What is ISDN?
The term "integrated" implies the merging or combining of multiple circuits on a single
facility. There are two versions of ISDN, BRI (Basic Rate Interface) and PRI
(Primary Rate Interface).
Basic Rate Interface
BRI is provisioned with two 64 Kbps B-channels (bearer channels) and one 16 Kbps D-channel
(data channel). Each of the B-channels can support voice or data for POTS (Plain
Old Telephone Service), FAX, or internet access. They can also be "bonded" together for a
single 128 Kbps circuit.
Normally one B-channel is used for regular phone calls and the other B-channel is used for
dial up Internet access. The D-channel is most commonly used for retail credit card
verification (i.e. swiping devices or smart cash registers).
Primary Rate Interface
- SOHO (Small Office/Home Office) applications (two phone lines on a single
cable pair for POTS, FAX, or dial-up Internet access)
- Video Conferencing (normally with bonded B-channels)
- Retail credit card verification (using the D-channel)
PRI is provisioned with 23 64kps B-channels and one 64Kbps D-channel. Each of the
B-channels can support voice or data for POTS (Plain Old Telephone Service), FAX, or
Internet access. Multiple channels can also be bonded together to provide for full
motion video conferencing. The D-channel is a full 64Kbps and is used for
PRI provides a direct digital connection via a 1.544 Mbps facility
to customers with
PRI compatible CPE (Customer
Premise Equipment). A PRI will give you access to both voice
and data services (such as DOD, DID, inbound calls, outbound calls, 800 service, and circuit switched data) on a
single circuit. This eliminates the need for numerous individual dedicated circuits.
PRI Channel Configurations
- PBX to PBX connectivity (PBX Trunking)
- Connecting dial-tone to ISPs (for dial-up Internet access traffic)
- Consolidation of multiple circuits onto a single facility (reduce line mileage
- 23B + D Channel Configuration- All ISDN-PRI arrangements must have at least one 23B + D channel arrangement. The D channel is for signaling and control functions. The twenty-three B channels provide 64 Kbps paths for the transfer of customer information.
- 23B + Backup D Channel Configuration- This feature provides a backup D channel as a standby spare, in the event that the primary D channel fails. It is required when more than forty-seven B channels (three or more pipes) are controlled by a single primary D channel. If the first D channel fails, the signaling switches to the backup D channel automatically.
- Circuit Switched Voice- digital voice transmission provides clear
transmissions for voice communications.
- Circuit Switched Data (Clear Channel 64 Kbps)- With its out-of-band
signaling, ISDN-PRI offers clear 64 Kbps channels for data communications.
- Dedicated B Channel Configuration- Services such as DOD, DID,
inbound calls, outbound calls, and
800 service can be directly assigned to specific B channels, similar to Digital
- Call-by-Call Service Selection- As an option to the dedicated B channel
arrangement, B channels may be configured to access multiple services on a per-call
basis. The customer premises equipment signals the local central office as to what
type of service to access for each call. This feature brings about trunking
efficiency and potential savings in trunking costs.
- Calling Line ID- ISDN-PRI is the only technology available that allows
PBX users to have access to the directory number ( up to 10-digits) of the calling
party. Directory number availability mirrors Caller ID service.