introduction to voip technology tutorials
DESCRIPTION
Session 1819. Introduction to VoIP Technology Tutorials. Agenda. What is VoIP? Why is it used? How is it used? Applications and architectures How does VoIP work? Protocols What do VoIP calls sound like? QoS How can I make sure that VoIP deployments will work properly? - PowerPoint PPT PresentationTRANSCRIPT
Copyright © 2004 OPNET Technologies, Inc. Confidential, not for distribution to third parties.
Introduction to VoIPTechnology Tutorials
Session 1819
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 2
1819 Introduction to VoIP
What is VoIP?
Why is it used?
How is it used? Applications and architectures
How does VoIP work? Protocols
What do VoIP calls sound like? QoS
How can I make sure that VoIP deployments will work properly? Modeling and simulation
Agenda
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 3
1819 Introduction to VoIP
What is VoIP?
Carrying voice conservations over Internet protocol packet networks Private
Public
There are other flavors of packetized voice: VoATM
VoFR
IP Network
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 4
1819 Introduction to VoIP
Why Use VoIP?
Cost savings
Integrated data and voice networks
Device interoperability using standards-based protocols
Flexibility in deriving new services
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 5
1819 Introduction to VoIP
Traditional Voice Versus VoIP
A traditional T1 can carry 24 telephone calls simultaneously
With VoIP, a T1 can carry 64 calls simultaneously!
G.729 8kbps compression, 20 msec frame size = 24 kbps
1544 / 24 = 64 calls per T1
T1 = 1544 kbps, DS0 = 64 kbps,
1544 / 64 = 24 DS0 per T1
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 6
1819 Introduction to VoIP
Devices
IP Telephones A telephone that directly connects to an IP network
Gateways Provide bulk conversion of connections between
signaling domains: PSTN connections to VoIP connections One VoIP signaling domain to another
Servers Handle registration, authentication, telephone
number to IP address conversion, bandwidth management, etc.
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 7
1819 Introduction to VoIP
How is VoIP Used?
Applications and architectures
Consumer
Campus
Enterprise
Service Provider
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 8
1819 Introduction to VoIP
Consumer: IP-to-IP
Uses PC software to make calls over public and private internets
Free!!But, no quality of service guaranteesExamples:
Microsoft NetMeetingTM
SkypeTM
Hybrids PC2PhoneTM
The InternetPC
PCModemModem
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 9
1819 Introduction to VoIP
Campus Applications – IP PBX
Connecting office telephones to PBX with VoIP linksVendors
Cisco Nortel
PSTN
LAN Switches
IP Telephones
Call Manager &IP-to-PSTN Gateway
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 10
1819 Introduction to VoIP
Enterprise Applications – Toll Bypass
Connecting enterprise PBXs with VoIP links to avoid paying for long distance charges Vendors:
Nortel NEC Avaya Toshiba Ericsson Cisco
Private Data Network or VPN
Public Switched Telephone Network
(PSTN)
PBX PBXRouter Router
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 11
1819 Introduction to VoIP
Service Provider Applications – Local AccessUsing broadband access to provide local and long distance
telephone serviceExample Services:
Vonage ATT CallVantageTM
Packet8 Broadvox Time Warner Cable
PC
BroadbandModem
Splitter
Ordinary Telephone
Broadband Service
ProviderPSTN
Access Provider
ISP
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 12
1819 Introduction to VoIP
Service Provider Applications – Trunking
Carrying voice traffic between switches over long haul networkAllows for consolidation with data networksExample Hardware:
Nortel Sonus
*LATA = local access and transport area
LATA #2
Private Data Network
LATA #1
LATA #3
LATA #4
LATA #5
LATA #6
PSTN
Gateway Gateway
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 13
1819 Introduction to VoIP
What is VoIP?
Why is it used?
How is it used? Applications and architectures
How does VoIP work? Protocols
What do VoIP calls sound like? QoS
How can I make sure that VoIP deployments will work properly? Modeling and simulation
Agenda
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 14
1819 Introduction to VoIP
IP Phone IP Phone
How Does VoIP Work?
Gatekeeper
LAN
1. Caller dials 555-1234 3. Gatekeeper responds with the IP address of the called party
4. Caller sends a call setup message to the called party
5. Called party accepts the call by picking up the telephone receiver. An “accept” message is sent back to the caller.
6. Voice packets flow between IP telephones
2. Gatekeeper performs authentication, call admission control, and address translation
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 15
1819 Introduction to VoIP
IP Phone
How Does VoIP Work? (IP-to-PSTN)
Gatekeeper
LAN
1. Caller dials 555-1234
3. Gatekeeper responds with the IP address of the gateway
4. Caller sends a call setup message to the gateway
2. Gatekeeper performs authentication, call admission control, and address translation
PSTNOrdinary Telephone
IP-to-PSTNGateway
7.Gateway converts the PSTN accept message into VoIP accept message and sends it back to the caller.
5. Gateway converts the VoIP signaling message to PSTN signaling message
6. Called party accepts the call by picking up the telephone receiver. An “accept” message is sent back to the gateway.
8. Voice packets flow between IP telephone and gateway. Gateway converts between packet data and timeslot data.
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 16
1819 Introduction to VoIP
Protocol Soup
Signaling H.323, SIP, MGCP, H.248, SCCP, etc.
CODECs G.711, G.723, G.729
Transport RTP, RTCP, CRTP, ECRTP, UDP, IP
Other RSVP, DiffServ, IntServ, MPLS, DNS, COPS (policy), Radius &
Diameter (authentication)
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 17
1819 Introduction to VoIP
Signaling Protocols
H.323 Distributed architecture Used for video conferencing, but also VoIP
SIP – Session Initialization Protocol Distributed architecture IETF RFC 2543
MGCP – Media Gateway Control Protocol Centralized architecture IETF RFC 2705
H.248 Centralized architecture Extends MGCP Collaboration between ITU and IETF Also known as RFC 2885, Megaco
SCCP – Skinny Client Control Protocol Cisco proprietary For use with Cisco CallManager
H.323
SIP
Distributed
MGCP
H.248
Centralized
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 18
1819 Introduction to VoIP
H.323 Details
ITU umbrella standard for packet-based multimedia communication systems Audio CODECs Video CODECs H.255 registration, admission, and status (RAS) H.225 call signaling H.245 control signaling Real-time transport protocol (RTP) Real-time control protocol (RTCP)
Early standard
Complex
Transport Protocols
RTP
RTCP H.255
RAS
H.225
Call Signaling
H.245
Control Signaling
T.120
Data
G.711
G.729
G.723
H.261
H.263
Call Manager ApplicationAudio Video
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 19
1819 Introduction to VoIP
H.323 Components
Terminals Hardware or software running H.323
protocols
Gateway Connects different networks
H.323-to-PSTN H.323-to-{other VoIP signaling protocol}
Gatekeeper (optional) Address translation Admission control Bandwidth control Zone control
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 20
1819 Introduction to VoIP
H.323 Call Setup
Gatekeeper
LAN
1. Caller dials 555-1234 3. Gatekeeper responds with the IP address of the called party
4. Caller sends a call setup message to the called party
6. Voice packets flow between IP telephones
2. Gatekeeper performs authentication, call admission control, and address translation
IP Phone IP Phone (555-1234)
5. Called party accepts the call by picking up the telephone receiver. An “accept” message is sent back to the caller.
H.323 Messages
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 21
1819 Introduction to VoIP
Session Initiation Protocol (SIP) Details
Recent standard
Simpler then H.323
Also used for video conferencing, network gaming, instant messaging
Similar to HTTP, textual coding
Uses URLs for addressing: sip:[email protected]
sip:[email protected]?subject=callme
tel:+1-919-555-1234
DTMFs carried in signaling message
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 22
1819 Introduction to VoIP
SIP Call Setup
SIP Proxy
IP Network
INVITE sip:[email protected]: [email protected]:[email protected]:[email protected]
INVITE sip:[email protected]: [email protected]:[email protected]:[email protected]
ACK [email protected] packets flow between IP telephones
Proxy for sip.com gets location information for called party.
IP Phone ([email protected])
IP Phone ([email protected])
OK 200From: [email protected]:[email protected]:[email protected]
OK 200From: [email protected]:[email protected]:[email protected]
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 23
1819 Introduction to VoIP
MGCP/H.248/Megaco Details
Based on master/slave principal More palatable to telco's Easier to rollout new feature since only the servers need to be updated,
not the individual telephones
Media Gateway Controller
Signaling Gateway
PSTN
H.248 Messages
Call Control (SIP, H.323, etc.)
SS7, etc.
Trunks
Media Gateway Controller
IP PhoneMedia Gateway
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 24
1819 Introduction to VoIP
Break!!!
Break!
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 25
1819 Introduction to VoIP
CODECS
Voice codecs create blocks of data at fixed intervals Usually 10 ms
Each block contains a fixed number of bytes depending on the coding scheme used 10-80 bytes/block
Codecs can typically be parameterized to put a given number of voice data bytes into a single IP packet 10, 20, 30, …, 240 bytes
Bandwidth saving techniques Silence suppression Compression
Tradeoffs Small packets = less delay, but more layer 2/3 overhead Large packets = more delay, less layer 2/3 overhead
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 26
1819 Introduction to VoIP
Typical CODEC Behavior
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 27
1819 Introduction to VoIP
CODEC Characteristics
Codec Compression Method
Codec Bit Rate
Block Length
Block Size
(bytes)
Blocks per
Packet
Voice Call Bandwidth Required
(Excl. L2 o/h)
Mean Opinion Score
Compression Delay (ms)
g711alaw PCM 64000 10 ms 80 2 80000 4.1 0.75
g711ulaw PCM 64000 10 ms 80 2 80000
g723ar53 ACELP 5300 10 ms 7 2 22000 3.65 30
g723ar63 MP-MLQ 6300 10 ms 8 2 23000 3.9 30
g723r53 ACELP 5300 10 ms 7 2 22000
g723r63 MP-MLQ 6300 10 ms 8 2 23000
g726r16 ADPCM 16000 10 ms 20 2 32000
g726r24 ADPCM 24000 10 ms 30 2 40000
g726r32 ADPCM 32000 10 ms 40 2 48000 3.85 1
g728 LD-CELP 16000 10 ms 20 2 32000 3-5
g729r8 CS-ACELP 8000 10 ms 10 2 24000 3.92 10
g729br8 CS-ACELP 8000 10 ms 10 2 24000 3.7 10
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 28
1819 Introduction to VoIP
Real-time Transport Protocol (RTP)
Media content typeTalk spurtsSender identificationSynchronizationLoss detectionSegmentation and reassemblySecurity (encryption)
V P X PayloadM Sequence Number
Timestamp
Synchronization Source Identifier (SSRC)
Payload
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 29
1819 Introduction to VoIP
RTP Control Protocol (RTCP)
Used for monitoring the quality of a session
Transferring that information to all of the participants in the session
Provides minimal session control
Sent on different port number from RTP
Messages: Sender Reports: Information about sent data, synchronization timestamp
Receiver Reports: Information about received data, losses, jitter and delay
Source Description:Name, Email, Phone, Identification
Bye: Explicit leave indication
Application defined parts: Parts for experimental functions
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 30
1819 Introduction to VoIP
Compressed RTP
Technique for reducing the bandwidth requirements for RTP-UDP-IP headers
Reduces all three headers from 40 bytes to 2-4 bytes
RTP Header = 12 bytes
UDP Header = 8 bytes
IP Header = 20 bytes
Utilizes the fact that much the headers’ contents remain the same from packet
to packet
Critical for low-speed uplinks
Versions: RFC 2508, CRTP for low-speed serial links
RFC 3545, Enhanced CRTP for high delay, packet loss, and reordering
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 31
1819 Introduction to VoIP
Other Issues
Interoperability between signaling protocols Gateways can convert between protocols
Handling modem and fax traffic Detection needed at gateway T.37/T.38 Fax Delivery of IP Modems must use G.711 with no echo
cancellation and no high pass filter
VoIP Network
IP-to-PSTNGateway
IP-to-PSTNGateway
Fax
Modem
Fax
Modem
PSTN PSTN
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 32
1819 Introduction to VoIP
What is VoIP?
Why is it used?
How is it used? Applications and architectures
How does VoIP work? Protocols
What do VoIP calls sound like? QoS
How can I make sure that VoIP deployments will work properly? Modeling and simulation
Agenda
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 33
1819 Introduction to VoIP
What Do VoIP Calls Sound Like?
Sound quality depends on many factors Telephone quality
Type of CODEC used
Higher compression leads to lower quality
Network performance
Quality of Service Metrics
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 34
1819 Introduction to VoIP
Subjective Versus Objective Quality ScoringMean Opinion Score (MOS)
A telephone industry standard for measuring voice quality Based on users’ perceptions of voice quality
Excellent = 5, Good = 4, Fair = 3, Poor = 2, Bad = 1 MOS should be > 4.0
E-model, ITU G.107 Predicts the MOS based on
CODEC characteristics Packet loss Delay Jitter
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
CODEC #1 CODEC #2
Excellent
Good
Poor
Bad
Fair
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 35
1819 Introduction to VoIP
Quality of Service Metrics
Packet Loss – What percentage of the packets are dropped Should be less than 1%
Delay – How much time elapses between when an utterance is spoken and when it is played back at the receiver Must be less than 150 ms for real-time conversations
Jitter – The variability in the delay Must be less than 30 ms De-jitter buffer helps fix the problem, but adds to the overall delay
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 36
1819 Introduction to VoIP
Example of Delay Budget
Delays of less than 150 ms are sought But the fixed components of delay can be high Careful control of the variable components (queuing) required
Delay Component Fixed/Variable Delay (msec)
Codec-Related
g729a Compression Delay fixed 5
g729a Sampling Delay (10 ms x 2) fixed 20
Queuing Delay on Trunk variable 5
Transmission Delay fixed 3
Propagation Delay fixed 25
Queuing at Intermediate Hops variable 20
De-jitter buffer fixed 50
Total of Fixed Delays 103
Total of Variable (Queuing) Delays 25
Total Delay 128
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 37
1819 Introduction to VoIP
Active Quality Measurement Systems
Use active network to monitor the QoS of a VoIP Network
Examine actual calls check performance
Set up extra calls on real network to test performance
Monitoring software is embedded in gateways and other devices
Use E-model to estimate MOS
Vendors Psytechnics RADCOM Agilent
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 38
1819 Introduction to VoIP
QoS Mechanisms – Queuing
Queuing – Mechanisms for giving different treatment to different types of packets First In, First Out (FIFO)
Default behavior
Priority queuing (PQ)
Strict ordering of queues
Weighted Fair Queuing (WFQ)
Each queue gets a percentage of the bandwidth during congestion
Combination
A single high-priority queue + WFQ + best-effort queue
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 39
1819 Introduction to VoIP
FIFO Queue Example
Voice packets can get delayed or even dropped due to interaction with data flows
Voice Flow
Data Flows
FIFO Queue
Packets lost due to tail drop during congestion
As the queue length grows, so does the average delay
The varying length of the queue adds to the jitter
Mu
ltiplexer
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 40
1819 Introduction to VoIP
Example of WFQ + Priority Queue
Voice packets are always transmitted first via the “Priority FIFO Queue”
Voice Flow
Data Flows
Priority FIFO Queue
Classifier
WFQ Queues Sch
edu
ler
Best-effort Queue
…
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 41
1819 Introduction to VoIP
QoS Mechanisms
Ethernet QoS – 802.1pIntServ – A mechanism for a reserving resources on
devices via RSVP signaling Fine-grained Not scalable
DiffServ – A static mechanism for marking packets at the edge of the network and giving per-class treatment within the network Coarse Scalable No signaling
MPLS-DiffServ-TE Using label switched paths to control the paths that packets take
through the network as well as the treatment they receive at each hopCall Admission Control (CAC)
Gatekeeper/Proxy function for limiting number of calls in system
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 42
1819 Introduction to VoIP
What is VoIP?
Why is it used?
How is it used? Applications and architectures
How does VoIP work? Protocols
What do VoIP calls sound like? QoS
How can I make sure that VoIP deployments will work properly? Modeling and simulation
Agenda
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 43
1819 Introduction to VoIP
Deployment Considerations
QoS strategy
Server location Signaling latency issues
Load balancing
Redundancy
Dial plan
PSTN backup
Electrical power
Connectivity to Voice Mail and other Integration Voice Response (IVR) systems
Cooperation between telecom and data teams
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 44
1819 Introduction to VoIP
Modeling and Simulation
Configuration analysis Process configuration files for errors and
security problems Readiness assessment
Propagation delay prediction Failure analysis
Capacity planning Using flow analysis to determine the appropriate
link sizes in a VoIP network Voice traffic conversion: erlangs to bits/sec
QoS configuration planning Setting queue sizes
Voice quality analysis Using discrete event simulation (DES) to model
packet loss, delay, jitter of voice calls Protocol modeling
Using ACE or DES to model and verify VoIP signaling protocols and signaling latencies
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 45
1819 Introduction to VoIP
Useful VoIP Links
Transition to VoIP in campus http://www.cisco.com/warp/public/cc/so/neso/vvda/avvid/ttpnp_bc.pdf
Market research http://www.sonusnetworks.com/contents/brochures/solutions/Market_Impact.pdf
General information http://www.voip-news.com/
http://www.voip-info.org/
SIP information http://www.cs.columbia.edu/sip/
CODEC calculator http://www.voip-calculator.com/calculator/lipb/
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 46
1819 Introduction to VoIP
Documentation References
H.323 ITU Standard for Voice/Video over IP
SIP – Session Initialization Protocol, IETF RFC 2543
MGCP – Media Gateway Control Protocol, IETF RFC 2705
H.248, Megaco, IETF RFC 2885
SCCP – Skinny Client Control Protocol
RTP – Real-time Transport Protocol, IETF RFC 1889
RTCP – RTP Control Protocol, IETF RFC 1889
CRTP for low-speed serial links, RFC 2508
Enhanced CRTP for high delay, packet loss, and reordering, RFC 2508
ITU-T.37 – Procedures for the Transfer of Facsimile Data Via Store-and-forward on the Internet
ITU-T.38 – Procedures for Real-time Group 3 Facsimile Communication over IP Networks
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 47
1819 Introduction to VoIP
Related OPNETWORK Sessions
1346 Planning and Analyzing VoIP Deployments Thursday, 14:00-16:00, Atrium Ballroom B
1352 Case Studies: VoIP and Circuit-to-Packet Thursday, 14:00-16:00, Continental A
1806 Introduction to QoS Mechanisms Thursday, 14:00-16:00, Continental C
1337 Case Studies: QoS I
1338 Case Studies: QoS II Thursday, 16:00-18:00, Polaris C
Copyright © 2004 OPNET Technologies, Inc` Confidential, not for distribution to third parties. 48
1819 Introduction to VoIP
Take-Away Points
VoIP can take many forms
Toll-bypass, PBX, access, trunking
Many signaling protocols and architectures will be deployed
Providing QoS guarantees is critical to VoIP success
Modeling and simulation tools can help address these issues
The VoIP market is growing – Get prepared!