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# Routing  in  Ad  Hoc   Wireless  Networks

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## Routing  in  Ad  Hoc   Wireless  Networks

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### Routing  Algorithms

•  Each  node  maintains  a  view  of  the  whole  network  topology

•  Find  the  shortest  path  over  the  network

•  Maintain  the  topology  information  by  periodical  ﬂooding

### •  Distance-­‐Vector  algorithm

•  Each  node  maintains  the  distance  of  each  destination  and  the   corresponding  next  hop

•  Periodically  send  the  table  to  all  neighbors

•  Also  known  as  distributed  bellman-­‐ford

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### Distance  Vector

C

Dest. Next Metric

A A 1

B B 0

C   C 2 Dest. Next Metric

A A 0

B B 1

C   B 3

1 2

Dest. Next Metric

A B 3

B B 2

C   C 0

B A

C

Dest. Next Metric

A A 1

B B 0

C   C 2 Dest. Next Metric

A A 0

B B 1

C   B 3

1 2

Dest. Next Metric

A B 3

B B 2

C   C 0

B A

(A, 1) (B, 0) (C, 1) (A, 1)

(B, 0) (C, 1)

2

2

update

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### •  Time-­‐variant  wireless  channel

•  Link  breakage  is  common  in  wireless  network  à  Connectivity  problem

•  Links  are  not  always  bidirectional  and/or  symmetric

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### C

Dest Cost Next  Hop

A 1 A

C 1 C

Dest Cost Next  Hop

A 2 B

B 1 B

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### C

Dest Cost Next  Hop

A Inﬁnity Null

C 1 C

Dest Cost Next  Hop

A 2 B

B 1 B

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### C

Dest Cost Next  Hop

A 3 C

C 1 C

Dest Cost Next  Hop

A 2 B

B 1 B

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### C

Dest Cost Next  Hop

A 3 C

C 1 C

Dest Cost Next  Hop

A 4 B

B 1 B

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S!

n4!

n2!

D1!

n8!

n7!

n6!

D2! n3!

n5!

### Existing  Routing  Protocols

S!

n4!

n2!

n3!

D!

S!

n4!

n2!

n3!

D!

➼X!

Table-Driven:!

• S and all other nodes maintain full routing information!

• Require periodic table update!

Hybrid Scheme!

• Network is divided into multiple zones!

• Use Table-Driven within the zone!

• Demand-Driven across the zones through boundary nodes!

Demand-Driven!

• Route is discovered when S wants to talk to D !

• A Route only needs to be maintained for as long as S and D are still talking !

• EX: Dynamic Source Routing (DSR)!

Zone A!

Zone B!

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### •  Proactive

•  Table  driven

•  Rely  on  periodic  update   to  keep  track  of  the   topology  change

•  No  latency  in  route   discovery

•  Need  large  storage  space   to  keep  information  of   the  entire  network

•  A  lot  of  routing

information  may  never   be  used

### •  Reactive

•  On  demand

•  Route  Discovery  by  local  ﬂood   or  gossiping

•  Additional  latency  during  route   discovery

•  Not  appropriate  for  real-­‐time   communication

•  Route  maintenance

•  Feedback  from  Link  Level   ACK

•  Issue  new  route  discovery   when  link  breaks

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### •  Sequence  number  indicates  the  “freshness”  of  a  route

•  Routes  with  more  recent  sequence  numbers  are  preferred  for  packet   forwarding

•  If  same  sequence  number,  one  having  smallest  metric  is  used

C. E. Perkins and P. Bhagwat. “Highly dynamic Destination Sequenced Distance-Vector routing (DSDV) for mobile computers”, In Proceedings of the SIGCOMM ’94

Conference on Communication Architecture, Protocols and Applications, pages 234-244, August ‘94.

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### •  For  each  reachable  node  in  the  network  the  routing  entry  contains:

•  Next  Hop

•  Distance  (Metric)

•  Sequence  Number

Destination Next Hop Distance Sequence Number

A A 0 S205_A

B B 1 S334_B

C C 1 S198_C

D D 1 S567_D

E D 2 S767_E

F D 2 S45_F

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### DSDV  –  Table  Update

C

Dest. Next Metric Seq

A A 1 A-­‐550

B B 0 B-­‐100

C   C 1 C-­‐588 Dest. Next Metric Seq

A A 0 A-­‐550

B B 1 B-­‐100

C   B 2 C-­‐588

Dest. Next Metric Seq.

A B 2 A-­‐550

B B 2 B-­‐100

C   C 0 C-­‐588

B

A 1 2

1 2 C

B A

update

(A, 1, A-500) (B, 0, B-102) (C, 1, C-588)

(A, 1, A-500) (B, 0, B-102) (C, 1, C-588)

Dest. Next Metric Seq

A A 1 A-­‐550

B B 0 B-­‐102

C   C 2 C-­‐588 Dest. Next Metric Seq

A A 0 A-­‐550

B B 1 B-­‐102

C   B 2 C-­‐588

Dest. Next Metric Seq.

A B 2 A-­‐550

B B 1 B-­‐102

C   C 0 C-­‐588

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Dest Cost Next

Hop Seq.  #

A 1 A 1

C 1 C 1

Dest Cost Next

Hop Seq.  #

B 1 B 1

C 1 C 1

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### C

Dest Cost Next

Hop Seq.  #

A Inﬁnity Null 2

C 1 C 1

Dest Cost Next

Hop Seq.  #

B 1 B 1

C 1 C 1

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### C

Dest Cost Next

Hop Seq.  #

A Inﬁnity Null 2

C 1 C 1

Dest Cost Next

Hop Seq.  #

A 2 B 1

C 1 C 1

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### •  Assign  a  metric  of  ∞  to

•  Any  route  through  a  hop  with  a  broken  link

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### DSDV  -­‐  Summary

•  Simple  (almost  like  Distance  Vector)

•  Loop  free

•  No  latency  for  route  discovery

•  Most  routing  information  never  used

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### •  Assumptions

•  All  nodes  are  willing  to  participate

•  The  network  size  is  small

•  The  degree  of  network  dynamics  is  moderate  with  respect  to  the   packet  transmission  latency

•  All  nodes  are  overhearing  (promiscuous)

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### •  Route  Discovery

•  Route  Request  (RREQ)

### •  Route  Maintenance

•  Route  Error  (PERR)

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### •  Source  node

•  Broadcasts  the  Route  Request  (RREQ)  <id,  target>

### •  Intermediate  node

•  Discards  if  the  id  has  been  seen  before,  or  node  is  in   the  route  record  (header  of  RREQ)

### •  Destination  Node

•  Use  previously  cached  route  to  source  node

•  Call  Route  Discovery  for  source  node,  with  route   reply  piggy  backed

•  Use  reverse  sequence  of  Route  Record,  in  case  of   bidirectional  links

D. B. Johnson, D.A. Maltz, and J. Broch. “DSR: The Dynamic Source Routing Protocol for Multi-Hop Wireless Ad Hoc Networks”, Ad Hoc Networking, pages 139-172, 2001.

A

A,B

A,B,F

A,B,F,E

A,B,F,E

A,B,F,E

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### •  Monitoring  the  route

•  Passive  Acknowledgement  –   overhearing  the  next-­‐hop  node   sending  packet  to  its  next-­‐hop

•  Set  a  bit  in  packet  to  request  explicit   next  hop  acknowledgement

### •  Route  Error

•  Notify  source  of  the  broken  link  via   Route  Error  (RERR)

•  Source  truncates  all  routes  which  use   nodes  mentioned  in  RERR

•  Initiate  new  route  discovery

### E F

F  transmits  the   packet  I  just  sent  to   her.  That  means  she

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### Optimization  1:  Route  Caching

•  Use  cached  entries  to  create  RREP   at  intermediate  node

•  S  ﬁnds    route  [S,E,F,J,D]  to    D,  S  also   learns    route  [S,E,F]  to  F

•  F  receives  Route  Request  [S,E,F]

destined  for  some  node  D,  F  learns   route  [F,E,S]  to    S

•  Promiscuous  mode  to  add  more   routes

•  Caching  overheard  RREQ/RREP   I  heard  A

said  B-­‐C-­‐D

### G H

I’m  4-­‐hop   away  from

D

I’m  2-­‐hop   away  from  D   Where  is  D  ?

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### Optimization  1:  Route  Caching

•  A  lot  of  neighbors  know  the  route  to  target  and  attempt  to  send  RREP   in  response  to  RREQ

•  Solution:  Delay  RREP  for  a  period  d=H*(h-­‐1+r)

•  r  :  random  number  between  0  and  1

•  H  :  small  constant  delay

•  h  :  number  of  hops  to  source  from  that  node

•  Out-­‐of-­‐date  cache

•  Cached  routes  may  become  invalid

•  Stale  or  invalid  information  may  be  propagated  to  whole  network

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### hop

•  Increase  TTL  to  a  larger  value

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### •  Gossip-­‐Based  Routing

•  Node  forward  packets  with   some  probability  pG  <  1

### •   How  good  is  it?

•  35%  less  overhead  than   ﬂooding

G

### S

D

Gossip: Probabilistic Flooding "

Z. Haas, J. Halpern and L. Li, Gossip-based ad hoc routing, in: IEEE INFOCOM (2002)

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### •  Sub-­‐Critical

•  Low  connectivity

•  Mobile  nodes  are  sparsely   distributed  in  the  network

•  Performance  is  limited  !!

### •  Super-­‐Critical

•  High  connectivity  region

•  Most  or  all  the  nodes  can   communicate

Connectivity: Fraction of nodes that is connected to the network!

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### •  Protocol  overview  -­‐  Pure  on-­‐demand  protocol

•  Node  does  not  maintain  knowledge  of  another  node  unless  it   communicates  with  it

•  Routes  discovered  on  as-­‐needed  basis  and  maintained  only  as  long  as   necessary

•  Nodes  not  involved  in  the  route  should  not  pay  any  cost

•  No  cost  to  deal  with  out-­‐of-­‐date

C. E. Perkins and E. M. Royer. “Ad-Hoc On Demand Distance Vector Routing”, Proceedings of the IEEE Workshop on Mobile Computing Systems and Applications (WMCSA), pages 90-100, 1999.

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### •  Initiation

•  Source  node  sends  a  Route  Request  (RREQ)  when  it  has  no   information  about  destination  node  in  its  table

•  RREQ  contains

•  Source  and  destination’s  address  and  sequence  number

•  Hop  count

### •  Reverse  Path  Setup

•  Reverse  paths  are  formed  when  a  node  hears  a  route  request

•  Neighbor  increments  hop  count  and  broadcasts  to  neighbors

•  Records  address  of  neighbor  which  ﬁrst  sends  the  RREQ

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### •  Intermediate  node  satisﬁes  RREQ  if

Destination  itself

Has  route  entry  in  table  with  destination  sequence  number  ≥  that  given  in   RREQ

### •  Unicasts  RREP  to  neighbor  which  sent  RREQ

•  Destination  address  and  sequence  number  (updated)

•  Hop  count



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### •  Other  nodes

•  RREQ  times  out  :  Route  Request  Expiration  Timer

•  Deletes  corresponding  pointers

### •  More  than  one  RREP  received

•  One  with  greater  destination  number

•  Lesser  hop  count

### •  Source  node  starts  transmission  -­‐  updates  if  a  better  RREP  is  received

C. E. Perkins and E. M. Royer. “Ad-Hoc On Demand Distance Vector Routing”, Proceedings of the IEEE Workshop on Mobile Computing Systems and Applications (WMCSA), pages 90-100, 1999.

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### •  In  case  of  broken  link

unsolicited  RERR  sent  to  aﬀected  source  node

•  Source  initiates  new  RREQ

Sequence  number  updated

•  Hop  count  set  =  ∝

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SNR=3

SNR=15 SNR=15

SNR=15 SNR=2

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### •  What  is  a  good  metric  for  link  quality?

•  ETX  (Expected  Transmission  Count)

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rev

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### 20%

 Independent networks (indep. basic service set, IBSS), also known as ad hoc networks.. 

Shih, “On Demand QoS Multicast Routing Protocol for Mobile Ad Hoc Networks”, Special Session on Graph Theory and Applications, The 9th International Conference on Computer Science

Keywords: Mobile ad-hoc network, Cluster manager electing, Fuzzy inference rule, Workload sharing, Backup manager... 致謝 致謝

This Supplementary Guide is prepared by Curriculum Development Council (CDC) Committee on Chinese Language Education and CDC Ad Hoc Committee on Supplementary Guide to the

In an ad-hoc mobile network where mobile hosts (MHs) are acting as routers and where routes are made inconsistent by MHs’ movement, we employ an associativity-based routing scheme

• As RREP travels backwards, each node sets pointer to sending node and updates destination sequence number and timeout entry for source and destination routes.. “Ad-Hoc On

Abstract— This paper has analyzed link probability, expected node degree, expected number of links, and expected area collectively covered by a finite number of nodes in wireless ad

Kyunghwi Kim and Wonjun Lee, “MBAL: A Mobile Beacon-Assisted Localization Scheme for Wireless Sensor Networks,” The 16th IEEE International Conference on Computer Communications