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Many believe that Voice over Internet Protocol (VoIP) is the inexpensive way to make long distance phone calls and they freely use the public Internet as their carrier. No carrier can assure acceptable voice quality if they use the Internet for transport. Internal network hardware required to assure voice quality within the private network is a substantial investment and merely adding the voice tasks to the data network without modification will adversely affect voice quality. This paper discusses some of these limitations and encourages you to review this carefully. |
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The term Voice over Internet Protocol or VoIP has attained celebrity status and people often boast of this technology as the way to avoid long distance costs, reduce over all costs, and even to snub the Public Switched Telephone Network (PSTN) local and long distance telephone carriers. To support this claim, there are several companies that offer phone service, local dial tone, and what appears to be conventional phone service using the public Internet as the carrier. According to their ads, all you need is a high speed Internet provider and that you are foolish to use your high priced traditional carrier. Should you have problems with voice quality, they claim the problem is due to inadequate bandwidth (Internet speed) or improper internal hardware on your end. In fact these may be part of the problem but they are not the only problems. VoIP is designed to use the Internet Protocol to send voice just like data is sent. This is not the same way voice has been sent traditionally. Traditionally, voice requires a dedicated circuit linking both parties. There is no other traffic on the circuit and sufficient capacity is provided to handle the voice load. This works very well. The Internet Protocol is different. It was designed to provide a highly redundant means of data communication. Data is divided into packets. Each packet is dispatched independently through a maize of routers and reassembled at the destination. The routers that forward packets are subject to failure, congestion, delay, and packet loss. Lost or damaged packets are resent. There is no rigid deadline for completing packet transmission because of the retransmission capability. This is how the highly redundant network performs. This works very well with data packets where there is no absolute time deadline for all packets to be received. VoIP differs from traditional voice in that the voice signal is transmitted using the standard Internet Protocol that is used for data. Lost, delayed, or damaged voice packets require a retransmission just like data packets. However, voice requires packets to arrive at their destination within a time deadline and is time sensitive whereas data transmissions are not. Retransmission of a lost packet usually takes too long and voice quality degrades – often to the degree it is unacceptable. Within a private (not using the Internet) network, VoIP packets are marked for priority handling. In the event of congestion, VoIP packets are dispatched first – thereby assuring timely transmission and rendering VoIP packet loss unlikely - provided the private network has sufficient capacity. The priority is handled via managed switches and managed routers that are capable of recognizing and propagating voice packets first. Site to site communication over a dedicated private leased line (e.g. a point to point T1) maintains and process priority marked VoIP packets provided appropriate network hardware is properly installed and the Carrier is . With proper equipment this works very well. The key is VoIP priority marking and priority handling. When congestion occurs, data packets are held and voice packets are dispatched first. This is a critical feature that assures timely voice packet transport. Merely increasing bandwidth without addressing packet priority does not assure voice packet priority and does not, in and of itself, assure quality transmission. The Internet is not designed for priority packet marking or priority handling of marked packets. All packets are handled in a first in – first out manner. When congestion occurs, packets will be delayed or lost – and voice quality will degrade to unacceptable level. Internet capacity at your gateway is not the only potential congestion location – actually congestion can happen at any router along the route – so merely beefing up the internet speed will not address congestion induced transmission problems. No carrier who uses the Internet for transport can assure quality voice transport – no matter who they are or what they claim. Properly designed and configured VoIP private networks can be suitable, economical, and reliable. However they require more engineering in their design and configuration. The traditional data network hardware has to be upgraded with equipment that marks voice for priority and propagates priority throughout all segments of the private network. VoIP is particularly suitable in a new facility where there is no data or voice network yet or where the traditional voice network is at end of life. If you are interested in learning whether VoIP is suitable for you, feel free to contact E Commerce Technology Michiana, Inc for a no obligation preliminary discussion. Gene T. Bohn |
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