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switched off before the end of 2025, making this a very immediate and urgent issue for many users, given the time needed to roll out any new solutions. The question for owners of devices using these networks therefore is how to migrate to the newer LTE or 5G networks with minimum cost and disruption. For some, this change will finally justify the replacement of the remote devices with more modern equivalents in order to take advantage of other new functionality available from them. For many, however, device replacement is seen as an expensive, high risk, and disruptive operation, being forced upon them solely because of the need to migrate away from 2G cellular communications.
Thankfully for these system owners, there is an option available which can transparently migrate their existing 2G (and/or PSTN dial up) devices onto a modern ethernet, LTE or 5G network, allowing their legacy systems to continue to operate with minimal change or disruption.
Replacement System Outline: In order to understand how this works, it is first necessary to understand the operation mode of most 2G based M2M systems. This effectively mirrors the mechanisms used in landline-based dial-up PSTN networks, the connection sequence of which is summarised in the following diagramme:
Figure 1 – 2G/PSTN dial up call establishment sequence.
Each device is connected to a modem which uses a protocol known as the ‘Hayes’
12 Figure 1 – 2G/PSTN dial up call establishment sequence. FEBRUARY 2024 | ELECTRONICS FOR ENGINEERS
or ‘AT’ command set. This defines a series of serial interface commands that can be used to obtain a connection to a remote device, transfer data across that connection, and subsequently disconnect the call. In order to migrate these legacy devices onto an ethernet, LTE or 5G network, what is needed is to effectively replace the AT modems with devices that support the AT command set via a serial interface, but which then can use an IP network to replicate
the functionality of the dial-up system. This means that the connection / data transfer / disconnection command sequences need to be supported, but more importantly that a mechanism exists to create a virtual point to point serial connection through the IP network. In reality, it is rare that only two devices are involved, and most of these systems have an architecture where a large number of remote devices will try to dial in to a single central server via one or more dial up numbers.
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