User's Guide

Glossary

AC

The Access Control field in frame header.

ACE

Address Copied Error. When a station reports this it indicates a problem with the station upstream rather than with itself, normally someone else on the Token Ring with this station's address. An isolating error.

Application Layer

Layer seven, the uppermost part of the OSI network layer model. This layer contains the user and application programs.

Backbone

The part of a network used as the primary path for transporting traffic between network segments.

Bandwidth

Information capacity, measured in bits per second, that a channel can transmit. The bandwidth of Ethernet is 10 Mbps, the bandwidth of Fast Ethernet is 100 Mbps. FDDI bandwidth is 100 Mbps. Token Ring bandwidth is 4/16 Mbps.

Bit

Either of the digits 0 or 1 when used in the binary numeration system. Eight bits equals a single byte. Broadcast . All good frames destined for the broadcast address, in other words sent out to all stations on the network. Some broadcasts are limited to the local network, and some broadcasts may cross onto other networks.

Broadcast

All good frames destined for the broadcast address, in other words, sent out to all stations on the network. Some broadcasts are limited to the local network, and some broadcasts may cross onto other networks.

Buffer

The space allocated to the storage of filtered packets as they are captured from the network. A probe only has a limited set of resources to hold buffer data. If one of the buffers uses all of the probe's resources, it will stop the other buffers from capturing packets. To conserve resources, you can slice packets or assign maximum sizes to buffers.

Bytes

The total number of bytes making up a frame - includes FCS octets.

Client

Any application that retrieves and displays data from probes or agents.

Collision

The best estimate of the number of collisions on an Ethernet segment.

Community Name

Also known as Community String. SNMP uses community names to limit access to certain device management functions. The Community Name used when accessing a device determines which functions may be accessed.

CRC Align Error

An Ethernet packet between 64 and 1518 octets long inclusive (includes FCS octets) - not an integral number of octets in length or has a bad FCS.

CSMA/CD Carrier

Carrier Sense Multiple Access with Collision Detection. The Ethernet protocol that allows each device to create and send its own data packets. CSMA/CD is used to avoid excessive collisions between packets as they are randomly transmitted. A CSMA/CD device first listens for other carriers, if it detects no other carriers, it will then allow the data packet to be transmitted. If a collision is detected, the device stops transmitting, waits a random length of time, and begins transmitting again

Data Link Layer

The second layer of the OSI reference model. This layer is responsible for controlling message traffic.

Data Packet (Packet)

A sequence of binary digits, including data and control signals that is transmitted across a LAN.

Default Gateway

The IP address of a device, usually a router or gateway, to which the probe directs all packets not destined for its subnet.

ED

Ending Delimiter - a distinctive byte marking the end of a frame or a token.

Forwarding

The process of sending a frame towards its destination by an intranet working device.

Fragment Packet

An Ethernet packet less than 64 octets long (excludes frame bits but includes FCS octets) - not an integral number of packets in length or has a bad FCS.

GARP

See Generic Attributes Registration Protocol.

GARP VLAN Registration Protocol (GVRP)

The IEEE 802.1p protocol that enables workstations to request admission to a specific VLAN rather than to a multicast domain.

Generic Attributes Registration Protocol (GARP)

A protocol defined by IEEE 802.1p. There are two versions: GARP Multicast Registration Protocol (GMRP) and GARP VLAN Registration Protocol (GVRP).

GARP Multicast Registration Protocol (GMRP)

The IEEE 802.1p protocol that enables workstations to request membership in a multicast domain. This joining action is called a leaf-initiated join. GMRP provides a standard protocol for sending traffic to only those ports that have requested multicast traffic. It is compatible with 802.1Q because it operates on a port basis.

GVRP

See GARP VLAN Registration Protocol.

HDLC

High-Level Data Link Control. OSI bit-orientated protocol.

Host

A device or computer on an IP network to which you can connect.

Jabber Packet

An Ethernet packet longer than 1518 octets (excludes frame bits but includes FCS octets) - not an integral number of octets in length or has a bad FCS.

ICMP

Internet Control Message Protocol. Internet protocol that reports errors and provides other information relevant to IP packet processing.

IEEE

Institute of Electrical and Electronics Engineers.

IETF

Internet Engineering Task Force, whose responsibilities include specification of protocols and recommendation of Internet standards via the Request for Comment (RFC) process.

Long Packet

See oversize packet.

MIB

Management Information Base.

Multicast

Good packets directed to the multicast address. Does not include broadcast packets. Multicasts are similar to broadcasts but have a more limited scope, for example they may be directed to all bridges on a ring.

Oversize Packet

An Ethernet packet longer than 1518 octets (including FCS octets) but otherwise well formed.

Network Layer

The third layer of the OSI reference model. This layer is responsible for controlling message traffic.

Octet

A digital unit of information comprising eight binary digits (bits) equivalent to a byte.

OSI

Open Systems Interconnection, a body of standards set by the International Standards Organization to define the activities that must occur when computers communicate. In the OSI Reference Model there are seven layers, and each contains a specific set of rules to follow at that point in the communication.

Packet

A unit of information that contains data, origin information; and destination information, which is switched as a whole through a network.

PACMIB

Port Address Correlation MIB maps port to host data and gathers port statistics for 3Com CoreBuilder devices on your network.

Probe

Station (or agent) responsible for gathering network data on a remote segment and passing it up to a central management station (or client). Usually configured and controlled by the client.

PDN

Public Data Network.

Physical Layer

The first layer of the OSI network layer model. This layer manages the transfer of individual bits of data over wires, or whatever medium, that is used to connect workstations and peripherals.

Presentation Layer

The sixth layer of the OSI network layer model. This layer controls the formatting and translation of data.

Protocol

A set of rules and procedures that govern the exchange of data between two communicating systems.

Protocol Number

The port or program number as defined by the parent protocol. For example, if you are adding a TCP child protocol, the protocol number will be the TCP port number.

PSTN

Public switched telephone network.

RMON

Remote MONitoring. Subset of SNMP MIB II which allows monitoring and management capabilities by addressing up to ten different groups of information. Defined in IETF document RFC 1757.

RMON2

Extends the capability of RMON to include protocols above the MAC layer.

Short Packet

See undersize packets.

Station

Any machine connected to the network - for example a fileserver, PC, workstation, printer or probe.

Subnet Mask

A filtering system for IP addresses. It defines the portion of the IP address used to identify the subnet. The remaining portion is used to represent host information. Devices and routers use the mask to identify the subnet on which a probe resides.

System Descriptor

A free-form field on RMON devices used by vendors to supply basic information about the device.

Transport Layer

The fourth layer of the OSI network layer model. This is responsible for error checking and correction, and some message flow control.

Trigger

A trigger represents a sequence of events that may occur on a network. When these events occur, an alarm is triggered.

Undersize Packets

An Ethernet packet less than 64 octets long (excluding frame bits but including FCS octets) but otherwise well formed.

Virtual Circuit

Circuit-like service provided by the software protocols of a network, enabling two end points to communicate as though connected by a physical circuit. Network nodes provide the addressing information needed in the packets that carry the source data to the destination.