Snmp Mib Objects; Snmp Extensibility Feature - 3Com V7111 - VCX 4 Channels Analog FXO Media Gateway User Manual

SNMP MIB Objects

The SNMP MIB is arranged in a tree-structured fashion, similar in many ways to a disk
directory structure of files. The top level SNMP branch begins with the ISO Internet directory,
which contains four main branches:
The mgmt SNMP branch contains the standard SNMP objects usually supported (at least
in part) by all network devices.
The private SNMP branch contains those extended SNMP objects defined by network
equipment vendors.
The experimental and directory SNMP branches, also defined within the internet root
directory, are usually devoid of any meaningful data or objects.
This tree structure is an integral part of the SNMP standard; however, the most pertinent
parts of the tree are the leaf objects of the tree that provide actual management data
regarding the device. Generally, SNMP leaf objects can be partitioned into two similar but
slightly different types that reflect the organization of the tree structure:
Discrete MIB Objects – Contain one precise piece of management data. These objects
are often distinguished from Table items by adding a .0 (dot-zero) extension to their
names. The operator must know the name of the object.
Table MIB Objects – Contain multiple pieces of management data. These objects are
distinguished from Discrete items by requiring a . (dot) extension to their names that
uniquely distinguishes the particular value being referenced. The . (dot) extension is the
instance number of an SNMP object. In the case of Discrete objects, this instance
number is zero. In the case of Table objects, this instance number is the index into the
SNMP table. SNMP tables are special types of SNMP objects, which allow parallel
arrays of information to be supported. Tables are distinguished from scalar objects, in
that tables can grow without bounds. For example, SNMP defines the ifDescr object (as
a standard SNMP object) that indicates the text description of each interface supported
by a particular device. Since network devices can be configured with more than one
interface, this object could only be represented as an array.
By convention, SNMP objects are always grouped in an Entry directory, within an object with
a Table suffix. (The ifDescr object described resides in the ifEntry directory contained in the
ifTable directory).

SNMP Extensibility Feature

One of the principal components of any respectable SNMP manager is a MIB Compiler that
allows new MIB objects to be added to the management system. When a MIB is compiled
into an SNMP manager, the manager is made aware of new objects that are supported by
agents on the network. The concept is similar to adding a new schema to a database.
Typically, when a MIB is compiled into the system, the manager creates new folders or
directories that correspond to the objects. These folders or directories can typically be
viewed with a MIB Browser, which is a traditional SNMP management tool incorporated into
virtually all network management systems.
3Com VCX V7111 VoIP SIP Gateways User Manual 105