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 Hoc Wireless 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 services (QoS)

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:

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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 in Transportation 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

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QoS in MAC layer

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1.

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 for WLAN’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 an AP

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 adhoc WLANs.

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. 38

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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Trigger-Based Distributed QoS Routing protocol (4) 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 breaks 51


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 destination

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Bandwidth Routing Protocol(5) 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

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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 SAB … 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

c a

abc

abc

3

1

2

3 3 62

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

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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

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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

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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

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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;

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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)

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QoS frameworks for Ad Hoc wireless networks

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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

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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

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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)

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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

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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

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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

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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

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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

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INSIGNIA(2)

Key components of INSIGNIA

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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 Uses a weighted RR service discipline

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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

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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

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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

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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

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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

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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

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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

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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 an ACF to

upstream node

When this happens, the packets are sent as best-effort packets from source to destination

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INORA(1)

USE

INSIGNIA in-band signaling mechanism

TORA routing protocol

Coarse Feedback Scheme

Class-based Fine Feedback Scheme

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INORA(2)

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INORA(3)

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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

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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

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SWAN(2)

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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 using AIMD (additive increase multiplicative decrease) algorithm Every T 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

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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

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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

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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

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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

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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

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Proactive RTMAC(2)

Breakway

clash

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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

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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

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Proactive RTMAC(5)

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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

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Proactive RTMAC(7)

Handling Clashs When clashs happens, the PRTMAC shifts one of the calls to a

new slot

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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

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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

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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

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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


summary

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Summary

The issues and challenges in providing QoS

Classfication of QoS

MAC/ network layer solution

frameworks

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

Technology

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