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Glossary
GL-2
Cisco 10008 Router Hardware Installation Guide
OL-0659-13
A
AAL
ATM adaptation layer. Service-dependent sublayer of the data link layer. The AAL accepts data from
different applications and presents it to the ATM layer in the form of 48-byte ATM payload segments. AALs
consist of two sublayers:the convergence sublayer and the segmentation and reassembly sublayer. Four
types of AAL recommended by the ITU-T are AAL1, AAL2, AAL3/4, and AAL5; the Cisco 10008 router
uses AAL5.
Access list
List kept by routers to control access to or from the router for a number of services. For example, access
lists can be used to prevent packets with a certain IP address from leaving a particular interface on the
router.
Add drop
Multiplexer
See ADM.
ADM
Add Drop Multiplexer. A multiplexer that allows a signal to be added into or dropped out of a SONET
span. See also SONET.
Alarm
A status condition that shows that a module or port is experiencing an abnormal operating condition.
See also Critical alarm, Major alarm, and Minor alarm.
Application-specific
integrated circuit
See ASIC.
APS
Automatic Protection Switching. A SONET switching mechanism that achieves network resiliency by
automatically switching from a primary circuit to a secondary circuit. This switching process occurs if
the primary circuit fails or if the error rate on the primary line exceeds a set threshold. The Cisco 10008
router supports 1+1 APS, which provides permanent electrical bridging to the service and protection
equipment, placed at both ends of the circuit.
ASIC
Application-specific integrated circuit. A chip that is built for a specific application.
Asynchronous
Transfer Mode
See ATM .
ATM
Asynchronous Transfer Mode. International standard for cell relay in which multiple service types
(such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow
cell processing to occur in hardware, thereby reducing transit delays. ATM is designed to take
advantage of high-speed transmission media such as E3, SONET, and T3.
Authentication
In security, the verification of the identity of a person or process.
Automatic
protection
switching
See APS.
Alarm
A status condition that shows that a module or port is experiencing an abnormal operating condition.
See also Critical alarm, Major alarm, and Minor alarm.