TDM (Time-division Multiplexing): Method to create multiple digital channels by assigning time slots on the medium.
Local loop: Connection to the subscriber from the central office (CO) switch.
Key system: Small-scale telecommunications equipment, commonly used by small businesses.
Glare: When outgoing and incoming calls collide on the same phone line.
PVDM (Packet Voice Digital Signal Processor Module): Hardware modules added to routers to provide resources for analog voice.
G.711: Medium-complexity audio codec with a bandwidth of 64 Kbps used in Cisco IP Phones.
Central office (CO): Facility where phone company equipment is located.
CAS (Channel-associated Signaling): Signaling in which signals are sent in the same channel as the voice traffic.
RTP (Real‑time Transport Protocol): Transport protocol for IP-based digital voice.
Loop start: Common signaling for home phones in which the circuit to the phone company is open (on-hook) or closed (off-hook).
PSTN (Public Switched Telephone Network): A common abbreviation for the traditional telephone system.
G.729: High-complexity audio codec with a bandwidth of 8 Kbps used in Cisco IP Phones.
DSP (Digital Signal Processor): Hardware chips dedicated to converting between analog and digital signals.
Trunk: Connections between central office switches and customers that can carry more than one call at a time.
CO switch: Phone company equipment that provides services to customers, such as call signaling, digit collection, call routing, setup, and teardown.
E.164: International numbering plan established by the ITU.
SS7: Used between phone companies to route calls and provide informational signaling.
Ground start: Signaling used more often in corporate business environments to avoid glare.
RTCP (RTP Control Protocol): Protocol to provide statistical and control information for VoIP calls.
MOS (Mean Opinion Score): Measurement used to compare codecs.
Q.931: Signaling protocol used on ISDN circuits.
PBX (Private Branch Exchange): Telecommunications equipment owned by a large corporation that allows an internal phone system that can utilize extensions.
Quantization: One of the steps in the process of converting an analog signal to a digital number.
CCS (Common Channel Signaling): Signaling that uses a separate, dedicated channel for all signals.
