Quality of Service

Transcription

Quality of Service

Uslugi z gwarantowana jakoscia
Quality of Service - Michal Przybylski, PCSS 2002
1
Plan wykladu
•
•
•
•
•
Koncepcja QBone
Metryki SLA
Overprovisioning
Architektura Diffserv
Istniejace implementacje mechanizmów
zapewniania QoS
• Problemy integracji QoS
2
Zmiany w Internecie
Wczoraj
Dzisiaj
Zastosowania
e-mail, WWW, FTP
wideokonferencje,
zdalne nauczanie,
telewizja interaktywna
Rodzaj ruchu
best effort
gwarantowana jakosc
uslugi
Pojemnosc
laczy
do 155 Mb/s
Gb/s
Zarzadzanie
siecia
uslugami
3
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)
4
extra1
5
extra2
6
extra3
7
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...
8
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
9
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)
10
One-way delay
1 flow traffic (UDP)
network load:
20%
avg. latency [ms]
250
40%
60%
200
80%
150
100%
120%
100
140%
50
160%
180%
0
76
576
1076
200%
frame size [Bytes]
100% = 5 Mbps (BE traffic)
11
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
12
SLA Metrics: Jitter
• Typical jitter budget:
=> Mouth to ear budget
=> Backbone propagation
=> Codec delay
=> Jitter Budget
100ms
– 30ms
– ~35ms
= 35ms
• Jitter budget allocation:
30ms for the access
5ms for the core => 10 hops => 500 µs/hop
13
SLA Metrics: Jitter
jitter [ms]
1 flow traffic (UDP)
network load:
14
20%
12
40%
10
60%
80%
8
100%
6
120%
4
140%
2
160%
180%
0
76
576
1076
200%
frame size [Bytes]
100% = 5 Mbps (BE traffic)
14
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
15
Packet loss
Sometimes hard to explain...
30.00
20%
packet loss [%]
25.00
40%
20.00
60%
15.00
80%
10.00
100%
125%
5 .00
150%
0 .00
0
500
1000
1500
packet size [bytes]
16
SLA Metrics: Throughput
• Throughput characterises the available user
bandwidth between an ingress POP and
egress POP. (i.e. maximum UDP transfer)
• Goodput
–Goodput (i.e. useful TCP throughput) is
dependent upon many factors including: roundtrip delay, loss rate, TCP implementation, router
queuing strategies...
17
TCP Throughput/UDP Goodput
TCP – empty network
No.
msg. size
UDP – empty network
1
250
bandwidth estimate
[Mbit/s]
5.022
2
500
5.586
2
500
8.190
3
1000
5.715
3
1000
8.939
4
1500
6.153
4
1500
8.786
TCP – 75% load
No
.
1
msg. size
2
500
3
4
No
.
1
msg size
250
bandwidth estimate
[Mbit/s]
7.389
UDP – 75% load
No
.
1
msg size
250
bandwidth estimate
[Mbit/s]
7.246
5.143
2
500
8.124
1000
5.125
3
1000
8.747
1500
5.615
4
1500
8.652
250
bandwidth estimate
[Mbit/s]
4.548
18
Packet size matters!
Throughput vs packet size
1500
2000
1900
1800
1700
1600
1500
1400
1300
1200
1100
1000
1200
1000
500
700
64
89
85
81
77
73
69
65
61
57
53
49
45
41
37
33
29
25
21
17
13
9
5
1
100
19
Technology matters!
20
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
21
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
22
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
23
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
24
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
25
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
26
Metody zapewniania QoS: over-provisioning
Problem:
• O ile wiecej pasma dostarczyc?
27
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
28
Over-provisioned Backbone
• Effective
• Simple
– Available bandwidth > aggregate traffic
demand
– QoS mechanisms kept at to edge
– Network is simple to design, deploy and
operate
29
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
30
“Not every week is like this”
(Source: Stephen Casner, Packet Design, NANOG 22)
99.99%
31
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
32
Metody zapewniania QoS - DiffServ!
• Zalety:
– 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
• Wady
– Wciaz nie ma zlotego srodka
33
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
34
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
35
Podstawowe elementy:
• per hop behavior - PHB
• domena diffserv
• mechanizmy obslugi pakietów
36
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
37
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)
38
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
39
Klasyfikacja pakietu na
wejsciu do domeny DS
Ta sama polityka
obslugi pakietów
PHB
PHB
PHB
B
Domena
DomenaDS
DS
A
PHB
klasa 1
klasa 2
40
Diffserv Architecture: RFC2475
Diffserv domain
VoIP
Bus
Classification and
conditioning (meter,
marking, policing) at
EDGE
BestEffort
VoIP
Packet “colour”
In DSCP
Bus
BestEffort
Aggregate PHBs in
CORE (EF, AF, DF, CSn)
41
Modul
Modul
pomiarowy
pomiarowy
Klasyfikator
Klasyfikator
Modul
Modul
znakujacy
znakujacy
Modul
Modul
ksztaltujacy
ksztaltujacy
ruch
ruch
42
Algorytmy kolejkowania
• CBQ – Class Based Queuing
• WFQ – Weighted Fair Queuing
• (W)RED – (Weighted) Random Early
Detection
• ECN – Explicit Congestion Notification
43
CBQ Example
LINK
60%
40%
Company A
Company B
30%
RealTime
HTTP
FTP
telnet
IP
DECnet
20%
10%
20%
20%
Video
Audio
20%
10%
44
Algorytmy kolejkowania - CBQ
Modul ksztaltujacy ruch – sposób dzialania
estymator
pakiety
klasyfikator
klasa domyslna
(15%)
klasa 1
(30%)
klasa 2
(45%)
Algorytm obslugujacy
(scheduler)
wazony Round Robin
odrzucanie
45
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
46
Przykladowa konfiguracja
• Polecenia konfigurujace urzadzenia
interface eth0 bandwidth 100M cbq
• Polecenia ustawiajace filtry
filter eth0 tcp_class 150.254.161.17 0 0 0 4 6
filter eth0 tcp_class 150.254.161.18 0 0 0 5 6
• Polecenia ustawiajace obsluge strumieni
class
class
class
class
cbq
cbq
cbq
cbq
eth0
eth0
eth0
eth0
cntl_class NULL pbandwidth 5 control
root_class NULL pbandwidth 95
tcp_class root_class pbandwidth 65 default
udp_class root_class borrow pbandwidth 35
47
Unprotected traffic
Competitive traffic influence
2000
1500
1000
Video
+
400kbit traffic
Video
500
Video
Video
Video+4Mbit traffic
64
61
58
55
52
49
46
43
40
37
34
31
28
25
22
19
16
13
10
7
4
1
0
48
Traffic with diffserv
1800
5%
Competitive traffic influence
3%
1700
1600
1500
1400
Video
+
4Mbit/s
Video
1300
Video
+
40Mbit/s
Video
85
81
77
73
69
65
61
57
53
49
45
41
37
33
29
25
21
17
13
9
5
1
1200
49
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
50
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
51
Random Early Detection (RED)
52
Backbone Diffserv Design (Cisco)
• 2 or 3 Aggregate classes
• Edge DSCP marking policy to indicate class
Class
DSCP IP Prec
VoIP
40
5
Bus
32
4
Network
48
6
BE
0
0
Binary PHB
101 000 EF
100 000 AF1
110 000 AF1
000 000 Default
53
• 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)
54
• 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
55
Typical Backbone Diffserv Design (Cisco)
PE1
class-map match-any VOIP
match ip precedence 5
class-map match-any BUS
!
policy-map OC3_POLICY
class VOIP
priority
class BUS
bandwidth percent remaining 90
random-detect prec 4 97 609 1
class class-default
bandwidth percent remaining 10
!
interface POS0/1
of Service
- Michal Przybylski,
PCSS 2002
ip Quality
address
10.0.1.1
255.255.255.252
service-policy output OC3_POLICY
PE3
P1
P2
PE2
P3
P4
PE4
Static!
No marking, policing,
shaping in the core!
RED as congestion
avoidance for each Data
(TCP) Class
56
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
57
MPLS and DiffServ
Using the EXP bits
0
1
2
3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
Label
EXP
S
TTL
• Copy or map precedence into EXP field
• Copy up the label stack
IPv4 Packet
Prec: xyz
MPLS Hdr
MPLS EXP: Prec: xyz
xyz
58
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
59
Architektura IntServ
• Uslugi zintegrowane – rezerwacja zasobów
w sieciach
– klasyfikatory
– kolejki
– mechanizmy rezerwacji
• statyczne
• dynamiczne (protokól RSVP)
60
RSVP Functional Diagram
Host
Router
Control
RSVPD
RSVPD
Routing
Process
Application
D
A
T
A
Packet
Classifier
Policy
Control
Policy
Control
Admissions
Control
Admissions
Control
Packet
Scheduler
DATA
Packet
Classifier
Packet
Scheduler
DATA
61
Architektura IntServ cd.
Zadanie transmisji z A do B (RSVP)
Informacja o zamiarze
wysylania danych
B
reserve
A
reserve
reserve
reserve
62
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
63
RSVP UDP Reservation (1)
R2
R3
PATH
2
1
PATH
R4
R1
PA
TH
3
Host A
24.1.70.210
TH
PA
Host B
128.32.32.69
R5
1. An application on Host A creates a session,
128.32.32.69/4078, 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, 128.32.32.69.
64
RSVP UDP Reservation (2)
R2
R3
PATH
R4
PATH
RESV
Host A
24.1.70.210
4
RESV
R1
PA
TH
TH
PA
RE
SV
5
SV
RE
Host B
128.32.32.69
6
R5
4. An application on Host B communicates
with the local RSVP daemon and asks for a
reservation in session 128.32.32.69/4078. 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, 24.1.70.210.
65
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
66
RSVP Service Types
• Controlled load
• Guaranteed service
67
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
68
Controlled Load Requirements
• Admission Control
– Ensure adequate resources are available
• Link bandwidth
• Computational power for processing flow
• Adequate buffer space to handle bursty traffic
• Operation
– Little or no average packet queuing delay
– Little or no congestion loss
– Time period: significantly longer than burst time
69
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
70
mechanizmy obslugi
siec
(10Mb/s)
Strumien
pakietów
Kolejki
pakietów
Aplikacja A
2Mb/s
2Mb/s
Klasyfikator
Aplikacja N
Modul
obslugi
kolejek
1Mb/s
.
.
71
Problemy zwiazane z IntServ
– duza liczba definiowanych przeplywów – duze
obciazenie wezlów sieci (osobno dla kazdego
polaczenia)
– Rozwiazanie nieskalowalne, zwykle nie
stosowane dla pojedynczych strumieni
72
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.
73
Istniejace implementacje mechanizmów
zapewniania QoS
•
•
•
•
ATM PVC oraz SVC
Windows QoS (RSVP)
Traffic Control oraz ALTQ
ATM Tag Switching (MPLS)
74
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)
75
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
76
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
77
Problemy integracji QoS
Istnieje wiele czynników utrudniajacych
zintegrowanie QoS
• mechanizmy komunikacji
• protokoly rezerwacji i sygnalizacji
• typy sieci
• dostawcy uslug
78
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
79

Quality of Service

Transcription

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