Before buying VSATs, an enterprise has to decide upon the network size, the type of network (dedicated or shared), network architecture (star or mesh), technology (TDMA or DAMA), and the spectrum band (extended C-band or Ku-band).

n Network Size: The buyer has to first decide upon the total number of sites that will be covered by a VSAT, the number of users per site, and the range of applications to be used. He will also have to ascertain the duration of usage by different applications and users. The various applications can be voice, fax, interactive data messaging, data broadcasting and data collection requirements, and can vary from corporate to corporate. Corporates will also have to specify the type of equipment (EPABX, telephone or LAN) to be connected to the VSAT, and the physical interfaces and protocols to be used for the interconnection.

n Type of Network: The corporate has to decide whether he wants a dedicated or a shared hub network. In a dedicated hub scenario, the hub infrastructure is utilized by a single corporate entity with all the VSATs in the network sharing the available resources. Such a hub is recommended only when the number of sites is large and the application is specific to the corporate. Unless the number of terminals are in the range of 300–350, it makes little economic sense to invest in a separate hub and operate as a private captive network. Typical users of such hubs are banks and stock exchanges.

In the case of shared hub, corporates share the hub along with the other service providers. The shared hub service providers also handle licensing and frequency coordination services. The advantage here is that users can concentrate on their business areas instead of creating expertise and skills in satellite communication systems, for effective utilization of the network.

n Network Architecture: The two types of network architecture in use are star and mesh. Star is the most commonly used architecture and uses VSATs and central hub stations. This architecture works for both point-to-multi-point and multi-point-to-point communication services. However, since the complete communication has to switch through the central hub station, the link uses double-hop satellite links, and hence, there is a delay of 540 ms. While this is acceptable for many data applications, it is not preferred for real-time voice and video-conferencing applications.

The mesh network uses identical-size VSATs for communication, directly through the satellite. Thus, it needs large antennae. Since single hop link is involved, this network is widely used for voice and video-conferencing applications. These networks can be configured on demand assigned basis.

n Technology Type: The corporate also has to decide whether it needs TDM/TDMA or the SCPC/DAMA technology. In the DAMA technology, VSATs are pre-allocated a designated frequency and it is quite similar to the terrestrial leased line. DAMA is ideal for voice because there is minimum delay, whereas TDM/TDMA is ideal for data applications.

n Spectrum: The buyer has to state which band to opt for. Satellite communication evolved exploring C-band and extended C-band, but Ku-band has been found to be more appropriate for VSAT networks. However, this band suffers from some attenuation during rain. Tropical countries like India prefer to exploit extended C-band before using Ku-band, as it is not severely affected by rain. Satellite transponders in extended C-band possess a bandwidth of 36 MHz, whereas Ku-band has a bandwidth of 36/54/72 or 77 MHz.

After selecting the above elements, the corporate buyer has to evaluate the type of VSAT that it plans to buy, the VSAT vendor, and the service provider.

n Speed: At present, the return speed varies from vendor to vendor and also from product to product. One can get speeds varying from 156 kbps to around 1.2 Mbps. So depending on the application and usage requirement, one can choose a particular product, based on a particular technology.

n Throughput: It specifies the end-to-end bandwidth that an enterprise gets and this is where technology plays its role. A few vendors have been talking about bandwidth conservation technologies like TCP/IP spoofing while others have been talking about PCMA/CRMA.

n Technology: As of now, there are four technologies in use. These are TDM/TDMA, FTDMA, MFTDMA, and CRMA. Vendors are also moving from proprietary standards to open standards, which is good for the corporate customer in the long run, as he will have the option to hop from one service provider to another, depending on the quality-of-service provided by different service providers. The open standard that everybody has been talking about is DVB RCS.

n Cost: The hardware cost varies, depending on the configuration that one goes for. Apart from the hardware costs, bandwidth charges too form an important component. Bandwidth costs can be negotiated depending on the number of VSATs installed, and this approach can prove to be cheaper than the per kbps option. The annual maintenance cost for the network is roughly around 6-8 percent of the hardware cost.

n Quality of Service (QoS): The user needs to aim for certain QoS demands for his applications to run smoothly. For voice quality, mean opinion score (MOS) level, blocking rate and bit error rate (BER) are specified. Interactive data services require tolerable response time. Network availability is one of the major QoS needs of the user.

n Selection of Service Provider: When the user opts for shared hub services, it is very important to select the right service provider who can meet all his requirements. The failure rate of remote VSAT equipment depends on the product, while performance quality depends on the technology, the product and the network architecture. End-to-end service to users and the overall network availability is the sole responsibility of the service provider. In an infrastructure project, such as a VSAT network, buyers can not easily shift from one service provider to another, since the technology platform is proprietary. Hence, one has to carefully evaluate the above criterion while choosing a VSAT service provider. Customer services can vary widely from vendor to vendor. An effective project management system and process adopted by the vendor will ensure on-schedule delivery of VSATs and networks. A service provider must provider comprehensive end-to-end services for onsite technical support, integration of VSATs with user terminals, network applications and integration ability, and process and infrastructure for delivering consistent service, optimum utilization of the network. Also, round-the-clock helpdesk service, training of corporate users, provision of transparent billing and service-level agreements, ongoing service reports and review procedures, support during crisis, demonstration of performance quality on demand, and assistance to network augmentation when needed, will be required by the user.