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Introduction to wireless adhoc network routing protocols

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????? ???? A ?. ?????. References. INTERNET-DRAFT, Dynamic ... Adaptive Routing Internet Draft, draft-ietf-manet-star-00.txt, work in progress, October 1999 ... – PowerPoint PPT presentation

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Title: Introduction to wireless adhoc network routing protocols


1
Introduction to wireless ad-hoc networkrouting
protocols
  • Speaker ????
  • ??? N9490001
  • ????? ???? A ?
  • ?????

2
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

3
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

4
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

5
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

6
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

7
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

8
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

9
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

10
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

11
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

12
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

13
Flooding Algorithm
14
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

15
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

16
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

17
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

18
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?

19
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

20
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

21
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

22
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

23
Features
  • Routing approach can be adaptive between ORA and
    LORA
  • Using Source-Tree to compute the route path

24
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

25
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

26
In Tree, there is only one route between any two
nodes
27
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

28
In Graph, there is one or more routes between
any two nodes
29
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

30
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)

31
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

32
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

33
ORA
  • Send LSU under these conditions
  • Source tree changes
  • Neighbor report a outdated LSU

34
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

35
Finished thanks!!
  • HAVE any question?
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