it sends updated AAx address table
synchronization process involves each AA multicasting                         along with its table in the UpdateAA message. In the case of
                                                                              actual crash, no AAs respond and hence eventually AAi mark
                                                                              the state of AAx as Aborted and starts the process of selecting
  1
    When an AA wants to completely relinquish its job, then it gives up the   an AA on behalf of AAx as explained in subsection III.E.
whole IP address block instead of dividing into two parts
  D. Message Losses                                                                reassigning new unique addresses. Once the IP address
  The message losses are handled traditionally by resending                        conflicts are resolved, the PID of the bigger partition
the same message for a maximum of MessageRetry times.                              will be broadcasted to all the nodes.
Even after maximum retries if a node fails to get a response                   3. In the meantime, the bigger partition address agents
then it concludes the other node has left the network. It can be                   suspend the new address assignments until a
argued that continuous message losses are because of                               confirmation message is received from the AA of
persistent communication problems in the MANET. However,                           smaller partition (AASmall) or MergeTimer expires. (If
in other words this means that the node is not accessible from                     timer expires, the AA of bigger partition (AABig) checks
network even after the maximum waiting period and hence the                        the status of merger with AASmall. If no response is
node is practically out of network                                                 received from AASmall, AABig announces merger failure to
                                                                                   other AAs in the partition. The address allocation
  E. Merging & partitioning of the Network                                         processed is resumed.)
  Since the MANET nodes are mobile, the network may split                      4. AASmall sends a confirmation message to the bigger
into multiple partitions. These partitions may merge again.                        partition AAs with the updated tables.
Moreover, two independent MANETs may also collide (for                         5. The bigger partition AAs updates its tables and sends a
example, two army battalions may come together). The                               reconfirmation message to the smaller partition address
network merging & partitions problem can be handled by                             agent.
using a partition identity (PID) [2]. The PID can be formed by               In the above procedure, it is assumed that the addressing
combining subnet identity and a random number. During                       agents of two partitions can be able to communicate with each
MANET initialization, the very first node (the first AA)                    other. If they cannot communicate directly they can use the
generates PID. Subsequently, all other nodes will receive PID               informing nodes as proxies.
as part of NewAddrSetup message.
    1) Network Partition Management                                                          V. PERFORMANCE EVALUATION
    When the MANET breaks into two partitions, one of the                      The proposed DHAPM protocol achieves robustness and
partitions will still have the AA which has generated PID.                  efficiency by maintaining distributed copies of allocation table
Hence, the partition identity will remain the same. Address                 and disjointed IP address blocks respectively. The table III
agents in this partition detect the abruptly departing nodes                briefly compares the performance of some stateful approaches.
during the synchronization process and clean their agent and                The new address assignment is fast and very efficient as it
address tables. In the second partition, during the                         depends only on the nearest AA and requestor. In the worst
synchronization process, address agents will discover that the              case, when AA is not directly reachable another node acts as
AA which has generated PID is no longer available and                       proxy. When a node leaves the network the corresponding AA
concludes that the network has partitioned2. In this case, after            needs to send only one message to the departing node. Only
updating agent & address tables, the AA which smallest IP                   when the node departs abruptly, the departing node address
address block will generate new random number and                           will not available for reassignment until the synchronization
broadcasts it to all nodes in the new partition. This procedure             process.
works properly even if the network splits into more than two                Synchronization of address agents involve every AA
partitions. To make this process more robust, the new partition             periodically multicasting its part of updated Address table to
ID is generated only after two or three synchronization                     the other AAs. So in the network of m AAs there will be m
periods. In addition, address agents continue assigning                     multicast messages. (Usually m<<n for large n).
addresses from their blocks until all IP addresses are                      The network load related to address allocations and allocation
exhausted. This process reduces the protocol overhead by                    table management is distributed among the AAs and all other
minimizing the possibility of duplicate addresses if the                    non-AA nodes have very little overhead. The memory
partitions merge together.                                                  requirement of address agents is bit more than other methods.
    2) Network or Partition Merge                                           However, non-AA nodes need no extra memory for address
    The network and partition merging are basically the same.               management and hence even low memory devices can also
In any case the merging can be detected by the difference in                participate in networking which is not the case in [2][4].
the PIDs. If the partition identities have the same subnet ID,                The proposed method and other methods ([2, 4, 5]) are
then it is partition merging otherwise it is network merging.               formulated mathematically and simulated using MATLAB
If two nodes detected a merger, they forward merger                         software. For simulation, a MANET3 with average size of 50
information to their respective address agents. The address                 nodes is formed. During the simulation, 60 new nodes join the
agents perform the following steps:                                         network, 10 nodes depart from the network and one address
   1. The address agents exchange their agent and address                   agent crashes abruptly. Node and AA Synchronization
        tables and inform the other address agents in the                   frequency is set as 5 seconds. The collected statistics are
        network about the merge.                                            shown in Table IV. The first five columns show the number of
   2. The address agents in the smaller partition check for the
        duplicate addresses and resolve the address conflicts by               3
                                                                                 Network simulator (ns-2) simulation results are not presented in this
                                                                            paper due to the space constraints and will be presented in the detailed
   2
     Please note that abrupt departure of AA which has generated PID also   version of the paper
results in new PID generation
different types of auto-configuration packets sent during the                host auto-configuration protocols will be addressed. Another
simulation period. The last column shows the total number of                 key research direction is to interact with the routing protocols
auto-configuration packets received during the simulation                    for the early detection of node crashes there by saving the
period. PRecv gives an indication of the overall communication               network resources.
overhead for each protocol as it is proportional to the number                                                 TABLE IV
                                                                                                          SIMULATION RESULTS3
of packets sent. From the table, it is evident that the proposed
protocol (DHAPM) performs more efficiently than the other                       Protocols          UC         MC       BC      MU       MB        PRecv
protocols. Although the number of unicast packets in buddy                      Central [5]        2662       0        87      0        59        5663
                                                                                ManetConf[2]       1788       0        131     405      60        6603
protocol [4] is less, it is much costlier than the DHAPM
                                                                                Buddy [4]          30         0        527     465      60        23122
protocol due to the huge number of broadcast packets.                           DHAPM              568        112      0       405      60        2219
                         TABLE III                                            3
                                                                                UC, MC, BC, MU, MB are number of unicast, multicast, broadcast, MAC
    PERFORMANCE COMPARISON OF DIFFERENT STATEFUL APPROACHES
                                                                              layer unicast, and Mac layer broadcast packets respectively. PRecv is the total
           Central [5]     ManetConf        Disjoint [4]     DHAPM            number of packets received.
                           [2]
Synchron   Not needed      All nodes will   Sync             Sync                                           REFERENCES
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In addition, scalability, security & overhead minimization of

				
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Description: Dynamic Host Configuration Protocol (DHCP) is a local area network protocol, using the UDP protocol, mainly for two purposes: to the internal network or Internet service provider automatically assigns IP addresses to users as to the internal network administrator for the central computer for all management tool.