QoS Routing for mobile ad hoc networks

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QoS Routing for mobile ad hoc networks

• Chenxi Zhu, M. Scott Corson
• INFOCOM02
• 2002. 09. 18
• Presented by Dong Wook Kim

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Contents

• Introduction
• The Network Model
• The Path Bandwidth Calculation Problem
• The QoS Routing Protocol
• Simulation Results
• Discussions of the QoS and Be Protocols
• Conclusion
• Discussions

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Introduction 1/2

• Quality of service is more difficult to guarantee
  in ad hoc network
• Low capacity
• Wireless bandwidth is shared among adjacent nodes
• Route change
• Network topology changes as the nodes move
• The ability to provide QoS is heavily dependent
  on how well the resources are managed at the MAC
  layer

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Introduction 2/2

• The object
• Develop a QoS routing protocol for ad hoc
  networks using TDMA
• Establish bandwidth guaranteed QoS routes in
  small networks whose topologies change at low to
  medium rate
• The protocol is based on AODV, and builds QoS
  routes on an On-demand basis
• (QoS requirement bandwidth of time slots)

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The Network Model 1/3
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The Network Model 2/3
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The Network Model 3/3
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The Path Bandwidth Calculation Problem 1/2
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The Path Bandwidth Calculation Problem 2/2

• For the link (nk1 ? nk), only three sets of
  slots, PBk1k ? PBk1k-1 ? PBk1k-2 are
  calculated
• this is sufficient because transmissions of links
  further downstream do not interfere with
  transmissions of (nk1 ? nk)

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PB3 calculation
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The QoS Routing Protocol 1/2

• Routing protocol is AODV
• Bandwidth is calculated on its path as a RREQ
  packet is forwarded hop by hop
• This excludes any node other than destination to
  generate a route reply (RREP)
• Except local reply when the route is
  re-established
• If BW(FP) lt R (required bandwidth), RREQ is
  dropped and no RREP is generated
• If a RREQ reaches the destination via a path P, a
  route satisfying the bandwidth requirement has
  been found

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When a source node (S) wants to setup a QoS route
for a flow a destination (D),
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The QoS Routing Protocol soft-state of a QoS
route 2/2

• The state of a QoS route at a node
• NONE
• REQ
• A RREQ to set up the QoS route has been
  processed, but the QoS route is not established
  yet
• RESV
• The QoS route has been set up and is used to
  forward data packets
• BRK_U
• The QoS route is broken at upstream of this node
• BRK_D
• The QoS route is broken at downstream of this
  node
• Transitions among these states are triggered
• receiving or transmitting a packet
• expiration of the timer associated with the state
• Link layer feedback

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1) NONE ? REQ i) When the source sends a RREQ
When a non-source node receives and forwards a
RREQ When the destination receives a RREQ and
verified ii) These nodes record reverse
pointer iii) The length of the timer is
Route_setup_time 2) REQ ? NONE i) When no route
is setup and the timer expires 3) REQ ? RESV i)
When the destination sends out a RREP ii) When a
node on the route receives a RREP iii) These
nodes record forward pointer iv) The length of
the timer is Route_setup_time 4) RESV ? RESV
(refreshed) i) When the route is used to transmit
a data packet belonging to this flow ii) The
timer is reset to Route_life_time 5) RESV ?
BRK_U i) When no data packet arrives for
Route_life_time ii) QoS route is broken at the
upstream iii) the time is set to Route_setup_time
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• 6) BRK_U ? RESV
• When the QoS route which was broken at upstream
  is restored
• 1gt a data packet belonging to this flow arrives
  (link is recovered)
• 2gt a node nk receives a RREQ packet from node
  nk1
• ? after calculating the bandwidth of the
  path FPk and verify
• ? sends out a RREP back to nk1 local
  reply
• (even though it may not be destination)
• what makes the local reply feasible
  is the part of the original QoS route from
• this node to the destination still
  exists
• local reply reduces the delay to
  restore a broken route
• ? a node sending a local reply also sends a
  route hold packet (RT_HLD) towards
• the destination

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• 7) BRK_U ? NONE
• i) If it cannot be restored when the timer
  expires
• ii) The slots TSkP are released
• 8) RESV ? BRK_D
• i) When a node finds the link to its downstream
  breaks
• ii) It sends a RERR towards the source
• iii) So, When it receives a RERR packet from its
  downstream neighbor
• 9) BRK_D ? REQ
• i) The source sends out a new RREQ as soon as it
  receives the RERR
• ii) When the node on the route receives and
  forwards a RREQ packet
• iii) The timer is set to Route_setup_time
• 10) BRK_D ? NONE
• i) If no RREQ arrives before the timer expires
• ii) The slots TSkP are released
• 11) RESV ? NONE

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Simulation Results
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Discussions of the QoS and BE Protocols

• BE protocol (original AODV protocol)
• Whether QoS can be achieved in a highly mobile
  network is questionable
• All the packets are sent through at most one
  route
• Cause congestion on this route under heavy
  traffic
• QoS routing protocol
• Packets transmitted on QoS routes are guaranteed
  of bandwidth
• Provide load balancing
• Disadvantages
• A QoS RREQ often travels further than a BE RREQ
• A long QoS route is more difficult to build and
  to maintain than a short one, especially under
  mobility
• It is not considered multiple QoS routes can be
  set simultaneously
• They may compete for the same set of slots and
  interfere with on another

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Conclusion

• An on-demand QoS routing protocol based on AODV
  is developed for TDMA-based mobile ad hoc network
• The QoS routing protocol is likely useful only
  for short routes, and in networks of low mobility
• QoS routes should be built and used as complement
  to, not substitute for, best-effort routes

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Discussions

• Correctness and reliability of the FA
• Why is it sufficient if we consider adjacent
  three sets of slots?
• If we use the FA, can we calculate correctly a
  bandwidth between adjacent nodes?
• Is there a obvious basis we are able to believe?
• The FA is made by these authors and doesnt be
  proved any theories
• Until now, most research areas have been limited
  only to use TDMA as the MAC layer protocol
• Generally, a node uses IEEE 802.11
• This area is worth researching with hard
  perspiration!!!