Post on 16-Apr-2017
transcript
VoIP—Voice over Internet Protocol
EE290F Spring 2004Xiaoxue Zhao
Content
PSTN-Public Switch Telephone Network Packet-Switched Network Comparison between PSTN and IP Netw
ork VoIP Standards VoIP Services QoS—Quality of Service
PSTN—Components Access Lines (Local Loops)
Connects customer premises to the local voice switch
SwitchesConnect access line to each other
TrunksConnects 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.
PSTN—Structure
Trunk Network
COSwitch
COSwitch
PBX
SignalingNetwork
Voice Channel Multiplexing
Residentialcustomers
Businesscustomers
Access lines
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
Packet-Switched Network
Packet—Unit of data containing the network address information
Network Layers “Best effort”
Application
Presentation
Session
Transport
Network
Data Link
Physical
ApplicationServices
Transport (TCP)
IP
NetworkAccess
Virtual Circuits
Virtual Circuit DataDesign philosophy Connection-oriented Connectionless
Addressing entity Circuit identifiers Node and network addresses
Unit of information Packet, frame, cell 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
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
Packetizing Voice
VoIP Issues SolutionsPacketizing 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)
Why VoIP?
Cost Reduction Simplicity Advanced Applications
Web-enabled call centers Collaborative white boarding Remote telecommuting
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/GatekeeperControl (GLP, MGCP)
Reliable/UnreliableTransport services (TCP/UDP)
Internet Protocol (IP)
Packet Network Infrastructure
Application Layer
Transport Layer
Network interface Layer
Network Layer
H.323
Packet-Based Multimedia Communications Systems
H.323 ArchitectureH.323 for IP Telephony
H.323 Architecture
H.323 terminal
H.323 multipoint control unit (MCU)
H.323 gatekeeper
H.323gateway
H.323terminal
H.323terminal
PSTN
V.70terminal
H.324terminal
Speechterminal
N-ISDN B-ISDNQoSLAN
H.322terminal
Speechterminal
H.320terminal
H.321terminal
LAN
H.323 for IP Telephony
Video Audio Control Data
H.261H.263
(video coding)
G.711G.722G.723G.728G.729
H.225
Terminal to gatekeepersignaling
H.225
Callsignaling
H.245 T.120
(Multipoint data transfer)
RTP(Real-time
Protocol)
RTCP(Real-time
Control Protocol)
RTP(Real-time
Protocol)
RTCP(Real-time
Control Protocol
)
Unreliable transport (UDP) Reliable transport (TCP)
SIP
Proposed by Internet Engineering Task Force (IETF)
Application layer control protocolBorrow design and architecture
from the Hypertext Transfer Protocol (HTTP)
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
Self-Provided Customer
IP connection Voice-enabled
device Examples: Sky
pe, MSN
Address Info
Internet
Address Info
Call setup andCall data
Independent of Internet Access
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
PSTN
Internet
Gateway
SIP phone
Analogue phone
SIP Server
Signaling and Call setup
Signaling and Call setupCall data
PSTN call PSTN signaling
Provided by Broadband Access Service Provider
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)
Access providernetwork
ATA
ATA
SIP Server for both users
Signaling and call setup
Signaling and call setup
Call data
Corporate Internal Use on Business LAN / WAN
No service provider
In-house telephony on LAN or WAN
Services are those of a full-featured PBX
EthernetLAN
Gatekeeper
PSTNGateway
IP Router
WAN or Internet
PSTN
ConverterGateway
PC based virtual phone
Analogue phone
Ethernetphone
Carrier Internal Use
Softswitch instead of circuit switch, including H.323 gatekeeper or SIP server
Most based on H.323
Mostly in international calls
CarrierNetwork
H.323Gateway
H.323Gateway
Carrier SoftSwitch
Analogue phone
Analogue phone
Call data
Signaling and set up
Signaling and set up
QoS—Quality of Service
Bandwidth Delay Jitter (Delay Variation) Information Loss Reliability Security
QoS Parameters
References
IP Telephony Walter J. Goralski and Matthew C. Kolon McGraw-Hill
Final Report for the European Commission—IP Voice and Associated Convergent Services