QoS in wirelessAd Hoc Networks

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QoS in wireless/Ad Hoc Networks

-Rohit Ranjan
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Outline

• What is QoS(Quality Of Service) ?
• QoS in Wired Networks.
• Problem in Wireless.
• How to provide QoS in Wireless domain?

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What is QoS ?
Quality of Service (QoS) is a broad term used to
describe the overall experience a user or
application will receive over a network.
The IP protocol was originally designed to
reliably get a packet to its destination with
little consideration to the amount of time
it takes to get there. IP networks must now takes
to get there. IP networks must now transport many
different types of applications. Many of these
applications require low latency,otherwise, the
end-user quality may be signifi-cantly affected
or in some cases, the applica-tion simply does
not function at all.
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QoS Performance Dimensions
A number of QoS parameters can be measured and
monitored to determine whether a service level
offered or received is being achieved. These
parameters consist of the following Network
Availability Network availability can have a
significan affect on QoS. Simply put, if the
network is navailable, even during brief periods
of time,the user or application may achieve
unpre-dictable or undesirable performance (QoS).
Bandwidth Bandwidth is probably the second
most signif-icant parameter that affects QoS.
Bandwidth allocation can be subdivided into two
types Available Bandwidth Guaranteed
Bandwidth Delay Network delay is the transit
time an applica-tion experiences from the ingress
point to the egress point of the network. Delay
can cause significant QoS issues with
applications such as voice and video, and
applications such as SNA and Fax transmission
that simply time-out and fail under cessive delay
conditions. Jitter Jitter is the measure of
delay variation between consecutive packets for a
given traffic flow.Jitter has a pronounced effect
on real-time, delay-sensitive applications such
as voice and video. These real-time applications
expect to receive packets at a fairly constant
rate with fixed delay between consecutive
packets. As the arrival rate varies, the jitter
impacts the applications performance. A minimal
amount of jitter may be acceptable but as jitter
increases, the application may become unusable.
Loss Loss can occur due to errors introduced by
thephysical transmission medium. For example,
most landline connections have very low loss as
measured in the Bit Error Rate (BER). However,
wireless connections such as satellite, mobile or
fixed wireless networks, have a high BER that
varies due to environment or geographical
conditions such as fog, rain, RF interference,
cell handoff during roaming and physical
obstacles such as trees, buildings and
mountains. Wireless technologies often trans-mit
redundant information since packets will
inherently get dropped some of the time due to
the nature of the transmission medium.
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Application Requirements
Table 1 illustrates the QoS performance
dimensions required by some common applications.
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QoS In Wired Networks
IntServ (Integrated Services) along the path.
Each router along the path performs admission
control and then recognises the individual
application data streams to provide the
service expected. It is argued that this model is
too complex and does not scale enough to be used
in the backbone of the Internet. Others argue
that The scalability problems of per-flow QoS
management in routers have resulted in a new
approach being taken in the IETF, known as
the differentiated services (Diffserv)
architecture. The objective is to provide
scalable QoS support by avoiding per-flow state
in routers. The basic idea is that IP packet
headers include a small label (known as the
Diffserv field) that identifies the treatment
(per-hop behaviour) that packets should be given
by the routers. Consequently, core routers are
configured with a few forwarding Differentiated
services (Diffserv) IP packet headers include
a small label (known as the Diffserv field)
that identifies the treatment (per-hop behaviour)
that packets should be given by the routers.
One advantage of differentiated services is that
the model preserves the favourable properties
that made the Internet successful it supports
scalable and stateless forwarding over
interconnected physical networks of various
kinds. The standard model is, however, limited to
differentiated
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QoS in Sensor Networks

• Focus of Researchers in Sensor Networks

• Directed diffusion, Power aware routing,
  Clustering ,Tiny OS etc

• Focus is on reducing the energy required

• Different packets might have different importance

Temperature sensor in forest 60F and 1000F

• Data delivery needs to be energy efficient but
  energy
• expenditure may vary according to importance of
  data

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QoS in Sensor Networks

• Packet scheduling is not the major concern

Nodes dont have much space for buffering so
question of when to schedule a packet to provide
service differentiation does not arrive.

• Two primary service differentiations
• - Reaching Probability
• - Latency

Highly importanbt pack should have higher prob to
reach dest
Highly important data should have lower latency

• Using Single path for low priority packets and
  flooding for high
• priority packets? (flooding no control in
  latency )

Single path forwarding ,flooding(increases the
reaching prob but overhead is too much)
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QoS in Sensor Networks
Three approach to provide guaranty in packet
delivery

• Selective acknowledgement scheme based on
  pripority level of packet.not feasible if not
  enough caching space

• Packet redundancy ( does not require
  retransmission or ack so latency will be
  significantly lower)

• Multi-packet forwarding
• Hybrid model
• Multi-path forwarding

• FEC(Forward error correcting code) strength

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Adaptive forwarding scheme

• Its a multi-path and multi-packet forwarding
  scheme
• Assumption network is not providing ACK
• Packet priority level Li , Reaching
  Probability Pi
• Initially for each node forwarding
  probability Fi 1
• for all priority levels Li
• Monitor nodes keeps track of No of packets
  received for each
• priority level since last routing update and
  calculates reliability
• Ri
• now compute Fi FiPi / Ri
• Send new Fi to its neighbors in next routing
  update(Reliability can be more than flooding)

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QoS Routing in Ad Hoc Wireless Networks- Rechard
lin and jain-Shing Liu

• End to end bandwidth calculation and allocation

• QoS parameters need to be propagated within the
  network

• We need to know minimal delay path as well as
  bandwidth

• Goal is to find a shortest path such that
  available bandwidth . on
  the path is above minimal requirements

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Bandwidth calculation ?

• Free slots(x) - slots which are not used by any
  adjacent host
• of x to send/receive packets from the point of
  view at node x

• Link_BW Common free slots of (A,B)

• Path_BW minimum of all the Link_BW( Link in
  the path)

Four cases to show how to calculate Path
Bandwidth
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Case 1
Link_BW(A,B) Link_BW(B,C)
Link Bandwidth for (A,B) and (B,C) are same -
(1,2,3,4)
B cant listen and transmit at the same time
Path_BW(C,A) floor( 4/2) 2 ( with 4 free
slots)
Path_BW(C,A) floor( 3/2) 2 ( with 3 free
slots)
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Case 2
Link_BW(A,B) is subset of Link_BW(B,C)
Assume, link_BW(A, B) 2,3
link_BW(B,C) 1,2,3,4 C should first use
slots in link_BW(B,C) - link_BW(A,B) to
maximize system utilization
C should use 1,4 first
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Case 3
Link_BW(A,B) and Link_BW(B,C) have no common slots
No Conflict
C can choose either slot 3 or 4 . And
path_BW(A,C) is of size 1
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Case 4 Its a General case
Its a combination of case 1-3
Consider the slots which are not Common in
Link_BW(A,B) and Link(B,C) first till one of the
special case 1-3 occurs
Path_BW of (A,C) is of size 4
Resolving slot scheduling at the same time as
available bandwidth is searched is NP-Complete
problem
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Rerouting when the path is broken

• Routing optimality is not important, find the
  new route quickly
• Standby route is easily computed using the DSDV
  algorithm(runner up)

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Link of VC is broken
Construct new VC from breakpoint if standby
route has enough BW
Stop the traffic flow from upstream node and
backtrack to intermediate node which has QoS
route to the destination
In worst case new VC will be reconstructed from
source node
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Some experimental results
20 mobile hosts 10001000 sq ft ( roaming
uniformly) Each node moves randomly with uniform
speed Data rate 4 Mbits/s Radio transmission
range 400 ft Two nodes can hear each other if
they are within range Three QoS for offered
traffic - Qos1,QoS2 and QoS3 QoSN - N numbers of
data slots in given frame frame length - 82 ms
and 16 data slots in data phase no of nodes is
more than data slots so they will compete
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References
QoS routing in ad hoc wireless networks
Chunhung Richard Lin Jain-Shing Liu Selected
Areas in Communications, IEEE Journal on ,
Volume 17 Issue 8 , Aug. 1999 Page(s) 1426
-1438