Friday, 1 March 2013

NATC installs DATUM DVB/SCPC V-SAT connection

Contributed by Corinna Bordewieck

On February 16, 2013, NATC successfully transferred one of its premium clients, with an office in Liberia’s southeast, over from an iDirect modem to a DATUM modem. While both systems use DVB/SCPC technology, switching to the DATUM modem in this case was preferential because it allowed us to more than double the client’s internet speed, from 1.5 MB/month to over 3 MB/month, at half the cost – clearly an optimal solution!

As many NATC blog readers may already know, DVB (digital video broadcasting) technology was developed to deliver digital television service using data packets of compressed audio, video and control data. DVB bundles data packets together from numerous, smaller data streams and transmits them over a multiplex, or multi-channel, system. On the receiving end, these packets are parsed out to individual users who have requested them. The multiplex system can also deliver IP (internet protocol) data at the same high speeds, and in fact, on the same system at the same time.

The broad bandwidth, coupled with the manner in which the information is transmitted, makes it preferable to use of DVB technology for the downstream channel of an internet connection: since this is the channel used to pull up websites and download information, it is for the vast majority of users the channel that sees higher traffic.

However, the connection we set up still uses SCPC, or a single channel per carrier, technology for the upstream channel. This is almost always the lower-traffic channel, and is used for tasks such as uploading data. Therefore, a DVB/SCPC system provides the greater bandwidth needed for the high traffic stream, but a narrower, single channel for the lower traffic stream. In this case, the downstream channel is 2.5 MB/month and the upstream is 512 KB/month, for a total of over 3 MB.

For some nice diagrams on Digital Video Broadcasting/Single Channel per Carrier Internet Protocol transmission, courtesy of atrexx, click here.

So, our client had their hardware on site and ready to go, but in order to get the connection up and running, our Head Technician had to configure the system itself. NATC works with a partner which has technicians placed in the UK and in Israel – since flying someone in from one of these locations to a remote area of Liberia would not be a very cost-effective plan, our Head Technician set up a configuration platform over the phone, using the Teamviewer program installed on his laptop to allow the overseas technician access to the system.

Once this was done, our Head Technician had to test the DATUM modem and DVB receiver, and then change the system over from the iDirect Modem to the DVB receiver and DATUM modem. The internet connection itself required several days more of monitoring in order to determine and fine-tune the frequency for the DATUM modem’s SCPC return channel. As mentioned above, the upstream SCPC channel has a much narrower bandwidth than the downstream DVB channel, and therefore it takes some time to home in on the frequency that will optimize the signal strength from the satellite.

All in all, the process of installation, configuration and troubleshooting took seven days – more than worth it when we successfully got our client up and running with their new, cheaper, faster connection.

Coming soon: connecting a client’s offices in the interior with their Monrovia headquarters, via CISCO VPN!

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