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VoIP

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Assignment for Week 8

· Study two of the references on VoIP.

· Make some suggestions as to how and why you think VoIP will affect your professional (not personal) career.

Note: one of the references on this topic was RTP/RTCP, which I’ve described in the Week08.

VoIP Protocol

Because of the prevalence of the Internet, and because IP is the protocol connecting almost all devices, VoIP is a powerful service platform for next-generation application.

Voice over IP (VoIP) uses the Internet Protocol (IP) to transmit voice as packets over an IP network. Therefore, VoIP can be achieved on any data network that uses IP, like the Internet, Intranets and Local Area Networks (LAN). Here the voice signal is digitized, compressed and converted to IP packets and then transmitted over the IP network. Signaling protocols are used to set up and tear down calls, carry information required to locate users, and negotiate capabilities. VoIP introduces the actual method of transmitting voice over an IP network and IP telephone. It describes telephony devices that use IP as the native transport for voice and call signaling. IP telephony needs VoIP to send calls over the network

How it works

Here is how a VoIP transmission is completed:

1. Because all transmissions must be digital, the caller’s voice is digitized. This can be done by the telephone company (which is how carriers use IP in their networks), by an Internet service provider (ISP), or by a PC on your desk.
2. Next using complex algorithms the digital voice is compressed and then separated into packets; and using the Internet protocol, the packets are addressed and sent across the network to be reassembled in the proper order at the destination. Again, this reassembly can be done by a carrier, and ISP, or by one’s PC.
3. During transmission on the Internet, packets may be lost or delayed, or errors may damage the packets. Conventional error correction techniques would request retransmission of unusable or lost packets, but if the transmission is a real-time voice communication that technique obviously would not work, so sophisticated error detection and correction systems are used to create sound to fill in the gaps.
4. After the packets are transmitted and arrive at the destination, the transmission is assembled and decompressed to restore the data to an approximation of the original form.

Advantages

The main advantage of VoIP is the cheaper option for the phone calls. Another key advantage is being able to combine phone calls with business data. It means you can adopt call-centre style technology with each incoming call triggering on-screen pop ups with customer details. Or you can add a ‘Click to call’ button on your website. When you consider that the average employee spends hundreds of hours a year on the telephone, it’s easy to see why VoIP is attracting a lot of attention. Many large organizations from banks to retail companies are using it for voice calls. As the cost of high-speed Internet access (such as Broadband) comes down, VoIP is now within reach of small businesses. Some telecommunication companies and Internet Service Providers (ISPs) are now offering Voice over IP deals targeted at the small business sector. Traditional phone calls work by allocating an entire phone line to each call. With VoIP, voice data is compressed, and with VoIP on your computer network you can add telephones and increase call capacity without running additional cabling.

Issues

There are several technology characteristics that might affect your decision to use this technology:

• VoIP delay or latency is characterized as the amount of time for speech to exit the speaker’s mouth and reach the listener’s ear.
• Propagation delay is caused by the speed of light in fiber or copper-based networks.
• Processing delay defines many different caused of delay and is caused by devices that forward the frame through network.
• Serialization delay is the amount of time it takes to actually place a bit or byte onto an interface.
• Jitter is the variation of packet inter-arrival time. Jitter is one issue that exists only in packet-based networks. While in a packet voice environment the sender is expected to reliably transmit voice packets at a regular interval. These voice packets can be delayed throughout the packet network and not arrive at the same regular interval at the receiving station
• Echo is normally caused by a mismatch in impedance from the four-wire network switch conversion to the two-wire local loop. Echo can be loud, and it can be long. The louder and longer the echo, the more annoying the echo becomes. Echo cancellers are limited by the total amount of time they wait for the reflected speech to be received, a phenomenon known as echo tail. It is important to configure the appropriate amount of echo cancellation when initially installing VoIP equipment. If it is not configured properly callers will hear echo during the phone call.
• Packet loss in data networks is both common and expected. Many data protocols, in fact, use packet loss. The protocols identify the condition of the network and can reduce the number of packet loss in that network. When putting voice on data networks, it is important to build a network that can successfully transport voice in a reliable and timely manner. Also it is helpful when a mechanism can be used to make the voice somewhat resistant to periodic packet loss.
• In normal conversations, some one speaks and someone else listens. Modern network contains a bidirectional, 64,000 bit-per-second channel, regardless of anyone is speaking. This means that in a normal conversation at least 50% of total bandwidth is wasted. By using VoIP, this wasted bandwidth can be utilized for other purposes when voice activity detection (VAD) is enabled. Typically, when the VAD detects a drop-off of speech amplitude, it waits a fixed amount of time before it stops putting speech frames in packets. This fixed amount of time is known as handover and is typically 200 ms.
• Digital-to-Analog conversion issues also currently plague toll networks. Each time a conversion occurs from digital to analog and back, the speech or waveform becomes less true. Although modern toll networks can handle at lease seven D/A conversion before voice quality is affected, compressed speech is less robust in the face of these conversions
• The circuit switches are organized in a hierarchical model in which switches higher in the hierarchy are called tandem switches. If the TDM switches compress voice and the tandem switch must decompress and recompress the voice, the voice quality can be drastically affected. Voice degradation occurs when there is more than one compression/decompression cycle for each phone call.

VoIP affect in my profession

Being in IT area for many years I think VoIP is getting more and more into this area of industries. Use of high-speed internet as a major form of communication and data exchange within this field has become a “common knowledge” instead of something exotic and unusual. Fiber optic technology enables wide range of companies, big and small, and individuals to have high speed internet affordable tool instead of a dream. In our company, for example, most of the communication and data exchange are done using Intra and Internet communication. Being international, it was critical to go this rout to save cost of development process using this technology. The high speed internet had become and enabler for wide use of VoIP. Phone and video conferencing become a very common way of group meetings, technical and business reviews. Our phone system is completely digital and uses VoIP technology with great success. Many of company’s sites and factories are outside of the US and all over the country, testing is mostly done in India, manufacturing in China and Mexico, and so on. Voice, data, and telecommunication over the Ethernet is so common and convenient that there is no go back to the phone switches, analog media, and handwriting – everything is electronically stored in digital format and is exchanged over high speed internet. VoIP will be getting better and better with advancing in the communication technology of the internet: LANs, WANs and others. It’s already started, that individuals appreciate more and more advantages of VoIP technology at home as well. The time of old fashion phones are almost over. Home and cell phones soon will become one thing and I mean within next few year. It’s scary to think about it, but at some point we all will be connected via one headset or embedded chip into ours bodies freely transferring all kind of data over the Ethernet throughout the world. VoIP is just the beginning of all of this.