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IP QoS features for TPS

Woo Young Jung

R&D Center, Corecess Inc.Mail : wyjung@corecess.com

Feb. 2003

Table of Contents

1. Internet QoS 개요

2. Microscopic Tools

3. Macroscopic Tools

4. Case Study

5. Summary

Simple and Flexible

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Contents

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Table of Contents

1.Internet QoS 개요2. Microscopic Tools

3. Macroscopic Tools

4. Case Study

5. Summary

Simple and Flexible

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Simple and Flexible

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QoS의 개념?

QoS (Quality of Service) is …특정한 응용프로그램에 필요한 요구사항을 만족하기 위하여

통신망 자원의 할당과 운영에 우선적인 처리를 하는 것

종단간에 Flow별로 요구조건이 만족되도록 하여야 한다

궁극적으로 이는 Biz Issue와 직결되어 있다

QoS Triangle

Internet QoS 개요

통신사업자

장비업자사용자

Higher Price!Well…

If Proved Well…I am not sure, yet

More Profit!

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Simple and Flexible

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QoS vs CoS

QoSQoS

CoS : per-hop

• end-to-end• per-flow

QoSCoS

A

C

DB

Internet QoS 개요

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QoS 관련 이슈들

어떻게 구현할 것인가?

트래픽/가입자별로 얼마나 (성능/품질)차이를 둘 것인가?L2/L3간의 Seamless QoS Mapping

요금정책 및 과금구조

운영비용 및 OSS사업자간 QoS Mapping 및 요금정산

Traffic Engineering vs Traffic ManagementQoS Measurement (SLA)

…

Internet QoS 개요

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Two IP QoS Approaches

Big Pipes (Overprovisioning)Network Bandwidth를 충분히 확보

Simple, but Expensive

심한 Congestion 상태에서는 현실적 대응불가Not the ultimate solution

Traffic ControlUsing diverse mechanism enhancing QoS

Protocols: IntServ, DiffServ, MPLS, IEEE 802.1p/Q, …

Enabling Technologies: QoS methods, such as policing, shaping, etc.

Complex, but less expensive.

Coincides with the needs of network equipment vendors and Service Providers

Internet QoS 개요

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Internet QoS 개요

제조업체라우터에 QoS 주요기능 구현되어 있음QoS 기능을 동작시키면 성능 저하가 발생함.

통신사업자대규모로 본격적인 서비스를 제공하는 상용망은 없음

Access망의 고속화에 따라 VoD등의 서비스를 위해 QoS 기능을 도입하려는 경향은 매우 큼

사업자 혹은 국가적으로 Trial 단계

사용자QoS 보장에 대한 요구는 있음

가격의 추가지불 의지??

QoS의 현상황

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Table of Contents

1. Internet QoS 개요

2.Microscopic Tools3. Macroscopic Tools

4. Case Study

5. Summary

Simple and Flexible

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Simple and Flexible

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Microscopic Tools

trafficstream

S/D IP Add, TCP/UDP Port Num,

ToS, …

Metering &Marking

Metering &Marking

tr_TCM, DSCP

Policing &Queueing

Policing &Queueing

WRED/SARED

WFQ

SchedulingScheduling

trafficstream

Classification& Mapping

Classification& Mapping

Mapping

Packet rewriting

ShapingShaping

Per-Hop Packet Processing

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Simple and Flexible

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Microscopic Tools

Per-Hop Packet Processing

Metering, Marking and Policing/Shaping

Classification/Mapping Queue Manager

Flow control,Policing/Shaping,

Queueing/Scheduling,Marking/remarking

QueueManager

Meter

Marker

Meter

Marker

Meter

Marker

flow 1

flow 2

flow m

Shaper/Policer

Shaper/Policer

Shaper/Policer

…

Customer 1

Queue 2

Queue 1

Queue 4

Queue 3

QueueManager

Queue 2

Queue 1

Queue 4

Queue 3

Classifier

Classifier

Edge nodeEdge node

Core nodeCore node

Customer 2

…

Customer n

Customer 3

output port/interface i

……

Classification/Mapping Queue Manager

Flow control,Policing/Shaping,

Queueing/Scheduling,Marking/remarking

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Simple and Flexible

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Microscopic Tools

Classification

Packet ClassificationTo identify packets to be of a certain class based on one or more fields in a packet

Classify packets into groups with the same or similar QoS metrics

Packets in a group are treated equally.

Performed in Edge Routers.Core Routers use the result of classification in order to perform high-speed switching/routing.

Why Packet Classification is Required?Simplify QoS schemes by handling all the traffic with the same or similar QoS requirements together.

Criteria of Packet ClassificationNetwork internal criteria : MAC Add, IP Add, Port Num, etc.Network external criteria : Subscriber, Service type, etc

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Microscopic Tools

Classification

S1b

Destination MAC Source MAC FCSType/Length IP Datagram

Ethernet Format (DIX 2.0/IEEE 802.3)

6B 6B 2B 4B

IEEE 802.1p/Q Format and VLAN ID

DestinationMAC (6B)

SourceMAC (6B)

TPID(2B)

CFI(1b)

VLANID(12b)

Type(2B) Data FCS

(4B)Pri

(3b)

MPLS over Ethernet Format

Type(2B)

TTL(8b)

Type(2B) IP Datagram FCS

(4B)Exp(3b)

Label(20b)

Dst.MAC

SrcMAC

Dst.MAC

SrcMAC

QoS information is Tagged onto

L2 MAC frame.

L2 MAC Frame Format

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Simple and Flexible

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Microscopic Tools

Classification

IP Packet Format

0

Ver H.Len Type of Service Total Length

Identification Fragment OffsetFlags

Time To Live Protocol Header Checksum

Source IP Address

Destination IP Address

PaddingIP Options

4 8 16 19 24 31

Data

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Simple and Flexible

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Microscopic Tools

Classification

Type of service (ToS) Field

Type of Service D UT R CPrec

IP Prec Value

Name

0 routine1 priority2 immediate3 flash4 flash-override5 critical6 internet7 network

IP Precedence FieldPrecedence (3b) : classify a packet into 8 priority levels (RFC791)

Service Profile Selector FieldD : Minimize Delay

T : Maximize Throughput

R : Maximize Reliability

C : Minimize Cost

U : Unused (MBZ: Must Be Zero)

RFC 1349 – Type of Service in the Internet Protocol Suite.

DTR DTRC after RFC1349.

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Microscopic Tools

Classification

Newly define the IP ToS FieldDSCP field (6b) + CU field (2b)

DS Field : 8 bitsUsed to select PHBReplace IPv4 ToS or IPv6 Traffic Class

DSCP(DiffServ Code Point) Field : 6 bits64 DSCPsxxx000 : backward compatible with IP Precedence (code selector)32 DSCPs are reserved by IETF to map to standard PHBs.

xxxxx0

remaining 32 DSCPs are used for local use or experimental use.

DSCP CUDPrec UT R C

DS Field

DSCP Field

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Microscopic Tools

Metering and Marking

DefinitionMetering : to measure the incoming IP packet streamMarking : to mark packets green, yellow, red according to the metering result

MeterMeter MarkerMarkerPacket Stream MarkedPacket Stream

Metering Result

RFC2697 – A Single Rate Three Color MarkerRFC2698 – A Two Rate Three Color MarkerRFC2859 – A Time Sliding Window Three Colour Marker (TSWTCM)RFC2963 – A Rate Adaptive Shaper for Differentiated Services

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Microscopic Tools

Single-Rate Three Color Marker

RFC2697

Marking is based on CIR, CBS, and EBSsr-TCM Algorithm

See next slide.Similar to the policing mechanism of Frame Relay.

Useful for ingress policing Only the length of the burst, not bit rate, determines service eligibility.

Operation ModesColor-Blind Mode

Meter assumes that the packet stream is uncolored.

Color-Aware ModeMeter assumes that some preceding entity has pre-colored the incoming packet stream.

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Microscopic Tools

Two-Rate Three Color Marker

RFC2698

Marking is based on CIR, PIR and CBS, PBS.tr-TCM Algorithm

See next slide.Similar to the policing mechanism of ATM.

Useful for ingress policing The bit rate, not burst length, determines service eligibility.A peak rate needs to be enforced separately from a committed rate.

Operation ModesColor-Blind ModeColor-Aware Mode

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Microscopic Tools

Queueing and Traffic control

What is Traffic Control?The process to drop packets fairly to avoid the performance degradation due to network congestion.

Why Traffic Control is Required?Since TCP composes most of network transmission.To resolve the performance degradation due to the global synchronization of TCP traffics due to buffer overflow (or tail drop).

Flow Control SchemesTail-DropRED (Random Early Detection/Discard), WRED (Weighted RED)RIO (RED with In/Out), MRED (Multi-level RED), GRED (Generalized RED in Linux), SRED (Stablized RED), FRED (Flow RED)BLUE – IBM, SARED (Shock Absorb RED)

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Microscopic Tools

Queueing and Traffic control

TCP Slow Start and Congestion AvoidanceCongestion Window Size(CWND) is initialized to 1 MSS(Maximum Segment Size).Whenever the sender receives ACK before timeout,

If CWND ≤ Threshold CWND = 2 * CWNDIf CWND > Threshold CWND = CWND + 1

If Timeout occurs,Threshold = Threshold / 2

CWND = 1 MSS

CWND

Time

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22 22

3333

1. Slow start2. RTT3. Congestion avoidance

Liner increase

1. Slow start2. RTT3. Congestion avoidance

Liner increase

Th.

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Microscopic Tools

Queueing and Traffic control

Tail-Drop MechanismUsed in the traditional FIFO queueingDrops the packets arriving after queue becomes fullTreats all traffic flows equallyGlobal Synchronization

Queue Size

Time

Total Queue

All TCP connections reduce their transmission rate on crossing over the maximum queue size.

The TCP connections increase their tx rate using the slow start and congestion avoidance.

The TCP connections reduce their tx rate again.It makes the network traffic fluctuate.

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Microscopic Tools

Queueing and Traffic control

Random Early Detection (RED)Queue 길이에 따라 random하게 패킷을 버림

KmaxThminTh0

maxp

)(kd

1

k

AQS AQS AQS

Drops no packets

Drop packets according to the Drop Function

Drop all packets

Selecting TH_max less than the max queue size degrades the whole performance. Should set TH_max as close to K as possible.

Drop Probability

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Microscopic Tools

Queueing and Traffic control

Weighted Random Early Detection (WRED)Traffic Class별로 다른 확률로 패킷을 버림

Drop Probability

0

Prob.

1

Max.QminR minY minG

Pg

Py

Pr

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Microscopic Tools

Policing/Rate Limiting

Policing/Rate limiting계약된 Bandwidth이상의 패킷을 버림

T

B/W

0T

B/W

0

target traffic rate

rate-limited trafficoffered traffic

• • •1 2 3 N

• • •

1 2 3 NRate limiting in an input port

Rate limiting in an output port

limiting

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Microscopic Tools

Rate Shaping

Rate Shaping순간적으로 계약된 Bandwidth이상으로 입력되는 패킷을

버퍼에 담아두어 일정한 완충효과를 줌.

T

B/W

0

target traffic rate

offered traffic

T

B/W

0

buffered

rate-shaped traffic

shaping

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Microscopic Tools

Scheduling

SchedulingQueue에 담긴 여러 개의 flow중 출력링크로 다음에 어떤 패킷을 전송할 것인가를 정하는 절차

FIFO입력 순서대로 출력되는 단일한 Queue로 구성

Strict Priority queueing우선순위가 정해진 여러개의 FIFO Queue로 구성

단순하지만 낮은 순위의 트래픽에 불이익이 너무 큼 (starvation)

Weighted Round Robin서비스 Round당 모든 Queue는 적어도 한번은 서비스를 받음

고정길이 패킷에 적당

Weighted Fair Queueing정해진 bandwidth에 적절하게 링크를 사용할 수 있음

가변길이 패킷에 적용가능

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Microscopic Tools

Scheduling - WFQ

Proposed by Lixia Zhang et al. in 1989

Designed to resolve the Problem of Fair QueueingSupports flows with different bandwidth requirementsAssigns bandwidth fairly to variable-length packets by approximating to the GPS System

WFQ OperationScheduler assigns the finish time to each packet and serves packets based on the finish time

The finish time is computed based on the output port speed, number of active queues, weight assigned to each queue, and packet length.

Scheduler

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70

135

5090

110145

155

30507090135 110145155

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Table of Contents

1. Internet QoS 개요

2. Microscopic Tools

3.Macroscopic Tools4. Case Study

5. Summary

Simple and Flexible

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Macroscopic Tools

QoS Network Architecture

A

C

DB

NMS OSS Policy Measurement AAA Billing

RSVPDiffServ

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Macroscopic Tools

Integrated Service (IntServ)

End-to-end flow 기반의 QoS를 위한 서비스 정의Queue에 담긴 여러 개의 flow중 출력링크로 다음에 어떤 패킷을 전송할 것인가를 정하는 절차

Application Class

Service ModelsControlled-Load ServiceGuaranteed Service

ApplicationsReal Time

Elastic

• Tolerant• Intolerant

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Macroscopic Tools

RSVP

개별 flow별로 Router에 자원을 할당하기 위한 시그날링 프로토콜

Receiver 기반의 프로토콜

Soft-State를 통한 flexibility 보유

MPLS Traffic Engineering을 위해 사용됨 RSVP-TE

A

C

DB

PATH Message

RESV Message

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Macroscopic ToolsDifferentiated Service (DiffServ)

IntServ의 Scalability Problem을 극복하기 위하여 도입됨

개별 flow단위의 제어가 아닌 flow group (Class)단위의 처리

Service typeExpedited Forwarding (EF) PHB: ”DSCP = 101110”

Assured Forwarding (AF) PHB

Best Effort: ”DSCP = 000000”

DSCP Values for each AF PHB Group

DSCP CU

DS Field

DSCP Field

100110011110010110001110highDrop precedence 3

100100011100010100001100mediumDrop precedence 2

100010011010010010001010lowDrop precedence 1

Class 4Class 3Class 2Class 1순위분류

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Macroscopic Tools

DiffServ Architecture

DS Boundary

ㅇ MF Cassification

ㅇ Traffic Conditioning

ㅇ Admission Control

DS Interior

ㅇ BA Cassification

ㅇ PHB Support

ㅇ Queue Mngt/Scheduling

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MPLS Traffic Engineering & QoS

MPLS Traffic Engineering네트웍 자원의 효율적인 이용을 위해 도입

최초 도입은 QoS와 무관

Routing Protocol에 의한 Shortest Path와 Flow Path (LSP)를 분리

Macroscopic Tools

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MPLS Traffic Engineering & QoS

MPLS TE and IntServLSP can be set up by RSVPClass별로 QoS 요구를 고려한 서로 다른 LSP의 구성이 가능하다

RSVP는 LSP별로 필요한 자원을 Router에 예약한다

Macroscopic Tools

A BRSVP Path

RSVP PathMPLS LSP

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MPLS Traffic Engineering & QoS

MPLS TE and DiffServ방법1: Label과 EXP field에 DSCP를 mapping 한다 (Label-inferred LSP) 방법2: EXP field에 DSCP를 mapping 한다 (EXP-inferred LSP)

Macroscopic Tools

Label(20bits)

EXP(3bits)

Policing/MarkingQueueing

Scheduling

Next-hop Context

QoSContext

Label(20bits)

EXP(3bits)

Policing/MarkingQueueing

Scheduling

Next-hop Context

QoSContext

Label-inferred LSP EXP-inferred LSP

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QoS RoutingMacroscopic Tools

현재의 Routing ProtocolSingle Metric Shortest Path RoutingDestination IP address 기반

현재의 Routing protocol의 문제점네트웍 자원을 효율적으로 사용하지 못함

트래픽 패턴의 변화에 대해 탄력적으로 대응할 수 없다 ( 망설계?)

QoS RoutingService Class에 따라 Forwarding Path를 달리 선정함

QoS Routing Issue네트웍의 QoS 자원의 현황을 파악하는 것이 어려움

현재 연구단계로서 적용된 상용망 없음

Routing Protocol Deployment는 매우 보수적인 영역이라 향후 도입전망 불투명

QoS Routing vs MPLS Traffic Engineering???????

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Measurement

의의SLA 만족을 위해 Performance Measurement가 매우 중요함

방법Polling of Network EquipmentActive Probing of Flow-path

“Ping”

“Traceroute”

문제점: 여러개의 Service Class에 대한 flow-path상태를 모두 파악할 수 없음

Macroscopic Tools

QueueManager

Queue 2

Queue 1

Queue 4

Queue 3

Classifier

Core nodeCore node Classification/Mapping Queue Manager

Flow control,Policing/Shaping,

Queueing/Scheduling,Marking/remarking

Ping

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Policy-based Control

PolicyCombination of rules and services, where the rules define the criteria for access to various network services and their associated level of resource consumption

Policy Decision Point (PDP)Network element where policy decisions are made

Policy Enforcement Point (PEP)Network element where policy decisions are enforced

Macroscopic Tools

RSVP Processor Admission Control System

Policy Enforcement Point

Policy Decision Point

AAA server

Topology and Policy DB COPS Protocol

RSVP Reservation

RSVP Reservation

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Billing

Billing ModelFlat RateBandwidth-basedData-based (Usage-based)

가격정책은 가입자 QoS와 직결된다

Premium service와 best-effort service간의 품질차이 유지기준은?

다음의 경우에 대한 망운영 정책은?1등급 가입자와 3등급 가입자간의 VoIP 통화시

Macroscopic Tools

Table of Contents

1. Internet QoS 개요

2. Microscopic Tools

3. Macroscopic Tools

4.Case Study5. Summary

Simple and Flexible

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Case StudyMultihop Simulation (RFC 2598)

RFC 2598: “An Expedited Forwarding PHB”Multihop 환경에서 DiffServ Expedited Forwarding PHB Simulation 포함

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Case StudyMultihop Simulation (RFC 2598)

1500 Byte Packet

Variation in Jitter with number of EF flows:

Service/arrival rate = 1.06, subscription rate = 56Kbps

(All values given as % of subscribed rate)

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Case StudyMultihop Simulation (RFC 2598)

Variation in Jitter of EF flows:

Service/arrival rate varies, subscription rate = 56Kbps

8 flow aggregate

1500 Byte Packet

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Case Study

Global Crossing (US Provider)

Service ClassPremium/Assured/Best effort

Operation 원칙MPLS Traffic Protection 적용 (Backup route pre-setup): 1999 2Q ~Traffic Engineering >Traffic management50% 이하의 부하로 운영

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Case Study

Global Crossing (US Provider)

Measured PerformanceCoast-to-Coast Round-trip Delay < 80msJitter < 2ms

ITU-T G.114 Delay Recommendation

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Case Study

GÉANT: Pan-European Exp.

GÉANT유럽 30개국을 연결하는 연구망

2001년 12월에 운영시작

Core Network 속도: 2.5 ~ 10Gbps

GÉANT Premium IP Service ModelBased on Diffserv EF PHB Architecture링크용량의 5~10%가 Premium IP 서비스에 할당됨.초기에는 H.323 Videoconferencing으로 시험 시작

Juniper M160 Router 사용

Traffic Class: Premium/Best effort/Signalling & ControlWRR Scheduling: Premium (90%)/Best effort (5%)

/Signalling & Control (5%)

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Simple and Flexible

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Case Study

GÉANT: Pan-European Exp.

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Case Study

GÉANT: Pan-European Exp.

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Case Study

GÉANT: Pan-European Exp.

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Summary

Internet QoS는 기술적인 측면와 사업적 측면이 결합된

복잡한 이슈다.Router내에서 구현되는 QoS기술은 Classification, Metering/Marking, Queueing, Scheduling등이 있다.

전체 네트웍 차원에서 이루어지는 QoS기술은 IntServ, DiffServ, MPLS Traffic Engineering, QoS Routing등이 있다.

운영/사업측면에서는 품질측정, 과금, 정책기반제어등의 운영체제가있어야 한다.QoS기반의 차별적인 서비스를 제공하는 상용망은 아직 없으나 Trial Service 차원의 검증은 부분적으로 이루어지고 있다.

Access망의 고속화로 인한 VoD등의 신규서비스(TPS)의 활성화는QoS의 도입을 촉진할 것으로 판단된다.