Xircom An Intel Company GEM3501 User Manual
Core Engine GSM/GPRS Modem Developer Guide Preliminary Draft: 7/6/2001
11
Part Number: 07100026, Revision: 002
Confidential
© 2001 Xircom, Inc., an Intel company All rights reserved.
All trademarks and copyrights are the property of Xircom, Inc., an Intel company
All trademarks and copyrights are the property of Xircom, Inc., an Intel company
early current versions of the modem will continue to be supported, as GSM technology
evolves to GPRS, and then on to third generation technologies, which are now in the
process of standardization and development.
evolves to GPRS, and then on to third generation technologies, which are now in the
process of standardization and development.
3.7 Modes of Operation
Core Engine offers several modes of operation to address a variety of application
requirements.
requirements.
3.7.1 Circuit Switched Data
Circuit switched data is the most widespread and traditional means of data and voice
transmission available today. A circuit switched connection occupies one network line for
the entire length of data transmission and during this time, no other user may access this
network line. A circuit switched connection is the optimal means for transmitting any
continuous amount of data, such as video transmission or voice.
transmission available today. A circuit switched connection occupies one network line for
the entire length of data transmission and during this time, no other user may access this
network line. A circuit switched connection is the optimal means for transmitting any
continuous amount of data, such as video transmission or voice.
A common example of a circuit switched network is the public telephone system. When
person A picks up the telephone and dials the number of person B, the network
determines and assigns a path for that transmission. The signal travels through each
assigned circuit switch to complete the connection.
person A picks up the telephone and dials the number of person B, the network
determines and assigns a path for that transmission. The signal travels through each
assigned circuit switch to complete the connection.
Once the signal has reached person B, a continuous two-way transmission path has been
established. On a long distance call, for example, many circuits would need to be
connected together to make the call possible. These circuits are dedicated to the call for
the duration of the transmission and cannot be shared by other users. This requires
substantial network resources to be allocated per user.
established. On a long distance call, for example, many circuits would need to be
connected together to make the call possible. These circuits are dedicated to the call for
the duration of the transmission and cannot be shared by other users. This requires
substantial network resources to be allocated per user.
3.7.2 Transparent and Non Transparent Transmissions
GSM provides two connection modes of transmission: transparent and non-transparent.
All Core Engine models support both modes. The transparent data mode delivers a
service with a variable error rate, with a guaranteed throughput and delay, whereas the
non-transparent mode delivers a constantly low forward error correction rate, but with a
non-guaranteed throughput or delay.
All Core Engine models support both modes. The transparent data mode delivers a
service with a variable error rate, with a guaranteed throughput and delay, whereas the
non-transparent mode delivers a constantly low forward error correction rate, but with a
non-guaranteed throughput or delay.
Not all networks support transparent services.
The non-transparent service delivers the most reliable performance and is closest to using
a modem over a fixed telephone line.
a modem over a fixed telephone line.
3.7.3 Short Message Service
To accommodate smaller messages, GSM uses short message service (SMS) for efficient
and timely data transmission and data retrieval. SMS is a point-to-point, storage and
forwarding, message service that is used in data transmissions such as paging,
notification, news flashes, and information retrieval.
and timely data transmission and data retrieval. SMS is a point-to-point, storage and
forwarding, message service that is used in data transmissions such as paging,
notification, news flashes, and information retrieval.
Short messages can carry up to 140 8-bit characters. (160, 7-bit characters available –
refer to the Core Engine Programmer Reference for configuration)
refer to the Core Engine Programmer Reference for configuration)
Short Messages can be sent and received simultaneously with a voice or data call and
are sent above the voice or data in the overhead-signaling path (Traffic & Bearer).
are sent above the voice or data in the overhead-signaling path (Traffic & Bearer).
Although similar in concept to traditional paging, the primary difference is that SMS is not
geographically restricted as paging systems are. Moreover, the GSM network stores and
resends the message if the receiver’s handset is turned off (In some cases, if a pager is
turned off, the message is simply lost).
geographically restricted as paging systems are. Moreover, the GSM network stores and
resends the message if the receiver’s handset is turned off (In some cases, if a pager is
turned off, the message is simply lost).