SNMP Devices: A General Overview

A SNMP device is, quite simply, a device that is managed using the Simple Network Management Protocol (SNMP). SNMP is an open-source protocol, meaning that any manufacturer can utilize it.While there are many protocols that devices can use, SNMP is one of the most common protocols used, because of its ease of use and access. This allows for managed devices to talk across your network, even if different manufacturers produced those SNMP devices.

SNMP Device Types.

Types of SNMP devices include switches, bridges, routers, access servers, computer hosts, hubs, and printers. These are devices that are part of your SNMP network and relay important information via SNMP about the status of your remote sites.

Perhaps the most important device for remote alarm monitoring and control is the general purpose remote telemetry unit (RTU). An RTU can monitor multiple devices and relay important status information to a master or person responsible to fix any issue. It can be used alone to monitor a single site or joined to a manager or master station if your network has multiple sites with multiple RTUs. It is important to note that not all RTUs have SNMP compatibility. If your network is SNMP-based, it is important to find an SNMP-compatible RTU.

MIB Flow Chart A generator, or other gear, sends a COS alarm to the RTU. The RTU then translates the alarm into SNMP and relays it to the manager to start corrective actions.

A manager, or master, is another very important SNMP device, but it is not always needed. When a company needs to monitor a lot of remote sites, they may use a manager. It joins all the RTUs and equipment they monitor into one, easy to monitor, streamlined platform. This allows the company to monitor a large amount of gear remotely from one central office.

A Basic SNMP Manager, or Master, Can be Limited.

A major drawback with using basic SNMP managers is that they can be limited to SNMP devices only. For a network of devices that use other protocols (such as TL1, TBOS, TABS, or ASCII text messages), other alarm masters will be needed to manage those devices. This may add extra screens to your network monitoring system. It may also require more staff and training to monitor. Both denote higher operating costs for your company.

Multi-Protocol Masters can Integrate SNMP Devices.

A multi-protocol master alarm system can join SNMP devices with other devices to present a common interface. All the events appear on a single management and control interface. This gets rid of the complexity of a lot of screens, additional operators and training.This can have significant cost advantages for your company.

SNMP Protocol Flexibility.

The SNMP protocol is quite simple in its design and gives manufactures a lot of latitude in adding SNMP on their units. This can be challenging for integration because each SNMP device can have large differences from other manufacturers devices with respect to its SNMP profile.

A SNMP Device Reports Events.

There are two main types of messages that an SNMP device can report. A manager can issue a "GET" request to an RTU (also sometimes called an SNMP agent). A "GET" message asks the RTU to report a value back to the manager so that it can access the status of a site or piece of gear. There are several types of these messages; "GET", "GET-NEXT" and "GET-RESPONSE". While each requires a response from the RTU, the information it requests is slightly different. Conversely, an SNMP device, usually an RTU, can send a message called a TRAP whenever a change-of-state (COS) event occurs. These TRAP messages are sent to a manager, which converts the TRAP into an remote alarm for management and control.

A third type of message exists, called a "SET" message. The "SET" request is only issued from a manager to an RTU and is intended to change a discrete or analog input. For instance, a "SET" request may require the RTU to turn on a generator or set a thermostat to specific temperature.