Comparative Analysis Of Internet Telephony Gateways Essay

, Research Paper

IP telephony, while still relatively new, is poised to revolutionize corporate telecommunications by at last enabling users to haul voice and data traffic over a single wide area network. International Data Corporation, predicts that the Internet telephony market will grow from US $3.5 million in 1995, to US $560 million 1999. Meanwhile, Tarifica in the UK estimates that AT&T will to lose between US $620 million and US $950 million in international calls to the Internet by 2001.

The problems with telephone systems as they are today, are getting increasingly higher for long distance phone class. Imagine even local ISP’s (Internet Service Providers) offering such low rates as $.02 a minute phone calls from Rapid City to Sioux Falls.

The idea behind IP telephony is enticingly simple, convert voice into packets for transmission over a company’s TCP/IP network. Although simple in principle, IP telephony presents some tough technical hurdles for vendors to surpass. This report will provide readers with a comparative analysis of the IP telephony products currently on the market, or scheduled to ship that will help you understand the significance of incorporating this technology for the benefit of the consumers.

Introduction

The basic concept behind IP telephony is deceptively simple: convert voice into a series of packets, and transmit them across an IP network to be reassembled on the receiving end. While theoretically simple, IP telephony designers face a number of technical challenges, many of them similar to those encountered in designing a digital cellular network. These challenges make designing a good IP telephony gateway a significant undertaking.

Vendors have approached IP telephony from several different angles. Some vendors have leveraged existing hardware such as Dialogic’s multi-port voice cards in conjunction with their own software. Other vendors have built their own DSP cards designed specifically for this task. Other vendors have built stand alone network appliances. And one vendor has taken this a step further by creating an Ethernet IP telephone.

Vendors designing IP telephony products face two fundamental issues. One is latency, or in laymen’s terms the time required for data to travel from point A to point B. Latency does not in of itself destroy data, but it makes for awkward conversation when it climbs above a few tenths of a second. The other fundamental issue is packet loss. TCP/IP, in its present incarnation, provides no guarantees to users that they can transmit a given amount of data within a given period of time. Network performance can fluctuate from moment to moment. Sometimes data will be transmitted immediately, sometimes it will be delayed or not sent at all.

In many respects, the problems facing designers are similar to digital cellular network design in that the underlying transport medium provides no guarantee that data will arrive intact. Therefore, vendors must assume the underlying network is unreliable and compensate for this by using error correction and interpolation techniques to minimize and compensate for lost or severely delayed packets. These problems are not insurmountable by any means, but they do require serious attention.

Common IP Telephony Gateway Architectures

Vendors have taken several approaches to IP telephony. They are:

PC server-based gateways built using industry standard (i.e. Dialogic, NMS) voice cards

PC server-based gateways built using specialized DSP cards designed for IP telephony

Stand-alone network appliances which connect directly to 10BaseT networks

Multi-purpose NIC cards with telephony capability

Stand-alone IP telephones

Rather than focus on specific products, this article will explore the relative benefits and disadvantages of each of these architectures. While product lines vary on a weekly basis, the fundamentals outlined in this article will still be relevant for some time to come.

PC Based-Server Gateways Based On Industry Standard Voice Cards

The first IP telephony gateway products were based on industry standard voice cards such as the Dialogic series voice cards. These cards are designed to play and record announcements to callers, and are typically used in office voice mail or interactive voice response systems.

These vendors had the benefit of being able to get their products to market quickly. However, these systems also have some important limitations:

Industry standard voice cards are not designed for real-time applications like IP telephony. The IP telephony software must deal with audio in discrete chunks rather than as a continuous stream. This introduces latency (delay) into a conversation. Industry standard voice cards are not designed to compress and decompress audio. This means the host PC containing the cards must do all of this processing on the host CPU. This also introduces latency, and limits the scalability of the gateway to no more than a few simultaneous conversations. Industry standard voice cards are generally not very easy to install and configure; they are not plug and play cards. Many of these systems use proprietary protocols to deliver phone calls, which means you are locked into one vendor’s solution. At US $1000 to US $2000 per port, these solutions are on the expensive side

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