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Q: Voice over IP ( Answered 5 out of 5 stars,   0 Comments )
Subject: Voice over IP
Category: Computers
Asked by: maxtel-ga
List Price: $30.00
Posted: 03 Nov 2003 16:18 PST
Expires: 03 Dec 2003 16:18 PST
Question ID: 272318
Where can I find technical information like software, hardware, and
protocols used for VoIP (voice over IP)?

Request for Question Clarification by easterangel-ga on 03 Nov 2003 16:36 PST

What level of technical information do you need? For example in
regards to protocols, do you just want basic information or a more
high level discussion?


Clarification of Question by maxtel-ga on 03 Nov 2003 21:51 PST
Thanks for your interest.

I need as much technical information as possible.
Subject: Re: Voice over IP
Answered By: byrd-ga on 04 Nov 2003 16:06 PST
Rated:5 out of 5 stars
Hello Maxtel,

Voice over Internet Protocol is a fascinating area of technological
development, one that has been around for less than ten years, and is
still growing as work continues on increasing its feasibility over a
greater area.  Fortunately, it has been and is being widely studied at
a deep technical level, and there is an absolute wealth of material
available, both commercial and educational, ranging from the
superficial to the extremely technical.

What I’ve done is locate quite a number of sources of this information
for you (provided together with search terms that will enable you to
expand on them), given a brief summary of the contents, listed the
links, and organized the information into four broad categories. 
First, I’ve listed general overviews and tutorials that explain the
history, and the concept and workings of VoIP, including overviews of
protocols; second, I’ve listed sites from which you can obtain more
specific technical information about the various protocols; third,
I’ve given you links to information on and sources of VoIP hardware,
and: fourth, links and information about VoiP software.  In addition,
please see the end of this answer for the specific search terms I
used, which you may also then use to locate as much additional
information as you wish.


A  good place to begin might be with this “Technical Brief: VoIP
Protocols,” which gives a good overview:


“Voice Over IP: Technical Issues: Standards and Protocols,” here: is
another good general introduction, as is


“Introduction to Voice over Internet Protocol”:


From Louisiana State University comes this very thorough treatment of
VoIP entitled “Voice over Internet Protocol,” by Deanna K. Dokey and
John S. Rushing, which gives an overview, not only of protocols, but
of all aspects of your question, including hardware and software. 
Definitely worth reading: 
The clickable links on the left hand side of the page will enable you
to navigate the entire report.


This tutorial, copyright 2003, from the “International Engineering
Consortium,” is offered as part of its continuing education
curriculum, and entitled simply “Voice Over Internet Protocol.”  You
may read the entire tutorial online, or download a PDF version of it
to your computer to use and retain.  It even has a self-test included
so you can track your understanding of the subject if you’d like.  The
course traces the history of VoIP from its early days in 1995 to the
projected future of the technology.  Along the way it offers an
in-depth look at the technology, together with many highly detailed
diagrams and sketches to aid in your understanding.

The introductory paragraph begins, “This tutorial discusses the
ongoing but rapid evolution of Internet telephony, the market forces
fueling that evolution and the benefits that users can realize, as
well as the underlying technologies. It also examines the hurdles that
must be overcome before Internet telephony can be adopted on a
widespread basis.”

Here’s the Table of Contents:

Definition and Overview
1 Introduction
2 Intranet Telephony Paves the Way for Internet Telephony
3 Technical Barriers
4 Standards
5 Future of Voice-over-Internet Protocol (VoIP) Telephony
Correct Answers
Comment on This Tutorial

You may find this document here:
and/or download the PDF version here:  *Note: You will have to register
prior to be allowed to download, but registration is free.  Also, if
you need a viewer to read PDF files, there is a link there to download
the Adobe Acrobat Reader as well.


Here is another overview-type tutorial from CommWeb that is a little
older and not quite as scientifically oriented as the preceding, but
nevertheless offers a good means of understanding the specifics of
VoIP and how it works, together with explanation of some associated
subjects such as TCP/IP and “Circuits, Packets, Frames and Cells,”
that will help to provide a good technical understanding of the
subject.  Not as long as the course above, there is no table of
contents, but you can find the article here:


Rakesh Arora, a student at Ohio State University, has published a very
detailed paper entitled “Voice Over IP: Protocols and Standards,”
which you can find here:
 This article is also some older than the others, and not as
comprehensive as the first, nor does it contain as many detailed
drawings and graphics, but it does have some very good technical
information, as well as clickable links to references and further
recommended reading.

The document abstract states: “This paper first discusses the key
issues that inhibit Voice over IP (VOIP) to be popular with the users.
Then I discuss the protocols and standards that exist today and  are
required to make the VOIP products from different vendors to
interoperate. The main focus is on H.323 and SIP (Session Initiation
Protocol), which are the signaling protocols. We also discuss some
hardware standards for internet telephony.”

 The table of contents is as follows:

1. Introduction 
1.1 Main Issues 
2. H.323 Standard 
2.1 Components of H.323 
2.2 H.323 Protocol Stack 
2.3 Definitions 
2.4 Control and Signaling in H.323 
2.5 Call Setup in H.323 
3. Session Initiation Protocol (SIP) 
3.1 Components of SIP 
3.2 SIP Messages 
3.3 Overview of SIP Operation 
3.4 Sample SIP operation 
4. Comparison of H.323 with SIP 
5. Supporting Protocols 
5.1 Media Gateway Access Protocol 
5.2 RTP and RTCP 
5.3 Real Time Streaming Protocol 
5.4 Resource Reservation Protocol 
5.5 Session Description Protocol 
5.6 Session Announcement Protocol 
6. Hardware Standards 
6.1 SCBus 
6.2 S.100 
7. Summary 
Appendix A: Functions of the key protocols and standards 
List of Acronyms 

Also, should you so desire, this paper can be downloaded as a PDF
file.  Scroll to the bottom of this page:  and
“shift click” on the designated link to do so.

Westbay Engineers, Ltd., a vendor of VoIP has published a white paper
that “describes the protocols involved in the transmission of voice
samples through an IP based network.  This document aims to give the
reader the basic grounding that is required to further investigate the
bandwidth requirements of voice over IP.”  It has some limitations,
and they state that  “This paper does not discuss header compression
schemes, and does not discuss layer 2 protocols.   Furthermore, this
paper only considers IPv4 and not IPv6.”  Here is the table of

Layered model 
IP (Internet protocol) 
UDP (User Datagram Protocol) 
RTP (Real-time Transport Protocol) 
The complete header 
RTP Payload 

Despite its relative brevity, you might find some very useful
information here, and the information presented is definitely of a
highly technical nature.  You can read it here: as well as find links to other
technical papers that expand upon the knowledge given.

High Tech Gateway, which specializes in “Turning Technology into
Business Solutions” also has a very good VoIP tutorial, which can be
found here:  
They’re trying to sell their products and services, yet they do give
some very good general information about the technology involved in
VoIP.  Follow the links on the left-hand side of the page to navigate
through the sections, which include

	Why IP?	
	VoIP Overview
	VoIP Applications
	VoIP Benefits
	VoIP Protocols
	Our Solutions

There are also drop-down menu boxes beneath this list, where you can
select further topics if you wish, that talk about the application of
this technology with regard to a broad list of subject, including
hardware, software, IT, wireless and a variety of end users.

IPTel is a consulting company that specializes in promoting SIP
technology.  SIP, which stands for “Session Initiation Protocol,” is
one protocol used in VoIP.  Nevertheless, despite the clear bias,
there is much good (and free) technical information available at their
site, here:    This page is entitled “What is
Internet Telephony?” and gives a good classification of devices, as
well as a description of the overall architecture and explanation of
protocols in general.  Also, be sure to click on the tabs along the
top menu bar, especially the “Technology” one for links to additional
information, including among others, a glossary, products, history,
and research and development.

Additional papers:

“Voice over IP: Brief Introduction to an Infrastructure Technology”

A presentation on Chapter 12, “Internet Telephony: Technology and
Standards Overview” from the book "Multimedia Communication:
Directions and Innovation", by Jerry D. Gobson, Oct 2000:

“Understanding Packet Voice Protocols (a white paper from Cisco
Systems, a vendor):

“Voice over IP,” a web-based report:

“Real Time Distributed Voice Over IP:”


All right, once you’ve studied the tutorials and the overall
information in these links, here are some links to more specific,
technical information about various VoIP protocols:


To begin, Protocols.Com has a VoIP reference page with an impressive
array of links to such indepth information on a wide variety of
protocols (as well as other information).  You can find it here:   If you would like to access
their restricted section, which includes technical papers, you will
need to register first, but registration appears to be free.  Here’s
the page where you can do so:


Here’s a link to an outline for a course on VoIP being offered by
“Acerra Technology Training” What makes the outline useful is that it
gives a pretty comprehensive list of protocols:


This list of technical PDF downloadable white papers includes one
entitled “Industry Standards Information,” which is further subtitled,
“IP Protocols: The Protocols that Matter For Voice, Video and Data
over IP Networks H.323, SIP, MEGACO and MGCP.”  Find it here:


The Voice Over IP Calculator site, , has a lot of useful
information and links, including a white paper on “VoIP Protocols,”
and much more.  Be sure to look the site over carefully for links to a
lot of good technical information.


Here’s a link to a search return on “VoIP Protocols” from Network
Computing Tech Library, which maintains a large database of white
papers and other information on this and related subjects.  You will
need to register to retrieve the full text of any of these papers, but
registration is free and will give you access to quite a bit of
  Here’s the registration page:


Implementing VoIP usually involves hardware such as 

IP based network (LAN or WAN)
Gateways – which can be any/all of the following:
	Standalone box
	PC with software and voice hardware
	Voice enabled router
	Card attached to PBX
Multipoint Control Units (MCUs)
IP Phones


Here’s a good overview of hardware requirements, with explanations and
drawings to simplify understanding:


Overview of VoIP system architecture with drawings and references to
detailed descriptions:


One vendor’s (Unitec) technical discussion about hardware needs and


This paper, entitled “Voice over IP: Products, Services and Issues,”
gives a good overview of major system components and products,
including gateways, gatekeepers and telephones, along with software
information and a list of vendors:  A
very detailed and thorough discussion.

Not surprisingly, there is a plethora of software for pulling these
elements together, with more being developed all the time.  Although
the specific software used can range from basic to highly complex and
sophisticated, the basic functions or modules that need to be included

Voice Processing (which includes PCM interface, echo cancellation,
idle noise detection, tone detector, packet voice protocol, and voice
	Call Signaling
	Packet Processing
	Network Management


Again, see this article: ,
referenced above for hardware requirements.


Although they are in business to sell software, there is nevertheless
a great deal of useful non-vendor-specific knowledge in this report on
VoIP software by GAO Research, Inc.:


This technical discussion on VoIP software architecture discusses the
two layers, the “upper” layer consisting of the main program with the
user interface, and the “lower” layer, which invokes the RTP stack and
controls its operation, beginning with the latter and working up:


This is an indepth technical report on “Open aXs Scalable Software
Architecture, concentrating on “VoIP and VoATM software architecture
for carrier-class gateway Equipment:”
with links to a printable PDF datasheet.


Article: “Real Time Voice Communications: Hardware and Software

Current news reports featuring VoIP and related topics:

Finally, you might want to have a look at this forum:  where you can
register and discuss VoIP with other users and interested parties. 
Frequently such discussion forums are useful as a networking tool that
can enable you to find and access sources you might otherwise
overlook.  Registration is free and you may post or not as you wish.

The International Telecommunication Union:

The Internet Engineering Task Force homepage: 

Telecommunications Information Networking Architecture Consortium:

Anand’s Online VoIP Resource Center:

TechOnline University (offers free courses and lectures):

Interesting websites related to Digital Signal Processing (DSP):


I hope the information and links given prove useful to you, and that
they meet or exceed your expectations.  Should anything need
clarification, or you have any questions, please use the “Request
Clarification” feature before rating and closing the question, so I
might be able to ensure your satisfaction with the information
provided.  Thank you for the opportunity to work on this interesting
Best wishes, 

Search terms used:
VoIP tutorials OR overview OR information
VoIP protocols technical information
VoIP hardware
VoIP hardware review OR list OR requirements
VoIP hardware components OR solutions
VoIP system architecture
VoIP software
VoIP software review OR list OR requirements
VoIP software architecture

I also used the above terms with the qualifier to limit the
search to educational institutions, which I thought might provide
information of a more general and less biased nature than some
commercial sites.

The returns were voluminous, however, so then I also followed a number
of links to find what seemed to be the most pertinent  - and most up
to date - technical discussions and papers.  I discarded the dead
ends, of which there were quite a few, and also tried to avoid the
most blatantly commercial sites, in order to focus on technical rather
than business issues.
maxtel-ga rated this answer:5 out of 5 stars
Excellent answer. Thank you very much.

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