G
LOSSARY AND
A
BBREVIATIONS
8029HEPTA-V2/GPS GPS - NTP Time Server with LAN Interface - V08.00
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hopf
Elektronik GmbH
Nottebohmstr. 41
• D-58511 Lüdenscheid • Tel.: +49 (0)2351 9386-86 • Fax: +49 (0)2351 9386-93 • Internet: http://www.hopf.com • E-Mail: [email protected]
14.4.3 SNMP (Simple Network Management Protocol)
Simple Network Management Protocol (SNMP) is a network protocol which was developed by
the IETF in order to be able to monitor and control network elements from a central station.
This protocol regulates the communication between the monitored devices and the monitoring
station. SNMP describes the composition of the data packets which can be transmitted and
the communication procedure. SNMP was designed in such a way that every network-
compatible device can be integrated into the monitoring. Functions of the network
management which can be provided by SNMP include:
•
Monitoring of network components
•
Remote control and configuration of network components
•
Fault detection and notification
Due to its simplicity, SNMP has become the standard which is supported by most management
programmes. SNMP Versions 1 and 2c hardly offer any safety mechanisms. The safety
mechanisms have been significantly expanded in the current Version 3.
Using description files, so-
called MIB’s (Management Information Base), the management
programmes are able to represent the hierarchical structure of the data of any SNMP agent
and to request data from them. In addition to the MIB’s defined in the RFC’s, every software
and hardware manufacturer can define his own so-
called private MIB’s which reflect the
special characteristics of his product.
14.4.4 TCP/IP (Transmission Control Protocol / Internet Protocol)
TCP and IP are generally used concurrently and thus the term TCP/IP has become established
as the standard for both protocols.
IP is based on network layer 3 (layer 3) in the OSI Layer Model whereas TCP is based on
layer 4, the transport layer. In other words, the expression TCP/IP signifies network
communication in which the TCP transport mechanism is used to distribute or deliver data
over IP networks. As a simple example: Web browsers use TCP/IP to communicate with web
servers.
14.5
Accuracy & NTP Basic Principles
NTP is based on the Internet protocol. Transmission delays and errors as
well as the loss of data packets can lead to unpredictable accuracy data
and time synchronization effects.
NTP protocol neither defines nor guarantees the accuracy or correctness
of the time server.
Thus the QoS (Quality of Service) used for direct synchronization with GPS or serial interface
does not apply to synchronization via NTP.
In simplified terms, accuracies of between 1msec and 1sec can be expected, depending on
the accuracies of the servers used.
