Important Note This presentation is based on the following book - PowerPoint PPT Presentation

Important Note  This presentation is based on the following book  References to some of the figures and facts can be found in the book  Middleware for Network Eccentric and Mobile Applications Garbinato, Benoît; Miranda, Hugo; Rodrigues, Luís (Eds.) 2009, Approx. 465 p., Hardcover ISBN: 978-3-540-89706-4 2

Outline of the Presentation  Routing metrics  Topological-Based Routing  DSDV , OLSR, DSR, AODV , DYMO  Geographical-Based Routing  Routing algorithms  Pre-processing algorithms  Pitfalls 3

Wireless Ad Hoc Network  A definition  (possibly) mobile nodes  Equipped with radio  No external infrastructure  The problem with routing  Limited and shared bandwidth  Frequent topology changes 4

Routing Metrics  Some reasons not to use hop count: Energy  Congestion  Link quality   Energy consumption by Rodoplu and Meng: u ( d ) = d α + c  (1)  A different approach (g is available battery in [0,1]):  (2) f ( a ) = 1/ g ( a )  Stojmenovic and Lin classify algorithms minimizing (1) as power-aware, (2) and cost-aware 5

Routing Metrics  Minimize energy consumed/packet  Minimize time to network partition  Minimize variance in node power levels  Minimize cost/packet  Minimize maximum node cost 6

Some Parameters to Classify Routing Protocols  Pro-active or Reactive  Does the node collect routing information only upon request or only when required?  Uniform or Non-Uniform  Does the topology knowledge change with the distance?  Link-state or distance-vector  Well-known difference already in IP routing  Hop-by-hop or source routing? 7

8

Destination-Sequenced Distance-Vector  It is based on RIP  Avoids looping with sequence numbers  Even sequence numbers – new routes  Odd sequence numbers – break old routes  Nodes only accept updates from  Higher sequence numbers or  Better paths (& same sequence number) 9

Optimized Link State Routing  Link State: nodes collect information of all the network  No cycles  Hop-by-hop routing  Extensive flooding  To mitigate flooding, OLSR creates clusters (sort of…)  OLSR uses HELLO and Topology Control messages  Nodes don’t propagate HELLO messages  They serve to create a two-hop view of the network  And to crate Multipoint Relays (MPRs) 10

HELLO Messages  HELLO Messages contain  List of neighbors with bi-directional links  Uni-directional links  Neighbors heard but confirmation not received  HELLO Messages reveal the 2-hop neighborhood 11

Multipoint Relays (MPRs) Minimize traffic by reducing duplicate transmissions  Each node picks a set of neighbors for its (re-)transimissions  This is the MPR set  The MPR set of N must cover the entire 2-hop neighborhood of  N All links to the MPR set must be bi-directional  Nodes that are not in the MPR don’t re-transmit  This requires each node M to know its MPR selectors  Which nodes use M as an MPR?   MPRs are announce in the HELLO messages They broadcast this info in their HELLO messages  12

Flooding of TC Messages  Based on the topology collected, nodes compute routing tables  One hop at a time 13

Dynamic Source Routing  Note the “source routing” in the name  Relies on three control messages  Route Request  Route Reply  Route Error  Nodes keep route caches  Of their own paths  Of snooped paths  Each route in the cache has an expiration period 14

Routing Steps  Route discovery simplified with discrete events 2 A B 3 1 S D 4 3 1 2 C 15

Routing Steps  Node checks its route cache  If path not available, send Route Request  Upon reception of Route Request (1 st time) Node checks its route cache  If no route is known node appends its address and re-  broadcasts Route Request If path available or node is destination send Route Reply   Nodes send the Route Reply using the reverse path What happens if links are not bi-directional?  16

Route Cache Optimizations  A knows the path ABCD  If it later discovers the path ABCE, it only adds CE in the Route Cache If A later knows it can reach C in a single hop   Automatically shortens paths to D and E  Forwarding nodes can snoop packets  Nodes can overhear route replies  Nodes delay route replies depending on path lengths 17

Route Maintenance  If the data link layer reports a problem node sends a Route Error back to the source  Message travels back to source  All routes having this hop must be truncated  Other mechanisms may substitute the data link layer reports  End-to-end mechanisms might be used in alternative  When communication is not bi-directional 18

Ad Hoc On Demand Distance Vector (AODV)  AODV is a distance-vector protocol  It followed DSDV  Like DSR, AODV also uses Route Requests and Route Reply messages  Unlike DSR, Route Messages don’t store routing information  Upon reception of Route Requests, nodes keep information of previous hops for some time 19

Ad Hoc On Demand Distance Vector (AODV)  Route Replies to D are sent back using the reverse path  Route Requests carry a “source sequence number”  This maintains fresh reverse-route paths  Source node also adds a “destination sequence number”  This discards paths in nodes with lower destination sequence numbers  Route Replies are propagated if the d.s.n. is the same and if they contain shorter paths 20

Ad Hoc On Demand Distance Vector (AODV)  Nodes must invalidate paths affected by links broken  They use Route Error messages  Either broadcast to many or unicast to one  Upon reception of the list of unreachable nodes from F, node N removes all destinations where F was the next hop  Optionally, the node F, upstream the link break, can issue a Route Request 21

Dynamic MANET On-Demand Routing Protocol (DYMO)  Improves AODV with more topological information  This is called “path accumulation” S S, A S, A, B S A B D D, B, A D, B D 22

A Brief Comparison  Let’s classify the previous routing algorithms  Source routing/Hop-by-hop routing?  Reactive/Proactive?  Link-state/Distance-vector? Reactive Source Routing DSR X AODV OLSR DSDV Link-state 23

A Brief Comparison How does the network recover from broken links?  DSDV:  Generate route update with ∞ cost and odd sequence number  OLSR:  Recalculate routing tables  DSR:  Detection when routing a packet  Route Error sent back to the source  AODV:  Detection when routing, but also when receiving a packet to some  unknown destination or if node receives RERR from neighbor for active routes 24

A Brief Comparison Maybe the most interesting comparison holds between AODV and  DSR There are many different scenarios showing advantage either to one  or the other DSR has variable length headers  This creates a routing overhead  And can disturb the MTU info to the upper layers  DSR can provide topological hints to upper layers  DSR doesn’t purge stalled routes  Management of routing tables is much simpler in AODV than in  DSR 25

Load-Balancing A  Caching of routes can make the E network very unfair! G D F  Node G will get H all the traffic B C 26

27

Determining Position  Global Positioning System  Signal strength information  Logical addresses  Moreover:  How can nodes determine the position of destination?  E.g., consider the Grid Location Service, or  Position-based distributed hash tables 28

Some (Greedy) Routing Algorithms  Greedy Algorithm  Compass Routing Algorithm  GEDIR Algorithm  There are many others!  E.g., MFR, NC 29

Is Greedy Routing Enough?  Greedy Fails in this case  GEDIR could succeed!  But it is not difficult to find a case where D GEDIR fails  With a loop of 2 nodes M S 30

Which Ones Are Loop-Free?  Compass is also not loop-free E  Worse: loops can be H arbitrarily long D F G 31

Face Routing  The following question is:  Can we ensure routing convergence?  Consider the idea of finding your way in a maze  Put the right hand on the wall  Walk until you reach the exit  This is called “right-hand routing” 32

Algorithm FACE-1 f 1 D f 5 f 4 P 3 P 1 S P 2 P 4 f 3 f 2 33

Algorithm FACE-1 Algorithm 1 Algorithm FACE-1 constant S ← source constant D ← destination constant r ← line segment SD P ← S while P � = D do f ← first face that intersects line segment P D from P to D for all edges e of f do if e intersects r at point P � and P � is closer to D than P then P ← P � end if end for traverse f again until reaching edge where P was found end while 34

FACE-2 Algorithm 1 Algorithm FACE-2 constant S ← source constant D ← destination P ← S while P � = D do f ← face of G with P on its boundary that intersects P D traverse f until reaching an edge UV that intersects P D at some point P � � = P P ← P � end while 35

Will FACE-1 and FACE-2 Always Converge?  Consider the path from D S to D  The intersection can make the routing fail in FACE-2 C S A  We need planar graphs B 36