IBM ATM OC-3c manual Byte, Cell Header, Connectionless, Connection oriented, 164, Firewall

2GLOSSARY

Byte

An Octet or 8 bits of data.

Cell

Basic ATM transmission unit. It is a 53-byte packet, consisting of a 5-byte header and a 48-byte payload. User traffic is segmented into cells at the source and reassembled at the destination.

Cell Header

The 5-byte ATM cell header contains control information regarding the destination path and flow control.

More specifically it contains the following fields: GFG, VPI, VCI, PTI, CLP and HEC.

CLP

Cell Loss Priority — A 1-bit field in the ATM cell header that corresponds to the loss priority of a cell. Lower priority (CLP = 1) cells can be discarded under congestion situations.

connectionless

Communications service where packets are transferred from source to destination without the need for a pre-established connection.

connection oriented

Communications service where an initial connection between the end points (source and destination) must be set up prior to data transmission. ATM and Frame Relay are Connection Oriented.

E.164

An 8-byte address format. In ATM it is typically used in public networks and it is provided by the telecommunication carriers, while 20-byte NSAP (Network Service Access Point) format addresses are used within private networks.

EFCI

Explicit Forward Congestion Indication — A 1-bit field in the PTI that contains information about whether congestion at an intermediate node has been experienced. The EFCI bit is set when a threshold (for example, buffer contents) has been exceeded.

ELAN

Emulated LAN — See LAN Emulation.

firewall

Isolation of LAN segments from each other to protect data resources and help manage traffic.

Flash EPROM

EPROM (Erasable Programmable Read-Only Memory) technology providing non-volatile storage that can be electrically erased in the circuit and reprogrammed; developed by Intel and licensed to other semi-conductor companies.

Flow Control

A method used in networking for congestion avoidance and traffic regulation.