MPDS - MPDS FAQ


MPDS stands for Mobile Packet Data Service. With MPDS the customer's data is packaged up in a way that allows it to be sent through a channel that is shared by other users. The customer is only charged for the amount of data packages sent vs. the per minute charge with your ISDN connection. This enables the user to be online around the clock and only be charged for the data transferred over the satellite connection. MPDS is based on the IP protocol. Hence, it is well suited for data. MPDS is a packet-based network that supports IP-based applications now used within the majority of office systems today. MPDS carries user data across a shared 64kbit/s channel offering the end-user a service billed on volume as opposed to time.

How to Set Up Your PC

You connect your PC to the RS232 port of the Capsat® Messenger and turn it on. To establish the MPDS you click a dial-in icon for your MPDS service. Now you are connected to the Internet, but contrary to a standard modem connection to an Internet you do not pay for the time you are connected but for the amount of data transferred. While in MPDS mode the TT-3080A is flagged busy in the Inmarsat-M system, i.e. it is not able to receive any call, e.g. mini-M or ISDN, until it leaves MPDS mode and returns to normal idle mode. The TT-3080A transceiver is connected to a PC or similar equipment via a standard RS-232 cable. In this manual the set-up of a PC running a MS-Windows operating system is described.
Please find information on how to set up of a MS-Windows based PC by clicking here.

MPDS Applications
MPDS is the most economic and convenient solution for applications like:

• E-mail
• Small to medium size file transfer
• LAN extension
• Database access
• Internet /intranet access and web browsing
• Compressed video and picture transmission
• SCADA
• IP Communication
  

Note that most Mobile Office Applications typically only use full bandwidth during a fraction of the connected time.

When you are connected to the Internet/network the data is not sent constantly in both directions. Instead the information is being sent and received in bursts, with gaps in between the bursts. This results in poor utilization of the Global Area Network bandwidth. During web browsing you are typically idle 85 % of the time and sending and receiving data for the remaining 15 %. Presently when you use the ISDN service you are charged by the amount of satellite channel time that you use. With the new MPDS service you are only charged for the data that you send and receive (in Mbites) and not the time that you are connected.

The MPDS and the ISDN compliment each other. Applications that require high bandwidth should be sent via ISDN while applications that require less bandwidth, should be sent via MPDS. With MPDS you can stay on-line all day and only be charged when you are actually transmitting or receiving.

MPDS extends the effectiveness of operatives in the field and the
support they receive by enabling an ‘always on’ connection. Secure and efficient integration with the company intranet enables personnel
to work much as they would when in the office.Volume related billing means that information and reports can be received when they are sent, without incurring the costs otherwise associated with a
continuous connection. MPDS benefits from the compatibility and
robustness of packet data and the proven reliability of Inmarsat’s
ISDN satellite channel.

A geophysics survey team is equipped with a GAN terminal connected to a PC used for data analysis and communication. The terminal keeps an ‘open’ MPDS connection that automatically sends system reports and continually monitors the company’s internal e-mail over its secure intranet. An e-mail is received from
the project manager asking for an urgent re-run of a particular seismic test.The team leader responds by making a voice call to clarify the test parameters.The results from the test are in the form of a 1MB data file which is uploaded using File Transfer Protocol (FTP) directly onto the company’s knowledge management system over a secured ISDN link.
Most computer applications work in a ‘half duplex’ manner which means they either send or receive information and are inactive in-between.The periods of inactivity are typically down to the user and the system at the other end processing and
responding to the request.This type of communication is suited to MPDS with examples being: small, frequent e-mails, IP/LAN connection, database access, thin client applications and web access.
Supervisory Control and Data Acquisition (SCADA) applications such as unmanned automated monitoring systems are similary suited to MPDS. Large file transfers, store and forward video, videoconferencing and broadcast quality audio links are better suited to full Mobile ISDN making effective use of the full
bandwidth available.

As with most software, different applications and file combinations will produce different results in terms of transfer times and efficiencies. In broad terms, MPDS is recommended for e-mails of less than 500 kilobytes and FTP file transfers of under 250 kilobytes.