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IP QoS features for TPS
Woo Young Jung
R&D Center, Corecess Inc.Mail : [email protected]
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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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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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Simple and Flexible
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Case Study
GÉANT: Pan-European Exp.
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Simple and Flexible
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Case Study
GÉANT: Pan-European Exp.
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Simple and Flexible
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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.