Session IV: Wireless Protocols Summary

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Session IV Wireless ProtocolsSummary
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Goals

• Protocols for QoS on the move for the wireless
  Internet.
• Better understanding of how channel access and
  network-layer work and inter-operate in ad hoc
  networks.

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Participants

• Prof. Mary Baker, Stanford University
• Security, packet scheduling
• Prof. Jennifer Hou, UIUC
• Topology control, JavaSim
• Prof. J.J. Garcia-Luna-Aceves, UCSC
• Channel access, routing, and topology control
• Prof. Elizabeth Belding-Royer, UCSB
• Security and intrusion detection

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Talks Today

• Flow-oriented protocols for large-scale wireless
  networks J.J.
  Garcia-Luna-Aceves
• Packet Scheduling in Ad Hoc Networks Mary Baker
• Design and Analysis of an MST-Based Topology
  Control Algorithm Jennifer Hou

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Flow-Oriented Protocols for Scalable Wireless
Networks

• J.J. Garcia-Luna-Aceves
• Computer Communication Research Group (CCRG)
• UC Santa Cruz
• http//www.cse.ucsc.edu/research/ccrg

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Premise

• In theory, multihop packet-radio networks (mobile
  ad hoc networks or MANETs) are great for
  establishing instant communication
  infrastructures.
• In practice, achieving multimedia communication
  on the move and instant information
  infrastructures is still a big challenge,
  specially in very large MANETs!
• Efficient use of channel bandwidth, coping with
  mobility, providing performance guarantees,
  handling hundreds to thousands of mobile nodes,
  coping with battery-life issues.
• Much more work is needed before MANETs can
  achieve QoS on the move on a large scale.
• MAC, routing, and topology management.
• They need to be addressed using an integrated
  approach!

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Channel Access

• Contention-based protocols
• No coordination, carrier sensing, collision
  detection, collision avoidance (e.g., 802.11b and
  a), and collision resolution.
• Conflict-free
• Fixed assignment (TDMA, FDMA), reservations,
  polling, token passing, topology-independent
  assignment, dynamic assignment.

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Collision Avoidance

• Positives
• Simple, very common.
• Channel assignment is related to the traffic that
  needs to use the channel.
• Limitations
• Really meant for WLANs, not MANETs.
• Collision avoidance is meant for unicast
  transmissions only!
• De facto standard (802.11) does not prevent
  collisions.
• Channel assignment is unfair and not very
  efficient.

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Numerical Results (ICNP 2002)

• Throughput for long data packet lrts lcts
  lack 5 ?, ldata 100 ?.

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Analysis Results

• IEEE 802.11 MAC protocol has fairness problem,
  i.e., some nodes can monopolize the channel for a
  long time while other nodes suffer severe
  throughput degradation.
• IEEE 802.11 MAC protocol has imperfect collision
  avoidance and cannot achieve the max throughput
  predicted in the analysis in most cases.
• When network size increases, CA becomes less
  effective and increasing spatial reuse becomes
  more important.
• Nice agreement with simulation results

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Dynamic Conflict-Free Assignment

• Positives
• Designed for MANETs.
• No collisions, better throughput and fairness.
• Support for multipoint communication.
• Negatives
• Channel assignment is not related directly to
  flows traversing the network.
• Although the capacity of the protocol is very
  high, the utilization of the channel may be lower
  depending on traffic patterns.

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Dynamic Conflict-Free Assignment

• Types
• Node activation (broadcast transmissions)
• Link activation (unicast transmissions)
• Hybrid activation (broadcast, unicast and
  multicast)
• Information used
• Complete topology information
• e.g., UxDMA (Ramanathan, WINET 99)
• Neighborhood information (2 hops)
• e.g., NAMA, LAMA, PAMA, HAMA
• (Bao an Garcia-Luna-Aceves ICNP 2002, Mobicom
  2001, Mobicom 2002)

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Distributed Scheduling Using 2-Hop
Neighborhood Data

• Determine the contenders of a node or link
  competing for activation.
• Use a neighbor protocol to distribute 2-hop
  information.
• Compute the priority of each contender at each
  node
• Use a hashing algorithm taking into account
  current time for fairness.
• Avoid hidden-terminal problems among winning
  contenders.
• Use code or space division.
• Choose at each node a subset of the suitable
  contenders for data transmission based on their
  priorities.
• This amounts to anticipatory collision
  resolution based on two-hop neighborhood
  information.

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Dynamic Scheduling (HAMA) vs UxDMA (ICNP2002)
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CA vs Dynamic Scheduling(Analytical, ToN
submission)
HAMA
NAMA
CA
CSMA

• Dynamic scheduling is much better than CA
  however, it is not enough!

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Need for Flow Activation

• With link or node activation, the opportunities
  for collision-free transmissions are not related
  to the flows traversing the MANET.
• Channel may go without use if there is no traffic
  to be transmitted by node A or over link (A,B)
  when the entity is activated.
• We need data packets to obtain access to the
  channel quickly and without conflicts!

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Flow-Aware Scheduled Transmission (FAST) Protocols

• Run the anticipatory collision resolution using
  flow identifiers as the entities competing for
  channel access.
• A flow ID can be
• sourcedestinationseq.number assigned by source
• Use a neighbor protocol to communicate competing
  flows.
• Flows can be unicast or broadcast, single hop or
  multihop.
• Some other details Distance of a node to flow
  source, hidden terminals.
• Note This assumes routing information is
  available to guide the dissemination of flow
  information (along shortest paths to flow
  destinations).

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Simplistic Scenario
M
N
O
P
I
J
K
L
E
F
G
H
C
D
A
B
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Results for Simplistic Case
Packets Received in Saturation
Fairness!
Fairness!
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Problems

• Supporting signaling flows (broadcast, one hop)
  and data flows (unicast, multihop)
• A hybrid approach is needed
• Expediting flow information dissemination as flow
  change.
• Analytical and simulation modeling of
  flow-oriented scheduling schemes.
• Good traffic and mobility assumptions,
  interactions among layers.
• Interaction between routing and scheduling
• Establishment of links for signaling flows
  enables routing control packets to be exchanged.
• Routing tables enable data flow establishment.

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Routing Issues

• Routing protocols are monolithic
• One flavor of signaling for all classes of
  destinations
• One flavor of routes (single path) for all
  classes of traffic to destinations.
• Routing layer in MANETs assumes that routing
  takes place over a given topology, just like
  Internet routing protocols like OSPF and RIP do.
• The existence of radio connectivity does not
  imply the availability of a logical link in a
  MANET.
• We need FAR MORE!

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Flow Adaptive Routing (FAR)

• Goal is Scaling and QoS Support
• Develop routing techniques that are node-centric
  (no clusters) and adapt dynamically to the flows
  in the network.
• How a routing table entry for a destination is
  obtained and maintained is a function of the type
  of flow towards the destination.
• Proactive and on-demand mechanisms used according
  to flow types.
• Different flows are given resources (paths)
  according to their types and priorities.
• Routing works in coordination with scheduling.

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FAR Our First Step Is NEST(poster)
No interaction with MAC. Node-oriented, rather
than flow oriented
Each common node (e.g., a) keeps paths to the two
netmarks proactively but not to the common nodes.
Paths to common nodes are found on demand. Much
of the traffic is to/from netmarks.
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Problems

• Combine update or route-discovery process with
  scheduling mechanism
• Primordial signaling flows must exist (broadcast,
  single hop)
• More signaling flows may have to be added
  (unicast or multicast, multiple hops)
• Data flows have to be added based on traffic
  demand (unicast or multicast, multiple hops)
• MAC and routing protocols must share information
  network layer must control MAC layer based on QoS
  constraints.
• How should netmarks be selected and be known
  based on flow characteristics?
• Topology management
• Not all nodes (netmarks) are equal!
• Some nodes may carry only some classes of flows

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Topology Management by Priority Ordering
(poster)
Uses 2-hop neighbor data. Enables the definition
of backbones for signaling and data
flow. Outperforms prior heuristics.
Can be extended to account for flow-oriented
classes of backbones. Mcast as topology
mgmt Note Flows and reputations, willingness
and centrality
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CART A Chicken Egg Triangle
scheduling establishes links needs routes to
destinations of flows
establishing routes needs links for
collision-free transmission of control
packets packet forwarding needs links for
collision-free transmission of data packets
Multicasting needs a convenient topology
topology control determines nodes links that
can be used for certain functions needs links
for collision-free transmission of control
packets, and dissemination of neighborhood data
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Moving Forward... Look at integrated scheduling,
routing and topology management
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Collaboration

• Use JavaSim to implement FAST at UIUC/UCSC
• Use JavaSim to implement FAR at UCSC
• Joint research on topology management between
  UIUC and UCSC
• Invited lectures

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Progress and Results

• 15 refereed papers being published in 2002
  (ACM Mobicom 2002 7 accept rate, IEEE ICNP
  2002 14.7 accept rate, , and other ACM and
  IEEE conferences).
• Two Ph.D. students will be graduating this and
  next quarter.
• Program Co-Chair of ACM MobiHoc 2002.
• Keynote speaker at ACM MSWIM 2002 Workshop.
• Research results are being applied to networks
  with directional antennas in collaboration with
  Raytheon (DARPA FCS program).