Siemens SINAUT ST7 System Manual page 278

Glossary
automatic general request, a general request can also be triggered at any time by the user
program or from the control center.
TD7onTIM does not support the general request.
GPRS
(General Packet Radio Service)
GPRS is an expansion of GSM mobile wireless that adds packet-oriented data transmission.
Network connections are established over GPRS either in the Internet or in private networks.
The data is transmitted using the Internet protocols TCP/IP or UDP/IP.
GPS
(Global Positioning System)
GPS is a worldwide US satellite navigation system for highly accurate location, navigation
and time distribution. It operates with 24 orbiting satellites (21 operational and 3 spare
satellites) on six satellite orbits at a height of approximately 20,000 kilometers. Each satellite
contains an atomic clock whose time is transmitted continuously along with the orbit data.
The GPS receiver receives data from a maximum of six satellites and calculates its position
based on these values. Once the position has been calculated, the transmission time of the
data from the individual satellites can be calculated. The GPS world time (UTC) is calculated
in the system based on these values.
GSM
(Global System for Mobile communications)
Worldwide standard for wireless transmission of voice, data, fax and text messages (SMS).
GSM-based wireless networks can be found in many countries throughout the world. A
distinction is made according to frequencies: PCS 850 MHz, GSM 900 MHz, DCS 1800 MHz
and PCS 1900 MHz.
Image memory / send buffer
A TIM has a send buffer and an image memory for buffering send messages.
Before it is forwarded to the communications partner, each message is entered in the send
buffer. Once it has been sent, the message is cleared from the send buffer. A message is
transmitted according to either the → send buffer principle or the → image memory principle.
The user specifies the transmission principle during configuration of the data messages.
The storage capacity of the send buffer depends on the particular TIM type and ranges from
10 000 to 56 000 data messages.
Image memory principle
A fixed position is reserved in the image memory for each data message transferred to the
TIM for transmission. Each newly transferred message always overwrites the old message in
the image memory. The image memory therefore contains all data messages with their most
recent content from the process.
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System Manual, 07/2009, C79000-G8976-C178-07
Station control system