ODMRP (On-Demand Multicast Routing Protocol in Multihop Wireless Mobile Networks )

1
ODMRP(On-Demand Multicast Routing Protocol in
Multihop Wireless Mobile Networks )

• Sung-Ju Lee
• William Su
• Mario Gerla
• Presented By
• Meenakshi Bangad

2
ODMRP

• Introduction
• Basic operation of ODMRP
• Performance Improvement of ODMRP using mobility
  prediction
• Simulation analysis of ODMRP
• Conclusion

3

• Introduction
• Issues in Ad Hoc Networks
• Bandwidth Constraints
• Frequent Topology changes
• Limited Battery power
• Problems with Current Multicast Routing
  Protocols
• They have a tree based structure, so as the
  node connectivity changes, the tree
  structures changes accordingly.
• Multicast trees require a global routing
  substructure
• involving excessive channel and
  processing overhead

4

• ODMRP
• Provides a richer connectivity among multicast
  members using a mesh based approach
• Supplies multiple route for one particular
  destination
• Helps in case of topology changes and node
  failure
• Uses a concept of Forwarding Group
• Only a subset of nodes forwards multicast packets
  via scoped flooding

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• Basic Operation of ODMRP
• On Demand Route and Mesh Creation
• Join Query
• Join Reply
• S floods a Join Query to entire network to
  refresh membership.
• Receiving node stores the backward learning into
  routing table and rebroadcasts the packet.
• Finally when query reaches a receiver creates a
  Join Reply and broadcasts its to its neighbors.
• Node receiving the Join Reply checks whether the
  next node id in Join Reply matches it own. If yes
  , it is a part of the forwarding group, sets its
• FG_FLAG and broadcasts its join reply built upon
  matched entries.
• Join Reply is propagated by each forwarding group
  member until it reaches source via a shortest
  path.

R
S
R
R
R
R
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• Concept of Forwarding Group
• Why a mesh?
• Links
• Multicast Routes
• Initial Route from S1 to R2 is lt S1 -A- B- R2gt
• Redundant Route lt S1- A- C- B- R2gt

FG
FG
FG
FG
FG
FG
R1
S1
A
B
S2
C
R3
S3
R2
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• Example of Join Reply Forwarding
• Join Reply of Node R1 Join Reply of Node I1

R1
S1
I1
R2
S2
I2
R3
Sender Next Node
Sender Next Node
S1 I1
S1 S1
S2 I2
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• Reliability in ODMRP
• Reliable transmission of Join Replies plays an
  important role in establishing and refreshing
  multicast routes, hence proper care should be
  taken for delivering the Join packets properly.
• As Join replies are broadcasted to more than one
  upstream neighbors, IEEE 802.11 MAC protocol
  fails here. (e.g. Join Reply from R1).
• Two approaches to solve this problem
• Sub-divide the join Replies into separate
  sub-tables, one for each distinct node. For e.g.
  Split the Join Reply at R1 into I1 and I2 and
  unicast these packets.
• It works good if the number of neighbors are
  limited.
• Passive Acknowledgement

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• Passive Acknowledgement
• A B C
• Transmission
• Passive Ack Transmission
• Source should send an active acknowledgement to
  the previous hop.
• Issues
• Hidden Terminal Problem Node may not hear
  acknowledgement from its upstream neighbors.
• It can be solved by carrying out retransmissions
  in unicast mode to selected neighbors with
  reduced sub-tables. An alternate route must be
  found on spot if packet delivery cannot
  be verified after certain no. of transmissions

A
B
C
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• Finding a route On spot
• Each node broadcasts a packet to its neighbors
  specifying that the next hop to a set of sources
  is unreachable.
• If a node upon receiving this packet has a route
  to the multicast source, it unicasts a Join reply
  to its next hop neighbors .
• If no route is known it simply broadcasts the
  packet specifying that the next hop is
  unavailable.
• In both cases it sets its FG_FLAG.
• It helps in establishing an alternate path until
  a more efficient route is established during the
  next refresh phase.

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• Data Forwarding
• A node forwards the received multicast data
  packet only when it is not a duplicate one and
  the setting of FG_FLAG for that multicast group
  has not expired.
• Soft state
• No explicit control packet need to be sent to
  join or leave a group.
• If a multicast source wants to leave a group, it
  simply stops sending the JOIN QUERY packets.
• If a receiver o longer wants to receive from a
  multicast group it does not send the JOIN REPLY
  for that group.
• Forwarding nodes are demoted to non-forwarding
  nodes if not refreshed( no Join Replies received)
  before they timeout.
• Unicast Capability
• It can operate as an unicast routing protocol
  also as well as coexist with any unicast routing
  protocol.

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• Selection of Timer values
• For Route Refresh Interval
• Small Route Refresh Interval used
• Fresh route Information and membership
  information obtained. Flow of more packets
  causing network congestion.
• Large Route Refresh Interval used
• Up to date information about the nodes in the
  network is not known.
• Less control traffic generated .
• For Forwarding group timeout Interval
• In heavy network load, timeout values should be
  small so that unnecessary nodes can timeout
  quickly and create excessive redundancy.
• In network with high mobility, the forwarding
  group timeout value must be larger so that
  alternate paths can be provided.
• Generally forwarding group timeout value must
  be 3 to 5 times larger than the route
  refresh Interval

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• Required Data Structures
• Route table
• Entry is updated upon receiving a JOIN
  QUERY.
• Stores the destination (source of the Join
  Query) and the next hop destination (node from
  which Join Query is received from).
• Forwarding Group Table
• Every node in the forwarding group maintains
  the group information. It records the multicast
  group id and the time when the node was last
  refreshed is recorded.
• Message cache
• Every node maintains this structure to
  detect duplicate.
• Whenever a node receives a Join query or a
  data packet it stores the source ID and the
  sequence number of the packet.
• Entries in here are not permanent.

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• Adapting the Refresh Interval via Mobility
  Prediction
• Periodic flooding of Join query to refresh routes
  and group membership is not a good idea due to
  bandwidth constraints.
• Enhancing the performance of ODMRP demands
  selection of an optimal route interval .
• GPS (Global positioning system) provides location
  and mobility information of a node. Thus Join
  Queries can be sent only when route breaks of
  ongoing data session are imminent.
• In the paper, assumption is made that the clocks
  are synchronized by NTP or GPS itself at boot
  time.
• By the knowledge of speed, direction and radio
  propagation range, one can determine how long a
  node will remain connected.

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• Adapting the Refresh Interval via Mobility
  Prediction
• Suppose 2 nodes i and j are within the
  transmission range r of each other.
• (xi, yi) co-ordinates of mobile host i
• (xj, yj) co-ordinates of mobile
  host j
• vi and vj speeds of i and j respectively
• oi and oj moving directions of I and j
  respectively
• Amount of time i and j will stay connected is
  predicted by
• Dt - ( ab cd ) (a2 c2) r2 (ad bc
  )2
• a2 c2
• where
• a vi cos oi - vj cos oj vj
• b xi xj
• c vi sin oi - vi sin oj and
• d yi - yi

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• Steps taken for Mobility Prediction
• Along with the Join query which the source sends,
  it also appends Location, Speed and Direction.
• Source sets the MIN_LET( Minimum Link Expiration
  Time) field to MAX_LET_VALUE since the source
  does not know any previous hop node.
• Next hop neighbor predicts the LET by using the
  showed equation.
• The minimum between the value and the MIN_LET
  value from the Join Query received is overwritten
  in the packet and sent. The location , speed and
  direction are also overwritten by its own value.
• Join Query upon reaching the multicast member,
  the predicted LET of the Last link is calculated
  and the minimum of the two (LET and MIN_LET in
  Join Query) is chosen to be the RET( Route
  Expiration Time)
• The RET is enclosed in Join Reply and is
  broadcasted.
• Nodes in a forwarding group when receive multiple
  join replies , the one with the minimum RET is
  chosen, attached to the packet and broadcasted.
• Source on receiving multiple Join Replies chooses
  one with minimum RET

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• Advantages of Mobility Prediction
• The whole idea of calculating the RET is new
  routes should be built via flooding before the
  minimum RET approaches.
• A minimum of a refresh interval should be set
  MIN_REFRESH_INTERVAL . It is required in case of
  high mobility of nodes to avoid excessive
  flooding.
• A maximum of a refresh interval should be set
  MAX_REFRESH_INTERVAL . This is required when the
  mobility of nodes is very slow.
• It may happen that a node suddenly moves
  out, new routes wont be constructed on time.
• It is also required if a new non-member node
  wants to join the group.

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• Route Selection Criteria
• Generally multicast receiver selects routes based
  on the minimum delay.
• Instead, a receiver can choose the most stable
  route one with the maximum RET.
• In this case the receiver needs to wait for some
  appropriate amount of time after the first join
  query calculate all possible routes and select on
  with largest RET and broadcasts the Join Reply.
• (1,2) (3,3) (i, j)
• (3,5) Link with delay i and LET j
• (4,5) (2,4)

B
S
A
R
C
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• Simulation Analysis
• ODMRP was simulated in GloMoSim simulation
  environment with 4 other multicast routing
  protocols.
• Channel and Radio was assumed to be a free space
  propagation model.
• The IEEE 802.11 MAC with Distribution
  Coordination function (DCF) was used.
• ORMRP implementation was carried out without
  mobility prediction scheme.

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• Metrics considered for Simulation
• Packet Delivery Ratio
• Number of packets transmitted per data packet
  delivered
• Number of control bytes transmitted per data byte
  delivered
• Number of control and data packets transmitted
  per data packet delivered

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• Simulation Results
• Mobility Speed
• Packet delivery ratio as well as the Number
  of data packets transmitted per data packet
  delivered is high even when the Mobility speed
  increases.
• Number of control bytes transmitted per
  data byte delivered as the function of mobility
  speed remains constant.
• Number of Senders
• As the number of Senders increases, the
  performance of ODMRP increases in terms of Packet
  delivery ratio and Number of data packets
  transmitted per data packet delivered.
• Control Packet overhead is high.
• Multicast Group Size
• Performance of ODMRP is unaffected by the
  growth in the number of multicast members.
• Network Traffic Load
• As the network load increases, the
  performance of ODMRP in terms of Packet delivery
  ratio keeps on decreasing , but its performance
  is still better than the other 4 protocols
  implemented.

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• Conclusion
• Features of ODMRP
• Simplicity
• Low channel and storage overhead
• Usage of Up-to-date shortest routes
• Reliable construction of routes and forwarding
  group
• Robustness to host mobility
• Maintenance and utilization of multiple paths
• Exploitation of the broadcast nature of the
  wireless environment
• Unicast routing capability
• Area to be looked into
• ODMRP has a problem of excessive flooding when
  number of multicast senders are more.
• One solution to this is to make the route
  refresh as receiver initiated or one can make
  ODMRP adaptive to the way the network changes.