Lecture 23 27. quality of services in ad hoc wireless networks

Chandra
Prakash
LPU
QOS IN AD-HOC
NETWORKS

Objective
 Introduction-
 Issues and Challenges in Providing QoS in Ad HocNetworks
 Classifications of QoS Solutions
 MAC Layer Solutions
 Network Layer Solutions;
 QoS Model and Frameworks for Ad HocWireless Networks
 Typical QoS routing protocols
 Conclusion and Open Issues

Introduction
 Mobile ad hoc networks (MANETs) are infrastructureless
and intercommunicate using single-hop and multi-hop paths
 Nodes act both as hosts and routers
 Topology changes could occur randomly, rapidly, and
frequently
 Routing paths are created and deleted due to the nodal
mobility

Applications of MANETs
 Collaborative computing
 Communications within buildings, organizations, ad hoc
conferences
 Communications in battlefields and disaster recovery areas
 Sensor networks

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
 It is the performance level of a service offered by the network to
the user
 Network or service provider provide different kinds of services to
the users.
 Services : can be characterized by a set of measurable
prespecified service requirements such as min. bandwidth, max
delay, max. delay variance (jitter) and max packet loss.
 QoS metrics could be defined in terms of one or a set of
parameters

Quality of Service (QoS)
 After accepting a service requirement from the user the network has to
ensure that the services requirements of the user’s flow are met, as per
the agreement, throughout the duration of the flow.
 Network has to provide a set of services guarantees while
transporting a flow.
Video frame without QoS Support Video frame with QoS Support

Target of QoS Routing
 To find a feasible path between source and destination, which
 satisfies the QoS requirements for each admitted connection
and
 Optimizes the use of network resources
A
B C
D
E F
G
<2,4>
<3,3>
<4,5>
Tuple: <BW,D>
QoS requirement: BW≥4
<2,2>
<5,4>
<4,4>
<5,3><4,2>
<3,4>
Shortest path
QoS Satisfying path

QoS in MANETs
 QoS require negotiation between host and network
 The use of QoS-aware applications are evolving in the wireless
environments
 Resource limitations and variations adds to the need for QoS
provisioning
 Real time traffic support in Ad Hoc Networks
 Requires mechanisms that guarantee bounded delay and jitter
 Can be classified two type of application
1. Hard real time application –
 requires strict QoS guarantees
 Include nuclear reactor control system , air traffic control systems and
missile control system
 Delay may lead to disastrous results.

QoS in MANETs
2. Soft real time application
Can tolerate degradation in the guaranteed QoS to a certain extent
Eg: voice telephony, video-on-demand, and video conferencing
Delay may degrade the service but do not produce hazardous results.
 Providing hard real time guarantee in MANET is extremely
difficult due to reasons such as unrestricted mobility of nodes,
dynamically varying network topology, time varying channel
capacity and the presence of hidden terminals .
 Research community is currently focusing on providing
QoS support for soft real time applications
 Use of MANETs in critical and delay sensitive applications
demands service differentiation

Different services require different QoS parameters.
– Multimedia
- Bandwidth, delay jitter & delay
– Emergency services
- Network availability
– Group communications
- Battery life
QoS parameters in ad hoc wireless networks:
11

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Issues and challenges in providing QoS in ad hoc wireless
networks:
1. Dynamically varying network topology:
 QoS session may suffer due to frequent path breaks.
 Require new path formation but results in delay.
2. Imprecise state information
State information is inherently imprecise due to dynamic changes in
network topology and channel characteristics
 Link-specific state information-
 bandwidth, delay, delay jitter, loss rate, error rate, stability, cost, and
distance values for each link.
1. flow-specific state information –
 session ID, source address, destination address, and QoS requirements of
the flow (such as maximum bandwidth requirement, minimum
bandwidth requirement, maximum delay, and maximum delay jitter).

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3. Lack of central coordination
 No central controller to coordinate the activity of nodes
4. Error prone shared radio channel
 Radio channel broadcast by nature
 Radio waves suffer from several impairments such as attenuation , multipath
propagation and inferences.
5. Hidden terminal problem
 results in retransmission of packets, which may not be acceptable for flows
that have stringent QoS requirements
6. Limited resource availability
 Heterogeneous nodes and networks
 Bandwidth, battery life storage space, and processing capability are limited in
adhoc wireless networks.
7. Insecure medium:
 De to broadcast nature communication is highly insecure

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Design choices for providing QoS:
resource reservation: resources are reserved at
1.Hard state : at all intermediate nodes throughout the duration of the QoS
session
2.soft state: small time intervals
State approach:
1.Stateful approach: each node maintains either global state information
or only local state information
2.Stateless approach: such information is maintained at the nodes.
QoS approach: If QoS requirements of a connection are guaranteed to be
met
1.hard QoS approach : for the whole duration of the session.
2.soft QoS approach: are not guaranteed for the entire session

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Design choices for providing QoS:
 Hard state vs soft state resource reservation: Hard state
resources are reserved at all intermediate nodes along the path from
the source to the destination throughout the duration of the QoS
session and for soft state small time intervals are used
 Stateful vs stateless approach: In the stateful approach, each node
maintains either global state information or only local state
information, while in the case of stateless approach no such
information is maintained at the nodes.
 Hard QoS vs soft QoS approach: If QoS requirements of a
connection are guaranteed to be met for the whole duration of the
session, the QoS approach is termed as hard QoS approach. If the
QoS requirements are not guaranteed for the entire session, the QoS
approach is termed as soft QoS approach.

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Classifications of QoS approaches
1. Based on the QoS approach:
a) Based on interaction between routing protocol and QoS provision
mechanism:
b) Based on interaction between network and MAC Layers
c) Based on the routing information update mechanism employed
1. Based on the Layer at which they operate:
a) QoS in Physical Layer
b) QoS in MAC layer
c) QoS Routing in Network Layer
d) QoS inTransportation layer
e) QoS in Application layer

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1. Based on the QoS approach:

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Coupled QoS approach:
•the routing protocol and the QoS provisioning mechanism closely
interact with each other for delivering QoS guarantees. If the
routing protocol changes, it may fail to ensure QoS guarantees
.
Decoupled approach:
• the QoS provisioning mechanism does not depend on any specific
routing protocol to ensure QoS guarantees.
a. Based on interaction between routing protocol
and QoS provision mechanism

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b. Based on interaction between network and MAC
Layers
Independent QoS approach: the network layer is not dependent
on the MAC layer for QoS provisioning.
The dependent QoS approach: requires the MAC layer to assist
the routing protocol for QoS provisioning.

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c. Based on the routing information update mechanism
employed
In the table-driven approach: each node in the network
maintains a routing table which aids in forwarding packets.
In the on-demand approach: no such tables are maintained
at the nodes, and hence the source node has to discover the
route on the fly.
The hybrid approach : bothabove

QoS Support in Physical Channels
 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

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2. Based on the Layer at which they operate:

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

2. IEEE 802.11
 In MANET radio channel operating in ISM band
 IEEE 802.11 –is a CSMA/CA protocol; most deployed as media access
technology
2 modes of operation
 Distributed coordination function (DCF) mode :
 Doesn’t use any kind of centralized control ;
 provide best effort services
 Point coordination function (PCF) mode :
 Requires an access point to coordinate the activity of all nodes in coverage
area
 designed to provide real time traffic support in infrastructure-based wireless
network thus not applicable in MANET
 DCF mode is must in implementation of IEEE802.11 standard forWLAN’s
while PCF is optional
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IEEE 802.11 DCF
 IEEE 802.11 is a CSMA/CA protocol
 In the distributed control function (DCF) mode:
 After the node has sensed the medium to be idle for a time
period longer than distributed inter-frame space (DIFS), it
begins transmitting
 Otherwise the node differs transmitting and backs off
 When the medium becomes idle for a period longer than DIFS,
the backoff timer is decremented periodically.The node starts
transmission as soon as the timer expires
 To reduce collisions, the sender and the receiver exchange RTS
and CTS packets

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

Point Coordination Function (PCF)
 Introduced to let stations have priority access to the wireless
medium
 Uses a point coordinator (PC), which operates at anAP
 PC decides which station should gain access to the channel
 Useful only in infrastructure based network
 PCF is not scalable to support real time traffic for a large
number of users.
 Need of new mechanis
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IEEE 802.11e
 IEEE 802.11e – new standard to support real time traffic
(QoS in both infrastructure and infrastructure less networks
)
 Enhanced DCF (EDCF)
 Hybrid coordination function (HCF)
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Enhanced DCF (EDCF)
 Support real time traffic by providing differentiated and
distributed DCF access to the wireless medium
 Each frame from the higher layer carries its user priority
(UP).
 After receiving each frame, the MAC layer maps it into an
access category (AC)
 Each AC has a different priority of access to the wireless up
to eight AC to support UP.
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Hybrid Coordination function (HCF)
 Combines feature of EDCF and PCF to provide the capability
of selectively handling MAC service data unit (MS-DU)
 Has upward compatibility with DCF and PCF.
 Usable only in infrastructure based BSS that provide QoS
 Use a QoS aware point coordinator called HC .
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3. DBASE
 Distributed bandwidth allocation/sharing/Extension
protocol supports multimedia traffic(both variable rate and constant bit
rate over adhocWLANs.
 In an adhoc WLAN, there is no fixed infrastructure to coordinate the
activity of individual stations.
 For real time traffic, a contention based process is used in order to gain
access to the channel.
 DBASE protocol permits real time station to acquire excess bandwidth
on demand.
 The non real time stations regulate their accesses to the channel
according to the standard CSMA/CA protocol.
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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

Ticket based QoS routing protocol
Source node issues a certain number of tickets in probe packets
for finding a QoS feasible path.
Each probe packet carries one or more packets.
For example, when the source node issues three tickets, it
means a maximum of three paths can be probed in parallel.
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Predictive location based QoS
routing protocol
 On demand routing protocol
 QoS aware admission control is performed.
 The QoS routing protocol takes the help of an update protocol
and location and delay prediction schemes.
 The update protocol aids each node in broadcasting its
geographic location and resource information to its neighbors.
 The update protocol has two types of update messages, namely
type 1 update and type 2 update.
 Each node generates a type 1 message periodically.
 A type 2 message is generated when there is a considerable
change in the node’s velocity or direction of motion.
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Cont…
 From its recent update messages, each node can calculate an
expected geographical location where it should be located at
a particular instant and then periodically checks if it has
deviated by a distance greater than from this expected
location. If it has deviated, a type 2 message is generated.
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Trigger-Based Distributed QoS Routing protocol (1)
 TDR
 Link failure, it Utilizes GPS
 Each node maintains the local neighborhood
information and active routes only
 INIR (Intermediate Node Initiated Rerouting)
 Rerouting is attempted from the location of an imminent
link failure
 SIRR (Source Initiated ReRouting)
 Rerouting is attempted from the source
 Database management
 For each neighbor, each node maintains received
power level, current geographic coordinates,
velocity, and direction of motion
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 Activity-based database
 The node maintains a source table (STn), a
destination table (DTn), or an intermediate table
(ITn)
 Depending on the role of the node in current session
 A flag indicating the node’s activity – NodActv
 NodActv = 0, means idle
 Also maintains an updated residual bandwidth
(ResiBWn) which indicates its ability to participate
in a session.
 Databases are refreshed when packets belonging to
the on-going sessions are received
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 Initial route discovery
1. The entry in source table is made, and NodActv sets to 0 (idle)
2. Selects the neighbors
1) lying closely toward the destination
2) with power level more than a threshold (Pth1)
and forward them a route discovery packet
1. The intermediate node checks if such packet was received
Yes  discard
NO  checks the ResiBW to meet the requirements
YES  an entry in IT is made, and NodActv sets to 0 (idle)
forwards the packets with hop count +1
4. Upon receiving the first packet, if destination is able to satisfy the ResiBW
and MaxBW, the route is made, and the ACK is sent back to source along
the route
 Route/ Reroute acknowledgement
 All the nodes along the route set the NodActv to 1 (active) and refesh
their ResiBW status
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 Alternate Route Discovery
 In SIRR
 When the received power level at an intermediate node falls below a threshold
Pth2, the intermediate node sends a rerouting indication to source
 In INIR
 When the power level falls below the threshold Pth1 (Pth1 > Pth2), a status query
packet is sent toward the source with a flag route repair status (RR_stat) set to 0
 If the upstream nodes are in rerouting process
o The RR_stat is set to 1, and reply back to the querying node
 If the query packet reaches source, the packet is discarded
 If the querying node receives no reply
 The SIRR could be triggered ( power level falls below Pth2)
 Or simply give up the control of rerouting
 Route Deactivation
 The source sends a route deactivation packet toward the destination
 The nodes received the packet update their ResiBW, and IT
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 Advantages
 Reduced control overhead
 Reduced packet loss during path breaks
 Disadvantages
 Threshold value?
 Fading / multi-path propagation/ velocity …etc
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QoS AODV (1)
 QoS Extensions to AODV protocol
 Modifications are made in routing table,
RouteRequest and RouteReply packet
 The following fields are appended to routing table
entry
 Max delay
 Min available bandwidth
 List of sources requesting delay guarantees
 List of sources requesting bandwidth guarantees
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Network layer solutions
QoS AODV (2)
 Max delay extension field
 In a RouteRequest msg.
 Indicates the max time (sec) allowed for a transmission for the current
node to the destination
 The node compares its node traversal time (the time processing a
packet) to the delay field in RouteRequest msg.
 If delay field is bigger, the msg. is discarded
 Otherwise, delay field = delay field – node traversal time
 In a RouteReply msg.
 Indicates the current estimation of cumulative delay for the current
intermediate node to the destination
 The destination node reply a RouteReply msg. to the source with the
max delay field set to 0
 Each node forwarding the RouteReply add its own node travaersal time, and
update the field
 The routing table in the node is also updated
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QoS AODV (3)
 Min bandwidth extension field
 In a RouteRequest msg.
 Indicates the min bandwidth (Kbps) that must be available along the
path
 The node compares its available bandwidth to the min bandwidth field
in RouteRequest msg.
 If the field is smaller, the msg. is discarded
 Otherwise, processes the msg. like usual AODV
 In a RouteReply msg.
 Indicates the min bandwidth available on the route between the source
and destination
 The destination node reply a RouteReply msg. to the source with the
min bandwidth field set to infinity
 Each node forwarding the RouteReply compares its own link capacity to the
BW field, and update the field
 The routing table in the node is also updated
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QoS AODV (4)
 List of sources requesting QoS guarantees
 A QoSLost msg. is generated when
 An intermediate node’s traversal time increases, or
 A link capacity decreases
 The QoSLost msg. is forwarded to all sources that could be
affected by the change (RouteReply msg. has been forwarded to)
 Advantages
 Simplicity in provisioning QoS of extensions in AODV
 Disadvantages
 Difficult to provide hard QoS
 No resources are reserved along the path
 Major part of delay is packet queuing delay, and contention at the
MAC layer, not the packet processing time
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Bandwidth Routing Protocol(1)
 The BR protocol consists of 3 algorithms
 An end-to-end path bandwidth calcucation algorithm
 A bandwidth reservation algorithm
 A standby routing algorithm
 The goal of this protocol is to find a shortest path satisfying the
bandwidth requirement
 Only bandwidth is considered to be QoS parameter
 In TDMA, bandwidth is measured in terms of the number of free slots
available at a node
 Each frame is divided into 2 phases: control phase and data phase
 Bandwidth :
the set of common free slots between 2 adjacent nodes
 The BR protocol assumes a half-duplex CDMA-over-TDMA system in
which 1 packet can be transmitted in 1 slot
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 Bandwidth
calculation
1. pathBW(S,A)
= linkBW(A,S) = {2,5,6,7}
2. pathBW(S,B)
since linkBW(A,B) = {2,3,6,7},
we assign slots [6,7] on
link(S,A), and [2,5] on link(A,B)
3. pathBW(S,C)
since linkBW(B,C) = {4,5,8},
we assign slot[4,8] on link(B,C)
4. pathBW(C,D)
since linkBW(C,D) = {3,5,8}
we assign slot[3,5] on link(C,D)
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 Slot assignment
 Requires periodic exchange of bandwidth information
 Assigns free slots during the call setup
 When a node receives a call setup packet,
it checks if the slot that sender will use is free or not, it also
checks if there is free slots for forwarding the incoming packets
Yes 
reserves the slot, updates the routing table, forwards the call
setup packet
No 
sends a Reset packet back to sender along the path to release the
slots assigned for this connection along the path
 If the connection has been set up, the destination sends a reply
packet back to the source
 The reservations are soft state to avoid resources lock-up due
to the path breaks51

 Standby routing mechanism
 To re-establish a broken connection, using DSDV
(Destination-Sequenced Distance Vector)
 The neighbor
 with the shortest distance to destination becomes the next-
node in primary path
 With the second shortest distance becomes the next-node
on standby route
 The standby route is not guaranteed to be link- or
node-disjoint
 if a primary path fails, and the backup path satisfies
the QoS requirements, a new path is set up by
sending a call setup packet hop-by-hop to the
destination52

 Advantages
 Efficient bandwidth allocation scheme
 The standby routing mechanism reduces the packet
loss during path breaks
 Disadvantages
 Impossible for a new node to enter the network
 If a node leaves, the corresponding slot remains
unused, there’s no way to reuse such slots
 The model needs a unique control slot in control phase of
superframe for each node in the network
53

On-Demand QoS Routing protocol(1)
 In OQR, routing is on-demand. Therefore,
there is no need to
 exchange control information periodically
 Maintain routing table at each node
 OQR is similar to bandwidth routing protocol
(BR)
 Network is time-slotted
 Bandwidth is the key parameter
 Uses the path bandwidth calculation to measure the
end-to-end available bandwidth
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 Route discovery
 Source node floods network with QRREQ packet, which has following
fields:
 Packet type, source ID, destination ID, sequence num, route list, slot array list
data and TTL
 The pair {source ID, sequence num} uniquely identify the packet
 A node N receiving a QRREQ performs the following steps
1. if the packet with same {source ID, seq. num.} is received, the packet is
discarded
2. else, N checks its address in route list. If it is in the list, the packet is
discarded
3. else,
-1) TTL = TTL -1, if TTL ==0, the packet is discarded
-2) calculate the BW from the source to N, if it doesn’t satisfy the QoS
requirements, the packet is discarded
-3) N appends the address to the route list, and re-broadcast the packet
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 Bandwidth reservation
 The destination may receive many QRREQ packets,
it selects the least-cost path among them
 The {route list, slot array list} from QRREQ is
copied to QRREP packet, and is sent back to source
 According route list field
 All the intermediate nodes receiving the QRREP
packet reserve the bandwith
 According to the slot array list field
 The reservation is soft state
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 Reservation failure
 Due to
 Route breaks
 The free slots is occupied by other connections
 When reservation fails, the node sends a ReservFail
packet back to source
 And source selects the next feasible path
 If no connection can be set up, the destination
broadcasts a NoRoute packet to inform the source
node
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 Route maintenance
 When a route breaks
 The upstream sends a RouteBroken packet to the source
 The upstream sends a RouteBroken packet to the source
 All the nodes receiving the RouteBroken packet frees the
reserved slots, and drop the data packet belonging to the
connection
 Source restarts the route discovery procedure
 Advantage
 Low control overhead
 Disadvantage
 The network needs to be fully synchronized
 High connection setup time
58

On-demand Link-State Multipath QoS Routing protocol(1)
 OLMQR idea:
 Finding 1 single path satisfying all the QoS requirements is
very difficult
 Searches mutlipath satisfying required QoS
 The BW requirement is split into sub-BW requirements
 Uses CDMA-over-TDMA channel model
 In this protocol
 The source floods QRREQ packets,
 destination collects these packets, selects multiple paths, and
sends the reply back to the source
 The operation of this protocol consists of 3 phases
 On-demand link state discovery
 Unipath discovery
 Multipath discovery and reply
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On-demand Link-State Multipath QoS Routing
protocol(2)
 On-demand Link-state Discovery
 A QRREQ packet contains the following fields
 Source ID, Destination ID, node history, free time-slot list, bandwidth
requirements, TTL
 When receiving QRREQ,
1. Node N checks its address in route list. If it is in the list, the packet is discarded
2. else,
-1) TTL = TTL -1; if TTL == 0, the packet is discarded
-2) add its add in node history field, and re-broadcasts the packet
 Build a partial view of network
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 Unipath discovery
 Build 2 trees: T and TLCF
 Given a path SAB …  K D, and a = BW(S,A), b=
BW(A,B) …
 Build T:
1.) Root is represented as abcd…xy
2.) ab means time slot is reserved
3.) build child abcd…, abcd…, abcd…, … ,abc…xy. Recusively
4.) the reserved time slots are calculated in every link
 Build TLCF:
Sort the reserved time slots in the same level in ascending order
from left to right
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 Unipath discovery, an example
S A B D
a
2,5,9,10
b
1,5,8,9
c
1,6,8,9
Build tree T:
abc
abc
c
abc
a
Build tree TLCF:
3
1
2 abc
ca
abc
abc
3
1
2
33
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 2 unipaths
are found
 S,A,B,D
2 time-slots
path
bandwidth
 S,E,F,D
 1 time-slot
path
bandwidth
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 Multipath discovery and reply
 The destination initiates the multipath discovery
operation by using unipath operation
 The sum of path bandwidths fulfills the original bandwidth
request
 Determines the max achievable path bandwidth of each
path
 The destination sends a reply packet back to source
along the path, and all nodes on the path reserves
the resources
 Advantage
 Better average call acceptance rate
 Disadvantage
 High control overhead to maintain and repair paths
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Asynchronous slot allocation strategies(1)
 AQR
 Uses RTMAC (real time MAC), and is an extension
of DSR (dynamic source routing)
 3 phases
 Bandwidth feasibility test phase
 Bandwidth allocation phase
 Bandwidth reservation phase
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 Bandwidth feasibility test phase
 RouteRequest packet
 If enough bandwidth is available, the packet is forwarded
 The routing loop is avoided by identifying <seq. num. ,
source ADD. ,and traversed path informations.
 Offset time field records the sum of processing time in all
nodes
 Used to estimate the propagation delay of transmission
 Reduces the synchronization problem
 The destination selects a shortest path with enough
bandwidth
 And construct a data structure called QoS frame for every
link in the path
 To calculate the free bandwidth slots
66

 Bandwidth allocation phase
 A bandwidth allocation strategy to assign free slots
to each intermediate link in the path
 Early fit reservation
 Minimum bandwidth-based reservation
 Position-based hybrid reservation
 K-hopcount hybrid reservation
 The information is included in RouteReply packet
through the path to the source
67

 Slot allocation strategies
 Early fit reservation (EFR)
1. Order the links in the path from source to destination
2. Allocate the first available free slot for the first link in the
path
3. For each subsequent link, allocate the first immediate free
slot after the assigned slot in the previous link
4. Continue step 3 until the last link is reached
 Attemps to provide the least end-to-end delay
 End-to end delay can be obtained as
tsf * (n-1) /2
n : hop count, tsf : the duration of the superframe
68

 Minimum bandwidth-based reservation (MBR)
1. Order the links in the non-decreasing order of free bandwidth
2. Allocate the first free slot in the link with lowest free bandwidth
3. Reorder the links, and assign the first free slot on the link with
lowest bandwidth
4. Continue step3 until bandwidth is allocated for all links
 Allocates the badwidth in increasing order of free bandwidth
 The worst case end-to-end delay can be (n-1)* tsf
70

 Position-based hybrid reservation (PHR)
1. Order the links in the increasing bandwidth
2. Assign a free slot of the link with least amount of bandwidth,
such that the position of assignment of bandwidth is
proportional to i/Lpath
o i is the position of the link, and Lpath is the length of the path
3. Repeat step 2, until bandwidth is allocated for all links
 K-hopcount hybrid routing (k-HHR)
if (pathlength > k )
use EFR
else
use PHR;
72

 Advantages
 Provide end-to-end bandwidth reservation in asynchronous
networks
 The slot allocation strategies can be used to plan for the delay
requirements
 Dynamically choose appropriate algorithms
 disadvantages
 Setup and reconfigure time can be high
 On-demand routing
 Bandwidth efficiency may not as high as fully synchronized
TDMA system
 Formation of bandwidth holes (short free slots can’t be used)
74

 QoS frameworks for Ad Hoc wireless networks
75

QoS frameworks for Ad Hoc
wireless networks
 A framework for QoS is a complete system that attempts to
provide required/promised services to each user
 The key component is QoS service model
 To serve users on a per session basis or on a per class
basis
 The other key components
 Routing protocol
 QoS resource reservation signaling
 Admission control
 Packet scheduling
76

QoS frameworks for Ad Hoc networks
QoS models(1)
 In wired network, IntServ and DiffServ have
been proposed
 IntServ provides QoS on a per flow basis
 3 types of services
 Guaranteed service
 Controlled load service,
 Best effort service
 RSVP is used
 Not scalable for internet
 DiffServ
 Flows are aggregate into service classes
 Both service model cant directly applied to ad
hoc wireless networks
77

QoS models(2)
 FQMM
 Flexible QoS model for mobile ad hoc networks
 A hybrid service model
 Per flow granularity of IntServ
 Aggregation of services into classes in DiffServ
 Assumes that the number of flows requiring per flow QoS
services is much less than the low-priority flows
 Nodes are classified into 3 different categories
 Ingress node (source)
 Responsible for traffic shaping
 Interior node (intermediate relay node)
 Egress node (destination)
 High priority flows are provided with per flow QoS services
 Lower priority flows are classified into service classes
78

QoS models(3)
79

QoS models(4)
 Advantages
 Provides the ideal per flow QoS services
 Overcomes the scalability problem
 Disadvantages
 Several issues remain un-solved
 Decision upon traffic classification
 Allotment of per flow or aggregated service for the given
flow
 Amount of traffic belonging per flow service
 The mechanisms used by the intermediate nodes to get
information regarding the flow
 Scheduling or forwarding of the traffic by the intermediate
nodes
80

QoS resource reservation signaling(1)
 The QoS resource reservation signaling
scheme is responsible for
 reserving the required reources
 Informing the applications to initiate transmission
 Signaling protocol consists of 3 phases
 Connection establishment
 Connection maintenance
 Connection termination
81

QoS resource reservation
signaling(2)
 MRSVP
 A resource reservation protocol for cellular networks
 Assumes that a mobile host predicts precisely the location that
the host is going to visit
 Reservation is made before the host uses the path
 2 types of reservation
 Active
 Data packets currently flow along that path
 Made by local proxy agent
 Passive
 Resources are reserved to be used in future
 Made by remote proxy agent
82

QoS resource reservation
signaling(3)
 Limitations of adapting MRSVP in Ad hoc network
 Random and unpredictable movement of
intermediate nodes
 Extremely to obtain the future locations of the host in
advance
 Passive reservations could fail
 Even the future location are known
 Finding a path and reserving the resources on that path
may not be a efficient solution
83

INSIGNIA
 Goal:To support adaptive services which can provide base QoS
assurances to real-time voice and video flows and data, allowing
for enhanced level of service to be delivered when resources
become available
 Designed to adapt user sessions to the available level of service
without explicit signaling between source-destination pairs
 QoS functionality is decoupled from the routing protocol
 INSIGNIA uses in-band signaling approach to restore the flow-
state in response to topology changes
 Uses the concept of “soft connection”

INSIGNIA(1)
 Developed to provide adaptive services in ad hoc
wireless networks
 2 service levels:
 Base QoS: Minimum QoS requirements
 extended QoS: when sufficient resources are available
 User sessions adopt to available service level without
explicit signaling between source- destination pairs
 2 design issues
 How fast can the application switch between base QoS and
extended QoS?
 How and when is ti possible to operate on the base QoS or
extended QoS for an adaptive application
85

INSIGNIA(2)
 Key
components of
INSIGNIA
86

INSIGNIA(3)
 Medium Access Control (MAC)
 Provide access to wireless medium
 INSIGNIA is transparent to underlying MAC protocol
 Packet Forwarding Module
 Classifies the incoming packets, and delivers them
 If the packet has INSIGNIA option
 Deliver it to INSIGNIA signaling module
 If the node is the destination of the packet
 Deliver it to application
 If the node is not the destination of the packet
 Relay it with the help of scheduling module
 Packet Scheduling Module
 The packets to be sent are scheduled based on the forwarding policy
87

INSIGNIA(3)
 Routing module
 Independent from other modules
 Any routing protocol can be used
 In-band signaling
 Used to establish, adapt, restore, and tear down adaptive
services between source-destination pairs
 Independent from MAC protocol
 Control information is carried along with data packets
 No explicit control channel
 Each data packet has an optional QoS field to carry control
information
 Can operate at speeds close to packet transmissions
 Better suited for highly dynamic mobile network
88

INSIGNIA(4)
 Admission control
 Allocates bandwidth to flows based on max/min bandwidth
requirements
 Soft state
 When a intermediate node receives a packet with RES flag on,
 If no reservation is made so far, the module allocates the resources
 If other reservation is made, the module re-checks the availble resources
 If no data are received for a period of time, the reservation
times out and get released in a distributed manner
 The value of timeout should be set carefully to avoid false restoration
 Time interval is smaller than the inter-arrival time of packets
89

INSIGNIA(5)
 The service level can be upgraded or degraded in a distributed
manner
 The INSIGNIA option field contains the following field
 Service mode
 Best-effort (BE) or requiring reservation (RES)
 payload type
 Base-QoS, enhanced QoS
 bandwidth indicator
 Has Min/Max value to reflect the status of the flow
 bandwidth request
90

INSIGNIA(6)
 For base-Qos application, bandwidth indicator is set
to min
 For exhanced-Qos application, bandwidth indicator
is set to max
 Can be degraded at intermediate nodes if no enough
resources are available
 Bandwidth indicator set to min
 Service mode set to BE
 Can be restored when resources are available
91

INSIGNIA(7)
 Releasing Resources
 The destination monitors the delivered flow, and measures the
QoS, and sends a reports back to source
 when source sends an enhanced QoS packet with MAX
requirements
 At non-bottleneck nodes, the resources are reserved as requested
 At bottleneck nodes, the bandwidth indicator flag are set to MIN
 So resources are over-allocated at non-bottleneck nodes
 When nodes receiving the report from destination
 they release the extra allocated resources
92

INSIGNIA(8)
 Route Maintenance
 Supports 3 types of flow restoration
 Immediate restoration
 Occurs when a rerouted flow immediately recovers to its original
reservation
 Degraded restoration
 Occurs when a rerouted flow is degraded for a period bfore it recovers
to its original reservation
 Permanent restoration
 Occurs when the rerouted flow never recovers to its original
reservation
93

INSIGNIA(9)
 Advantages
 An integrated approach provisioning QoS
 Disadvantages
 Supports only adaptive applications
 Multimedia applications
 Transparent to MAC protocol
 fairness and reservation scheme have a significant influence in provisioning QoS
guarantees
 Assumes that routing protocol provides new routes when topology changes
 The route maintenance mechanism significantly affects the real time traffic
 The QoS can be downgraded
 No suitable for realtime application
94

INORA
 Coarse feed back scheme
 When a node fails to provide QoS, it sends an admission control failure
(ACF) msg. to its upstream node
 The upstream reroutes the flow through other nodes
 If no neighbor can provide the requested QoS, it sends anACF to
upstream node
 When this happens, the packets are sent as best-effort packets
from source to destination
 123
95

INORA(1)
 USE
 INSIGNIA in-band signaling mechanism
 TORA routing protocol
 Coarse Feedback Scheme
 Class-based Fine Feedback Scheme
96

INORA(2)
97

INORA(3)
98

INORA(4)
 Advantages
 Search multiple paths with lesser QoS guarantees (Compare
with INSIGNIA)
 Use the INSIGNIA in-band signaling mechanism
 Disadvantages
 May not be suitable for applications that require hard service
guarantees
 Because of the failure flow may only service as BE
99

SWAN(1)
 Stateless wireless ad hoc network
 Assimes a best-effort MAC protocol
 Uses feedback-based control mechanisms to support real-time
services and service differentiation
 Uses local rate control, a source-based admission control, an
explicit congestion notification (ECN)
 Unlike INSIGNIA and INORA, intermediate nodes don’t have
to maitaining the per-flow state information
100

SWAN(2)
101

SWAN(3)
 Local rate control of BE traffic
 Assumes most traffic are BE
 Uses the bandwidth left out by real time traffic
 Traffic rate controller determines the departure rate of the
traffic usingAIMD (additive increase multiplicative decrease)
algorithm
 EveryT secs, tx rate = tx rate + c (Kbps)
 If rx rate exceeds the threshold
tx rate = tx rate * r percent
 If shaping rate is greater than g percent of the actual rate
shaping rate is adjusts to be g percent above the actual rate
102

SWAN(4)
 Source-Based admission control of real-time traffic
 The real time traffic should be admitted up to an admission
control rate; the best effort traffic should be allowed to use any
remaining bandwidth
 Process of admitting a new real time session
 The source sends a probe packet to estimate the end-to-end bandwidth
 Each intermediate nodes update the bottleneck bandwidth field
 Admits the real time sessions only if sufficent bandwidth is available
 No bandwidth request is in probe packet, and no resource
allocation or reservation is done during the lifetime of an
admitted session
103

SWAN(4)
 Routing algorithms
1. Each node continuously estimates the locally available bandwidth
2.When a node detects congestion conditions, it starts marking the ECN bits
in real time packets
3.When destination receives these packets, it sends a regulate msg. back to
source
4.The source re-establish the session based on the original bandwidth
requirements by sending a probe packet to destination
 The above approach is not efficient, the SWAN model consider 2
approaches
 Source-based regulation
 Network-based regulation
104

SWAN(5)
 Source-based regulation
 The source waits for a random amount of time after receiving a regulate
msg. , then initiates the re-establishment process
 Avoid flash-crowd conditions
 Network-based regulation
 The congested nodes randomly select a congestion set of rt-sessions, and
mark only packets in this set
105

SWAN(6)
 Advantages
 scalable
 disadvantages
 Can’t provide Hard QoS
 In worst case, the admitted rt-traffic can be dropped of live in
BE mode
 Don’t perform well when most traffic is real time
106

Proactive RTMAC(1)
 PRTMAC is a cross layer framework
 On-demand QoS extension of DSR routing protocol at layer 3
 RTMAC at layer 2
 Provides bandwidth availability estimation
 Uses an out-of-band signaling channel to gather additional
information about the on-going real-time calls
 A narrow band control channel that operates over a transmission range with
twice that of the data transmission, is used as the out-of-band signaling
channel
 A greater transmission range than data channel
 Mobility affects the real-time traffic in 2 ways
 Breakaways
 Reservation clashs
107

Proactive RTMAC(2)
 Breakway  clash
108

Proactive RTMAC(3)
 Operation of PRTMAC
 Every node sends out control beacons
at regular intervals over control
channel
 The calls the source node is carrying
 Start- and end- time of the real time
call
 The slot reservation status
 Signal strength is used to estimate the
relative distance between 2 nodes
109

Proactive RTMAC(4)
 Crossover-time prediction
 The time when a node crosses another node’s data transmission
range
 A node stores number of <time, signal strength> tuples
received from other nodes
110

Proactive RTMAC(5)
111

Proactive RTMAC(6)
 Handling Breakaways
 Local reconfiguration
 When a node’s downstream node is down, the node tries the local reconfiguration
 End-to-end reconfiguration
 Sends a RouteError packet back to source
 Combines these two
 Node C checks if there is a path to F in its routing table
 If there is one, C makes the reservation.
 When a call is interrupted, and local reconfiguration is tried for a number of times, the end-to-
end reconfiguration is attempted
112

Proactive RTMAC(7)
 Handling Clashs
 When clashs happens, the PRTMAC shifts one of the calls to a
new slot
113

Proactive RTMAC(8)
 when clash happens,
 suppose that N is responsible for reconfig calls
 N tries to find a free slot in N and C
 By going through its reservation table and its
neighbor’s table corresponding to C
 If success 
 Shifts the call
 If failed 
 Low priority gets dropped, and undergoes an
end-to-end reconfiguration
114

Proactive RTMAC(9)
 Diffserv provisioning in PRTMAC
 Class 1
 Real-time calls
 Preempt the law priority calls
 Class 2
 End-to-end bandwidth reservation
 Best-effort
115

Proactive RTMAC(10)
 Advantage
 Provides better rt-traffic support and service differentiation in
high mobility ad hoc wireless networks
 disadvantage
 Having another control channel may be a problem in low-power
and resource-constrained environments
116

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

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

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

Outline
 Introduction
 Issues and challenges in providing QoS in Ad
hoc wireless networks
 Classifications of QoS solutions
 MAC layer solutions
 Network layer solutions
 QoS frameworks for Ad Hoc wireless networks
 summary
120

Summary
 The issues and challenges in providing QoS
 Classfication of QoS
 MAC/ network layer solution
 frameworks
121

Lecture 23 27. quality of services in ad hoc wireless networks

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