What's New

19 January 2016

M2M Networking – Migrating from Analog to Cellular Connectivity

The Challenge of Migrating from Analog to Cellular Connectivity

In today’s WAN management applications, Network Administrators oversee a diverse network of equipment, both new and old, that is deployed around the globe. For years, dial-up analog modems have been used to make contact over the PSTN to remote sites for legacy M2M activities such as out-of-band network access, substation communications, SCADA, fuel tank monitoring, and energy management.

As PSTN service in some areas across the U.S. becomes less available and more expensive, a transition plan to M2M cellular connectivity is becoming inevitable. However, the operation of cellular modems and cellular networks is inherently different from the operation of analog modems via the PSTN, making the transition difficult and expensive.

The Solution

USRobotics has developed a technology called “Modemulation” that can simplify the migration from analog to cellular connectivity in remote M2M networks.

USR3520 Modemulator & Cell Gateway

USR3520 Modemulator & Cell Gateway

The USR3520 “Modemulator”™ & M2M 3G Cellular Gateway is a simple and flexible drop-in cellular replacement for legacy M2M applications that require peer-to-peer connectivity. Compatibility with both the PSTN and cellular networks provide seamless connections that are indistinguishable to the system and allow rolling deployments or the flexibility to utilize the network that is right for each situation. Retain all current legacy software and remove the need for a new system redesign for the most efficient and cost-effective solution for dial-up replacement. The Modemulator & M2M 3G Cellular Gateway has unequaled network and carrier flexibility for reliable, secure connections for mission critical M2M applications.

Using a USR3520 Modemulator at the network operations center, a Network Administrator can contact a remote Modemulator over the cellular data network by entering the same dial command that is used for dial-up modems. Two Modemulators replace two dial-up modems and operate as a seamless “drop-in replacement” for dial-up modems and the PSTN.

The Modemulator can also route a connection over the PSTN from a local dial-up modem to a dial-up modem at a remote site that hasn’t been upgraded yet. Both cellular and dial-up sites can be managed conveniently using one terminal and the same familiar dial command.

How the USR3520 Modemulator Works

The host Modemulator interfaces to a terminal’s serial port, just as a dial-up modem would. The Modemulator accepts commands and returns responses that emulate a dial-up modem. The remote Modemulator interfaces to the console port of the networking equipment (or port server), just as a dial-up modem would.



An Administrator assigns an arbitrary phone number to each remote Modemulator, and enters that phone number and the IP address and port number of each remote Modemulator into a phonebook in the host Modemulator. When a dial command (e.g. ATDT555-1234) is entered into the Modemulator from the terminal, it searches its phonebook for an associated IP address. If an entry is found, it will connect to the remote Modemulator, allowing the Operator to manage the remote networking equipment.

The connection is made to a GSM or CDMA 3G cellular data network, and the data routing is provided by a Mobile Virtual Network Operator (MVNO). A special service from the MVNO allows routing from one cellular device to another within their network, without crossing a firewall or traversing the public Internet. Such private data routing is extremely secure because 1) cellular data networks do not allow direct device-to-device communication, 2) the subscriber’s private sub-net is isolated from other devices on the MVNO network, and 3) routing from the public Internet is blocked by the MVNO firewall.

USR3520 Modemulator Diagram

USR3520 Modemulator Diagram

If an entry is not found in its phonebook, the Modemulator realizes that the phone number is addressing a dial-up site and automatically routes the dial command to an attached dial-up modem.

Key benefits of the USR3520 Modemulator:
1. Drop-in analog to cellular replacement
2. Retain all current software – no need for system redesigns or costly overhauls
3. Major cost savings for a quick and easy technology upgrade
4. Replace hardware on an ad hoc basis with a system that allows both analog and cellular connections
transparent to the software or user
5. Standard operating procedure is unchanged
6. Significant reduction in monthly recurring costs when replacing POTS lines.
7. Readily available throughout the channel for quick delivery and installation.

Download USR3520 Modemulator/3G Gateway Data Sheet (PDF)

Contact Multi-Link for product specs and support 800-535-4651 or email sales@multi-link.net