IP QoS features for TPS Feb. 2003 Woo Young Jung R&D Center, Corecess Inc. Mail : wyjung@corecess.com Contents Table of Contents 1. Internet QoS 개요 2. Microscopic Tools 3. Macroscopic Tools 4. Case Study 5. Summary 22
Table of Contents 1.Internet QoS 개요 2. Microscopic Tools 3. Macroscopic Tools 4. Case Study 5. Summary 33 Internet QoS 개요 QoS 의개념? QoS (Quality of Service) is 특정한응용프로그램에필요한요구사항을만족하기위하여통신망자원의할당과운영에우선적인처리를하는것 종단간에 Flow별로요구조건이만족되도록하여야한다 궁극적으로이는 Biz Issue와직결되어있다 QoS Triangle Higher Price! 사용자 Well If Proved 통신사업자 Well I am not sure, yet More Profit! 장비업자 44
Internet QoS 개요 QoS vs CoS QoS end-to-end QoS per-flow CoS : per-hop A B D C QoS CoS 55 Internet QoS 개요 QoS 관련이슈들 어떻게구현할것인가? 트래픽 / 가입자별로얼마나 ( 성능 / 품질 ) 차이를둘것인가? L2/L3간의 Seamless QoS Mapping 요금정책및과금구조 운영비용및 OSS 사업자간 QoS Mapping 및요금정산 Traffic Engineering vs Traffic Management QoS Measurement (SLA) 66
Internet QoS 개요 Two IP QoS Approaches Big Pipes (Overprovisioning) Network Bandwidth 를충분히확보 Simple, but Expensive 심한 Congestion 상태에서는현실적대응불가 Not the ultimate solution Traffic Control Using 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 77 Internet QoS 개요 QoS 의현상황 제조업체 라우터에 QoS 주요기능구현되어있음 QoS 기능을동작시키면성능저하가발생함. 통신사업자 대규모로본격적인서비스를제공하는상용망은없음 Access 망의고속화에따라 VoD 등의서비스를위해 QoS 기능을도입하려는경향은매우큼 사업자혹은국가적으로 Trial 단계 사용자 QoS 보장에대한요구는있음 가격의추가지불의지?? 88
Table of Contents 1. Internet QoS 개요 2.Microscopic Tools 3. Macroscopic Tools 4. Case Study 5. Summary 99 Microscopic Tools Per-Hop Packet Processing traffic stream Classification & Mapping Metering & Marking Policing & Queueing S/D IP Add, TCP/UDP Port Num, ToS, tr_tcm, DSCP WRED/SARED Scheduling WFQ Shaping Mapping traffic stream Packet rewriting 10 10
Microscopic Tools Per-Hop Packet Processing Edge node Classification/ Mapping Metering, Marking and Policing/Shaping Queue Manager Flow control, Policing/Shaping, Queueing/Scheduling, Marking/remarking Customer 1 Customer 2 Customer 3 Customer n Classifier Meter Marker Meter Marker Meter Marker flow 1 Shaper/Policer flow 2 Shaper/Policer flow m Shaper/Policer Queue Manager Queue 1 Queue 2 Queue 3 Queue 4 output port/interface i Core node Classification/ Mapping Queue Manager Flow control, Policing/Shaping, Queueing/Scheduling, Marking/remarking Classifier Queue Manager Queue 1 Queue 2 Queue 3 Queue 4 11 11 Microscopic Tools Classification Packet Classification To 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 Classification Network internal criteria : MAC Add, IP Add, Port Num, etc. Network external criteria : Subscriber, Service type, etc 12 12
Microscopic Tools Classification L2 MAC Frame Format Ethernet Format (DIX 2.0/IEEE 802.3) Destination MAC Source MAC Type/ Length IP Datagram FCS 6B 6B 2B 4B IEEE 802.1p/Q Format and VLAN ID Destination MAC (6B) Source MAC (6B) TPID (2B) Pri (3b) CFI VLANID Type (1b) (12b) (2B) Data FCS (4B) MPLS over Ethernet Format QoS information is Tagged onto L2 MAC frame. Dst. MAC Src MAC Type (2B) Label (20b) Exp (3b) S 1b TTL (8b) Dst. MAC Src MAC Type (2B) IP Datagram FCS (4B) 13 13 Microscopic Tools Classification IP Packet Format 0 4 8 16 19 24 31 Ver H.Len Type of Service Total Length Identification Flags Fragment Offset Time To Live Protocol Header Checksum Source IP Address Destination IP Address IP Options Padding Data 14 14
Microscopic Tools Classification Type of service (ToS) Field Type of Service Prec D T R C U IP Precedence Field Precedence (3b) : classify a packet into 8 priority levels (RFC791) IP Prec Name Value 0 routine 1 priority 2 immediate 3 flash 4 flash-override 5 critical 6 internet 7 network Service Profile Selector Field D : 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. 15 15 Microscopic Tools Classification Newly define the IP ToS Field DSCP field (6b) + CU field (2b) DS Field Prec D T R C U DSCP CU DS Field : 8 bits Used to select PHB Replace IPv4 ToS or IPv6 Traffic Class DSCP Field DSCP(DiffServ Code Point) Field : 6 bits 64 DSCPs xxx000 : 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. 16 16
Microscopic Tools Metering and Marking Definition Metering : to measure the incoming IP packet stream Marking : to mark packets green, yellow, red according to the metering result Metering Result Packet Stream Meter Marker Marked Packet Stream RFC2697 A Single Rate Three Color Marker RFC2698 A Two Rate Three Color Marker RFC2859 A Time Sliding Window Three Colour Marker (TSWTCM) RFC2963 A Rate Adaptive Shaper for Differentiated Services 17 17 Microscopic Tools Single-Rate Three Color Marker RFC2697 Marking is based on CIR, CBS, and EBS sr-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 Modes Color-Blind Mode Meter assumes that the packet stream is uncolored. Color-Aware Mode Meter assumes that some preceding entity has pre-colored the incoming packet stream. 18 18
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 Modes Color-Blind Mode Color-Aware Mode 19 19 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 Schemes Tail-Drop RED (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) 20 20
Microscopic Tools Queueing and Traffic control TCP Slow Start and Congestion Avoidance Congestion Window Size(CWND) is initialized to 1 MSS(Maximum Segment Size). Whenever the sender receives ACK before timeout, If CWND Threshold CWND = 2 * CWND If CWND > Threshold CWND = CWND + 1 If Timeout occurs, Threshold = Threshold / 2 CWND = 1 MSS CWND Th. 1 2 2 3 1 1 3 1. Slow start 2. RTT 3. Congestion avoidance Liner increase Time 21 21 Microscopic Tools Queueing and Traffic control Tail-Drop Mechanism Used in the traditional FIFO queueing Drops the packets arriving after queue becomes full Treats all traffic flows equally Global Synchronization 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. Queue Size Total Queue Time 22 22
Microscopic Tools Queueing and Traffic control Random Early Detection (RED) Queue 길이에따라 random 하게패킷을버림 d (k) 1 Drop Probability p max Selecting TH_max less than the max queue size degrades the whole performance. Should set TH_max as close to K as possible. 0 Th min Th max K k AQS AQS AQS Drops no packets Drop packets according to the Drop Function Drop all packets 23 23 Microscopic Tools Queueing and Traffic control Weighted Random Early Detection (WRED) Traffic Class 별로다른확률로패킷을버림 Prob. Drop Probability 1 Pr Py Pg 0 Rmin Ymin Gmin Max.Q 24 24
Microscopic Tools Policing/Rate Limiting Policing/Rate limiting 계약된 Bandwidth 이상의패킷을버림 B/W offered traffic B/W rate-limited traffic limiting target traffic rate 0 T 0 T Rate limiting in an input port 1 2 3 N Rate limiting in an output port 1 2 3 N 25 25 Microscopic Tools Rate Shaping Rate Shaping 순간적으로계약된 Bandwidth 이상으로입력되는패킷을버퍼에담아두어일정한완충효과를줌. shaping B/W offered traffic B/W buffered target traffic rate rate-shaped traffic 0 T 0 T 26 26
Microscopic Tools Scheduling Scheduling Queue에담긴여러개의flow중출력링크로다음에어떤패킷을전송할것인가를정하는절차 FIFO 입력순서대로출력되는단일한 Queue로구성 Strict Priority queueing 우선순위가정해진여러개의 FIFO Queue 로구성 단순하지만낮은순위의트래픽에불이익이너무큼 (starvation) Weighted Round Robin 서비스 Round 당모든 Queue 는적어도한번은서비스를받음 고정길이패킷에적당 Weighted Fair Queueing 정해진 bandwidth 에적절하게링크를사용할수있음 가변길이패킷에적용가능 27 27 Microscopic Tools Scheduling - WFQ Proposed by Lixia Zhang et al. in 1989 Designed to resolve the Problem of Fair Queueing Supports flows with different bandwidth requirements Assigns bandwidth fairly to variable-length packets by approximating to the GPS System WFQ Operation Scheduler 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. 90 50 30 145 110 70 Scheduler 155 145 135 110 90 70 50 30 155 135 28 28
Table of Contents 1. Internet QoS 개요 2. Microscopic Tools 3.Macroscopic Tools 4. Case Study 5. Summary 29 29 Macroscopic Tools QoS Network Architecture NMS OSS Policy Measurement AAA Billing A B D C RSVP DiffServ 30 30
Macroscopic Tools Integrated Service (IntServ) End-to-end flow 기반의 QoS를위한서비스정의 Queue에담긴여러개의flow중출력링크로다음에어떤패킷을전송할것인가를정하는절차 Application Class Applications Real Time Elastic Tolerant Intolerant Service Models Controlled-Load Service Guaranteed Service 31 31 Macroscopic Tools RSVP 개별 flow별로 Router에자원을할당하기위한시그날링프로토콜 Receiver 기반의프로토콜 Soft-State를통한flexibility 보유 MPLS Traffic Engineering을위해사용됨 RSVP-TE A PATH Message B D C RESV Message 32 32
Macroscopic Tools Differentiated Service (DiffServ) IntServ의 Scalability Problem을극복하기위하여도입됨개별 flow단위의제어가아닌 flow group (Class) 단위의처리 Service type Expedited Forwarding (EF) PHB: DSCP = 101110 Assured Forwarding (AF) PHB Best Effort: DSCP = 000000 DSCP Values for each AF PHB Group DS Field DSCP CU DSCP Field 분류 순위 Class 1 Class 2 Class 3 Class 4 Drop precedence 1 low 001010 010010 011010 100010 Drop precedence 2 medium 001100 010100 011100 100100 Drop precedence 3 high 001110 010110 011110 100110 33 33 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 34 34
Macroscopic Tools MPLS Traffic Engineering & QoS MPLS Traffic Engineering 네트웍자원의효율적인이용을위해도입 최초도입은 QoS 와무관 Routing Protocol 에의한 Shortest Path 와 Flow Path (LSP) 를분리 35 35 Macroscopic Tools MPLS Traffic Engineering & QoS MPLS TE and IntServ LSP can be set up by RSVP Class 별로 QoS 요구를고려한서로다른 LSP 의구성이가능하다 RSVP 는 LSP 별로필요한자원을 Router 에예약한다 A RSVP Path MPLS LSP RSVP Path B 36 36
Macroscopic Tools MPLS Traffic Engineering & QoS MPLS TE and DiffServ 방법 1: Label 과 EXP field 에 DSCP 를 mapping 한다 (Label-inferred LSP) 방법 2: EXP field 에 DSCP 를 mapping 한다 (EXP-inferred LSP) Next-hop Context Next-hop Context Label (20bits) EXP (3bits) QoS Context Policing/Marking Queueing Scheduling Label (20bits) EXP (3bits) QoS Context Policing/Marking Queueing Scheduling Label-inferred LSP EXP-inferred LSP 37 37 Macroscopic Tools QoS Routing 현재의 Routing Protocol Single Metric Shortest Path Routing Destination IP address 기반 현재의 Routing protocol 의문제점 네트웍자원을효율적으로사용하지못함 트래픽패턴의변화에대해탄력적으로대응할수없다 ( 망설계?) QoS Routing Service Class 에따라 Forwarding Path 를달리선정함 QoS Routing Issue 네트웍의 QoS 자원의현황을파악하는것이어려움 현재연구단계로서적용된상용망없음 Routing Protocol Deployment 는매우보수적인영역이라향후도입전망불투명 QoS Routing vs MPLS Traffic Engineering??????? 38 38
Macroscopic Tools Measurement 의의 SLA 만족을위해 Performance Measurement 가매우중요함 방법 Polling of Network Equipment Active Probing of Flow-path Ping Traceroute 문제점 : 여러개의 Service Class에대한flow-path상태를모두파악할수없음 Core node Classification/ Mapping Queue Manager Flow control, Policing/Shaping, Queueing/Scheduling, Marking/remarking Classifier Ping Queue Manager Queue 1 Queue 2 Queue 3 Queue 4 39 39 Macroscopic Tools Policy-based Control Policy Combination 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 Policy Decision Point COPS Protocol Topology and Policy DB Policy Enforcement Point RSVP Processor Admission Control System AAA server RSVP Reservation RSVP Reservation 40 40
Macroscopic Tools Billing Billing Model Flat Rate Bandwidth-based Data-based (Usage-based) 가격정책은가입자 QoS와직결된다 Premium service와 best-effort service간의품질차이유지기준은? 다음의경우에대한망운영정책은? 1등급가입자와 3등급가입자간의 VoIP 통화시 41 41 Table of Contents 1. Internet QoS 개요 2. Microscopic Tools 3. Macroscopic Tools 4.Case Study 5. Summary 42 42
Case Study Multihop Simulation (RFC 2598) RFC 2598: An Expedited Forwarding PHB Multihop 환경에서 DiffServ Expedited Forwarding PHB Simulation 포함 43 43 Case Study Multihop 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) 44 44
Case Study Multihop Simulation (RFC 2598) 1500 Byte Packet Variation in Jitter of EF flows: Service/arrival rate varies, subscription rate = 56Kbps 8 flow aggregate 45 45 Case Study Global Crossing (US Provider) Service Class Premium/Assured/Best effort Operation 원칙 MPLS Traffic Protection 적용 (Backup route pre-setup): 1999 2Q ~ Traffic Engineering >Traffic management 50% 이하의부하로운영 46 46
Case Study Global Crossing (US Provider) Measured Performance Coast-to-Coast Round-trip Delay < 80ms Jitter < 2ms ITU-T G.114 Delay Recommendation 47 47 Case Study GÉANT: Pan-European Exp. GÉANT 유럽 30 개국을연결하는연구망 2001 년 12 월에운영시작 Core Network 속도 : 2.5 ~ 10Gbps GÉANT Premium IP Service Model Based on Diffserv EF PHB Architecture 링크용량의 5~10% 가 Premium IP 서비스에할당됨. 초기에는 H.323 Videoconferencing으로시험시작 Juniper M160 Router 사용 Traffic Class: Premium/Best effort/signalling & Control WRR Scheduling: Premium (90%)/Best effort (5%) /Signalling & Control (5%) 48 48
Case Study GÉANT: Pan-European Exp. 49 49 Case Study GÉANT: Pan-European Exp. 50 50
Case Study GÉANT: Pan-European Exp. 51 51 Summary Internet QoS는기술적인측면와사업적측면이결합된복잡한이슈다. Router내에서구현되는 QoS기술은 Classification, Metering/Marking, Queueing, Scheduling등이있다. 전체네트웍차원에서이루어지는 QoS기술은 IntServ, DiffServ, MPLS Traffic Engineering, QoS Routing등이있다. 운영 / 사업측면에서는품질측정, 과금, 정책기반제어등의운영체제가있어야한다. QoS기반의차별적인서비스를제공하는상용망은아직없으나 Trial Service 차원의검증은부분적으로이루어지고있다. Access 망의고속화로인한 VoD 등의신규서비스 (TPS) 의활성화는 QoS 의도입을촉진할것으로판단된다. 52 52