Prestige 2302 Support Notes
All contents copyright (c) 2005 ZyXEL Communications Corporation.
43
SNMP variables are defined using the OSI Abstract Syntax Notation One (ASN.1). ASN.1 specifies how a
variable is encoded in a transmitted data frame; it is very powerful because the encoded data is self-defining.
For example, the encoding of a text string includes an indication that the data unit is a string, along with its
length and value. ASN.1 is a flexible way of defining protocols, especially for network management protocols
where nodes may support different sets of manageable variables.
The set of variables that each node supports is called the
Management Information Base
(MIB).
MIB
is made
up of several parts, including the Standard MIB, specified as part of SNMP, and Enterprise Specific MIB,
which are defined by different manufacturer for hardware specific management.
The current Internet-standard MIB, MIB-II, is defined in RFC 1213 and contains 171 objects. These objects are
grouped by protocol types (including TCP, IP, UDP, SNMP, etc.) 'system' and 'interface.'
The Internet Management Model is as shown in figure 1. Interactions between the NMS and the managed
devices can be any of the four command types:
6.
Reads
Read is used to monitor the managed devices. NMSs read variables are maintained by the devices.
7.
Writes
Write is used to control the managed devices. NMSs write variables are stored in the managed devices.
8.
Traversal operations
NMSs use these operations to determine which variables a managed device supports and to sequentially
gather information from variable tables (such as the IP routing table) in the managed devices.
9.
Traps
The managed devices asynchronously report certain events to NMSs using traps.
