VOIP

yummy1984

Par 100 posts (V.I.P)
VoIP is a very simple concept. Instead of using a traditional telephone company's internal network for voice services, VoIP connections use the Internet. By using this electronic highway, you can take advantage of the Net's ubiquitous presence to obtain lower-cost telephone services.

Although voice travels through the telephone company's dedicated network via time-division-multiplexing (TDM) protocol, TDM is not suitable for the Net. In 1996, when the International Telecommunication Union (ITU) adopted the H.323 communications standard for the Net, VoIP started. One of the first general appearances was via Microsoft Messenger and the chat facility. It worked because the user's computer had a set of chips allowing bidirectional conversion between analog and digital, and the user provided a plug-in microphone. Around 1991 Motorola introduced very low-cost high-speed integrated chips to handle analog-to-digital/digital-to-analog (ATD/DTA) conversion for audio encoding and decoding. Multiple chips could be built into hardware cards to handle concurrent audio sessions. Today, all personal computers (PCs) have these chips integrated into the motherboard.



Audio Components of a VoIP System

How do DTA and ATD converters work? An analog telephone device connects to an adapter box. This adapter includes an ATD chip that samples the input analog audio signal around 20,000 times a second (even though the chip can do it 10 times faster). Each sample measures the audio signal voltage and transforms the audio voltage measurement into a number. The numbers are collected and are placed in a record, one number behind the other. Every few milliseconds the completed record is replaced by another empty one. The completed one is compressed (to reduce transmission time), and this compressed record is sent out to a destination via the Internet.

On the receiving end, the record containing the stream of numbers is read, decompressed, and placed in a receiving queue. The first record in the queue is the active one. From this record, one number at a time is read and presented to a DTA chip, creating an output (audio). The presentation rate to the DTA converter is equal to the session initiation protocol (SIP)-negotiated rate at which the record was filled, allowing audio to be reproduced at the same pitch and speed at which it was measured by the sampler.

VoIP had to wait for suitable protocols and hardware devices in order to act as a bridge between the Internet and legacy telephone systems. The H.323 standards on which VoIP depends allow you to use the Internet to concurrently transmit voice, video, and faxes. VoIP works with hardware interfaces to emulate a telephone exchange or a private branch exchange (PBX). A PBX device connects to the local telephone system via either an integrated or external VoIP gateway. The gateway providing the interface between the phone system and the Internet is often referred to as a point of presence (POP). Many such POPs are PC-based and consist of hardware. In simpler terms, the VoIP gateway will determine if your originating telephone call will route through the Internet or via the public phone system.

The initial telephone protocols to traverse the Internet were many, and required a substantial knowledge of protocols, definitions, recommendations, and standards such as inter-asterisk exchange (IAX), SIP, H.323, H.225, real-time transport protocol (RTP/RTCP), remote function call (RFC) 3550, H.245, H.501, H.450, H.460, T.120, T.38, Skinny Call Control Protocol (SCCP), Unified Networks IP Stimulus (UNIStim), and more. Eventually several of the critical protocols were merged into one, the SIP.

Prior to VoIP, one's telephone number was assigned to a physical location. One of the features of VoIP, however, is portability of telephone number location. The absence of a fixed physical location means that your telephone number follows your laptop, or follows a telephone adapter installed on a universal serial bus (USB) adapter. Now, a visit to a foreign country will still provide home-based telephone service to the assigned telephone number. Certain business requirements were imposed on VoIP vendors and their customers to respect emergency calls, among others. This requirement was resolved for statically located telephones (residences and businesses), but remains unresolved for portable VoIP phones.

After registering as a telephone company, a VoIP vendor will begin providing telephone services in competition with the traditional telephone companies. Between VoIP providers, certain agreements are negotiated to permit POP-to-POP connections. Between the POPs, arrangements are made to provide free domestic long-distance calls, and (in some cases) free calls to international cities.

VoIP Solution Overview

Requirement
high-speed access to the Internet using anything from a single cable connection up to speeds provided by one or more T1 lines;
one or more server PCs with installed interface cards;
VoIP software; and
a connection interface to the Internet that is programmed as a POP gateway.
 
VoIP is a very simple concept. Instead of using a traditional telephone company's internal network for voice services, VoIP connections use the Internet. By using this electronic highway, you can take advantage of the Net's ubiquitous presence to obtain lower-cost telephone services.

Although voice travels through the telephone company's dedicated network via time-division-multiplexing (TDM) protocol, TDM is not suitable for the Net. In 1996, when the International Telecommunication Union (ITU) adopted the H.323 communications standard for the Net, VoIP started. One of the first general appearances was via Microsoft Messenger and the chat facility. It worked because the user's computer had a set of chips allowing bidirectional conversion between analog and digital, and the user provided a plug-in microphone. Around 1991 Motorola introduced very low-cost high-speed integrated chips to handle analog-to-digital/digital-to-analog (ATD/DTA) conversion for audio encoding and decoding. Multiple chips could be built into hardware cards to handle concurrent audio sessions. Today, all personal computers (PCs) have these chips integrated into the motherboard.



Audio Components of a VoIP System

How do DTA and ATD converters work? An analog telephone device connects to an adapter box. This adapter includes an ATD chip that samples the input analog audio signal around 20,000 times a second (even though the chip can do it 10 times faster). Each sample measures the audio signal voltage and transforms the audio voltage measurement into a number. The numbers are collected and are placed in a record, one number behind the other. Every few milliseconds the completed record is replaced by another empty one. The completed one is compressed (to reduce transmission time), and this compressed record is sent out to a destination via the Internet.

On the receiving end, the record containing the stream of numbers is read, decompressed, and placed in a receiving queue. The first record in the queue is the active one. From this record, one number at a time is read and presented to a DTA chip, creating an output (audio). The presentation rate to the DTA converter is equal to the session initiation protocol (SIP)-negotiated rate at which the record was filled, allowing audio to be reproduced at the same pitch and speed at which it was measured by the sampler.

VoIP had to wait for suitable protocols and hardware devices in order to act as a bridge between the Internet and legacy telephone systems. The H.323 standards on which VoIP depends allow you to use the Internet to concurrently transmit voice, video, and faxes. VoIP works with hardware interfaces to emulate a telephone exchange or a private branch exchange (PBX). A PBX device connects to the local telephone system via either an integrated or external VoIP gateway. The gateway providing the interface between the phone system and the Internet is often referred to as a point of presence (POP). Many such POPs are PC-based and consist of hardware. In simpler terms, the VoIP gateway will determine if your originating telephone call will route through the Internet or via the public phone system.

The initial telephone protocols to traverse the Internet were many, and required a substantial knowledge of protocols, definitions, recommendations, and standards such as inter-asterisk exchange (IAX), SIP, H.323, H.225, real-time transport protocol (RTP/RTCP), remote function call (RFC) 3550, H.245, H.501, H.450, H.460, T.120, T.38, Skinny Call Control Protocol (SCCP), Unified Networks IP Stimulus (UNIStim), and more. Eventually several of the critical protocols were merged into one, the SIP.

Prior to VoIP, one's telephone number was assigned to a physical location. One of the features of VoIP, however, is portability of telephone number location. The absence of a fixed physical location means that your telephone number follows your laptop, or follows a telephone adapter installed on a universal serial bus (USB) adapter. Now, a visit to a foreign country will still provide home-based telephone service to the assigned telephone number. Certain business requirements were imposed on VoIP vendors and their customers to respect emergency calls, among others. This requirement was resolved for statically located telephones (residences and businesses), but remains unresolved for portable VoIP phones.

After registering as a telephone company, a VoIP vendor will begin providing telephone services in competition with the traditional telephone companies. Between VoIP providers, certain agreements are negotiated to permit POP-to-POP connections. Between the POPs, arrangements are made to provide free domestic long-distance calls, and (in some cases) free calls to international cities.

VoIP Solution Overview

Requirement
high-speed access to the Internet using anything from a single cable connection up to speeds provided by one or more T1 lines;
one or more server PCs with installed interface cards;
VoIP software; and
a connection interface to the Internet that is programmed as a POP gateway.

Hey friend, thanks for sharing such a nice article and explaining about the concept of VOIP. Well, i am also uploading a document where you would get more detailed information with images, so download and check it once.
 

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