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Mobile Ad Hoc Networks

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Title: Mobile Ad Hoc Networks


1
Mobile Ad Hoc Networks
2
Organization
  • Introduction and Architecture
  • Applications and Challenges
  • Media Access Control
  • Routing in Ad Hoc Networks
  • Transport Layer Issues
  • Overarching Issues

3
MANETs Introduction
  • MANETs are mobile nodes that form a network in an
    ad hoc manner
  • The nodes intercommunicate using single or
    multi-hop wireless links
  • Each node in MANETs can operate as a host as well
    as a router
  • The topology, locations, connectivity,
    transmission quality are variable

4
MANETs Operations
D
Y
X
S
5
MANET Applications
  • Civil
  • Wireless LANs/WANs mobile and stationary
  • Remote data collection and analysis
  • Taxi/Cabs, Buses scheduling
  • Disaster recovery
  • Communications over water using floats
  • Vehicular Ad Hoc Network
  • Defense
  • Battlefield communications and data transfer
  • Monitoring and Planning

6
Issues and Challenges
  • Operating in presence of unpredictable mobility
    and environmental changes
  • Operating in an error prone media
  • Low bandwidth channels
  • Low power devices with limited resources
  • Maintaining and retaining connectivity and states
  • Security infrastructure and communication

7
MAC for MANET
  • Special requirements
  • Avoid interferences among simultaneous
    transmissions
  • Yet, enable as many non-interfering transmissions
    as possible
  • Fairness among transmissions
  • No centralized coordinators, should function in
    full distributed manner
  • No clock synchronization, asynchronous operations

8
Carrier-Sensing in MANET
  • Problems
  • Hidden terminal problem
  • Exposed terminal problem

9
MACs Suitable for MANET
  • MACA Karn90
  • Propose to solve hidden terminal problem by
    RTS/CTS dialog
  • MACAW Bharghavan94
  • Increase reliability by RTS/CTS/DATA/ACK dialog
  • IEEE 802.11 IEEE 802.11WG
  • Distributed and centralized MAC components
  • Distributed Coordination Function (DCF)
  • Point Coordination Function (PCF)
  • DCF suitable for multi-hop ad hoc networking
  • Also use RTS/CTS/DATA/ACK dialog

10
IEEE 802.11 DCF
  • Uses RTS-CTS exchange to avoid hidden terminal
    problem
  • Any node overhearing a CTS cannot transmit for
    the duration of the transfer
  • Any node receiving the RTS cannot transmit for
    the duration of the transfer
  • To prevent collision with ACK when it arrives at
    the sender
  • Uses ACK to achieve reliability

11
IEEE 802.11 DCF
  • CSMA/CA
  • Contention-based random access
  • Collision detection not possible while a node is
    transmitting
  • Carrier sense in 802.11
  • Physical carrier sense
  • Virtual carrier sense using Network Allocation
    Vector (NAV)
  • NAV is updated based on overheard RTS/CTS
    packets, each of which specified duration of a
    pending Data/Ack transmission
  • Collision avoidance
  • Nodes stay silent when carrier sensed busy
    (physical/virtual)
  • Backoff intervals used to reduce collision
    probability

12
Disadvantage of IEEE 802.11 DCF
  • 802.11 DCF not considered perfect for MANET
  • High power consumption
  • Hidden terminal problem not totally solved,
    exposed terminal problem not solved
  • Cause fairness problem among different
    transmitting nodes
  • Can only provide best-effort service
  • Active research area in MAC for MANET

13
MAC Advanced Topics
  • Support for QoS provisioning
  • Power Efficiency
  • MAC for Directional Antenna

14
QoS-aware MAC protocols
  • IEEE 802.11 Real-time extension
  • Black burst contention scheme
  • MACA/PR (Multihop Access Collision Avoidance with
    Piggyback Reservation)

15
Extend 802.11 DCF for Service Differentiation
Campbell01
  • For high priority packets
  • Backoff interval in 0,CWh
  • For low priority packet
  • Backoff interval in CWh1, CW
  • After collision, packet with smaller CW is more
    likely to occupy medium earlier

16
Black Burst Sobrinho99
  • Provides differentiation among real-time flow and
    best-effort flow
  • Provides fairness and priority scheduling among
    real-time flows
  • Fully distributed

17
Black Burst
A
C
B
Media
Busy
A
B
C
Carrier Sense
18
Black Burst
A
B
C
DIFS
Media
Busy
A
B
C
Black Bursts
19
Black Burst
A
B
C
DIFS
Media
Busy
A
B
C
20
Black Burst
A
B
C
DIFS
Media
Busy
A
B
C
21
Black Burst
A
B
C
Media
Busy
A
B
C
22
Black Burst
A
B
C
DIFS
RT A
Media
Busy
RT A
A
B
C
23
Black Bursts
  • All nodes begin the priority contention phase
    together
  • Higher priority node transmit a longer burst than
    low priority node
  • After transmitting its burst, a node listens to
    the channel
  • If channel still busy, the node has lost
    contention to a higher priority node

24
MAC Advanced Topics
  • Power Efficiency
  • Power Saving Make wireless interface sleep at
    appropriate times
  • Power Control Use the appropriate transmission
    power

25
Power Saving
  • Power Consumptions
  • From Spec. of Orinoco 11b WLAN PC Card Proxim
    Co. 2003
  • Battery Voltage 5V
  • Dose mode 9 mA ( 45 mW)
  • Receiver mode 185 mA ( 925 mW)
  • Transmit mode 285 mA ( 1425 mW)

26
MAC Layer Approach
  • Basic idea turn on/off the radio of specific
    nodes at appropriate times
  • IEEE 802.11
  • PAMAS
  • S-MAC
  • STEM
  • Asynchronous Wakeup patterns

27
PS Mode in WLANs
  • ATIM (Ad hoc Traffic Indication Map) window
    short interval during which the PS hosts wake up
    periodically.
  • Assume that hosts are fully connected and
    synchronized.
  • In the beginning of each ATIM window, each mobile
    host will contend to send a beacon frame.
  • Successful beacon serve for synchronizing mobile
    hosts clock.
  • This beacon also inhibits other hosts from
    sending their beacon
  • To avoid collisions among beacons, use random
    back-off 0-2CWmin 1

28
PS Mode in WLANs
  • After the beacon, host can send a direct ATIM
    frame to each of its intended receivers in PS
    mode.
  • After transmitted an ATIM frame, keep remaining
    awake
  • On reception of the ATIM frame, reply with an
    ACK and remain active for the remaining period
  • - Data is sent based on the normal DCF access.

29
Problems
  • PS mode of 802.11 is designed for single hop
    (fully connected) ad hoc network.
  • If applied for multi-hop
  • Clock synchronization
  • Communication delay and mobility are all
    unpredictable
  • network merging
  • Neighbor discovery
  • When a host in PS mode, both its chance to
    transmit and to hear others signal is reduced
    gt inaccurate neighbor information
  • Network partitioning
  • Inaccurate neighbor information may lead to long
    packet delay or even network (logically)
    partitioning problem.

30
PAMAS Singh98
  • A node avoids overhearing packets not addressed
    to it
  • so, reduce power consumption of processing
    unnecessary packets
  • Use of a separate channel for signaling

31
PAMAS
  • When to turn off?
  • when a node has no packets to send, it should
    power itself off if a neighbor starts
    transmitting
  • if at least one neighbor is transmitting and
    another is receiving, the node should power
    itself off
  • How long to be powered off?
  • It knows the duration of others transmission
  • What if the intended receiver is powered off?
  • Have to wait for it to wake up

32
STEM Schurgers02
  • Sparse Topology and Energy Management
  • Basic idea to wake up nodes only when they need
    to forward data
  • using asynchronous beacon packets in a separate
    control channel to wake up nodes
  • latency is traded off for energy savings

33
Wakeup mechanisms
  • On-demand wake-up
  • STEM, Remote Activated Switch(RAS)
  • Scheduled rendezvous
  • 802.11, Bluetooth, etc
  • Asynchronous wakeup
  • Power saving protocols Tseng02
  • Asynchronous wake-up Zheng03

34
MANET Power Saving Protocols Tseng02
  • Three asynchronous wakeup patterns
  • Dominating-awake-interval
  • Periodically-fully-awake-interval
  • Quorum-based

35
Tsengs Protocol
  • Beacon interval
  • For each PS host, it divides its time axis into a
    number of fixed length interval
  • Active window
  • On state
  • Beacon window
  • PS hosts send its beacon
  • MTIM window
  • Other hosts send their MTIM frames to the PS
    host.
  • Excluding these three windows, PS host with no
    packet to send or receive may go to the sleep
    mode.

36
Dominating-Awake-Interval
  • Dominating awake property
  • AW gt BI/2 BW
  • This guarantees any PS hosts beacon window to
    overlap with any neighboring PS hosts active
    window.
  • In every two beacon interval, PS host can receive
    all its neighbors beacon ? short response
    time?suitable for highly mobile
  • The sequence of beacon intervals are
    alternatively labeled as odd and even interval

37
Periodicallyfully-awake-interval
  • Two types of beacon interval
  • Low power intervals
  • AW is reduced to the minimum
  • PS host send out its beacon to inform others its
    existence
  • Fully awake intervals
  • AW is extended to the maximum
  • Arrives periodically every T intervals
  • PS hosts discover who are in its neighborhood,
    and can predict when its neighboring host will
    wake up.

38
Quorum-based
  • PS host only picks 2n-1 intervals (one column and
    one row) out of the n x n quorum
  • Quorum interval
  • Beacon MTIM, AW BI
  • Non quorum intervals
  • Start with an MTIM window, after that, host may
    go to sleep mode, AWMW

39
Asynchronous Wakeup FormalizedZheng03
  • Formalize the asynchronous wakeup schedule as a
    block design problem in combinatorics
  • Give theoretical analysis and an optimal design
  • Three components
  • neighbor discovery
  • neighbor prediction
  • neighbor reservation

40
Slot Assignments
124
235
346
457
561
672
713
SLOTS
1
2
3
4
5
6
7
Slot assignment for (7,3,1) design The schedule
repeats after 7 slots, has three ON slots, and
any two schedules overlap at least 1 slot.
41
MAC for Directional Antenna
  • Benefits of Directional Antenna
  • More spatial reuse
  • With omni-directional antenna, packets intended
    to one neighbor reaches all neighbors as well
  • Increase range, keeping transmit power constant
  • Reduce transmit power, keeping range comparable
    with omni mode
  • Reduces interference, potentially increasing
    spatial reuse

42
More Spatial Reuse
Omni-directional antenna
Directional antenna
A
B
A
B
C
D
C
D
Both A and C can transmit simultaneously
While A is transmitting to B, C cannot transmit
to D
43
Antenna Model
  • 2 Operation Modes Omni and Directional

A node may operate in any one mode at any given
time
44
Antenna Model
  • In Omni Mode
  • Nodes receive signals with gain Go
  • While idle a node stays in omni mode
  • In Directional Mode
  • Capable of beamforming in specified direction
  • Directional Gain Gd (Gd gt Go)
  • Symmetry Transmit gain Receive gain

45
Directional Packet Transmission

B
A
D-O transmission
Bs omni receive range
D-D transmission
A
B
Bs directional receive beam
46
MAC Designs for Directional Antenna
  • Most proposals use RTS/CTS dialog
  • They differ in how RTS/CTS are transmitted
  • Omni-directional transmit ORTS, OCTS
  • Directional transmit DRTS, DCTS
  • Current proposals
  • ORTS/OCTS Nasipuri00
  • DRTS/OCTS Ko00
  • DRTS/DCTS Choudhury02

47
ORTS/OCTS
  • Sender sends omni-directional RTS
  • Receiver sends omni-directional CTS
  • Receiver also records direction of sender by
    determining the antenna on which the RTS signal
    was received with highest power level
  • Similarly, the sender, on receiving CTS, records
    the direction of the receiver
  • All nodes overhearing RTS/CTS defer transmissions
  • Sender then sends DATA directionally to the
    receiver
  • Receiver sends directional ACK

48
ORTS/OCTS cont.
  • Protocol takes advantage of reduction in
    interference due to directional
    transmission/reception of DATA
  • All neighbors of sender/receiver defer
    transmission on receiving omni-directional
    RTS/CTS
  • ? spatial reuse benefit not realized

49
D-MAC
  • Uses directional antenna for sending RTS, DATA
    and ACK in a particular direction, whereas CTS
    sent omni-directionally
  • Directional RTS (DRTS) andOmni-directional CTS
    (OCTS)

50
DMAC DRTS/OCTS
A
B
C
E
D
DRTS(B)
OCTS(B,C)
OCTS(B,C)
DRTS(D)
OCTS(D,E)
DATA

DATA
ACK
ACK
51
DMAC Pros and Cons
  • Benefit Can allow more simultaneous
    transmissions by improving spatial reuse
  • Disadvantage Can increase ACK collisions

52
Directional NAV
  • Physical carrier sensing still omni-directional
  • Virtual carrier sensing be directional
    directional NAV
  • When RTS/CTS received from a particular
    direction, record the direction of arrival and
    duration of proposed transfer
  • Channel assumed to be busy in the direction from
    which RTS/CTS received

53
Directional NAV (DNAV)
  • Nodes overhearing RTS or CTS set up directional
    NAV (DNAV) for that Direction of Arrival (DoA)

D
CTS
C
X
Y
54
Directional NAV (DNAV)
  • Nodes overhearing RTS or CTS set up directional
    NAV (DNAV) for that Direction of Arrival (DoA)

D
C
DNAV
X
Y
55
Directional NAV (DNAV)
  • New transmission initiated only if direction of
    transmission does not overlap with DNAV, i.e.,
    if (? gt 0)

B
D
DNAV
?
A
C
RTS
56
Routing in Ad Hoc Networks
  • Unicast
  • Source node to destination node
  • Single or multiple hops
  • Multicast
  • Source node to multiple destination nodes
  • Varied number of hops
  • Members could join and leave

57
Issues in MANET Routing
  • Factors affecting the routing of packets in
    MANETs
  • Bandwidth limitation
  • Power limitation
  • Node heterogeneity
  • Multi-hops
  • Mobility

58
Classification of Unicast Routing Protocols
  • Flooding-based Routing
  • Precomputed (proactive) Routing
  • On-demand (reactive) Routing
  • Location or Position-Based Routing
  • Hybrid Routing
  • Power/Energy-Aware Routing

59
Flooding-Based Routing
D
S
60
Proactive Routing
  • Nodes maintain global state information
  • Consistent routing information are stored in
    tabular form at all the nodes
  • Changes in network topology are propagated to
    all the nodes and the corresponding state
    information are updated
  • Routing state maintenance could be flat or
    hierarchical

61
Examples of Proactive Routing
  • Destination Sequenced Distance Vector (DSDV)
  • Wireless Routing Protocol (WRP)
  • Hierarchical State Routing Scheme

62
Destination Sequenced Distant Vector (DSDV)
Routing Perkins94
  • Table-Driven algorithm based on Bellman-Ford
    routing mechanism
  • Every node maintains a routing table that records
    the number of hops to every destination
  • Each entry is marked with a sequence number to
    distinguish stale routes and avoiding routing
    loops
  • Routes labeled with most recent sequence numbers
    is always used
  • Routing updates can be incremental or full dumps

63
Wireless Routing Protocol (WRP) Murthy96
  • Table-based protocol
  • Each node is responsible for maintaining four
    tables
  • distance table,
  • routing table,
  • link-cost table, and
  • message retransmission list (MRL) table

64
WRP - Continued
  • The mobile nodes inform each other of link
    changes through the use of update messages
  • Update messages are sent only between neighboring
    nodes, which modify their tables and send updates
    to their neighbors
  • The existence and status of the neighboring nodes
    is determined through ACKs of messages or
    periodic hello messages

65
Hierarchical Routing Schemes
  • Cluster Gateway Source Routing (CGSR)
  • Nodes are divided into clusters each cluster has
    a cluster-head (uses a distributed cluster-head
    selection algorithm)
  • Uses DSDV for cluster-head-to-gateway routing

66
CGSR Chiang97
67
On-demand (Reactive) Routing
  • A path is computed only when the source needs to
    communicate with a destination
  • The source node initiates a Route Discovery
    Process in the network
  • After a route is discovered, the path is
    established and maintained until it is broken or
    is no longer desired

68
Ad hoc On-demand Distance Vector (AODV) Routing
Perking99
  • AODV builds on the DSDV algorithm
  • Creates route on a demand basis and maintains
    only as long as they are necessary
  • Loop freedom is routing is achieved through the
    maintenance of sequence numbers
  • AODV uses routing table to store routing
    information the routing table contains the
    destination and the next-hop IP addresses
  • AODV is able to provide both unicast and
    multicast ability

69
AODV Route Discovery
  • When a source desires to send a message to any
    destination, and if the routing table does not
    have a corresponding entry, it initiates a route
    discovery process.
  • The source broadcasts a route request (RREQ)
    packet to its neighbors, which in turn, forwards
    it to their neighbors, and so on, until either
    the destination node or an intermediate node with
    a valid route to the destination is located.
  • The intermediate nodes set of a reverse route
    entry for the source node in their routing table.
  • The reverse route entry is used for forwarding a
    route reply (RREP) message back to the source.
  • An intermediate node while forwarding the RREP to
    the source, sets up a forward path to the
    destination

70
AODV
F ?
C
A
E
S
I am F
D
B
F
71
AODV
To F, Next-hop is B
C
A
E
S
D
B
F
72
Dynamic Source Routing (DSR) Johnson96
  • On-demand source-based routing approach
  • Packet routing is loop-free
  • Avoids the need for up-to-date route information
    in intermediate nodes
  • Nodes that are forwarding or overhearing, cache
    routing information for future use
  • Two phases Route Discovery and Route Maintenance

73
DSR Route Discovery
  • Route discovery is initiated if the source node
    does not have the routing information in its
    cache
  • The source node broadcasts a route request packet
    that contains destination address, source
    address, and a unique ID
  • Intermediate nodes that do not have a valid
    cached route, add their own address to the route
    record of the packet and forwards the packet
    along its outgoing links

74
DSR Route Reply
  • Route reply is generated by the destination or a
    node that has a valid cached route
  • The route record obtained from the route request
    is included in the route reply
  • The route is sent via the path in the route
    record, or from a cached entry, or is discovered
    through a route request
  • Route maintenance is accomplished through route
    error packets and acknowledgments

75
DSR
I am F Route1 SACEF Route2 SBDF
F ?
C
A
E
S
D
B
F
To F, route is SBDF
Choose Route2
76
Zone Routing Protocol (ZRP) Haas97
  • ZRP is a hybrid of reactive/proactive protocol
  • A routing zone is defined for each node, which
    includes nodes whose minimum distance in terms of
    number of hops is less than a predefined number
  • A proactive routing approach is used for
    intra-zone communication and a reactive approach
    is used for inter-zone communication
  • For intra-zone route discovery, bordercasting
    technique is used

77
ZRP-Example
F
M
E
G
D
H
A
L
B
K
I
J
Border nodes
BoarderCast efficiently deliver route request to
all boarder nodes.
  • Routing Zone of A (Zone radius 2)
  • IARP Intra-zone routing protocol
  • IARP runs at the center of each zone
  • IARP uses proactive routing method
  • Each node has its own zone

78
ZRP-Example
F
M
E
Q
V
G
N
D
H
A
P
R
W
L
B
K
O
U
S
I
J
T
Center of zone
Source/Destination node
IERP Inter-zone routing, uses reactive routing
method
79
ZRP-Example
F
M
E
Q
V
G
N
D
H
A
P
R
W
L
B
K
O
U
S
I
J
T
Center of zone
Source/Destination node
IERP Inter-zone routing, uses reactive routing
method
80
ZRP-Example
F
M
E
Q
V
G
N
D
H
A
P
R
W
L
B
K
O
U
S
I
J
T
Center of zone
Source/Destination node
IERP Inter-zone routing, uses reactive routing
method
81
Location Informed Protocols for MANET
  • Location informed approach assume each mobile
    node is aware of its location, for example, by
    means of GPS
  • This approach is practical with the development
    of low-cost GPS receiving device
  • Categorization
  • Location aided routing (route discovery)
  • LAR, LAKER, PANDA, ...
  • Position based routing (packet forwarding)
  • DREAM, GPSR, GRA, ...

82
Location Aided Route Discovery
  • Example Location aided routing (LAR) protocol
    Ko98

D
S
Network area
83
Position Based Packet Forwarding
  • Examples geodesic forwarding (in GPSR)

84
Position Based Packet Forwarding Void Area
  • Difficulty in geodesic forwarding void area

A
B
S
D
C

85
LAKER Knowledge Guided Route Discovery Li03
  • Even more limited search space compared to LAR

86
LAKER Dealing With Void Area
  • Bypassing void area smartly

87
Multicasting in MANETs
  • Ad hoc multicasting should
  • Guarantee message delivery to all interested
    members
  • Minimize control messages in order not to
    interfere with data transmission
  • Maintain membership information as nodes join and
    leave at will
  • Repair broken links because of topology change

88
Route structure consideration
  • Tree structured protocols
  • More optimal route
  • More suitable for high load
  • More expensive to maintain
  • Mesh structured protocols
  • More resilient to topology change
  • More likely to repair link breakage locally
  • Link redundancy

Multicast source Multicast receiver Forwarding
node Group neighbor node
89
Taxonomy of current protocols
90
Hierarchical Multicasting
91
Relation to Underlying Unicast Protocol
  • Closely coupled MCEDARSinha99
  • Unicast-independent AMRoute Liu99
  • Double role serve both using one protocol
  • MAODV Royer99
  • ODMRP Lee99

92
Tree-Structured Routing MAODV Royer99
  • MAODVMulticast operation of Ad hoc On-demand
    Distance Vector
  • Multicast tree shared by the group.

93
MAODV- Route Request
Step 1 Flooding of Join Request
1
Multicast group member Multicast tree
member Non-Tree nodes Multicast Tree
Link ROUTE_REQ Message
2
4
3
7
5
f
6
b
e
c
d
a
94
MAODV- Route Request
Step 2 Join Reply trace back to source
1
Multicast group member Multicast tree
member Non-Tree nodes Multicast Tree
Link ROUTE_REP Message
2
4
3
7
5
f
b
6
e
c
d
a
95
MAODV- Route Request
Step 3Route Activation
1
Multicast group member Multicast tree
member Non-Tree nodes Multicast Tree
Link ROUTE_ACT Message
2
4
3
7
5
f
b
6
e
c
d
a
96
MAODV- Route Request
Step 4 Tree branch addition
Multicast group member Multicast tree
member Non-Tree nodes Multicast Tree Link
97
MAODV--Repairing
  • Link break detection
  • Periodical hello messages between neighbors
  • Hello message time_out
  • hello_interval?(1allowed_hello_loss)

98
MAODV--Repairing
  • Down-stream node of the broken link is
    responsible of repairing
  • Route Request is first given small TTL to hope
    the local operation

99
Mesh-based Routing ODMRP Lee99
  • On-Demand Multicast Routing
  • Source-based mesh
  • Membership information is maintained by the source

100
ODMRMesh setup
Step 1 Source periodically flood JOIN DATA packet
JOIN DATA packet Receiver Source
4
3
2
1
6
5
7
8
9
10
101
ODMR Mesh setup
Step 2 Receiver broadcasts JOIN TABLE
4
3
2
1
6
5
7
8
9
10
Finally, forwarding group is set to be 2,3,5,8
102
TCP in Ad hoc Networks
  • TCP is tuned for wired networks, in which
  • Low BER
  • Loss is mainly due to congestion
  • Route is relatively fixed during a connection
    life time
  • However, in wireless ad hoc networks
  • High BER
  • Route Changes
  • Network Partitions
  • Multi-path Routing

103
Effect of High BER
  • Bit errors cause packets to get corrupted and
    dropped
  • result in losses of TCP data segments or ACKs
  • Either fast retransmit or Retransmission Time-Out
    (RTO) is triggered

104
Effect of Route Changes
  • Discovering a new route may take significantly
    longer than TCP sender RTO
  • Route change may cause packets to arrive
    out-of-order

105
Effect of Network Partitions
  • If the sender and the receiver of a TCP
    connection lie in different partitions
  • Multiple consecutive timeouts
  • Inactivity for up to 1 or 2 minutes after
    partitions get connected

106
Effect of Multi-path Routing
  • Routes are short-lived due to frequent link
    breaks
  • To reduce delay due to route re-computation, some
    routing protocols (such as TORA) maintain
    multiple routes between a source-destination pair

107
Effect of Multi-path Routing
  • Multi-path routing can result in packet arrival
    out-of-order

108
Consequences
  • TCP sender misinterprets losses as congestion
  • Retransmits unACKed segments
  • Invokes congestion control
  • Enters slow start recovery
  • These are undesirable because
  • Why retransmit when there is no route
  • Throughput is always low as a result of frequent
    slow start recovery
  • Why use TCP at all in such cases?
  • For seamless portability to applications like
    file transfer, e-mail and browsers which use
    standard TCP

109
Approaches to Improve TCP
  • Hide error losses from the sender
  • So the sender will not reduce congestion window
  • Let the sender know, or determine, cause of
    packet loss
  • If due to errors, it will not reduce congestion
    window

110
Where to Do Modifications?
  • At the sender only
  • ATCP Liu01
  • At the receiver only
  • At intermediate node(s) only
  • Combinations of the above

111
ATCP Approach
  • ATCP utilizes network layer feedback (from the
    intermediate nodes) to take appropriate actions
  • Network feedback is
  • ICMP The Destination Unreachable ICMP message
    indicates route disruption
  • ECN Indicates network congestion
  • With ECN enabled, time out and 3 dup ACKs are
    assumed to no longer be due to congestion

112
ATCP in the TCP/IP Stack
Sender
Receiver
TCP
TCP
A-TCP
IP
IP
Link layer
Link layer
Note from now on, the terms ATCP and TCP are
referred to as ATCP sender and TCP sender,
respectively
113
Adapt to Ad-hoc Environment
  • High BER
  • Retransmits lost segments without shrinking the
    congestion window.
  • Delays due to route change and partition
  • Stops transmitting and resumes when a new route
    is found.
  • Multi-path routing
  • On receipt of duplicate ACKs, TCP sender should
    not invoke congestion control, because multi-path
    routing shuffles the order in which segments are
    received.

114
TCP/ATCP Behavior
  • RTO or 3rd dup ACK
  • Retransmits unACKed segments
  • ACK with ECN flag
  • Invokes congestion control
  • Destination Unreachable ICMP message
  • Stops transmission
  • Wait until a new route is found ? resume
    transmission
  • ATCP monitors TCP state and spoofs TCP in such a
    way to achieve the above behaviors

115
ATCP states
  • Normal (when a connection is opened)
  • Congested
  • Disconnected
  • Loss
  • During operation, ATCP transits from one state to
    another and put TCP in Persist mode when
    appropriate

116
TCP Persist Mode
  • Triggered by an ACK carrying zero advertised
    window size from TCP receiver
  • Parameters are frozen
  • Persist timer is started
  • TCP sender sends a probe segment each time
    persist timer expire
  • When TCP sender receives an ACK carrying non-zero
    advertised window size from TCP receiver
  • ? TCP sender resumes transmission

117
Advantages of ATCP
  • ATCP improves TCP performance
  • Maintains high throughput since TCPs unnecessary
    congestion control is avoided
  • Saves network resources by reducing number of
    unnecessary re-transmissions
  • End-to-End TCP semantics are maintained
  • ATCP is transparent
  • Nodes with and without ATCP can set up TCP
    connections normally

118
Overarching Issues
  • Power Aware Communication
  • Quality of Service (QoS)
  • Security

119
Power Aware Routing
  • Aka Energy efficient, Maximum Battery lifetime,
  • Minimum transmission power multiple small hops
    instead of single hop transmission
  • Residual battery capacity attempt balance
    traffic among different nodes
  • Geographical Adaptive Fidelity (GAF) Routing
  • Consider other factors e.g. link quality and
    retransmission

120
Quality of Service (QoS)
  • QoS A set of service requirements that are met
    by the network while transferring a packet stream
    from a source to a destination
  • QoS metrics could be defined in terms of one or a
    set of parameters
  • Examples delay, bandwidth, packet loss,
    delay-jitter, etc.

121
QoS in MANETs Mohapatra03
  • The use of QoS-aware applications are evolving in
    the wireless environments
  • Resource limitations and variations adds to the
    need for QoS provisioning
  • Use of MANETs in critical and delay sensitive
    applications demands service differentiation

122
Compromising Principles
  • Soft QoS
  • After the connection set-up, there may exist
    transient periods of time when QoS specification
    is not honored
  • The level QoS satisfaction is quantified by the
    fraction of total disruption
  • QoS Adaptation
  • As available resources change, the network can
    readjust allocations within the reservation range
    (dynamic QoS)
  • Applications can also adapt to the re-allocations

123
QoS Support in Physical Channels
  • Since wireless channel is time varying, the SNR
    in channels fluctuates with time
  • Adaptive modulation which can tune many possible
    parameters according to current channel state is
    necessary to derive better performance
  • Major challenge channel estimation accurate
    channel estimation at the receiver and then the
    reliable feedback to the transmitter
  • Wireless channel coding needs to address the
    problems introduced by channel or multipath
    fading and mobility
  • Cross-layer issue Joint source-channel coding
    takes both source characteristics and channel
    conditions into account

124
QoS Provisioning at the MAC Layer
  • For providing QoS guarantee for real-time traffic
    support in wireless networks, several MAC
    protocols based on centralized control have been
    proposed
  • For multihop networks
  • The MAC protocol must be distributed in nature
  • It should solve the hidden and exposed terminal
    problems

125
QoS Support using IEEE 802.11 DCF
  • IEEE 802.11 DCF is a best-effort type control
    algorithm
  • The duration of backoff is decided by a random
    number between 0 and the contention window (CW).
  • Service differentiation can be achieved by using
    different values of CW
  • When packets collide, the ones with smaller CW is
    more likely to occupy the medium earlier

126
MACA/PR Lin97
  • Multihop Access Collision Avoidance with
    Piggyback Reservation provides guaranteed
    bandwidth support for real-time traffic
  • The first packet in a real-time stream uses
    RTS/CTS dialogs to make reservations in the path
  • The sender schedules the next transmission after
    the current data transmission and piggybacks the
    reservation in the current data packet
  • Upon receiving the data packet correctly, the
    receiver updates its reservation table and sends
    an ACK
  • ACK serves for the renewal of reservation, not
    for recovering from packet losses

127
QoS-aware Routing at the Network Layer
  • Types of MANET routing protocols
  • Proactive, table-based routing schemes
  • Reactive, on-demand routing schemes
  • Constraint-based routing schemes
  • These algorithms are based on the discovery of
    shortest paths
  • QoS-aware routing protocol should find a path
    that satisfies the QoS requirements in the path
    from source to the destination

128
CEDAR Singha99
  • Core Extraction Distributed Ad hoc Routing scheme
    dynamically establishes the core of the network,
    and then incrementally propagates the link states
    of stable high-bandwidth links to the core nodes
  • The route computation is on demand basis
  • Components of CEDAR
  • Core extraction
  • Link-state propagation
  • Route computation

129
Integrating QoS in Flooding-Based Route Discovery
  • Ticket-based probing algorithm Chen99
  • During the QoS-satisfying path search, each
    probing message is provided a limited number of
    tickets to reduce the scope of flooding
  • When one or more probes arrive at the
    destination, the path and delay/bandwidth
    information is used to perform reservation for
    the QoS-satisfying path
  • A simple imprecise model is used for the
    algorithm

130
PANDA Approach Li03
  • Positional Attributes based Next hop
    Determination Approach (PANDA) discriminates the
    next hop based on the desired QoS metric
  • Instead of using a random rebroadcast delay, the
    receiver opts for a delay proportional to its
    ability in meeting the QoS demands
  • The decisions at the receivers are made based on
    a predetermined set of thresholds

131
QoS Support using Bandwidth Calculations Lin99
  • The end-to-end bandwidth can be calculated and
    allocated during the admission control phase
  • Using TDMA, time is divided into slots, which in
    turn are grouped into frames
  • Each frame contains two phases control and data.
  • During the control phase, each node takes turns
    to broadcast its information to all the neighbors
    in a predetermined slot.
  • At the end of control phase, each node knows
    about the free slots between itself and its
    neighbors
  • Thus bandwidth calculation and allocation can be
    done in a distributed manner

132
Multi-path QoS Routing Liao01
  • The algorithms searches for multiple paths
    between the source and the destination that
    collectively satisfies the QoS requirements
  • Suitable for ad hoc networks with limited
    bandwidth
  • A ticket based probing scheme is adopted for the
    path searching process

133
Transport Layer Issues for QoS Provisioning
  • TCP performs poorly in terms of end-to-end
    throughput in MANETs
  • The assumption used in Internet that packet
    losses are due to congestion is not valid in
    MANET environments
  • TCP performance improvement in wireless networks
  • Local retransmissions
  • Split-TCP connections
  • Forward error corrections (FEC)
  • Explicit feedback mechanisms to distinguish
    between losses due to errors and congestion is
    necessary for QoS provisioning in MANETs
  • Efficient techniques for resource management is
    necessary for QoS provisioning

134
Application Layer Issues
  • Application level QoS adaptation belong to
    adaptive strategies that play a vital role in
    supporting QoS
  • Flexible user interfaces, dynamic QoS ranges,
    adaptive compression algorithms, joint
    source-channel coding, joint source-network
    coding schemes
  • Adaptive real-time audio/video streaming support
    can be provided by enhancing
  • Compression algorithms, layered encoding, rate
    shaping, adaptive error control, and bandwidth
    smoothing

135
Inter-Layer Design Approaches
  • Efficient intercommunication protocols need to
    conserve scarce resources something difficult
    to achieve following the strict separation of the
    protocol layer functionalities
  • Inter-layer or cross-layer issues needs to be
    examined
  • Examples INSIGNIA and iMAQ

136
Security Issues
  • Environments and Philosophies
  • Closed vs. open world assumption
  • Prevention vs. Detection
  • Malicious vs. Selfish behavior

137
Vulnerabilities
  • Wireless links vulnerable to jamming
  • Inherent broadcast nature facilitates
    eavesdropping
  • Tradeoffs between resource constraints and
    security
  • Mobility/dynamics make it difficult to detect
    anomalies such as bogus routes
  • Self organization is inherent, cannot have
    central authorities/infrastructures, such as for
    key management

138
Attacks
  • Motivation
  • Better service
  • Monetary benefits
  • Gaining confidential information
  • Power saving
  • Preventing someone else from getting proper
    service

139
Attacks Indications
  • Create routing loops
  • Black holes
  • Misrouting along sub-optimal paths
  • Incorrect forwarding acknowledge ROUTE REQUEST,
    and do not forward it at all
  • Bogus routing information advertise a
    non-existent route
  • Choose a very short reply time, so the route will
    be prioritized and stays in cache longer
  • Do not send error messages in order to prevent
    other nodes from looking for alternative routes
  • Use promiscuous mode to listen in on traffic and
    gather information
  • Cause DoS attack caused by overload, by sending
    route updates at short intervals

140
Solutions
  • Authentication by imprinting (closed world)
  • Incentives to cooperate per hop payment in
    every packet/counters embedded in nodes
  • Localized certification based on Public Key
    Infrastructure
  • ARIADNE Secure on-demand routing protocol which
    prevents attackers from tampering
  • SEAD One way hash functions used to add security
    to DSDV (adds latency)

141
Detection
  • Intrusion detection techniques
  • Distributed and cooperative
  • Using statistical anomaly detection approaches
  • Cooperate with other network layers
  • Majority voting to classify behavior
  • Watchdog and Pathrater
  • CONFIDANT

142
Nodes bearing Grudges Buchegger02
  • Give the nodes incentive for cooperation
  • Nodes must behave in a manner that is best both
    for them and the group
  • Punish the non cooperating nodes
  • (A beautiful mind !!)

143
Selfish Gene Dawkins76
  • In many schemes, the malicious nodes are relieved
    of carrying traffic for others, while their
    traffic is still transferred
  • Looks more like encouragement
  • Biological example
  • Suckers
  • Cheats
  • Grudgers

144
From Birds to Network Nodes
  • The Monitor
  • Trust Manager
  • Reputation System
  • Path Manager

145
Components
  • The Monitor
  • Neighborhood watch
  • Look out for deviations no forwarding, route
    salvaging, unusually frequent route updates
  • Trust Manager (Distributed and adaptive)
  • Trust function to calculate trust levels
  • Forwarding of ALARM messages
  • Filtering ALARMs based on trust level of
    reporting node

146
Components
  • Reputation System
  • Own experience greatest weight
  • Observations smaller weight
  • Reported experience weight function according to
    trust level
  • Path Manager
  • Remove malicious nodes from routes between well
    behaved nodes
  • Educate nodes to not provide paths between
    malicious nodes

147
ARIADNE Hu02
  • Aims to create a secure on-demand routing
    protocol
  • Uses TESLA, an authentication scheme that
    requires loose time synchronization
  • Incorporate security features into DSR
  • Focuses on active attackers

148
Attacker Model
  • Passive versus Active
  • Passive only eavesdrops
  • Threats against privacy/anonymity
  • Active injects packets as well as eavesdrops
  • Active-n-m attacker
  • Compromises n good nodes and owns m nodes in the
    network
  • Attacker have all keys of compromised nodes and
    distributes it among all its nodes
  • Active-VC attacker
  • Owns all nodes on a vertex cut

149
Overview of TESLA
  • Broadcast authentication protocol
  • Authenticate routing messages
  • Only one MAC(Message Authentication Code)
  • Secure authentication in point-to-point
    communication
  • Asymmetric primitive by clock synchronization and
    delayed key disclosure
  • One-way key chain
  • Each sender chooses random initial key KN,
    generates one-way key chain as Ki HN-i (KN)
  • Schedule for disclosing keys
  • Each sender pre-determines the schedule
  • For example, disclose Ki at Ti T0 i ? t

150
Overview of TESLA
  • Receiver can determine which key is disclosed
  • Based on loose time synchronization(?)
  • Sender picks Ki which will not be disclosed until
    ? 2? time passes and add MAC using Ki
  • Discard the packet if security condition fails
  • TESLA security condition
  • Ki used to authenticate a packet cannot have been
    disclosed yet
  • tr ? t0 i ? t - ? implies Ki is not disclosed
    yet
  • ? is small ? may discard some packets? is large
    ? long delay for authentication? does not affect
    security

151
ARIADNE Route Discovery
  • Target authenticates Route Requests
  • Initiator includes a MAC with KSD
  • Data Authentications
  • Initiator authenticates nodes in Route Reply
  • Target authenticates nodes in Route Request and
    return only legitimate paths
  • TESLA, digital signatures, standard MACs
  • Per-hop hashing
  • One-way hash functions to verify that no hop was
    omitted

152
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