Satellite ATM Network Architectures: An Overview

IEEE Network • September/October 1998 he global information infrastructure (GII) of the United States has included satellite asynchronous transfer mode (SATM) as part of the communications infrastructure to support global mobile communications, information transport and access. The Telecommunications Industry Association (TIA) has recently formed an SATM group to study the various technical issues (e.g., reference models, media access, and mobility management) related to SATM. In addition, the ATM Forum Wireless ATM Group has established liaison with TIA to initiate standardization efforts on SATM [1]. This article reflects the increased interest expressed by industry, academia, and regulatory bodies in SATM network architectures. Current satellite network configurations comprise mainly ground, user, and space segments. The ground segment consists of gateway Earth stations (GESs), a network control center (NCC), and operation control centers (OCCs). Satellites communicate with fixed and mobile users via satellite–user links and gateway stations. Location tracking of mobile terminals is performed at GESs. Most of the GESs are connected to mobile switching centers of the land mobile network. The ground NCC provides functions such as mobile registration, verification, billing, network database distribution, and network resource allocation and management. OCCs, on the other hand, are responsible for satellite orbital tracking, ranging, and control. Processed information from OCCs is then distributed to GESs in order to support location tracking and handoffs. The user segment relates to a fixed, handheld, or vehicle-mounted unit requiring global integrated services (data, voice, and video). A dual-mode mobile user terminal can have access to both satellite and terrestrial cellular/wireless networks. Finally, the space segment consists of low/middle/geostat ionary Earth orbit (LEO/MEO/GEO)1 satellites with or without intersatellite links (ISLs) and OBP capability. Satellites are now commonly termed based on their distance from and spatial relationship with the earth. A GEO satellite orbits at an altitude of 22,300 mi above the earth, providing substantially wide coverage. An example application of GEO service is mobile car phone systems. LEOs and MEOs orbit at 500–7000 mi in altitude; compared to GEOs, LEOs are nearer to the Earth, making smaller handheld devices possible. However, because LEOs/MEOs yield smaller coverage areas, a constellation of satellites is needed to provide coverage of the Earth. The Global Positioning System (GPS), for example, uses 24 LEOs satellites to provide position and location services for portable and vehicle-mounted GPS devices. Traditional satellites, especially GEOs, mainly act as Satellite ATM Network Architectures: An Overview