VSAT internet basics

This page covers VSAT internet basics. The internet served using VSAT terminal in hilly remote areas is known as VSAT internet.

Internet is served through various transmission mediums e.g. DSL, fiber optic, copper line, cellular technologies (GSM, CDMA, LTE etc.) , indoor technologies (LAN, WLAN etc.) and so on. VSAT uses satellite for internet application.

The VSAT internet is ideal for places where it is difficult to install cellular towers or lay copper or fiber optic cables such as hilly terrain areas. As internet uses satellite which is installed at 36000 Km, it is easy to avail its service.

Like other internet systems, VSAT can be used for both upload and download applications. As we know internet uses HTTP protocol for browsing. It also uses protocol such as FTP/TFTP for upload and download of a file from internet.

VSAT internet block diagram

VSAT internet block diagram

The figure-1 depicts VSAT internet block diagram. As shown it consists of user computer or laptop, VSAT, Satellite, Hub station, internet infrastructure including servers.
Let us understand subsystems mentioned in the VSAT internet block diagram with example of downloading a file from internet.
• Once the VSAT connection with satellite and Hub Station has been established, VSAT link acts as leased line for internet. Most popular VSAT operates at C band, Ku band and Ka band. In C band downlink frequency will be from 6 GHz band while uplink frequency is from 4 GHz band. The file download occurs on downlink frequency while file upload occurs on uplink frequency.
• ISP (Internet Service Provider) line is connected at Hub station which is being used by all the VSATs available in the network.

Advantages and Disadvantages of VSAT internet

Following are the advantages of VSAT internet:
• VSAT provides internet to the areas where other means of internet such as fiber, copper or cellular systems are not feasible to be installed.
• It is a more secure way of communication. Often encryption unit is provided before satellite modem to increase the security level.

Following are the disadvantages of VSAT internet:
• Download time or delay is higher due to multi-hop communication between VSAT and Hub station via satellite. It requires 120 ms for electro-magnetic waves to travel from VSAT to satellite having distance of 36000 Km at the rate of 3 x 108 m/sec. Two hops will have 240 ms of delay.
• The system is more complex, in case of any issues it will be very difficult for the users to troubleshoot. Under this circumstances, it is recommended to call up VSAT internet service provider for support.
• The data rate in VSAT internet, depends on satellite bandwidth allocated to the particular VSAT. It does not only rely on bandwidth of internet connection taken at the hub station by the company.


Refer following sub topics related to VSAT technology:
Article on VSAT   VSAT NMS protocol  RF Terminology   Satellite Terminology  Access types  SCPC  MCPC  RF Transceiver  C band RFT  Microstrip  RF upconverter design   Power Amplifier  what is modulation  satellite Modem  Link Budget