Authors: Ing-Ray Chen and Ding-Chau Wang

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Modeling and Analysis of Regional Registration
Based Mobile Multicast Service Management
Presented by Anish Sunkara Mahmoud ElGammal
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Overview

• Introduction
• Related Work
• Protocol Description
• Simulation Model
• Performance Evaluation
• Conclusions and Future Work

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Introduction

• Multicasting delivering data from a single
  source to multiple receivers.
• Results in great cost savings when implemented
  efficiently
• Minimizing data duplication otherwise, little
  advantage to multiple connections to the source.
• Minimizing the distance traveled by each packet
  otherwise, results in low QoS.
• Challenges faced by mobile multicasting
• Dynamic group membership.
• Dynamic member topology.

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Important Terms

• MH Mobile Host ( leaf node in the multicast
  tree)?
• MMA Mobile Multicast Agent ( non-leaf node in
  the multicast tree)?
• HA Home Agent
• FA Foreign Agent

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Basic Schemes for Mobile Multicasting 1/2 Remote
Subscription (RS)?

• MHs have to subscribe to their multicast group
  whenever they enter or change their foreign
  network.
• Update frequency to multicast tree hand-off
  frequency.
• Advantages
• Data is always delivered on the optimal shortest
  path.
• Disadvantages
• High overhead for reconstructing the multicast
  tree whenever a hand-off occurs.
• Doesn't handle source mobility.

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Basic Schemes for Mobile Multicasting 2/2
Bi-directional Tunneling (BT)?

• Each MH receives its multicast data via unicast
  from its HA.
• Advantages
• Handles source mobility as well as recipient
  mobility.
• No need to update the muticast tree on each
  hand-off.
• Disadvantages
• The routing path for muticast packet delivery may
  be far from optimal.
• Must replicate and tunnel multicast packets to
  each MH regardless of which foreign networks they
  reside in (limited scalability).

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Proposed Solution (URRMoM)?

• User-oriented Regional Registration-based Mobile
  Multicast.
• A user-centric design allowing each MH to
  determine its optimal MMA service area
  dynamically.
• Combines the advantages of RS and BT.
• Attempts to minimize the total network traffic
  generated due to multicast packet delivery, as
  well as multicast tree maintenance overhead.

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Related work (1/3)?

• Local Registration
• Each MA manages a list of multicast groups that
  have MHs in its service area.
• An MA receives multicast packets for a group, and
  then tunnels them to FAs that host visiting MHs
  in the group.
• Advantages
• Relatively stable structure.
• Avoids frequent modifications to the multicast
  tree.
• Disadvantages
• Doesn't adapt to each MH's mobility pattern,
  resulting in a high traffic volume.
• Each MA represents a single point of failure.

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Related work (2/3)?

• mMOM (Mobility-based Mobile Multicasting)
• MHs apply either RS or BT according to mobility.
• High mobility -gt BT
• Low mobility -gt RS
• Every MH must re-register with its FA after a
  period of residence time.?
• According to whether the FA receives the
  re-register message or not, the MH's degree of
  mobility is decided, and either BT or RS is used.
• Advantages
• Simple and Practical
• Disadvantage
• Does not allow co-located care-of-address to be
  used as in Mobile IP.

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Related work (3/3)?

• Range-Based Mobile Multicast (RBMoM)?
• Employs a Mobile MA (MMA) to tunnel packets to
  the FA to which the MH is currently attached.
• The information about which MMA is currently
  serving a MH is recorded at the MHs HA.
• If a MH is out of the current MMAs service
  range, then a MMA handoff occurs and another MMA
  will take over the multicast service for the MH.
• Adapts to MH mobility, but incurs unnecessary
  communication overhead
• When an FA subscribes to the multicast tree as an
  MMA, all other FA in its range have to be
  notified of this subscription.
• Each time a MH moves into the area of a FA, it
  has to query it for the nearest MMA.

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URRMoM Protocol Description

• The MMA is responsible for tunneling multicast
  packets to the FA under which the MH currently
  resides as long as the FA lies within the MMA's
  service area.
• Each MH has only one MMA at a time with its MMA
  being changed from time to time as it roams in
  the network.
• Similar to BT, except that a MH receives
  multicast data by its MMA which changes
  dynamically instead of from the HA which is
  static.

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URRMoM Protocol Description

• The regional service size of a regional MMA is
  expressed in terms of the number of subnets
  covered by the regional MMA.
• Each MH keeps a counter to record the number of
  subnets the MH has crossed within the service
  area of its MMA.
• When the MH crosses the boundary of a subnet, the
  MH will first check if the new FA of the subnet
  is already in the multicast group (if the FA is
  itself a MMA of other MHs).

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• If the current FA is already a MMA for other MHs,
  the MMA of the MH will be updated to the current
  FA even though the MH is still within the service
  area of the last MMA. The counter in the MH will
  be reset to 0 after a MMA reset.
• If the current FA is not in the multicast tree
  yet, the counter in the MH will be incremented by
  one in response to the subnet crossing event.
  Multicast packets would be tunneled from the MMA
  to the current FA before they are finally
  forwarded to the MH.

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• When the MH moves across the regional service
  area such that the counter reaches the regional
  area size (R) and if the new FA is not an MMA
  itself, the new FA will subscribe to the
  multicast tree and become a new MMA for the MH.
• When all MHs under a MMA leave, the MMA will
  unsubscribe from the multicast tree.

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Types of Moves in RRMoM
Intra-Regional Inter-Regional
Definition Occurs when a MH performs a location handoff within a multicast service area of a regional MMA. Occurs when a MH moves across a service area (that is, the counter reaches R), thus incurring a multicast service handoff.
Action The MMA is changed only if the new FA it enters into is itself a MMA for other MHs. In this case, the MHs MMA is updated to the current FA. Otherwise, the MHs MMA remains the same. The MMA will always be changed. If the new FA is itself a MMA, then the MHs MMA is simply updated to the current FA. Otherwise, the current FA becomes the MHs new MMA and a multicast tree subscription event is triggered to add the new MMA to the multicast tree.
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Finding Optimal R

• There exists an optimal service area size that
  will minimize the network traffic generated due
  to mobile multicast services.
• This value is a function of
• MH mobility and population.
• The size and topology of the network.

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Simulation Model

• The model considers a multicast group with a
  single source.
• The source is a fixed host.
• Group memberships don't change, but MHs may roam
  dynamically from one subnet to another.
• M MHs in the group.
• The network is a square nxn mesh where each node
  has exactly 4 neighbors.
• Each node corresponds to a subnet with a FA.
• Each MH can move in any of the four directions
  randomly with equal probability.

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Simulation Model (cont.)
Each node corresponds to a subnet, each having
its own FA.
Is fixed
A MH in one node can move freely into any of
the four directions connecting it to the other
nodes with equal probability.
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Simulation Model (cont.)

• Assuming that a MH's residence time in FA is
  exponentially distributed with mean µ.
• It can be shown that the arrival rate of a MH to
  any FA in our nxn mesh is ? µ/(n2-1)
• The arrival/departure process of M MHs to a FA
  can be modeled as an M/M/8/M
• When a FA is not serving any MHs, it will
  subscribe from the multicast tree.

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Simulation Model (cont.)

• The probability of a FA not serving any hosts is
  P0, which can be calculated as (1-1/n2)M
• The average number of members in the multicast
  group being served by a single FA can be
  calculated as
• A MMA on average will cover R subnets, so the
  average number of multicast members a MMA covers
  is
• Thus, the number of MMAs in the system is roughly
  
• The probability that a FA that a MH just entered
  is a MMA (PMMA) can be calculated as
• The optimal service size R depends on the
  tradeoff between the multicast group management
  costs vs. the tunneling cost.

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Symbol Meaning
Move a timed transition for the MH to move across a subnet areas.
Moves Mark(moves)1 means that the MH just moved across a subnet.
MH2MMA a timed transition for the MH to inform the current MMA of the CoA change.
PMMA probability that the FA that the MH just enters is already a MMA in the multicast tree.
Xs Mark(Xs) holds the number of subnets crossed by the MH in a multicast service area.
Subscribe a timed transition to inform the multicast source that the current FA will be added into the multicast tree.
R service area covered by a MMA (number of subnets covered by a MMA).
Release a timed transition for the MH to claim the current FA as its MMA.
GuardMark(tmp2)ltgt0 a guard for transition Release that is enabled if the MH moves to a subnet whose FA is already a MMA.
GuardMark(Xs)R a guard for transition Subscribe that is enabled if the number of tokens in place Xs is equal to R.
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Symbol Meaning
? arrival rate of a MH to any FA in the n by n network.
µ MHs departure rate in a FA.
M number of MHs in the multicast group.
Pi probability of state i in the queuing network model.
?m number of join or leave operations to the multicast tree per unit time.
?p number of multicast packets delivered per unit time.
ß average number of hops to reach the source for multicast tree subscription/un-subscription.
R number of subnets (or FAs) in one service area covered by a MMA.
n average number of MHs in the multicast group in one FA.
rsub transition rate of Subscribe.
qi probability of state i in the underlying Markov or semi-Markov model of the SPN model.
t 1-hop communication delay in wired networks.
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Cost Function

• CMaintenance Cost incurred per unit time due to
  control packets for tree management MMA
  Subscription cost MMA Un-subscription cost
• CService Cost per unit time for delivering
  multicast packets from the multicast source to
  MHs in the multicast group.
• Goal is to find optimal service area when given a
  set of parameter values characterizing the
  operating and workload conditions.
• Observations
• Optimal Service size by a MMA Determined by
  trade off between C (maintenance) C (service)
• Expect Cm to increase and Cs to decrease as R
  (Regional Area Size) decreases
• As R increases, Cm will decrease and Cs will
  increase.

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Maintenance Cost

• ?m Number of join or leave operations to the
  multicast tree/unit time
• rsub Rate at which a member subscribes a new
  MMA to the multicast tree after it has crossed R
  subnets
• Let ß Average number of hops separating a MMA
  and multicast source.
• Let t Average per-hop communication cost.
• Total Subscription Rate rsub x M
• Total Un-subscription Rate

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Service Cost

• CService Cost for multicast packet delivery,
  given by the rate at which packets are generated
• ?P Number of multicast packets delivered per
  unit time.
• Number of hops for multicast packet delivery from
  the multicast source to MMAs is
• Number of hops through which packets are tunneled
  from various MMAs to M MHs is
• The steady state probability of state i, qi , 1lt
  i lt R, needed is solved easily from the SPN
  model utilizing solution techniques such as SOR
  or Gauss Seidel.

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Numeric Data Analysis

• Total traffic generated as a function of the
  service area size R expressed in terms of the
  number of subnets
• Optimal service area size under which the network
  traffic generated is minimized
• As the mesh network becomes larger (as n
  increases), the optimal service area size becomes
  larger and larger

Cost vs. Regional Area Size (R) with varying n.
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Cost vs. R with Varying Number of MHs

• The network traffic generated vs. R as M varies
  in an 8 by 8 mesh network.
• As M increases the optimal R decreases.

Cost vs. R with varying number of MHs
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Effect of the Distance between Source and MMA

• As ß increases, the optimal range R increases for
  the case when M is fixed at 100
• Reason, s the distance separating the source and
  MMA increases, the maintenance cost increases, so
  the system prefers to have a large service are to
  reduce the rate of tree subscription/un-subscripti
  on operations

Effect of Distance between Source and MMA
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Comparison of URRMoM vs RS and RBMoM

• A comparison of the network traffic generated due
  to maintenance vs. the network size n for URRMoM
  vs. RS and RBMoM at optimizing R values under the
  same set of parameter values.
• URRMoM always produces the least amount of
  network traffic compared with RS and RBMoM
• Reason, RS is just a special case in which R1,
  while URRMoM incurs a overhead

Comparison of URRM0M vs RS and RBMoM
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Simulation

• An SMPL simulation has been conducted to validate
  the analytical results reported in Numerical Data
  and Analysis section.
• To ensure statistical significance of simulation
  results, a batch mean analysis (BMA) technique
  has been adopted in which simulation period is
  divided into batch runs with each batch
  consisting of 2,000 cost rate observations for
  computing an average value.

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Results

• Cost vs R with varying n

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Results

• Cost vs R with varying number of MHs

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Results

• Comparison of URRMoM Vs. RS and RBMoM

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Conclusions

• The proposed URRMoM model combines the advantages
  of RS and RBMoM models.
• This approach combines distinct performance
  advantages of remote subscription and
  bi-directional tunneling.
• The proposed URRMoM system has simpler system
  requirements less computation complexity than
  the RBMoM system.
• Effect of Key parameters such are Regional Area
  Size (R) are provided.
• Both Analytical and Simulated results are shown
  to optimize the service size covered by the MMA.

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Future Work

• Plan to perform empirical validation of the
  URRMoM system in an experimental testbed.