The greatest challenge to developers of VSATs is to build versatile and reliable data communication systems that could compete with existing terrestrial technology. Consumer broadband Internet access is a reality for more than 40 million homes in developed countries, but pushing this out in a global context has proven to be a challenge. Implementers of VSAT networks have their own challenges to face, that of properly sizing the network and maintaining its performance as requirements change. The purpose of this paper is to provide some guiding principles how to approach the problem of capacity planning and network sizing.
Key words: Satellite Communication, VSAT
Collecting Requirements for the VSAT Network We are taking the systems approach to this problem, which consists of determining the requirements, sizing the network, and determining overall performance against the requirements. The typical requirements for a data communication network fall into the following categories.
• The applications that the network is to support, in specific terms such as software, user devices, message content, and standards to be employed.
• The number of connections / users and locations that are to be serviced, which defines the geographic properties and the connections of the requirements. The output of this part of the exercise is the topology of the network.
• The traffic or information volume that is offered to the network by each user or by an expected volume of users considering the particular amount of information as well as the timing of its occurrence (also referred to as its temporal nature).
• Throughput is the amount of useful data that is transferred per unit of time, measured in bits per second, packets per second, or the like. This provides an estimate of the aggregate bandwidth required from the VSATs, hub, and satellite.
• Time delay (also called latency) is the amount of time required to transfer a specific amount of data. Applications should be subdivided as to their fundamental needs in this area—real-time applications versus non-real-time applications. Latency is collection of line transfer time, access protocol time, propagation time, and node processing time. Interestingly, satellite system users focus on propagation time, which is only one of the factors. If this is a circuit-switched type of network, then the call setup time must also be considered. All of these times are the sum of a number of contributors, some of which are constant and some of which are variable or random in nature.
• Response time is measured from when a user initiates a request to when the response is displayed on the user’s terminal device. This applies mostly to data communication networks where users employ PCs or other types of display terminals, phones, and video systems.
• Other service demands that are unique to the user community, such as mobility and transportability, growth, and ability to support new and evolving applications.
• Service management aspects, such as reliability, availability, mean time to repair (MTTR), and help-desk and accounting support.
Each requirement has a definite impact on the, cost, complexity and capacity of the network, VSAT or otherwise. Requirements (first, second and third) are the basic inputs for the design of the network, defining the structure, distribution, and timing of the information to be carried and/or distributed among users. Believe it or not, this is the hardest thing to determine because in most situations it is simply not known with any precision. Another real but less good reason is the internal structure of the organization where functional groups tend to not want to share this kind of information. Breaking down these barriers can be extremely time taking, tedious and this is a reason why the network fails to satisfy users who were unable to have their particular needs presented in the final design of the network.
The remaining requirements (fourth, fifth and sixth) are performance measures that can be obtained from a live network. User fulfillment is often driven by them, this is the reason why it is important that they should be understood before a major commitment is made to a particular technology. In the nonappearance of a working network, tests with a pilot system can gain insight knowledge. It turns out that the user experience and level of approval is based on what they already know from using other networks and services. If their expectation is low, then any improvement will be made favorably.
ABSTRACT The greatest challenge to developers of VSATs is to build versatile and reliable data communication systems that could compete with existing terrestrial technology