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1
Module D3
• More on Cellular Networks– Femtocells– Frequency Management– Mobility Management
• Wireless Ad Hoc Networking– Routing
mobnet.epfl.ch
2
Looking for an assistant-étudiant!• Wanted: experienced web developer to build a new website for a
research topic.• Existing minimal version: https://genomeprivacy.org/• Goal: make that web site look more professional • Expected profile:
– Be proficient in web building techniques (html, css, php/jsp, javascript,etc)
– Have previous experience in website development• Salary: 24 CHFrs/hour• Bulk of the work to be done in April / early May• Interested candidates please send to [email protected]
by the end of April 8th: your resume + transcript of grades record and list of websites you have built (or contact me)
Femtocells
3
• Home base stations for mobile networks– Licensed spectrum– Low-power, low-range– At user’s premises– Operated by cell. provider– Cellular access through
fixed broadband connection (ADSL,…)
• Why femtocells?– Better throughput, coverage, lower prices for users– Unload wide area cellular networks, reduce op. costs
• Examples in Switzerland: – Sunrise Indoor Box– Orange Booster Box (only business customers)
Femtocell Deployment
Building with poor receptionFemtocellPhone
Carrier antenna
Carrier core network
Femtocell Gateway
Internet
Obstacle
4
Network Architectures UMTS LTE
5
Security and Privacy Challenges• New threats
– Attacks on femtocells– Attacks on backhaul and core network (IPsec
tunnel)
Source: www.SafeNet-Inc.com
6
FGW:FemtocellGateway
Femtocells : Radio Measurements
Measurements carried out byCarl Hedari and Charles-Edmond Renouardwith the contribution from Igor Bilogrevic
7
• Radiation pattern shows the performance of the antenna– The signal does not propagate equally all around the femtocell
– W-CDMA Femtocell, ~5 MHz channel bandwidth
Femtocells – Radio Measurements
8
Anechoic Chamber at EPFL
Designed to stop reflections of RF
• Simulates a quiet space of infinite dimension
• Removes all source of exterior RF
Avoids jamming Swiss carriers and allows isolating the femtocell
9
Spectrum Analyzer – One Femtocell
Femtocell :
• Frequency : 2.137 GHz (UMTS)
• Power : -60.25 dBm
• Channel : 2.1351 GHz to 2.1396 GHz
10
Spectrum Analyzer
Spectrum Analyzer – Two Femtocells
• Another femtocell brought into the anechoic chamber
The femtocell listens to stations emitting on the same frequency and adapts its power output.
11
Spectrum Analyzer – Two Femtocells
12
One femtocell operating normallyPower : -60.25 dBm
The same femtocell and another femtocell nearby. Power : -54.18 dBm
With two active femtocells, the received power was increased by 6 dB (4 times more power)
Radio Traces : Measures
• 1 Femtocell• 1 Mobile from Operator X• 1 Mobile from Orange CH
• An antenna was plugged into a 6 GHz capable Oscilloscope, and put inside the chamber to “listen”
• The radio traces are displayed on the screen
13
Inside the anechoic chamber
Experiment 1 : Call established from Orange CH to X
50cm 50cm ∞
Oscilloscope(not spectrumanalyzeranymore)
Fs = 5 GHz
FemtocellMobile X Orange CH
14
Femtocell & Mobile X
Experiment 2 : Call established between two Orange mobiles
2m 2.5m
Oscilloscope Orange CH Orange CH
Fs = 2.5 MHz
Note: The sampling theorem was not respected for practical issues 15
16
Frequency Management
17
Frequency Management• In all countries of the world, the licensed spectrum is
managed by the government and (usually) leased to private operators
• Regulation authority – In Switzerland: Federal Commission for Communications, or
ComCom; assisted by BAKOM– In the US: FCC– In the EU: each country still has its national regulation authority
• Some political willingness (especially in the US) to reduce the role of the FCC Dynamic Spectrum Allocation (cognitive radios)See the IEEE DySpan conference (ieee-dyspan.org)
18
Procedure for Frequency Allocation
• 2 main options– Auction– Beauty contest
• Usually fixed price• Based on very detailed dossiers+ : price pre-determined- : temptation/suspicion of bribery; no price discovery
19
Auctioning of Frequencies• Goal of auction: best possible allocation of frequencies to
operators• Auctions are not meant to maximize the revenue for the
government• Splitting of the frequency bands in blocks (e.g., of 2*5Mhz)• Issue: how to combine the auctioned blocks• Caps in high-value bands to avoid unfair behavior• Typical duration of allocation: 10 to 20 years• Minimal (or starting) price: xxx CHFrs/MHz*Year (defined
by law in the case of CH)
20
The case of Switzerland• 3 main cellular operators (cellcos)
– Swisscom (state-controlled) has 60% of the mobile market– Failed attempt of merger of Orange and Sunrise (in 2010)
• Good quality of service, but high prices• Swiss pecularities: topography, super-tight emission
regulations, site acquisitions (to set up base stations) often problematic, expensive manpower, high-revenue and change-averse population
• All licencies (800, 900, 1800, 2100 and 2600MHz) (re-)allocated as of 2013 or 2016 until 2028 (auction run in February 2012; generated 996 MCHFrs)
21
22
non-ionizing radiation
Previous frequency allocation in CH
• GSM 900 Frequencies• Allocation until 31.12.2013• No free frequencies
• GSM 1800 Frequencies• Allocation until 31.12.2013• Some frequencies available (ex. Tele2)
• UMTS Core Band• Allocation until 31.12.2016• Some frequencies available
68MHz
Low frequencies
High frequencies
GSM900
Sunrise (50%)
Swisscom (40%)
Orange (10%)
Orange (40%)
Sunrise (19%)
Swisscom (21%)
In&Phone (8%)ex. Tele2 (12%)
Sunrise (25%)
Orange (25%)
Not allocated (25%)
Swisscom (25%)
GSM1800
UMTS core band (2100 MHz)
146MHz
140MHz
Courtesy: BAKOM
Location of base stations:http://map.funksender.admin.ch/webgis/bakom.php
Frequency allocation plan:www.bakom.admin.ch/themen/frequenzen/00652/00654/index.html?lang=en
24
Previous frequency allocation in CHGSM 900
Company Bands Expiration
Swisscom 2 x 13.6 MHz 31.12.2013
Sunrise 2 x 17 MHz 31.12.2013
Orange 2 x 3.2 MHz 31.12.2013
GSM 1800
Company Bands Expiration
Swisscom 2 x 15.2 MHz 31.12.2013
Sunrise 2 x 13.6 MHz 31.12.2013
Orange 2 x 29.4 MHz 31.12.2013
Ex.Tele2 2 x 8.6 MHz free
In&Phone 2 x 5.8 MHz 31.12.2013
UMTS 2100
Company Bands Expiration
Swisscom 2 x 15 MHz FDD + 5 MHz TDD 31.12.2016
Sunrise 2 x 15 MHz FDD + 5 MHz TDD 31.12.2016
Orange 2 x 15 MHz FDD + 5 MHz TDD 31.12.2016
BWA (3.5 GHz)
Company Bands Expiration
Swisscom 2 x 21 MHz 31.12.2016
Callix (Inquam) 2 x 21 MHz 31.12.2016
25
Why an invitation to bid?
All mobile radio frequencies auctioned together • Bidders can purchase a new, future-proof spectrum package• A world first
Expiring licences:• GSM licences (900 + 1800 MHz): End of 2013• UMTS licences (2100 MHz): End of 2016
Many new mobile radio frequencies are available:• "Digital dividend" (in the 800 MHz band)
ð Good propagation properties (even inside houses)ð Switzerland one of the first countries in Europe
• UMTS extension band (2600 MHz) ð Suitable for LTE technology with high bandwidths
Goals: - more frequencies for more bandwidth in mobile communications - efficient use of spectrum with new technologies (LTE)
Note: This slide and some of the following adapted from a slideshow kindly provided by Urs von Arx and Martin Dummermuth (BAKOM)
26
Rapidly growing data traffic in mobile radioRapidly increasing amounts of data on mobile radio networks
ð Doubling every 9-12 months
More and more smartphones (iPhone, Android devices, etc):
ð huge number of apps (incl. social networks such as Facebook and Twitter)
ð mobile internet, mobile TV, YouTube...
ð "Cloud computing" also mobile: same content present everywhere
Business Mobility:
ð office applications and content on all devices
ð new, flexible forms of working
All internet applications and content anywhere, anytime on a mobile phone
Increase in network capacity essential
27
New mobile radio technologies are coming
HSPA+ (Evolved High Speed Packet Access "plus") • Considerable increase in transfer rates (compared with UMTS)• Market-ready devices are already available
LTE (Long Term Evolution of UMTS; 4G)• 3 to 4 times higher spectrum efficiency than UMTS/HSPA• Increase in data rates to up to 100 Mbit/s in the downstream• Greater capacity in the network at a relatively low cost
New generation of mobile communications e.g. mobile HDTV, video streaming, on-line gaming…
Why an auction?• A transparent procedure
• The market determines the value of frequencies
• The market decides on the scope of the licences (not the regulator): ð therefore: auction of small frequency blocks ð Operators can acquire a new spectrum package which corresponds to their business models for the future
• Equal treatment of all candidates: ð All were able to take part on equal termsð No unilateral preference for any new entrants
Network operators purchase spectrum corresponding to their needs
No new market entry of an other network operator
29
Result of the auction: CHFrs 996'268'000
Frequency band Orange Sunrise Swisscom
800 MHz 20 MHz 20 MHz 20 MHz
900 MHz 10 MHz 30 MHz 30 MHz
1800 MHz 50 MHz 40 MHz 60 MHz
2.1 GHz FDD 40 MHz 20 MHz 60 MHz
2.1 GHz TDD 0 0 0
2.6 GHz FDD 40 MHz 50 MHz 40 MHz
2.6 GHz TDD 0 0 45 MHz
Adjudication price 154‘702‘000 481‘720‘000 359‘846‘000
30
Goals of the frequency allocation achieved
• Consumers benefit: ü Technological innovation continues; new broadband services.ü High quality and good coverage
• Technological progress supported:ü free choice of technology ü Operators can use LTE (high-speed broadband even in peripheral regions)
• A frequency allocation with a promising future:ü All network operators acquire good spectrum + more spectrum
• Long-term planning and investment security: ü Network operators can plan up to 2028
• Appropriate proceeds from the auction: ü A scarce public resource allocated appropriately ü Benefits the community
31
Reasons for the chosen form of the auction
• The participants in the auction can bid on frequency packages.
• The frequency packages correspond to their business model
• Value, for which bidders are prepared to pay
• Continuity for existing licensees:
• Consistent with the existing frequency allocation
32
Multi-phase sequence of the auction
• Auction in two stages. The bidders were able:
1. to combine frequency ranges optimally;
2. bid in a second phase bid for the preferred frequencies within the individual ranges.
• The auction took place over the internet from the bidders' company headquarters
33
Example: Combinatorial Clock Auction
Clock rounds
Excess demand
in any band?
Supplementary round (fine tune
expression of wishes)
Assignment of frequencies
No
Yes
Increase price of band(s) with excess demand
34
Bidding restrictions
Bidding restrictions (spectrum caps)
• Maximum extent of frequencies per frequency band
• Competition
• Enabling competition during the auction
• Increasing competition as much as possible after the auction by ensuring sufficient spectrum per bidder
• No bidder may acquire the entire 900 MHz spectrum (GSM)
• No market displacement of existing operators possible
• Existing UMTS operators can purchase at least the current range of frequencies in the 2100 MHz band (UMTS)
• No single bidder can dominate the major part of the GSM spectrum (900 MHz, 1800 MHz)
35
Distribution of the frequency spectrum (I)
Swisscom
Sunrise
Orange
0 50 100 150 200 250 300
93.8
96.2
99.4
255
160
160
Spectrum distribution before and after the auction
purchased at auction
to date
MHz
beforeauction
36
Distribution of the frequency spectrum (II)
255
160
160
Spectrum distribution Auction result (MHz)
SwisscomSunriseOrange
37
Allocation of the frequency spectrum
800MHz (paired)
900MHz (paired)
1800MHz (paired)
2100MHz (unpaired)
2100MHz (paired)
2600MHz (paired)
2600MHz (unpaired)
Sp
ect
rum
dis
trib
utio
n
0 10 20 30 40 50 60 70
20
30
60
0
60
40
45
20
30
40
0
20
50
0
20
10
50
0
40
40
0
Auction result Spectrum allocation
OrangeSunriseSwisscom
MHz
38
References on Auctions
• Cramton, Shoham and Steinberg (eds.): Combinatorial Auctions, MIT Press, 2006
• Ausubel, Lawrence M. and Paul Milgrom (2002), “Ascending Auctions with Package Bidding,” Frontiers of Theoretical Economics, 1, 1-45, http://www.bepress.com/bejte/frontiers/vol1/iss1/art1.
39
Mobility Management
40
2. Receive the ID of the LA
3. Compare with stored ID
4. If different, update and ask for registration
User Tracking: Geographic-based Strategy
Location area 1 (ID = 1) Location area 2 (ID = 2)
• Base stations periodically broadcast the ID of the LA• Users compare their last LA ID with the current ID, and transmits a registration message whenever the ID is different
• When there is an incoming call directed to a user, all cells within its current LA are paged
1. Change LA
5. Inform the HLR of the new LA ID
Location and Identity Privacy• Temporary Mobile Subscriber identifiers – TMSI –
changed after crossing Location Area (LA) border or time-out trigger
LA 0
LA 1
LA 2
LA 3
Pseudo A
Pseudo B
Pseudo C
Pseudo D
41
42
Handover
BS1 BS2
A B
t
Receivedsignal level
Level at B
Level at which handover is made(call transferred to BS2)
43
44
MTSO:MobileTelecommunicationsSwitching Office(also called MSC:Mobile Switching Center)
45
Handover Strategies• The handover power level must be carefully
chosen– Too small => risk of superfluous handovers– Too high => risk of losing the call due to weak
signal• Mobile Assisted Handover (MAHO)
– Mobiles measure power from surrounding base stations
– Report to the serving base station– Handover if the power received from another
station exceeds the serving station power by a certain threshold for a certain amount of time
Hard/Soft Handover
Hard: Communicate with one cell at a timeSoft: Communicate with two cells simultaneously
g TDMA & FDMA: Hard– Could technically use soft handover, but would be costly as
it would require multiple parallel radio modules
g CDMA: Soft – Needed to avoid near-far problem (i.e., Detect weaker
signal amongst strong signals)
46
47
Roaming Principle
Roaming agreement
Subscriberdatabase(IDs,keys,bills,…)
Home network
Subscriberdatabase(IDs,keys,bills,…)
Visited network
User
48
Roaming Architecture
Servicelogic
HomeLocationRegister
BaseStation
Servicelogic
VisitingLocationRegister
BaseStation
PSTN + Data Network
HomeNetwork
VisitedNetwork
49
50
Mobile Ad Hoc Networks
51
The classic solution for mobile networks
• 2nd generation (GSM, IS-41), 3rd generation (UMTS), 4th generation (LTE)• Huge, expensive fixed infrastructure• License for a share of the spectrum• Operational responsibility: network operators (telcos, ISPs)
52
The new paradigm: ad hoc networks
• Terminal and node merge • Everything is potentially mobile• Initial applications: communication in the battlefield (Packet Radio
Networks, in the 70’s)• The network is self-organized when it is run by the users themselves• Similar trend at the application layer: peer-to-peer
(e.g., Napster Gnutella, BitTorrent)
53
Application examples of ad hoc networks
• Sensor networks• Hybrid cellular / ad hoc networks (multi-hop cellular
networks)• Cars
– Collision avoidance– Optimization of traffic flows– …
• Crisis networks (e.g., rescue operations after major disaster)• Military networks
• Similar concept: Delay Tolerant Networks (DTNs)
54/58
Sensor networks
• Large number of sensor nodes, a few base stations• Sensors are usually battery powered:
– Main design criteria: reduce the energy consumption
• Multi-hop communication reduces energy consumption:– Overall energy consumption can be reduced, if packets
are sent in several smaller hops instead of one long hop
– Fewer re-transmissions are needed due to collisions
55/58
Wireless Mesh NetworksWired Access Point (WAP)
(a) A WiFi Network
• Wireless Mesh Network (WMN): Same coverage as with WiFi networks but with only one WAP (and several TAPs).
• WMNs allow a fast, easy and inexpensive network deployment.
• However, the lack of security guarantees slows down the deployment of WMNs
Transit Access Point (TAP)
(b) A Mesh Network
56
What is a VANET(Vehicular Ad hoc NETwork)?
Roadside base station
Inter-vehicle communications
Vehicle-to-roadside communications
Emergency event
• Communication: typically over the
Dedicated Short Range Communications (DSRC) (5.9 GHz)• Example of protocol: IEEE 802.11p• Penetration will be progressive (over 2 decades or so)
57
A smart vehicle
F o r w a r d r a d a r
C o m p u t i n g p l a t f o r m
E v e n t d a t a r e c o r d e r ( E D R )
P o s i t i o n i n g s y s t e m
R e a r r a d a r
C o m m u n i c a t i o n f a c i l i t y
D i s p l a y
(GPS)
Human-Machine Interface
58
Vehicular communications: why?
• Combat the awful side-effects of road traffic– In the EU, around 40’000 people die yearly on the roads; more
than 1.5 millions are injured– Traffic jams generate a tremendous waste of time and of fuel
• Most of these problems can be solved by providing appropriate information to the driver or to the vehicle
• More information: ACM VANET Workshop; ivc.epfl.ch
59
Upper bound for the throughput of ad hoc networks
If we have:
- identical randomly located nodes
- each capable of transmitting bits/s
Then the throughput ( ) obtainable by each node
for a destination is
( )log
n
W
n
randomly chosen
Wn
n n
Ref: P. Gupta, P. Kumar, The Capacity of Wireless NetworksIEEE Transactions on Information Theory, March 2000
60
Intuition behind the upper bound
N nodes (users)
O(N) users O(N) users
Cut set ~ N
O(N) transmissions from left to right
over
O( ) transmission links
mean
O( ) capacity per attempted transmission
N
1N
Ways to improve scalability:• Directional antennas• Locality of the traffic• Hybrid system
Ways to improve scalability:• Directional antennas• Locality of the traffic• Hybrid system
61
Routing in ad hoc networks• Peculiarities
– Node mobility– High rate of link failure Traditional routing approaches are not well suited
• Assumptions– Multihop communication– Symmetric links (in most cases)– Omnidirectional antennas (in most cases)– All nodes have equal capabilities and responsibilities
• Figures of merit– Latency of route discovery– Overhead (bandwidth, energy, processing power)– Security
• Current status of research: – Many, many proposals– Optimal solution depends on deployment scenario: mobility patterns, radio
model, traffic characteristics,…
62
Brief reminder : Link-state protocols
• Example: OSPF• May consume a lot of resources to update the
routes• Techniques to alleviate the problem : limit the
propagation of information• Does not seem to be well suited to cope with
mobility
63
Distance vector routing (1/2)
0 1 5
1 0 1 3
5 1 0 7
3 7 0
A
B
D
C
13
1
5 7
A
B
C
D
A B C D
1 0 1 3
Distancevector
Distancevector of B
2 1 2 4
+ Distance from A to B =
Cost to dest.via B
Take the minTake the min
0 1 2,B 4,B
(1 row stored in each node)
64
Distance vector routing (2/2)
• Even if the updates are asynchronous, the routing tables converge
• The algorithm is often called Bellman-Ford• Problem: undesirable behaviour when links go
up and down (e.g., count to infinity problem)
65
Routing protocols for wireless ad hoc networks
Response time,bandwidth
Response time,bandwidth EnergyEnergy
Mobile ad hoc networks Sensor networks
Proactiveprotocols
Proactiveprotocols
Reactiveprotocols
Reactiveprotocols
Destination-SequencedDistance-Vector (DSDV)
Optimized Link-State Routing(OLSR)
Ad Hoc On-DemandDistance-Vector(AODV)
DynamicSourceRouting(DSR)
Geography-based routing
Geography-based routing
Cluster-based(or hierarchical)routing
Cluster-based(or hierarchical)routing
Geodesic packetforwarding
66
Dynamic source routing (DSR)
• Reactive routing protocol• 2 phases, operating both on demand:
– Route discovery• Used only when source S attempts to to send a packet to destination D• Based on flooding of Route Requests (RREQ)
– Route maintenance• makes S able to detect, while using a source route to D, if it can no longer
use its route (because a link along that route no longer works)
67
DSR: Route discovery (1)
E G
M
H
R
FA
B
C
I
DS
K
N
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PJ
Q
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DSR: Route discovery (2)
E G
M
H
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FA
B
C
I
DS
K
N
L
PJ
Q
(S)
69
DSR: Route discovery (3)
E G
M
H
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FA
B
C
I
DS
K
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PJ
Q
(S,A)
(S,E)
70
DSR: Route discovery (4)
E G
M
H
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FA
B
C
I
DS
K
N
L
PJ
Q
(S,E,G)
(S,B,C)
71
DSR: Route discovery (5)
E G
M
H
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FA
B
C
I
DS
K
N
L
PJ
Q
(S,E,G,J)
(S,A,F,H)
72
DSR: Route discovery (6)
E G
M
H
R
FA
B
C
I
DS
K
N
L
PJ
Q (S,A,F,H,K)
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DSR: Route discovery (7)
E G
M
H
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FA
B
C
I
DS
K
N
L
PJ
Q
(S,A,F,H,K,P)
74
DSR: Route discovery (8)
E G
M
H
R
FA
B
C
I
DS
K
N
L
PJ
Q
RREP(S,E,G,J,D)
75
DSR: Route Discovery (9)
• Route reply by reversing the route (as illustrated) works only if all the links along the route are bidirectional
• If unidirectional links are allowed, then RREP may need a route discovery from D to S
• Note: IEEE 802.11 assumes that links are bidirectional
76
DSR: Data delivery
E G
M
H
R
FA
B
C
I
DS
K
N
L
PJ
Q
DATA(S,E,G,J,D)
77
DSR: Route maintenance (1)
E G
M
H
R
FA
B
C
I
DS
K
N
L
PJ
Q
DATA(S,E,G,J,D)
X
78
DSR: Route maintenance (2)
E G
M
H
R
FA
B
C
I
DS
K
N
L
PJ
Q
XRERR(G-J)
When receiving the Route Error message (RERR), S removes the broken link from its cache.It then tries another route stored in its cache; if none,it initializes a new route discovery
When receiving the Route Error message (RERR), S removes the broken link from its cache.It then tries another route stored in its cache; if none,it initializes a new route discovery
79
DSR: Optimization of route discovery: route caching
• Principle: each node caches a new route it learns by any means
• Examples– When node S finds route (S, E, G, J, D) to D, it also learns
route (S, E, G) to node G– In the same way, node E learns the route to D– Same phenomenon when transmitting route replies
• Moreover, routes can be overheard by nodes in the neighbourhood
• However, route caching has its downside: stale caches can severely hamper the performance of the network
80
DSR: Strengths
• Routes are set up and maintained only between nodes who need to communicate
• Route caching can further reduce the effort of route discovery
• A single route discovery may provide several routes to the destination
81
DSR: Weaknesses• Route requests tend to flood the network and generally
reach all the nodes of the network• Because of source routing, the packet header size grows
with the route lengh• Risk of many collisions between route requests by
neighboring nodes need for random delays before forwarding RREQ
• Similar problem for the RREP (Route Reply storm problem), in case links are not bidirectional
Note: Location-aided routing may help reducing the number of useless control messages
82
Ad Hoc On-Demand Distance Vector Routing (AODV)
• As it is based on source routing, DSR includes source routes in data packet headers
• Large packet headers in DSR risk of poor performance if the number of hops is high
• AODV uses a route discovery mechanism similar to DSR, but it maintains routing tables at the nodes
• AODV ages the routes and maintains a hop count • AODV assumes that all links are bi-directional
83
AODV : Route discovery (1)
E G
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C
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DS
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AODV : Route discovery (2)
E G
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Note: if one of the intermediate nodes (e.g., A)knows a route to D, it responds immediately to S
Note: if one of the intermediate nodes (e.g., A)knows a route to D, it responds immediately to S
: Route Request (RREQ)
85
AODV : Route discovery (3)
E G
M
H
R
FA
B
C
I
DS
K
N
L
PJ
Q
: represents a link on the reverse path
86
AODV : Route discovery (4)
E G
M
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FA
B
C
I
DS
K
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PJ
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AODV : Route discovery (5)
E G
M
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B
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DS
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AODV : Route discovery (6)
M
D
K
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PJ
E G
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FA
B
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S
N
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AODV : Route discovery (7)
M
D
K
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PJ
E G
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FA
B
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S
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AODV : Route reply and setup of the forward path
M
D
K
L
PJ
E G
H
R
FA
B
C
I
S
N
Q
: Link over which the RREP is transmitted
: Forward path
91
Route reply in AODV
• In case it knows a path more recent than the one previously known to sender S, an intermediate node may also send a route reply (RREP)
• The freshness of a path is assessed by means of destination sequence numbers
• Both reverse and forward paths are purged at the expiration of appropriately chosen timeout intervals
92
AODV : Data delivery
M
D
K
L
PJ
E G
H
R
FA
B
C
I
S
N
Q
Data
The route is not included in the packet headerThe route is not included in the packet header
93
AODV : Route maintenance (1)
M
D
K
L
PJ
E G
H
R
FA
B
C
I
S
N
Q
Data
X
94
AODV : Route maintenance (2)
M
D
K
L
PJ
E G
H
R
FA
B
C
I
S
N
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XRERR(G-J)
When receiving the Route Error message (RERR), S removes the broken link from its cache.It then initializes a new route discovery.
When receiving the Route Error message (RERR), S removes the broken link from its cache.It then initializes a new route discovery.
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AODV: Destination sequence numbers
• If the destination responds to RREP, it places its current sequence number in the packet
• If an intermediate node responds, it places its record of the destination’s sequence number in the packet
• Purpose of sequence numbers:– Avoid using stale information about routes– Avoid loops (no source routing!)
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AODV : Avoiding the usage of stale routing tables
S DA
B
DSN(D) = 5
: Forward path
S
D
A
B
DSN(D) = 5
… …
…
DSN(D) = 8
1. 2.
S
D
A
B
DSN(D) = 5
…
… DSN(D) = 8
3.
RREQS
D
A
B
DSN(D) = 5
…
… DSN(D) = 8
RREP
4.
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AODV : Avoiding loops
A B S D
C
: Forward path
• Assume there is a route between A and D; link S-D breaks; assume A is not aware of this, e.g. because RERR sent by S is lost• Assume now S wants to send to D. It performs a RREQ, which can be received by A via path S-C-A• Node A will reply since it knows a route to D via node B• This would result in a loop (S-C-A-B-S)• The presence of sequence numbers will let S discover that the routing information from A is outdated• Principle: when S discovers that link S-D is broken, it increments its local value of DSN(D). In this way, the new local value will be greater than the one stored by A.
X
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AODV (unicast) : Conclusion
• Nodes maintain routing information only for routes that are in active use
• Unused routes expire even when the topology does not change
• Each node maintains at most one next-hop per destination
• Many comparisons with DSR (via simulation) have been performed no clear conclusion so far
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FlashLinQ (Qualcomm)
• Vision: extend users’ sensing capabilities• Operates in licensed spectrum• All devices globally synchronized to a common
external timing source (e.g., GPS or cellular base stations)
• All devices operate in OFDMA (Orthogonal Frequency-Division Multiple Access)
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Balloon-Mounted Base StationsLoon Project by Google
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Conclusion on wireless ad hoc networks
• Extensive research activity over the last decade
• Scalability is still an open issue• Commercial deployments are expected as an
extension of the cellular network
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April 15, 15:00 – 15:45, in this room:Special session on career management
(by JP Hubaux)
- How to choose my first job?- Should I do an MBA? A PhD?- Should I go to the US?- How about joining a start-up company? Or even create a new one?- How do I get the «big picture» of the job market?- I want to stay in Switzerland, are there interesting companies here?
Note: There is a Quiz D3 but there is no Homework D3
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References on wireless ad hoc networks
Overview of ad hoc network routing protocols: see the references mentioned at: http://en.wikipedia.org/wiki/Ad_hoc_networking
Research conference: ACM MobiHoc (especially for the theoretical aspects)
For FlashLinQ (Qualcomm et al.):W. Xinzhou et al., a synchronous distributed scheduler for peer-to-peer ad hoc networks, IEEE/ACM Transactions on Networking (TON), Volume 21 Issue 4, August 2013
See also « device-to-device communications »
Hands-on Radio Planning - Exercise 1 (Zinal)
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Antenna in the valley, height = 2mAntenna in the valley, height = 50m
Antenna at the top of the moutain (Garde de Bordon, 3’310m) , height = 50m
Note: these are not the frequencies used in the real network!
Hands-on Radio PlanningExercise 2 (Vaud Triangle)
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3 antennas: (i) above Gimel, (ii) at the Mont-Pèlerin, and (iii) above EclépensNote: these are not the frequencies used in the real network!
Hands-on Radio PlanningExercise 2 (Vaud Triangle)
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3 antennas: (i) above Gimel, (ii) at the Mont-Pèlerin, and (iii) above Eclépens(with « Mesh » function)
Note: these are not the frequencies used in the real network!
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