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Department of Information Engineering
University of Padova, ITALY
On Providing Soft-QoS in
Wireless Ad-Hoc Networks
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WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Department of Information Engineering
University of Padova, ITALY
Special Interest Group on
NEtworking & Telecommunications
On Providing Soft-QoS in
Wireless Ad-Hoc Networks
Andrea Zanella, Daniele Miorandi, Silvano Pupolin, Paolo Raimondi
{andrea.zanella, daniele.miorandi, silvano.pupolin}@dei.unipd.it
WPMC 2003, 21-22 October 2003
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Motivations



Ad-hoc networks are a valuable solution to

Extend in a multi-hop fashion the radio access to wired networks

Interconnect wireless nodes without any fixed network structure
In these contexts, providing QoS is a key issue

audio/video streaming

interactive games

multimedia
A possible QoS support method

WPMC 2003
QoS-routing & Call-Admission-Control (CAC) mechanisms

Constrained Shortest Path Routing Problem (NP-complete)

MAC-layer Resource Reservation (MRR) and scheduling strategies
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Hard & Soft QoS
Hard-QoS

Widely used in wired
networks


Integrated Services: flow
Soft-QoS

Suitable for wireless
networks

Applications may work even
based (RSVP)
if, for short periods of time,
Differentiated Services:
QoS requirements are not
class based
satisfied

Deals with limited bandwidth
and radio channel
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Aim of the study

Reference network scenario

Low-profile multi-hop wireless networks

Intermediate nodes capable of basic functionalities
• Routing – Link monitoring – Basic computation

Border nodes capable of rather complex functionalities
• Call Admission Control (CAC) – MAC layer Resource Reservation (MRR)

Goal

Providing Soft-QoS support over low-profile multi-hop networks
WPMC 2003

Define Soft QoS parameters

Define distributed statistical CAC

Define statistical MAC-layer Resource Reservation (MRR) mechanism

Modify AODV in order to support Soft-QoS routing
Yokosuka, Kanagawa (Japan) 21-22 October 2003
What’s Soft-QoS?
Soft-QoS definition
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Soft-QoS parameters


QoS parameters required per link

Minimum peak band: Br

End-to-End Delay: Dr
Soft QoS parameter: Target Satisfaction index

r = percentage of pcks expected to satisfy QoS
constrains
WPMC 2003

r = 1  hard QoS (or “wealthy” clients)

r = 0  pure best-effort (or “poor” clients)
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Call Admission Control
Distributed CAC
mechanism
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Path Service Levels


Path: P = (p1,…, pN)
Service levels:

Path Bandwidth: minimum available bandwidth along the path
B
in
{
b
}
Pm
p
j

p
P
j
Path Delay: total delay introduced by the path
D
P
d
p
j
p
P
j

Bandwidth bpj and delay dpj of each link are assumed to be
(independent) random variables
BP & Dp are random
variables!
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Call Admission Control

Path is feasible if

Bandwidth constrained requests
P
rB
PB
r r

Delay constrained requests
P
rD
PD
r r

However, this would require the collection of the
complete statistics of link bandwidth and link delay…
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Gaussian approx

But when statistics are tough to be determined… we may (always?) resort
to the Gaussian approximation!

Statistics are univocally determined by mean and standard deviation values of
link delay and available bandwidth

Such values can be easily determined by each intermediate node

QoS routing algorithm collects and delivers such statistics to the destination node

Destination node performs CAC in a straightforward manner:

Bandwidth constrained requests
B

rm
b
p
j 

Q
r


 bp 
p
P
j
j


Delay constrained requests
D

rm
D
P

1
Q

 D  r
P


WPMC 2003

Yokosuka, Kanagawa (Japan) 21-22 October 2003
MRR
Statistical MAC-layer
Resource Reservation
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Resource Bounds

Once a connection is accepted, resources should be reserved…

To avoid complex static reservation mechanisms and flow
differentiation we resort to statistical resource reservation:

Each node processes all the packets in the same way

Packets of different flows get the same service from the same link

For each link, nodes compute the Resource Bounds, i.e., the minimal
residual resources that should be guaranteed to preserve QoS levels of
accepted connections that go through that link
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Example of Bandwidth bound
Actual Sat.
Index 
P(bj > B)
Bandwidth Bound
Target Satisfaction
Index r
Required Path
Bandwidth Br
WPMC 2003
Bandwidth B
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Bandwidth Bounds

Bandwidth-constrained requests
B

ˆbj 
B
m
m
r
b
r
p
k



 Q
ˆbj s
m
u
c
h
th
a
tQ
 b  r
 b 
P 
j
p
k
k

p


p
kj

B

m
r
b
j


ˆbj B
m
Q
Q
rb
j
ˆ  b 

j




1
r
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Delay Bounds

Delay-constrained requests

Extra-delay margin is computed for the entire path
ˆD
D

rm
P

ˆD
m
s
u
c
h
th
a
t1
Q

P
 D  r
P


 
1
ˆ
ˆD
m

D


Q
1


r
D
P
P

Each link along the path is assigned a fraction of the extra delay
time inversely proportional to the average link delay
ˆdj m
m

d
j
ˆ m

m
1m
1m
d
j

k
P
WPMC 2003
D
j
D
j
d
k
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Maximum Sustainable traffic

The tightest resource margins of the links along the path
are made available at the source

The source derives the maximum sustainable traffic rate,
i.e., the maximum traffic that may be injected into the
network without violating the QoS agreements of the
connections already established
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
How to create a path
Soft-QoS routing
algorithm
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Path creation & maintenance

Soft-QoS routing is largely inspired to AODV

Each Route Request (RREQ) packet gathers statistical information
on the minimum bandwidth and maximum delay along that portion of
the path

RREQ is propagated only whether bandwidth request is satisfied

The destination node back propagates a Route Reply (RREP)
packet along the selected path

RREP acquaints intermediate nodes with new resource bounds and
updates maximum sustainable traffic rate limit

Source node is required to respect the maximum sustainable traffic
rate limit or to refuse the connection
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Simulation Results
Simulation of Soft-QoS
routing algorithm
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Simulation Scenario


Bluetooth Scatternet

Round Robin Polling

Gateways spend 50 slots in each piconet
Poisson packets arrival process


Mixed packet formats with average length of 1500 bits
Delay-constrained requests
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Gaussian Approximation


1 hop
Local slave-to-slave connections
in each piconet

Data rate=9.6 Kbit/s



6 hops
Gaussian approx is fairly close
to empirical delay CDF
Gap increases for long-distance
and high traffic connection
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Simulation setup

Target connection c1




Target connection c2




Dr = 50 ms
r = 0.2
r = 20 kbit/s
Dr = 200 ms
r = 0.9
r = 30 kbit/s
Target connection c3



WPMC 2003
Dr = 200 ms
r = 0.9
r = 20 kbit/s

Target connection c4




Dr = 50 ms
r = 0.2
r = 60 kbit/s
Transversal connections




Starting after 20 s, last for 10 s
On average 1 request/s
Random source, destination & QoS
requests
Rate: 520 kbit/s
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Satisfaction & Delay dynamics

WPMC 2003
Satisfaction

Delay
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Conclusions

We have proposed a basic Soft QoS routing algorithm for low-profile
ad hoc networks

Provides Soft-QoS guarantees

Requires



basic nodes’ functionalities

statistical link state monitoring (mean and standard deviation)
Does not require

service differentiation

static resource reservation
Drawbacks

Lower resource utilization

Higher rate of connection request rejection
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Department of Information Engineering
University of Padova, ITALY
On Providing Soft-QoS in Wireless Ad-Hoc Networks
Andrea Zanella, Daniele Miorandi, Silvano Pupolin, Paolo Raimondi
Questions?
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Extra Slides…
Spare Slides
WPMC 2003
Yokosuka, Kanagawa (Japan) 21-22 October 2003
Statistical Resource Reservation

Resource bounds
Minimal residual resources that should be guaranteed
to preserve QoS levels of accepted connections


Bandwidth-constrained
Resource bounds

Delay-constrained

Extra-delay margin given to
each link along the path is
inversely proportional to the
mean link delay

B

m
r
b
j


ˆbj B
m
Q
Q
rb
j
ˆ  b 

j




1
r
Actual Satisfaction
ˆdj m
m

d
j
ˆ m

m
1m
1m
d
j

k
P
WPMC 2003
 
1
ˆ
ˆD
m

D


Q
1


r
D
P
P
D
j
d
k
Yokosuka, Kanagawa (Japan) 21-22 October 2003
D
j