Two-way satellite-only communication: Bandwidth

Satellite Internet customers range from individual home users with one PC to large remote business sites with several hundred PCs.

Home users tend to use shared capacity to reduce the cost , while still allowing high peak bit rates when congestion is absent. There are usually restrictive time-based bandwidth allowances so that each user gets their fair share, according to their payment. When a user exceeds their allowance, the company may slow down their access, deprioritize their traffic or charge for the excess bandwidth used. For consumer satellite Internet, the allowance can typically range from 200 MB (“megabyte,” a multiple of the unit byte for digital information  storage or transmission with three different values depending on context: 1048576 bytes (220) generally for computer memory; and one million bytes (106) generally for computer storage) per day to 17,000 MB per month. A shared download carrier may have a bitrate of 1 to 40 Mbit/s and be shared by up to 100 to 4,000 end users.

The uplink direction for shared user customers is normally time division multiple access (TDMA), a channel access method for shared medium networks, which involves transmitting occasional short packet bursts in between other users (similar to how a cellular phone shares a cell tower).

Each remote location may also be equipped with a telephone modem; the connections for this are as with a conventional dial-up ISP. Two-way satellite systems may sometimes sometimes use the modem channel in both directions for data where bandwidth is more important than bandwidth, reserving the satellite channel for download data where bandwidth is more important than latency, such as for file transfers, a generic term for the act of transmitting files over a computer network like the Internet.

In 2006, the European Commission, the executive body of the European Union responsible for proposing legislation, implementing decisions, upholding the Union’s treaties and day-to-day running of the EU, sponsored the UNIC project which aims at developing an end-to-end scientific test bed for the distribution of new broadband interactive TV-centric services delivered over low two way-satellite to actual end-users in the home. The UNIC architecture employs DVB-S2–“Digital Video Broadcasting-Satellite-Second Generation” (“DVB-S2”), a digital television broadcast standard that has been designed as a successor for the popular DVB-system–standard for downlink and DVB-RCS, an acronym for “Digital Video broadcasting-Return Channel via Satellite or (“Return channel over system”)–standard for uplink.

Normal VSAT dishes (1.2-2.4 m diameter) are widely used for VOIP phone services. A voice call is sent by means of packets via the satellite and Internet. Using codes and compression techniques the bit rate needed per call is only 10.8 kbit/s each way.

See: NewSat’s VSAT Internet From Satellite Services


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