Transcript Ad Hoc Wireless Routing
Wireless Ad hoc networks
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Routing
Proposed ad hoc Routing Approaches
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Conventional wired-type schemes (global routing, proactive ):
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Distance Vector; Link State Proactive
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OLSR ad hoc routing: , TBRPF On- Demand, reactive
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DSR routing: (Source routing), MSR, BSR AODV (Backward learning)
Wireless multihop routing challenges
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mobility need to scale to large numbers (100’s to 1000's) need to support multimedia applications (QoS)
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unreliable radio channel (fading, external interference, mobility, etc) limited bandwidth limited power
Conventional wired routing limitations
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Distance Vector (eg, Bellman-Ford, BGP):
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Tables grow linearly with # nodes
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routing control network size O/H linearly increasing with
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convergence problems (count to infinity); potential loops ( mobility ?)
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Link State (eg, OSPF):
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link update flooding O/H caused by network size and frequent topology changes
CONVENTIONAL ROUTING DOES NOT SCALE TO SIZE AND MOBILITY
DV LS Intra-AS RIP OSPF Inter-AS BGP
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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”
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(1) if the network is “dense”, use fewer
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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:
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OLSR : Optimal Link State Routing
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TBRPF : Topology Broadcast Reverse Path Routing
LSR (Link State Routing)
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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)
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In OLSR only a subset of neighbors (
MPR -Multipoint Relay Selectors)
retransmit control messages:
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Reduce size of control message;
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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
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Reduce flooding overhead Adapted for dense network OLSR retains all the advantages of LSR :
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stable; Does not depend upon any central entity; Tolerates loss of control messages; Supports nodes mobility
On-Demand Routing Protocols
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Routes are established “on demand” as requested by the source Only the active routes are maintained by each node Channel/Memory overhead is minimized
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Two leading methods for route discovery: source routing and backward learning (similar to LAN interconnection routing)
Existing On-Demand Protocols
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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)
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RFC 4728 – February 2007 Forwarding:
source route
driven instead of hop-by-hop route table driven
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Mobility ?
No periodic routing update message is sent The first path discovered is selected as the route Two main phases
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Route Discovery
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Route Maintenance
DSR - Route Discovery
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To establish a route, the source floods a
Route Request
message with a unique request ID The
Route Request
ID numbers packet “picks up” the node
Route Reply
message containing path information is sent back to the source either by
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the destination, or
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intermediate nodes that have a route to the destination Each node maintains a
Route Cache
which records routes it has learned and overheard over time
DSR - Route Maintenance
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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 Error
packet to original sender to perform new route discovery
MSR - Multipath Source Routing
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Direct Descendant of DSR On-demand + Source Routing +
Multipath
Probing-based adaptive
load balancing
among multiple paths Motivation of MSR
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Efficiently using the network resource Alleviate the oscillation in adaptive single path routing
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Fast re-routing Reducing computing & storage requirement Exploiting computing of link capacity power of host instead
Distributing Traffic among Multiple Paths
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Quantities: A heuristic equation
Probing-based
adaptive control
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Decoupling between transport layer and network layer: SRPing
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Cost effective Scheduling: Packet Weighted Round Robin TCP out-of-order (re-sequencing) problem
Distributing Traffic among Multiple Paths
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Heuristic equation
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Rationale: Autonomous system, homogeneous assumption, bandwidth-delay product constant
d W i j
min
d d j
max
j
,
U
i
where ,
j
is the delay of route with index
i
,
i R d j
max
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.
MSR Summary
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Reduce network congestion Improve throughput, delay, mobility, fault tolerance (CBR & FTP) Acceptable routing overhead?
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Little more than that of DSR
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Route discovery
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Route maintenance
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Probing (unicast) add little O/H Good candidate for QoS support
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QoS-MSR, reliable-MSR Acceptable packet out-of-order level ?
Backup Source Routing (BSR)
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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
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Wireless extensions by CMU Adopt methods used in [Broch98, Johnson99] Two major files:
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Movement pattern file
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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
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MSR vs. DSR vs. BSR Performance Metrics
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Packet delivery ratio
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Data throughput
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End-to-end delay
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Packet drop probability
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Queue size
Simulation Results with UDP Traffic -- Packet delivery ratio for 20 sources 8
Simulation Results – CBR
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End-to-end throughput
200 DSR MSR 150 100 50 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Connection No.
Simulation Results with UDP Traffic -- Average end-to-end delay for 20 sources 11
Simulation Results - CBR
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Packets dropped at each node
15 DSR MSR 10 5 0 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.
Previous Work on Using Multiple Paths
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Alternate use (primary and backup)
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It works OK for CBR traffic (BSR, Bypass DSR, Node Disjoint M-path AODV, etc)
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TCP does not get much benefit . Backup path is used only after timeout; not efficient in mobility/errors.?
Concurrent use (ie, packet scattering)
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MSR
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TCP does well in a static , error free net with long paths (up to 50% improvement)
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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
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TCP data packet duplication on multiple paths
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May introduce less O/H than repeated end to end retransmissions Improve end-to-end route robustness when single route is not stable:
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Replicate packet on multiple paths
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Combat random, non correlated link losses Combat path breakage
Variable Loss Rate [ 0.05; 0.1
; 0.15
; 0.2] Original TCP Mobility(m/s) Multipath TCP