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7/29/2019 QoS in Wireless Network
http://slidepdf.com/reader/full/qos-in-wireless-network 1/43
QoS in wireless systems
Preetam Patil
Leena Chandran-Wadia
7/29/2019 QoS in Wireless Network
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QoS in Wireless Systems 2
Contents
QoS in wired systems technologies - ATM, IP/MPLS
mechanisms - scheduling, routing, admission
control….
architecture – DiffServ
QoS in wireless
Wireless ATM
GPRSMANETS
Perspective
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QoS in Wireless Systems 3
Case for QoS
“QoS is a means to convergence but agoal in itself from network point of view.”
Over provisioning of resources is not
enough…
Different applications have different QoS
requirements.
Particularly important from the point of how
TCP reacts to packet losses and delays.
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QoS in Wired Networks
What is QoS? - “Better than best effort” Associated metrics include
Guarantees on bandwidth
Bounds on delay (queuing, multiplexing)Bounds on delay variation (jitter)
Bounds on loss probability
Minimize cost
Ideally we would like to have “end-to-end QoS” and associated pricing
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QoS in Wireless Systems 5
QoS Mechanisms
support for real-time flows in the n/wmarking such flows - precedence (ToS)
admission control
assign to different queuespriority scheduling
buffer management
constrained routingmechanisms for signaling - within n/w as
well as between users and n/w
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QoS in Wireless Systems 6
Performance measures
QoS services (depending on the level)generally involve putting all or at least afew of these mechanisms into place
Fairness - access to excess capacity
Isolation - protection from excess trafficfrom other users
Efficiency - number of flowsaccommodated per service level
complexity - implementation, controloverhead
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QoS in Wireless Systems 7
IP QoS Approaches
Two broad families:Per-flow service
Integrated Services and RSVP
Since per-flow information needs to be
maintained, too complex and not scalable
Aggregated service
Differentiated services
Only class-based information required, hencemore scalable, and easier to implement
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Differentiated Services(DiffServ)
Goals and motivationsData path scalability
Coarse granularity service classes (no
per-flow state) Minimum impact on packet forwarding
performance
Realizable through simple
mechanisms
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DiffServ… - continued
Rapid deployment Standardize service codepoints in IP
header and associated expected local
behaviour (Per Hop Behaviour - PHB)
Wide range of possible
implementations
Avoid chicken and egg problem of
signalling deployment andapplication/user support
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How it works -
IP TOS field in IPV4 or Traffic Class field inIPV6 used to mark packets
Pre-configured set of service classes
(behaviours)
Expedited Forwarding (local behaviour only)
Virtual leased line type of service
Assured Forwarding (local behaviour only)
Several service classes with dropprecedence within each class
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QoS in Wireless Systems 11
DiffServ Components
Edge functionsFlow classification and packet marking
Traffic conditioning
Core functions
Enforcement of Per Hop Behaviours
Boundary functions
Conformance enforcement
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DiffServ Components… continued
ComponentsClassifiers
Select packets and assigns DS code
pointTraffic conditioners
Enforces rate limitations
Per Hop Behaviours Differentiated packet treatments
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QoS in Wireless Systems 13 QoS in Wireless Systems 13
Multi-Protocol Label Switching
(MPLS) An attempt to exploit benefits of ATM
label-switching and flexibility of IP routing.
Has roots in IP tag-switching.
MPLS works between L2 and L3.
Designed to work over different link-layer
technologies- Ethernet, Frame-relay, etc.
Different network protocols supported.
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MPLS Features
Packets are forwarded based on a 20-bitfixed-length label in packet-header
instead of destination IP address
A path (LSP - Label Switched path) isfirst established using a signalling
protocol
Label Distribution Protocol
extensions to RSVP
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QoS in Wireless Systems 15
MPLS Architecture
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MPLS Architecture- contd..
LSR- routers supporting MPLS are calledLabel Switching Routers
Ingress LSR - LSR where packets in a
flow enter the MPLS domainEgress LSR - LSR where packets in a
flow leave the MPLS domain
FEC - packets to be forwarded in samemanner are assigned to same
Forwarding Equivalence Class (FEC)
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QoS and Traffic Engineering in
MPLS
MPLS and DiffServ similar in the way packets
are looked up and classified at the Ingress
LSPs can be set up for Different Service
classes, or bits in MPLS header can be usedto mark flows for QoS
LSPs can be explicitly set up based on QoS
and Traffic-Engg objectives (CR-LSPs)
Many extensions to MPLS for QoS and TE
proposed
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QoS in Wireless Systems 18
ATM Reference Model
Complete protocol stack, alternative toTCP/IP - fully QoS capable!!
4 layer (upper, adaptation, ATM and
physical), 3 dimensional model
Different from both OSI and TCP/IP
User Plane (data transport, flow, error
control) and Control Plane (connection
management) Plane and Layer Management (RM and
interlayer coordination)
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Service Differentiation
Two major componentsData path: identifies packets eligible for
services and enforces them
Packet classifiers
scheduling and Buffer management
Control path: determines if and how
guarantees can be provided
signalingadmission control
QoS routing
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ATM - Connection Oriented Cell
Switching
Call setup: synchronization before datatransfer
input 3 3
conn Id 1 2
output2 2 conn Id 1 2
Switch
S1
Switch
S2
Switch
S4
Switch
S3
input 1 1
conn Id 1 2
output 4 3conn Id 1 1
input 1 1
conn Id 1 2
output4 3 conn Id 1 2
23 1 3 1 2
2 4
21
input 1
conn Id 2
output 2 conn Id 1
Host A Host C
Host B
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ATM Logical Connections
Transmission Path
Virtual Path
Virtual Channels
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ATM Connection Terminology
Virtual Channel Connection (VCC),also called VC
identified by one VPI/VCI at an interface
Virtual Channel Link
Virtual Channel Identifier
no global identifier
Two types
Switched - SVCs (need connection setup)
Permanent - PVCs (service provider)
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More Connection Terminology
Virtual Path Connection, also calledVP
identified by one VPI at one interface
Virtual Path LinkVirtual Path Identifier
no global identifier
Virtual paths make it possible for CPNto have closed user groups, with anetwork of VPs
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ATM Cells - NNI
VPI
VPI VCI
VCI
VCI PT
HEC
48 bytes
VPI
PT
CLP
HEC
Virtual Path Identifier
Virtual Channel Identifier
Payload Type
Cell Loss Priority
PayloadHeader Error Control
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QoS in Wireless Systems 25
Service Categories
CBR - Constant Bit Rate (T1/E1 circuit)VBR - Variable Bit Rate
rt VBR - real-time Video conferencing
nrt VBR - multimedia E-mail
ABR - Available Bit Rate (Browsing theweb)
UBR - Unspecified Bit rate (Background
file transfer). Useful for sending IPpackets
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ATM Perspective
Standardization took too much time no native ATM applications were written
meanwhile, runaway success of the
Web and of MBone meant that killer applications were all running IP
this meant LANs would remain Ethernet
and WANs would run IP over ATM
But... ATM Hardware is selling as muchas IP switches and routers today!!
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Wireless ATM
User (data) plane largely unchangedControl plane
MATM adapter (handsets): UNI + Mobility
WATM & AP: support control of Radio Access (signal strength etc.)
Switches: Signaling to support mobility
QoS
Wireless QoS: reservation adds to delayHandover QoS: blocking, re-negotiation
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QoS in Wireless Networks
What’s different in Wireless ? A premium on efficiency (due to limitations in
spectrum resource)
Low reliability in the worst case
Traffic limited by interference Similar to congestion, but more easily controllable
“Cost” of one stream related not only to rate
parameters, but also to reliability(energy per bit)
and acceptable delayBest error- control coding techniques are at the
physical and media- access layers
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Wireless Systems – GPRS
Varying Conditions of Radio interfaceQoS profile consists of parameters like
precedence:
delay: includes radio access delay (uplink)or radio scheduling delay (downlink), radio
transit delay, GPRS-network transit delay
reliability: error rates much higher
throughput: specified by maximum bit rate
and mean bit rate
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GPRS (1)
Each GPRS subscription will beassociated with one QoS profile (HLR)
SGSN will negotiate QoS for the flow
Based on subscribed default in HLR
The requested profile from the MN
Current availability of GPRS resources
SGSN must distribute resources fairly
among flows, it may renegotiate QoS if necessary
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GPRS (2) QoS Classes
Four traffic classesConversational,streaming, interactive,
background
(1) Conversational, streaming: for carrying
real-time flowsdifference is the extent of delay sensitivity
Forward error correction
(2) interactive, background: for traditional
internet traffic interactive class has higher response
better error recovery using retransmissions
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QoS Profile Parameters
Eight other parameters are used for definingthe specific QoS-profile
MAX bit rate, Guaranteed bit rate
Delivery order, Reliability
PDU size information, Transfer delay
Traffic handling priority, Allocation priority
Values will depend on main traffic class
More complex, but will reflect differentapplications better
Applications must signal QoS requirements
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Conversational Class
Assumed to be relatively non-burstyReal time, low delay - Voice
Characterized by
maximum bit rateguaranteed bit rate
guaranteed transfer delay
rest optional, but usually specified lower classes specify fewer parameters
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Re-negotiation of QoS
MN, BSS & SGSN have the capability totrigger a modification of the QoS profile
associated with an ongoing data flow
due to congestion or shortage of radioresources
in order to map QoS parameters of the
packet data network into the GPRS
network
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Traffic Flow Templates
Assign different QoS-profiles to different applications -Signaling done using RSVP API
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QoS in MANets
Availability of link state information andits management is difficult
QoS of wireless link is apt to change indynamic environment
mobility of hosts
resource limitations (time varying)
DiffServ a possible solution
what are the boundary routers?concept of SLA does not exist
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QoS in MAC protocols
MAC protocol design goalssolve medium contention
deal with hidden/exposed terminal problem
improve throughputQoS MACs must provide resource
reservation and QoS guarantees to real-
time trafficWireless LANs – Black burst contention etc
Manets – MACA/PR
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MACA/PR
Multiple Access Collision Avoidance withPiggyback ReservationsRapid and reliable transmission to non-real time
datagrams
Guaranteed b/w support to real-time traffic
NRT traffic waits for “free” window inreservation table plus additional random timeequivalent to single hop round-trip delay
proceed with RTS-CTS-PKT-ACK dialogue Reservation table records all reserved send
and receive windows of all stations in range
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MACA/PR - RT
To send first data packet of a RT connection,sender initiates RTS-CTS and then proceedswith PKT-ACK
For subsequent data packets only PKT-ACK
is needed If sender fails to receive several ACKs then
restarts RTS-CTS dialogue
MACA/PR does not retransmit after collisions
To reserve b/w for real-time traffic, RTscheduling information is carried in headersof PKTS and ACKs
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MACA/PR -RT
Sender piggybacks reservation informationfor its next data packet transmission on the
current data PKT
Receiver inserts reservation in its
Reservation table and confirms it with the ACK to the sender
Neighbors of receiver R will defer their
transmission on receiving the ACK ACK also tells them next scheduled receiving
time of R, so they can avoid transmission
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MACA/PR -RT
Real-time packets are protected fromhidden hosts by the propagation of
reservation tables among neighbors, not
by RTS-CTS dialogues
Thus, through piggybacked reservation
of information and the maintenance of
reservation tables, bandwidth is
reserved and guaranteed for real-time
traffic…
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Perspective
Essentially, concept of QoS must beaccepted and supported by every
element in the value chain
Infrastructure and terminal developersMobile network operators
Application developers
End users