Digital Voice Ports

Cisco Aug 10, 2025

Digital ports allow for multiple calls

Digital Signalling

Channel Associated Signaling (CAS)

Steals bits from user data for signaling
Advantage: all channels are available for data
Disadvantage: User bandwidth is reduced

Common Channel Signaling (CCS)

Dedicates a single channel to signaling
Advantages: more signalling information available, no user bandwidth used
Disadvantage: lose a complete channel

ISDN

Two versions of IDSN: BRI and PRI
Standard-based signaling protocols
- Q.921 - Error Detections/Corrections (Layer 2)
- Q.931 - Call Setup/Teardown/information (Layer 3)
Non-facility associated signaling (NFAS) allows a single D channel for multiple PRI interfaces
QSIG (Based on Q.931) allows PBX-to-PBX interconnects
The last channel 23 is the control channel for T1
Channel 15 is the control channel for E1

show controllers t1

CAS Configuration

controller t1 1/0
  no shut
  ds0-group 1 timeslots 1-24 type fxo-ground-start

CCS Configuration

isdn switch-type primary-5ess !!Needs to match provider

controller t1 1/0 
	no shut
	pri-group timeslots 1-24 type fxo-ground-start

interface serial 1/0:23
  isdn incoming-voice voice