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Wireless Ad hoc networks Routing. Proposed ad hoc Routing Approaches. Conventional wired-type schemes (global routing, proactive ): Distance Vector; Link State Proactive ad hoc routing: OLSR, TBRPF On- Demand, reactive routing: DSR (Source routing), MSR, BSR AODV (Backward learning) - PowerPoint PPT Presentation
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Wireless Ad hoc networks– Routing
Proposed ad hoc Routing Approaches• Conventional wired-type schemes (global
routing, proactive):– Distance Vector; Link State
• Proactive ad hoc routing:– OLSR, TBRPF
• On- Demand, reactive routing:– DSR (Source routing), MSR, BSR – AODV (Backward learning)
• Scalable routing :– Hierarchical routing: HSR, Fisheye– OLSR + Fisheye– LANMAR (for teams/swarms)
• Geo-routing: GPSR, GeRaF, etc– Motion assisted routing– Direction Forwarding
Wireless multihop routing challenges
• mobility• need to scale to large numbers (100’s to
1000's)• need to support multimedia applications
(QoS)
• unreliable radio channel (fading, external interference, mobility, etc)
• limited bandwidth• limited power
Conventional wired routing limitations• Distance Vector (eg, Bellman-Ford, BGP):
– Tables grow linearly with # nodes– routing control O/H linearly increasing with
network size– convergence problems (count to infinity);
potential loops (mobility?)• Link State (eg, OSPF):
– link update flooding O/H caused by network size and frequent topology changes
CONVENTIONAL ROUTING DOES NOT SCALE TO SIZE AND MOBILITY
DV LSIntra-AS RIP OSPFInter-AS BGP
Proactive ad hoc schemes– OLSR and TBRPF
• Link State explodes because of Link State update overhead
• Question: how can we reduce the O/H?• Answer: Link State with “Topology reduction”
– (1) if the network is “dense”, use fewer forwarding nodes
– (2) if the network is dense, advertise only a subset of the links
• Two leading IETF Link State schemes enhance scalability in large scale networks: – OLSR : Optimal Link State Routing– TBRPF: Topology Broadcast Reverse Path
Routing
LSR (Link State Routing)
• In LSR protocol a lot of control msg unnecessary duplicated
24 retransmissions to diffuse a message up to 3 hops
Retransmission node
OLSR (Optimal Link State Routing)
• In OLSR only a subset of neighbors (MPR-Multipoint Relay Selectors) retransmit control messages:– Reduce size of
control message;– Minimize flooding 11 retransmission to diffuse
a message up to 3 hops
Retransmission node
OLSR Overview
• RFC 3626, October 2003• In LSR protocol a lot of control messages
unnecessarily duplicated• In OLSR only a subset of neighbors (MPR-Multipoint
Relay Selectors) retransmit control messages– Reduce flooding overhead– Adapted for dense network
• OLSR retains all the advantages of LSR:– stable;– Does not depend upon any central entity;– Tolerates loss of control messages;– Supports nodes mobility
On-Demand Routing Protocols
• Routes are established “on demand” as requested by the source
• Only the active routes are maintained by each node
• Channel/Memory overhead is minimized
• Two leading methods for route discovery: source routing and backward learning (similar to LAN interconnection routing)
Existing On-Demand Protocols
• Dynamic Source Routing (DSR) -- CMU• Multipath Source Routing (MSR) – TJU• Backup Source Routing (BSR) – UofO+TJU• Ad-hoc On-demand Distance Vector (AODV)• Associativity-Based Routing (ABR)• Temporarily Ordered Routing Algorithm (TORA)• Zone Routing Protocol (ZRP)• Location assisted routing (LAR, DREAM)• Signal Stability Based Adaptive Routing (SSA)• On Demand Multicast Routing Protocol
(ODMRP) – UCLA
Dynamic Source Routing (DSR)
• RFC 4728 – February 2007• Forwarding: source route driven instead of
hop-by-hop route table driven– Mobility ?
• No periodic routing update message is sent• The first path discovered is selected as the
route• Two main phases
– Route DiscoveryRoute Discovery – Route MaintenanceRoute Maintenance
DSR - Route Discovery
• To establish a route, the source floods a Route Route RequestRequest message with a unique request ID
• The Route Request packet “picks up” the node ID numbers
• Route ReplyRoute Reply message containing path information is sent back to the source either by– the destination, or– intermediate nodes that have a route to the
destination• Each node maintains a Route CacheRoute Cache which
records routes it has learned and overheard over time
DSR - Route Maintenance
• Route maintenance performed only while route is in use
• Monitors the validity of existing routes by passively listening to acknowledgments of data packets transmitted to neighboring nodes
• When problem detected, send Route ErrorRoute Error packet to original sender to perform new route discovery
MSR - Multipath Source Routing
• Direct Descendant of DSR • On-demand + Source Routing + Multipath • Probing-based adaptive load balancing among
multiple paths• Motivation of MSR
– Efficiently using the network resource– Alleviate the oscillation in adaptive single
path routing– Fast re-routing– Reducing computing & storage requirement– Exploiting computing power of host instead
of link capacity
Distributing Traffic among Multiple Paths
• Quantities: A heuristic equation• Probing-based adaptive control
– Decoupling between transport layer and network layer: SRPing
– Cost effective • Scheduling: Packet Weighted Round Robin• TCP out-of-order (re-sequencing) problem
Distributing Traffic among Multiple Paths
• Heuristic equation– Rationale: Autonomous system, homogeneous
assumption, bandwidth-delay product constant
where , is the delay of route with index i,
is the maximum delay of all the routes to the same destination, R is a factor to control the switching frequency between routes. U is a bound value to insure that should not to be too large.
jdmax
maxmin ,j
j
ji
i
U RdWd
jid
MSR Summary
• Reduce network congestion • Improve throughput, delay, mobility, fault
tolerance (CBR & FTP)• Acceptable routing overhead?
– Little more than that of DSR – Route discovery – Route maintenance
• Probing (unicast) add little O/H• Good candidate for QoS support
– QoS-MSR, reliable-MSR• Acceptable packet out-of-order level ?
Backup Source Routing (BSR)• Establish and maintain backup routes that
can be utilized after the primary path breaks• Define a new routing metric - route
reliability, and use it to provide the basis for the backup path selection
• Reduce the frequency of route discovery flooding, which is a major overhead in on-demand protocols
• Can improve the performance significantly in more challenging situations of high mobility
Simulation Methodology
• ns – Wireless extensions by CMU• Adopt methods used in [Broch98, Johnson99]• Two major files:
– Movement pattern file– Communication pattern file
• 50 mobile hosts placed randomly within a 1500m×300m area
• 20 connections• Different traffic types: CBR & FTP• Two set of simulations: Max speed 20m/s &
1m/s
Performance Evaluation
• MSR vs. DSR vs. BSR
• Performance Metrics
– Packet delivery ratio
– Data throughput
– End-to-end delay
– Packet drop probability
– Queue size
Simulation Results with UDP Traffic
0 100 200 300 400 500 6000.84
0.86
0.88
0.90
0.92
0.94
0.96
0.98
1.00
Pause time (s)
Pac
ket
deli
very
rat
io
DSRMSRBSR
-- Packet delivery ratio for 20 sources
8
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Connection No.
0
50
100
150
200
Thro
ughp
ut, p
ackets
/seco
nd
DSRMSR
Simulation Results – CBR• End-to-end throughput
Simulation Results with UDP Traffic
0 100 200 300 400 500 6000
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Pause time (s)
Ave
rage
end
to
end
dela
y (s
)
DSRMSRBSR
-- Average end-to-end delay for 20 sources
11
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Node No.
0
5
10
15
# o
f d
rop
s
DSRMSR
Simulation Results - CBR
• Packets dropped at each node
Previous Work on Using Multiple Paths
• Alternate use (primary and backup)– It works OK for CBR traffic (BSR, Bypass -
DSR, Node Disjoint M-path AODV, etc)– TCP does not get much benefit. Backup path
is used only after timeout; not efficient in mobility/errors.?
• Concurrent use (ie, packet scattering)– MSR– TCP does well in a static, error free net with
long paths (up to 50% improvement)– With mobility & errors, TCP suffers out-of-
order problems because of RTT difference on the two paths
“TCP Performance on multiple paths in ad hoc nets..” Liaw et al ICC 2004
Static net, no errors, opt W: max improvement 50%; typical improvement between 8% and 18%
Multiple Path TCP with Packet Replicas
• TCP data packet duplication on multiple paths– May introduce less O/H than repeated end to
end retransmissions• Improve end-to-end route robustness when
single route is not stable:– Replicate packet on multiple paths– Combat random, non correlated link losses– Combat path breakage
Variable Loss Rate [ 0.05; 0.1; 0.15; 0.2] T
otal
Th
rou
ghp
ut(
bit
s/s)
Original TCP Multipath TCP
Mobility(m/s)
Where do we stand?
• OLSR and TBRPF can dramatically reduce the “state” sent out on update messages
• They are very effective in “dense” networks.
• However, the state still grows with O(N)• Neither of the above schemes can handle
large scale nets from 10’s to thousands of nodes
• What to do?
The previous schemes reduce control traffic O/H but do not significantly reduce routing table size
Solution: use hierarchical routing to reduce table size
In the process, reduce also control traffic O/HProposed hierarchical schemes include:
– Hierarchical State Routing (HSR)– Fisheye State Routing (FSR)– Landmark Routing – Zone routing (hybrid scheme)
Hierarchical Routing
Routing
• Current MANET solutions have limitations: – (a) proactive routing solutions (eg, Optimal
Links State -OLSR) do not scale because of table size and control traffic overhead
– (b) on demand routing cannot handle high mobility and dense traffic patterns
– (c) explicit hierarchical routing introduces excessive address maintenance O/H in high mobility
• MANET protocols do not scale• UCLA approach: LANMAR
– Exploit implicit hierarchy induced by group mobility
Solution: Landmark Routing Overlay
• Main assumption: nodes move in groups• Groups are predefined or dynamically
recognized • Node address: < group ID , Host address>• Landmark elected in each group• Landmarks advertisements maintain the
landmark overlay
Logical SubnetLogical Subnet
LandmarkLandmark
LANMAR Overlay Routing (cont)
• Builds upon existing MANET protocols– (1) “local ” routing algorithm that keeps
accurate routes within local scope < k hops (e.g., OLSR)
– (2) Landmark routes advertised to all mobiles using DSDV
Logical SubnetLogical Subnet
LandmarkLandmark
LANMAR Overlay Routing (cont)• Packet Forwarding:
– A packet to “local” destination is routed directly using local tables
– A packet to remote destination is routed to Landmark corresponding to logical addr.
– Once the landmark is “in sight”, the direct route to destination is found in local tables
• Benefits: low storage, low update traffic O/H
Logical SubnetLogical Subnet
LandmarkLandmark
Landmark Routing In action
Logical SubnetLogical Subnet
LandmarkLandmarkLM1 LM2
LM3
sourcesourcedestdest
Long haul routinglocal routing
1. Node address = {subnet ID, Host ID}2. Look up local routing table to locate dest fail3. Look up landmark table to find destination subnet
LM14. Send a packet toward LM1
Link Overhead of LANMAR• Dramatic O/H reduction from linear to O(N) to O (sqrtN)
LANMAR enhances MANET routing schemes
We compare:
(a) MANET routing schemes: DSDV, OLSR and FSR; and
(b) same MANET schemes, BUT with LANMAR overlay on top
Delivery Ratio
• DSDV and FSR decrease quickly when number of nodes increases• OLSR generates excessive control packets, cannot exceed 400 nodes
OLSR
DSDV
FSR
LANMAR-DSDV
LANMAR-OLSR
LANMAR-FSR
Georouting - Key Idea
• Each node knows its geo-coordinates (eg, from GPS or Galileo)
• Source knows destination geo-coordinates; it stamps them in the packet
• Geo-forwarding: at each hop, the packet is forwarded to the neighbor closest to destination
• Options:– Each node keeps track of neighbor
coordinates– Nodes know nothing about neighbor
coordinates
Greedy Perimeter Stateless Routing for Wireless Networks (GPSR)
• Greedy forwarding– Each nodes knows own coordinates– Source knows coordinates of destination– Greedy choice – “select” the most forward
node
Finding the most forward neighbor
• Beaconing: periodically each node broadcasts to neighbors own {MAC ID, IP ID, geo coordinates}
• Each data packet piggybacks sender coordinates
• Alternatively (for low energy, low duty cycle ops) the sender solicits “beacons” with “neighbor request” packets
Greedy Perimeter Forwarding
D is the destination; x is the node where the packet enters perimeter mode; forwarding hops are solid arrows;
> Greedy forwarding failure. x is a local maximum in its geographic proximity to D; w and y are farther from D.> Node x’s void with respect to destination D
Got stuck? Perimeter forwarding
GPSR vs DSR
TCP over GPSR, AODV, DSR and DSDV
Speed(m/s)
Th
rou
gh
pu
t (K
bp
s)
GPSR commentary• Very scalable:
– small per-node routing state – small routing protocol message complexity– robust packet delivery on densely deployed,
mobile wireless networks• TCP is extremely sensitive to path breakage
(timeout) -- It does very well with georouting• Outperforms DSR and AODV• Drawback: it requires knowledge of dest geo
coordinates (explicit forwarding node address)– Beaconing overhead– nodes may go to sleep (on and off)