ISDN PRI

There are two main services associated with ISDN – Basic Rate Interface (BRI) and Primary Rate Interface (PRI). Both services consist of multiple channels over which data can be sent (known as B channels) and also include a signaling channel (the D channel). The D channel is used for control and signaling purposes, such as setting and tearing down ISDN call. Referred to as “out-of-band” signaling, this method ensures that other ISDN calls do not interfere with existing connections, that bandwidth on the B channels is reserved for data only, and ultimately results in quicker call setup and teardown.

Basic Rate Interface (BRI) ISDN

Basic Rate Interface ISDN is made up of two 64 Kbps B channels that are used for sending and receiving data in full duplex, and one 16K D channel for signaling. In total, an ISDN BRI interface provides 144K of bandwidth (64+64+16). ISDN BRI is often referred to as 2B+D. Many Cisco router models include built-in BRI interfaces, but they can also be added using modular WAN interface cards.

Primary Rate Interface (PRI) ISDN

For companies with higher bandwidth requirements, ISDN Primary Rate Interface (PRI) service exists. In North America, PRI service consists of 23 64 Kbps B channels, and one 64Kbps D channel, for a total possible bandwidth of 1.544Mbps (T1 equivalent).

In Europe, PRI service consists of 30 B channels and 1 D channel, for a total bandwidth of 2.048Mbps (E1 equivalent). ISDN PRI interfaces are typically implemented as modular WAN interfaces on Cisco routers, although some models do include built-in PRI ports.

ISDN PRI provides:

• Guaranteed dynamic bandwidth over non-shared lines.
• Ability to prioritize call demand for each type of traffic (DID, DOD, data and toll-free)
• A wide range of features at one standard cost.

Features:

• DID, DOD, Data and Toll-Free Support
• Call-by-Call Service
• Calling Line ID/Calling Line ID Blocking
• Non-Facilities Associated Signaling
• Back-Up D Channel
• 64 Kbps Clear Channel