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					           Ad-Hoc Networks
           Establishing node-to-node communication
                 with no infrastructure needed


Authors:   Đorđe Trifunović, djole@europemail.com
           Nikola Milanović, nikola99@EUnet.yu
           Prof. Dr. Veljko Milutinović, vm@etf.bg.ac.yu
What will you learn from this tutorial?
      This tutorial will guide you through the following sections:

   Introduction
   Mobile networks
   Routing in ad-hoc networks
   Security in ad-hoc networks
   Bluetooth
   The IEEE/UB ad-hoc multihop sensor network and Bluetooth;
    lessons learned from the research by:
        –   Gvozden Marinković (mgvozden@eunet.yu)
        –   Aleksandar Radovanović (biblbroks@sezampro.yu)
        –   Aleksandar Berić (alberic@eunet.yu)
        –   Branislav Čukanović (chuka@beotel.yu)
        –   Nikola Milanović (nikola99@eunet.yu)




                                  Page Number: 2/130
Introduction to
Ad-Hoc Networks

    Evolution of network
    communications –
    A new stage…
Introduction

   Two basic groups of ad-hoc networks:
     – Networks of mobile computers handled by users
     – Wireless sensor networks
   Basic characteristic:
    ability to establish network communication between hosts
    without any infrastructure needed.
     – The most significant advance compared to classic fixed systems
     – Reveals a very large scale of new possibilities




                               Page Number: 4/130
Introduction

 Ad-hoc networks may be considered
  as a new stage in evolution of network communications
 Fixed computer networks:
    – Concepts and mechanisms educed and amended for long time…
    – Lot of experiences acquired…
    – A useful base for origin and development of mobile networks...




                              Page Number: 5/130
Introduction

 Wireless communication has its peculiarities.
 Taking the already developed solutions is not possible.
    – In the beginning:
      modifications and adaptations of existing mechanisms.
    – Later: more and more of new ideas,
      relieved from the ballast of obsolete concepts.




                              Page Number: 6/130
Mobile Networks


     Meet the family…
Mobile Networks

 Not long time ago,
  mobile networks were treated
  just as extensions of fixed networks.
 Actors are:
    – Fixed hosts (FH)
    – Mobile hosts (MH)
    – Base stations (also known as mobility support routers – MSR)




                              Page Number: 8/130
Mobile Networks

Mobility Support Router (MSR)

 Every MSR supports the area limited by its range (wireless cell).
 MSR can communicate with MHs currently located in its cell.
    – MHs directly communicate only with MSRs
    – MHs can freely move from one cell to another



                                                     MH

                                    MSR

                                               MH
                           MH



                              Page Number: 9/130
Mobile Networks

Sending packets from FH to MH

 MSRs are bridges between the wired network and mobile hosts.
 When some fixed host (FH) wants to send a packet
  to a mobile host (MH), communication is divided into two parts:
    – Standard communication inside the fixed network,
      from FH to the proper MSR;                         MH
    – Wireless communication between MSR and MH.

                                 FH
                 FH
                                                          MSR

                                             FH                     MH
                         FH


                              Page Number: 10/130
Mobile Networks

Hiding mobility

 Mediation of MSR is entirely transparent to FH.
 For this kind of communication,
  indirect protocols were developed,
  with the purpose of hiding mobility
  from immobile hosts.                              MH


                                FH
                FH
                                                     MSR

                                            FH             MH
                        FH


                             Page Number: 11/130
Mobile Networks

One-hop wireless communication

 Direct communication between mobile hosts does not exist
 Mobility is very limited
  and dependant on the existing wired infrastructure:
     – MHs can move only within areas determined by the range of MSR,
       as well as by the range of its own transmitter;
     – Mobility is limited to only one hop
       between mobile host and fixed network
   Anyhow, a step towards real, multihop wireless networks.
     – Nature of wireless communications had to be considered
     – Later was of great benefit for development of ad-hoc networks




                              Page Number: 12/130
Mobile Networks

Nature of wireless communications

   Wireless vs wired links:
     –   Slower
     –   Less reliable
     –   Prone to loss of signal due to noise and fading
     –   With much more limited bandwidth
     –   With much more frequent occurrence
         of asymmetric quality of communication
   Mobile hosts are often disconnected from the fixed network
    for short or long periods of time:
     – Moving out of range
     – Exhausted battery
     – …



                                 Page Number: 13/130
Mobile Networks

Realizations and usage possibilities

 Wireless Local Area Network (WLAN);
 Connecting mobile and portable computers
  to existing widely used fixed networks like the Internet;
 …




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Mobile Networks

Drawbacks and limitations

   Infrastructure is needed…
     – Requires large investments
     – Time consuming installation
     – Communication cannot be always established
       where needed
     – Expensive maintenance




                             Page Number: 15/130
Mobile Networks

 In many cases it is necessary to establish a connection
  even if infrastructure does not exist, or is damaged.
 Typical example:
  alarming rescuers in case of earthquake, flood,
  war destruction…
 Communication must be established
  without any preliminary setup (ad-hoc).




                           Page Number: 16/130
Mobile Networks

Ad-Hoc Networks

   Mobile hosts
    can communicate
    between each other
    on much greater distances
    than covered by their ranges.
     – That is practicable
       thanks to presence
       of other mobile hosts
       that can be reached by the source host,
       and that are willing to retransmit its packets further on
     – Thus, propagating from one MH to another,
       packets are conveyed to the destination
   That is how multihop wireless communication
    through a temporally formed ad-hoc network is realized.



                                Page Number: 17/130
Routing in Ad-Hoc Networks


       How to find
      the right way?
Routing in Ad-Hoc Networks

   Efficient routing of packets
   In conventional networks,
    the most widely used routing algorithms are such as
    distant vector or link state
   Periodical broadcast,
    with the purpose of keeping routing tables up-to-date
   In some cases
    those algorithms were adapted to be used in ad-hoc networks
   We will just mention two representatives:
     – Destination-Sequenced Distance-Vector (DSDV)
     – Wireless Routing Protocol (WRP)
   Benefit: Route to every host in the network is always known.
    But…




                             Page Number: 19/130
Routing in Ad-Hoc Networks

   Drawbacks of adapted conventional routing algorithms
    seem to be of much more significance than the benefits:
     –   Large bandwidth overhead
     –   Batteries quickly become exhausted
     –   Significantly reduced scalability
     –   Unneeded cumulation of redundant routes
     –   Often not able to quickly enough respond to dynamics of changes
         in systems in which the hosts can move




                               Page Number: 20/130
Routing in Ad-Hoc Networks

On-demand routing protocols

 Because of specified constraints of said solutions,
  we are going to pay more attention on another approach,
  which is fundamental for the so-called on demand routing protocols.
 We will shortly describe three of those protocols,
  which attack the problem from different standpoints,
  introducing different assumptions
  and diversely prioritising problems that are to be solved:
    – Dynamic Source Routing (DSR)
    – Ad-Hoc On-Demand Distance Vector Routing (AODV)
    – Temporally Oriented Routing Algorithm (TORA)




                           Page Number: 21/130
Routing in Ad-Hoc Networks

 All the proposed solutions
  contribute to the apparent reclamation of performance,
  compared to classic algorithms,
  which work much better in the stationary environment
  for which they were designed in the first place.
 Algorithms that will be presented here are just specimens
  of a large number of solutions developed by now (ietf.org).
 New algorithms are still being developed and evolved.




                           Page Number: 22/130
Routing Protocols - DSR

1. Dynamic Source Routing (DSR)

   Based on the concept of source routing:
     – Sender provides the sequence of nodes
       through which the packets will be sent
     – Sequences are held in route cache
       that every host must maintain for itself
   Route is determined dynamically, when it is needed:
     – There are no periodical advertisements of routers
     – Instead, every host initiates route discovery
       when it needs to send a packet to another host
       for which initiator does not have the associated route in its cache




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Routing Protocols - DSR

Route Discovery – route request

   Initiated by sending a route request packet:
     – Propagates through the network
       until it reaches the destination host (if the route exists);
     – On its way, it collects addresses of all visited hosts,
       and stores them into its route record;


                                                                5
                          1        3              1,3,4
                                           1,3
                                                                    1,3,4,5
                 1
                src               1,2            4
                      1
                                                        1,3,4        6
                              2
                                                                    dst

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Routing Protocols - DSR

Route Discovery – route reply

 The first route request packet that arrives to destination is accepted,
  its route record is copied and returned to the initiator
  using the route reply packet.
 Destination host returns the route reply
  to the initiator of route discovery, using the route from its own cache.


                  (1,3,4,6)                          5
                               3
                                        (1,3,4,6)
              1
                                             4      (1,3,4,6)

                         2                                  6


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Routing Protocols - DSR

Route Discovery – route reply (2)

   If destination host does not have
    a route to the source host in its cache,
    there are two options:
     1. Route reply is returned using inverse route
        that was found by the route request packet;
     2. Destination host initiates route discovery
        to find a route to the original initiator.


   First option requires symmetric links:
     – Transfer quality must be the same
       in both directions;
     – But that is often not the fact
       in mobile communications.


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Routing Protocols - DSR

Route Discovery – route reply (3)

   Second opportunity (inverse route discovery,
    from destination to source) is more significant:
     – Providing support for non-symmetric links
       (very important merit of this algorithm).
     – I that case, the original route reply
       must be sent together with new route request,
       i.e. attached to it (that is called piggybacking)




                                Page Number: 27/130
Routing Protocols - DSR

Route Maintenance

 Implemented by acknowledgements
  and route error packets.
 Acknowledgements may be:
    – hop-by-hop – links must be symmetric
    – end-by-end – important when links are not symmetric




                             Page Number: 28/130
Routing Protocols - DSR

Route Maintenance (2)

   When using hop-by-hop
    acknowledgement:
    – Host which did not
      get acknowledgement                                     ?
      for its retransmission
      sends route error packet
      with information about hop that broke down;
    – Upon that error packet, source host truncates routing tree
      being held in its cache, at the point of that hop:


   When using end-by-end acknowledgement:
    – Information about the point of breakage does not exist;
    – Source host may only assume that the last hop is broken.


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Routing Protocols - DSR

Modifications / Optimisations

 Various modifications and amendments
  of this algorithm are feasible.
 We’ll mention just one of them –
  capability of working in the so-called
  promiscuous receive mode:
    – Host auscultate packets
      that were sent to other hosts,
      and updates its own cache
      according to the information thus received;
    – This, however,
      causes more power to be used
      and more rapid battery discharge .




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Routing Protocols - DSR

Summary – DSR merits

 Ability to work with asymmetric links.
 No periodical routing advertisement:
    – Enables bandwidth and energy conservation;
    – Overhead does not exist
      when there are no changes in the network.
   Can be easily improved to become able
    for providing multiple routes:
    – That way, it is not always necessary
      to initiate new route discovery when some link breaks.




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Routing Protocols - DSR

Summary – DSR drawbacks

Caused by the nature of source routing.
 Large bandwidth overhead:
     – Route request packets rapidly grow
       as they propagate through the network
       (in their route records they store information
       about every host over which they passed);
     – That causes potential huge route reply packets;
     – Also larger message packets,
       because addressing demands the whole route to be specified.
   Scalability problems – acceptable size of the network is limited:
     – Diameter of the network (the largest number of hops
       needed for communication between any two hosts in the network)
       directly refers to bandwidth overhead.


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Routing Protocols - DSR

Summary

   Dynamic Source Routing protocol
    is suitable for appliance in ad-hoc networks:
     – with moderate numbers of mobile hosts;
     – which move with moderate velocities.




                             Page Number: 33/130
    Routing Protocols - AODV

2. Ad-Hoc On-Demand
   Distance Vector Routing (AODV)

   New route is discovered in a manner
    that looks similar to route discovery by DSR:
     – Source host (src) broadcasts route request (RREQ) to all of its neighbours
       when needs to discover route to some destination host (dst);
     – Then, it waits for route reply (RREP).
   But similarity is discontinued at this point.

                                    ?
                                  src




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Routing Protocols - AODV

Route Request

   Sequence number
    – Number that every host generates for itself.
    – It is incremented every time when something
      is changed in adjacency (e.g., when some link breaks).
    – For every route, destination sequence number (DSN)
      is stored in the routing table
    – Last DSN that src earlier knew for any route to dst, is sent in RREQ,
      together with current sequence number of src
      and other information needed:

                  RREQ (src, dst, srcSN, dstDSN, … )




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Routing Protocols - AODV
   RREQ does not contain the route record:
     – Does not collect information
       about hosts through which it propagates;
     – Remembers only the number of hops.
   Instead, the host through which RREQ propagates
    adds inverse route (towards src) to its routing table:
     – Stores, together with other relevant information,
       the address of the neighbour (n1) that sent RREQ to it;
     – If that host later receives relevant RREP, it will automatically know
       that reply should be transferred to the neighbour (n1);
     – In that case, it also records the address of the neighbour (n2)
       that sent RREP, thus establishing route towards dst.


                         n1    RREQ
                                             RREP          n2
                          route to src      route to dst


                                 Page Number: 36/130
Routing Protocols - AODV

   Instead of recording the whole route, as with DSR applied,
    host here keeps only next hop (among other relevant information
    about some destination), i.e. address of its neighbour
    to which it transfers packets addressed to the destination:

      D                        3
                                                   5
      S         1            6: 4,6
      N      6: 3,4,6                        4
                         2
                                            6: 6       6

      A                        3
                                                   5
      O         1             6: 4
      D        6: 3                          4
                         2
      V                                     6: 6       6

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Routing Protocols - AODV

Route Reply

   When RREQ reaches a host that has a route to dst,
    comparison of DSNs from the packet and from the routing table
    is made:

     – If DSN from RREQ is greater                       DSN=10        DSN=10
        the host’s route to dst is not recent enough
        the host rebroadcasts the request;                     DSN(dst)=8

     – Otherwise, the host returns RREP to src,
       with the calculated information about the discovered route
       (total hop count, lifetime that remains…),
       among which more recent DSN,                        DSN=12
                                                          DSN=10
       copied from the routing table of the host.
                                                                 DSN(dst)=12


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Routing Protocols - AODV

 RREQ may reach dst itself, and then dst returns RREP to src.
 Anyway, RREP is returned using inverse route
  formed by intermediate hosts during the propagation of RREQ.




                                                   dst



                src




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Routing Protocols - AODV

Route Maintenance

 For every route
  that a host is acquainted with,
  it maintains the list of neighbours
  that use that route,
  so that it is able to notice them
  about eventual link breakage
  on the route.
 Link breakage is detected
  by the absence of hello messages,
  which must be emitted by every host
  after the specified time interval expires.




                            Page Number: 40/130
Routing Protocols - AODV

Summary – Advantages of AODV over DSR

   Significantly smaller
    network bandwidth overhead:
     – Both control and message packets are smaller;
     – The reason is the requirement of only two addresses when routing
       (destination and next hop), instead of the whole route
       as with sequenced routing;
     – This is good for scalability,
       because the size of a packet
       does not depend on the network diameter.
   Provides support for multicasting.




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Routing Protocols - AODV

Summary – AODV drawbacks

 Works only with symmetric links.
 Hosts must periodically advertise hello messages:
     – Increased bandwidth overhead;
     – Reduced possibility of energy conservation
       by remaining in the sleep mode.
   Does not support multi path routing
    (offers only one route per destination):
     – Every time when some link
       on the route breaks,
       new route must be discovered;
     – Increased probability of congestion.




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Routing Protocols - TORA

3. Temporally Oriented
   Routing Algorithm (TORA)

 Offers an interesting approach to problem solution.
 Conceived as link-reversal algorithm.
 The idea is to define topology of a network
  using a directed acyclic graph (DAG):
    – Hosts represented as nodes
      and with directed links;
    – Direction of link is realized
      by assigning height to every node,
      so that the link is directed
      from the node with greater height
      to the node with lower height.



                             Page Number: 43/130
Routing Protocols - TORA

General idea

 The destination node should have the minimal height in the graph.
 Other nodes get greater and greater height
  as the distance from the destination grows.
 Packets may be sent only from “higher” to “lower” nodes,
  i.e., only via downstream links.




                           Page Number: 44/130
Routing Protocols - TORA

DAG Forming

 Starts when node that does not have downstream links
  wants to send a packet to a destination node.
 Initially, all nodes in the graph have undetermined height (NULL),
  except the destination node that has the height of ZERO
  (which is considered less even from NULL).
 Source node then broadcasts QRY packet to its neighbours.
 QRY packet propagates through the network,
  marking every node over which it passes
  as “interested for route discovery”
  by setting its route request flag.




                           Page Number: 45/130
Routing Protocols - TORA

 When QRY packet arrives to a node
  that has at least one downstream link,
  the node then emits the UPD packet.
 UPD propagates back through the network,
  setting the height to all nodes with the route request flag set,
  at the same time resetting those flags.
 Every further node gets greater height
  then the precedent one on the path of the UPD propagation.




                                                     dst
                src



                            Page Number: 46/130
Routing Protocols - TORA

 Many downstream links can lead to the same destination.
 Algorithm enables multiple path routing.




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Routing Protocols - TORA

   In case of link break:
     – If the node still has downstream links left, no action is performed
     – Otherwise, the node broadcasts a UPD packet, thus recovering DAG
   Recovering is a one-pass process,
    except in the case of network partitioning




                               Page Number: 48/130
Routing Protocols - TORA

Advantages of TORA:

   Fast route discovery
   Multiple path routing
   Recovering is localised
   Multicast support
   Lightweight Adaptive Multicast (LAM) algorithm




                            Page Number: 49/130
Routing Protocols - TORA

Downsides of TORA:

 Requires external timing mechanism (GPS…)
 DAG becomes less optimal as the time passes
    – Can be solved using refresh packets




                             Page Number: 50/130
Routing Protocols - TORA
TORA is designed for:
 Large networks
 Many nodes with dense distribution




                          Page Number: 51/130
Issue of Security
in Ad-Hoc Networks



   There is no need to see
   his identification...
Attributes of security

The attributes of security are:
   Availability
   Confidentiality
   Integrity
   Authentication
   Non-repudiation.




                   Page Number: 53/130
    Attributes of security

   Availability    ensures the survivability of network services
  despite denial of service attacks.
 A denial of service attack could be launched
  at any layer of an ad hoc network.
 On the physical and media access control layers,
  an adversary could employ jamming
  to interfere with communication on physical channels.
 On the network layer disruption of the routing protocol
  can cause a break of the network.




                               Page Number: 54/130
    Attributes of security

   Confidentiality ensures that certain information
    is never disclosed to unauthorized entities.
   Leakage of information could have devastating
    consequences.
   Routing information must also remain confidential in some cases.




                               Page Number: 55/130
    Attributes of security

   Integrity guarantees that a message being transferred is
  never corrupted.
 A message could be corrupted because of benign failures,
  such as radio propagation impairment,
  or because of a malicious attacks on the network.




                             Page Number: 56/130
Attributes of security


   Authentication enables a node
  to ensure the identity of the peer
  node it is communicating with.
 Without authentication, an
  adversary could masquerade a
  node, thus gaining unauthorized
  access to resource and sensitive
  information and interfering with
  the operation of other nodes.




                            Page Number: 57/130
Attributes of security

   Non-repudiation ensures that that the origin
  of a message cannot deny having sent the message.
 Non-repudiation is useful for detection and isolation
  of compromised nodes.




                           Page Number: 58/130
Challenges and opportunities
  Attacks ranging from passive eavesdropping
   to active impersonation, message replay, and message distortion.
  Eavesdropping might give an adversary access
   to secret information, violating confidentiality.
  Active attack might allow the adversary:
      –   to delete messages,
      –   to inject erroneous messages,
      –   to modify messages, and
      –   to impersonate a node
    Violating availability, integrity, authentication, and non-repudiation.




                                Page Number: 59/130
Challenges and opportunities
  We should take into account the attacks
   launched from within the network, by compromised nodes.
  The ad-hoc networks should have a distributed architecture
   with no central entities.
  Introducing any central entity into our security solution
   could lead to significant vulnerability.




                           Page Number: 60/130
    Challenges and opportunities
   There are two sources of threats to routing protocols:
     – from external attackers
     – from compromised nodes




                              Page Number: 61/130
Challenges and opportunities
 Detection of incorrect information is difficult
 Outdated routing information
 False routing information generated by compromised nodes
  could be considered as the outdated information
 If routing protocols can discover multiple routers,
  nodes can switch to an alternative route




                         Page Number: 62/130
Challenges and opportunities
 Another way is to use diversity coding
 Diversity coding takes advantage of multiple paths
  in an efficient way, without message retransmission
 Even if certain routes are compromised,
  the received node may still be able to validate
  and to recover messages




                          Page Number: 63/130
Challenges and opportunities
   Cryptographic schemes
    – digital signature
    – public and private keys
 Key management service
 A public key infrastructure is superior in distributing keys
  and in achieving integrity and non-repudiation.
 In a public key infrastructure,
  each node has a public/private key pair.
 Public keys can be distributed to other nodes,
   while private keys should be kept confidential
   to individual nodes.




                                Page Number: 64/130
Challenges and opportunities
   There is a trusted entity called Certification Authority (CA)
    for key management.
   The CA has a public/private key pair
   Public key is known to every node
   CA signs certificates binding public keys to nodes
   The trusted CA has to stay on-line to reflect the current binding
   Although no single node is trustworthy in an ad hoc network
    we can distribute trust to an aggregation of nodes.
   Assuming that any t+1 nodes will unlikely be all compromised,
    consensus of at least t+1 nodes is trustworthy.




                             Page Number: 65/130
Challenges and opportunities
 This is the principle of distributed trust.
 To accomplish distribution of trust in key management service
  one can use threshold cryptography.
 An (n,t+1) threshold cryptography
  scheme allows n parties to share
  the ability to perform a cryptographic
  operation (e.g., creating a digital
  signature), so that any t+1 parties
  can perform this operation jointly,
  whereas it is infeasible for most t
  parties to do so, even by collusion.




                          Page Number: 66/130
Challenges and opportunities
 We divide the private key k of the service into n shares
  (s1,s2,…,sn), assigning one share to each server.
 Each server generates a partial signature for the certificate using
  its private key share
 With t +1 correct partial signature,
  the combiner is able to compute the signature for the certificate.
 Compromised servers cannot generate
  correctly signed certificates by themselves




                             Page Number: 67/130
    Challenges and opportunities
   A combiner can verify the validity of a computed signature
    using the service public key.
   In case verification fails
    the combiner tries another set of partial signatures.
   A problem with threshold cryptography is that it assumes
    synchronous system and an ad hoc network is asynchronous by its nature
   Any synchrony assumption is a vulnerability in the system
   Fortunately there is an asynchrony prototype of such a key management
    service, which has been implemented recently.




                               Page Number: 68/130
    Summary

   An ad hoc network is very vulnerable to many kinds of attacks.
   We have to protect not only the data, but also the routing information.
   The best way for that is a cryptography scheme
    with public/private key management, combined with distribution of trust.
   But it is not cheap and it is complex.
   A lot of things still have to be done in this area in the future.




                                Page Number: 69/130
Bluetooth


Following the steps of
King Harald...
    Bluetooth

Special Interest Group (SIG):
   Ericsson Mobile Communications AB
   IBM Corp.
   Intel Corp.
   Nokia Mobile Phones
   Toshiba Corp.




                             Page Number: 71/130
    Bluetooth

Bluetooth wireless technology:
   Open specification for short-range wireless connectivity
   Effortless, instant connections
   Wide range of communication devices
   Based on a radio link
   Facilitates fast and secure transmission of both voice and data
   Operates in a globally available frequency band




                                Page Number: 72/130
  Bluetooth

Bluetooth module:

• ports (USB, UART, PCM)
• baseband
• voltage regulator
• crystal
• radio
• antenna interface
• flash




                           Page Number: 73/130
Bluetooth

External interfaces:
• USB 1.1 (12 Mbps), full USB slave functionality
• UART (Rx, Tx, RTS and CTS), 460.8 kbs
• PCM (sync 8kHz, clock 200kHz-2MHz)



Antenna Interface:
• 50 ohm Bluetooth ISM band antenna (2.4 - 2.5 GHz)




                            Page Number: 74/130
Bluetooth

Communication layers:
• Base Band (BB)
• Link Manager (LM)
• Host Controller Interface (HCI)



Additional software:
• L2CAP
• RFCOMM




                             Page Number: 75/130
Bluetooth

Base Band General Description:
• Frequency hop transceiver
• Shaped, binary FM modulation
• Symbol rate is 1 Ms/s
• Slotted channel is applied with a nominal slot length of 625 ms.
• Time-Division Duplex (TDD) scheme
• Information is exchanged through packets
• Each packet is transmitted on a different hop frequency
• Combination of circuit and packet switching.




                              Page Number: 76/130
 Bluetooth
Bluetooth can support:
• Asynchronous data channel
• Up to three simultaneous synchronous voice channels
• Channel which simultaneously supports asynchronous data
  and synchronous voice




                               Page Number: 77/130
 Bluetooth

Bluetooth system consists of:
• Radio unit
• Link control unit
• Link management and host terminal interface functions




                                Page Number: 78/130
 Bluetooth

Connection types:            Master/slave communication:
• point-to-point             • piconets
• point-to-multipoint        • scatternets




                        Page Number: 79/130
Bluetooth

Other features:
• Link Manager Protocol
• Logical Link Control
• Service Discovery Protocol
                                                 Potential platform for
• RFCOMM                                       ad-hoc network realization!
• IrDA
• Telephony Control Protocol
• ...




                               Page Number: 80/130
Design of ad-hoc multihop sensor net
with Bluetooth: Lessons learned


        How to make your
        electronic devices
        cooperate with each other?
Introduction

The main goals of this project:

   Creating hw/sw specification for replacing and/or upgrading the
    existing wire systems for data acquisition and process control
     – Development of routing protocol
     – Connecting Bluetooth with a microcontroller (router)
     – Integration of routing protocol on the base Bluetooth chip
   Universal platform for wireless integration:
     – Stable and universal hardware platform
     – Reliable and easy replaceable software




                               Page Number: 82/130
System Overwiev

An open data acquistion system, based on wireless
ad-hoc multihop sensor network:

   Routing protocol
   Interface and routing module (IFRM)
   Personal Digital Assistant (PDA)
   Digital Signal Processing System (DSPS)
   Software for data acquisition (Shell)
   Internet accessible database




                           Page Number: 83/130
System Overview
                                            DSPS     PDA

simulated
 sensors                                    IFRM     IFRM
                                        Bluetooth   Bluetooth




                                       AD-HOC
             Bluetooth
                                       network



Web Server   Web
 database    client



                      Page Number: 84/130
System Overview

Basic advantages:
   Universal and open platform
   Can be implemented in any environment


Possibilites of use:
   Factories
   Power plants
   Health-care institutions
   Rescue actions
   Research of inhospitable terrain




                            Page Number: 85/130
System Overview

Main problems:
   Providing critical data transmission rate
   Stable ad-hoc networks


Proposed solutions:
   Bluetooth technology
   Designed routing protocol




                             Page Number: 86/130
Implementation - routing protocol

Designed with the following guidelines:
   speed
   reliability
   simplicity


 Existing solutions considered:
 DSR
 AODV
 TORA




                     Page Number: 87/130
Implementation - routing protocol

The routing algorithm defines three types of messages:
 Route Request (RREQ)
 Route Reply (RREP)
 Route Error (RERR)




                         Page Number: 88/130
Implementation - routing protocol

Route Request:

 RREQ:
 Hop Count   BCID     Dest Address    DSN          Source Address   SSN
 Hop Count – number of hops to the ending node
 BCID – unique RREQ identifier
 Destination Address – address to which the route is requested
 DSN – the last known sequence number
 Source Address – address of the node that issued RREQ
 SSN – current route sequence number




                             Page Number: 89/130
Implementation - routing protocol

Route Reply:

RREP:
                Destination               Source
 Hop Count                     DSN                    Lifetime
                  Address                 Address
Hop Count – numer of hops between the source and destination
Destination Address – address of node for which a route is found
DSN – route sequence number
Source Address – address of the node that sent RREQ
Lifetime – time in which the route is considered valid




                           Page Number: 90/130
Implementation - routing protocol

Route Error:

RERR:
                  Unreachable             Unreachable
 DestCount
                  Dest Address               DSN
DestCount – number of unreachable nodes
Unreachable Dest Address – address of the unreachable node
Unreachable DSN – last knows DSN, incremented by 1




                           Page Number: 91/130
Implementation - routing protocol

Functioning of the protocol:

 Master
 Gateway
 Slave




                     Page Number: 92/130
 Implementation - routing protocol
Possible network topology



   11 M4       master
                                   16 M3
               gateway
      8                                         9
      10       plain node
                                            2

          10                           12                                   14
                                                        3       6
                            0 M0                    7                13
     11 M4                                                                15 M5
                                   4    M1                  5   M2




                                   Page Number: 93/130
Implementation - routing protocol

System initialization:

 Forming of piconets
 Creation of neighboor tables
 Initialization of empty routing tables




                               Page Number: 94/130
 Implementation - routing protocol

Routing table entry

  Dest              Hop       Last        Next
            DSN                                       Precursors   Lifetime
 Address           Count    Hop Count     Hop
Dest Address – address of the destination node
DSN – destination sequence number
Hop Count – number of hops to destination
Last Hop Count – hop count before route invalidation
Precursors – list of forwarding nodes
Lifetime – time for which route is valid




                                Page Number: 95/130
Implementation - routing protocol

Sending RERR:

 Link is broken
 No active route to destination
 RRER is received from a neigboring node




                            Page Number: 96/130
Implementation - routing protocol

Simulation:

   Starting topology specified in the configuration file
   Number of nodes is not limited
   For each node, a separate thread of execution is created
   Messages and destinations are being generated in random fashion
   Traversing of nodes between piconets




                              Page Number: 97/130
 Implementation - routing protocol
Process of route discovery (RREQ forwarding)
                                                                        16 M3 M0            2       0
                                                            RREQ              M1            2       0
                                         M0     M1      0


                                                            2

                                                                       RREQ

                     RREQ
            11 M4                                               RREQ     4
                                8                                              M1
      M0   8     0                       RREQ    RREQ       1                 M0        1       0

                                              0 M0

                                                                 RREQ



                                                 RREQ
                            5       M2                                 3 M0        M1       0
                                                                                                RREP
               M0    3,7        0
               M1    3,7




                                           Page Number: 98/130
 Implementation - routing protocol
Process of route discovery (RREP forwarding)

                   6       M1       0



                                         RREP 4       M1
                                     1             M0        1         0
                                RREP               6         3,7       0
                   0 M0
           6   1       0

                                              RREP


                                            3 M0        M1         0




                                Page Number: 99/130
    Implementation - routing protocol
Usability analysis:
   Advantages compared to classic broadcast algorithms


            number of connections




                                                  number of nodes




                               Page Number: 100/130
    Implementation - routing protocol
Usability analysis:
   Elimination of redundant piconets



                                                                  slave hosts break connections
                                       master                                                     master
                       1                3           4                            1                 3       4
                                   2                                                          2

                                            master is detecting
                                            a new host
               5               5        5                                 5               5        5


           host is entering piconet                                   host is entering piconet

                                                             master
                                            1                 3           4
                                                        2
                                                                      5




                                                Page Number: 101/130
Implementation - IFRM
The routing protocol was implemented
in a separate hardware module:

   Serial (UART) connection with Bluetooth
   HCI level




                              Page Number: 102/130
Implementation - IFRM
The main functions of IFRM:
   Forming of a wireless multihop ad-hoc network
   Link maintenance
   Packet routing
   Route discovery
   Providing a transparent interface
    between the ad-hoc network and any serial (RS-232) device
   Providing PDA functionality




                               Page Number: 103/130
Implementation - IFRM
The architecture of IFRM:

                                                CON6
       External RAM                             ICSP
           16 KB
                                                                                       to Bluetooth
        (8 Kwords)                                                       CON4             module
                                                                      serial port 2
                                         PIC 17C756A
                                         microcontoller
                                                                         CON3              to host
                                                                      serial port 1   (sensor, PC, etc.)
       External FLASH
            ROM
            64 KB
         (32 Kwords)          CON2 & CON5                 signaling
                                I/O ports                   LEDs




                        to keyboard       to LCD
                         (optional)      (optional)



                                      Page Number: 104/130
 Implementation - IFRM
Routing protocol - host side
The modified AODV protocol, with the following restrictions:
    – Size of routing tables is limited to 79 entries
    – Communication in the network is server centric

                                MH                      MH
                                                                  MH



                                                             MH
                                                                                 MH
                                         MH
                     MH

                                                                       MH

                                               SERVER
                                                                  MH



                               MH
                                                                            MH
                                                        MH


                          MH


                       MH – mobile host (e.g. sensor)
                                  data flow

                                         Page Number: 105/130
 Implementation - IFRM
Routing protocol - host side

The modified AODV protocol, with the following restrictions:
    –   End-to-end flow control is omitted
    –   CRC checking and retransmission are not implemented
    –   Packet sequence is not checked
    –   Restrictions due to fact that Bluetooth modules do not conform
        to the Bluetooth V1.0B specification




                                  Page Number: 106/130
 Implementation - IFRM
Routing protocol - host side

Assumptions due to uncomformance to V1.0b specification:
   – In course of full-duplex communication
     there is no implicit master-slave switch
   – Inquiry and paging are possible
     without interfering with the current transmission
   – Only the master can broadcast on the piconet
   – A node can transparently be a member in more piconets
     (Bluetooth baseband controller is capable of transparent TD multiplexing)
   – It is possible to have more than 7 nodes in a piconet
     (parking and unparking is done transparently by the baseband controller)




                                Page Number: 107/130
 Implementation - IFRM
Routing protocol - host side

Bugs and workarounds:
   – Sending two consecutive broadcast packets causes a reset
   – During maximum full-duplex transfer,
     packets or parts of the packets disappear




                               Page Number: 108/130
 Implementation - IFRM

Connection of IFRM with the mobile host



                            IFRM
                                                                 Ad-hoc
          HOST                                       BLUETOOTH
                            Routing                              network
  (e.g. sensor, PC, etc.)                             MODULE




                              Page Number: 109/130
    Implementation - IFRM

Routing protocol - server side

   No routing module
   The software performs routing
   Special mechanism for implicit destination address discovery




                               Page Number: 110/130
    Implementation - IFRM
Routing protocol - server side

   Communication with Bluetooth
     –   TCP ports
     –   For each mobile host exists a corresponding TCP port on the sever
     –   Port numbers start from 10 000
     –   All communication is performed over the TCP/IP connections on these ports
     –   The mapping of ports and hardware addresses of Bluetooth modules is static



                 SERVER (PC)
                                                                   Ad-hoc
                  Expert system                BLUETOOTH
                                                                   network
                                                MODULE




                                   Page Number: 111/130
    Implementation - PDA
The role of PDA is to provide mobility to the expert.

   PDA is capable of receiving two types of messages:
     – Sensors have reported irregular data, but expert system managed to stabilize
       the system. The confirmation is required.
     – Sensors have reported irregular data and expert system did not manage
       to stabilize the system. The remote command and presence is required.
   PDA is capable of sending two types of messages:
     – Confirmation of received warning
     – Command that initiates some action in the system, based on received data
   In this phase, the internal battery supply is not designed.




                                  Page Number: 112/130
    Implementation - DSPS
DSPS is realised as an example of device
that can be connected to this platform.

 Based on TI Digital Signal Processor
 Gathering of information from different peripherals
 Real-time processing
 Transferring data to server over IFRM




                              Page Number: 113/130
 Implementation - DSPS
The DSPS architecture:         CON8:
                               Address, Data &
                               Control DSP Bus              Signaling
                                                            LED



                                                                    PWM
          CON8:    Resistor                                                    CON6:
          Analog   Capacitor                TI                      Capture    Event
          Inputs   Diode                                                       Manager
                   Matrix              TMS320LF2407                 Timer      A


                                    SPI                 SCI             CAN BUS
                                    Interface           Interface        Interface
                   CON 9:
                   Synchronous                  MAX3225             PCA82C250
                   Serial Link



                                                CON2:               CON3:
                                                RS232               CAN BUS
                   LCD (optional)


                         Page Number: 114/130
    Implementation - DSPS
DSPS Communication:

 Standard RS-232 connection (MAX3225cpp)
 CAN driver
 Synchronous Serial Interface (SPI)




                            Digital
                            Signal                Interface
        Analog Input                              Module
                          Processing              (IFRM)
                            Module




                           Page Number: 115/130
    Implementation - DSPS
DSPS function:

 Finding spectrum of some analog signal using FFT
 Transferring data to server via transparent ad-hoc network
 Receiving commands from the system,
  thus creating positive feedback system




                              Page Number: 116/130
    Implementation - Shell
Multipurpose software platform:

   Data acquisition
   Decision making
   Signal processing
   Slarming
   Tracking the current state
    of the system
   Database administration




                                 Page Number: 117/130
    Implementation - Shell
Communication with sensors:

 TCP/IP ports
 Two-way socket communication
 Conformance to IEEE 999-1992. SCADA specification




                             Page Number: 118/130
Implementation - Shell
                         System configuration:

                          Type of the sensor
                          Name of the sensor
                          Factory address of
                           corresponding Bluetooth module
                          Range of allowed values




            Page Number: 119/130
    Implementation - Shell
Readings display

 Simple view
 Graph view
 Real-time
  monitoring
 History




                   Page Number: 120/130
 Implementation - Shell
Spectrum analysis




                    Page Number: 121/130
    Implementation - Shell
Database

 Realized with MySQL Server
 ODBC
 Flexible, DBMS independent




                               Page Number: 122/130
    Implementation - Shell
Expert System

   Monitoring (controlling)
   Knowledge base
   Algorithm of direct chaining
   Based on preconditions (sensor readings) and using the rules,
    the expert system reaches a decision
   Depending on the actual application,
    any expert system with its knowledge base can be easily integrated




                               Page Number: 123/130
Implementation - Internet connectivity
The system database can be accessed from a Web client,
with the purpose of shortening the response time.

   MySQL Server
   PHP 4.0.4
   Apache Web Server 1.3.14




                               Page Number: 124/130
Implementation - Internet connectivity
Standard three-tier architecture is used:


                 http request           server
    web client
                 http reply




                                                       sql query
                                                                   DBMS
                                                       recordset
                                      PHP script




                                Page Number: 125/130
Implementation - Internet connectivity
Web client access:

 Username and password
 Choosing between sensors
 Formulating search queries:
     – by time
     – by value
   Extending the system
    towards full Internet automation




                                  Page Number: 126/130
Testing and integration
Separate component testing:

   Routing protocol
   IFRM
   DSPS
   PDA
   Shell
   Database
   Internet connectivity




                            Page Number: 127/130
Testing and integration
Component integration:

 Shell and database
 Internet access
 Communication between Shell and IFRM




                           Page Number: 128/130
Testing and integration
Final integration:

 Modification of the simulator
 Testing IFRM in the network with more than 100 nodes
 Integration of DSPS




                             Page Number: 129/130
Summary
   Indicating a new course of development of wireless communication
   Integration of different electronic devices in a single information network
   Open system: any device capable of serial communication can be connected
   Creation of custom ad-hoc networks
   Java-enabled microcontrollers
   Integration of the routing protocol on the Bluetooth baseband
   Possible improvements:
     –   Additional research of the routing protocol
     –   Testing IFRM in real-world working conditions
     –   Making software even more modular
     –   Development of several classes of sensors
     –   Potential GPS integration
     –   Internet automation




                                   Page Number: 130/130

				
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