Introduction to wireless ad-hoc network routing protocols

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Introduction to wireless ad-hoc networkrouting
protocols

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References

• INTERNET-DRAFT, Dynamic Source Routing protocol,
  1999
• Source .J. GARCIA-LUNA, M. SPOHN Source Tree
  Adaptive Routing Internet Draft,
  draft-ietf-manet-star-00.txt, work in progress,
  October 1999

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Ad hoc routing environment

• Nodes do not have a priori knowledge of topology
  of network around them, they have to discover it.
• Network topology changes rapid and frequently
• The power supply is not permanent

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Routing algorithms design considerations

• keep routing table reasonably small
• keep table up-to-date when nodes die, move or
  join
• require small amount of messages/time to converge
  
• save energy

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Routing algorithm types

• Classify by how router obtain control information
• Pro-active (Table-driven)
• These algorithms maintain fresh list of
  destinations and their routes.
• Reactive (On-demand)
• When no designed route is found, protocol finds
  one. Route is not so fresh as pro-active

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Reactive (On-demand) parameters

• All on-demand protocols differ on the following
  mechanisms
• How to flood-search packet and their response?
• How to cache information heard from node search?
• How to determine the cost of a link?
• How to determine the existence of a neighbor?
• You will see this in the following DSR protocol
  introduction

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Routing algorithm types (cont)

• Classify by what information router use
• Distance-vector
• Exchanges (target, distance)
• Exchanging routing table directly, and computing
  optimum path
• RIP, BGR
• Link-stat
• Exchanges (link (u, v), status)
• Exchanges link status and stores into topological
  database then compute optimum path on topological
  database
• OSPF, ad-hoc table driven protocols

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Routing algorithm design approach

• ORA (Optimum routing approach)
• Almost all wired routing algorithms,
• table driven ad-hoc routing algorithms
• LORA (Least-overhead routing approach)
• Limit the routing control information bandwidth
  (overhead)
• On-demand ad-hoc routing algorithms

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Dynamic Source Routing Protocol

• Reactive (On-demand)
• Source Route protocol
• INTERNET-DRAFT
• Expires 19 January 2005
• Simple to demonstrate the reactive protocol
• The reason that I choose it to presentation to u

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DSR is based on source routing

• each data packet sent carries in its header the
  complete, ordered list of nodes through which the
  packet will pass
• Header source-gtb-gtc-gt..-gtdestination
• WHY?
• allows the sender to select and control the
  routes used for its own packets

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DSR protocol algorithm

• Does route to destination is in route cache?
• Yes, send data.
• No, execute Route Discovery.
• A problem?
• The route information may be not be newest status
  of the current topology

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DSR Route Discovery procedure

• Send RREQ packet, Route Request
• RREQ will floods to neighbors recursively until
  destination
• RREQ will records the node it have passed
• Destination will compute a better route and put
  it with RREP, Route Reply
• Destination replies RREP to source, and now
  source knows the route to destination

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Flooding Algorithm
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Nodes receive the RREQ

• Does target in RREQ is me?
• Yes, reply RREP to initiator (sender)
• No, next question.
• Does initiator, route id and target is the same
  as the prior packet received
• Yes, discard the packet.
• No, append my address to the route records in
  RREQ and boradcast RREQ to neighbors

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Target replay RREP

• Does route to initiator is in route cache?
• Yes, send RREP to initiator
• No, execute Route Discovery for initiator but
  piggyback RREP on the RREQ to initiator (avoid
  route discover recursively)
• Why not reverse the route in route record as the
  route to initiator?
• It assumes the route is not bidirectional, this
  is common status in wireless transmission

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Send Buffer

• Packet will be stored in send buffer if its
  destination address is not discovered
• Packet will be stamped a stored time that it was
  placed in this buffer
• Packet will be discarded when the stored time is
  expired after send buffer timeout
• Buffer is FIFO Queue

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Send Buffer(2)

• If packet remains in the send buffer, the node
  will occasionally initiate new Route Discovery
  for the packets destination address
• exponential back-off algorithm to limit the rate
  to initiate new route discovery
• Doubling timeout between two successive discovery
  initiated

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Exponential back-off

• After i collisions, a random number of slot times
  between 0 and 2i - 1 is chosen
• 1st collision, the wait time may be 0, 1
• 2nd collision, wait time may be choose from 0,1,2
  and 3
• 3nd collision?

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Route maintenance

• In source route, each node transmitting the
  packet is responsible for confirming the data can
  flow over the link from the node to the next hop
• Acknowledgement is simple in wireless network,
  passive acknowledgement
• B can confirms receipt at C by overhearing C
  transmit the packet forwarding to D

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Software Acknowledgement

• network has no acknowledgement foundation
• the node transmitting the packet can explicitly
  requests a DSR-specific software acknowledgement
  be returned by the next node along the route
• When sender receives an SA, it will not send SA
  request for a period of time

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Software Acknowledgement(2)

• Node retransmitted SA request to a node C for a
  maximum times and has not been received any SA
  reply, it marks the node C broken link and return
  Route Error
• Flooding the Route Error to the source and node
  passed
• Source choose or discovery another route to
  destination node

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Source-Tree adaptive routing (STAR)

• Table-driven
• Source .J. GARCIA-LUNA, M. SPOHN Source Tree
  Adaptive Routing Internet Draft,
  draft-ietf-manet-star-00.txt, work in progress,
  October 1999

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Features

• Routing approach can be adaptive between ORA and
  LORA
• Using Source-Tree to compute the route path

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Route information router had

• Neighbor set
• Topology graphadjacent links source trees of
  neighbors
• Topology graph ? routers source tree
• Source tree ?route-selection algorithm ?route
  table

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Source Tree

• The set of links to destinations
• Each destination has only one route
• source tree can be viewed as set consist of route
  to each destination
• Derived route path from source tree is simple and
  quickly

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In Tree, there is only one route between any two
nodes
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Topology Graph cached available routes

• In Graph, there is one or more routes between
  any two nodes
• Topology Graph ? Source Tree
• Source tree stores active route set
• Topology Graph stores partial available route set

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In Graph, there is one or more routes between
any two nodes
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Link information is obtained by exchange source
trees

• Link information is obtained by exchange source
  trees
• Result
• When report a link to destination failed also
  indicates the new link to the destination
• Not send a LSU for failed link explicitly

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Exchange fail links comparison

• Exchange fail links info by LSU
• A discover L(B, W) failed
• A ? LSU(B, W, failed) (explicitly report failed)
• A ? LSU(C, W, new)
• Exchange fail links info by Source Tree
• A discover L(B, W) failed
• Compute new ST from TG
• A ? LSU(ST) (update implicitly failed link)

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LSU structure

• LSU(u, v, l, t)
• u denotes the link head
• v denotes the link tail
• l denotes the cost of the link
• t denotes the timestamp assigned to the LSU

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LSU exchange

• Valid LSU
• u, link head is the source of the LSU
• Timestamp of LSU is greater than timestamp in TG
  with the same source
• Remove link in TG
• If the link is not in any source tree reported by
  neighbors, then delete it from TG

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ORA

• Send LSU under these conditions
• Source tree changes
• Neighbor report a outdated LSU

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LORA

• Keep a route as long as it leads to the
  destination
• Not keep the optimum route
• Send LSU under these conditions
• Unreachable destination
• New destination
• Possible permanent routing loops
• Cost of routes exceeding the threshold

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Finished thanks!!

• HAVE any question?