qos in wireless network

7/29/2019 QoS in Wireless Network

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QoS in wireless systems

Preetam Patil

Leena Chandran-Wadia



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




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.




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




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




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




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




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




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




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




DiffServ Components

Edge functionsFlow classification and packet marking

Traffic conditioning

Core functions

Enforcement of Per Hop Behaviours

Boundary functions

Conformance enforcement




DiffServ Components… continued

ComponentsClassifiers

Select packets and assigns DS code

pointTraffic conditioners

Enforces rate limitations

Per Hop Behaviours Differentiated packet treatments



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.




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




MPLS Architecture




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)




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




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)




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




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




ATM Logical Connections

Transmission Path

Virtual Path

Virtual Channels




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)




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




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




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




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!!




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




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




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




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




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




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




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




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




Traffic Flow Templates

Assign different QoS-profiles to different applications -Signaling done using RSVP API




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




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




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




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




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




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…



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

qos in wireless network

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