Uslugi z gwarantowana jakoscia. Quality of Service - Michal Przybylski, PCSS

Transkrypt

1 Uslugi z gwarantowana jakoscia Quality of Service - Michal Przybylski, PCSS

2 Plan wykladu Koncepcja QBone Metryki SLA Overprovisioning Architektura Diffserv Istniejace implementacje mechanizmów zapewniania QoS Problemy integracji QoS Quality of Service - Michal Przybylski, PCSS

3 Zmiany w Internecie Zastosowania Rodzaj ruchu Pojemnosc laczy Zarzadzanie Wczoraj , WWW, FTP best effort do 155 Mb/s siecia Dzisiaj wideokonferencje, zdalne nauczanie, telewizja interaktywna gwarantowana jakosc uslugi Gb/s uslugami Quality of Service - Michal Przybylski, PCSS

4 Koncepcja QBONE The goal of the QBone is to provide an interdomain testbed for differentiated services (DiffServ), where the engineering, behavior, and policy consequences of new IP services can be explored. QBone - an interdomain testbed for differentiated services (DiffServ) that seeks to provide the higher-education community with end-to-end services in support of emerging advanced networked applications. (QBone Architecture) Quality of Service - Michal Przybylski, PCSS

5 extra1 Quality of Service - Michal Przybylski, PCSS

6 extra2 Quality of Service - Michal Przybylski, PCSS

7 extra3 Quality of Service - Michal Przybylski, PCSS

8 Service Level Agreement & QoS Podstawowe metryki uzywane do okreslania jakosci uslug: Delay, jitter, loss, throughput, availability Per flow sequence preservation (packet reordering) Quality of Service oznacza istnienie pewnego kontraktu, w którym gwarantowane sa parametry uslugi, np..: opóznienie nie wieksze niz 25 ms w 95% czasu utrata pakietów na poziomie... Quality of Service - Michal Przybylski, PCSS

9 SLA Metrics: One-way delay The time between reception of an IP packet at an ingress POP and its transmission at an egress POP Comprised of four components: Propagation delay: ~5ms/1000km for fibre Switching / processing delay: typically 10-20µs per packet Scheduling / queuing delay Serialisation delay: dependent upon line rate: 6ms for 1500 byte packet at 2Mbps, 80µs at STM-1, 1.25µs at STM-64 VoIP target one-way delay bound of 150ms (G.114) RTT target of 250ms is common for interactive business data applications Quality of Service - Michal Przybylski, PCSS

10 SLA Metrics: One-way delay One way delay is hard to measure due to requirement for fine time synchronisation on both measurement nodes More popular method is to measure RTT, i.e. using ICMP Ping. (OWD=RTT/2?) Caution! assymetric links (OWD!=RTT/2) Quality of Service - Michal Przybylski, PCSS

11 One-way delay avg. latency [ms] flow traffic (UDP) frame size [Bytes] 100% = 5 Mbps (BE traffic) network load: 20% 40% 60% 80% 100% 120% 140% 160% 180% 200% Quality of Service - Michal Przybylski, PCSS

12 SLA Metrics: Jitter Delay variation generally computed as the variation of the delay for two consecutive packets of the same size Comprised of the variation in the components of delay: Propagation delay Switching / processing delay Queuing / scheduling delay Jitters buffers remove variation but contribute to delay Quality of Service - Michal Przybylski, PCSS

13 SLA Metrics: Jitter Typical jitter budget: => Mouth to ear budget 100ms => Backbone propagation 30ms => Codec delay ~35ms => Jitter Budget = 35ms Jitter budget allocation: 30ms for the access 5ms for the core => 10 hops => 500 µs/hop Quality of Service - Michal Przybylski, PCSS

14 SLA Metrics: Jitter jitter [ms] flow traffic (UDP) frame size [Bytes] 100% = 5 Mbps (BE traffic) network load: 20% 40% 60% 80% 100% 120% 140% 160% 180% 200% Quality of Service - Michal Przybylski, PCSS

15 SLA Metrics: Loss The probability that a packet will be dropped in transit between receipt at an ingress POP and transmission at an egress POP Observation: A US backbone typically offers a monthly average loss on its network of < 1% Typical targets for VoIP of < 0.25% loss Packet loss impacts attainable TCP throughput Quality of Service - Michal Przybylski, PCSS

16 Packet loss Sometimes hard to explain packet loss [%] % 40% 60% 80% 100% 125% 150% packet size [bytes] Quality of Service - Michal Przybylski, PCSS

17 Throughput characterises the available user bandwidth between an ingress POP and egress POP. (i.e. maximum UDP transfer) Goodput SLA Metrics: Throughput Goodput (i.e. useful TCP throughput) is dependent upon many factors including: roundtrip delay, loss rate, TCP implementation, router queuing strategies... Quality of Service - Michal Przybylski, PCSS

18 TCP Throughput/UDP Goodput TCP empty network No. msg. size bandwidth estimate [Mbit/s] TCP 75% load No. msg. size bandwidth estimate [Mbit/s] UDP empty network No. msg size UDP 75% load No. msg size bandwidth estimate [Mbit/s] bandwidth estimate [Mbit/s] Quality of Service - Michal Przybylski, PCSS

19 Packet size matters! Throughput vs packet size Quality of Service - Michal Przybylski, PCSS

20 Technology matters! Quality of Service - Michal Przybylski, PCSS

21 SLA Metrics: Availability Can be defined as network availability or service availability Network availability defined as the fraction of time the network is available between a specified ingress point and a specified egress point can overlap with the other SLA parameters, e.g. 0% packet loss implies 100% network availability Service availability Defines as the fraction of time the service is available with the defined SLAs Quality of Service - Michal Przybylski, PCSS

22 SLA Metrics: Per flow sequence preservation (packet reordering) Not commonly committed in SLAs today, but important for good service perception The impact on the network services has not been yet fully investigated Some sources indicate influence on Real-Time Video Usually higher layers are able to cope with reordering Quality of Service - Michal Przybylski, PCSS

23 Service perception For IP telephony users: glitch as soon as two consecutive packets are dropped 40ms of downtime Gateway / user drops the call if loss of connectivity lasts more than 1-2 seconds Improving service perception is an incentive to designing networks for tight SLAs Quality of Service - Michal Przybylski, PCSS

24 SLA Definitions Today SLA statistical definitions do matter min/avg/max versus percentile Measured time interval interval between probes SLAs definitions today tend to be loose averaged over a month averaged over many POP-to-POP pairs (temptation to add short pairs to reduce average ) Round-trip Quality of Service - Michal Przybylski, PCSS

25 Deploying SLA services on an IP Backbone Important aspects: Physical network design and topology Diffserv: per-hop congestion management Capacity planning and active monitoring Traffic engineering Tuning IGP Convergence Quality of Service - Michal Przybylski, PCSS

26 Metody zapewniania QoS: over-provisioning Zapewniony poziom uslugi jest zalezny od szybkosci lacza, rodzaju oraz natezenia ruchu w tym laczu Rozwiazanie problemu: Zaoferowac szersze pasmo niz wymagania uzytkowników (okreslenie poziomu wymagan!) Efekty: Niska utrata pakietów Niskie opóznienie Niewielki jitter Quality of Service - Michal Przybylski, PCSS

27 Metody zapewniania QoS: over-provisioning Problem: O ile wiecej pasma dostarczyc? Quality of Service - Michal Przybylski, PCSS

28 Over-provisioning (Source: Stephen Casner, Packet Design, NANOG 22) Jitter Measurement Summary for the Week 69 million packets transmitted Zero packets lost 100% jitter < 700µs Quality of Service - Michal Przybylski, PCSS

29 Over-provisioned Backbone Effective Simple Available bandwidth > aggregate traffic demand QoS mechanisms kept at to edge Network is simple to design, deploy and operate Quality of Service - Michal Przybylski, PCSS

30 Overprovisioned Backbone - Drawback Risk related to provisioning failure No service isolation VPN, VoIP, Internet: same fate! Expensive design for the aggregate!!! Internet receives the same quality as VoIP Quality of Service - Michal Przybylski, PCSS

31 Not every week is like this (Source: Stephen Casner, Packet Design, NANOG 22) 99.99% Quality of Service - Michal Przybylski, PCSS

32 Over-provisioning Expensive Aggregate bandwidth overprovision comes at a cost, however: e.g. 150Mbps of VoIP and 1.5Gbps of data between two POPs => 1.65Gbps of aggregate load => requires 3.3Gbps of bandwidth for 2x over-provisioning => typically provisioned using 2x STM16/OC48 => hence 5Gbps of bandwidth used to support 1.65Gbps aggregate load with 150Mbps of low delay, low jitter, low loss traffic Quality of Service - Michal Przybylski, PCSS

33 Metody zapewniania QoS - DiffServ! Zalety: Wady Mniejsze ryzyko Tansze Overprovisioning stosowany dla wybranych klas ruchu (np. rezerwujemy 10% pasma dla ruchu szacowanego na 5%) Przyklady VoIP > 3 or 4 Business > 2 Internet > 1.2 Wciaz nie ma zlotego srodka Quality of Service - Michal Przybylski, PCSS

34 Architektura diffserv This architecture achieves scalability by implementing complex classification and conditioning functions only at network boundary nodes and by applying per-hop behaviors to aggregates of traffic which have been appropriately marked using the DS field in the IPv4 or IPv6 headers. Per-application flow or per-customer flow need not to be mantained within the core of the network RFC 2475 Quality of Service - Michal Przybylski, PCSS

35 Architektura diffserv cd. diffserv róznicowanie jakosci uslug Podstawowa zaleta diffserv jest agregacja przeplywów. Zapewnianie jakosci uslug nie odbywa sie na poziomie pojedynczego polaczenia, lecz na poziomie pewnej klasy (grupy) polaczen Quality of Service - Michal Przybylski, PCSS

36 Architektura diffserv cd. Podstawowe elementy: per hop behavior - PHB domena diffserv mechanizmy obslugi pakietów Quality of Service - Michal Przybylski, PCSS

37 Architektura diffserv - PHB Poniewaz diffserv bazuje na specjalnym oznakowaniu (kolorowaniu) pakietów, wazne jest okreslenie sposobu obslugi pakietów o danym priorytecie w wezle sieci PHB Pakiety w sieciach IP znakujemy uzywajac pola DSCP 6 bitów (dawniej TOS) pakietu IP Quality of Service - Michal Przybylski, PCSS

38 Architektura DiffServ DSCP TOS DiffServ Per-Hop Behavior Expedited Forwarding (EF) Low-latency/jitter scheduler (often a PQ) Assured Forwarding (AF) Bandwidth allocation and Multi-level Congestion avoidance (RED) Quality of Service - Michal Przybylski, PCSS

39 Architektura diffserv cd. Domena diffserv to taka domena sieciowa, której wszystkie wezly uzywaja jednakowej polityki do obslugi pakietów przez nia przechodzacych. Polityke taka definiuje sie poprzez odpowiedni zestaw PHB Quality of Service - Michal Przybylski, PCSS

40 Architektura diffserv cd. Klasyfikacja pakietu na wejsciu do domeny DS Ta sama polityka obslugi pakietów A klasa 1 klasa 2 PHB PHB Domena DS PHB PHB B Quality of Service - Michal Przybylski, PCSS

41 Diffserv Architecture: RFC2475 Diffserv domain VoIP Bus Best- Effort Classification and conditioning (meter, marking, policing) at EDGE Packet colour In DSCP VoIP Bus Best- Effort Aggregate PHBs in CORE (EF, AF, DF, CSn) Quality of Service - Michal Przybylski, PCSS

42 Architektura diffserv cd. Modul pomiarowy Klasyfikator Modul znakujacy Modul ksztaltujacy ruch Quality of Service - Michal Przybylski, PCSS

43 Algorytmy kolejkowania CBQ Class Based Queuing WFQ Weighted Fair Queuing (W)RED (Weighted) Random Early Detection ECN Explicit Congestion Notification Quality of Service - Michal Przybylski, PCSS

44 CBQ Example LINK 60% 40% Company A Company B 30% Real- Time HTTP FTP telnet IP DECnet 20% 10% 20% 20% Video Audio 20% 10% Quality of Service - Michal Przybylski, PCSS

45 Algorytmy kolejkowania - CBQ Modul ksztaltujacy ruch sposób dzialania estymator pakiety klasyfikator klasa domyslna (15%) klasa 1 (30%) Algorytm obslugujacy (scheduler) wazony Round Robin klasa 2 (45%) odrzucanie Quality of Service - Michal Przybylski, PCSS

46 Class Based Queuing (CBQ) Combines scheduling and link sharing Hierarchical link sharing Hierarchical queues Enables protocol, organization isolation Scheduling Does not define a particular scheduling algorithm General scheduler for low latency when no congestion Link-sharing policing scheduler when congested Scheduling per hierarchy Quality of Service - Michal Przybylski, PCSS

47 Przykladowa konfiguracja Polecenia konfigurujace urzadzenia interface eth0 bandwidth 100M cbq Polecenia ustawiajace filtry filter eth0 tcp_class filter eth0 tcp_class Polecenia ustawiajace obsluge strumieni class cbq eth0 cntl_class NULL pbandwidth 5 control class cbq eth0 root_class NULL pbandwidth 95 class cbq eth0 tcp_class root_class pbandwidth 65 default class cbq eth0 udp_class root_class borrow pbandwidth 35 Quality of Service - Michal Przybylski, PCSS

48 Unprotected traffic Competitive traffic influence Video Video + 400kbit traffic Video Video 0 Video+4Mbit traffic Quality of Service - Michal Przybylski, PCSS

49 Traffic with diffserv Competitive traffic influence 5% 3% Video Video + 4Mbit/s Video Video + 40Mbit/s Quality of Service - Michal Przybylski, PCSS

50 Weighted Fair Queuing (WFQ) Traffic placed into queues according to flow specification, flow filter Fair queuing Implements fairness of bit by bit scheduling on a per packet basis Gives queues a fair share of total bandwidth Weighted Queue are not weighted evenly for scheduling Proven: adequate for Guaranteed Service Quality of Service - Michal Przybylski, PCSS

51 Random Early Detection (RED) Random Early Detection (RED) Queue management algorithm for congestion control Random packet drops as average queue length increases Can use Explicit Congestion Notification bit instead of dropping packet Works well for TCP Useful for congested Controlled Load service Quality of Service - Michal Przybylski, PCSS

52 Random Early Detection (RED) Quality of Service - Michal Przybylski, PCSS

53 Backbone Diffserv Design (Cisco) 2 or 3 Aggregate classes Edge DSCP marking policy to indicate class Class DSCP IP Prec Binary PHB VoIP EF Bus AF1 Network BE AF1 Default Quality of Service - Michal Przybylski, PCSS

54 Backbone Diffserv Design (Cisco) VoIP EF PHB (usually a strict PQ most optimum) Capacity planned for overprovisioning factor > 2. Usually 3 (33%) or 4 (25%) Business AF1 PHB: 90% of the remaining BW Capacity planned for OP factor > 1.5 Internet AF2 PHB: 10% of the remaining BW Underbooked in terms of guaranteed BW; backbone capacity dimensioned to avoid congestion for the majority of the time (aggregate OP is > 1) Quality of Service - Michal Przybylski, PCSS

55 Backbone Diffserv Design (Cisco) When congestion happens VoIP is preserved over Business, which is preserved over BE Ensures higher availability for VoIP SLA than for Business, and for Business SLA than BE Static scheme is simple to design, deploy an operate Capacity planning needed to provide accurate demand forecasts based upon sound knowledge of existing traffic ensuring adequate provisioning of bandwidth Quality of Service - Michal Przybylski, PCSS

56 Typical Backbone Diffserv Design (Cisco) class-map match-any VOIP PE1 P1 P2 PE2 match ip precedence 5 class-map match-any BUS match ip precedence 4 match ip precedence 6! policy-map OC3_POLICY class VOIP PE3 P3 P4 PE4 priority class BUS bandwidth percent remaining 90 Static! random-detect prec No marking, policing, random-detect prec shaping in the core! class class-default bandwidth percent remaining 10 RED as congestion random-detect prec avoidance for each Data! (TCP) Class interface POS0/1 ip Quality address of Service Michal Przybylski, PCSS service-policy output OC3_POLICY

57 Diffserv Support over MPLS diffserv is supported today over MPLS <draft-ietf-mpls-diff-ext-09.txt> All of the mechanisms are available today to allow Diffserv QoS to be deployed in an MPLS network Two methods defined: Using the 3-bit EXP field in the MPLS header and mapping DSCP to EXP Label inferred CoS : Mapping a label per-cos Quality of Service - Michal Przybylski, PCSS

58 MPLS and DiffServ Using the EXP bits Label EXP S TTL Copy or map precedence into EXP field Copy up the label stack IPv4 Packet MPLS Hdr Prec: xyz MPLS EXP: xyz Prec: xyz Quality of Service - Michal Przybylski, PCSS

59 MPLS and Diffserv However, using MPLS capabilities for traffic engineering provides us with some extra tools for engineering the QoS of our backbone: Traffic Engineering Diffserv-aware traffic engineering Fast Re-route Quality of Service - Michal Przybylski, PCSS

60 Architektura IntServ Uslugi zintegrowane rezerwacja zasobów w sieciach klasyfikatory kolejki mechanizmy rezerwacji statyczne dynamiczne (protokól RSVP) Quality of Service - Michal Przybylski, PCSS

61 RSVP Functional Diagram Host Control Router RSVPD RSVPD Application D A T A Policy Control Admissions Control Routing Process Policy Control Admissions Control Packet Classifier Packet Scheduler DATA Packet Classifier Packet Scheduler DATA Quality of Service - Michal Przybylski, PCSS

62 Architektura IntServ cd. Zadanie transmisji z A do B (RSVP) Informacja o zamiarze wysylania danych B A reserve reserve reserve reserve Quality of Service - Michal Przybylski, PCSS

63 Resource Reservation Senders advertise using PATH message Receivers reserve using RESV message Flowspec + filterspec + policy data Travels upstream in reverse direction of Path message Merging of reservations Sender/receiver notified of changes Quality of Service - Michal Przybylski, PCSS

64 RSVP UDP Reservation (1) R2 R3 1 2 PATH Host A R1 PATH 3 R5 PATH R4 PATH Host B An application on Host A creates a session, /4078, by communicating with the RSVP daemon on Host A. 3. The PATH message follows the next hop path through R5 and R4 until it gets to Host B. Each router on the path creates soft session state with the reservation parameters. 2. The Host A RSVP daemon generates a PATH message that is sent to the next hop RSVP router, R1, in the direction of the session address, Quality of Service - Michal Przybylski, PCSS

65 RSVP UDP Reservation (2) R2 R3 PATH Host A RESV R1 PATH RESV R5 PATH RESV 6 R4 PATH 5 RESV 4 Host B An application on Host B communicates with the local RSVP daemon and asks for a reservation in session /4078. The daemon checks for and finds existing session state. 6. The RESV message continues to follow the next hop path through R5 and R1 until it gets to Host A. Each router on the path makes a resource reservation. 5. The Host B RSVP daemon generates a RESV message that is sent to the next hop RSVP router, R4, in the direction of the source address, Quality of Service - Michal Przybylski, PCSS

66 Resource Reservation Model Senders advertise using flowspecs RSVP daemons forward advertisements to receivers, update available bandwidth, minimum delay Receivers reservations use flowspec, filterspec combination (flow descriptor) Sender/receiver notified of changes Reservations are merged in multicast case Quality of Service - Michal Przybylski, PCSS

67 RSVP Service Types Controlled load Guaranteed service Quality of Service - Michal Przybylski, PCSS

68 Controlled Load Service Definition Service that gives a flow the QoS it would receive if the network was unloaded. Statistical guarantee No delay bounds Motivation Support delay sensitive applications Minimal functionality Quality of Service - Michal Przybylski, PCSS

69 Controlled Load Requirements Admission Control Ensure adequate resources are available Operation Link bandwidth Computational power for processing flow Adequate buffer space to handle bursty traffic Little or no average packet queuing delay Little or no congestion loss Time period: significantly longer than burst time Quality of Service - Michal Przybylski, PCSS

70 Guaranteed Service Definition Service providing guaranteed delay and bandwidth Firm guarantee on end-to-end queuing delays Delay Two parts: Fixed delay: transmission delays, etc Queuing delay Queuing delay is a function of token bucket and data rate Often assumed that application has no control over delay Application can choose queuing sizes Quality of Service - Michal Przybylski, PCSS

71 Architektura IntServ cd. mechanizmy obslugi Strumien pakietów Klasyfikator Aplikacja A Aplikacja N Kolejki pakietów 2Mb/s 2Mb/s 1Mb/s.. siec (10Mb/s) Modul obslugi kolejek Quality of Service - Michal Przybylski, PCSS

72 Architektura IntServ cd. Problemy zwiazane z IntServ duza liczba definiowanych przeplywów duze obciazenie wezlów sieci (osobno dla kazdego polaczenia) Rozwiazanie nieskalowalne, zwykle nie stosowane dla pojedynczych strumieni Quality of Service - Michal Przybylski, PCSS

73 Architektura IntServ cd. RSVP znalazlo zastosowanie do rezerwacji pasma dla zagregowanych strumieni. Protokól ten jest powszechnie wykorzystywany w MPLS oraz w sieciach optycznych z protokolem GMPLS, gdzie zestawiane sa przy jego pomocy np. tunele oraz sciezki zapasowe. Quality of Service - Michal Przybylski, PCSS

74 Istniejace implementacje mechanizmów zapewniania QoS ATM PVC oraz SVC Windows QoS (RSVP) Traffic Control oraz ALTQ ATM Tag Switching (MPLS) Quality of Service - Michal Przybylski, PCSS

75 ATM PVC PVC - Permanent Virtual Circuit SVC - Switched Virtual Channel Rózne kontrakty pracy kanalu wirtualnego CBR (constant bit rate) ABR(available bit rate) UBR (unspecified bit rate) VBR (variable bit rate) Quality of Service - Michal Przybylski, PCSS

76 Windows QoS (RSVP) Platforma Windows NT wspomaga zarzadzanie jakoscia uslug przy pomocy uslug zintegrowanych oraz protokolu RSVP. Rezerwacja pasma jest dokonywana w aplikacji - przed rozpoczeciem kazdej sesji komunikacyjnej Trwaja prace badawcze nad implementacja mechanizmów diffserv w Windows NT Quality of Service - Michal Przybylski, PCSS

77 Traffic Control oraz ALTQ Linux Traffic Control FreeBSD ALTQ (ALTernate Queuing) zestaw nowych funkcji ruterów, wykorzystujacy mechanizmy diffserv. pozwala na zastosowanie róznych algorytmów kolejkowania i kontroli ruchu do kazdej z klas Quality of Service - Michal Przybylski, PCSS

78 Problemy integracji QoS Istnieje wiele czynników utrudniajacych zintegrowanie QoS mechanizmy komunikacji protokoly rezerwacji i sygnalizacji typy sieci dostawcy uslug Quality of Service - Michal Przybylski, PCSS

79 Na tapecie... Testy mechanizmów QoS w urzadzeniach sieciowych nowej generacji Testy narzedzi monitorujacych parametry ruchu IP => monitoring infrastructure Studia nad technikami budowy sieci optycznych nowej generacji (w trakcie) z nowymi uslugami Quality of Service - Michal Przybylski, PCSS