Snmp Management; Snmp Message Standard - Nortel VoIP Gateway Configuration Manual

Appendix G

SNMP Management

SNMP (Simple Network Management Protocol) is a standard network-based client/server-based
control protocol used to manage devices in the network. The client program (called the Network
Manager) makes connections to a server program, called the SNMP Agent. The SNMP Agent,
embedded on a remote network device, serves information to the Network Manager regarding the
device's status. The database used by the Agent to retrieve information, is referred to as the SNMP
Management Information Base (MIB), and is a standard set of statistical and control values. Apart
from the standard MIBs documented in IETF's RFCs, SNMP additionally allows the usage of
private MIBs, containing a non-standard information set.
Directives, issued by the network manager client to an SNMP Agent, consist of the identifiers of
SNMP variables (referred to as MIB object identifiers or MIB variables) along with instructions to
either get the value for the identifier, or set the identifier to a new value.
The definitions of MIB variables supported by a particular agent are incorporated in descriptor
files, written in Abstract Syntax Notation (ASN.1) format, made available to network management
client programs so that they can become aware of MIB variables and their usage.
The VoIP Gateway contains an embedded SNMP Agent supporting both general network MIBs
(such as the IP MIB), VoIP-specific MIBs (such as RTP, MGCP, etc.) and a proprietary MIB
enabling a deeper probe into the inter-working of the gateway. All the supported MIBs files are
supplied as part of the release.

SNMP Message Standard

Four types of SNMP messages are defined:
• Get
Request that returns the value of a named object.
• Get-Next
Request that returns the next name (and value) of the "next" object supported by a network
device given a valid SNMP name.
• Set
Request that sets a named object to a specific value.
• Trap
Message generated asynchronously by network devices. It notifies the network manager of a
problem apart from polling of the device.
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