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
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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
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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
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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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