Transactional Language 1: Beginner's Guide To This Telemetry Protocol.

Transaction Language 1 (TL1) is a set of ASCII-based instructions, or "messages". These messages allow a human user or an Operations Support System (OSS) to manage a network element (NE) and its resources.

TL1: A Standardized Protocol.

Bellcore developed TL1 in 1984 as a standard (MML) man-machine language to manage network elements. Before the development of TL1, most vendors designed gear around their own proprietary protocols. These incompatible protocols caused headaches for operators, programmers, and support technicians. Having a lot of protocols means more training, more support issues, and more screens to monitor.

With the creation of TL1, Bellcore hoped to introduce a single, open protocol for managing network elements. It was intended to replace the diverse protocols used by different vendors.

After divestiture, many new companies began using a variety of protocols within their networks, but TL1 remains arguably the most widely used protocol in North America today.

TL1 is a highly structured management interface that uses a standard command line interface while providing for vendor extensions where appropriate. Messages for fault, configuration, performance, security and testing can all be accommodated by a TL1 interface.

The TL1 protocol is considered a legacy protocol because of its age but is still being used in a variety of new equipment. Mediation of TL1 is increasingly important with different protocols being used in contemporary telemetry monitoring networks.

A Man-Machine Language.


In addition to being open, TL1 is powerful because it bridges the gap between human users and network gear. It is structured enough to be parsed by machines, but also verbose enough to be read by human staff. Since special decoders or debuggers are not necessary, TL1 is a frequent command line interface choice for equipment manufacturers. TL1 messages are also embedded with the database information required to interpret the meaning of an alarm.

How Understanding TL1 Will Help You.

TL1 is a multi-vendor and multi-technology protocol with comprehensive management support. There's a very good chance that TL1 protocol plays a significant role in your network. A solid foundation of TL1 knowledge allows you to do your job more effectively. With this white paper, you're just a few pages away from the core knowing you need.

Is TL1 Easy to Understand?

TL1 is a set of ASCII-based instructions, or "messages". Because TL1 is text-based, you won't be intimidated by a jumble of code or hexadecimal protocols. This makes the learning curve for basic TL1 much shorter than with other protocols.

This doesn't mean, however, that you won't need a basic introduction to TL1 basics. You must learn the basics before you can read, understand, and write TL1 commands. Fortunately, TL1 message formats are very well defined and documented, and you can learn about the most frequently used commands in this guide.

The structure of the system is very similar to other protocols. You typically have a TL1 collection device, such as an RTU, and a TL1 monitoring device or master. The alarm collection device monitors the TL1 equipment and then sends alarms to the master if there is an alert. The master can also request information from the collection device. If your master is not TL1 compatible, you will want to make sure that your RTU can mediate TL1 to a language readable by the master.

What kind of messages does TL1 consist of?

The TL1 language consists of a set of messages. There are 4 kinds of messages:

  • Response Messages:


    The response message is a reply sent by the NE in response to an input message. The response comes upon the completion of the task requested by the TL1 input message. It states whether or not the requested task was completed successfully.
  • Autonomous Messages:


    Autonomous messages, the most frequently used TL1 response type, are output messages sent by the NEs to report alarms. They can also report performance data, configuration changes, or condition changes.
  • Command Messages:


    TL1 commands request an action to be executed by the recipient of the message.
  • Acknowledgment Messages:


    An acknowledgment message is a special reply sent by the NE in connection with a delayed command. This special response is issued after the receipt of the command and indicates the status of the request.

TL1 alarm collection solutions

The KDA-TL1 is an alarm and control remote with 64 discrete alarm points and 8 control points. It reports alarms via pagers and to an OSS in TL1 over TCP/IP when equipped with a Network Interface Adapter (NIA) card.

The NetGuardian is an alarm and control remote with 32 discrete alarm points, 8 controls and 8 analogs. It reports alarms to pagers, e-mail, DCP masters, multiple SNMP managers and multiple TCP ports. It features a web browser interface for user-friendly monitoring and provisioning. It also acts as a terminal server for 8 serial ports, providing reach through access via TCP/IP to a proxy port for each device. Using the proxy ports of theNetGuardian, legacy equipment reporting TL1 can be mediated to your existing LAN/WAN.

TL1 monitoring solutions

The T/Mon NOC is a multi-protocol, multifunction network alarm manager designed as a single-platform solution for all alarm monitoring applications. The T/Mon NOC collects alarm data from a wide variety of equipment, regardless of manufacturer or protocol, and displays the state of your entire network in one interface, eliminating the need for specialized terminals.

In the case of TL1 monitoring, the T/Mon NOC eliminates the need for laborious interpretation of TL1 messages. The instant a TL1 alarm is generated, the user is notified with a blinking, color-coded icon based on its severity. The T/Mon NOCs customizable displays present network events in plain English, in terms that your staff will immediately understand and take action on. The T/Mon NOC interface is easy to use and ensures that system operators will have the right information to take corrective action in an emergency.

TL1 mediation and forwarding

The T/Mon NOC can not only receive TL1 from serial and TCP/IP transports, it can also mediate other protocols and report them in TL1 to a higher level network master over serial or TCP/IP transports.

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