G
LOSSARY AND
A
BBREVIATIONS
8030HEPTA/NCD Network Clock Device - V04.00
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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]
14.3.3 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-com-
patible 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 mech-
anisms 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 spe-
cial characteristics of his product.
14.3.4 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 commu-
nication 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.
14.3.5 PTP (Precision Time Protocol)
The Precision Time Protocol (PTP) is a standard for synchronising clocks in computer net-
works. Unlike NTP it focuses on a higher accuracy and local networks.
In a network with several PTP-devices, every PTP-device executes the Best Master Clock-
algorithm, to determine which PTP-device has the highest accuracy. That PTP-device serves
as reference clock and is called Grandmaster Clock.
The Grandmaster Clock sends SYNC messages periodically to distribute the actual time to
the slaves. The slaves periodically send Delay Request- or Path Delay Request-messages to
the Grandmaster Clock. The Grandmaster Clock replies to those messages with a Delay Re-
spond or Path Delay Respond message. The PTP-devices take sending and reception
timestamps of those messages and attach those timestamps to the messages. These
timestamps allow the slave to calculate the network delay and the exact actual time. For cal-
culating the network delay the slave assumes, that the network delay in both directions is the
same.
The PTP-devices use either Ethernet or UDP for their network communication. UDP uses the
Ports 319 and 320.
