VSAT

A VSAT (Very Small Aperture Terminal) is a small earth station, typically a $0.6$–$2.4\,m$ dish, made of an indoor unit (IDU: modem and user interface) plus an outdoor unit (ODU: dish, BUC, LNB, feed).

Topology	Description	Use
Star	Remotes reach a central hub in two hops	Banking, corporate, Internet
Mesh	Remotes talk directly through the satellite (one hop)	Voice, site-to-site
Hybrid	Combination of star and mesh	Large enterprise networks

VSAT network topologies.

VSAT topologies: star (remotes reach the hub in two hops) and mesh (remotes communicate directly in one hop).

The end-to-end signal path identifies the indoor and outdoor equipment between the user terminal, satellite, and hub or remote.

VSAT path: user $\to$ IDU $\to$ ODU (BUC/LNB/dish) $\to$ satellite $\to$ hub or remote VSAT.

Part	Function
IDU	Indoor unit: modem and user interface
ODU	Outdoor unit: dish, BUC, LNB, feed
BUC	Block upconverter: converts and amplifies the uplink
LNB	Low-noise block downconverter: receives and downconverts the downlink

VSAT indoor and outdoor units.

Note

Key Point — VSAT in practice

• Applications: bank ATM/branch links, rural Internet and telephony, enterprise private networks, disaster recovery, tele-education and telemedicine, and oil/gas/hydro remote sites.

• Advantages: rapid deployment, independence from terrestrial infrastructure, wide coverage and a reliable backup link.

• Limitations: propagation delay (GEO), rain fade at Ku/Ka, limited bandwidth versus fibre, and the need for clear line of sight.