Ad Hoc and Mesh Networks: Architecture and Technology Overvie Hoc Mesh Talk 11... · Ad Hoc and...
Transcript of Ad Hoc and Mesh Networks: Architecture and Technology Overvie Hoc Mesh Talk 11... · Ad Hoc and...
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Ad Hoc and Mesh Networks:Architecture and Technology Overview
Rutgers, The State University of New JerseyD. Raychaudhuri
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Introduction: The Mesh Network Opportunity ….
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Ad Hoc and Mesh Networks: 1st Gen Products
From Firetide
Peer-to-peer network that allows groups of nearby users to communicate,
exchange files, stream media, work collaboratively, …
Ad Hoc Mesh
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Ad Hoc and Mesh Networks: BackgroundSeveral distinct motivations for ad hoc and mesh
Connecting ad hoc cluster of mobile users (tactical, vehicular, P2P)Networks involving embedded low-power devices (sensor nets)Access without wired infrastructure (rural, developing countries)Short-range radio cost-performance wide area
1st generation products were for specialized marketsTactical, specialized ad hoc applicationsSensing applications with power constraints
2nd gen products are for existing telecom markets, exploiting exceptional cost-performance of commodity radios…
Initially rural telecom, hobbyists metro mesh todayNow migrating to mainstream broadband accessIs cellular next?
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Ad Hoc and Mesh Networks: The PC Analogy
Wired High-Speed Network(Ethernet Switch or Internet)
Wired High-Speed Network(Ethernet Switch or Internet)
Mainframe Computer
Distributed PC’s
Cellular BTS TowerNetworked Low-Cost Radios
~$10K/GIPS
~$0.5K/GIPS – cheap but uncoordinated CPU cycles
Distributed PC solution dominatesfor most regimes except supercomputing
Technical issues: communication latency, overhead,parallel computation issues, execution control, unreliable networks, etc. mostly solved!
Lower cost, higher capacity, more robust??
~$1M/Mbps (long-range)
~1K/Mbps – cheap short-range but uncoordinatedbasic transmission
?? Distributed PC solution dominatesfor most regimes except supercomputing
Lower cost, higher capacity, more robust??
Technical issues: communication latency, overhead,Concurrent transmission issues, network control, unreliable channels, etc. not solved yet!
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Ad Hoc and Mesh Networks: The PC Analogy (contd.)
The $49 Mesh Node from Meraki Networks*!
1000 node metro mesh would cost just ~$50K in capital to cover a ~10 sq-Km area…!!
*Stanford and MIT student startup
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Ad Hoc and Mesh Networks: Product Space
Radio Range
End-UserServiceBit-Rate
1 m 10 m 100 m 1Km 10 Km
10 Kbps
100 Kbps
100 Mbps
1 Mbps
10 Mbps
2G Cellular
3G Cellular
AccessNetworks(WiMax)
MetroMesh
802.11b
802.11a,g
IndoorMesh LAN
Wide-area access
WLAN office/home and campus access
Dense office
& home access
UWB
DenseAP
Mesh Regime
TacticalAd hoc net
Mesh extends 802.11x radios to cover:
Metro mesh (medium range, high capacity)Access networks (extended range, lower capacity)Indoor WLAN (higher capacity, coverage)
Region of use can be even greater with new non 802.11 radios
Cellular wide-area equivalentSwitched Ethernet equivalent indoors
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Ad Hoc and Mesh Networks: 2nd Gen Products
Dual-radio ad-hoc router(includes wired interface for AP sites)
(above photo shows WINLAB’s ORBIT node)
RadioNodes
~50-100 mspacing
Ad-hocRadiolinks
Access Point (wired)
Ad-Hoc Radio Node
Office WLAN (faster, more scalable) than current 802.11 Metro Area Mesh Network (dense, high capacity, low cost)
Commercial vendors: Tropos, Motorola, Nortel, Nokia, …
Commercial vendors: Firetide, Cisco, …
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Ad Hoc and Mesh Networks: Problems with Current Technology
1st gen, and to some extent, 2nd gen solutions suffer from several technical problems:
Poor scalability – too many hops!CSMA/CA MAC implies “exposed nodes” which cannot tx in parallelMAC protocols never designed for multi-hop wireless to begin with!Topology changes rapidly – increases routing overheadOverall control overhead can be very highRouting unaware of changes in PHY speed/quality“Self-interference” effect for TCP flows
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Ad Hoc and Mesh Networks: Technology IssuesProducts are being released, but…
Mobile ad hoc networks don’t really work well for tactical & vehicularMesh network performance is marginal, OK for low-cost scenarios only
Major technical challenges areScalability (overcoming Gupta & Kumar) – hierarchies, multi-channelPHY capacity improvements – collaboration, MIMO, network codingTopology discovery and self-organization in mobile scenariosReducing control overheads in existing 802.11 MAC and MANET routingMitigating MAC “exposed node” problem for parallel transmissionsIntegrated or cross-layer MAC & routing approaches without the performance problems of conventional layered protocolsIntroducing service features such as QoS, multicast, …Network Security!
WINLAB research covers several of the above topics...
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Key Technologies
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Key Technologies: Hierarchical ArchitectureHierarchical structure essential for scalability
Classical “Gupta & Kumar” result shows mesh throughput per node does down as sqrt(n)System can scale with multiple frequencies and proper ratio of MN, FN and APE.g, if MN~100, ~10 FN’s & ~3 AP’s needed (…note significant reduction in # wired nodes)
Wired Internet Infrastructure
Gateway node
Potential bottleneck
“Flat” mesh network with ad-hoc routing: does not scale!
Wired Internet InfrastructureMulti-tiered
Interfaces towired network
Hierarchical architecture with multi-radio forwarding nodes and AP’s
Ad-hoc associations
Ad-hoc associations
Throughput per node scales ~ 1/sqrt(n)
Throughput per node scales with right ratio of FN’s, AP’s
Grid Portals/Access Points
Multi-radioForwarding Node
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System offered load (Mbps)
Sys
tem
Thr
ough
put (
Mbp
s)
Total System Throughput for flat and hierarchical topologies
FlatHierarchical
Sample experimental result on ORBIT showing linear scaling & ~2.5X capacity (for a mesh network with ~20 MN, 4FN, 2AP)
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Transmit Power Required: 1mW
AssocReq
Transmit Power Required: 10mW
FN
AP
• Scan all channels, record neighbors• Decide neighbor based on objective• Associate with neighbor
Key Technologies: Discovery and Self-OrganizationOnly a subset of available links made available to routing – achieves balance between routing overhead and route availabilityDynamic topology formation based on different such as max throughput, min delay or power
Send beaconsFN
AssocReq AssocReq
Logical topology
FN
Interface TwoSend beaconsAccept AssociationsForward client Data
Interface OneScan all channelsFind minimum delay links to APAssociate with AP
Wired Internet Infrastructure
PHY
MACDISCOVERY
ROUTING
Sample Result showingsignificant reduction in routing
overhead
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0 200 400 600 800 1000 12000
100
200
300
400
500
600
700
800
900
1000
O ffe red Load (k bps )
Syst
em th
roug
hput
(kbp
s)
S y s tem th roughpu t (S c ena rio I)
M H M e tricPA R M A
0 500 10000.5
0.6
0.7
0.8
0.9
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Offered Load (kbps)
Pac
ket D
eliv
ery
Rat
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Packet Delivery Ratio (Scenario I)
MH MetricPARMA
0 500 1000
100
200
300
400
500
600
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Offered Load (kbps)
End
-to-E
nd D
elay
(ms)
End-to-end Delay (Scenario I)
MH MetricPARMA
Improved performance with PARMA compared to MH metric.PARMA has the same behavior as MTM when no congestion.
Routing Metric = Σ pkt size/link speed + MAC congestion
Key Technologies: Cross Layer Routing
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Key Technologies: Multi-Channel MeshMulti-channel mesh (>>1 radio per node) can improve performance significantly by supporting concurrent transmissions & reducing/eliminating 802.11 MAC overheads
Many 2nd gen mesh products use 5-6 radios per nodeAlgorithms for optimizing throughput given constraints on # radios, # channelsPossible to use 802.11a hardware and avoid MAC effects entirely
f1
f2
f3
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Key Technologies: Clean-Slate PHY/MAC for Mesh
Wideband, agile short-range OFDM radio design optimized for speedFor example, ~2 x 20 Mhz bandwidth, max bit-rate ~250 MbpsAdditional low-bit rate PHY for control, flexible TDMA based MACRadios can switch channels and bit-rates on a slot-by-slot basis (~ms) –allows for unconstrained FD/TDMA allocations
2x20 Mhz
Agile RF Front End D/A
OFDMBaseband
MAC controlInterface
~25-200 MbpsService data
Programmable radio board at WINLAB
2.4 GhzRF
1 Mbps802.11b
PHY
ControlPlane data
PHY Module
#1
PHY Module
#2Control
PHY
ComputingModule
Grid Node Platform
Note: 2 x 200 Mhz agile radios with TD capabilityshould be sufficient for ~50 mbps duplex per node
Assuming ~3-4 hops to a wired AP
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Key Technologies: Global Control PlaneImportant architectural idea – clean separation of control & data planesReduces control overhead and enables contention-free global MAC/routing algorithmsCan use a single low rate channel (e.g. 1 mbps 802.11b) for control
http://www.uninett.no/wlan/throughput.html
Example of WLAN throughput breakdown
Control penaltyIn current WLANs
(increases with bit-rate)
Low Bit Rate PHY
Bootstrapping/Discovery
Link stats
Flow stats
Control Plane Data Plane
Fast/Agile PHY
Lower MAC
Integrated MAC/Routing
Frequency assignments,TDMA schedule and route
selection
Distributed or Global ControlIntegrated MAC/Routing Algorithm
Broadcast MAC & Routing
Control Plane
Data Plane
Ethernet and 802.11 drivers
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Key Technologies: Integrated Routing and MAC
Global allocation of routes and MAC time slots at the same time to completely eliminate contentionAllocation algorithm works on both frequency (FD) and time (TD)Algorithm checks for compatible time slot and freq at each receiverAllows for more parallel transmissions (fewer “exposed nodes”) and eliminates packet contentionSignificant performance improvement over conventional layered 802.11 + AODV etc.Requires GCP-type capability for distribution of control
Comparison of Individual and Aggregate Throughput
0200000
400000600000800000
1000000
12000001400000
flow 1 flow 2 flow 3 flow 4 flow 5 Total
Global Scheduling
802.11
Aloha
Slot Aloha
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Key Technologies: Cognitive Radio
AA
BB
D
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Cognitive radios provide PHY, MAC flexibility needed to implement cooperative multi-channel ad hoc networks with better performance
Cognitive radio can achieve multi-channel + flexible MAC performance PHY can be optimized between neighboring nodesHigh spectrum efficiency possible via dynamic spectrum algorithmsNetworks may utilize a control channel similar to GCP, etc.
Bootstrapped PHY &control link
End-to-end routed pathFrom A to F
PHY A
PHY BPHY C
Control(e.g. CSCC)
Multi-mode radio PHYAd-Hoc Discovery
& Routing Capability
Adaptive WirelessNetwork Node
(…functionality can be quitechallenging!)
~250 Mbps
Control Plane
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A
B
C
D E
R1 R2 R3
R4 R5
rejected
rejected
flow 1 (t1)
flow 2 (t2)
flow 3 (t3)
request
Responsebw resv
:::
W
Hops=0
:::ForwardingSet a timer
Check bandwidth availability
WNhopsB contupconsume ×++= )1
2,1min(
drop
:::
W
Hops=0
:::Resv BwSet a timerforwarding
Check bandwidth availability
upconsume
contconsume BWNhopsB +×= )
2,min(
drop
Establishes QoS routes with reserved bandwidth on a per-flow basisMonitors interference from adjacent nodesPerforms admission control to maintain network utilization below the congestion point
Key Technologies: QoS-Aware Routing
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Location is a more natural addressing mechanism
Location becomes more important than a network address
Opportunistic message forwarding within geographic perimeterRetransmissions from different vehicles Delay-tolerant networking
Desired message delivery zone
(Idealized) Broadcast range
Irrelevant vehicles in radio range for few seconds
Passing vehicle,in radio range for tens of seconds
Following vehicle,in radio range for minutes
Key Technologies: Geocasting in Ad Hoc Vehicular Networks
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Experimental Results
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Access PointUS Robotics 2450 AP
AMD Elan SC400 processor
1 MB Flash, 4 MB RAM
Prism-2 based PCMCIA card
Forwarding nodeCompulab 586 CORE
AMD Elan SC520 CPU
2 MB NOR flash + 64 MB NAND Flash on board
Dual PCMCIA slots
SensorsIntrinsyc Cerfcube
Intel PXA 250 (XScale processor)
CF-based wireless support
HA
RD
WA
RE
PLA
TFO
RM
SOFT
WA
RE
802.11b ad-hoc mode
Experimental Results: WINLAB Prototype circa 2002
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Experimental Results: ORBIT Radio Grid
ORBIT: 400 nodes in 20m x 20m– two 802.11 radios each (atheros and intel-based)Intended for ad hoc and mesh network studies
Antennas
Mini ITX-based SSF PC
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Urban
300 meters
500 meters
Suburban
20 meters
ORBIT Testbed
20 meters
HallwayOffice
30 meters
Experimental Results: Radio Mapping
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Experimental Results : ORBIT Proof-of-Concept for Metro Mesh Scenario
Flat Hierarchical
System Parameters: 0.9 sq. km, 20 mobiles/sensors, 4 FNs, 2 APs802.11a with multiple frequencies
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System offered load (Mbps)
Sys
tem
Thr
ough
put (
Mbp
s)
Total System Throughput for flat and hierarchical topologies
FlatHierarchical
Flat
Hierarchical
• “SOHAN” system evaluated for realistic deployment scenario with ~25 nodes
• Results show that system scales well and significantly outperforms flat ad-hoc routing (AODV)
APFN
MN
Mapping on to ORBITRadio grid emulator
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Mapping of the actual path onto ORBIT.
Emulated path.Emulated path.Actual path.Actual path.A B
C
D
E
F
H
G
Experimental Results: Mobility Emulation for MANET Studies
Goal: Emulate mobility for MAC and higher layers for larger number of nodes
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ObjectivesDemonstrate a vehicular 802.11a experiment.Actors : Sender, ReceiverDetails : Receiver is stationary. Sender moves around the parking lot. Sender transmits ICMP packets addressed to the receiver. Both nodes use 802.11a, channel 36. Receiver logs per-packet RSSI using Libmac.
Results (Snapshot of RSSI)
Experimental setup
Experimental Results: ORBIT Vehicular Setup
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Experimental Results: Ongoing Work
IRMA – Integrated Routing and MAC (..requires software MAC capability under development)
Includes a global control plane (GCP)Centralized and distributed control algorithms to be compared
Cross-layer routing with DCMA cut-through switching MAC
Switched multi-radio mesh scenarioBased on DCMA (Acharya) MAC, distributed cross-layer routing
Vehicular ad hoc network scenariosDense MAC experimentsGeocasting protocol evaluation