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QOS
Module 12
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Points clés du module
• Les trois raisons d’échec de la voix• Les précautions nécessaires pour réussir avec la
VoIP• Implémenter la VoIP sur des LANs
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Sommaire
• Contrôle du délai• Sources du délai• Contrôle de la jigue• Fonction LFI• Contrôle de la sérialisation du délai• Process de compression de l’en-tête RTP• Contrôle du délai de Queuing
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Contrôle du délai
ITU’s G.114 recommendation: 0 to 150 (ms) one-way delay
Time (ms)
0 100 200 300 400
Walkie talkieWalkie talkie
One hop satelliteOne hop satellite
Put the old PBX back in now.Put the old PBX back in now.
InteractiveInteractive
Delay target
500 600 700 800
PBXPBX
VOIPVOIP
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Les sources du délai
G.729 look ahead
20 ms packet20 ms
5 ms
Processing 10 ms
61 ms
1,500 byte data packet
7.8 ms
66 byte voice packet
.33 ms
66 byte voice packet .33 ms
G.729 3 ms
Processing 10 ms
165.3 ms total
Jitter buffer 40 ms
Serialization
Queuing
Network
Serialization
Queuing
1,500 byte data packet 7.8 ms
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Délai de traitement du codec
ADPCM, G.726 32 Kbps 10 ms 2.5 ms 10 ms
CS-ACELP, G.729A 8.0 Kbps 10 ms 2.5 ms 10 ms
MP-MLQ, G.723.1 6.3 Kbps 30 ms 5 ms 20 ms
MP-ACELP, G.723.1 5.3 Kbps 30 ms 5 ms 20 ms
CodecCodec RateRate SampleSize
SampleSize
BestCaseBestCase
WorstCase
WorstCase
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Délai de l’algorithme
ADPCM, G.726 0 ms
CS-ACELP, G.729A
5 ms
MP-MLQ, G.723.1
7.5 ms
MP-ACELP, G.723.1
7.5 ms
ADPCM, G.726 0 ms
CS-ACELP, G.729A
5 ms
MP-MLQ, G.723.1
7.5 ms
MP-ACELP, G.723.1
7.5 ms
CodecCodec Algorithmic DelayAlgorithmic Delay
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Délai de paquetisation
PCM,
G.711
64
Kbps 160 20 240 30
ADPCM,
G.726
32
Kbps 80 20 120 30
CS-ACELP,
G.729
8.0
Kbps 20 20 30 30
MP-MLQ,
G.723.1
6.3
Kbps 24 30 48 60
MP-ACELP,
G.723.1
5.3
Kbps 20 30 40 60
CoderCoder PayloadSize (Bytes)
PayloadSize (Bytes)
PacketizationDelay (ms)
PacketizationDelay (ms)
PayloadSize (Bytes)
PayloadSize (Bytes)
PacketizationDelay (ms)
PacketizationDelay (ms)
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Le délai de serialisation
19.2 56 64 128 256 384 512 768 1024 1544 2048
38 15.83 5.43 4.75 2.38 1.19 0.79 0.59 0.40 0.30 0.20 0.15
48 20.00 6.86 6.00 3.00 1.50 1.00 0.75 0.50 0.38 0.25 0.19
64 26.67 9.14 8.00 4.00 2.00 1.33 1.00 0.67 0.50 0.33 0.25
128 53.33 18.29 16.00 8.00 4.00 2.67 2.00 1.33 1.00 0.66 0.50
256 106.67 36.57 32.00 16.00 8.00 5.33 4.00 2.67 2.00 1.33 1.00
512 213.33 73.14 64.00 32.00 16.00 10.67 8.00 5.33 4.00 2.65 2.00
1024 426.67 146.29 128.00 64.00 32.00 21.33 16.00 10.67 8.00 5.31 4.00
1500 625.00 214.29 187.50 93.75 46.88 31.25 23.44 15.63 11.72 7.77 5.86
2048 853.33 292.57 256.00 128.00 64.00 42.67 32.00 21.33 16.00 10.61 8.00
Taille de la trame (octets)
Vitesse de la ligne (Kbps)
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Délai de queuing
56 Kbps Line
214 ms serialization delayfor 1500-byte frame at 64 Kbps
Real-time MTU Elastic MTU
In Out
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Gestion de la jigue
V V VV V V V
Voice frames sent to the Network
Dejittered voice frames to DSP
V VV
V V VV V V VV VV
The voice packets were sent with 20 millisecond spacing.
V V VV V V VV VV
0+5+10-10+50-25-5-20
60555070556085686260Delay in ms
Jitter
Variation ranges from +10 to –25 = 35 ms jitter.
10 9 8 7 6 5 4 3 2 1
10 9 8 7 6 5 4 3 2 1
10 9 8 7 6 5 4 3 2 1
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Exemple de latence LFI
1,500 byte data packet
214 ms
66 byte voice packet 10 ms
1,500 byte data packet 214 ms
66 byte voice packet 10 ms
597 ms total
61 ms
G.729 look ahead
20 ms packet
Processing
G.729
Processing
Jitter buffer
Serialization
Queuing
Network
Serialization
Queuing
20 ms
5 ms
10 ms
3 ms
10 ms
40 ms
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Multilink PPP avec LFI
56 Kbps link
Elastic MTU Real-time MTU
Addendum to PPP specification
214 ms serialization delayfor 1,500 byte frame at 64 Kbps
56 Kbps link
Elastic MTU Elastic MTU
Real-time MTU Elastic MTU
In Out
In Out
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Fonctionnement du LFI
LLQ
Classify
Low latency queuing
LLQLFI
Traffic destinedfor interface
1,500 byte Ethernet
frame
Voice packets
Classification by port and socket
Fragment size based on serialization delay
Fragmented framesinterleaved with time-sensitive traffic
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Gestion du lien Gigabit
Gigabit Ethernet link
In Out
A 1,500 byte frametakes 12 sec to serialize.
Voice frame
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Latence avec LFI sur un lien à 56 k
189 ms total
1,500 byte data packet
10 ms
66 byte voice packet 10 ms
1,500 byte data packet 10 ms
66 byte voice packet 10 ms
G.729 look ahead
20 ms packet
Processing
G.729
Processing
Jitter buffer
Serialization
Network
Serialization
Queuing
20 ms
5 ms
10 ms
3 ms
10 ms
40 ms
QueuingLFI
61 ms
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Matrice LFI
XX: Fragmentation not an issue due to bandwidth and interval combination
Real-Time Packet Interval
56 Kbps70
bytes140
bytes210
bytes
10 ms 20 ms 30 ms
64 Kbps80
bytes160
bytes240
bytes
128 Kbps160
bytes320
bytes480
bytes
256 Kbps
512 Kbps
768 Kbps
1,536 Kbps
320bytes
640bytes
960bytes
640bytes
1,280bytes
1,920bytes
960bytes
1,920bytes
2,880bytes
1,920bytes
3,840bytes
5,760bytesX X
XXX
X
(10 ms)
Example:
.010 seconds x 56 Kbps
8 bits per byte= 70 bytes
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Gestion du délai de sérialisation
Branch office
Branch office
1st
1stBANK1stBANK
1stBANK1stBANK 1stBANK1stBANK
Branch office
56 Kbps
Link
256 Kbps link 768 Kbps link
Compress
Uncompress
Uncompress
Compress
RTP
UDP
IP
Corporationmain site
= 2 bytes
RTP header compression:Approximately 11.2 Kbps per call
Must be a link:HDLC, PPP, Frame Relay, ATM AAL-5, MPLS
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Délai de Queuing
* Approximately nineteen 78 byte packets equal one 1,500 byte packet.
Low latency queuing:The only optionCreates a priority queue for voice
packetsWill not starve other queues if priority
queue is constantly fullCisco’s choice for voice packet queuing
Classify
Voicevideodata
Priority
Guaranteed bandwidth 1
Dequeuing rules________________________
LLQ
Queues
Guaranteed bandwidth 2
Best effort
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Connexion Admission Control
• Téléphone : Interdire des services, c’est mieux que de dégrader des services
• Data : Dégrader des services, c’est mieux que d’interdire des services
Busy tone?No busy tone?
Should the call be
allowed to go through?
CAC
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RSVP
ER
CR
CR CR
CR
ER
ER
CR
ER
ER
CAC
CAC
CACCAC
You need a 32 Kbps connection to talk with me.
CAC
CAC
CR = Core routerER = Edge routerCR = Core routerER = Edge router
PATH message
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RSVP Half Duplex
ER
CR
CR CR
CR
ER
ER
CR
ER
ER
Established reservation: Half the job is done.
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Chemin inverse
ER
CR
CR CR
CR
ER
ER
CR
ER
ER
CAC
CAC
CACCAC
You need a 32 Kbps connection to talk with me.
OK
CAC(Reserve penguin)
CAC
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RSVP – établissement de la réservation
ER
CR
CR CR
CR
ER
ER
CR
ER
ER
Full duplex reservation
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RSVP – Synchronisation QoS avant qu’un téléphone ne sonne
SETUP
CALL PROCEEDING
PATH
PATH
RESV
RESV
ALERTING
CONNECT
RELEASE COMPLETE
PATH TEAR
PATH TEAR
PATH TEAR
PATH TEAR
RESV CONFIRMATION
Call setup initiated
OGW TGW Reservation limited
Call connected
Normal call disconnect initiated
OGW TGW Reservation teardown
initiated
OGW TGW Reservation initiated
OGW Originating Gateway TGW Terminating Gateway
OGW TGW Reservation teardown initiated
H.323 Call setup signaling RSVP reservation initiated by TGW RSVP reservation initiated by OGW
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Diffserv
ER
CR
CR CR
CR
ER
ER
CR
ER
ER
VPN
CoS 7: Pilot
CoS 6: First
CoS 5: Business
CoS 4: Coach
CoS 3: Standby
CoS 2: Baggage
CoS 7 - Pilot
CoS 6 - First
CoS 5 - Business
CoS 4 - Coach
CoS 3 - Standby
CoS 2 - Baggage
CoS 7 - Pilot
CoS 6 - First
CoS 5 - Business
CoS 4 - Coach
CoS 3 - Standby
CoS 2 - Baggage
CoS 7 - Pilot
CoS 6 - First
CoS 5 - Business
CoS 4 - Coach
CoS 3 - Standby
CoS 2 - Baggage
CoS 7 - Pilot
CoS 6 - First
CoS 5 - Business
CoS 4 - Coach
CoS 3 - Standby
CoS 2 - Baggage
CoS 7 - Pilot
CoS 6 - First
CoS 5 - Business
CoS 4 - Coach
CoS 3 - Standby
CoS 2 - Baggage
CoS 7 - Pilot
CoS 6 - First
CoS 5 - Business
CoS 4 - Coach
CoS 3 - Standby
CoS 2 - Baggage
I want a first class connection.
CRCheck DSCPForward packets ER
ClassifyMarkPolice
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Type IP du champ serviceIP
Dat
agra
m
Ethernet Version .2 header
(14 octets)
Entête IP (minimum length 20 octets)
Entête UDP (8 octets)
G.729 (20 octets)
Data link trailer (4 octets)
Entête RTP (12–16 octets)
20 msVoice
Contributing Source (optional)
Synchronization Source
Time Stamp
V P X CC M PT Sequence Number
Length Checksum
Source Port Destination Port
Options and Padding
Destination Address
Source Address
Time to Live Protocol Header Checksum
Identifier Flags Fragment Offset
Ver IHL Type of Service Total Length
Source Address (cont.) Type
Source Address
Destination Address (cont.)
Destination Address
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Champ IP TOS
TOS field
2 bits6 bits
DSCPDSCP CUCU
DSCP (DIFF-SERV code point)000000 = DE (Default)101100 = EF (Expedited Forwarding)
DSCP (DIFF-SERV code point)000000 = DE (Default)101100 = EF (Expedited Forwarding)
TOS field