Glossary

When visiting another country, the first task is to learn the language. Telcos are a foreign realm for many data networkers. They have different customs, attitudes, and a different language. This glossary should help you talk the talk and look up terms quickly when necessary.

A

AIS

Alarm indication signal. AIS is also known as the blue alarm. When no incoming signal is detected, a CSU/DSU transmits an unframed all-ones pattern to the network to maintain synchronization and announce its presence to the network.

ACCM

Asynchronous control character map.

AMI

Alternate Mark Inversion. An encoding scheme, also known as bipolar return to zero, in which one bits (marks) are transmitted as pulses and zeros (spaces) are indicated by the absence of a pulse. Pulses alternate in polarity.

ANI

Automatic Number Identification. A similar service to CLID, which transmits the number of the calling party.

asynchronous

Data transmission that relies on the endpoints to send explicit stop and start instructions. While easier to do than synchronous transmission, the overhead of start and stop messages makes it impractical for high-speed links.

B

B8ZS

Bipolar with 8 Zero Substitution. An encoding scheme that replaces eight zeros with intentional bipolar violations. Eight zeros are replaced with a code that has two intentional bipolar violations. The substitution takes the form 000V10V1, where V is a pulse of the same polarity as the previous pulse. B8ZS enables clear channel transmission because it ensures ...

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