| The hub modem transmits an
outbound carrier which is received by the remote VSATs. The hub modem also
receives an inbound carrier from each remote.
Carrier sizes, either inbound or outbound, may be from 2.4kbit/s to
10Mbit/s bit rates.
The outbound carrier is normally shared amongst several sites. For
example you might buy 300 kbit/s downlink and then share this amongst 3
sites, each with 6 PCs.
Return link carriers to the hub are typically smaller capacity, e.g. 33
kbit/s.
Lower bit rate return links are normally dedicated to assure high speech
quality for VoIP calls and to avoid overheads due to TDMA which involves
transmission in the form of a series of bursts with gaps in between and
delays due to carrier recovery headers on the front of each burst.
TDMA also interferes with good speech quality for VoIP calls. Return
link bit rate needs to be approx one third of the outlink bit rate for mixed
internet access and VoIP. For VoIP alone the capacity needs to be the
same each way.
The hub modem is connected to the internet via a Cisco router to the main
American internet backbone, for worldwide terrestrial connectivity. |
The customer VSAT terminal
comprises a CDM570L modem with header and payload compression, QoS and 8-QAM
and 16-QAM options and 3 watt TRIA
(integrated 3 watt BUC and universal LNB, transmit receive module).
Dish size will be 89cm, 1.2m, 1.8m or 2.4m diameter.
The customer may connect a hub or switch or wireless router and as many
LAN PCs as required (up to 253 maximum).
The VSAT modem is remotely controlled and managed from Global Teleports
(UK) at Brookmans Park (UK).
Monthly prices approx $700 per month per 100kbit/s. Lower prices,
as much as half price, may be possible with extra large dish to allow 16-QAM
modulation to work. The highest price corresponds to smallest dish.
Think in terms of these example options:
100kbit/s total ($700 per month) : 60k downlink and 40k uplink, both dedicated,
suitable for small internet cafe with 5 PC and 1 VoIP phone.
400kbit/s total ($28,000 per month): 280k downlink shared 3:1 and three 40kbit/s
dedicated uplinks, suitable for 3 schools or internet cafes, each with 8 PCs
and 1 VoIP phone. South Africa satellite dish pointing and lat long calculator |
