Voice ip voip over dsl

Satellite networks allow users to fit a solution to their real--and changing--requirements.

The evolution of the Web in the last 10 years has made having some form of Internet protocol (IP) connection common, be it a local area network (LAN) connection, dial-up, DSL or cable modem. Using the Internet is now almost customary for interactive videoconferencing, streaming audio and video, and real-time applications--besides the usual Web surfing and the data traffic that drove its creation. Voice over Internet protocol (VoIP) is up-and-coming as an IP application. The major advantages of using VoIP include the pervasive nature of IPconnections that lead to the development of many applications to utilize it. This, in turn, has driven the trend toward all-IP networks.

Previously, network engineers designing a voice-over-packet network would consider voice-over-frame relay (VoFR) and voice-over-ATM (VoATM) systems, but the lure of a one-protocol, all-IP network, makes VoIP attractive. VoIP allows complete integration of voice and data over a common LAN infrastructure, processed by common data/VoIP routers.

When IPpackets must travel between LANs over the wide area network (WAN), voice and data IP packets are treated alike, and are encapsulated by the same WAN protocol (e.g., HDLC, FR, or ATM) and share the same WAN data transport system, which will include satellite links for many networks. In fact, the huge demand for Internet connectivity has resulted in a corresponding increase in IP traffic carried via satellite. It has also led to the development of numerous special-purpose satellite IP delivery systems, which transport IP packets directly, without encapsulation in a WAN protocol--like frame relay or ATM--using relatively small VSAT systems.

While, today, broadband IP solutions dominate the voice-over-satellite (VSAT) market for data delivery, such systems will increasingly be used also to carry VoIP traffic. In fact, there are some distinct advantages to using VoIP with satellite IP delivery over terrestrial IP networks. The greatest benefit is distance-insensitive connectivity, one of the prime drivers behind the development of satellite communications. Satellites provide connectivity within the satellite-coverage footprint, with every site theoretically capable of reaching all other sites in the network, regardless of the terrestrial distance between them.

Terrestrial networks are limited to the land-bound connections running between nodes--reaching from one end of a large region to another may involve crossing dozens of interconnect points. The land lines eventually end, and IP service or any service beyond the terrestrial infrastructure must wait for the copper line to be installed. Satellite networks deploy quickly and cost-effectively provide seamless connectivity with existing broadband terrestrial networks.

An often disregarded benefit of satellite networks is the delivery of almost identical quality of service across an endless number of locations. Terrestrial networks are a composite of subnetworks with different topologies (e.g., ring fiber networks with star topology terminating points or metropolitan networks) and tens or hundreds of switching or routing points in between.

In the case of IP traffic over terrestrial networks, those routing points between source and destination often have unpredictably heavy congestion, causing a large variability in latency. This variation in latency will lead to VoIP packet jitter, severely degrading voice quality, and requiring large playback buffers on VoIP equipment (termed jitter buffers). Satellite networks, on the other hand do not require large jitter buffers, as the jitter is predictable.

The flexibility afforded by modern broadband satellite networks cannot be duplicated with terrestrial networks. Satellite networks allow users to fit a solution to their real requirements, even if those requirements change over time. A number of flexible satellite IP networking products are available, so selecting the appropriate IP telephony equipment for the network topology and configuring it to account for the unique nature of satellite links is only a matter of time.

Broadband Internet protocol requirements have given the satellite industry a new life. Although the catalyst for this renewal is the growth in the Internet, satellite solutions must also support telephony requirements. This is particularly true in the developing regions, where delivery of dial tone for voice services will not be supplied by an alternate public switched voice network. Such satellite networks may also address the basic communications requirement, telephony, and not just the desire for Internet access.

In many ways, IP telephony and satellite IP networks are a perfect fit, with satellite networks able to provide quick telephone connectivity to anyplace in the satellite footprint. IP telephony can be a practical and cost-efficient voice solution when implemented in a broadband IP network with appropriate optimization, including delay management and efficiency improvement. In high-end, corporate networks, integrating IP telephony and IP data services with a mesh satellite IP network is an option worth investigating.

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Kingsley is manager of applications engineering and Fakhari is a vice president for Lockheed Martin Global Telecommunications Products, Bethesda, MD.