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7/27/2019 Routing in Wireless Ad Hoc Networks
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Routing in WirelessAd Hoc Networks
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MANETs
Nodes are computing and communicationdevices, e.g laptops, PDAs, mobile phones,even sensors
Nodes organize and maintain the networkby themselves
A node is both a host and a router IP is used at the network layer First and foremost issue: routing
4
Problems with Routing
1.Self-organizing networks Need for distributed algorithms
2.Topology changes dynamically Mobile nodes (joining in or leaving) Unannounced loss of network connectivity due
to the time-varying channel nature
3. Link failure / repair Network partitions Loop formation during temporary node failures
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Problems with Routing
4. Asymmetric links: links may be unidirectional
5. Limited bandwidth Protocols using flooding create high traffic
and control overhead
8. New performance criteria
Number of hops (delay) Available Bandwidth Route stability despite mobility Energy consumption
6
Routing Protocols for MANETs
Find/maintain a route provided itexists
Another problem is to ensure that aroute exists, e.g., through power control
[Ramanathan00,Wattwnhofer00]
Assume that nodes are willing tocooperate
7
Topology based routing Proactive approach, e.g., DSDV, OLSR Reactive approach, e.g., DSR, AODV Hybrid approach, e.g., Cluster, ZRP
Routing Protocols for MANETs
Position based routing Location Services: e.g., DREAM, Quorum-
based, GLS, Home zone etc.
Forwarding Strategy: e.g., Greedy, GPSR,RDF, Hierarchical
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The Proactive Approach
Based on distance vector and link-statemechanisms
Attempts to maintain consistent, up-to-daterouting information from each node to everyother node in the network
Respond to changes by propagating updatesthroughout the network
Good for connection-less traffic where youmay send traffic to any node at any time
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The Reactive Approach
Routes are only created when desired by thesource node
Route discovery protocol Route discovery ends either when a route is
discovered or all possible communication
paths have been examined
Once a route is established, its maintained bysome sort of route maintenance protocol
10
Trade-off
Reactive more suitable for a mobileenvironment with limited bandwidth
Proactive preferred when time constraintsare important
ProactiveApproach
ReactiveApproach
Latency Low High
Overhead High Low
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Proactive Protocols
DV for fixed networks, DSDV forwireless networks
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Distance Vector Routing
Route discovery algorithm used by RIP(DVR does not address routemaintanance)
Based on Bellman-Ford or Ford-Fulkersonalgorithms but DVR does not require ana-priori knowledge of the network
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Distance Vector Routing (1)
Each node has a routing table where distanceto all reachable destinations are recorded
Each node is responsible for keeping trackand informing its neighbors of its distanceto each destination (main idea at the basisof distance vector-based protocols)
A router computes its distance to a destinationbased on its neighbors distance to thedestination
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Distance Vector Routing (2)
A node must know its own ID and the cost of its links toeach neighbor (the cost can be expressed in terms ofnumber of nodes, bandwidth, latency, )
1. Initially, each node sets the cost of the link to itself to0 and to any other node to infinity
2. A node broadcasts its routing table3. A node, upon receiving information from neighbors,
computes minimum cost-path toward destination andmakes changes to its routing table if needed
4. Either periodically or every time a node updates itstable, it broadcasts it to neighbors.
The algorithm converges by iteration
15
Distance Vector Routing (3)
At node i, the minimum cost path betweennodes i andj is computed as
where:
is the path cost at time step n
is the cost of the link between iandits neighbor k
Dn+1
(i, j) =min Dn(i, j),min
kd(i,k)+D
n(k, j){ }
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Distance Vector Routing forAddress D
R
12
3
45
172
35
5
41
Link cost
Link number
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Distance Vector Routing for
Address D
R
12
3
4
5
97
62
11829
81
172
35
5
41
Cost fromneighbor todestination D
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Distance Vector Routing forAddress D
R
12
3
4
5
98
99
97
123 70
Cost for Rto get to Dvia this link
Minimum
cost route
17
2
35
541
97
62
118 29
81
19
Distance Vector Routing forAddress D
R
70
70
7070
70
Cost fromR to D12
3
4
5
17
2
35
5
41
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Problems with Distance Vector
1. Does not scale well with the number of nodesin the network (overhead O(n2))
2. Slow convergence to the lowest cost route3. Slow recovery time if there are link failures,
hence routing problems during disruptiontimes
Count-to-infinity: Router loops may takeplace when degradation of a link cost occurs
Solved only when the cost of thealternative route including a loop reachesthe cost of the degraded link
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Count-to-Infinity: An Example
A
B
A
B1
2
3
2 A
B5
4 A
B7
6
Node D becomes unreachableD
Cost of the link A-B and B-D equal to 1 =>cost of the path between A and D equal to 2
Route cost to D
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It occurs only if A sends its update before B
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DSDV (1):Destination SequencedDistance Vector Routing
Proposed by Perkins [94], based on Bellman-Ford routing mechanism
Each node maintains a routing table thatrecords all possible destinations
Each table entry contains1. Destination node ID (i.e., IP address)2.Next hop3.Number of hops to the destination4.A sequence number (SN) is used to
distinguish old vs. new routes and avoidloops
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DSDV (2)
Routing tables are periodically transmitted tomaintain table consistency
A full dump record reports on the entirerouting table. Lots of traffic, since eachtable is probably larger than the networkprotocol data unit
Incrementalupdates provide information onchanges performed since last full dump
A new route broadcast contains The address of D The number of hops to reach D The SN of the route SN unique to this broadcast
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DSDV (3)
Every change is broadcast to the neighbors(incremental update)
Upon reception of a route update:If the node doesnt have such information, it adds
an entry to its table
Otherwise, it checks the SN and updates the tableonly in case of fresher information
The route with most recent SN is used If two routes have the same SN, the route with the
smaller metric (== shorter route) is used
When a link fails, an metric is used and the route SNis increased
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MH4
ForwardingTable
MH5
MH1
MH8
MH7
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26
34
5
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1
8
7
050-83MH6MH8
128-72MH6MH7
076-61MH6MH6
392-52MH6MH5
710-40MH4MH4
564-32MH2MH3
128-21MH2MH2
516-12MH2MH1
SNCostNextDest
MH4Forwarding
Table
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MH6
MH3MH4
MH5
MH2
MH1
MH8
MH7
MH1 moves
MH6
MH1
28
MH3MH4
MH5
MH6
MH2
MH1
MH8
MH7
New MH4
ForwardingTable
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New MH4Forwarding
Table
050-83MH6MH8
128-72MH6MH7
076-61MH6MH6
392-52MH6MH5
710-40MH4MH4
564-32MH2MH3
128-21MH2MH2
518-13MH6MH1
SNCostNextDest
34
5
62
1
8
7
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DSDV (3)
Every change is communicated to the neighbors(incremental update)
Upon reception of a route update:If the node doesnt have such information, it adds
an entry to its table
Otherwise, it checks on the SN and updates thetable only in case of fresher information
The route with most recent SN is used If two routes have the same SN, the route with the
smaller metric (== shorter route) is used
When a link fails, an metric is used and theroute SN is increased
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Count-to-Infinity: An Example
A
B
A
B1
2
3
2 A
B5
4 A
B7
6
Node D becomes unreachableD
Cost of the link A-B and B-D equal to 1 =>cost of the path between A and D equal to 2
Route cost to D
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SN of the route notified by A is older than theone of the route declared invalid by B -> As infois not considered. B sends an update to A, and Atoo declares the route to D (through B) as invalid
NewSN
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Detecting Link Failure
Detection: If data is flowing over a link, failure of
link layer to deliver a packet can be usedto assume link failure
If a node does not hear for a long time(how long?) from its neighbor
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DSDV (4)
Nodes also keep track of the settling time ofroutes, i.e., the average time that routes to adestination will fluctuate before the routewith the best metric is received
A broadcast of a routing table will be delayed bythe length of the settling time
This avoids fluctuations in the table data andreduces the update packets
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Advantages
Has moderate memory requirementsGuarantees loop-free paths (thanks toSNs)Simple update coordination protocolDisadvantages
Provides only a single path between each given S/D pairRequires selection of the periodic update interval,settling time and number of update intervals that shouldexpire before a route is considered stale: difficult toestimate
Update overhead: if full dump updates are used, overheadgrows as O(n2)
DSDV: Advantages andDisadvantages
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OLSR
Optimized Link State Routing[Jacquet00] OLSR is based on the link state routing
approach
Traditional approach in Link State Routing: Every node generates control packets to
advertise its links status (i.e., its one-hopneighbors and the links cost)
Such information is propagated over thewhole network (flooding)
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OLSROptimized Link State Routing[Jacquet00]
However, in OLSR: Sources build routes proactively by using
MultiPoint Relay nodes (MPRs)
Only MPRs need to generate and forward linkstate updates
OLSR thus leads to efficient flooding ofcontrol messages in the network: superfluousbroadcast packet retransmission as well asthe size of the link state packets are reduced
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MPRs and Their Selection
Every node in the network selects its own MPR(s) A node selects as its multipoint relays those one-hop
neighbors that allows the node to reach its two-hopneighbors through symmetric links
Nodes exchange neighbor lists to know their 2-hopneighbors and link type, and choose the MPRs
No. of MPRs per node should be minimized
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MPRs: Example (1)
Hp: all links are bi-directional
A
B F
C
D
E H
GK
J
E
Nodes C and E are multipoint relays of node A
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MPRs: Example (2)
C and E forward information received from A Node E is a multipoint relay also for node H If the link H-J were unidirectional, then K would also be
selected as MPR by H
Note that C selects A as MPR, while E selects A and H
A
B F
C
D
E H
GK
J
Node that has broadcast state information from A
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MPRs: Example (3)
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Controlled Flooding of Link State Updates
24 retransmissionsto deliver a messageup to 3 hops
11 retransmissions todeliver a message upto 3 hops
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Controlled Flooding of Link State Updates
OLSR is particularly suited for densenetworks
In sparse networks, every neighborbecomes a multipoint relay, then OLSR
reduces to pure link state protocol
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How It Works: Hellos
Node N broadcasts Hello messages every Hellointerval to its 1-hop neighbors:
Hello message contains list of known 1-hopneighbors and
the link status (symmetric, asymmetric, or MPR) ofits 1-hop neighbors
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How It Works: Neighbor Table
Node N builds a Neighbor Table that includes all its 1-hopneighbors and, for each of them, all 2-hop neighbors thatcan be reached through it. The link types are also recorded.
N selects its MPR nodes among its 1-hop neighbors suchthat it can reach all nodes that are 2-hops away throughsymmetric links
MPR election requires symmetric link to node NOnce N selects a neighbor, say X, as MPR, N tags its link
with X as MPR and, through the next Hello, N will notifyX about it
X maintains the list of nodes that selected itself as MPR
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How It Works: Topology Control
MPR nodes broadcast Topology Control (TC) messagesevery TC interval to advertize link states, specifically
TC message contains list of 1-hop neighbors whohave selected this node as an MPR
Only MPR nodes can forward TC messages (butnote that still all network nodes receive them) ->
more efficient flooding
TC messages are used to build the Topology Table(and for routing table calculation afterwards)
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Some Observations
For (any) control messages it is not requireda reliable transmission since they areperiodically sent
Each control message inlcludes a sequencenumber so that old messages with outdatedinformation can be detected and discarded
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How It Works: Topology Table
Each node maintains a topology table where theinformation obtained from the received TCmessages is recorded
Each entry includes: Address of a potential destination (i.e., the
MPR selector in the received TC)
Address of the last hop to that destination(i.e., the MPR that generated that TC)
MPR selectors set sequence number
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How It Works: Routing Table
Each node maintains a Routing Table where routes toany potential destination are recorded
The Routing Table is built based on the Topology Tableand the Neighbor Table
Each entry includes: Address of the potential destinationAddress of the next hop to reach that destination
Estimated distance to the destination Note that the Routing Table is re-calculated at every
change in either the Topology Table or the NeighborTable
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Building the Routing Table (1)
Initialization:
Set h to 1; Use the Neighbor Table: take the 1-hop
neighbors (whose link status is not uni-directional) as destinations (i.e., h =1 ) andcreate the corresponding entry in theRouting Table;
set their distance to h = 1.
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Building the Routing Table
Iterative procedure:
1) For each entry in the Topology Table:(i) if its destination does not correspond to anydestination in the Routing Table and(ii) if its last hop (i.e., MPR) is the destination of anentry in the Routing Table with distance equal to h, thenadd a new route entry in the routing table where:
dest = dest of the entry in the Topology Table; next-hop = next-hop of the route entry whose dest is
the last-hop in the Topology Table;
Set distance = h+1;3) Set h = h+1 and go to step 1 (till all entries in the
Topology Table have been processed)
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Some Observations (1)
Hello interval impact on overhead vs. protocolreactivity:
Recall: Hellos are sent by all nodes to senseneighbors (but they are not rebroadcast)
TC interval impact on overhead vs. protocolreactivity:
Recall: TC messages are sent only by MPR nodesto advertize link state and allow routing tablecalculation
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Some Observations (2)
Route are all composed of MPRs only (except sourceand destination): MPRs form a network backbone thatis in charge of routing all traffic
MPR nodes selection impact: How much more traffic must MPR nodes handle?
Higher load leads to higher energy consumption
Node mobility impact Consequences? Particularly for MPR nodes
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Reactive Protocols
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DSRDynamicSource Routing [Johnson96]
Entirely on demand: No periodic messages oradvertisements at any layer
Dynamic: it maintains a soft state, i.e., all state isdiscovered when needed and can be easily re-discovered if needed after a failure without impactingthe protocol functioning
Source Routing: the source specifies in the header ofeach data packet the entire route, not only the nexthop (no need for routing tables)
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Assumptions
The network is fairly small (up to 200 nodes,i.e., network diameter of 10-15 nodes)
Each node maintains a cache containing allsource routes of which it is aware
Routes in the cache are continuouslyupdated as they are learned
Several routes can be cached to the samedestination
Either bi- or uni-directional links can be used
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DSR: Two Phases
The protocol consists of two phases:
Route discovery: Started by S when S needs to send data to D
and doesnt have any route to D in cache
Route Maintenance: While using a route to D, S can detect if
the route is not longer valid and, in case, sendan error message
Upon route failure, S may use another route(if it knows it) or start a new route discovery
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L
H
J
D
C
G
S
N
K
BA
Route Discovery
RREQ
Initiator ID
Initiator seq#
Dest ID
Partial route
TTL
Initiator seq#
Dest ID
Time to go
RREQ Table
If no reply by the time to go, S sends a new RREQtill a max no. of attempts have been made
Unique ID
QoS cost
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L
H
J
D
C
G
S
N
K
B
A
Route Discovery
RREQrecently
seen?
DiscardRREQ
yes
no
myAddrin partialroute?
yes
no
store RREQID in list
decrease TTL andbroadcast packet
myAddr=target?
no
S
S
S,C
S,LS,C
S,CS,L
S,L
knownroute?
append myAddrto partial route
no
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L
H
J
D
C
G
S
N
K
B
A
Route discovery succeeded !
Route Discovery
S,L,J
S,C,G
S,C,H
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L
H
J
D
C
G
S
N
K
B
A
RREP
Route Reply
S,L,J,D
S,C,G,KS,C,G,K
S,L,J,D
S,L,J,D
S,L,J,D
Place route record andcost into RREP
(cost depends ontarget QoS metric)
RREP sent by reversingtheroute followed by RREQ. If
unidirectional, use any cachedroute to S. If none, send anRREQ and piggyback RREP
myAddr=target?
yes
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L
H
J
D
C
G
S
N
K
B
A
DATA
Data Delivery
Write route inpacket header
and send packetto next hop
S,L,J,D
S,L,J,D
S,L,J,D
S,L,J,D
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L
H
J
D
C
G
S
N
K
B
A
RREP
Route Caching
S,L,J,D
S,L,J,D
S,L,J,D
Place cached route andcost into RREP
(cost depends ontarget QoS metric)
RREP sent by reversingtheroute followed by RREQ. If
unidirectional, use any cachedroute to S. If none, send anRREQ and piggyback RREP
knownroute?
yes
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Route Caching
Advantages of route caching Speeds up routing Reduces propagation of route requests
S caches the route to D contained in the RREP For each D, more than one route can be
cached, thus S can perform traffic routingover several possible routes
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Route Maintenance
Along a source route, each node transmitting apacket is responsible for correct transmissionconfirmation
An ACK is needed for confirmationMAC or link-layer ACKs can be usedOverhearing next node forwarding the packet
(passive ACK: A hears B sending to C)
Use of DSR-ACKs: the node transmitting the packetcan require an ACK (which may follow a differentroute back)
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Route Maintenance
S
BC
G
D
H
F
Mark link to nexthop as broken
ReceivedACK?
yes
Max#ACKreqexceeded
?
Remove fromcache all routes
including that link
Send an RERRto everysource that sent a packetto be routed over that link
no Route Cache (S)D: S,B,C,F,DD: S,B,C,G,H,DC: S,B,C
RERR
RERR
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Route Maintenance
Nodes overhearing RERR remove fromtheir cache all routes including the brokenlink
S uses another route from its cache, if ithas any; otherwise it starts a new route
discovery The transport layer (e.g., TCP) should take
care of data retransmissions
74
Optimizations
Promiscuous mode: listening to arbitrary routes inuse (A hears B sending to C)
Replace with shorter routes / Store new routesBut promiscuous mode takes energy
Packet salvagingUpon link failureIf intermediate node has another route to D, it
replaces the original source
However, no double salvage is allowed !!!
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Packet Salvaging: An Example (1)
Initial route: S (source) B C F D (destination) However, S and C have an alternative route to D in
their cache (S-B-Z-F-D and C-I-G-H-D, respectively)
At a certain time, F moves out of the network
SB
C
G
F D
HL
I
M
I
L
Z
76
Packet Salvaging: An Example (2)
Unfortunately, S receives no RERR, from either C orZ, then S keeps sending its packets toward C
C can salvage the packets by replacing the originalroute (S-B-C-F-D) in the packet with the new route(C-I-G-H-D)
SB
C
G
D
HL
I
M
I
L
Z
77
Packet Salvaging: An Example (3)
Now, assume the G-H link fails, then if G couldsave the packet again, a loop could be formed.Indeed (i) G does not know that the packet wasoriginated by S (it only sees C as originator), (ii)S could reply with the route S-B-Z-F-D
SB
C
G
F D
HL
I
M
I
REQREQ
REQ
REQ
REQ
REPREP
REP
REP
REP
L
Z
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" Enrirely reactive" Soft state and support of unidirectional links" Source routing
" No need for routing decisions by intermediate nodes" Nodes can learn new routes from relayed packets" Guarantee that routes are loop-free
" Caching" Reduced route discovery overhead" One route discovery may yield many routes to D, dueto intermediate nodes replying from local caches
DSR: Advantages
80
" RREQ flooding may be huge" Possible collisions between RREQs propagated byneighboring nodes
" Contention between RREPs come back due to use oflocal caches (RREP Stormproblem)
" Packet delays/jitters due to on-demand routing" Headers may become too long with respect todata payloads -> suitable for small networks
" Cached routes may become invalid; stale cachescan adversely affect performance
DSR: Disadvantages
81
AODVAd-Hoc On Demand Distance Vector [Perkins99]
Builds routes on demand Attempts to improve DSR by using routing
tables at the nodes so that packets do nothave to include routes
Avoids loop formation by using sequencenumbers
Similar procedures of route discovery androute maintainance as in DSR
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Assumptions
Each node maintains:
A broadcast ID to be used for RREQs Broadcast ID is incremented for each RREQ Combination of the node IP address & broadcast ID
uniquely identifies an RREQ
A (small) routing table with an entry for eachuseful destination node
83
Routing Table
A routing table entry includes:
Destination IP address Sequence number assigned to the path by the
destination (Destination Sequence Number, DSN)
Hop count Next hop List of nodes from which RREP msgs may be receivedand from which RREQ msgs are received Active route timeout (lifetime) Routing flag indicating whether the path is active or not
85
L
H
J
D
C
G
S
N
K
B
A
Route Discovery
RREQ
Initiator ID
Dest. Sequ. #
Dest ID
Broadcast ID
A new RREQ by node S for a destination isassigned a higher DSN (for the inverse routewith S as a destination)
TTL
QoS cost
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86
L
H
J
D
C
G
S
N
K
B
A
Route Discovery
knownroute with
higherDSN?
SendRREP
yes
no no
sets up a reversepathpointing to
the source
TTL-- thenre-broadcast
RREQ
RREQalreadyseen?
no
DiscardRREQ
yes
store RREQ
myAddr=target?
87
L
H
J
D
C
G
S
N
K
BA
Route discovery succeeded !
Route Discovery
89
L
H
JC
G
D
S
N
K
B
A
RREP
Route Reply
Place route record andcost into RREP
(cost depends ontarget QoS metric).
DSN is increased
RREP sent onreverse path
myAddr=target?
yes
Nodes on the route set a forward pathto D as they receive the RREP
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90
L
H
J
D
C
G
S
N
K
B
A
DATA
Data Delivery
Send data packet tonext hop using routing
table entry(no route in packet
header)
91
Remarks
D replies to the first arrived RREQ thusAODV favors the least congested route(that is not always the shortest one)
As OLSR, it only supports symmetric links!RREP forwarded along the route followed bythe RREQ
92
Timeouts
A routing table entry maintaining areverse path is purged after a timeoutinterval long enough to let the RREPcome back to the source
A routing table entry is purged if theroute has not been used for anactive_route_timeoutinterval
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93
Route Maintenance
HELLO messages are periodically exchangedamong neighboring nodes to maintain localconnectivity
Absence of Hello messages is used as anindication of link failure
Hello messages can also contain the ID of theneighbors from which a node has heard
A node can also use MAC acknowledgementsor packet retransmissions done by a neighborto check on the next hop reachability
95
Link Failure
S
BC
F
D
G
E
Route Table (C)D: EDSN: 5Active ...
RERR
RERR
C sends RERRto upstreamneighbors
yes
C detectslink failure
C increases DSNand includes it in
the RERR
Route Table (C)D: EDSN: 6Inactive ...
RREQ
RREQ
Route Table (S)D: BDSN: 5Active ...
Route Table (S)D: BDSN: 6Inactive ...
RREQ
RREQ
RREQ
Route DSN:5Route DSN:6Route DSN:7
96
Link Failure: A Remark
Loop formation avoided thanks toDSN !
S B C
DE
F RREQ
RERR
RREQ
RREQ
C-F-E-S-B-C
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Advantages
No need to include route in the packet headerNodes maintain routing tables containing entries onlyfor routes in use
DSNs allow nodes to avoid invalid/broken routesDSNs prevent formation of loops
Disadvantages
" Unused routes expire even if topology is unchanged" Multiple routes for each pair S-D are not supported" Need for symmetrical links
Advantages & Disadvantages
98
Routing Performance
Several performance comparisons[Broch98Mobicom,Johansson99Mobicom,Das00Infocom,Important03Infocom]
99
QoS Routing
Associate each link with a cost E.g., transmission power, transmitters residual
energy, traffic load, available bandwidth
RREQs used to collect the cost (or minimumcost) of all traversed links along a route
S
BC
F
D
G
E
S-B TxPw
RREQ
+ B-C TxPw + C-E TxPw + E-D TxPw
+ F-G TxPw+ G-D TxPw+ C-F TxPw
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100
QoS Routing
Destination responds with a Route Reply to aRREQ if
it is the first RREQ with a given (current)sequence number, or
the route cost is smaller than all otherroutes cost received with the currentsequence number
Possible modifications to routing protocols,such as DSR, to make them QoS-aware
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QoS Routing
Optimal routing decision requires constantupdates on link state information (e.g., delay,bandwidth, loss rate, link stability) resultingin large overhead
Dynamic nature of ad hoc networks makesmaintaining the precise link state information
very hard Even after resource reservation, QoS still
cannot be guaranteed due to the frequenttopology changes
Routing in VANETs
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Which Protocol Is Suitable?
Proactive and reactive protocols may not be suitable: Proactive protocols: routing tables might often
contain stale information, due to the highly-dynamicnetwork topology
Reactive protocols typically imply high latency dueto the route discovery phase
Positioning systems can be exploited to efficientlyroute traffic in VANETs geographic routing
Geographic Routing (1)
Position-based schemes: nodes determine theirgeographical position through GPS; using Hello
messages a node can also acquire the position of its
neighboring nodes
It is assumed that the destination coordinates areknown (easy if its an RSU) and they are included in the
data packet
If the destination is a vehicle, then its position canvary over time and message delivery may fail
Geographic Routing (2)
Next hops are determined based on their position ormovement direction with respect to the intendeddestination
Self-election is possible, or the current forwardercan select the next one
In the basic greedy geographic technique, the packet isforwarded at each step to the neighbor whose position isclosest to destination
Greedy forwarding, however, is susceptible to problemof dead-ends
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106
Dead-end with Geographic Routing
Both Es neighbors (i.e., C and D) arefurther away from the destination thanthe sender (E)
Adopt the right-hand rule to solve theproblem: E-C-F-B (same as to get out ofa maze)
A similar approach is used in sensornetworks; however in VANETs, several
factors can help:
the spatial-constrained topology(roads)
the delay-tolerant nature of thetraffic, along with the fact that
nodes move and can get closer to
the destination themselves
Mobility Models
109
Taxonomy of Mobility Models
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110
Random Walk
Equal probability ofhopping in anydirection
111
Random Waypoint[Johnson and Maltz96]
Node at Xn: Picks next waypoint Xn+1 uniformly in area Picks speed Vn uniformly in [vmin,vmax] Moves to Xn+1 with speed Vn Pause atXn+1 for Tpause
Xn
Xn+1
112
Problems with RWP (1)
Distributions of node speed, position,distances, etc change with time
Node speed:100 users average
1 user
Time (s)
Speed(m/s)
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113
Problems with RWP (2)
Distributions of node speed, position,distances, etc change with time
Distribution of node position:
Time = 0 sec Time = 2000 sec
114
Non-uniform Node Distribution (3)
115
Why does it matter ?
A.In the mobile case, thenodes are more oftentowards the center,distance between nodes isshorter, performance isbetter
The comparison is flawed.Should we use for staticcase the same distributionof node location as randomwaypoint. Is there such adistribution to compareagainst?
Random waypoint
Static
A (true) example: Compare impactof mobility on a protocol:
Experimenter places nodesuniformly for static case,according to random waypointfor mobile case
Finds that static is better Q.Find the bug !
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Issues with Mobility Models
Is there a stable distribution of thesimulation state (time-stationarydistribution), reached if we run thesimulation long enough ?
If so: How long is long enough ? If it is too long, is there a way to get to
the stable distribution without running longsimulations (perfect simulation)?
117
Random Direction[Nain05]
Select independently fromone another:
1. (uniform) direction and speed2. travel time At borders: wrap-around or
reflection
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Random Direction Properties
If nodes are uniformly distributed in thearea at t=0
Then, for any t>0, the nodes will beuniformly distributed in the area, providedthey move independently of each other
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References on MANETs & Routing
Tutorial by Nitin Vaidya: http://www.crhc.uiuc.edu/~nhv/
IETF MANET Working Group http://www.ietf.org/html.charters/
manet-charter.html
http://protean.itd.nrl.navy.mil/manet/manet_home.html
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References on Routing
C.E. Perkins, P. Bhagwat, Highly dynamic DestinationSequenced Distance Vector routing (DSDV) for mobilecomputers, Sigcomm 1994
Z.J. Haas, M.R. Pearlman, The Zone Routing Protocol(ZRP) for ad hoc networks, , 1999
B. Karp, H. T. Kung. GPSR: Greedy perimeter statelessrouting for wireless networks, MobiCom 2000
S. Basagni, I. Chlamtac, V.R. Syrotiuk, B.A. Woodward,A distance routing effect algorithm for mobility(DREAM), MobiCom1998
N. Guba, T. Camp, GLS: a location service for an ad hocnetwork,Grace Hopper Celebration2002
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References on Routing
[Johnson96] D.B. Johnson, D.A. Maltz, "Dynamicsource routing in ad hoc wireless networks", MobileComputing, vol. 353, 1996
[Perkins99] C.E. Perkins, E.M. Royer, "Ad hoc on-demand distance vector routing," 2nd IEEE Workshopon Mobile Computing Systems and Applications, 1999
J. Broch, D.A. Maltz, D.B. Johnson et al., Aperformance comparison of multi-hop wireless ad hocnetwork routing protocols, MobiCom 1998
AODV Linux freeware implementations: http://moment.cs.ucsb.edu/AODV/aodv.html#Implementations
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S.R. Das, C.E. Perkins, E.M. Royer, PerformanceComparison of two on-demand routing protocols for adhoc networks, Infocom 2000
P. Johansson, T. Larsson, N. Hedman et al., Scenario-based performance analysis of routing protocols formobile ad-hoc networks, MobiCom 1999
F. Bai, N. Sadagopan, A. Helmy, " IMPORTANT: Aframework to systematically analyze the Impact ofMobility on Performance of RouTing protocols for Adhoc NeTworks," Infocom2003
Two papers by A. Helmy et al. at ICC 2004
References on Routing
Recommended