Paper Mobile Service Discovery Protocol MSDP for Mobile AdHoc Networks

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Paper - Mobile Service Discovery Protocol (MSDP)
for Mobile Ad-Hoc Networks
Liang, Jui-Chi Chen, Jyh-Cheng Zhang,
Tao Autonomous Decentralized Systems, 2007.
ISADS '07. Eighth International Symposium
on 21-23 March 2007 Page(s)352 - 362 Digital
Object Identifier 10.1109/ISADS.2007.50
2007. 07. 04 Keon-il Jeong
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Contents
1. Introduction 2. Related works 3. The Mobile
Service Discovery Protocol 4.Simulation
Results 5.Conlustion
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Introduction

• MANET
• The networks are dynamically changing
• Has several common characteristics with p2p
  network
• Unstable links
• Deploying p2p networks directly in MANETs will
  induce heavy message overhead
• MSDP has
• Low message overhead
• Message overhead has greater influence on the
  overall performance
• Scalability and robustness
• The number of nodes in a MANET can change
  dynamically
• MANET should have stable performance and be
  scalable and robust

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Related Works

• ORION p2p file sharing protocol
• Search file by broadcasting message
• Group-based Service Discovery(GSD)
• Uses DARPA Agent Markup Language(DAML) to
  describe service information
• On-Demand Multicast Routing Protocol(ODMRP)
• Reduce the service query overheads
• Multi-layered Cluster structure
• Service discovery messages are delivered using
  clustered structure
• Allia Alliance-based Service Discovery protocol
• According to some rules, dynamic groups can be
  formed
• Konark
• Is programmed to run on cell phones
• MSDP
• Group nodes in a MANET into clusters and use DHT

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The Mobile Service Discovery Protocol
1. Dynamic Cluster Formation

• Every node
• Has a 128-bit integer as the unique
  identifier(UID)
• Apply the SHA1 to nodes IP address or MAC
  address
• Has three states - Unknown, Member, or Head
• The radius of the cluster is CSIZE hops from the
  cluster Head
• Has a countdown timer whose maximum value is
  TIMER_MAX sec
• Broadcasts a Hello Message(HM) every
  HELLO_INTERVAL sec
• With time-to-live field set to one
• HM contains the UID and state of the sender
• HM contains the neighbor information and the
  cluster information including nodes within CSIZE
  hops and cluster heads within (2 X CSIZE 1) hops

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The Mobile Service Discovery Protocol
1. Dynamic Cluster Formation

• Sending rate of the HM can be changed
• Upon hearing a HM, a node handles incoming HMs
• Store the UID and state of each node the HM
  carries in its Neighbor Table

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The Mobile Service Discovery Protocol
1. Dynamic Cluster Formation

• A node executes alogorithms2 when its countdown
  timer expires

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The Mobile Service Discovery Protocol
1. Dynamic Cluster Formation

• The cluster formation process
• Assume that all nodes are initially in Unknown
  state (a)
• They exchange HMs and learn the existence of
  their neighbors
• The timers of the nodes with local minimal UIDs
  will expire first
• Then make these nodes changes their states to
  Head (b)
• When the Unknown nodes receive HMs from the Head
  nodes
• Then they change their states to Member (c)
• A node does not have local minimal UID nor is it
  under coverage of any Head nodes (Node 6)
• After the timer of this node expires, it becomes
  Head node (d)
• Finally, all nodes are either in Head or Member
  state and clusters are formed

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The Mobile Service Discovery Protocol
1. Dynamic Cluster Formation
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The Mobile Service Discovery Protocol
2. Service Discovery and Caching

• Use SHA1
• Input service information or description
• Output an integer key
• Use Consistent Hashing
• Map the integer to one of the keys in the UID key
  space
• Keys in the UID key space are sorted in
  increasing order and form a circular linked-list
• If the size of the key space is n, takes an
  integer i as input and finds the nearest key k
• K is the smallest key that is no less than (i mod
  n)
• If (i mod n) is greater than the largest key in
  the key space, then k is the smallest key in the
  key space

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The Mobile Service Discovery Protocol
2. Service Discovery and Caching

• When a user want to find a specific service
• Packs service description along with the 128-bit
  ID used to represent the description in a Service
  Request packet
• And sends the packet to the Head he belongs to
• When a Head receives the Service Request
• It uses consistent hashing to map the ID to one
  of its Member nodes
• And relays the Service Request
• When the Member node receives the Service Request
• It checks its own service database
• If found, it sends back a Service Reply
  containing the service information
• Otherwise, it sends back a Service Reply with no
  service information
• If the user receives a Service Reply that
  indicates no service
• With the help of the local cluster head broadcast
  a Service Request to all Head nodes
• Head nodes query all the Member nodes they have

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The Mobile Service Discovery Protocol
2. Service Discovery and Caching

• If the user receives a Service Reply that
  indicates no service (Cont.)
• Eventually, the user will receive a Service Reply
• After assuring the availability of the service,
  the user sends out a Service Publish packet to
  his cluster head
• The head uses consistent hashing to map the
  service information to a Member node and relays
  the packet to that Member
• The Member receives the Service Publish
• Then caches the service information in its
  database
• Later when other users in the cluster wish to
  access the same service, their requests can be
  fulfilled locally
• Caching service information can reduce the
  message overhead occurs during service discovery
  process

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The Mobile Service Discovery Protocol
2. Service Discovery and Caching

• In the MSDP, the service information items are
  cached in soft states
• When a service information has not been accessed
  for EXPIRE_PERIOD seconds
• It will be removed from the cache database
• Two advantages of using soft state to store
  service information
• First, service providers do not have to
  periodically update their service
• Less network resources are consumed
• Second, frequently used services will stay and
  services that are not in popular demands will be
  removed quickly
• This leads to more efficient use of node storage
  space

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Simulation Results

• Implemented the MSDP and the Chord in ns2
• Three metrics
• Message overhead
• Is the total number of packets generated
• Reply-to-Query Ratio (RQR)
• The probability that a user correctly receives a
  service reply of a service request he sends
• Cache-to-Reply Ratio (CRR)
• The probability that a service reply sent by a
  user is received from a local cache

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Simulation results

• The simulation results under static scenario

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Simulation results

• The simulation results under different mobile
  moving speed
• From pedestrian speed(5 m/s) to vehicular
  speed(20m/s)
• The degradation of the RQR of the MSDP is mainly
  due to the underlying physical layer limitation
• The degradation of the RQR of the Chord is due to
  the physical layer limitation and the large
  amount of message overhead (a)

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Simulation results
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Simulation results

• The simulation results under different mobile
  moving speed with slow moving service providers
  (Figure 4)
• The service provider is less than 2 m/s while the
  speed of the ordinary mobiles ranges from 5 m/s
  to 20 m/s
• The simulation results under different mobile
  moving speed with fast moving service providers
  (Figure 5)
• The moving speed of service providers ranges from
  5 m/s to 20 m/s while the speed of ordinary users
  is less than 2 m/s
• The number of service providers is fixed at 20
• The MSDP can efficiently maintain the stability
  of clusters and provide good quality of service
  in terms of RQR
• The RQR of the Chord protocol is unfavorable due
  to the large amount of message overhead

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Simulation results
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Simulation results
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Conclusion

• The MSDP
• Combines dynamic cluster formation and
  distributed hash tables
• Can efficiently organize the MANET to provide
  service information caching
• has steady performance in terms of service
  information discovery and caching
• is able to minimize the network resources
  consumption
• In the future
• Extend out work to cross-layer design that
  combines network routing protocol with service
  discovery protocol
• Extend our MSDP to work under other environment
  and on different hardware technologies