Terms

STDM - Synchronous Time-Division Multiplexing
DS0 - Level 0. One timeslot. A timeslot carries 8 bits. Frame rate is 8000 hz. 8 * 8000 = 64Kbps.
B8ZS - Binary Eight Zero Substitution. A special way to encode 0000 0000 for DS0 lines.
T1 Frame - T-Carrier, Level 1. Aggregates 24 DS0 frames, or 192 bits. The T1 gets an extra bit, for framing so 193. 193 * 8000 is 1.544 Mbps.
Super Frame - 12 T1 frames.
Framing Search - Each T1 frame uses the extra bit to encode part of the superframe bit pattern 0101 1101 0001 or (5, 13, 1).
APS - Automatic Protection Switching. The device engaging in APS sends the data on both links, the working link and the protected link. The recieving device devices which to use.
DS1 - Data Stream, Level 1.
T1 - T-Carrier, Level 1, Carries 24 DS0 frames, or 192 bits. The T1 gets an extra bit, for framing so 193. 193 * 8000 is 1.544 Mbps.
ACR - Access Circuit Redundancy

The common STDM system in the US is T-Carrier.

Cisco CEM Terms

ACR - Adaptive Clock Recovery, A technique to recovery the clock based on the fill level of the jitter buffer.