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4000/5000 Modems’ User Guide

Chapter 7: Serial IP – Packet Assembly

Disassembly

The purpose of this feature is to enable access to remote legacy devices (with no

TCP/IP stack) over the wireless packet network.

This feature is particularly used in telemetry applications such meter reading and

SCADA devices. In case of a serial connection between an attached terminal and the

modem, there are instances when data exchanged between the terminal and modem

is not IP traffic but raw serial data (typically layer 2 data). In this case, the modem

operational mode should be set to Serial IP.

When set in Serial IP mode, upon reception of the IP packets, the modem strips off

the IP headers from those packets and sends them to the attached device as raw data

perceived correctly by the device. When the device is sending data, the modem

encapsulates the data in IP packets to be transmitted over-the-air to an assigned

destination. Flush parameters are essential for precise local serial communication.

Such parameters are directly related to the type of protocol running on the attached

device at the data link layer level. Depending on the type of application (direction of

data traffic) and type of IP protocol used, the modem should be set accordingly.

If the attached terminal is queried by a remote application, the Serial IP Listening

Server on the modem should be configured accordingly. The modem performs socket

handling on its own end according to IP packets received from the remote application.

The flush parameters determine the encapsulation of data received from attached

terminal. Flush on time out parameter is a multiple of 100 milliseconds, which is the

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BlueTree 5000 Guide de l'utilisateur Page 28