1 Introduction
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outstanding performance under poor and moderate signal conditions. As PACTOR-3 also
achieves very high throughput rates under good signal conditions, it is well-suited to HF
channels with good SNR and low signal distortion as well. During the development of
PACTOR-3, high importance was given to compatibility with ordinary SSB transceivers
(using standard 2.4 kHz wide IF-filters). Therefore, PACTOR-3 can achieve its maximum
speed with using unmodified, common SSB transceivers. The occupied bandwidth is
around 2200 Hz.
Thus PACTOR-3 is the ideal means of fast and reliable data communication over (the
sometimes difficult medium) HF-radio. The new protocol is fully backwards compatible
to existing PACTOR-1/2 networks.
The properties of the PACTOR-3 protocol summarized:
•
Under virtually all signal conditions, PACTOR-3 is faster than PACTOR-II. Under
average signal conditions a speed gain by a factor 3x to –4x is achieved, under very
favourable conditions the speed improvement can exceed 5x.
•
Maximum data throughput (without compression) greater than 2700 Bit/sec, around
5200 Bit/sec if PMC (online text compression) is applied.
•
PACTOR-3 is at least as robust as PACTOR-2 under extremely poor signal
conditions.
•
Maximum bandwidth only about 2200 Hz.
•
Low crest factor (high mean output power).
•
High spectral efficiency – PACTOR-3 makes very good use of the bandwidth.
•
Fully backwards compatible to existing PACTOR-I/II networks.
1.6.2
PACTOR-IP-Bridge
The PACTOR-IP-Bridge (PIB) is a new Network –Integration Protocol developed by
SCS
. The dominant protocols of the Internet like TCP/IP, as well as the Point-to-Point
Protocol (PPP), which have become standard for establishment of links between Internet
applications, are combined with the PACTOR modes. The result of this intelligent
protocol combination is a data transparent and relatively fast Internet access via HF-radio
using standardized user interfaces. The PTC appears to an attached PC as if it were a
Hayes compatible "telephone modem”. The PTC locally takes over both the complete
PPP and TCP/IP handling. Except for a minimum fraction of protocol overhead, the
physical PACTOR link only carries useful data. The huge amount of overhead of the
TCP/IP and PPP protocols (which are designed for broad banded wired links) is reduced
to the absolute minimum required. By locally carrying out the PPP protocol between the
PC and the PTC a further decisive advantage arises: Because of the very short timeouts,
PPP used to be nearly impossible over slow communication channels with relatively large
delays. Timeout problems are now solved by the PACTOR-IP-Bridge.
Summarizing the qualities of the PIB:
•
TCP/IP-transparent and relatively fast Internet access via HF-radio.
•
Internet-services accessible via PACTOR, e.g. E-Mail (SMTP/POP3), FTP, HTTP, ...
•
Up to 4 Internet channels ("sockets") over one physical PACTOR link.
•
Extreme compression of the TCP/IP and PPP"overhead".