User Manual

DM15/25 Integrator’s Manual 34 OF 38

PSTN

MSC

Automatic

Call

Director

(Digital

PBX)

Application

Server

operator

module

V.27ter

Burst modem application

data base

PBX control

modem

RX/TX

data

-Natural Microsystems AG/4000 Card.

- Four T1 Lines, 96 ports.

Host Modem Server

The 250 Byte Message Protocol

The key feature of the 250-byte protocol is that it allows applications to send up to 250 bytes of data

during a voice call. The voice conversation is suspended while data is transferred.

The 250-byte protocol utilizes powerful error detection and correction algorithms to maximize the

chance of delivering error free data. The data in each packet is duplicated three times to enable

majority logic correction, the data is encoded with a convolution encoder that allows multiple bit

error correction, and each ten data bytes are protected by a 16 bit CRC. If a first attempt to send the

data packet fails then it is retransmitted up to two more times. The time to send 250 bytes varies

between 5 and 15.5 seconds depending on the number of retransmissions.

6.5.5 Telematics capability

Sony Ericsson DM-15/DM-25 modules can be used in two different modes. The two modes are

called NAM-1 and NAM-2. In NAM-1 mode the module is a TDMA dual mode phone.

Applications can use NAM-1 mode to place analog or digital calls. NAM-1 also supports digital

data modes such as short message service. In NAM-2 mode, also called “telematics” mode, the

module behaves similar to an AMPS-only phone. Applications can use telematics mode to send

short data packets on an analog voice channel.

In order to switch between NAM-1 and NAM-2 modes the module must be reset, therefore

applications that desire to use both modes are necessarily more complex. The NAM-1 and NAM-2

modes share the same ESN as well as most of the configuration settings. The important exceptions

are MIN, band order, SID and SOC. These parameters can be set independently for telematics