voip (ppt)

Packet Voice Protocols and VoIP

Fall 2002 – Computer Networking

Seyed Ali Ahmadi

04/11/23 VoIP - Packet Voice Protocols 2

VoIP Technology

Identify the different generations of VoIP

Explain the basic operations of a VoIP Gateway

Describe an ITSP business case

How gateway architecture affects service providers


VoIP technology

Recent Evolution of packet voice and VoIP

VoIP technology

VoIP evolution scenarios


1- Recent Evolutions in VoIP

Describe existing voice over data architectures and name their predecessors

How an ITSP work ?

Characteristics of an Internet call

Advantages and Disadvantages of ITSP


VoFR and VoATM Are Similar to VoIP

Voice is sent as packets intermingled with other traffic types

Voice may be compressed for efficiency

Delay and Delay variation are issues

Priority for voice traffic is required for best performance


VoIP Generations

PC-to-PC

PC-to-Phone

Phone-to-Phone

Traditional PBX migration to VoIP

IP PBX


ISTP Technology

Different Types of IP calls

How ITSP deploy gateways


Generic Gateway


Dedicated Infrastructure for ITSP

Eliminate dependence on performance of the InternetCarries strictly voice traffic or Prioritize voice over dataOffers cheap long distance as initial servicePositioned as enhanced service provider from regulatory point of view


Place gateways in countries with high international tariffs or high calling volumes.These Gateways support standard end user business interfaces to PSTN T1 E1 Analog ISDN


Regulatory Status

Most of the world has taken a hands-off position in regulating the enhanced service providersIn genera ITSPs have mostly positioned them as ISPsAs a result, ITSPs typically do not pay carrier fees such as connection, access or settlement feesIP telephony is regulated in some countries and illegal in some others.


2- VoIP Protocols and Technology


A little on historyCommunication pattern shift from PSTN to VoIPWhy VoIP?Cost savingOpen standards and Multivendor

interoperability Integrated voice and Data network


VoIP Protocols

H.323

Media Gateway Control Protocol (MGCP)

Session Initiation Protocol (SIP)

H.248–Media Gateway Control (MEGACO)


Great Voice Myth

“In order to have a reliable and robust Voice network, there should be one and only one protocol for each function in packet switch network.”

This is not how we are actually doing it now!!

The VoIP networks of today and tomorrow will be constructed using the protocols and applications that best fit the associated technology and business requirements.


Protocol Terminology

ITU: International Telecommunication Union

IETF: Internet Engineering Task Force



H.248 Gateway Control Protocol Collaboration between ITU & IETFAlso referred to as IETF RFC 2885

(MEGACO)



H.323 ITU recommends for “ Packet based

Multimedia communication systems”.Most common VoIP protocolDistributed Architecture



SIP: Session Initiation Protocol IETF RFC 2543 Distributed Architecture

Real-time Transport Protocol – RTP A transport protocol for real-time application IETF RFC 1889 Provides transport for audio/media of VoIP

communication Used by All of VoIP signaling protocols



MGCP Media Gateway Control Protocol IETF RFC 2075Centralized Architecture for Multimedia

applications such as VoIP


Distributed vs. Centralized


Centralized ArchitectureMostly used in older networks

Worked well for basic telephony services

Trade off between easy management and endpoint innovation

Associated with MGCP and H.248

Intelligence focused in centralized Gateway unit (media agent)

Endpoints are relatively or completely dumb.


Centralized ArchitecturePros & Cons

Centralizes management, provisioning and call control

Simplifies call flow for legacy voice features

Stifles innovation of endpoint features

Limitations in building VoIP networks beyond legacy voice features


Distributed Architecture

Associated with H.323 and SIP protocol

Allows Network Intelligence to be distributed between endpoints and control devices.

Intelligence: Call state Calling features Calling routines … any aspect of call handling


Distributed Architecture Pros & Cons

More flexible

VoIP is treated like any other distributed IP application

Well understood by engineers who design and run IP data networks

More complex than the Centralized Architecture


H.323

Originally designed as a transport protocol for MM Apps. in LANStill used for Video ConferencingMost widely used VoIP signaling and call controlUmbrella Protocol: All aspects of call transmission From call establishment to capabilities exchange

to network resources


H.323

Defines:RAS

RegistrationAdmissionStatus

H.225 for call set-upH.245 for capabilities exchange

voip (ppt)

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