paketový přenos hlasu - zcu.czledvina/vyuka/pds/pds_2005/07_voice-martan.pdf · 1 ©1999, cisco...
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1© 1999, Cisco Systems, Inc. 4010985_05f9_c1
PPaketový paketový přřenos hlasuenos hlasuJaroslav MartanJaroslav Martan
Cisco SystemsCisco Systemsjmartanjmartan@@ciscocisco.com.com
24010985_05f9_c1 © 1999, Cisco Systems, Inc.
ObsahObsah
• Výhody paketového přenosu hlasu• Kódování a komprese• Voice over Frame Relay
• Voice over ATM• Voice over IP• Problémy paketového přenosu
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34010985_05f9_c1 © 1999, Cisco Systems, Inc.
Data Is Overtaking VoiceData Is Overtaking Voice
Evolution from TDM-based transport to packets/cells or a combination
Relative Load30
25
20
15
10
5
01990 1995 2000 2005
Data Is 23xVoice
Traffic
DataData
Data Is 5xVoice Traffic
VoiceVoice
Year
Source: Electronicast
44010985_05f9_c1 © 1999, Cisco Systems, Inc.
TDM Transport EfficiencyTDM Transport Efficiency
Wasted Bandwidth
Single WAN Link
LAN
Voice
Video
Legacy
PBX
Types of Traffic
Time Slot Assignments
• Wasted bandwidth• No congestion
Utilization
5050––60%60%
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54010985_05f9_c1 © 1999, Cisco Systems, Inc.
Packet Transport EfficiencyPacket Transport Efficiency
Cells/Frames/Packets
LAN
Voice
Video
Legacy
Types of Traffic
Individual Packets
• High bandwidth efficiency• Congestion management
Utilization
9090––95%95%
PBXPBX
QUEUE
64010985_05f9_c1 © 1999, Cisco Systems, Inc.
Voice Network TransportVoice Network Transport
• Voice Network Transport is typically TDM circuit-based:
T1/E1DS3/E3SONET (OC-3, OC-12, etc.)
• But can also be packet-based:ATMFrame RelayIP
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74010985_05f9_c1 © 1999, Cisco Systems, Inc.
Planning and ImplementationPlanning and Implementation
• TodayTie-line replacementToll-bypassOff Premise Extension (OPX)Router key system replacementSmall office IP phone system (< 100 users)
• TomorrowVirtual call centersCampus IP phone system (> 1000 users)Enhanced integrated data/voice applicationsUnified messaging
84010985_05f9_c1 © 1999, Cisco Systems, Inc.
Layer 2—VoFR, VoATMLayer 3—VoIP
Voice Transport MechanismsVoice Transport Mechanisms
• Operates in heterogeneous network (ubiquitous)
• Connectionless (requires sequence numbers)
• “Soft” QoS• Layer 2 and 3 overhead
• Standards-based H.323 (MGCP coming)
• Requires rigid homogenous network or L2 gateways
• Connection oriented(frames arrive in order)
• “Hard” QoS• Layer 2 overhead
• Standards based(FRF.11/12, ATM AAL1/2/5)
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94010985_05f9_c1 © 1999, Cisco Systems, Inc.
ObsahObsah
• Výhody paketového přenosu hlasu• Kódování a komprese• Voice over Frame Relay
• Voice over ATM• Voice over IP• Problémy paketového přenosu
104010985_05f9_c1 © 1999, Cisco Systems, Inc.
Voice CompressionVoice Compression
• Objective: reduce bandwidth consumptionCompression algorithms are optimized for voice
Unlike data compression: these are “loose”
• Drawbacks/tradeoffsQuantization distortion
Tandem switching degradation
Delay (echo)
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114010985_05f9_c1 © 1999, Cisco Systems, Inc.
Bandwidth(Kbps)
Quality
UnacceptableUnacceptable BusinessQuality
BusinessQuality
TollQuality
TollQuality
8
16
32
24
64
0
*PCM (G.711)*PCM (G.711)
*ADPCM 32 (G.726)*ADPCM 32 (G.726)*ADPCM 24 (G.726)*ADPCM 24 (G.726)
*ADPCM 16 (G.726)*ADPCM 16 (G.726) *LDCELP 16 (G.728)*LDCELP 16 (G.728)
*CS-ACELP 8 (G.729)*CS-ACELP 8 (G.729)* LPC 4.8* LPC 4.8
(Cellular)(Cellular)
Voice Compression TechnologiesVoice Compression Technologies
124010985_05f9_c1 © 1999, Cisco Systems, Inc.
SpeechSpeech--Coding SchemesCoding Schemes
• Waveform codersNon-linear approximation of the actual waveform Examples: PCM, ADPCM
• VocodersSynthesized voice Example: LPC
• Hybrid codersLinear waveform approximation with synthesized voiceExample: CELP
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134010985_05f9_c1 © 1999, Cisco Systems, Inc.
Digitizing Voice: PCM Digitizing Voice: PCM Waveform Encoding ReviewWaveform Encoding Review
• Nyquist Theorem: sample at twice the highest frequency
Voice frequency range: 200-3400 HzSampling frequency = 8000/sec (every 125µs)Bit rate: (2 x 4 kHz) x 8 bits per sample= 64,000 bits per second (DS-0)
• By far the most commonly used methodCODEC
PCM64 Kbps = DS-0
144010985_05f9_c1 © 1999, Cisco Systems, Inc.
Voice CompressionVoice Compression——CELP CELP
• Code excited linear predictive
• Very high voice quality at low-bit rates, processor intensive, use of DSPs
• G.728: LD-CELP—16 Kbps• G.729: CSA-CELP—8 Kbps
G.729a variant— “stripped down” 8 kbps(with a noticeable quality difference)to reduce processing load, allows twovoice channels encoded per DSP
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154010985_05f9_c1 © 1999, Cisco Systems, Inc.
Voice CODECs: Hybrid Coders Voice CODECs: Hybrid Coders
FilteringFilteringSamplingSampling
QuantizingQuantizingEncodingEncoding
AnalysisAnalysis SynthesisSynthesis
PCM Encoder111001001001011Sample Frames
HumanSpeech Model
VocalCordsThroatNoseMouth
ModelParameters 10110010
Parameters
PCMDecoder
ModelParameters
164010985_05f9_c1 © 1999, Cisco Systems, Inc.
Digital Speech Interpolation (DSI)Digital Speech Interpolation (DSI)
• Voice Activity Detection (VAD)• Removal of voice silence • Examines voice for power, change of
power, frequency and change of frequency• All factors must indicate voice “fits into
the window” before cells are constructed• Automatically disabled for fax/modem
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174010985_05f9_c1 © 1999, Cisco Systems, Inc.
Voice “Spurt” Silence
Pink Noise
Time
Voice Activity(PowerLevel) SID Buffer SID
Hang Timer No Voice Traffic Sent
B/W Saved
- 54 dbm
- 31 dbm
Voice “Spurt”
Voice Activity DetectionVoice Activity Detection
184010985_05f9_c1 © 1999, Cisco Systems, Inc.
Voice Band TrafficEncoding/Encoding/
CompressionCompressionResultResult
Bit RateBit Rate
G.711 PCMG.711 PCMAA--Law/Law/µµ--LawLaw 64 kbps (DS0)64 kbps (DS0)
G.726 ADPCMG.726 ADPCM 16, 24, 32, 40 kbps16, 24, 32, 40 kbps
G.729 CSG.729 CS--ACELPACELP 8 kbps8 kbps
G.728 LDG.728 LD--CELPCELP 16 kbps16 kbps
G.723.1 CELPG.723.1 CELP 6.3/5.3 kbps6.3/5.3 kbpsVariableVariable
Bandwidth RequirementsBandwidth Requirements
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194010985_05f9_c1 © 1999, Cisco Systems, Inc.
Voice CODEC Cheat SheetVoice CODEC Cheat Sheet
EncodingCompression
EncodingCompression
G.711PCM
G.711PCM 4.14.1 6464
MeanOpinionScore
MeanOpinionScore
NativeBit Rate
Kbps
NativeBit Rate
Kbps
G.729CS-ACELP
G.729CS-ACELP 3.923.92 88
G.729aCS-ACELP
G.729aCS-ACELP 3.73.7 88
G.723.1ACELP G.723.1ACELP 3.653.65 5.35.3
G.726ADPCM G.726
ADPCM 3.853.85 3232
G.728LD-CELP
G.728LD-CELP 3.613.61 1616
AA
VoiceQualityVoice
Quality
AA
BB
CC
BB
CC
DD
BWBW
AA
AA
AA
CC
BB
AA
DTMFDTMF
BB
CC
CC
BB
BB
AA
DualCompDual
Comp
BB
CC
DD
BB
CC
AA
CPUCPU
CC
BB
CC
BB
CC
AA
Musicon
Hold
Musicon
Hold
CC
DD
DD
BB
CC
204010985_05f9_c1 © 1999, Cisco Systems, Inc.
ObsahObsah
• Výhody paketového přenosu hlasu• Kódování a komprese• Voice over Frame Relay
• Voice over ATM• Voice over IP• Problémy paketového přenosu
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214010985_05f9_c1 © 1999, Cisco Systems, Inc.
4 Bytes4 Bytes 1488 Bytes1488 Bytes 4 Bytes4 Bytes
Payload = 1488
5 Bytes5 Bytes 48 Bytes48 Bytes
Payload = 48
Frame/Packet
Cell
Packet EfficiencyPacket Efficiency
• Small vs large packet sizes • Fixed vs variable sized packets
Overhead = 8
Overhead = 5
Efficiency = 99.5%
Efficiency = 89.6%
OH Payload
OH Payload OH
224010985_05f9_c1 © 1999, Cisco Systems, Inc.
VoFRVoFR Multiplexing ModelMultiplexing Model
Source: Frame Relay Forum
VoFR ServiceVoFR Service
Sub-Channel
1(Voice)
Voice/DataSub-Channel Multiplexing
VoFR Service UserVoFR Service User
Frame Relay Physical InterfaceFrame Relay Physical Interface
FRF.3.1FRF.3.1MultiprotocolMultiprotocolEncapsulationEncapsulation
Data UserData User
Frame RelayData Link Connection
N
Data UserData User
Frame RelayData Link Connection
17
Frame RelayData Link Connection
16
FRF.3.1FRF.3.1MultiprotocolMultiprotocolEncapsulationEncapsulation
Sub-Channel
2(Voice)
Sub-Channel
3(Data)
Sub-Channel
N
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234010985_05f9_c1 © 1999, Cisco Systems, Inc.
FRF.11 ConceptFRF.11 Concept
• Extension of frame relay application support for compressed voice
• Multiplexing of up to 255 sub-channels
• Support of multiple payloads
• Support of data sub-channel
244010985_05f9_c1 © 1999, Cisco Systems, Inc.
FLAGFLAG
FLAGFLAG
Frame Relay HeaderFrame Relay Header
FRF.11 SubFRF.11 Sub--Frame HeaderFrame Header
PayloadPayload
FCSFCS
FRF.11 Frame FormatFRF.11 Frame Format
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254010985_05f9_c1 © 1999, Cisco Systems, Inc.
Sub FrameSub FrameFrame RelayFrame RelayFrameFrame
Sub FrameSub Frame Sub FrameSub FrameSub FrameSub Frame
Voice and Data EncapsulationVoice and Data Encapsulation
• Multi frames transport
264010985_05f9_c1 © 1999, Cisco Systems, Inc.
Voice PayloadVoice Payload Voice PayloadVoice Payload Voice PayloadVoice Payload Data PayloadData Payload
FrameFrameDLCI Information FieldInformation Field CRC
SubSub--Frame 3Frame 3
Voice PayloadVoice Payload3
SubSub--Frame 2Frame 2
Voice PayloadVoice Payload2
SubSub--Frame 1Frame 1
Voice PayloadVoice Payload
FrameFrameDLCI Information FieldInformation Field CRC
SubSub--Frame 1Frame 1
Multiple SubMultiple Sub--Channel Payloads Channel Payloads in an FRF.11 Frame in an FRF.11 Frame
Source: Frame Relay Forum
1 Data PayloadData Payload4
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274010985_05f9_c1 © 1999, Cisco Systems, Inc. © 1999, Cisco Systems, Inc. www.cisco.com 27
VoFR Service UserVoFR Service User
VoFR ServiceVoFR ServicePrimary PayloadsPrimary Payloads Signaled PayloadsSignaled Payloads
Service Data Units
Frame Relay ServiceFrame Relay Service
Faults DialedDigits
FAX Bits (CAS
Signaling)
SilenceInformation
Voice Data FAX
Source:Frame Relay Forum
VoFRVoFR ServicesServices
284010985_05f9_c1 © 1999, Cisco Systems, Inc.
Small PayloadLow DelayHigh OverheadHigh PPSHigh CPU Load
Large PayloadHigh DelayLow OverheadLow PPSLow CPU Load
10 ms of voice 10 ms of voice 10 ms of voice
10 ms of voice
10 ms of voice
10 ms of voice
hdrcrc
hdr
hdr
crc
crc
crc 10 ms of voice 10 ms of voice 10 ms of voice
hdr
Original Voice Information
1 Large Frame1 Large Frame
3 Small Frames3 Small Frames
Voice Payload OptionsVoice Payload Options
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294010985_05f9_c1 © 1999, Cisco Systems, Inc.
Full Mesh of PVCs Voice PVCs Go to One Central Site
Site D
Site B
Site C
Site A
Site D
Site B
Site C
Site A
Network Design OptionsNetwork Design Options
• Separate voice and data PVCs—Maximizes quality of service• Combine voice and data on one PVC—Minimizes recurring costs• Or use some combination
304010985_05f9_c1 © 1999, Cisco Systems, Inc.
Frame Relay PVC (<64K CIR)
FRF.11/12Frame Relay PVC
PVCCarrying
Voice
Data/Voice Over Frame RelayData/Voice Over Frame Relay
7200
72007200
25003600250025002600
2600
Central Site
BranchSites
Frame RelayCarrier Network
VV
VV VV
VV
VV3600
3600
VoFR ServiceVoFR Service
Sub-Channel
1(Voice)
Voice/DataSub-Channel Multiplexing
VoFR Service UserVoFR Service User
Frame Relay Physical InterfaceFrame Relay Physical Interface
FRF.3.1FRF.3.1MultiprotocolMultiprotocolEncapsulationEncapsulation
Data UserData User
Frame RelayFrame RelayData Link ConnectionData Link Connection
NN
Data UserData User
Frame RelayFrame RelayData Link ConnectionData Link Connection
1717
Frame RelayFrame RelayData Link ConnectionData Link Connection
1616
FRF.3.1FRF.3.1MultiprotocolMultiprotocolEncapsulationEncapsulation
Sub-Channel
2(Voice)
Sub-Channel
3(Data)
Sub-Channel
N
High-Speed Access Port at Central Sites (T1/E1)
Low-Speed Access Portat Branch Sites (64Kbps CIR)
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314010985_05f9_c1 © 1999, Cisco Systems, Inc.
CalculatingCalculating VoFRVoFR BandwidthBandwidth
• Assumptions• G.729 Codec at 8Kbps• 50 PPS (using 2–10ms samples)• 2 bytes of DLCI header• 2 bytes of FRF.11 header• 1 byte of sequence number• 2 byte CRC
324010985_05f9_c1 © 1999, Cisco Systems, Inc.
Calculating VoFR BandwidthCalculating VoFR Bandwidth
• Voice payload calculation20 Msec voice sample * 8 Kbps (for G.729)/8 bits/byte = 20 bytesNote: to derive the payload for G.711, substitute 64 kbps = 160 bytes
• Packet size calculations 20 byte payload + 7 byte Header = 27 bytes (Header = DLCI/FRF.11/seqn/CRC)
• Bandwidth calculations27 b/voice packet * 8 bits/byte * 50 pps = 10.8 Kbps per call
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334010985_05f9_c1 © 1999, Cisco Systems, Inc.
CIR Critical FactorsCIR Critical Factors
• PVC designFull mesh vs star
Shared vs separate PVCs for voice and data
• Potential concurrent calls Bandwidth per call
Switched through calls
• Pre-existing data environmentUtilization prior to adding voice
344010985_05f9_c1 © 1999, Cisco Systems, Inc.
VoFR SummaryVoFR Summary
• FRF.11 standards-based voice and function syntax
• FRF.12 standards-based fragmentation for data, mitigates delay and delay variation
• Proper PVC design for network requirements
• Balance voice quality, delay,bandwidth, CIR
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354010985_05f9_c1 © 1999, Cisco Systems, Inc.
ReferencesReferences
• [1] FRF.3.1, R. Cherukuri (ed), MultiprotocolEncapsulation Implementation Agreement, June 22–1995
• [2] FRF.9, D. Cantwell (ed), Data Compression Over Frame Relay Implementation Agreement, January 22–1996
• [3] FRF.11.1 K. Rehbehn, R. Kocen, T. Hatala (eds), Voice Over Frame Relay Implementation Agreement, December 1998
• [4] FRF.12, A. Malis (ed), Frame Relay Fragmentation Implementation Agreement, 1997
• [5] ITU Recommendation Q.922, ISDN Data Link Layer Specification for Frame Mode Bearer Services, 1992
364010985_05f9_c1 © 1999, Cisco Systems, Inc.
Web SitesWeb Sites
• Ciscohttp://www.cisco.com—search on VoFR
• Frame Relay Forumhttp://www.frforum.com/
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374010985_05f9_c1 © 1999, Cisco Systems, Inc.
ObsahObsah
• Výhody paketového přenosu hlasu• Kódování a komprese• Voice over Frame Relay
• Voice over ATM• Voice over IP• Problémy paketového přenosu
384010985_05f9_c1 © 1999, Cisco Systems, Inc.
Cells
Voice
Data
Video
Characteristics of ATMCharacteristics of ATM
• Uses small—fixed-sized cells• Connection-oriented• Supports multiple service types• Applicable to LAN and WAN
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394010985_05f9_c1 © 1999, Cisco Systems, Inc.
48 Byte48 BytePayloadPayload
53 Bytes ATM ATM Adaptation LayerAdaptation Layer
(AAL)(AAL)
ATM LayerATM Layer5 Byte Header5 Byte Header
Physical LayerPhysical Layer
ATM Cell ATM Cell
404010985_05f9_c1 © 1999, Cisco Systems, Inc.
AAL-1 Cell Tax AAL-2 Cell Tax
AAL-3/4 Cell Tax AAL-5 Cell Tax
1 Byte1 Byte
5 Byte5 ByteHeaderHeader
47 Byte47 BytePayloadPayload
11––4848BytesBytes
5 Byte5 ByteHeaderHeader
11––47 Byte47 BytePayloadPayload
5 Byte5 ByteHeaderHeader
44 Byte44 BytePayloadPayload 4 Bytes4 Bytes
5 Byte5 ByteHeaderHeader
48 Byte48 BytePayloadPayload
No TaxNo Tax
AAL Cell TaxAAL Cell Tax
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414010985_05f9_c1 © 1999, Cisco Systems, Inc.
CBR Equipment CBR Equipment
ATM CESInterworking
Function
ATM Access Interface
ATM CESInterworking
Function
CBR ServiceInterface
ATM NetworkPBX PBX
CES Reference ModelCES Reference Model
424010985_05f9_c1 © 1999, Cisco Systems, Inc.
DS1
Nx64
Nx64DS1
DS1
DS1
Structured Unstructured
StructuredStructured vsvs Unstructured CESUnstructured CES
• Intended to emulate point-to-point fractional DS1 or E1 circuit
• Allows Nx64 Kbps independentemulated circuits to share one DS1
• Can be configured to minimizeATM bandwidth
• Intended to emulate point-to-point DS1 or E1 circuit
• Allows one 1.54 or 2.04 Mbpsemulated circuit per DS1
• Can be used with equipment with non-standard framing
• Allows simple configuration of service
ATM NetworkATM Network
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434010985_05f9_c1 © 1999, Cisco Systems, Inc.
Central Site
Public ATM Network
Data/Voice Over ATM (AAL5)Data/Voice Over ATM (AAL5)
VV
VV
VV
444010985_05f9_c1 © 1999, Cisco Systems, Inc.
VoiceVoiceVoiceVoice
Voice PKT
Voice PKT
Data PKT
Data PKT
PBX PBX
DataDataDataData
• AAL 5 does not require convergence sub-layer• 48 Byte payload available for voice/data• Voice payload = voice sample + padding = 48 bytes• 5 byte ATM header
VVVV
ATM AAL5 Voice and Data CellsATM AAL5 Voice and Data Cells
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454010985_05f9_c1 © 1999, Cisco Systems, Inc.
53 Bytes
ATM LayerATM Layer5 Byte Header5 Byte Header
20 Byte Voice20 Byte VoicePayloadPayload
28 Byte28 BytePaddingPadding
48 Bytes
ATM AAL5 Voice CellsATM AAL5 Voice Cells
• G.729 compression with 20 ms voice sample
• No AAL5 CS “cell tax”
• 28 Bytes “overhead” due to padding
464010985_05f9_c1 © 1999, Cisco Systems, Inc.
VoATM BandwidthVoATM Bandwidth
• Voice payload calculation20 msec voice sample * 8 Kbps (for G.729)/8 bits/byte = 20 bytesNote: to derive the payload for G.711, substitute 64 Kbps = 160 bytes
• Packet size calculations20 byte payload + 28 byte pad +5 byte header = 53 bytes
• Bandwidth calculations53 b/voice packet * 8 bits/byte * 50 pps = 21.2 Kbps per call
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474010985_05f9_c1 © 1999, Cisco Systems, Inc.
T1/E1 ATM
ISP
T1/E1
Digital PBX
CiscoMC3810
CiscoMC3810
PSTN
Service Provider
256kFrame Relay
Frame Relay/ATMFrame Relay/ATM InterworkingInterworking
• Network interworkingFRF.5Frame Relay encapsulation
• Service interworking compatibleFRF.8Carrier compatible
HeadquartersHeadquartersRegional OfficeRegional Office
484010985_05f9_c1 © 1999, Cisco Systems, Inc.
VoATMVoATM——SummarySummary
• ATM reference model• Fixed size cells—Delay • Service category—CBR, VBR, ABR• Service criteria for QoS, SCR, CDVT• Chose service for requirements—
Circuit emulation (AAL1) voice over AAL5
• Combined networks
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494010985_05f9_c1 © 1999, Cisco Systems, Inc.
Web SitesWeb Sites
• Ciscohttp://www.cisco.com
• ATM Forumhttp://www.atmforum.com/
504010985_05f9_c1 © 1999, Cisco Systems, Inc.
ObsahObsah
• Výhody paketového přenosu hlasu• Kódování a komprese• Voice over Frame Relay
• Voice over ATM• Voice over IP• Problémy paketového přenosu
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514010985_05f9_c1 © 1999, Cisco Systems, Inc.
IP UbiquityIP Ubiquity
Packet
Frame
H.323 Endpoint B
H.323 Endpoint A
R2
R1
Ethernet
e
TokenRing
ATM orFrame Relay
Voice
Voice
Voice
Voice
Voice
Voice
Voice
Voice
Voice
UDP RTPIP
UDP RTPIP
UDP RTPIP
UDP RTPIP
UDP RTPIP
UDP RTPIP
UDP RTPIP
TokenRingTokenRing
FR orATMFR orATM
802.3802.3
524010985_05f9_c1 © 1999, Cisco Systems, Inc.
H.323H.323——Multimedia Standard Multimedia Standard for IP Networksfor IP Networks
• The H.323 standard provides a foundation for audio, video, and data communications across IP-based networks, including the Internet
• Original standard approved in 1996 and H.323 V2 was approved January 1998
• H.323 is an umbrella recommendation from the International Telecommunications Union (ITU) that sets standards for multimedia communications over Local Area Networks (LANs) that do not provide a guaranteed Quality of Service (QoS)
• H.323 is H.320 Recast for IP LAN
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534010985_05f9_c1 © 1999, Cisco Systems, Inc.
System ControlSystem ControlH.245
Control
Call Control H.225.0
RAS Control H.225.0
Video CodecH.261, H263
Video CodecH.261, H263
User DataApplications
T.120
User DataApplications
T.120
H.225.0 LayerH.225.0 Layer
AudioI/O
Equipment
AudioI/O
Equipment
Audio CodecG.711, G.722,
G.723, G.723.1, G.728, G.729
Audio CodecG.711, G.722,
G.723, G.723.1, G.728, G.729
Receive Path Delay
Receive Path Delay
System Control and
User Interface
System Control and
User Interface
VideoI/O
Equipment
VideoI/O
Equipment
SessionLayer
and Above
LAN StackLAN Stack
VoIP Uses ITU H.323VoIP Uses ITU H.323
544010985_05f9_c1 © 1999, Cisco Systems, Inc.
IP Layered Model H.323 VoIP Model
IP Address
Email IDE.164 Phone No.
Audio Codec(G.711, G.729, G.723.1,..)H.225, H.245, RTP, RTCP
Frame Relay DLCI,802.3 MAC, ATM VPI/VCI
V.35, T1, T3
UDPPort Number
CallerCaller
Application
Presentation
Data Link
Physical
UserUser
TCP UDP
IP
Session
H.323 VoIP LayersH.323 VoIP Layers
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554010985_05f9_c1 © 1999, Cisco Systems, Inc.
H.323H.323——System ComponentsSystem Components
• H.323 defines four major components for a network-based communications system
TerminalsGatewaysGatekeepersMultipoint Control Units
564010985_05f9_c1 © 1999, Cisco Systems, Inc.
H.324H.324TerminalTerminal
H.323H.323GatekeeperGatekeeper
WANRSVP
H.323H.323TerminalTerminal
H.323H.323GatewayGateway
H.323H.323TerminalTerminal
H.323H.323TerminalTerminal
H.323H.323MCUMCU
Scope of H.323
V.70V.70TerminalTerminal
SpeechSpeechTerminalTerminal
H.320H.320TerminalTerminal
SpeechSpeechTerminalTerminal
PSTN ISDN
H.323H.323——System ComponentsSystem Components
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574010985_05f9_c1 © 1999, Cisco Systems, Inc.
TCP Connection
SETUP
CONNECT (H245 Address) Q.931
TCP Connection
H.245 Messages
Open Logical Channels(RTCP Address)
(RTCP and RTP Addresses)(RTCP Address)
(RTCP and RTP Addresses)
H.245
RTP StreamRTP Stream
RTCP StreamMedia
H.323
H.323 Generic Call FlowH.323 Generic Call Flow
584010985_05f9_c1 © 1999, Cisco Systems, Inc.
4 Bytes
4 Bytes
4 Bytes
RTP Timestamp
Synchronization Source (SSRC) ID
Sequence NumberPayloadTypeMCC
VER
RTP/RTCPRTP/RTCP——RFCs 1889/1890RFCs 1889/1890
• End-to-end network transport function Payload type identification—voice, video, compression typeSequence numberingTime stampingDelivery monitoring
• RTCP (Real-Time Control Protocol)
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594010985_05f9_c1 © 1999, Cisco Systems, Inc.
PSTNQoS IPNetwork GatewayGateway
FXOFXSE&MT1PRI
Frame RelayATMEthernetFDDIToken Ring
G.711 PCMAnalog
G.711 PCMG.726 ADPCMG.728 LD-CELPG.729 CS-ACELPG.729A CS-ACELPG.723.1 ACELP
L2 VoiceUDPRTPIP
H.323 GatewayH.323 Gateway
604010985_05f9_c1 © 1999, Cisco Systems, Inc.
Gatekeeper FunctionsGatekeeper Functions
• Mandatory services:Address translationAdmissions controlBandwidth controlZone management
• Optional services:Call control signalingCall authorizationBandwidth management and reservationCall managementGatekeeper management information data structureDirectory services
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614010985_05f9_c1 © 1999, Cisco Systems, Inc.
Connection PlaneConnection PlaneConnection NegotiationConnection NegotiationTranscodingTranscodingBearer SwitchingBearer SwitchingMedia Control: H.323Media Control: H.323
SwitchingLogic
SwitchingLogic
OSSOSS
BillingBillingNet. Mgt.Net. Mgt.Fault Mgt Fault Mgt ServiceService
ProvisionProvision--inging
Cust. Cust. ProvisionProvision--
inging
Call Control PlaneCall Control PlaneSignaling and Call ControlSignaling and Call ControlService Access FunctionService Access FunctionSwitchSwitch--Based Service LogicBased Service LogicEnd to End VoiceEnd to End VoiceServicesServices
CallLogicCall
LogicH.323H.323
Services PlaneServices PlaneIN Service Logic IN Service Logic AAA, AAA, Address ResolutionAddress Resolution
ServiceLogic
ServiceLogic
H.323H.323——H.323 Direct Call ModelH.323 Direct Call Model
624010985_05f9_c1 © 1999, Cisco Systems, Inc.
GatekeeperGatekeeper GatekeeperGatekeeper
RASRAS
GK to GKGK to GKProtocolProtocol
H.225H.225H.245H.245
H.323H.323——Gatekeeper Routed Gatekeeper Routed Call ModelCall Model
OSS
BillingBillingNet. Mgt.Net. Mgt.Fault Mgt. Fault Mgt.
ServiceServiceProvisionProvision--
ingingCust. Cust.
ProvisionProvision--inging
Connection PlaneConnection PlaneConnection NegotiationConnection NegotiationTranscodingTranscodingBearer SwitchingBearer SwitchingMedia Control: H.225, H.245Media Control: H.225, H.245
Call Control PlaneCall Control PlaneSignaling and Call ControlSignaling and Call ControlService Access FunctionService Access FunctionSwitchSwitch--Based Service LogicBased Service LogicEnd to End Voice End to End Voice ServicesServices
Services PlaneServices PlaneIN Service Logic IN Service Logic AAA, Directory ServiceAAA, Directory ServiceAddress ResolutionAddress Resolution
ServiceLogic
ServiceLogic
RASRAS
IN/AININ/AIN——CTI APIsCTI APIs
CallLogicCall
Logic
SwitchingLogic
SwitchingLogic
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634010985_05f9_c1 © 1999, Cisco Systems, Inc.
Gatekeeper Mandatory ServicesGatekeeper Mandatory Services
• Address TranslationTranslates H.323 aliases or E.164 addresses into IP transport addresses (e.g. 10.1.1.1 port 1720)
• Admissions ControlAuthorizes access to the H.323 network
• Bandwidth ControlManages endpoint bandwidth requirements
• Zone ManagementProvides the above functions to all terminals, gateways, and MCUs that register to it
644010985_05f9_c1 © 1999, Cisco Systems, Inc.
RAS MessagesRAS Messages
• GRQ/GCF/GRJ (Discovery)Unicast—Multicast, find a gatekeeper
• RRQ/RCF/RRJ (Registration)Endpoint alias/IP address binding, endpoint authentication
• ARQ/ACF/ARJ (Admission)Destination Address Resolution, Call Routing
• LRQ/LCF/LRJ (Location)Inter-gatekeeper communication
• DRQ/DCF/DRJ (Disconnect)Get rid of call state
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33
654010985_05f9_c1 © 1999, Cisco Systems, Inc.
Gatekeeper A Gatekeeper B
ARQ
LRQ
IP Network
Phone A Phone B
Gateway A Gateway B
H.225 (Q.931) SetupH.225 (Q.931) Connect
RTP
ACF
LCF
V
ARQ
ACF
H.245
H.323 Message ExchangeH.323 Message Exchange
V
664010985_05f9_c1 © 1999, Cisco Systems, Inc.
Directory-Gatekeeper Directory-Gatekeeper
ARQ
LRQ IP Network
Phone A
Phone BGateway A Gateway B
H.225 (Q.931) SetupH.225 (Q.931) Connect
RTP
ACFLCF
VVVV H.245
LRQLRQ
ARQACF
LRQ Forwarding in ActionLRQ Forwarding in Action
GK GK
GK GK
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34
674010985_05f9_c1 © 1999, Cisco Systems, Inc.
H.323 ResourcesH.323 Resources
• H.323 Standardsftp://itu-t:[email protected]/
• VoIP Forumftp://ftp.imtc-files.org/imtc-site/VoIP-AG/Incoming
• General Informationhttp://www.pulver.com
684010985_05f9_c1 © 1999, Cisco Systems, Inc.
SIP Goals
Intelligent EndpointsIntelligent Endpoints——SIPSIP
• To supports some or all of five facets of establishing and terminating multimedia communications:
User location
User capabilities
User availability
Call setup
Call handling
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35
694010985_05f9_c1 © 1999, Cisco Systems, Inc.
SIP Architectural ElementsSIP Architectural Elements
• Clients• Servers
ProxyRedirectUser agent
704010985_05f9_c1 © 1999, Cisco Systems, Inc.
SIP Call FlowSIP Call Flow——ProxyProxy
cs.tu-berlin.de
Lion
[email protected]: [email protected]: [email protected]: [email protected]
1
200 OKFrom: [email protected]: [email protected]: [email protected]
8
[email protected]: [email protected]
9
200 OK12
INVITEhgs@playFrom: [email protected]: [email protected]: [email protected]
Tune
Play hgs
herr
ing
22
Hgs
@pl
ay 33
Location Server44
cs.columbia.edu
200 OKFrom: [email protected]: [email protected]: [email protected]
66
CONNNECTEDhgs@playFrom: [email protected]: [email protected]: [email protected]
1010
1111
?
7
200 OK
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36
714010985_05f9_c1 © 1999, Cisco Systems, Inc.
SIP Call FlowSIP Call Flow——RedirectRedirect
Lion
Play hgs
66
Tune
herr
ing
22
Hgs
@pl
ay 33
Location Server??cs.columbia.edu
[email protected]: [email protected]: [email protected]: [email protected]
1
302 Moved TemporarilyLocation: [email protected]: [email protected]: [email protected]: [email protected]
4
5 INVITEhgs@playFrom: [email protected]: [email protected]: [email protected] OKFrom: [email protected]: [email protected]: [email protected]
7
[email protected]: [email protected]
8
200 OK9
724010985_05f9_c1 © 1999, Cisco Systems, Inc.
SIP ResourcesSIP Resources
• SIP standardftp://ftp.ietf.org/internet-drafts/draft-ietf-mmusic-sip-04.txt
• General SIP informationhttp://www.cs.columbia.edu/~hgs/sip/
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37
734010985_05f9_c1 © 1999, Cisco Systems, Inc.
SIPSIP vsvs. H.323 Comparison. H.323 Comparison
• ScopeSIP—Full-featured multimedia protocolH.323—Full-featured video conferencing
• StatusSIP—Basic SIP ready for proposed standardH.323—V3 in ITU approval cycle
• InteroperabilitySIP—Initial bake-off, some interoperability achievedH.323—Demonstrated, but problematic
744010985_05f9_c1 © 1999, Cisco Systems, Inc.
SIP vs. H.323 ComparisonSIP vs. H.323 Comparison
• Call setup overheadSIP—as little as one round tripH.323—7 or 8 round-trips (2 in V2)
• Call control functionsSIP—Relies on existing protocolsH.323—Based on GK functions
• Control transportSIP—UDP (multicast, firewalls)H.323—TCP
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38
754010985_05f9_c1 © 1999, Cisco Systems, Inc.
Repeat: Voice Is Not A NetworkRepeat: Voice Is Not A Network
• Voice is an Application
• Complete understanding of Voice Application fundamentals helps us to design and build better Networks
764010985_05f9_c1 © 1999, Cisco Systems, Inc.
Packet TelephonyPacket TelephonyArchitecture ChoicesArchitecture Choices
• Intelligent Network/Simple EndpointsSS7, Gateway Control Protocol (SGCP/MGCP)
• Simple Network/Intelligent EndpointsSession Initiation Protocol (SIP)
• Hybrid—Intelligent Network and EndpointsH.323
• Layer 2 Access Networks Voice CarriageVoFR (FRF11), VoATM
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39
774010985_05f9_c1 © 1999, Cisco Systems, Inc.
ObsahObsah
• Výhody paketového přenosu hlasu• Kódování a komprese• Voice over Frame Relay
• Voice over ATM• Voice over IP• Problémy paketového přenosu
784010985_05f9_c1 © 1999, Cisco Systems, Inc.
Data and VoiceData and VoiceOpposite Needs/BehaviorOpposite Needs/Behavior
Data• Bursty
• Greedy
• Drop sensitive
• Delay insensitive
• TCP retransmits
Data• Bursty
• Greedy
• Drop sensitive
• Delay insensitive
• TCP retransmits
Voice• Smooth
• Benign
• Drop insensitive
• Delay sensitive
• UDP best effort
Voice• Smooth
• Benign
• Drop insensitive
• Delay sensitive
• UDP best effort
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40
794010985_05f9_c1 © 1999, Cisco Systems, Inc.
TDM
Frame/Packet
Cell
TDM vs Frame vs CellTDM vs Frame vs Cell
• TDM—Constant delay, wasted bandwidth
• Frame/packet—Variable delay, highly efficient
• Cell—Improved delay, less efficient
804010985_05f9_c1 © 1999, Cisco Systems, Inc.
QosQos TerminologyTerminology
Policing• Limiting the packet rate• No buffering• Input and output mechanism• Drop policies for traffic that exceeds
ratetail drop, RED, WRED
• CAR, Queue tail-drop
Traffic Shaping• Limiting the packet rate• Buffering to smooth traffic flow• Output mechanism• GTS, FRTS, ATM shaping
Queuing / Scheduling• Queuing: Organize packets waiting
to go out on an interface• Scheduling: When interface is free -
decide which of the waiting packets to send next
• Nodal significance• CQ, PQ, WFQ, CBWFQ...
Tagging / Marking / Colouring• Set bits in packet header• Indication to guide priority and
queuing machanisms• Network significance• Can be changed/adjusted by any
network node• IP Precedence, DSCP
Call Admission Control• Disallow new traffic if insufficient
resources available
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814010985_05f9_c1 © 1999, Cisco Systems, Inc.
Voice PayloadVoice Payload
– – –– – –
Commonality—Voice Packets Ride on UDP/RTPCommonality—Voice Packets Ride on UDP/RTP
Voice over IP ProtocolsVoice over IP Protocols
VoIP Is Not Bound to H.323 (H.323 Is a Signaling Protocol)Many Other Signaling Protocols—MGCP, SGCP, SIP, Etc.
PhysicalPhysical
LinkLink
NetworkNetwork
TransportTransport
G.711, G.729, G.723(.1)G.711, G.729, G.723(.1)
RTP/UDPRTP/UDP
IPIP
MLPPP/FR/ATM AAL1MLPPP/FR/ATM AAL1
824010985_05f9_c1 © 1999, Cisco Systems, Inc.
Encoding/CompressionEncoding/Compression Resulting Bit RateResulting Bit Rate
““PayloadPayload”” Bandwidth Bandwidth Requirements for Various CodecsRequirements for Various Codecs
G.723.1 CELPG.723.1 CELP
G.728 LD-CELPG.728 LD-CELP
G.729 CS-ACELPG.729 CS-ACELP
G.727 E-ADPCMG.727 E-ADPCM
G.726 ADPCMG.726 ADPCM
G.711 PCM A-Law/u-LawG.711 PCM A-Law/u-Law
6.3/5.3 kbps6.3/5.3 kbps
16 kbps16 kbps
8 kbps8 kbps
16, 24, 32, 40 kbps16, 24, 32, 40 kbps
16, 24, 32, 40 kbps16, 24, 32, 40 kbps
64 kbps (DS0)64 kbps (DS0)
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834010985_05f9_c1 © 1999, Cisco Systems, Inc.
LinkHeader IP Header UDP
HeaderRTP
Header
VoIP Packet
X Bytes20 Bytes 8 Bytes 12 Bytes
Voice Payload
X Bytes
Note—Link Layer Sizes Vary per Media
Not Including Link Layer Header or CRTPCisco Router at G.711 = 160 Byte Voice Payload at 50 pps (80 kbps) Cisco Router at G.729 = 20 Byte Payload at 50 pps (24 kbps)Cisco IP Phone at G.711 = 240 Byte Payload at 33 pps (74.6 kbps)Cisco IP Phone at G.723.1 = 24 Byte Payload at 33 pps (17k bps)
VoIP Packet FormatVoIP Packet Format
• Payload size, PPS and BPS vendor implementation specific• For example:
844010985_05f9_c1 © 1999, Cisco Systems, Inc.
8K CS-ACELP, G.729xx 10 ms of voice is represented by 10 bytes of voice payload
Voice Represented (msec) 10 20 30 40 50 60Voice Payload (bytes) 10 20 30 40 50 60
Packet Rate (pps) 100.00 50.00 33.33 25.00 20.00 16.67
32K ADPCM, G.726 10 ms of voice is represented by 40 bytes of voice payload
Voice Represented (msec) 10 20 30 40 50 60Voice Payload (bytes) 40 80 120 160 200 240
Packet Rate (pps) 100.00 50.00 33.33 25.00 20.00 16.67
64K PCM, G.711 10 ms of voice is represented by 80 bytes of voice payload
Voice Represented (msec) 5 10 15 20 25 30Voice Payload (bytes) 40 80 120 160 200 240
Packet Rate (pps) 200.00 100.00 66.67 50.00 40.00 33.33
Voice PayloadVoice Payload vsvs. Frame Rate. Frame Rate
BW-needed-per-call = #bytes-per-packet * 8 * pps
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854010985_05f9_c1 © 1999, Cisco Systems, Inc.
MediaMedia Link Layer Header SizeLink Layer Header Size
Bit RateBit Rate
Example—G.729 with 60 Byte Packet (Voice and IP Header) at 50 pps (No RTP Header Compression)
Note—For ATM a Single 60 Byte Packet Requires Two 53 Byte ATM Cells
ATMATM
Frame RelayFrame Relay
PPPPPP
EthernetEthernet
5 Bytes Per Cell5 Bytes Per Cell
4 Bytes4 Bytes
6 Bytes6 Bytes
14 Bytes14 Bytes
42.4 kbps42.4 kbps
25.6 kbps25.6 kbps
26.4 kbps26.4 kbps
29.6 kbps29.6 kbps
“Varying Bit Rates per Media”
Various Link Layer Header SizesVarious Link Layer Header Sizes
864010985_05f9_c1 © 1999, Cisco Systems, Inc.
RouterIP
IP
IP
IP
IP
IP
MultilayerCampus
MultilayerCampus
Requirement - “End to End” Quality of Service (QoS)
Router
Domains of QoS Consideration Domains of QoS Consideration
WAN
CampusCampus WAN Edge/EgressWAN Edge/Egress WANBackbone
WANBackbone
Avoiding Loss, Delay and Delay Variation (Jitter)Strict Prioritization of Voice
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44
874010985_05f9_c1 © 1999, Cisco Systems, Inc.
IP
IP
IP
IP
IP
IP
WAN
1. Congestion on WAN Link2. Proper QoS Mechanisms Not Deployed3. Campus Congestion Less Concerning
1. Congestion on WAN Link2. Proper QoS Mechanisms Not Deployed3. Campus Congestion Less Concerning
Edge/EgressEdge/Egress1. Global WAN Congestion2. Central to Remote Circuit Speed Mismatch3. Remote Site to Central Site over Subscription4. Improper PVC Design/Provisioning
1. Global WAN Congestion2. Central to Remote Circuit Speed Mismatch3. Remote Site to Central Site over Subscription4. Improper PVC Design/Provisioning
WANWAN
Router
MultilayerCampus
MultilayerCampus
Router
LossLossSources of Packet LossSources of Packet Loss——CongestionCongestion
884010985_05f9_c1 © 1999, Cisco Systems, Inc.
Inter-NodeTrunks
“The Cloud/Carrier”Frame Relay, ATMWAN Switch Fabric
Customer PremisesEquipment Access
Lines
InterInter--Node Trunk Over SubscriptionNode Trunk Over SubscriptionOften 3:1 or HigherOften 3:1 or Higher
Anatomy of a CarrierAnatomy of a Carrier
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894010985_05f9_c1 © 1999, Cisco Systems, Inc.
56kbps
Router RouterWAN Switch
IGX/8400WAN Switch
IGX/8400Inter-Nodal Trunk
Access56kbps
AccessT1
IngressQueue
EgressQueueT1
TrunkQueue
TrunkQueue
GlobalTrunk Congestion
Egress Port CongestionVC Over Subscription
Packets Arrive atGreater than PIR or CIR
PIR = Peak Information Rate
T1IngressQueue
Where WAN CongestionWhere WAN Congestionand Delay Can Occurand Delay Can Occur
904010985_05f9_c1 © 1999, Cisco Systems, Inc.
Router RouterWAN Switch
IGX/8400WAN Switch
IGX/8400Inter-Nodal Trunk
Access56kbps
AccessT1
IngressQueue
EgressQueueT1
56kbps
TrunkQueue
TrunkQueue
BurstingBursting——What Is Your What Is Your Guarantee? OptionsGuarantee? Options
Mark Data DE (Discard Eligible)Only Drop Data
Upon Congestion
Data Gets Dropped 1stCompared to Other
Subscribers
Mark Data DE (Discard Eligible)Only Drop Data
Upon Congestion
Data Gets Dropped 1stCompared to Other
Subscribers
Two PVC’s—Data + Voice
Voice—Keep Below CIRData—Allow for BurstingNeed DLCI Prioritization
at WAN Egress
Two PVC’s—Data + Voice
Voice—Keep Below CIRData—Allow for BurstingNeed DLCI Prioritization
at WAN Egress
Active Traffic Management
ABR, FECN/BECN, ForeSight
Only Invoked when congestion/Delays has
Already Occurred
Active Traffic Management
ABR, FECN/BECN, ForeSight
Only Invoked when congestion/Delays has
Already Occurred
Shape to CIR—No BurstingThe Safest
Not Popular
Shape to CIR—No BurstingThe Safest
Not Popular
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914010985_05f9_c1 © 1999, Cisco Systems, Inc.
56kbps
Router RouterWAN Switch
IGX/8400WAN Switch
IGX/8400Inter-Nodal Trunk
Access56kbps
AccessT1
IngressQueue
EgressQueueT1
TrunkQueue
TrunkQueue
ABR—Available Bit RateCan Send a Rate Down
from Point of Congestion
ABR—Available Bit RateCan Send a Rate Down
from Point of Congestion
FECN/BECN NotificationRequires Far End to
Reflect a FECN and Send and BECN Back to Source
Indicating a Rate Down
FECN/BECN NotificationRequires Far End to
Reflect a FECN and Send and BECN Back to Source
Indicating a Rate Down
Foresight/CLLMCan Send a Rate Down
from Point of Congestion
Speeds up Rate Down Time over FECN/BECN
Foresight/CLLMCan Send a Rate Down
from Point of Congestion
Speeds up Rate Down Time over FECN/BECN
Congestion Must Occur to Invoke, Congestion Relief Can be as Long as One Round Trip Time
ABR/Foresight
ABR/Foresight
ABR/Foresight
FECN/BECN
Congestion Detection and FeedbackCongestion Detection and FeedbackEffectiveness Depends on Round Trip DelayEffectiveness Depends on Round Trip Delay
924010985_05f9_c1 © 1999, Cisco Systems, Inc.
Router RouterWAN Switch
IGX/8400WAN Switch
IGX/8400Inter-Nodal Trunk
Access56kbps
AccessT1
IngressQueue
EgressQueueT1
56kbps
Packets Leak into Trunk at PIR—(Peak Information Rate)Typically Lowest Access Rate—56 kbps
Packets De-Queue at Line RatePackets Arrive at Line Rate
Placed in Ingress Queue
TrunkQueue
TrunkQueue
WAN Queuing and BufferingWAN Queuing and Buffering
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934010985_05f9_c1 © 1999, Cisco Systems, Inc.
AA
First Bit Transmitted
Last Bit Received
Network
Sender Receiver
tNetwork Transit Delay
ProcessingDelay
ProcessingDelay
End-to-End Delay
DelayDelay
PBXPBX PBXPBX
944010985_05f9_c1 © 1999, Cisco Systems, Inc.
IP
IP
IP
IP
IP
IP
WANRouter
MultilayerCampus
MultilayerCampus
Router
DelayDelay——FixedFixedSources of Fixed DelaySources of Fixed Delay
Codec Processing—Packetization (TX)Serialization
De-Jitter Buffer
Codec Processing—Packetization (TX)Serialization
De-Jitter Buffer
Edge/EgressEdge/EgressPropagation Delay—6us per Km
Serialization DelayPropagation Delay—6us per Km
Serialization Delay
WANWAN
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954010985_05f9_c1 © 1999, Cisco Systems, Inc.
Delay VariationDelay Variation——““JitterJitter””
t
t
Sender Transmits
Sink Receives
A B C
A B C
D1 D2 = D1
Sender Receiver
Network
D3 = D2D3 = D2
964010985_05f9_c1 © 1999, Cisco Systems, Inc.
IP
IP
IP
IP
IP
IP
WANRouter
MultilayerCampus
MultilayerCampus
Router
Queuing Delay (Congestion)De-Jitter Buffer
No or Improper Traffic Shaping ConfigLarge Packet Serialization on Slow Links
Variable Size PacketsLess Common in Campus
Queuing Delay (Congestion)De-Jitter Buffer
No or Improper Traffic Shaping ConfigLarge Packet Serialization on Slow Links
Variable Size PacketsLess Common in Campus
Edge/EgressEdge/EgressGlobal WAN Congestion
Central to Remote Site Speed Mismatch (Fast to Slow)
PVC Over Subscription (Remote to Central Site) Bursting Above Committed Rates
Global WAN CongestionCentral to Remote Site Speed Mismatch
(Fast to Slow)PVC Over Subscription (Remote to Central Site)
Bursting Above Committed Rates
WANWAN
DelayDelay——VariableVariableSources of Variable DelaySources of Variable Delay
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974010985_05f9_c1 © 1999, Cisco Systems, Inc.
Voice Delay GuidelinesVoice Delay Guidelines
One Way DelayOne Way Delay(msec)(msec) DescriptionDescription
00––150150 Acceptable for Most User ApplicationsAcceptable for Most User Applications
150150––400400 Acceptable Provided That Acceptable Provided That Administrations Are Aware Administrations Are Aware of the Transmission Time Impact of the Transmission Time Impact on the Transmission Quality on the Transmission Quality of User Applicationsof User Applications
400+400+ Unacceptable for General Network Unacceptable for General Network Planning Purposes; However, It Is Planning Purposes; However, It Is Recognized That in Some Exceptional Recognized That in Some Exceptional Cases This Limit Will Be ExceededCases This Limit Will Be Exceeded
ITU’s G.114 Recommendation
984010985_05f9_c1 © 1999, Cisco Systems, Inc.
Cumulative Transmission Path DelayAvoid the “Human Ethernet”
Time (msec)
0 100 200 300 400
CB ZoneCB ZoneSatellite QualitySatellite Quality
Fax Relay, BroadcastFax Relay, BroadcastHigh QualityHigh Quality
Delay Target
500 600 700 800
ITU’s G.114 “Recommendation” = 0–150 msec 1-Way Delay
Delay Budget Goal < 150 ms Delay Budget Goal < 150 ms
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994010985_05f9_c1 © 1999, Cisco Systems, Inc.
An ExampleAn Example
• Assumptions:We have eight trunksWe are going to use CS-ACELP that uses 8 Kbps per voice channelOur uplink is 64 KbpsVoice is using a high priority queue and no other traffic is being used
1004010985_05f9_c1 © 1999, Cisco Systems, Inc.
Delay CalculationDelay Calculation
PropagationDelay—32 ms
Coder DelayCoder Delay25 ms25 ms
Serialization DelaySerialization Delay3 ms3 ms
Dejitter BufferDejitter Buffer50 ms50 ms
Queuing DelayQueuing Delay6 ms6 ms
LosLosAngelesAngeles MunichMunich
(Private Line Network)
TotalTotal 110 msec110 msecDejitter BufferDejitter Buffer 50 msec50 msec
32 msec32 msecNetwork Delay (e.g., Public Frame Relay Svc)Network Delay (e.g., Public Frame Relay Svc)
Serialization Delay 64 kbps TrunkSerialization Delay 64 kbps Trunk 3 msec3 msec21 msecMax Queuing Delay 64 kbps TrunkMax Queuing Delay 64 kbps Trunk
5 msec5 msec
Packetization DelayPacketization Delay——Included in Coder DelayIncluded in Coder Delay
Coder Delay G.729 (5 msec Look Ahead)Coder Delay G.729 (5 msec Look Ahead)
Propagation Delay (Private Lines)Propagation Delay (Private Lines)
Fixed Fixed DelayDelay
Variable Variable DelayDelay
Coder Delay G.729 (10 msec per Frame)Coder Delay G.729 (10 msec per Frame) 20 msec20 msec
82
VariableVariableDelayDelay
ComponentComponent
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1014010985_05f9_c1 © 1999, Cisco Systems, Inc.
Variable Delay CalculationVariable Delay Calculation
• We have eight trunks, so in the worst case we will have to wait for seven voice calls prior to ours
• To put one voice frame out on a 64Kbps link takes 3msec
• 1 byte over a 64Kbps link takes 125 microseconds. We have a 20 byte frame relay frame with 4 bytes of overhead. 125 * 24 = 3000 usecs or 3 msec
• Does not factor in waiting for a possible data packet or the impact of variable sized frames
• Assumes voice prioritization of frames
1024010985_05f9_c1 © 1999, Cisco Systems, Inc.
Elastic Traffic MTUElastic Traffic MTUReal-Time MTUReal-Time MTU
56 kbps Line
214 ms Serialization Delayfor 1500 Byte Frame at 56 kbps
Large Packets “Freeze Out” Voice—Results in Jitter
Large Packets on Slow LinksLarge Packets on Slow Links
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1034010985_05f9_c1 © 1999, Cisco Systems, Inc.
SolutionsPoint to Point Links—MLPPP with Fragmentation and InterleaveFrame Relay—FRF.12 (Voice and Data Can Use Single PVC)ATM—(Voice and Data Need Separate VCs on Slow Links)
SlowSlow--Link Efficiency ToolsLink Efficiency Tools
Elastic Traffic MTUReal-Time MTU
Elastic MTU Real-Time MTUElastic MTU Elastic MTU
214-ms Serialization Delayfor 1500-byte Frame at 56 kbps
Before
After
Fragmentation and InterleaveNot Needed on Links Greater than 768 kbps
1044010985_05f9_c1 © 1999, Cisco Systems, Inc.
Fragment Size =
56 kbps56 kbps70
Bytes70
Bytes
FragmentSize
FragmentSize
64 kbps64 kbps80
Bytes80
Bytes
128 kbps128 kbps 160Bytes160
Bytes
256 kbps256 kbps
512 kbps512 kbps
768 kbps768 kbps
1536 kbs1536 kbs
320Bytes320
Bytes640
Bytes640
Bytes1000Bytes1000Bytes
2000Bytes2000BytesXX
LinkSpeedLink
Speed
Assuming 10 ms Blocking Delay per FragmentAssuming 10 ms Blocking Delay per Fragment10 ms
Time for 1 Byte at BWExample: 4 G.729 Calls on 128 kbps Circuit
Fragment Blocking Delay = 10 ms (160 bytes)
Q = (Pv*N/C) + LFI
Q = (480 bits*4/128000) + 10 ms = 25 ms
Worst Case Queuing Delay = 25 msWorst Case Queuing Delay = 25 ms
Q = Worst Case Queuing Delay of Voice Packet in ms Pv = Size of a Voice Packet in Bits (at Layer 1)N = Number of Calls C = Is the Link Capacity in bpsLFI = Fragment Size Queue Delay in ms
Fragment Size MatrixFragment Size Matrix
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Real Time Packet Interval
LinkSpeed
56kbps70
Bytes140
Bytes210
Bytes280
Bytes700
Bytes1400Bytes
10ms 20ms 30ms 40ms 50ms 100ms 200ms
64kbps80
Bytes160
Bytes240
Bytes320
Bytes400
Bytes800
Bytes1600Bytes
128kbps160
Bytes320
Bytes480
Bytes640
Bytes800
Bytes1600Bytes
256kbps
512kbps
768kbps
1536kbs
350Bytes
3200Bytes
320Bytes
640Bytes
960Bytes
1280Bytes
1600Bytes
3200Bytes
6400Bytes
640Bytes
1280Bytes
1920Bytes
2560Bytes
3200Bytes
6400Bytes
12800Bytes
1000Bytes
2000Bytes
3000Bytes
4000Bytes
5000Bytes
10000Bytes
20000Bytes
2000Bytes
4000Bytes
6000Bytes
8000Bytes
10000Bytes
20000Bytes
40000BytesXX XX XX XX XX XXXXXX
XXXXXXXX
XX XX XX XX XXXXXXXX
XX XXXX
XX
XX—Fragmentation not an issue due to BW + Interval Combination
Fragmentation Frame Size MatrixFragmentation Frame Size Matrix
1064010985_05f9_c1 © 1999, Cisco Systems, Inc.
Frame Size
768kbps
1536kbs
10us
5us
64Bytes
9ms
8ms
4ms
2ms
1ms
640us
320us
18ms
128Bytes
16ms
8ms
4ms
2ms
1.28ms
640us
36ms
256Bytes
32ms
16ms
8ms
4ms
2.56ms
1.28ms
72ms
512Bytes
64ms
32ms
16ms
8ms
5.12ms
2.56ms
144ms
1024Bytes
128ms
64ms
32ms
16ms
10.24ms
5.12ms
1500Bytes
46ms
214ms
187ms
93ms
23ms
15mss
7.5ms
LinkSpeed
143 us143 us 9 ms9 ms 18 ms18 ms 36 ms36 ms 72 ms72 ms 144 ms144 ms 214 ms214 ms
1Byte
1Byte
64Bytes
64Bytes
128Bytes128
Bytes256
Bytes256
Bytes512
Bytes512
Bytes1024Bytes1024Bytes
1500Bytes1500Bytes
125 us125 us 8 ms8 ms 16 ms16 ms 32 ms32 ms 64 ms64 ms 128 ms128 ms 187 ms187 ms
62.5 us62.5 us 4 ms4 ms 8 ms8 ms 16 ms16 ms 32 ms32 ms 64 ms64 ms 93 ms93 ms
31 us31 us 2 ms2 ms 4 ms4 ms 8 ms8 ms 16 ms16 ms 32 ms32 ms 46 ms46 ms
15.5 us15.5 us 1 ms1 ms 2 ms2 ms 4 ms4 ms 8 ms8 ms 16 ms16 ms 23 ms23 ms
10 us10 us 640 us640 us 1.28 ms1.28 ms 2.56 ms2.56 ms 5.12 ms5.12 ms 10.24 ms10.24 ms 15 ms15 ms
5 us5 us 320 us320 us 640 us640 us 1.28 ms1.28 ms 2.56 ms2.56 ms 5.12 ms5.12 ms 7.5 ms7.5 ms
56 kbps56 kbps
128 kbps128 kbps
256 kbps256 kbps
768 kbps768 kbps
1536 kbs1536 kbs
512 kbps512 kbps
64 kbps64 kbps
When Is Fragmentation Needed?When Is Fragmentation Needed?
• Depends on the queuing delay caused by large frames at a given speed—fragmentation generally not needed above 768 kbps
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QoS NeedsQoS Needs
• CampusBandwidth minimizes QoS issues
• WAN edgeQoS “starts” in the WAN—a must
• WAN considerationsOften forgotten or misunderstood—a must
1084010985_05f9_c1 © 1999, Cisco Systems, Inc.
Router
3 33 3
2 23 2 2 2 11
1 1VoIP
SNA
Data
VVV
Three Classes of QoS ToolsThree Classes of QoS Tools
• PrioritizationClassification + Queuing
• Slow Link EfficiencyLink Fragmentation and Interleave (LFI )Compression, Voice Activity Detection (VAD)
• Traffic ShapingSpeed Mismatches
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RTP HeaderCompressionVersion IHL Type of Service Total Length
Identification Flags Fragment Offset
Header ChecksumProtocolTime to Live
Source Address
Destination Address
PaddingOptions
Source Port Destination Port
ChecksumLength
PTPTMMCCCCXXPPV=2V=2 Sequence NumberSequence Number
TimestampTimestamp
Synchronization Source (SSRC) IdentifierSynchronization Source (SSRC) Identifier
VoIP Bandwidth SolutionVoIP Bandwidth Solution
• 20 ms @ 8 kbps yields20-byte payload
• IP header 20;UDP header 8;RTP header 122X payload!
• Header compression40 bytes to 2 or 4 bytes
• Hop-by-Hop on slow links <512 kbps
• CRTP—CompressedReal-time Protocol
1104010985_05f9_c1 © 1999, Cisco Systems, Inc.
Link EfficiencySend Fewer PacketsSend Fewer Packets
• VAD“B” versions of G.729 contain a built-in IETF VAD algorithm, no need to configure VADRule-of-thumb: 30-35% reduction in BW - a more valid assumption for larger pipes (T1 and above)
Depends on application (e.g. Music-on-Hold makes VAD 0%)• Variable Payload Size
Specify #samples per packet
Changes the BW, delay and pps characteristics of the callUsability depends on the delay budget of the networkvalues > default: decreases BW, and increases delayvalues < default: increases BW, and decreases delay
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VersionLength
ToSToS1 Byte1 Byte Len
Standard IPV4: Three MSB Called IP Precedence(DiffServ Will Use Six D.S. Bits Plus Two for Flow Control)
Layer 3 IPV4
ID offset TTL Proto FCS IP-SA IP-DA Data
PREAM. SFD DA SA TAGTAG4 Bytes4 Bytes PT DATA FCS
Three Bits Used for CoS(User Priority)
Layer 2 802.1Q/p
DataPacket
Traffic Differentiation MechanismsTraffic Differentiation MechanismsIP Precedence and 802.1pIP Precedence and 802.1p
• Layer 2 mechanisms are not assured end-to-end• Layer 3 mechanisms provide end-to-end classification
1124010985_05f9_c1 © 1999, Cisco Systems, Inc.
IP Packet
Data
3 BitPrecedence
Field
ToS Field
4096(1 + IP Precedence)
Weight =
IP Precedence Weight
0 40961 20482 13653 10244 8195 6826 5857 512
IP PrecedenceIP Precedence““Controlling WFQControlling WFQ’’s Des De--queuing Behaviorqueuing Behavior””
• IP PrecedenceNot a QoS Mechanism turned on in the router“In Band” QoS Signaling—Set in the End Point
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VC1
VC2
VC3
VC4
SiSi
ATMNetwork
VC Bundle
Precedence to VC MappingPrecedence to VC Mapping
• VC bundle—multiple VCs for each IP adjacency • Separate VC for each IP CoS • WRED, WFQ, or CBWFQ runs on each VC queue
Note:Note:
WAN QoS is Only asWAN QoS is Only asGood as Specified ATMGood as Specified ATM
VC Parameters VC Parameters
Assign to VC Based on:Assign to VC Based on:
IP PrecedenceIP PrecedenceRSVPRSVP
Policy RoutingPolicy Routing
1144010985_05f9_c1 © 1999, Cisco Systems, Inc.
Queuing OverviewQueuing Overview
• Queuing and scheduling significant when:there is contention for BW, i.e. congestiontraffic shaping smoothingshare voice & data on same infrastructure
• Several sets of queues:VC queues (FR, ATM)Interface queues
Transmit ring queues (driver)
• Queuing method for voice much more significant on slow access links (<2M)
• WFQ is inadequate to provide good voice quality under all circumstances
Prioritization - Queuing
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Priority and Custom Queuing (PQ, CQ)Priority and Custom Queuing (PQ, CQ)
PQ• 4 Queues: High, Medium,
Normal, Low• Packets classified by
protocol or interface• FIFO within priority• Absolute priority
scheduling• Lower priority queues may
starve
PQ and CQ are not recommended for voice
CQ• 16 Queues• Packets classified by
protocol or interface• FIFO within priority
• Weighted round robin scheduling
• WRED and RSVP not supported
• Guarantees BW per queue, not delay
Prioritization - Queuing
1164010985_05f9_c1 © 1999, Cisco Systems, Inc.
Weighted Fair Queuing (WFQ)Weighted Fair Queuing (WFQ)
500kbps flowTransmit
Scheduling
24kbps Voice flow
Classify
1 De-queue
Dynamic Queue Per Flow
56kbpsLine Speed
Processor
22 2 2 12
When congestion exists, traffic in queues shares bandwidth based on the weights
““Not as effective when MANY flowsNot as effective when MANY flows””
2 22 2
1 12 1 2 2 11
Router Queue Structure
Default on links 2meg or less
24kbps flow gets 28kbps
(only needs 24kbps)
500kbps flow gets 28kbps
Prioritization - Queuing
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Weighted Fair Queuing (WFQ)Weighted Fair Queuing (WFQ)
IP Prec <12.0(5)T Weight >=12.0(5)T Weight0 4096 327681 2048 163842 1365 109233 1024 81924 819 65545 682 54616 585 46817 512 4096
RSVP 4 4RTP Reserve 128 N/ARTP Priority N/A 0
32768(1 + IP Prec)Weight =
Before 12.0(5)T 12.0(5)T and later
4096(1 + IP Prec)Weight =
Prioritization - Queuing
1184010985_05f9_c1 © 1999, Cisco Systems, Inc.
De-queue
2 22
1 1
4 4
3
6 66
5 5
......
...
Reserved queues(RSVP and RTP Reserve)
IP Precedence 7
IP Precedence 0(Best Effort/Hash queues)
...
Weighted Fair Queuing (WFQ)Weighted Fair Queuing (WFQ)
• Packets within the same weight are scheduled based on arrival time• Routing protocols and LMI bypass WFQ algorithm• ALL RSVP traffic queued at weight 4, not just voice• RSVP traffic at weight 128 until reservation succeeds, then 4
Q Classification:• Source
address• Dest address• Source port• Dest. Port• IP Precedence
Weight:• IP Precedence• RSVP/RTP
Reserve
Prioritization - Queuing
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1194010985_05f9_c1 © 1999, Cisco Systems, Inc.
Example A
56 kbps Link
2—VoIP Flows A+B at 24 kbps (IP Prec 0)2—FTP Flows at 56 kbps (IP Prec 0)
14 kbps = X 56 kbps1 4 )(
14 kbps NotNot Suitable for a 24 kbps FlowExample of Many Flows with WFQ and
Equal Precedence Flows
Example B
56 kbps Link
2—VoIP Flows A+B at 24 kbps (IP Prec 5)2—FTP Flows at 56 kbps (IP Prec 0)
24 kbps = X 56 kbps6 14)(
24 kbps SuitableSuitable for a 24 kbps Flow
WFQ Preferring IP Precedence WFQ Preferring IP Precedence Weighted Weighted ““FairFair”” QueuingQueuing
Flow A BW =Flow A BW = Flow A “Parts”Sum of all Flow “Parts”
Flow A “Parts”Sum of all Flow “Parts”
Circuit BandwidthCircuit BandwidthXX(( ))
IP PrecedenceIP PrecedenceFlow Bandwidth Calculation ExampleFlow Bandwidth Calculation Example
1204010985_05f9_c1 © 1999, Cisco Systems, Inc.
Moral of the Story: Know Your Environment, Voice Traffic Patterns etc. Recommendations for
Certain Bandwidth’s to FollowExample C
56 kbps Link2—VoIP Flow’s at 24 kbps (IP Prec 5)4—FTP Flows at 56 kbps (IP Prec 0)
21 kbps = X 56 kbps6 16)(
21 kbps Not Not Suitable for a 24 kbps Flow
RTP Header Compression Would Help Sinceit Would reduce VoIP Flow to 11.2 kbps
Also RSVP or CBWFQ
IP PrecedenceIP PrecedenceNo Admission ControlNo Admission Control
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IP Precedence and WFQIP Precedence and WFQ
Example B
56kbps link
2 VoIP Flows, 24K (IP Prec 5)2 FTP Flows, 56K (IP Prec 0)
X 56kbps = 24K24K6 14)(
24K SUITABLESUITABLE for a 24KVoIP flow
With IP Precedence
Example A
56kbps link
2 VoIP Flows, 24K (IP Prec 0)2 FTP Flows, 56K (IP Prec 0)
X 56kbps = 14K14K1 4 )(
14kbps NOTNOT suitable for a 24K VoIP flow
No IP Precedence
Calculating given Flow BW based on IP Precedence under congestion
Example C
56kbps link
2 VoIP Flows, 24K (IP Prec 5)6 FTP Flows, 56K (IP Prec 0)
X 56kbps = 18.6K18.6K6 18)(
18.6K NOTNOT suitable for a 24K VoIP flow
More flows with IP Precedence
Flow A BWFlow A BWFlow A “Parts” (1 + IP Prec)Sum of all Flow “Parts” Circuit BW =X( )
Prioritization - Queuing
1224010985_05f9_c1 © 1999, Cisco Systems, Inc.
Classify
De-queue
2 22
1 1
3
6 66
5 5
......
Default class-queue
WFQ System(unclassified traffic)
ClassClass--Based WFQ (CBWFQ)Based WFQ (CBWFQ)
OR
Class queuesMax: 63(64 including the default class-queue)
Prioritization - Queuing
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1234010985_05f9_c1 © 1999, Cisco Systems, Inc.
QoS Queuing ToolsIP RTP Priority (Point-to-Point Links + Frame Relay)IP to ATM QoS (Multiple VCs or CBWFQ within VC)
Identifying and Giving Priority to Voice
“Protecting Voice from Data”
WFQ
Router
3 33 3
2 2 5 3 2 1 11
1 1VoIP(High)
Data(Low)
Data(Low)
VV V
4 44 4Data(Low)
PQWANCircuit
Prioritization ToolsPrioritization Tools
1244010985_05f9_c1 © 1999, Cisco Systems, Inc.
WRED Benefit for VoIP:Maintain Room in Queue, and if Packets Must be
Dropped “Avoid” Dropping Voice
Packets ClassifiedPackets Classifiedas Gold Are Droppedas Gold Are Droppedat 90% Queue Depth at 90% Queue Depth
Packets ClassifiedPackets Classifiedas Blue Start Droppingas Blue Start Droppingat a 50% Queue Depth. at a 50% Queue Depth. Drop Rate Is IncreasedDrop Rate Is Increased
as Queue Depth Is Increased as Queue Depth Is Increased
Weighted REDWeighted RED
• WRED:In the event packets need to be dropped, what class of packets should be dropped
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Queuing strategy: random early detection (RED)mean queue depth: 56drops: class random tail min-th max-th mark-prob
0 4356 0 20 40 1/101 0 0 22 40 1/102 0 0 24 40 1/103 0 0 26 40 1/104 0 0 28 40 1/105 0 0 30 40 1/106 0 0 33 40 1/107 0 0 35 40 1/10
rsvp 0 0 37 40 1/10
Uncontrolled Congestion
Uncontrolled Uncontrolled CongestionCongestion
Managed CongestionManaged Managed
CongestionCongestion
Adjustable Drop Probabilities(from “show interface”)
UncontrolledUncontrolledCongestionCongestion
ManagedManagedCongestionCongestion
DataDataFlowFlow
Prec = 0Prec = 0
VoiceVoiceFlowFlow
Prec = 5Prec = 5
WRED Congestion AvoidanceWRED Congestion AvoidanceMaximize Data GoodputMaximize Data Goodput
• Accommodate burstiness• “Less” drop probability for higher priority flows (VoIP)• Does not protect against flows that do not react to drop
For example, extremely heavy UDP flow can overflow WRED queue
1264010985_05f9_c1 © 1999, Cisco Systems, Inc.
End Points Send Unicast Signaling Messages (RSVP PATH + RESV)
RSVP PATH Message
RSVP RESV Message
RSVP enabled router sees the PATH and RESERVE messages and allocate the
appropriate queue space for the given flowNon RSVP enabled
routers pass the VoIPflow as best effort
FXS FXS
RSVPRSVP
• IETF signaling protocolReservation of bandwidth and delay
• Flow can be signaled by end station or by router (static reservation)
• For H.323 VoIP:Effective as a BW reservations mechanismNot effective as Call Admisions Control: RSVP signaling takes place after call setup as port numbers need to be known
Bandwidth Reservation
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Central to Remote Speed Mismatch
Traffic Shaping—Prevents Delay or Loss in WAN—A MustA Must
Remote to Central Over Subscription—Do NotDo Not
Add additional T1’s at Central Site, orTraffic Shaping—from Remotes at Reduced Rate (< Line Rate)
Remote SitesT1
CentralSite
128 kbps
256 kbps
512 kbps
768 kbps
T1
WAN Provisioning/WAN Provisioning/Design ConsiderationsDesign Considerations
Frame Relay, ATM
1284010985_05f9_c1 © 1999, Cisco Systems, Inc.
Moral of the StoryMoral of the Story——““Know Your CarrierKnow Your Carrier””
Bursting ConsiderationsBursting Considerations““GuidelinesGuidelines””
• Single PVC—limit bursting to committed rate (CIR)The safest—you are guaranteed what you pay for
• Single PVC—mark data discard eligibleYour data gets dropped first upon network congestion
• Single PVC—utilize BECN’s, foresight or ABROnly invoked when congestion has already occurredRound trip delays—Congestion indication must get back to source
• Dual PVCs—one for voice and one for dataOne for data (may burst), one for voice (keep below CIR)
Must Perform PVC prioritization in frame cloud (Cisco WAN gear does)Fragmentation rules still apply for data PVC
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Traffic Shaping OverviewTraffic Shaping Overview
• VoIP-over-serial:
needs no traffic shapingBW is guaranteed at line speed
• VoIPovFR and VoFR:
Use FRTS - applicable per VCGTS is applicable only per interface - does not have the desired effect when voice and data PVCs exist on the interfaceSet min-CIR equal to “voice bandwidth” + a little overhead to ensure good voice quality under WAN congestion situationsOn PVC carrying voice, shape strictly to CIR - don’t burst
• VoATM:Use ATM traffic shaping
Traffic Shaping
1304010985_05f9_c1 © 1999, Cisco Systems, Inc.
1. Central to Remote-Site Speed Mismatch2. To Avoid Remote to Central Site Over-Subscription3. To Prohibit Bursting above Committed Rate
What Are You Guaranteed Above Your Committed Rate?
Traffic ShapingTraffic Shaping——When and Why?When and Why?
RemoteSites
T1
CentralSite
Frame Relay, ATM
128 kbps
256 kbps
512 kbps
768 kbps
T1
Result:Buffering which Will Cause Delayand Eventually Dropped Packets
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Traffic Shaping“Average” Traffic Rate Out of an Interface
Challenge—Traffic Still Clocked Out at Line RateCIR (Committed Information Rate)
Average Rate over Time, Typically in Bits per Second
Bc (Committed Burst)Amount Allowed to Transmit in an Interval, in Bits
IntervalEqual Integer of Tme Within 1 sec, Typically in ms. Number of Intervals per Second
Depends on Interval Length Bc and the Interval Are Derivatives of Each Other
Interval Bc CIR
125 ms 8000 bits 64 kbps= =
Be (Excess Burst)Amount Allowed to Transmit Above Bc per Second
Example
Understanding Shaping ParametersUnderstanding Shaping ParametersFrame RelayFrame Relay
1324010985_05f9_c1 © 1999, Cisco Systems, Inc.
Rate
Time
Port speed
CIR <Bc=Bc >Bc
Frame Relay Traffic ShapingFrame Relay Traffic Shaping
• Frame relay traffic shaping shapes total PVC traffic to conform to CIR, Bc and Be.
• It is possible to use access lists to mark some data streams as DEEnsures that if the total PVC traffic exceeds the traffic contract (CIR/Bc) and the carrier network tags or drops traffic to compensate, the data is dropped and the voice is not affected
However, there is no mechanism which allows non-voice traffic to be marked DE only when in excess of the traffic contract.
Traffic Shaping
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0 ms 125 ms 250 ms 375 ms 500 ms 625 ms 75 0ms 875 ms 1000 ms
125 ms Interval = 8000 bits
64000 bps
High Volume Data Flow Towards a 128 kbps Line Rate Shaping to 64 kbps
Net Result:Line Rate128 kbps
Interval = Bc CIR
Bits per Interval ofTime at 128 kbps Rate
128,000bits
0bits
16000bits
32000bits
48000bits
64000bits
80000bits
96000bits
112000bits
8000 X 8 = 64 bkps
62.5 ms
Cisco Default Bc=1/8 CIR = 125 ms Interval
ExampleExample——Traffic Shaping in ActionTraffic Shaping in Action
TimeTime—1 Second1 SecondWhen 8000 bits (Bc) TransmittedWhen 8000 bits (Bc) TransmittedCredits Are Exhausted and No MoreCredits Are Exhausted and No More
Packet Flow in that Interval.Packet Flow in that Interval.This Happens at the 62.5 ms PointThis Happens at the 62.5 ms Point
of the Interval.of the Interval.
When a New Interval Begins Bc (8000 bit). Credits When a New Interval Begins Bc (8000 bit). Credits Are Restored and Transmission May Resume. Are Restored and Transmission May Resume. Pause in Transmission Is 62.5 ms in the Case. Pause in Transmission Is 62.5 ms in the Case.
1344010985_05f9_c1 © 1999, Cisco Systems, Inc.
0 ms 125 msTime
Set Bc Lower if Line Rate to CIR Ratio Is HighExample: T1 Line Rate Shaping to 64 kbps
Traffic Flow
125 msInterval
0bits
193000bits
5 ms5 ms0 ms 15 msTime
Traffic Flow
Bits per incrementof time at 128kbps
0bits
23000bits
.6 ms.6 ms
125ms Interval = 8000 Bc 64kbps CIR
T1 can transmit 193,000 bits in 125 ms
Bc = 8000
15ms Interval = 1000 Bc
64kbps CIR
T1 can transmit 23,000 bits in 15 ms
Bc = 1000
120 ms120 ms 10 ms10 ms
15 msInterval
Bc setting Considerations for VoIPBc setting Considerations for VoIP
At T1 Rate 8000 Bits (Bc)At T1 Rate 8000 Bits (Bc)Are Exhausted in 5 ms. HaltingAre Exhausted in 5 ms. Halting
Traffic Flow for that PVCTraffic Flow for that PVCfor the Rest of that Interval.for the Rest of that Interval.
Even for Voice!Even for Voice!
120 ms of Potential Delay120 ms of Potential Delayfor Voice Until New Intervalfor Voice Until New Interval
Begins and Bc Credits Begins and Bc Credits Are RestoredAre Restored
At T1 Rate 1000 Bits (Bc)At T1 Rate 1000 Bits (Bc)Still Are Exhausted in 5 ms. Still Are Exhausted in 5 ms.
Halting Traffic Flow for that PVCHalting Traffic Flow for that PVCfor the Rest of that Interval.for the Rest of that Interval.
Even for Voice!Even for Voice!
10 ms of Potential Delay10 ms of Potential Delayfor Voice Until New Intervalfor Voice Until New Interval
Begins and Bc Credits Begins and Bc Credits Are RestoredAre Restored
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High Speed WAN BackboneHigh Speed WAN BackboneFrame Relay/ATM ExampleFrame Relay/ATM Example
Regional OfficeHeadquarters
7500> 2 meg
7200High Speed
WAN
ATM
•• PrioritizationPrioritizationIP-ATM CoS - with IP
Prec
•• Link EfficiencyLink EfficiencyN/A
•• Traffic ShapingTraffic ShapingShape to VC
Parameters
Burst with care
Frame Relay
•• PrioritizationPrioritizationWFQ - With IP Prec
•• Link EfficiencyLink EfficiencyFRF.12 if remote is low
speed
•• Traffic ShapingTraffic ShapingFrame Relay Traffic
Shaping
Shape to CIR or Burst with care
Point to Point
•• PrioritizationPrioritizationDWFQ/CBWFQ - with IP
Prec
•• Link EfficiencyLink EfficiencyN/A
•• Traffic ShapingTraffic ShapingN/A
1364010985_05f9_c1 © 1999, Cisco Systems, Inc.
Central / Regional Office7200 / 7500
64 kbps
Pt to Pt Considerations•• PrioritizationPrioritization
PQ-WFQ/IP RTP Priority (if available)WFQ/CBWFQ with IP Precedence
•• Link EfficiencyLink EfficiencyMLPPP with Fragmentation and
InterleaveVAD (If Desired)CRTP (If Desired)
•• Traffic ShapingTraffic ShapingN/A
Branch Office
3600
Low Speed WAN Edge: PtLow Speed WAN Edge: Pt--toto--PtPt
Low Speed Edge: <2M
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1374010985_05f9_c1 © 1999, Cisco Systems, Inc.
Branch Office
Central / Regional Office7200 / 7500
128 kbps
T1
3600
FrameRelay
Remote Branch Considerations
•• PrioritizationPrioritizationPQ-WFQ/IP RTP Priority (if
available) WFQ with IP Precedence
•• Link EfficiencyLink EfficiencyFRF.12VAD (If Desired)CRTP (If Desired)
•• Traffic ShapingTraffic ShapingFRTSShape to CIR or Burst with care
Central Site Considerations•• PrioritizationPrioritization
PQ-WFQ/IP RTP Priority (if available) WFQ with IP Precedence
•• Link EfficiencyLink EfficiencyFRF.12 PVCs to low speed remotes MUST
use FRF.12VAD (If Desired)CRTP (If Desired)
•• Traffic ShapingTraffic ShapingFRTSShape to CIR or at minimum remote’s line rate - Burst with care
Low Speed WAN Edge: Frame Low Speed WAN Edge: Frame RelayRelay
Low Speed Edge: <2M
1384010985_05f9_c1 © 1999, Cisco Systems, Inc.
Central / Regional Office7200 / 7500
ATM
Central Site + Remote Branch Considerations•• PrioritizationPrioritization
IP-ATM CoS with IP Precedence
•• Link EfficiencyLink EfficiencyT1 and above “typically” not needed
•• Traffic ShapingTraffic ShapingShape to VC ParametersBurst with care
Low Speed WAN Edge: ATMLow Speed WAN Edge: ATM
ATM typically greater than T1
Branch Office
3600
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1394010985_05f9_c1 © 1999, Cisco Systems, Inc.
SummarySummary
• Voice traffic engineering principles still apply
• Packet-based voice trunks can provide efficiency with high quality if properly engineered
• The biggest impact on voice quality over a data network will be as a result of the delay and delay variation
1404010985_05f9_c1 © 1999, Cisco Systems, Inc.
QoSQoS Tools CategoriesTools Categories
• PrioritizationPurpose: Give priority treatment to real-time sensitive traffic
Queuing /Scheduling: WFQ, CBWFQ, IP RTP Priority (PQ-WFQ), WREDClassification (Tagging, Marking, Colouring): IP Precedence, CAR, DSCP, IP RTP Reserve, IP RTP Priority
• Link/Bandwidth EfficiencyPurpose: Limit delay on slow links
Fragmentation & Interleaving (LFI): FRF.12, MLPPP, MTU SizeCompression: Header compression (CRTP), payload compression (codec)
Send Fewer Packets: Variable Size Payload, VAD
• Traffic ShapingPurpose: Smooth out speed mismatches
GTS, FRTS, ATM TS
• Bandwidth ManagementPurpose: Check/reserve/restrict bandwidth for certain flows
BW Reservation/Guarantee: RSVP, CBWFQ, IP RTP PriorityCall Admissions Control: RSVP, GK zone bandwidth, # ingress ports
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ChallengeChallenge SolutionsSolutions
Packet ResidencySlow Link Freeze-out by
Large Packets
InterleavingFRF.12, MLPPP, IP MTU Size
Reduction, Faster Link
Bandwidth ConsumptionHeader Size on Low
Bandwidth Links
CompressionCodecs, RTP Header Compression,
Voice Activity Detection
WANOversubscription, Bursting
Traffic ManagementRouter Traffic Shaping to CIR, High Priority PVC, Data Discard Eligibility
VoIP Low Speed Link (<768 VoIP Low Speed Link (<768 KbpsKbps) ) Challenges and SolutionsChallenges and Solutions
CongestionDelay and Delay Jitter
Intelligent QueuingWFQ, IP Precedence, RSVP,
Priority Queuing
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