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Introduction to VoIP
Technology Tutorials
Session 1819
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2008 OPNET Technologies, Inc.
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1819 Introduction to VoIP
What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda
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1819 Introduction to VoIP
What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda: What is VoIP?
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1819 Introduction to VoIP
What is VoIP?
Telephony over an IP network
Internet
IP Phone
Cell Phone
Soft Phone
PSTN Traditional
Phone
IP Phone
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1819 Introduction to VoIP
Why Use VoIP?
Cost savings (toll-bypass, etc.)
Integrated data and voice networks
Device interoperability using standards-based protocols
Flexibility in deriving new services
Network
Voice Data
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1819 Introduction to VoIP
A traditional T1 can carry 24 telephone calls simultaneously
With VoIP, a T1 could carry 64 calls simultaneously
Traditional Voice vs. VoIP
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
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1819 Introduction to VoIP
What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda: VoIP Components
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1819 Introduction to VoIP
End-user devices IP-enabled Phones
Soft Phones
Media Gateway Controllers
Call setup and management
Can be hardware or software
Media Gateway
Convert signal from digital to analog (and vice versa)
Basic Components
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1819 Introduction to VoIP
Interactive Voice Response (IVR)
A computerized system designed to interact with acaller
Voicemail System
A centralized system for sending, storing andretrieving messages
Emergency Responder
A system in charge of ensuring that 911 calls will gothrough
Advanced Components
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1819 Introduction to VoIP
Example Network
Coleman Technologies, Inc. 2008 - Used with Permission.
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1819 Introduction to VoIP
Example Network
Coleman Technologies, Inc. 2008 - Used with Permission.
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1819 Introduction to VoIP
Example Network
Coleman Technologies, Inc. 2008 - Used with Permission.
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1819 Introduction to VoIP
Example Network
Coleman Technologies, Inc. 2008 - Used with Permission.
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1819 Introduction to VoIP
Example Network
Coleman Technologies, Inc. 2008 - Used with Permission.
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1819 Introduction to VoIP
Example Network
Coleman Technologies, Inc. 2008 - Used with Permission.
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1819 Introduction to VoIP
Example Network
Coleman Technologies, Inc. 2008 - Used with Permission.
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1819 Introduction to VoIP
What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda: VoIP Control Plane Protocols
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1819 Introduction to VoIP
IP Phone
Call Setup (IP-to-IP)
Server
LAN
1. Caller dials 555-1234 3. Server responds with
the IP address of the
called party
5. Called party accepts the call
by picking up the telephone
receiver. An accept message
is sent back to the caller.
2. Server performs
authentication, call
admission control, and
address translation
4. Caller sends a callsetup message to the
called party
IP Phone
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1819 Introduction to VoIP
Ordinary
Telephone
IP Phone
Call Setup (IP-to-PSTN)
server
LAN
1. Caller dials
555-1234
3. Server responds with
the IP address of the
gateway
4. Caller sends a call
setup message to the
gateway
2. Server performs
authentication, call
admission control, and
address translation
PSTN
IP-to-PSTN
Gateway
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.
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1819 Introduction to VoIP
SCCP Skinny Client Control Protocol Cisco proprietary Most commonly used
H.323 ITU-T & IETF
Distributed
SIP Session Initialization Protocol Very modular, ease of use, fastest growing protocol Distributed IETF RFC 2543
MGCP Media Gateway Control Protocol IETF RFC 2705 Centralized
H.248/Megaco ITU and IETF, extends MGCP - RFC 2885 Centralized
Others:
Avayaproprietary
IAX Inter-Asterisk eXchange Native to Asterisk PBX
UNIStim(Nortel) Nortel proprietary
XMPP - Jingle Jabber, Google Talk
Skype
Control Plane Protocols
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1819 Introduction to VoIP
Session Initiation Protocol (SIP)
Fastest growing standard
Simpler than H.323
Also used for video conferencing, network gaming, instant messaging
Similar to HTTP, textual coding
Addressing:
sip:[email protected]?subject=callme
tel:+1-919-555-1234DTMFs (Dual-tone multi-frequency) carried in signaling message
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1819 Introduction to VoIP
IP Phone
IP Phone
SIP Components
SIP Proxy Server
IP Network
INVITE sip:[email protected]
From: [email protected]
Call-ID:[email protected]
INVITE sip:[email protected]
From: [email protected]
Call-ID:[email protected]
[email protected] packets flow
between IP telephones
Proxy for sip.com gets
location information for
called party.
OK 200
From: [email protected]
Call-ID:[email protected]
OK 200
From: [email protected]
Call-ID:[email protected]
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1819 Introduction to VoIP
Interoperability Between Protocols
Gateways can convert between protocols
SIP
H.323
PSTNMegaco
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1819 Introduction to VoIP
What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda: VoIP Data Plane Protocols
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1819 Introduction to VoIP
Real-time Transport Protocol (RTP)
Indicates nature of the content
Maintains sequence of packets
Time stamping
Delivery monitoring
V P X PayloadM Sequence Number
Timestamp
Synchronization Source Identifier (SSRC)
Payload
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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
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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 links
However, it adds delay! (~3ms)
Versions:
RFC 2508, CRTP for low-speed serial links
RFC 3545, Enhanced CRTP for high delay, packet loss, and reordering
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1819 Introduction to VoIP
What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda: CODECs
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1819 Introduction to VoIP
CODECs
Conversion analog digital
Sampling: create blocks of data at fixed intervals
Each block contains a fixed number of bytes
Customizable to insert more or less samples in one IP packet
Small packets less delay, but more layer 2/3 overhead
Large packets more delay, less layer 2/3 overhead
Bandwidth saving techniques Silence suppression
Compression
CODEC
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1819 Introduction to VoIP
Typical CODEC Behavior
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1819 Introduction to VoIP
What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda: Design Considerations and
Architectures
1819 I t d ti t V IP
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1819 Introduction to VoIP
IP-PBX: Hosted vs. Premise-Based
Hosted solutions Switching and intelligence is remote
On-site equipment: mainly phones, some switches
Premised-Based solutions Switching and intelligence is local
On-site equipment: phones, servers, switches
System is not flexible/customizable Easy maintenance
New services are dependant on the provider Cheap
DisadvantagesAdvantages
Maintenance (servers, upgrades, etc)
More difficulty growing the system
High startup cost Flexibility in services deploymentDisadvantagesAdvantages
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1819 Introduction to VoIP
Call Centers
Different options:
Hosted / On-demand
Premised-based
Outsourced
Adding value to a Call Center:
Integration with CRM application to create a seamless experience
Speech recognition
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1819 Introduction to VoIP
What to Look for in a Gateway
Software vs. hardware?
How many simultaneous VoIP calls can it handle?
How many foreign exchange offices (FXO) does it provide? Supported VoIP protocols?
Supported CODECs?
Compatibility with existing VoIP devices?
SIP
H323
MGCP
VS.
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What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda: VoIP Performance
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Sound Quality
Sound quality depends on many factors
Telephone quality
Type of CODEC usedHigher compression leads to lower quality
Network performance
Quality of Service Metrics
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VoIP Performance 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 receiverMust be less than 150 ms for real-time conversations
Jitter The variability in the delay
Computed as: expected arrival time actual arrival time
Must be less than 30 ms
De-jitter buffer helps fix the problem, but adds to the overall delay
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Call Quality Scoring
Mean Opinion Score (MOS)
A telephone industry standard for measuring voice quality
Based on users perceptions of voice quality
E-model, ITU-T G.107
CODEC characteristics
Packet loss
Delay
Acoustic conditions
Assumes fixed dejitter buffer delay
MOS VQMon
Provided by Telchemy, Inc Extension of the E-Model
Incorporates the effects of time-varying IP network impairments
PESQ
ITU-T Recommendation P.862
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What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda: QoS Mechanisms for VoIP
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QoS Mechanisms Queuing
Queuing Mechanisms for giving different treatment to different
types of packets
First In, First Out (FIFO)
Priority queuing (PQ)
Strict ordering of queues
Weighted Fair Queuing (WFQ)
Each queue gets a percentage of the bandwidth during congestion
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FIFO Queue Example
Voice Flow
Data Flows
FIFO Queue
Packets lost due to taildrop during congestion
As the queue length grows, so
does the average delay
The varying length of the
queue adds to the jitter
Multiplexer
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Example of WFQ + Priority Queue
Voice Flow
Data Flows
Priority Queue
Cl
assifier
WFQ Queues Scheduler
Best-effort Queue
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Example of WFQ + Priority Queue
Voice Flow
Data Flows
Priority Queue
Cl
assifier
WFQ Queues Scheduler
Best-effort Queue
Rate Limiter
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QoS Mechanisms
Ethernet QoS 802.1p
IntServ A mechanism for a reserving resources on devices via RSVPsignaling
Fine-grained Not scalable
DiffServ A static mechanism for marking packets at the edge of thenetwork 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 hop
Aggregate RSVP More scalable IntServ.
Call Admission Control (CAC) Gatekeeper/Proxy function for limiting number of calls in system
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What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures VoIP Performance
QoS Mechanisms for VoIP
Security VoIP Management Lifecycle
On the Horizon
Agenda: Security
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Security
Main types of attacks:
Denial of Service (DoS /DDoS)Saturation of the targeted server(s)
VoIP EavesdroppingTapping into VoIP calls
Vishing
VoIP + phishing = vishing
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Protocols
EncryptionStandard protocols could be more exposed than
proprietary
Security
Network architecture
Separate VoIP traffic (ex: Hosting VoIP on a VPN)
Separate trusted and untrusted zones
UsersTraining of employees
Protection at 3-level
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What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda: VoIP Management Lifecycle
1819 Introduction to VoIP
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VoIP Management Lifecycle
Pre-Deployment Planning &
Testing
Evaluating deployment
Performing readiness assessment
Planning deployment
Predicting call quality
Studying potential QoS deployment
Monitoring and Troubleshooting
Tracking call quality
Evaluating effect on data traffic
Troubleshooting performance problems
Re-engineeringAdding capacity or QoS mechanisms
Tuning queues based on measured data
Trending traffic and predict future bottlenecks
Testing configuration changes
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What is VoIP?
VoIP Components
VoIP Control Plane Protocols
VoIP Data Plane Protocols
CODECs
Design Considerations and Architectures
VoIP Performance
QoS Mechanisms for VoIP
Security
VoIP Management Lifecycle
On the Horizon
Agenda: On the Horizon
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Hype Cycle
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Mobile VoIP
Different approaches:
Mobile device uses SIP directly
Bridging SIP/RTP into the mobile networks SS7 infrastructure
i2Telecom, Tango Networks, Outsmart, NewStep, BridgePort, BroadSoft
Voice-over-Wifi is already here
Fixed and Mobile telephony Convergence (FMC): provide seamlessroaming from GSM/CDMA to VoIP
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IMS Convergence
IP based telephony and multimedia services
Convergence of voice, data, video and mobile technology
Features:
IP-based
QoS-enabled
Common multimedia services platform
Independent of the users location
1819 Introduction to VoIP
U f l V IP Li k
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Useful VoIP Links
General information http://www.voip-news.com/
http://www.voip-info.org/ SIP information
http://www.sipforum.org/
VoIP Security Alliancehttp://www.voipsa.org/
VoIP Bandwidth calculatorhttp://www.voip-calculator.com/calculator/lipb/
VoIP testerhttp://www.testyourvoip.com/
1819 Introduction to VoIP
Documentation References
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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
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R l d OPNETWORK S i
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Related OPNETWORK Sessions
1346 Pre-Deployment Analysis of VoIP in Enterprise Networks
Tuesday 09:00 to 12:00
Thursday 09:00 to 12:00
1365 Planning VoIP Migrations for Service Provider Networks
Tuesday 14:00 to 17:00
Thursday 09:00 to 12:00
1468 Monitoring and Troubleshooting VoIP with ACE Live
Monday 16:00 to 18:00
Wednesday 16:00 to 18:00
Thursday 16:00 to 18:00
1806 Introduction to QoS Mechanisms
Monday 09:00 to 12:00
Thursday 09:00 to 12:00
1819 Introduction to VoIP
T k A P i t
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Take-Away Points
Providing QoS is critical to VoIP success
Technology is not complicated but therequirements are stringent
The VoIP market is moving, and growing
Monitor
Stay
Informed
Plan
1819 Introduction to VoIP
APPENDIX: EXAMPLE OF PACKET
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APPENDIX: EXAMPLE OF PACKET
Block no 1 Block no 2 IP Header RTP UDP
Payload 160 bytes 20 bytes 12 bytes 8 bytes
TOTAL 200 bytes
40 bytes64 kbps +20 msec
Bandwidth: = 80 kbps
Using G.711
