VSAT NETWORK APPLICATIONS AND TYPES

VSAT NETWORK APPLICATIONS AND TYPES
OF TRAFFIC
VSAT networks have both civilian and military applications. These
will now be presented.
1.4.1 Civilian VSAT networks
1.4.1.1 Types of service
As mentioned in the previous section, VSAT networks can be configured
as one-way or two-way networks. Table 1.1 gives examples
of services supported by VSAT networks according to these two
classes.
It can be noted that most of the services supported by two-way
VSAT networks deal with interactive data traffic, where the user
terminals are most often personal computers. The most notable
exceptions are voice communications and satellite news gathering.
Voice communications on a VSAT network means telephony with
possibly longer delays than those incurred on terrestrial lines, as
a result of the long satellite path. Telephony services imply full
connectivity, and delays are typically 0.25 s or 0.50 s depending on
the selected network configuration, as mentioned above.
Satellite news gathering (SNG) can be viewed as a temporary
network using transportable VSATs, sometimes called ‘fly-away’
stations, which are transported by car or aircraft and set up at a
location where news reporters can transmit video signals to a hub
Table 1.1 Examples of services supported by VSAT networks
ONE-WAY VSAT NETWORKS
Stock market and other news broadcasting
Training or continuing education from a distance
Distribute financial trends and documents
Introduce new products at geographically dispersed locations
Distribute video or TV programmes
In-store music and advertising
TWO-WAY VSAT NETWORKS
Interactive computer transactions
Low rate video conferencing
Database inquiries
Bank transactions, automatic teller machines, point of sale
Reservation systems
Sales monitoring/Inventory control
Distributed remote process control and telemetry
Medical data/Image transfer
Satellite news gathering
Video teleconferencing
Voice communications
located near the company’s studio. Of course the service could be
considered as inbound only, if it were not for the need to check
the uplink from the remote site, and to be in touch by telephone
with the staff at the studio. As fly-away VSATs are constantly
transported, assembled and disassembled, they must be robust,
lightweight and easy to install. Today they weigh typically 100 kg
and can be installed in less than 20 minutes. Figure 1.11 shows a
picture of a fly-away VSAT station.
1.4.1.2 Types of traffic
Depending on the service, the traffic flow between the hub and the
VSATs may have different characteristics and requirements.
Data transfer or broadcasting, which belongs to the category of oneway
services, typically displays file transfers of one to one hundred
megabytes of data. This kind of service is not delay sensitive, but
requires a high integrity of the data which are transferred. Examples
of applications are computer download and distribution of data to
remote sites.
Interactive data is a two-way service corresponding to several
transactions per minute and per terminal of single packets 50 to
250 bytes long on both inbound and outbound links. The required
response time is typically a few seconds. Examples of applications
are bank transactions and electronic funds transfer at point of sale.
Inquiry/response is a two-way service corresponding to several
transactions per minute and terminal. Inbound packets (typically
30–100 bytes) are shorter than outbound packets (typically
500–2000 bytes). The required response time is typically a few seconds.
Examples of applications are airline or hotel reservations and
database enquiries.
Supervisory control and data acquisition (SCADA) is a two-way
service corresponding to one transaction per second or minute
per terminal. Inbound packets (typically 100 bytes) are longer than
outbound packets (typically 10 bytes). The required response time
ranges from a few seconds to a few minutes. What is most important
is the high data security level and the low power consumption of the
terminal. Examples of applications are control and monitoring of
pipelines, offshore platforms, electric utilities and water resources.
Table 1.2 summarises the above discussion.
Military VSAT networks
VSAT networks have been adopted by many military forces in the
world. Indeed the inherent flexibility in the deployment of VSATs
makes them a valuable means of installing temporary communications
links between small units in the battlefield and headquarters
located near the hub. Moreover, the topology of a star-shaped network
fits well into the natural information flow between field units
and command base. Frequency bands are at X-band, with uplinks
in the 7.9–8.4 GHz band and downlinks in the 7.25–7.75 GHz band.
The military use VSAT must be a small, low weight, low power
station that is easy to operate under battlefield conditions. As
an example, the manpack station developed by the UK Defence
Research Agency (DRA) for its Milpico VSAT military network is
equipped with a 45 cm antenna, weighs less than 17 kg and can be
set up within 90 seconds. It supports data and vocoded voice at
2.4 kbs−1. In order to do so, the hub stations need to be equipped
with antennas as large as 14 m. Another key requirement is low
probability of detection by hostile interceptors. Spread spectrum
techniques are largely used [EVA99, Chapter 23].
1.5 VSAT NETWORKS: INVOLVED PARTIES
The applications of VSAT networks identified in the previous section
clearly indicate that VSAT technology is appropriate to business or
military applications. Reasons for this are the inherent flexibility
of VSAT technology, as mentioned in section 1.1, cost savings and
reliability, as will be discussed in section 3.3.
Which are the involved parties as far as corporate communications
are concerned?
– Theuser is most often a company employee using office communication
terminals such as personal computers, telephone sets or
fax machines. On other occasions the terminal is transportable,
as with satellite news gathering (SNG). Here the user is mostly
interested in transmitting video to the company studio. The
terminal may be fixed but not located in an office, as with
supervisory control and data acquisition (SCADA) applications.
– The VSAT network operator may be the user’s company itself,
if the company owns the network, or it may be a telecom
company (in many countries it is the national public telecom
operator
is then a customer to the network provider and/or the
equipment provider.
– The VSAT network provider has the technical ability to dimension
and install the network. It elaborates the network management
system (NMS) and designs the corresponding software. Its inputs
are the customer’s needs, and its customers are network operators.
The network provider may be a private company or a
national telecom operator.
– The equipment provider sells the VSATs and/or the hub which
it manufactures. It may be the network provider or a different
party.
For the VSAT network to work, some satellite capacity must be
provided. The satellite may be owned by the user’s company but
this is a rare example of ‘vertical integration’, and most often the
satellite is operated by a different party. This party may be a national
or international private satellite operator.
The above parties are those involved in the contractual matters.
Other parties are on the regulatory side and their involvement will
be first presented in section 1.9.
Figure 1.12 summarises the above discussion. The terminology
will be used throughout the book and therefore Figure 1.12 can
serve as a convenient reference.