Glossary of Network Terms

Bandwidth

The data rate of a device or link

Broadcast packet

A packet sent to all nodes on a LAN. Packets intended for all nodes on a LAN use the address 255.255.255.255 as the destination address.

Collision

The result of two or more nodes on a LAN transmitting at the same time, producing a garbled transmission.

CRC (cyclic redundancy check)

An error detection scheme used by the probe to ensure that packets received by the probe have not been corrupted during transmission from the source node.

CRC/Alignment Error packets

One or more bit(s) is missing, resulting in a size mismatch error.(Alignment error)

A packet with legal size but with a faulty FCS (Frame Check Sequence). (CRC error)

CSMA\CD (Carrier Sense Multiple Access\Collision Detection)

The network access-control mechanism that is based on collisions and utilized by ethernet networks. On contention-based networks, like ethernet networks, each station must detect an idle network prior to transmitting. If more than one station transmits simultaneously, a collision occurs, all stations are notified, and the colliding stations try retransmitting after waiting a random amount of time.

Fragments

Packets with size less than 64 bits. Such kind of packets is the result of a collision or a jam over the network segment.

Gateway

A dedicated computer that is used to route frames from one dissimilar network to another.

hostTopN

The hostTopN group is the fifth group of the RMON MIB definition. The hostTopN group defines the reports that describe the hosts that top a list sorted by one of their statistics, for example, in packets, out packets. The available statistics are samples of their base statistics over a time interval specified by the management station.

hostTopN Studies

hostTopN studies are used to find the major (hostTopN) contributors to specific components of traffic. The data is displayed in a bar chart, which lets you clearly see the rank order.

 

The R/3 System consists of more than two physical network segments, one database server, several application servers and several front ends. Different factors can cause performance bottlenecks. These factors can be

To identify these problems, the R/3 administrator must be able to define the cause of poor performance in an R/3 System and take appropriate corrective action.

IP Address (Internet Protocol Address)

A 32-bit address that is divided into network-identifier and host-identifier fields, which are used to identify a particular physical network or a particular device attached to that physical network (respectively).

Jabber

Packets with size larger than 1518 bits. Such kind of packets is the result of defective hardware and/or software, or the result of protocols that do not conform to the Ethernet or 802.3 specifications.

LanProbe

A device on the LAN that monitors all frames and produces network management information including current and historical traffic statistics and snapshots of selected frames. Probes are also known as monitors.

MAC address (level 2 or physical address)

A 12-digit (48 bit) hexadecimal number that identifies a specific network station and allows messages to be directed to that station only. Because the IEEE has assigned identifiers for each hardware manufacturer, no two pieces of equipment have the same address. The address assigned according to the IEEE plan is referred to as a device's globally-administered station address. Some devices provide an option for the user to assign a different station address that will override the original. This type of address is referred as a locally-administered station address. The station address is also commonly called a MAC address, Ethernet address, or physical address.

Management Information Base (MIB)

The data that the LanProbe collects is known as the Management Information Base (MIB). The MIB is not a physically distinct database, but rather a concept that encompasses configuration and status values normally available on the agent system. MIB data conforms to an Internet-standard structure of management information and is stored in memory on the LanProbe. LanProbes can access the MIB values.

The MIB objects are defined using the Internet-standard Structure of Management Information (SMI) and are a virtual data storage on the agent system.

MIBs are organized into MIB modules. An MIB module is a file defining all the MIB objects in a subtree. Many hardware and software vendors, including SAP, have developed MIB extension for their own products.

Multicast packets

Packets addressed to a subset of nodes in the network. (A packets is sent to more than one node in the network, but not to all of the nodes of the network).

Network agent

A hardware device or software program that can collect network segment performance data. A hardware device is called a LanProbe. A software program is called an agent, or power agent.

Node

A computer or other addressable device on a network, including PCs, terminals, probes, routers, and mainframes.

Packet

A bit stream consisting of fields that contain data, addresses and control information. In the IEEE 802.3 environment, this structure is often referred as the MAC frame. Packet is used in the Ethernet environment and is used in this guide because it is the more commonly understood term. Different protocols have different packet and frame specifications.

Physical address

See MAC address

Probe

See LanProbe

RMON agents

A network agent which collects RMON performance data.

RMON Agent Interoperability

The RMON Monitor works with standard RMON agents, or LanProbes. The agents supported are all fully compliant with the RMON MIB specification, RFC 1271.

The RMON Monitor supports the SNMP-RMON MIB for Ethernet and Token Ring.

This lets you

The Network Monitor can recognize if network resources are saturated, or if the same network resources can be used from additional R/3 or other application systems.

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Table: RMON Error Types

 

< 64 Bytes

64 to 1518 Bytes

>1518 Bytes

Well Formed pckts

Undersize

GOOD

Oversize

FCS Error pckts

Fragment

CRC or Alignment Error

Jabber

RMON (Remote MONitoring) Standard

The RMON MIB (RFC 1271) is a relatively new part of the SNMP standard. It is a sophisticated MIB designed specifically for remote monitoring and troubleshooting in networks. RMON agents operate autonomously and in real time to provide a rich set of network statistics for alarm and packet analysis.

The RMON MIB defines statistical measurements of network performance, traffic levels, errors and other important trends. Alarm thresholds are described as well on any of these parameters. Traffic and error levels are defined for each node and for every station on the segment.

Simple Network Management Protocol (SNMP)

Information is exchanged between an Network Monitor and a network agent using the Simple Network Management Protocol (SNMP). The Network Monitor uses the SNMP protocol to:

The Network Monitor sends read-write SNMP type requests for information to the LanProbes, and the LanProbe sends back replies containing the information requested

Requests for information on a LanProbe are accompanied by a community name, which is a password that allows the Network Monitor access to that information

Top performer

The station which is contributing the most traffic to the network.

Network Monitor: Overview