1. VoIP—Voice over Internet Protocol
EE290F Spring 2004
Xiaoxue Zhao

2. Content PSTN-Public Switch Telephone Network Packet-Switched Network
Comparison between PSTN and IP Network
VoIP Standards
VoIP Services
QoS—Quality of Service

3. PSTN—Components Access Lines (Local Loops)
Connects customer premises to the local voice switch
Switches
Connect access line to each other
Trunks
Connects voice switches to each other
PBX—Private Branch Exchange
Signaling—Connectionless PSTN
Used for basic call set up, management, tear down and enhanced call features etc.

4. PSTN—Structure Voice Channel Multiplexing Access lines Trunk NetworkCO
Switch
PBX
Signaling
Network
Voice Channel Multiplexing
Residential
customers
Business
Access lines

5. PSTN—Features Connection-Oriented, Circuit-Switched
Guaranteed Bandwidth
“All the bandwidth all the time.”
Stable Delays
Connection Establishment
Information Transfer
Connection Release
Connection-Oriented
Connectionless

6. Packet-Switched Network
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Services
Transport (TCP) IP
Network
Access
Packet—Unit of data containing the network address information
Network Layers
“Best effort”

7. Virtual Circuits Virtual Circuit Data Design philosophy
Connection-oriented
Connectionless
Addressing entity
Circuit identifiers
Node and network addresses
Unit of information
Packet, frame, cell
Network entities
Switches
Routers
Bandwidth use
All allowed by network
Depends on number and size of frames
Examples
Frame relay, X.25, ATM, most other WANs
Internet Protocol (IP), Ethernet, most other LANs

8. Fixed and low <=64kb/s
Comparison
Network Features
PSTN (Voice)
Internet (Data)
Switch
Circuit Switched
Packet Switched
Connection
Connection Oriented
Connectionless
Bit Rate
Fixed and low <=64kb/s
Wide variation to Gb/s
Bursts
Nonexistent
High (100/1000:1)
Error tolerance
User error control
Error free
Info resending
Can not (real time)
Can be done very fast
Delay
Must be low and stable
Can be high and vary

9. Packetizing Voice VoIP Issues Solutions Packetizing delay
Small packets for VoIP
Serial delay
Priorities and jitter buffers
“High” bit-rate voice (64kb/s)
Voice compression
Constant-bit-rate voice (PMC)
Silence suppression and comfort noise
Resend due to errors
Real-time Transport Protocol (RTP)

10. Why VoIP? Cost Reduction Simplicity Advanced Applications
Web-enabled call centers
Collaborative white boarding
Remote telecommuting

11. VoIP Standards H.323—ITU-T Session Initialization Protocol (SIP)—IETF
Voice Coding Methods (ITU-T G series, etc.)
Call Control/Session Initialization (H.225, H.245, SIP)
Timing (RTP)
Gateway/Gatekeeper
Control (GLP, MGCP)
Reliable/Unreliable
Transport services (TCP/UDP)
Internet Protocol (IP)
Packet Network Infrastructure
Application Layer
Transport Layer
Network interface Layer
Network Layer

12. H.323 Packet-Based Multimedia Communications Systems
H.323 Architecture
H.323 for IP Telephony

13. H.323 Architecture LAN H.323 terminal H.323 multipoint
control unit (MCU)
gatekeeper
gateway
PSTN
V.70
H.324
Speech
N-ISDN
B-ISDN
QoS
LAN
H.322
H.320
H.321
LAN

14. H.323 for IP Telephony Video Audio Control Data H.261 H.263
(video coding)
G.711
G.722
G.723
G.728
G.729
H.225
Terminal to gatekeeper
signaling
Call
H.245
T.120
(Multipoint data transfer)
RTP
(Real-time Protocol)
RTCP
(Real-time Control Protocol)
Unreliable transport (UDP)
Reliable transport (TCP)

15. SIP Proposed by Internet Engineering Task Force (IETF)
Application layer control protocol
Borrow design and architecture from the Hypertext Transfer Protocol (HTTP)

16. VoIP Services Self-provided Customer Independent of Internet access
Provided by broadband access service provider
Corporate Internal Use on Business LAN / WAN
Carrier Internal Use

17. Self-Provided Customer
Internet
Address Info
Call setup and
Call data
IP connection
Voice-enabled device
Examples: Skype, MSN
Address Info

18. Independent of Internet Access
PSTN
Internet
Gateway
SIP phone
Analogue phone
SIP Server
Signaling and Call setup
Signaling and
Call setup
Call data
PSTN call
PSTN signaling
Customer in agreement with IP telephony company, independent of ISP
Uses gateway to connect to PSTN
Calls can be made to either VoIP users or PSTN users
IP connection and Voice-enabled device
Examples: Vonage, Packet8, Net2Phone

19. Provided by Broadband Access Service Provider
network
ATA
SIP Server for
both users
Signaling and call setup
Signaling and
call setup
Call data
Customer in agreement with IP telephony company with is also ISP
Uses gateway to connect to PSTN
Provider is in control of the network so offer quality guarantees
Analogue terminal adapters are provided
Example: Yahoo!BB (Japan)

20. Corporate Internal Use on Business LAN / WAN
Ethernet
LAN
Gatekeeper
PSTN
Gateway
IP Router
WAN or Internet
Converter
PC based virtual phone
Analogue
phone
No service provider
In-house telephony on LAN or WAN
Services are those of a full-featured PBX

21. Carrier Internal Use
Carrier
Network
H.323
Gateway
SoftSwitch
Analogue phone
Call data
Signaling and set up
Softswitch instead of circuit switch, including H.323 gatekeeper or SIP server
Most based on H.323
Mostly in international calls

22. QoS—Quality of Service
QoS Parameters
Bandwidth
Delay
Jitter (Delay Variation)
Information Loss
Reliability
Security

23. References
IP Telephony Walter J. Goralski and Matthew C. Kolon McGraw-Hill
Final Report for the European Commission—IP Voice and Associated Convergent Services