In order to have a good understanding of ISDN, you need to know more than its uses. You need to know about ISDN’s protocol groups, its protocols, how to identify reference points, and ISDN channels.

Critical Information

This section takes an in-depth look at the following ISDN topics:
• ISDN Protocols
• ISDN Function Groups
• ISDN Reference Points
• ISDN Channels

ISDN Protocols

ISDN protocols are defined by the ITU-T. There are three diverse categories of ISDN protocols whose functions are specified by their first letter:
• E protocols apply to ISDN on an existing telephone network.
• I protocols deal with concepts, terminology, and services.
• Q protocols pertain to switching and signaling.

ISDN Function Groups

Function groups connecting to the ISDN network are known as terminals. These come in two types:
• TE1 (terminal equipment type 1) devices are BRI machines that understand ISDN standards.
• TE2 (terminal equipment type 2) devices predate ISDN standards. To use a TE2 device, you have to use a terminal adapter (TA) to generate BRI signals for a Cisco router interface.

ISDN Reference Points

ISDN uses four different reference points to define logical interfaces between functional groupings such as TAs and NT (network termination) devices. They are as follows:
R declare the position place between non-ISDN equipment and a TA.
S declare the position place between user terminals and an NT2 device.
T declare the position place between NT1 and NT2 devices.
U declare the position place between NT1 devices and line-termination equipment in a carrier network. (This type of reference point is used only in North America, where the NT1 function isn’t provided by the carrier network.)

ISDN Reference Points

Figure shows the ISDN functions and reference points.

Note The S and T reference points are generally one and the same.

ISDN Channels

As discussed earlier, there are two types of channels used in BRI ISDN: B and D. Here’s what each one does:

• B, or bearer, channels have a 64Kbps capacity. They can be used for voice or data. Two B channels in a BRI can be combined for a total of 128Kbps.
• D or data channels has a16Kbs capacity and it used for call signaling or clocking

Exam Essential

Understand the different protocols used in ISDN.
The Q protocols specify switching and signaling. E protocols apply to ISDN on an existing telephone network. I protocols deal with concepts, terminology, and services.

Key Term and Concept

reference point Used to define logical interfaces in ISDN.

Related posts:

1. State a Relevant use and Context for ISDN Networking
2. State a Relevant use and Context for ISDN Networking
3. Function of the MAC Address
4. key Frame Relay Terms and Features Exam Points
5. Layered Model Exam Points
6. OSI Network layer Exam Points
7. TCP-IP Network-layer protocol Exam Points
8. key Frame Relay Terms and Features
9. Network Congestion Problem in Ethernet Networks
10. TCP-IP Network-layer protocol