Verilink AS2000: The Basics (880-502981-001) Product Manual Instrukcja Użytkownika Pobierz pdf (Strona 171)

Acronyms and Definitions

Verilink Access System 2000: Basics Glossary-51

X.21 International Telegraph and

Telephone Consultative Committee

recommendation relating to

characteristics of interfaces

between data terminal equipment

and data circuit-terminating

equipment for synchronous

operation on a public, circuit-

switched data network (ISDN).

X-bits There are two X-bits (message bits)

per DS3 frame, located in the first

bit position in block 1 of subframe

1 and subframe 2. In any one DS3

frame the two X-bits must be

identical, either both ones or both

zeros. X-bits are used to transmit

“degraded seconds” from the far-

end of the system to the near-end

of the system when the far-end

terminal detects an incoming out-

of-frame or alarm indication signal

(AIS) condition by changing both X-

bits to “0” for one second.

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