voice over ip for carriers. 2all rights reserved © 2001, alcatel agenda advantages of packet...
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Voice over IPfor Carriers
2 All rights reserved © 2001, Alcatel
Agenda
Advantages of packet switching for voice communications
VoIP applications
VoIP technology overview
VoIP standards
Quality-of-Service in VoIP networks
Addressability in VoIP networks
VoIP regulatory considerations
3 All rights reserved © 2001, Alcatel
What is VoIP?
Technical answer:
“the ability to make phone calls over IP-based data network”
Commercial answer:
”the Multi-Billion Revenue Opportunity for the 21st Century”
VoIP > IP Telephony typically “IP Telephony” indicates using IP terminals most VoIP is between normal telephones
VoIP < “Voice over Packet” includes Voice over Frame Relay, ATM
4 All rights reserved © 2001, Alcatel
Circuit switching served voice wellfor 100 years!
Transmission circuits and switch path assigned during call setup for the duration of the call
Call blocks if not enough network resources available Essentially one class of service: 3.5 kHz, 64 kb/s Poorly matched for bursty data transmission
User - A User - B
LoopTrunkGroup
CentralOffice - A
CentralOffice - B
Signal System 7Data link
Signal TransferPoint
TransitOfficeClass 5
Switching System Connection ThroughSwitching Fabric
Class 4Switching System
5 All rights reserved © 2001, Alcatel
Packet SwitchingWell-matched for data transmission
Great fit for bursty data transmission! Packets sent at full rate of transmission facility Supports variable information transfer rates Resources not consumed when nothing to send Potential to eliminate call setup phase
But … Transmission capacity used for header Buffering introduces varying delays
HeaderPacket
PayloadInput Buffer
Output BufferHdr. Trans
Hdr. Trans
RoutingFabric
6 All rights reserved © 2001, Alcatel
VoIP Network Architecture
Media gateways provide voice packetization Media gateway controller provides call control logic Signaling gateway provides interworking with SS7
signaling of PSTN
IPnetwork
MediaGateway
MediaGateway
Controller
MediaGateway
PSTNnetwork
SignalingGateway
7 All rights reserved © 2001, Alcatel
Advantages of VoIP
Regulatory arbitrage (e.g., lack of access charges) Low entry barrier competition with incumbent carriers Cheaper switching systems
Per Gb/s, IP routers cheaper than TDM Class 5 switching systems
Ability to operate one network for voice and data Cost savings through use of
low-bit-rate voice Ability to offer more complex services
E.g., Multimedia, multiport calls Intelligent terminals (e.g., PC)
Better (graphical) user interface Clean slate design:
Separation of feature intelligencefrom switching fabric supplier
Self-provisioning networks
8 All rights reserved © 2001, Alcatel
PSTN Vs VoIP Network Costs
Network costs (transmission and switching costs) contribute only 10-15 % of overall cost of a voice call terminated by an ILEC or a PTT, and 20-30% of overall costs for calls not terminated by a ILEC or a PTT
Of the network costs, switching costs range between 50 % of network costs for domestic calls to 15 % of network costs for international calls, transmission costs contributing the rest
Negligible savings in transmission costs through the use of VoIP: lower bandwidth for VoIP offset by need for over-provisioning bandwidth to ensure quality
TDM Switch costs in traditional PSTN replaced by cost of Router plus cost of Gateway [GW] plus cost of Gateway Controller [GWC] plus cost of new OSS/NMS/Billing /Provisioning
No network cost savings, and very likely a cost penalty, in the initial years, in going from PSTN voice to VoIP for public networks
9 All rights reserved © 2001, Alcatel
PSTN versus VoIP
Today’s PSTN VoIP
Underlying Technology
TDM circuit switching Packet switching
QoS guarantees Yes No
Network resource reserved at call setup
Yes No
Network elements Class 4, Class 5 switching systems
Gateways, gateway controllers, routers
Call processing intelligence
Mostly integrated in switching system
In separate gateway controllers
Bandwidth per call 64 kb/s Variable 8 – 32 kb/s
Signaling DTMF, SS7 SIP, H.323
Transport TDM in access, edge, core
ATM, FR, native IP in access; ATM native
IP in core
How reliability achieved
Redundancy within each network
element
Redundant routes through network
10 All rights reserved © 2001, Alcatel
VoIP versus Voice-over-the-Internet
Voice-over-the-Internet
No bandwidth guarantees
No prioritization of traffic within network
All traffic receives “best effort” service
Each Internet user is at the mercy of all other users
Voice quality ranges from acceptable to atrocious
However
Internet technology continues to evolve (e.g., IPv6)
Development of Next Generation Internet
11 All rights reserved © 2001, Alcatel
What does “Carrier Grade” really mean?
“Five 9’s” reliability (down time of 5 minutes a year) Full redundancy of electronics, power supplies, fans, etc. No down time for upgrades or maintenance
Accounting and billing capabilities Interoperability with legacy telecommunications
equipment Feature parity with equipment it replaces Service quality measurements Support for CALEA, unbundling, and other governmental
mandates NEBS compliance for operation in central offices
Both safety and performance requirements Scalability to millions of subscribers Integration into the myriad of Operations Support
Systems
12 All rights reserved © 2001, Alcatel
VoIP market
Voice over Internet Protocol (VoIP) gateway sales will increase 280 percent during the next five years, reaching $3.8 billion in 2003, according to research by Cahners In-Stat Group.
Voice over Internet Protocol (VoIP) gateway sales will increase 280 percent during the next five years, reaching $3.8 billion in 2003, according to research by Cahners In-Stat Group. IP TELEPHONY OVER LAN MARKET FORECASTED TO GROW
138% AVERAGE ANNUALLY OVER NEXT 5 YEARSSeptember 22, 1999 - IP Telephony
[IP PABXes], according to a study from The Phillips Group-InfoTech, will spawn a $1.9 billion industry by the year 2004 with an average annual industry growth of 138 percent over the next 5 years.
IP TELEPHONY OVER LAN MARKET FORECASTED TO GROW 138% AVERAGE ANNUALLY OVER NEXT 5 YEARSSeptember 22, 1999 - IP Telephony
[IP PABXes], according to a study from The Phillips Group-InfoTech, will spawn a $1.9 billion industry by the year 2004 with an average annual industry growth of 138 percent over the next 5 years.
IDC Forecasts IP Telephony Market Will Soar to 2.7 Billion Minutes of Use and $480 Million in Revenues by Year end
1999Business Use Will Accelerate in 2001September 1, 1999 - The worldwide Internet protocol (IP) telephony will explode from 310 million minutes of use in 1998 to 2.7 billion by year end 1999. By 2004, IP telephony minutes will reach 135 billion. Revenues for this service will skyrocket from $480 million in 1999 to $19 billion by 2004. IP Telephony Services: Market Review and Forecast, 1998-2004.
IDC Forecasts IP Telephony Market Will Soar to 2.7 Billion Minutes of Use and $480 Million in Revenues by Year end
1999Business Use Will Accelerate in 2001September 1, 1999 - The worldwide Internet protocol (IP) telephony will explode from 310 million minutes of use in 1998 to 2.7 billion by year end 1999. By 2004, IP telephony minutes will reach 135 billion. Revenues for this service will skyrocket from $480 million in 1999 to $19 billion by 2004. IP Telephony Services: Market Review and Forecast, 1998-2004.
13 All rights reserved © 2001, Alcatel
Growth in VoIP
0.0
5.0
10.0
15.0
20.0
25.0
2000 2001 2002 2003 2004 2005 2006
Re
ve
nu
es
($
bill
ion
)
Early growth from expense
savings
Later growth from revenue
generation from new services
Early deployment by
enterprises and CLECs
Later deployment by
incumbent carriers
(source: Frost & Sullivan)
14 All rights reserved © 2001, Alcatel
Class 5 DLCClass 5DLC
VoIP Applications
Some trends can be discerned:
First wave: Bypassing the PSTN
Second wave: Replacing the PSTN
Third wave: Value-added services
PSTN
15 All rights reserved © 2001, Alcatel
PSTN bypass – IP Telephony (PC to PC)
Microsoft NetMeeting or similar through dial-up connection to ISP
All VoIP processing in the PC no special infrastructure required
Issues: software compatibility QoS / latency over public Internet
Internet
Class 5 DLCClass 5DLCRAS RAS
modem modem
RADIUSserver
RADIUSserver
16 All rights reserved © 2001, Alcatel
PSTN bypass – IP Telephony (PC to phone)
From Multimedia PC to any phone
Required: VoIP gateway on the phone side gateway manager billing system (unless free)
Issues: software compatibility QoS / latency over public Internet
Internet
Class 5 DLCClass 5DLCRAS
RADIUSserver
VoIPGateway
GateKeeper
modem
17 All rights reserved © 2001, Alcatel
PSTN bypass – IP Telephony (phone to phone)
From any phone to any phone First VoIP application – 1995 Caused by high international tariffs
Required: VoIP gateway on both sides gateway manager billing system (unless free)
Issues: QoS / latency over public Internet sometimes it takes 24 digits to reach
a subscriber…
Class 5 DLCClass 5DLCVoIP
Gateway
GateKeeper
VoIPGateway
IPnetwork
18 All rights reserved © 2001, Alcatel
PSTN bypass – Enterprise gateway
Link PABXes on company sites through data network first Voice over Frame Relay, next Voice over IP
Required: VoIP gateway at each site
sometimes integrated in WAN router
Issues: dial plan configuration not easy!
IPnetwork
PABX PABX
PSTN
VoIPGateway
VoIPGateway
19 All rights reserved © 2001, Alcatel
PSTN bypass – IP PABX
Two steps:
A. PABX with integrated IP gateway B. Fully integrated enterprise LAN
Required: IP PABX IP phones (step 2)
Issues: dial plan configuration not easy! how to quarantee QoS on LAN? (step 2)
IPnetwork
IP-PABX IP-PABXIP-phone
PSTN
A B
20 All rights reserved © 2001, Alcatel
PSTN replacement – Softswitch
Replace complete Class 4 / Class 5 switch very ambitious undertaking! different introduction strategies
Required Softswitch - contains Call Control & Mgmt software Trunking Gateway – interfaces to “legacy” PSTN Access Gateway – interfaces to DLCs
Issues: immaturity of standards (MGCP vs Megaco debate)
DLCClass 5DLCAccess
GatewayTrunkingGateway
Softswitch
IPnetwork
21 All rights reserved © 2001, Alcatel
PSTN replacement – Integrated access network
Integrating Access Gateway into DLC
Required: “Next Gen” DLC, with integrated IP gateway
Issues: immaturity of standards
NexGenDLC
NexGenDLC
Softswitch
IPnetwork
22 All rights reserved © 2001, Alcatel
Class 5
PSTN
GateKeeper
VoIPGateway
IntegratedAccess Device
PSTN replacement – Integrated Access Devices
Target: single voice/data access network for example wireless access network (LMDS, WLL)
Required: Integrated Access Device (IAD) gateway to PSTN
Issues: immaturity of standards
IntegratedAccess Device
IPnetwork
Softswitch
23 All rights reserved © 2001, Alcatel
Value Added Services
Converged services Internet Call Waiting Click to Call Unified messaging …
Video telephony (3rd time right?)
24 All rights reserved © 2001, Alcatel
Application Scenario
Mike Brown uses his Palm XIXv for voice calls and Internet access. He subscribes to “Mobile Web” from Verizon Wireless.
Mike is wallpapering, but has some trouble. He calls Home Depot for help. Mike reaches Home Depot’s IVR and is greeted with the
following: “Hi Mike, welcome back to Home Depot, the only choice you need in home improvement supplies and help. Press 0 at any time to speak with an operator. To help with you home improvement needs, we have created a number of short videos which are available free of charge to Preferred Customers such as yourself. To access the video library, say ‘Video’. Otherwise, please say ‘Sales’ for sales; ‘Delivery’ to schedule a delivery; “’Service’ for Customer Service, or ‘Message’ to leave a message. Have a great day.”
Mike mumbles ‘Video’.
25 All rights reserved © 2001, Alcatel
Application Scenario (Cont.)
Announcement “Welcome to Home Depot’s video library. Our database indicates you have a PalmPhone so we will play the streamed video. Please say ‘email’ if you prefer the video as email attachment. [short silence]Please make your selection from the following list of home improvement videos by pressing the corresponding number at any time. 1 for hardwood floors, 2 for interior painting, 3 for wallpapering, 4 for outside lighting”
Mike says ‘3’. Announcement: “Thank You. We hope the video on
wallpapering is helpful. Please press ‘video’ on your screen, and your video should start within a few seconds. Have a great day.”
Mike presses “play video” on the PalmPhone screen. Video starts (advertising opportunity/branding
opportunity, with hotlinks back to Home Depot site and context-sensitive buttons to contact product specialists).
Standards for VoIP
27 All rights reserved © 2001, Alcatel
The H.323 Protocol Stack
H.225RAS
channel
H.225RAS
channel
Q.931call
setup
Q.931call
setup
H.245control
H.245control
AudioAnd
VideoControl
RTCP
AudioAnd
VideoControl
RTCP
T.120T.120
AudiocodecG.711G.723G.729
AudiocodecG.711G.723G.729
VideoCodecH.261H.263
VideoCodecH.261H.263
RTPRTP
Transport Layer (TCP or UTP)Transport Layer (TCP or UTP)
IPIP
System control user interface Mic CameraData
applications
28 All rights reserved © 2001, Alcatel
Real-Time Transport Protocol
Developed by IETF Provides end-to-end delivery services for data with real-
time characteristics such as interactive audio and video. Supports a wide variety of fixed and variable-speed audio
and video signals Applications typically run RTP on top of UTP Supports multicast distribution
V=2
P X CC M PT Sequence Number
Timestamp
Synchronization Source Identifier
Contributing Source Identifiers (0 to 15 entries)
P – PaddingX – ExtensionCC – Contribution source count
M – Marker (for silence suppression)PT – Payload type
29 All rights reserved © 2001, Alcatel
RTP Control Protocol (RTCP)
Sent from receiver back to source Used to monitor the quality of service Feedback allows modifications to be made at source 5 percent of session bandwidth allocated to RTCP
V=2 P PT=SR=200 Length
SSRC of sender
NTP Timestamp (Network time)
NTP Timestamp
RTP Timestamp (Network time in RTP units)
Sender’s packet count
Sender’s octet count
SSRC of first cource
Fraction lost Cumulative number of packets lost
Extended highest sequence number received
Interarrival jitter
Last SR
Delay since last SR
30 All rights reserved © 2001, Alcatel
H.225 RAS Control
Gatekeeper Optional network entity Offers bandwidth control services Offers address translation to enable use of aliases
H.225 Operates between a Gatekeeper and the endpoints it
controls Provides functions of discovery, registration, admission,
bandwidth change, disengage
GatekeeperEndpoint
GatewayMultiportControl Unit
H.225
31 All rights reserved © 2001, Alcatel
Call Signaling in H.232
Q.931 Establishes and tears down calls between endpoints (Q.931 is the signaling protocol for the ISDN user-network
interface) H.245
Negotiates and establishes media streams between call participants
Takes care of multiplexing multiple media streams for functions such as lip synchronization between audio and video
Q.931
H.245
32 All rights reserved © 2001, Alcatel
Session Initiation Protocol (SIP)
User to user protocol Developed by IETF (RFC 2543) Establishes and maintains session level information
Creating and tearing down of sessions, session parameters, and media type
Supports personal mobility Heavily influenced by http protocol A light weight protocol compared to H.323
Fewer messages required on a typical call Allows for faster call setup
Flexible in enabling other information to be included messages Allows user devices to exchange specialized information
to enable new services E.g., indicate when a busy terminal will become free
Example SIP addressing; sip:9729965000@gateway
33 All rights reserved © 2001, Alcatel
Internet call processing
Decentralized (independent, self-reliant, user to user):
ITU H.323
IETF Session Initiation Protocol (SIP)
Centralized (intelligence in Softswitch):
IETF MEGACO
ITU H.248
34 All rights reserved © 2001, Alcatel
Softswitch Architecture
Softswitch separates function of Gateway from the media gateway
AccessGateway
TrunkGateway
Softswitch
IPNetwork
PSTNNetwork
MGCPOr
Megaco
SIP-TTo other
Softswitches
35 All rights reserved © 2001, Alcatel
ATM QoS Parameters
Peak-to-peak cell delay variation
Maximum cell transfer delay
Cell loss ratio
Cell error ratio
Severely errored cell block ratio
Cell misinsertion rate
Negotiated at start of call
Controlled viaNetwork design
36 All rights reserved © 2001, Alcatel
Real-Time Multimedia over ATM (RMOA)
Developed by ATM Forum More efficient and scalable than H.323 VoIP over ATM New type of gateway: the H.323 to H.323 gateway
Placed at the edges of an ATM network Intercepts H.323 signaling messages to set up virtual circuits in
the ATM network Efficient: IP and UDP headers not carried on the ATM network Takes advantage of QoS capabilities of the ATM network
ATMnetwork
PSTNSwitch
PSTNSwitch
IP Network
VoIPGateway
VoIPGateway
H.323Gateway
H.323Gateway
37 All rights reserved © 2001, Alcatel
Resource Reservation Protocol (RSVP)
Specified in RFC 2215 Reserves resources along path from received back to sender Implements various services
Guaranteed service – no packet loss and minimal delay Controlled load service – service like a lightly loaded network Number of parameters associated with each service
Comprehensive, close to circuit emulation, but at significant cost
Application RSVPProcess
PolicyControl
AdmissionControl
PacketScheduler
PacketClassifier
Control
RoutingProcess
RSVPProcess
PolicyControl
AdmissionControl
PacketScheduler
PacketClassifier
Control
Host Router
38 All rights reserved © 2001, Alcatel
Adding QoS to IP Networks: Diffserv
Relatively simple means for prioritization traffic (RFC 2475) Makes use of the IPv4 Type of Service (TOS) field Defines two types of packet forwarding:
Expedited Forwarding – assigns a minimum departure rates greater than the per-agreed maximum arrival rate
Assured Forwarding – packets are forwarded with high probability if arrive no faster that per-agreed maximum
Keeps core relatively simple Pushes processing to the edge
Meter
Classifier MarkerShaper /Dropper
VoIP access via DSL and Cable
Modems
All rights reserved © 2001, Alcatel
Cable Telephony
Where to put the RJ-11 telephone jack? On cable modem On set-top box On separate telephony modem On interface on side of house
Local powering or network powering options
Headend
Headend
VideoContent
FiberNode
InternetService
GatewayPSTN
All rights reserved © 2001, Alcatel
What is DOCSIS?(Data Over Cable System Interface
Specifications)
Started 12/95 by MCNS consortium (Multimedia Cable
Network System)
Goal: Interoperable cable modems and Cable Modem
Termination Systems (CMTS)
Steamed rolled slower (ATM-based) IEEE 802.14
standardization process
Gaining momentum in Europe as EuroDOCSIS
(8 MHz channelization)
Testing and certification by Cable Labs
All rights reserved © 2001, Alcatel
Who are the DOCSIS Cable Modem Suppliers?
3Com Ambit Arris Interactive Askey Computer Corp. Best Data Castlenet Cisco Systems Com21 Dassault DeltaKable DX Antenna ELSA E-Tech Future Networks GadLine Toshiba
Turbocom General
Instrument GVC Joohong Motorola Net N Sys Nortel Philips Powercom Samsung Sohoware Sony Tarayon Thomson Zoom ZyXel
All rights reserved © 2001, Alcatel
Cable ModemsMore suppliers, lower prices
0
1000
2000
3000
4000
5000
6000
1990 1992 1994 1996 1998 2000
Cab
le M
odem
Pri
ce
5 Suppliers
32 Suppliers
All rights reserved © 2001, Alcatel
What is Packet Cable?
Network specification by Cable Labs
Based on DOCSIS 1.1
Support for voice services
Complete network architecture specification
First using GR 303 gateways (to legacy telephone networks)
Evolving to Softswitch (next generation IP networks)
Trials underway
All rights reserved © 2001, Alcatel
CableLabs Packet Cable Architecture
Managed IPNetwork
HFC AccessNetwork(DOCSIS)
MTACable
Modem CMTS
CallManagement
Server(CMS)
AnnouncementController
(ANC)
AnnouncementPlayer(ANP)
AnnouncementServer
PSTN
OSSBack OfficeServers andApplications
HFC AccessNetwork(DOCSIS)
MTACable
Modem CMTS
Media GatewayController
(MGC)
Media Gateway(MG)
Signaling Gateway(ANP)
46 All rights reserved © 2001, Alcatel
Status of VoIP over Cable
Cable executive panel at Cable 2001 (June 11, 2001):
Most cable operators will not roll out significant VoIP until at least the end of 2002
Concerned about the operational issues that come with providing a voice service
General agreement that VoIP economics work in their favor if combined with existing cable services
Some view VoIP as primary line replacement; others (e.g., Time Warner) as second line service
All rights reserved © 2001, Alcatel
North America Cable Telephony
02,0004,0006,0008,000
10,00012,00014,00016,000
Mill
ion
Ho
useh
old
s
CircuitSwitched
VoIP
Total
Cable projected to capture 15 % telephony market share by 2005
Shift from proprietary TDM solutions towards VoIP DOCSIS
Residential VoIP happening first in the Cable Access Market
North America Cable TelephonyMarket Size
48 All rights reserved © 2001, Alcatel
Class 5Switch
ATMSwitch
VoiceGate Way
Integrated Access Device
DSLAM LAN1 VC for Voice1 VC for Data
ADSLDS3 / OC-3
GR303
HOME/BUSINESS
CO / CEVCO
4-16
Voice over DSL
Integrated Access Device (IAD) provides LAN interface and provides multiple telephone interfaces
IAD could be integrated into NID at side of the home Voice Gateway provides same switch interface as though lines
were concentrated on a Digital Loop Carrier system GR303 allows for number portability, billing and additional
voice features
PSTN
DataNetwork
49 All rights reserved © 2001, Alcatel
IP
ATM
DMT
AnalogSpectrum
• Voice over IP
• Voice over ATM
• Voice over TDM
• Voice in separate spectrum(e.g., ADSL over DAML)
Voice over ADSL Alternatives
Choice of Voice over ATM in initial implementations– AAL-2– Low-delay, clear 64 kb/s PCM and 32 kb/s ADPCM– QoS support within ATM– Full PSTN quality– V.90 modem support
Support for Voice over IP gaining momentum Maturing of QoS capabilities Potential of IAD becoming a SIP terminal
Layer 3
Layer 1
Layer 2
Alt
ern
ativ
es f
or V
oDS
L
Quality issues for the transport of
voice over packet-based networks
51 All rights reserved © 2001, Alcatel
The three essential stages of packet-based voice transport
one-way Mouth-to-Ear (M2E) delay
overall distortion (codec & packet loss)
Encoding and packetization stage Packet transport stage
Echo control performed close to destination
(Concatenation of)(Concatenation of) Packet-based Packet-based
Network(s)Network(s)
Dejittering and decoding stage
52 All rights reserved © 2001, Alcatel
PacketizationPacketizationdelaydelay
Total Total queuingqueuing
delaydelay
DejitteringDejitteringdelaydelay
TotalTotalminimalminimal
delaydelay
M2E delay
Components of the M2E delay
Packetization delay is chosen by the source terminal or the source terminal or ingress GWingress GW
Minimal delay and queuing delay depend on QoS QoS provided by traversed network(s)provided by traversed network(s) Each network component has its specific contribution
Dejittering delay is chosen by the destination terminal the destination terminal or egress GWor egress GW
53 All rights reserved © 2001, Alcatel
Trade-off M2E delay vs. packet loss in destination or egress GW
Packet lossPacket loss
DejitteringDejittering delaydelay
Delay of first packet
Minimal delay
M2E delay
Pdf(delay)Pdf(delay)
Static dejittering mechanism = delay first packet over dejittering delay and then read dejittering buffer periodically
Choose dejittering delay on save side: for the case when first packet is the fastest possible Adaptive dejittering
54 All rights reserved © 2001, Alcatel
Contributions to distortion
Voice compression encoding/decoding
voice activity detection
transcoding
Packet loss in network
in dejittering buffer
Remarks packet loss concealment techniques
trade-off packet loss vs. delay when choosing the dejittering delay
55 All rights reserved © 2001, Alcatel
Trade-offs
Packet Packet size size
Network (transport) parametersNetwork (transport) parameters minimal delayminimal delay delay jitterdelay jitter packet losspacket loss
Codec Codec
Efficiency of transport Efficiency of transport Voice quality Voice quality
Dejittering Dejittering delay delay
Echo Echo control control
Header Header compression compression
56 All rights reserved © 2001, Alcatel
The E-modelITU-T Rec. G.107
RR = = RR00 - - IIss - - IIdd - - IIee + + AA
Rating Factor in [0,100]Rating Factor in [0,100]
Objective network parameters
Basic signal-to-Basic signal-to-noise rationoise ratio
Distortion Distortion impairmentimpairment
AdvantageAdvantagefactor factor
Mean Opinion Score (MOS)
Predictions of user reactions:
E-model
Subjective quality measures
Impairments Impairments which occur which occur
simultaneously simultaneously with voice with voice
signalsignal
ImpairmentImpairments caused by s caused by
delaydelay
57 All rights reserved © 2001, Alcatel
Subjective quality of a voice communication
Defined quality categories in ITU-T Rec. G.109
R-value range 100 - 90 90 - 80 80 - 70 70 - 60 60 - 0
Speech transmissionquality category
best high medium low (very) poor
PSTN quality
GSM quality
(very) poor(very) poor
bestbest
highhigh
mediummedium
lowlow
Traditional PSTN qualityTraditional PSTN quality
1
1.5
2
2.5
3
3.5
4
4.5
5
0 10 20 30 40 50 60 70 80 90 100
Rating R
MO
S
58 All rights reserved © 2001, Alcatel
The E-model in the context of VoP
In the transport of Voice over Packet-based (VoP) Networks M2E delay distortion
is likely to be higher, acoustic echo may be more important and 4-to-2-wire
hybrid echo might be different
than in circuit-switched voice transport With the E-model we determine (the influence of Id and
Ie)
RR = = ff ( ( M2E delay, level of echo M2E delay, level of echo ;; codec(s), packet losscodec(s), packet loss))
We do not consider influence of Ro , Is and A as their influence is not fundamentally different in packet-based and circuit switched transport
59 All rights reserved © 2001, Alcatel
Influence of distortion
RR = = ff ( ( M2E delay, level of echo M2E delay, level of echo ;; codec(s), packet losscodec(s), packet loss)) Intrinsic rating RRintint = rating for a M2E delay of 0 ms In the context of VoIP, there are two impairments that
mainly hamper the quality of a voice call The impairment Ie associated with the use of “special
equipment” or distortion Coding Packet loss Transcoding
The impairment Id associated with the M2E delay
60 All rights reserved © 2001, Alcatel
Speech Coding Techniques
Waveform coding – Tries to preserve the time-domain picture of the signal Sampling – 2 X highest frequency preserved Quantizing – the accuracy of each sample
Linear – simple digital / analog conversion Logarithmic – more accuracy for weak signals Adaptive – match measurement to size of signal
Sounds great at high bit rates but degrades quickly at lower bit rates
Vocoding – Tries to represent the characteristics of the human voice Prametric Vocoders
Dozen coefficients to define vocal tract Indication of voiced or unvoiced Excitation energy Pitch
Synthetic sounding at all bit rates but works OK at low bit rates Vector Quanitization – Matches information signal with entries
in a code book. Uses lots of processing power but provides the best quality at lower
bit rates
61 All rights reserved © 2001, Alcatel
Major Parameters of Standard Codecs
Origin Standard TypeCodecBit rate
VoiceFrame (ms)
Look ahead (ms)
Algor.delay (ms)
leIntrinsicquality
ITU-T
G.711 PCM 64
0.125 0 0.125
0 94.3
G.726G.727
ADPCM
16 50 44.3
24 25 69.3
32 7 87.3
40 0.125 0 0.125 2 92.3
G.728 LD-CELP12.8
0.625 0 0.62520 74.3
16 7 87.3
G.729(a) CS-ACELP 8 10 5 15 10 84.3
G.723.1ACELP 5.3
30 7.5 37.519 75.3
MP-MLQ 6.3 15 79.3
ETSI
GSM-FR RPE-LTP 13 20 0 20 20 74.3
GSM-SR VSEPL 5.6 20 0 20 23 71.3
GSM-ESR ACEPL 12.2 20 0 20 5 89.3
62 All rights reserved © 2001, Alcatel
Intrinsic quality of codecs as function of their bit rate
0
10
20
30
40
50
60
70
80
90
100
0 8 16 24 32 40 48 56 64
codec bit rate (kb/s)
Intr
insi
c ra
ting
Rin
t
G.711
G.726
G.728
G.729
G.723.1
GSM-EFR
GSM-FR
GSM-HR
63 All rights reserved © 2001, Alcatel
Influence of packet loss on distortion
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12 14 16packet loss ratio (%)
Intrin
sic
ratin
g R
int
G.729(A) + [email protected] kb/s + VADGSM-EFRG.711 with PLCG.711 without PLC
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CODECG.711
(64kb/s)G.726
(40kb/s)G.726
(32kb/s)G.726
(24kb/s)G.726
(16kb/s)G.728
(16kb/s)GSM-FR(13kb/s)
G.728(12.8kb/s)
GSM-EFR(12.2kb/s)
G.729(8kb/s)
G.723.1(6.3kb/s)
GSM-HR(5.6kb/s)
G.723.1(5.3kb/s)
G.711(64kb/s) 94.3 92.3 87.3 69.3 44.3 87.3 74.3 74.3 89.3 84.3 79.3 71.3 75.3G.726
(40kb/s) 92.3 90.3 85.3 67.3 42.3 85.3 72.3 72.3 87.3 82.3 77.3 69.3 71.3G.726
(32kb/s) 87.3 85.3 80.3 62.3 37.3 80.3 67.3 67.3 82.3 77.3 72.3 64.3 68.3
G.726(24kb/s) 69.3 67.3 62.3 44.3 19.3 62.3 49.3 49.3 64.3 59.3 54.3 46.3 50.3
G.726(16kb/s) 44.3 42.3 37.3 19.3 0 37.3 24.3 24.3 39.3 34.3 29.3 21.3 25.3G.728
(16kb/s) 87.3 85.3 80.3 62.3 37.3 80.3 67.3 67.3 82.3 77.3 72.3 64.3 68.3GSM-FR(13kb/s) 74.3 72.3 67.3 49.3 24.3 67.3 54.3 54.3 69.3 64.3 59.3 51.3 55.3G.728
(12.8kb/s) 74.3 72.3 67.3 49.3 24.3 67.3 54.3 54.3 69.3 64.3 59.3 51.3 55.3GSM-EFR(12.2kb/s) 89.3 87.3 82.3 64.3 39.3 82.3 69.3 69.3 84.3 79.3 74.3 66.3 70.3
G.729(8kb/s) 84.3 82.3 77.3 59.3 34.3 77.3 64.3 64.3 79.3 74.3 69.3 61.3 65.3G.723.1(6.3kb/s) 79.3 77.3 72.3 54.3 29.3 72.3 59.3 59.3 74.3 69.3 64.3 56.3 60.3GSM-HR(5.6kb/s) 71.3 69.3 64.3 46.3 21.3 64.3 51.3 51.3 66.3 61.3 56.3 48.3 52.3G.723.1(5.3kb/s) 75.3 73.3 68.3 50.3 25.3 68.3 55.3 55.3 70.3 65.3 60.3 52.3 56.3
Transcoding matrix
Transcoding is the translation of one codec format into another (via the linearly quantized 8 kHz sampled voice format)
65 All rights reserved © 2001, Alcatel
Influence of M2E delay
RR = = ff ( ( M2E delay, level of echo M2E delay, level of echo ;; codec(s), packet losscodec(s), packet loss)) In the context of VoIP, there are two impairments that
mainly hamper the quality of a voice call The impairment Ie associated with the use of “special
equipment” or distortion The impairment Id associated with the M2E delay
Loss of interactivity Talker echo Listener echo
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Rating as function of M2E delay for traditional G.711 codec (no
packet loss)
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400mouth-to-ear delay (ms)
ratin
g R
EL=11 dBEL=21 dBEL=31 dBEL=41 dBEL=51 dBEL=infinity
packet loss = 0.0%
Interactivity Interactivity boundbound
(150 ms)(150 ms)
Echo Echo controlcontrolboundbound
(25 ms)(25 ms)
Maximum Maximum boundbound
(400 ms)(400 ms)
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Influence of echo control
Echo control can increase the echo loss value EL Echo Controllers compliant with ITU-T Rec. G.168
increase EL by at least 30 dB Even perfect echo control is possible (at the expense of
some distortion) Electrical echo (introduced in 4-to-2-wire hybrid) has
typically EL = 21 dB Acoustic echo is dominant in non-optimized terminals
and is harder to control than electrical echo Echo controller is simpler, if it is close to source of echo Echo control is required in an VoP transport
environment
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Rating for G.711 codec (without PLC)Packet loss: 0%, 0.5% and 1%
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400mouth-to-ear delay (ms)
ratin
g R
EL=11 dBEL=21 dBEL=31 dBEL=41 dBEL=51 dBEL=infinity
packet loss = 0.5%
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400mouth-to-ear delay (ms)
ratin
g R
EL=11 dBEL=21 dBEL=31 dBEL=41 dBEL=51 dBEL=infinity
packet loss = 1.0%
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400mouth-to-ear delay (ms)
ratin
g R
EL=11 dBEL=21 dBEL=31 dBEL=41 dBEL=51 dBEL=infinity
packet loss = 0.0%
69 All rights reserved © 2001, Alcatel
Rating for G.729 codec with VAD Packet loss: 0%, 1%, 2%, 3% and 4%
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400mouth-to-ear delay (ms)
ratin
g R
EL=11 dBEL=21 dBEL=31 dBEL=41 dBEL=51 dBEL=infinity
packet loss = 0.0%
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400mouth-to-ear delay (ms)
ratin
g R
EL=11 dBEL=21 dBEL=31 dBEL=41 dBEL=51 dBEL=infinity
packet loss = 1.0%
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400mouth-to-ear delay (ms)
ratin
g R
EL=11 dBEL=21 dBEL=31 dBEL=41 dBEL=51 dBEL=infinity
packet loss = 2.0%
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400mouth-to-ear delay (ms)
ratin
g R
EL=11 dBEL=21 dBEL=31 dBEL=41 dBEL=51 dBEL=infinity
packet loss = 3.0%
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400mouth-to-ear delay (ms)
ratin
g R
EL=11 dBEL=21 dBEL=31 dBEL=41 dBEL=51 dBEL=infinity
packet loss = 4.0%
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M2E delay and packet loss bounds
If there is no packet loss, the M2E delay can exceed 150 ms If the M2E delay is below 150 ms some packet loss can be tolerated
Origin Standardcodec bit rate (kb/s)
PL bound(%)
G.711 without PLC 64 1G.711 with PLC 64 10G.729(A) + VAD 8 3.4
[email protected] kb/s + VAD 6.3 2.1ETSI GSM-EFR 12.2 2.7
ITU-T
Origin Standardcodec bit rate (kb/s)
M2E delaybound (ms)
G.711 64 40016 NA24 NA32 32440 379
12.8 21216 324
G.729(A) 8 2965.3 2216.3 253
GSM-FR 13 212GSM-HR 5.6 180
GSM-EFR 12.2 345ETSI
ITU-T
G.726G.727
G.728
G.723.1
Bounds under perfect echo control
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Quality of a telephone conversation (using the E-model of ITU-T Rec.
G.107 and G.109)
0
5
10
15
20
25
30
35
40
45
0 50 100 150 200 250 300 350 400
M2E delay (ms)
dis
tort
ion
(Very) Bad(Very) Bad
PoorPoor
MediumMedium
HighHigh
BestBest
Perfect Perfect echo controlecho control
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ConclusionsQuality of a telephone call
(Perfect) echo control is strongly recommended Under perfect echo control the intrinsic quality
remains constant if M2E delay < 150 ms Choose codec to have an intrinsic quality that is
good enough e.g. G.711, G.729, ...
Avoid transcoding from one low bit rate codec into another
Keep M2E delay and packet loss under control bounds are codec-dependent
There is a trade-off between M2E delay and distortion
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ConclusionsSetting the parameters
The quality with which the voice flows are transported influence the overall quality, but …
… the choice of the codec, packet size and dejittering delay is also primordial In the choice of the codec there is a trade-off between
efficiency and quality In the choice of the packet size there is a trade-off
between efficiency and quality Tuning the dejittering mechanism correctly is important
to attain high quality
Addressability inVoIP Networks
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Addressibility in VoIP
Question: How do you dial a VoIP user if all you have is their telephone number?
alcatel.com
ge.com
fcc.gov
ibm.com
Users resistant to change services if they have to change phone numbers
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What is ENUM?
Telephone number mapping (RFC 2916, RFC 2915)
Allows a phone number to enable a caller to reach all
kinds of devices (fax, IP telephone, email, etc.) by
knowing a single contact number
Originally proposed by Patrik Falstrom of Cisco
Uses DNS structure to map an E.164 phone number
into a series of Internet addresses:
SIP, H323, SMTP, VPIM, IPP, etc.
Enables Local Number Portability, 800 services
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DNS-B(0.5.8.9.1.9.1.e164.arpa)
DNS-A(9.1.9.1.e164.arpa)
How does ENUM work?
proxy.comINVITE
INVITE
Answer = sip:n
iel@pro
xy.com
“(919) 850-5500"
Qu
ery
0.0.
5.5.
0.5.
8.9.
1.9.
1.e1
64.a
rpa
Au
tho
rity
= D
NS
-B
Query 0.0.5.5.0.5.8.9.1.9.1.e164.arp
a
78 All rights reserved © 2001, Alcatel
What is TRIP?
Telephony Routing over IP
Identifies gateway for PSTN destinations
Being developed in IETF; currently only in IETF draft
Distributes routes to E.164 prefixes (gateways)
Enables policy based routing
Based on BGP
Real-time recalculation of routes whenever paths
becomes unavailable
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How does TRIP work?
GW-AGW-B
LS-Y
LS-Z
16132-16135,GW-A16136-16139,GW-B
1613,NHSx 1613,NHSw
1613,NHSx
NHSxLS-X
LS-W
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ENUM Implementation Issues
Should ENUM databases be public or commercial? Public ENUM (NeuStar) Commercial ENUM: (NetNumber) (VeriSign keeping its options open on both)
Which agency within the government will be responsible for ENUM implementation within the US
Selection of a Tier 1 ENUM operator for the United States portion of the North American Numbering Plan
State Dept Study Group A ENUM Ad Hoc Formed to develop a recommendation to the USG on its
participation in global and national ENUM implementation Ad Hoc participants intend to form an industry forum to
address the ENUM implementation in the United States
RegulatoryConsiderations
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Context
The third ITU-T World Telecommunication Policy Forum (Geneva, March 7-9 2001) discussed issues related to “Internet Protocol (IP) Telephony”.
The WTPF discussed the impact of IP telephony on regulation and policies of ITU member states and ways for offering technical assistance to developing countries.
A report of the secretary-general and draft opinions for the forum are finalized and available on the ITU website (http://www.itu.int/wtpf).
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What is at stake ?
Beyond the technological hype surrounding IP telephony, the real issue is the structure of the 21st century world-wide telecom network and the nature - and mere existence ! - of the settlement system governing the interconnection between operators.
Many developing countries are fearing that widespread deployment of unregulated IP telephony traffic will dramatically lower the revenue stream drawn from the settlement system and, by way of consequence, the eventual insolvency of their local PTO(s).
The secretary-general’s report on IP telephony is quite objective and factual but the WTPF draft opinion recommendations reflect conflicting interests.
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The “Netheads” view
Driven by CISCO, VON coalition, global operators (Worldcom, AT&T) .
Objective: convince reluctant (mainly developing) countries to allow free competition of IP telephony with their local PTO.
Mantra: IP is “the new” technology for telecommunications; IP is much more efficient (cost) than legacy TDM; IP networks open the way for new services and help reduce the
“digital divide”; IP telephony should not fall under the telecom regulation regime
(or this regime should evolve) because it uses a new technology.
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The EU view
Advocates the principle of technological neutrality. EU has a strict definition of voice telephony in terms of the
following four principles: it is offered commercially as such; it is provided to the public; it is provided to and from PSTN termination points; it involves speech transport and switching of voice in real-time
with the same level of reliability and quality as existing PSTN networks.
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Other Regulatory Implications
Regulatory parity (regulating services vs. technologies) Should a telephone call be
regulated differently if it is TDM, VoIP, FTTH, DOCSIS?
Protocol conversion Is gateway functionality protocol
conversion in a CI-II / CI-III context? Unbundling
What are the UNE’s of a VoIP network?
How should competitive access provided in a VoDSL and FTTH environment?
CPE Deregulation With gateway functionality moving
to the end user
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Further Reading …
David J Write, Voice over Packet Networks, J. Wiley, 2001.
Jonathan Davidson and James Peters, Voice over IP Fundamentals, Cisco Press, 2000.
Daniel Minoli and Emma Minoli, Delivering Voice of IP Networks, Wiley Computer Publishing, 1998.
David Collins, Carrier Grade Voice over IP, McGraw-Hill, 2001.
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