General Information

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This page contains our original overivew of SNMP. The SNMP 101 link contains much of the same information just organized differently. We keep this page as is on our web site because search engines and other sites have been linking to this page for over 10 years.

About SNMP... (new to SNMP? Skip further down)

SNMP provides a universal method of exchanging data for purposes of managing devices that reside on a network. The use of SNMP is most dominant in the telecommunications industry. Several Control Solutions products are capable of providing SNMP access to their data.

SNMP, Modbus, and LonWorks have this in common: They provide a protocol for accessing individual variables within a device connected to a network. Modbus refers to these variables as "registers" while LonWorks and SNMP both refer to "variables". Most often the variables are 16 or 32 bits of data.

SNMP stands for Simple Network Management Protocol, and operates at the application layer in the OSI Network Reference Model. ASN.1 and BER provide the presentation layer. UDP and IP provide the transport and network layers. In the case of Control Solutions products, Ethernet provides the data link layer, and the physical connection is the RJ-45 connector.

SNMP provides access to data via a set of "variables" which have "names" constructed in a format defined by the SNMP protocol. An SNMP variable name resembles an IP address with integer number fields separated by dots (decimal points or periods), with the difference being that the SNMP variable name may have many more than the 4 fields found in the IP address. The collection of variables or "managed objects" found in an SNMP device is known as the Management Information Base (MIB).

The MIB provides the map of hierarchial order of all managed objects and how they are accessed. The MIB is defined at the source level using ASN.1 (Abstract Syntax Notation ver. 1), and encoded for transmission using BER (Basic Encoding Rules). The set of rules used to specify the format used for defining managed objects that are accessed via the SNMP protocol is known as Structure of Management Information (SMI). All of this is generally transparent to the user of the Control Solutions i.CanDoIt software, but must be understood by developers wishing to develop applications that interface to i.CanDoIt at the host level.

Additional information and specifications for the SNMP protocol may be found in documents known as RFCs which may be found on various sites on the Internet. One of these is http://www.cse.ohio-state.edu/cs/Services/rfc/index.html. The RFC documents are very dry reading. There are a variety of books available on the subject in more readable form, some of which may be found in local book stores. A readily readable introduction to SNMP may be found in Section I of "Windows NT SNMP" by James D. Murray (O'Reilly) ISBN: 1-56592-338-3.

New to SNMP?

Are you an equipment vendor that has been informed by a customer that you need to have an SNMP interface? Don't panic. Here is what you need to know about SNMP: It's just another protocol. That's it. The underlying concept is the same as Modbus or most other device level protocols. It is simply a way of addressing data over a communications interface. It is generally done by assigning each device on the network a unique ID, and within each device, each available piece of data has an identifier. In Modbus, that data identifier is called a register number. In SNMP, that identifier is called an OID and looks like an overgrown IP address.

If the Modbus analogy means little because you are unfamiliar with Modbus, then think of an Excel spread sheet. We assign one row per device, and within each device we have several columns of data. The "protocol" is simply the agreed upon means of addressing the rows and columns of data. That protocol agreement is somewhat like simply agreeing that all formal letters we write will begin with "Dear Sir" and end with "Sincerely". In protocol talk, the "Dear Sir" is called a header, and the "Sincerely" is sometimes called the tail, and usually contains some form of error checking to make sure we got the rest of the letter right. The body of the letter says something like "please send me row 5, columns 9 through 14" or "please accept the new value of '450' I am sending you for row 3, column 11".

How do we add SNMP to existing equipment? Many OEM controllers have a Modbus port. If you have that, we have a gateway that will adapt Modbus to SNMP. If you do not have Modbus, Control Solutions also has physical I/O with SNMP access. If you simply have a switch contact, or a sensor that provides 0-10VDC or 4-20mA, we can put that information into SNMP form. Select one of the SNMP menus above to see our SNMP options.