20-01-2011, 01:08 PM
[attachment=8313]
What is VoIP?
“Technology used to transmit voice conversations over a data network using the Internet Protocol. Such data network may be the Internet or a corporate Intranet.” (shiftnetworksglossary.cfm)
“Or”
“Ability of an IP network to carry telephone voice signals as IP packets in compliance with International Telecommunications Union Telecommunication Standardization Sector (ITU-T) specification H.323. VoIP enables a router to transmit telephone calls and faxes over the Internet with no loss in functionality, reliability, or voice quality.” (trapezenetworkstechnology/glossary_6.asp)
“VoIP works through sending voice information in digital form in packets, rather than in the traditional circuit-committed protocols of the public switched telephone network.” (interconnect.co.za/links.html)
“Or”
“Voice over IP (also called VoIP, IP Telephony, and Internet telephony) refers to technology that enables routing of voice conversations over the Internet or any other IP network. The voice data flows over a general-purpose packet-switched network, instead of the traditional dedicated, circuit-switched voice transmission lines. (en.wikipediawiki/VoIP)
How is this Useful?
“VoIP can turn a standard Internet connection into a way to place free phone calls. The practical upshot of this is that by using some of the free VoIP software that is available to make Internet phone calls, you are bypassing the phone company (and its charges) entirely.”
[attachment=8311]
[attachment=8312]
VoIP as Revolutionary Technology
“It has the potential to completely rework the world's phone systems, because it uses packet-switching rather than circuit-switching. Which makes VoIP more efficient, and less costly.”
Three different Flavors of VoIP
Three different ways to place a call are;
ATA
Simplest and most common way
Uses a device called an ATA (analog telephone adaptor). Which allows us to connect a standard phone to our computer or our Internet connection for use with VoIP. The ATA is an analog-to-digital converter.
IP Phones
Specialized phones look just like normal phones with a handset, cradle and buttons.
Uses an RJ-45 Ethernet connector instead of standard RJ-11 phone connectors.
Connect directly to our router and have all the hardware and software necessary right onboard to handle the IP call.
Computer-to-computer
Easiest way to use VoIP.
All we need is the software, a microphone, speakers, a sound card and an Internet connection, preferably a fast one like DSL modem.
How stuff Works?
Existing phone systems are driven by a very reliable but somewhat
inefficient method for connecting calls called circuit switching.
- When a call is made between two parties, the connection is
maintained for the duration of the call.
- Because we’re connecting two points in both directions, the
connection is called a circuit. This is the foundation of the Public
Switched Telephone Network (PSTN).
Here's how a typical telephone call works:
We pick up the receiver and listen for a dial tone. This let us know that we have a connection to the local office of our telephone carrier.
We dial the number of the party we wish to talk to.
The call is routed through the switch at our local carrier to the party we are calling.
A connection is made between our telephone and the other party's line using several interconnected switches along the way.
The phone at the other end rings, and someone answers the call.
The connection opens the circuit.
We talk for a period of time and then hang up the receiver.
When we hang up, the circuit is closed, freeing our line and all the lines in between.
Circuit switching keeps the connection open and constant.
VoIP uses Packet switching for transmitting voice information into digital form.
Packet switching opens a brief connection -- just long enough to send a small chunk of data, called a packet, from one system to another.
It works like this:
The sending computer chops data into small packets, with an address on each one telling the network devices where to send them.
Inside of each packet is a payload (a piece of the e-mail, a music file or whatever type of file is being transmitted inside the packet).
The sending computer sends the packet to a nearby router and forgets about it. The nearby router send the packet to another router that is closer to the recipient computer. That router sends the packet along to another, even closer router, and so on.
When the receiving computer finally gets the packets (which may have all taken completely different paths to get there), it uses instructions contained within the packets to reassemble the data into its original state.
Packet switching is very efficient because it lets the network route the packets along the least congested and cheapest lines. Also frees up the two computers communicating with each other so that they can accept information from other computers, as well.
How it is that analog audio is turned into packets for VoIP transmission?
Codecs:
Stands for coder-decoder.
Converts an audio signal into a compressed digital form for transmission and then back into an uncompressed audio signal for replay.
Accomplish the conversion by sampling the audio signal several thousand times per second.
Convert each tiny sample into digitized data and compresses it for transmission.
A G.729A codec has a sampling rate of 8,000 times per second.
Operate by using advanced algorithms that help them sample, sort,
compress and packetize audio data.
Codec works with the algorithm to convert and sort everything out, but none of that is any good without knowing where to send the data?
Soft Switches:
E.164 is the name given to the standard for the North American Numbering Plan (NANP).
Which is numbering system that phone networks use to know where to route a call based on the numbers entered into the phone keypad. In that way, a phone number is like an address:
(313) 555-1212 313 = State
555 = City
1212 = Street address
To route the phone call to the region denoted by the area code.
The "555" prefix sends the call to a central office.
Network routes the call using the last four digits. which are associated with a specific location. So based on that system, no matter where you are in the world, the number combination "(313) 555" will always put you in the same central office, which has a switch that knows which phone is associated with "1212."
Soft Switches: (Contd.)
The central call processor is a piece of hardware running a specialized database/mapping program called a soft switch. Think of the user and the phone or computer associated with that user as one package -- man and machine. That package is called the endpoint. The soft switch connects endpoints.
Soft switches know:
Where the endpoint is on the network
What phone number is associated with that endpoint
The current IP address assigned to that endpoint
So when a call is placed using VoIP, a request is sent to the soft switch asking which endpoint is associated with the dialed phone number and what that endpoint's current IP address is. The soft switch contains a database of users and phone numbers. If it doesn't have the information it needs, it hands off the request downstream to other soft switches until it finds one that can answer the request. Once it finds the user, it locates the current IP address of the device associated with that user in a similar series of requests. It sends back all the relevant information to the softphone or IP phone, allowing the exchange of data between the two endpoints.
How do these different pieces of hardware and software will communicate efficient and will understand each other?
Protocols:
Several protocols are currently used for VoIP.
They define ways in which devices like codecs connect to each other and to the network using VoIP.
They also include specifications for audio codecs.
The most widely used protocol is H.323, a standard created by the International Telecommunication Union (ITU).
H.323 is a comprehensive and very complex protocol that was originally designed for video conferencing. It provides specifications for real-time, interactive videoconferencing, data sharing and audio applications such as VoIP.
H.323 is a suite of protocols and also incorporates many individual protocols that have been developed for specific applications.
An alternative to H.323 emerged with the development of Session Initiation Protocol (SIP). SIP is a much more streamlined protocol, developed specifically for VoIP applications. Smaller and more efficient than H.323, SIP takes advantage of existing protocols to handle certain parts of the process
Media Gateway Control Protocol (MGCP) is a third commonly used VoIP protocol that focuses on endpoint control. MGCP is geared toward features like call waiting.
Frequently Asked Questions (FAQs)
If I have VoIP service, who can I call? Depending upon your service, you might be limited only to other subscribers to the service, or you may be able to call anyone who has a telephone number - including local, long distance, mobile, and international numbers. If you are calling someone who has a regular analog phone, that person does not need any special equipment to talk to you. Some VoIP services may allow you to speak with more than one person at a time.
Can I use my Computer While I talk on the Phone? In most cases, yes. Does my Computer Have to be Turned on? Only if your service requires you to make calls using your computer. All VoIP services require your broadband Internet connection to be active.
How Do I Know If I have a VoIP phone Call? If you have a special VoIP phone or a regular telephone connected to a VoIP adapter, the phone will ring like a traditional telephone. If your VoIP service requires you to make calls using your computer, the software supplied by your service provider will alert you when you have an incoming call.
