Shared VSAT

Shared VSAT

ASC offers shared VSAT communication services throughout Australia and the South Eastern and Western Pacific Regions. Satellite Bandwidth is limited in availability which makes service costs quite expensive. This is where the iDirect TDM/TDMA and DVB-S2 technology comes into play in finding a way of using satellite bandwidth more efficiently to provide a greater IP throughput to users on a large network. Therefore ASC’s shared VSAT services use iDirect’s TDM/TDMA and DVB-S2 technology to provide users more cost effective solutions.


TDM/TDMA is used in almost all large VSAT networks. The service provider operates a large hub earth station with VSAT’s placed at customers remote sites. Large hub earth stations mean that VSAT’s can have small antennas and require lower power transmitters which mean a lower cost per VSAT to the customer. As the remote VSAT antennas are quite small they are unable to directly to each other. This is why TDM/TDMA networks are always a “Star” topology. ASC has supplied and implemented Mesh Topology networks which allow not only communications through the Hub Earth Station but from remote to remote.

Time Division Multiplexing (TDM) is a scheme where many VSAT’s share one high speed “outbound” carrier from the Hub Earth Station. All data streams are merged into one stream and broadcast to all VSAT’s on the one outbound carrier from the Hub Earth Station. Each VSAT then takes it’s own packets and ignores all others.

Time Domain Multiple Access (TDMA) is used for the “inbound” traffic from the remote VSAT’s. The VSAT’s take it in turns to transmit on a common frequency channel which has been divided into timeslots and allocated to remotes. The position of the VSAT’s timeslot in the schedule assigned by the HUB is determined by using the location of the HUB, the VSAT and the Satellite in the sky. Each VSAT then transmits in bursts in the appropriate timeslot in the service schedule. This then allows more VSAT’s to transmit more data while using the same bandwidth as all other remote VSAT’s on the network.


DVB-S2 still operates in TDM/TDMA format but is uses different encoding and compression techniques. DVB is Digital Video Broadcasting where obviously the carrier that is being transmitted is a completely digital signal. DVB-S is digital technology that enables digital data to be transmitted over satellite and it has been combined with MPEG-2 compression standards to create a secure standard for transmitting data over the satellite that allows for more efficient use of satellite bandwidth (MHz) to provide high speed IP throughputs (Mbps). DVB-S2 technology networks are much larger than those supported by conventional VSAT systems.

The advantages to the customer using DVB-S2 services are that the Remote VSAT antenna size is smaller and service availability is higher. The RF Power requirements of the Remote VSAT system may also be lower which also reduces the cost of the service to the user.