ATM Configuration and Troubleshooting Guide

Glossary 331
Glossary
A
AAL ATM Adaptation Layer. The AAL
translates digital voice, image, video, and
data signals into the ATM cell format, and
vice versa. There are five AALs defined
(AAL1 through AAL5) that provide different
services. For example, AAL5 supports
connection-oriented variable bit rate data
services.
ABR Available Bit Rate. An ATM traffic
type that optimizes the transmission
resources available during data
transmission. Configuring a PVC or SVC for
ABR means that if the network conditions
change (for example, if congestion occurs, the
source can adapt its transmission rate
accordingly—based on feedback from the
network and destination—while remaining
within the limits of the three pre-configured
parameters: Peak Rate, Minimum Rate, and
Initial Rate).
ARP Address Resolution Protocol. Provides
a way of finding the physical address that
corresponds to a given higher-level address
or alias. An example is the Internet Protocol
Address Resolution Protocol (ARP), which
returns the IEEE 802.3 address
corresponding to a given IP address.
ARP client A client system used in an IP
subnet that uses the address resolution
protocol (ARP). An ARP client obtains an
ATM address from an ARP server by
providing the IP address of the desired
destination system.
ARP server Maintains a table of IP
addresses to ATM address mappings.
Handles address resolution requests from
ARP clients. Each request includes an IP
address that is used by the ARP server to
determine the corresponding ATM address.
ATM Asynchronous Transfer Mode. A form
of digital transmission based on the transfer
of units of information known as cells. It is
suitable for the transmission of image, voice,
video, and data.
ATM address A unique 40-digit address
associated with an ATM adapter, consisting
of a 26-digit Network Prefix, a 12-digit End
System Identifier (ESI), and a 2-digit
Selector.
B
BUS Broadcast and Unknown Server. The
BUS is a multicast server used to flood
unknown destination address traffic and
forward multicast and broadcast traffic to
clients within a particular ELAN. The BUS
to which the LEC connects is identified with
a unique ATM address. In the LES, this is
associated with the broadcast MAC address
(all 1s) and this mapping is normally
configured into the LES.
C
CBR Constant Bit Rate.An ATM traffic type
that reserves a specific bandwidth for ATM
traffic on a VC. This bandwidth is defined
when the PVC is configured. CBR is defined
by its Peak Rate.
cell A transmission unit of fixed length used
in cell relay transmission techniques, such
as ATM. An ATM cell is made up of 53 bytes
(octets), including a 5-byte header and a
48-byte data payload.
CLP The last bit of byte four in an ATM cell
header. Indicates the cell loss priority and is
set by the user. Indicates if the cell can be
discarded by the network under congested
conditions.