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Routing and Location Management
in Mobile Ad-hoc Networks
By
Sumesh J. Philip
(09/20/2001)
Contents
Introduction
Routing Protocols



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Table Driven (WRP, DSDV)
On Demand (DSR, AODV, TORA)
Performance Evaluation
Geographic (LAR, DREAM)
Location Management for Large Scale Networks
(GLS, SLURP, SLALOM)
References
Mobile Ad-Hoc Network
Collection of mobile nodes
forming a network
No centralized
administration or standard
support services
Highly co-operative, each
host is an independent
router
Hosts use wireless RF
transceivers as network
interface
Conferences/Meetings
Search and Rescue
Disaster Recovery
Automated Battlefields
MaNet Constraints and Issues
Lack of a centralized entity
Network topology changes frequently and
unpredictably
Routing and Mobility Management
Channel access/Bandwidth availability
Hidden/Exposed station problem
Lack of symmetrical links
Power limitation
Conventional Routing Protocols ?
Not designed for highly dynamic, low bandwidth
networks
“Count-to-infinity” problem and slow convergence
Loop formation during temporary node failures
and network partitions
Protocols that use flooding techniques create
excessive traffic and control overhead
MaNet Protocols
Proactive Protocols
 Table driven
 Continuously evaluate
routes
 No latency in route
discovery
 Large capacity to keep
network information
current
 A lot of routing
information may never
be used!
Reactive Protocols
 On Demand
 Route discovery by some
global search
 Bottleneck due to latency
of route discovery
 May not be appropriate
for real-time
communication
Wireless Routing Protocol (WRP)
A Path finding algorithm; uses predecessor to
destination in the shortest path
Eliminates the “Count-to-infinity” problem and
converges faster
Neighbor connectivity via periodic “Hello”
messages
Update messages sent upon detecting a change
in neighbor link
Each node i maintains a Distance table (iDjk),
Routing table (Destination Identifier, Distance iDj
, Predecessor Pj ,the successor Sj), link cost table
(Cost, Update Period)
Processing Updates and creating Route Table
 Update from k causes i to re-compute the
distances of all paths with k as the predecessor
 For a destination j, a neighbor p is selected as the
successor if p->j does not include i, and is the
shortest path to j
Operation
(0, J)
J
10
1
X
B
5
10
1 (10,
(2, B)
K)
1
K
(,K)
K)
(11,
(1,
B)
(10,
(2,
K) I)
I
Destination Sequenced
Distance Vector (DSDV)
Each Route is tagged with a sequence number
originated by destination
Hosts perform periodic & triggered updates,
issuing a new sequence number
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 used
Topology changes
Broken links assigned a metric of ∞
Any route through a hop with a broken link is
also assigned a metric of ∞
“∞ routes” are assigned new sequence numbers
by any host and immediately broadcast via a
triggered update
If a node has an equal/later sequence number
with a finite metric for an “∞ route”, a route
update is triggered
DSDV Operation
Damping Fluctuations
Routes preferred if later sequence numbers, or
smaller metric for same sequence numbers
Problem : Table fluctuations if worse metrics are
received first, causing a ripple of triggered
updates
Solution : Use average settling time as a
parameter before advertising routes
Tantamount to using two tables, one for
forwarding packets and another for advertising
routes
Dynamic Source Routing (DSR)
Each packet header contains a route, which is
represented as a complete sequence of nodes
between a source-destination pair
Protocol consists of two phases


route discovery
route maintenance
Optimizations for efficiency

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Route cache
Piggybacking
Error handling
DSR Route Discovery
Source broadcasts route request (id, target)
Intermediate node action
 Discard if id is in <initiator, request id> or node is
in route record
 If node is the target, route record contains the full
route to the target; return a route reply
 Else append address in route record; rebroadcast
Use existing routes to source to send route reply;
else piggyback
DSR Route Maintenance
Use acknowledgements or a layer-2 scheme to
detect broken links; inform sender via route error
packet
If no route to the source exists


Use piggybacking
Send out a route request and buffer route error
Sender truncates all routes which use nodes
mentioned in route error
Initiate route discovery
Optimizations for efficiency
Route Cache
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Use cached entries for
during route discovery
Promiscuous mode to
add more routes
Use hop based delays
for local congestion
Must be careful to
avoid loop formation
Non propagating
RREQs
Optimizations
Piggybacking

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Data piggybacked on route request Packet
Problem : route caching can cause piggybacked
route replies to be discarded
Improved Error Handling
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when network becomes partitioned, buffer packets
and use exponential back-off for route discovery
Listen to route replies promiscuously to remove
entries
Use negative information to ignore corrupt replies
Ad-hoc On Demand
Distance Vector (AODV)
On demand protocol that uses sequence
numbers (DSDV) to build loop free routes
Key difference from DSR is that source route is
no longer required
Path discovery
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Reverse Path setup
Forward path setup
Table management and path maintenance
Local connectivity management
AODV Reverse path setup
Counters : Sequence number, Broadcast id
Reverse Path
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Broadcast route request (RREQ) < source_addr,
source_sequence-# , broadcast_id, dest_addr,
dest_sequence_#, hop_cnt >
RREQ uniquely identified by <source_addr ,
broadcast_id>
Route reply (RREP) if neighbor is the target, or knows
a higher dest_sequence_#
Otherwise setup a pointer to the neighbor from whom
RREQ was received
Maintain reverse path entries based on timeouts
AODV Forward path setup
RREQ arrives at a node that has current route to
the destination ( larger/same sequence number)
unicast request reply (RREP)<source_addr,
dest_addr, dest_sequence_#, hop_cnt,lifetime> to
neighbor
RREP travels back to the source along reverse
path
each upstream node updates dest_sequence_#,
sets up a forward pointer to the neighbor who
transmit the RREP
AODV Operation
D
X
X
S
Protocol Maintenance
Route Table management

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Route request expiration timer purges reverse
paths that do not lie on active route
Active neighbor relays a packet within
active_route_timeout

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Route cache timer purges inactive routes
New routes preferred if higher destination
sequence number or lower metric
AODV Maintenance
Path maintenance
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Upon link breakage, affected node propagates an
unsolicited RREP <dest_sequence_#+1, ∞> to all
upstream nodes
Source may restart route discovery process
Local connectivity management
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Broadcasts used to update local connectivity
information
Inactive nodes in an active path required to send
“hello” messages
Temporally Ordered
Routing Algorithm (TORA)
Link reversal algorithm

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Destination oriented Directed Acyclic Graph (DAG)
Full/Partial reversal of links
Assigns a reference level (height) to each node
Adjust reference level to restore routes on link
failure
Multiple routes to destination; route optimality
not important
Query, Update, Clear packets used for creating,
maintaining and erasing routes
Creating Routes
A
QRY
UPD
QRY
UPD
B
QRY
UPD
UPD E
C
UPD
QRY
D
G (DEST)
F
QRY
UPD
UPD
H
Route Maintenance
UPD
A
B
UPD
E
C
UPD
D
F
G (DEST)
X
H
Erasing Invalid Routes
Performance Analysis
Simulation Environment
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Network Simulator, 50 nodes in a 1500x300m
rectangular flat grid
Random waypoint mobility
Constant bit rate traffic
Address resolution : ARP implementation in BSD Unix
Medium Access Control : IEEE 802.11
Physical Layer model : combines both free space and
two ray ground reflection model
Protocols studied : DSDV(SQ), AODV, DSR, TORA
Performance Analysis
Metrics
 Packet Delivery Ratio : Ratio of number of packets


generated by CBR sources to that received by CBR
sinks at destination
Routing Overhead : number of routing packets
sent; each transmission counts as one
transmission
Path Optimality : Difference between length of
actual path took and the length of the shortest
path
Packet Delivery Ratio
95-100% in most cases
for DSR, AODV
Stale route entries in
DSDV cause drops
Short lived loops in TORA
as part of link reversal
All protocols perform well
when there is low node
mobility
Routing Overhead (packets)
Route caching and nonpropagating RREQs in
DSR
TORA

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Sum of mobility
dependant, independent
overhead for TORA
Congestive collapse
Nearly constant for DSDV
due to periodic updates
Routing Overhead (Bytes)
DSR more expensive than
AODV except at high
mobility
Smaller packets in AODV,
may be more expensive in
terms of media access,
power and network
utilization
Path Optimality
DSDV, DSR use routes
close to optimal
TORA not designed to find
shortest path
TORA, AODV use paths
close to optimum when
node mobility is low
Geographic Routing
Not many invariants to play with (IP address,
local connectivity)
Nodes physically located closer likely to be
connected by a small number of radio hops
Possible to obtain node location via a GPS system
Geographic forwarding

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Packet header contains the destination’s location
Most forward with fixed radius
Distance Routing Effect
Algorithm for Mobility (DREAM)
Proactively disseminate location information
Distance Effect :

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Closer nodes are updated more frequently
“age” field in location update
Mobility Effect :

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rate of location update controlled by mobility
No bandwidth wastage for no movement
Geographic forwarding
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If no entry for destination in table, flood
Otherwise forward data to m neighbors in the direction of
destination
Location Aided Routing (LAR)
On Demand protocol; used restricted flooding for
locating destination
Flooding is restricted to a “request zone”,
defined by an “expected zone”
A node forwards a route request only if it belongs
to the “request zone”
Tradeoff between latency of route determination
and message overhead
Resorts to flooding when prior information of
destination is not available
LAR Scheme 1
Source calculates the “expected zone”, defines a
“request zone” in the request packet and initiates
route discovery
Node I receiving the route request forwards the
request if it falls inside the “request zone”,
otherwise discards it
When destination receives the request, replies
with a route reply including current location, time
and average speed
Size of request zone is large at low and high
node speeds
LAR Scheme 2
Source calculates the distance Dists to destination
(xd, yd) and initiates route discovery with both
parameters
Node I calculates it’s distance Disti from (xd, yd)
and forwards the request only if Disti<= Dists +
δ, otherwise discards the request
Node I replaces Dists with Disti before
forwarding the request
Non zero δ increases probability of route
discovery
LAR schemes
D(xd,yd)
D(xd,yd)
R = v(t-t0)
N
I
N
I
J
S (xs,ys)
Scheme 1
J
S (xs,ys)
Scheme 2
Issue of Scalability
The number of packets each node has to forward and the
amount of state kept at each node grow slowly with the
size of the network
Most existing protocols break down for large networks
Table driven

incur large overheads due to routing table maintenance
On-demand


flood the entire network with discovery packets, wastes network
resources
long latency for discovery
Protocols which use geographic routing use global flooding
to build tables or destination discovery; may not be
scalable
Location Management
C’s radio range
A
C
B
D
F
G
E
A addresses a packet to G’s latitude, longitude
C only needs to know its immediate neighbors to forward
packets towards G.
Geographic forwarding needs a location service!
Desirable Properties of
Location service
Spread load evenly over all nodes.
Degrade gracefully as nodes fail.
Queries for nearby nodes stay local.
Per-node storage and communication costs grow
slowly as the network size grows
Grid Location Service (GLS)
sibling level-0
squares
sibling level-1
squares
sibling level-2
squares
s
n s
s
s
s
s
s
s
s
• s is n’s successor in that square.
(Successor is the node with “least ID greater than” n )
GLS Updates
... 1
11
2
...
9
1
9
11, 2
6
23
23, 2
Invariant (for all levels):
For node n in a square,
n’s successor in each
sibling square “knows”
about n.
...
3
...
2
16
29
...
7
6
...
...
17
...
26
...
21
5
...
25
...
4
...
location table content
8
...
19
location update
GLS Query
... 1
11
2
...
9
1
9
11, 2
6
23
23, 2
...
3
...
2
16
29
...
7
6
...
...
17
...
26
...
21
5
...
25
...
4
location table content
...
8
...
19
query from 23 for 1
Scalable Location based
Routing Protocol (SLURP)
Hybrid Protocol that has a deterministic manner
of discovering the destination
Each node selects a ‘home region’ using f (ID ) ,
which maintains the node’s current location
Nodes that wish to communicate with a node
query its ‘home region’ using f 1 ( ID)
Can use most forward with fixed radius without
backward progression to send data, once location
is known
3/2
Routing overhead  (vN )
Protocol Operation
[12]
[10]
Scalable Location
Management (SLALOM)
Define a hierarchy of grids : Order(3), Order(2),
Order(1)
Assign a Order(1) ‘home region’ for each node in
an Order(2) grid
Nodes that wish to communicate with another
node query its ‘home region’ in their Order(2)
grid
To reduce location update overhead, define ‘far’
and ’near’ home regions; ‘near’ regions updated
frequently
Routing overhead  (vN 4/3 )
Protocol Operation
References
S. Murthy and J.J Garcia Luna Aceves, A Routing Protocol for Packet Radio Networks, Proc. IEEE Mobicom,
Nov. 1995
Y. B. Ko, N. H. Vaidya, Location Aided Routing in Ad-Hoc networks, Proceedings of ACM/IEEE Mobicom’98,
Dallas, TX, Oct. 1998
Josch Broch, David B. Johnson, and David A. Maltz. The Dynamic Source Routing protocol for Mobile AdHoc networks, Internet-Draft, draft-ietf-manet-dsr-00.txt, March 1998.
Charles Perkins, Ad-Hoc On Demand Distance Vector (AODV) Routing. Internet-Draft, draft-ietf-manetaodv-00.txt, November 1997.
Charles E. Perkins and Pravin Bhagwat, Highly dynamic Destination Sequenced Distance Vector (DSDV) for
mobile computers, In Proceedings of the SIGCOMM '94 Conference on Communication Architectures,
Protocols and Applications, pages 234-244
Josh Broch, David A. Maltz, David B. Johnson, Yih-Chun Hu, and Jorjeta Jetcheva. A Performance
comparison of multi-hop wireless Ad-Hoc network routing protocols. In Proceedings ACM/IEEE MobiCom,
pages 85-97, October 1998.
Jinyang Li, John Janotti, Douglas S. J. De Couto, David R. Karger, and Robert Morris, A Scalable Location
Service for Geographic Ad Hoc Routing, The Sixth Annual International Conference on Mobile Computing
and Netwroking, pages 120-130, August 2000.
Seung-Chul M. Woo and Suresh Singh, Scalable Routing in Ad-Hoc Networks, Technical Report, TR00.001,
March 2000
V. Park, S. Corson, A Highly Adaptive Distributed Routing Algorithm for Mobile Wireless Networks, IEEE
Infocom97
Basagni S. and Chlamtac, I. and Syrotiuk, V. R. and Woodward, B. A. A Distance Routing Effect Algorithm
for Mobility (DREAM), Proceedings of the Fourth Annual ACM/IEEE International conference on Mobile
Computing and Networking, MobiCom'98, pp. 76-84, Dallas, TX, October 25-30, 998