User Manual

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Cellular Networks
Short Message Services (SMS)
SMS messages, as specified by the ETSI organization (documents GSM 03.40 and GSM 03.38) and can be
up to 160 characters long, where each character is 7 bits according to the 7-bit default alphabet. Eight-
bit messages (max. 140 characters) are usually not viewable on phones as text messages. Instead, they
are used for data in 16-bit messages (max. 70 characters) and used for Unicode (UCS2) text messages
viewable on most phones.
SMS is a point-to-point store and forward technology with 2 basic functions:
• Transmit a message from the short message service center to the mobile station. SMS-DELIVER PDU
(Protocol Data Unit)
• Transmit a message from the mobile station to the service center. SMS-SUBMIT PDU (Protocol Data Unit)
SMS messages contain up to 140 octets which is equivalent to
• 160 Latin characters (7 Bit Coding) in Text Mode, or
• 70 Unicode characters (double byte), such as Arabic or Chinese characters.
SMS Summary
• Up to 140 octets or 160 characters for every message
• No IP-based communication, only suitable for sending/receiving serial data
Circuit Switch Data (CSD)
Circuit Switched Data (CSD) is the original form of data transmission developed for Time Division Multiple
Access (TDMA) based mobile phone systems like Global System for Mobile Communications (GSM). GSM
CSD bearer service is the most widely used data service providing a “non-transparent” data rate of 9.6
Kbps. “Non-transparent” in this context means error correction and flow control.
Usually, GSM network operators support the non-transparent CSD bearer service through a modem
interworking function. This means that a mobile station (mobile phone) initiates a data call and the network
routes the call to the modem interworking function, which is located at the Mobile Switching Center (MSC)
of the GSM network, which then dials the number supplied by the mobile station.
Confirm that your cell phone service provider allows fax/data type connections for your cellular service plan.
Please note that we are not referring to high-speed wireless data services or SMS. We are referring to your
cellular service plan’s ability to transmit a “fax call” connection, which has been widely included in cellular
service plans for years. This feature is typically referred to as CSD (circuit switched data).
• CSD Summary
- Up to 9.6 Kbps
- Circuit-switched connection
- IP-based communication possible with dedicated link, but speed is slow and billed by connection setup,
most operators remove CSD service
- Most GSM operators provide the service
- In North America, CSD has been completely phased out by the end of 2007