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Digi Connect® Application Guide Cellular IP Connections (Uncovered)
When connecting remote devices to a cellular network, users must take into account the requirements of the application and the available IP addressing schemes available by the wireless telco. Specifically, consideration must be given in wireless solutions regarding which side of the connection initiatescommunication. Each wireless carrier handles usage and management of IP addresses differently; therefore customers must be prepared to carefully examine the type of IP connectivity options available and make sure that they work with the targeted application. The purpose of this paper is to help users understand the IP connectivity options available and steer them towards the best solution based on: • • • •Type of Cellular Application o Mobile Originated vs. Mobile Terminated IP Addressing Schemes o Static vs. Dynamic o Private vs. Public IP Addressing on GSM Networks IP Addressing on CDMA Networks

Mobile Applications
In order to establish what type of application your scenario falls into, you must first ask yourself: “Where is the traffic originating from?” or said differently, “Which end is thefirst to initiate the connection?” Consider this simple diagram:
Remote Site Remote LAN / Devices Host Site (HQ)

Cellular IP Network

Customer WAN or Internet

Digi Connect WAN/ RG

Mobile Interface gets IP address from Cellular Provider

The answer would fall among these three possible applications:


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Cellular IP Connections (Uncovered)• Mobile Originated – Remote device makes first communication. A remote device or workstation initiates an out-going data connection. This connection could be terminated by a host application at headquarters (HQ) or a remote web server (i.e., web browsing). Some carriers refer to this as mobile originated data. Another typical example of mobile originated data is a client-tosite VPN.
Workstation Initiates


Wireless Network Digi Connect WAN Internet

Host Application, Web server, etc.

Mobile Terminated – Host makes first communication. A host application at HQ requests information from the remote devices and/or workstations. In this case the remote site must terminate the IP connection. This is sometimes called mobile terminated data. Common applications includetelemetry, SCADA and other forms of polling.
Remote Site Remote LAN / Devices
Host Initiates Traffic


Wireless Network

Customer WAN

Host Application polls remote or sends to remote

Digi Connect WAN

Mobile Connection is Active so Accepting Incoming Data

Both Mobile Originated and Terminated. Two common examples are site-to-site VPN and telemetry applications where thehost polls the remote while the remote is able to proactively send out alarms.

Why is this important? Devices like the Digi Connect wireless products obtain their IP address from the cellular network. Cellular data providers have various plans that provide different IP addressing options. For example,many plans provide only private IP addresses. Other plans may provide public IP addresses, butthe may block via firewall any incoming traffic from outside the cellular network.


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Cellular IP Connections (Uncovered) IP addressing and security options are very important items to consider when working with your cellular provider. This document is intended to help you and your provider determine which IP addressing and security schemes are needed.Engage your provider’s technical staff early in the process to ensure a smooth transition to utilizing cellular IP traffic. This will make your “un-tethered” IP connectivity experience a pleasant one.

Wireless Carrier IP Addressing Schemes
Although every wireless telco offers different IP addressing options, they all fall into one of the categories below: Public vs. Private IP Addresses If...