ISDN (Integrated Services Digital Network) is a standard digital telephone designed to replace analog connections using standard copper wire used in standard telephone lines.
ISDN was developed to provide digital transmission of both voice and data, with better quality and faster than that of classical systems Public Switched Telephone Network (PSTN).
Familiar with the digital protocol
There are two types of ISDN channels:
- Channel B - is known as the Bearer (”B”) and a 64 kbps channel used to transfer voice, video, data or multimedia content. These aggregates may be having a wider use of bandwidth.
- Channel D - known as Delta channel (D) may be either 16 Kbps or 64 Kbps and is used mainly for switching signals between equipment. Some say that the separation of data channels and control adds security ISDN.
Note: The Digital Signal 0 (DS0) is a digital signal based on 64K that can be used to describe a single channel Bearer.
BRI (Basic Rate Interface)
Also called BA (Basic Access), operates on a single 16 Kbps D channel and two B channels at 64 Kbps Although usually not stated, the overall speed of BRI is 192 kbps, because you have this additional 48 kbps for framing and synchronization channel D (64 * 2) + (16 + 48) = (128 + 64) = 192 Kbps
PRI (Primary Rate Interface)
Also known as PA (Primary Access), can operate in two different ways, depending on geographic location. For European locations, the PRI has 30 B channels at 64 Kbps and a single D channel of 64 Kbps, giving a total of 2,048 Mbps is also called E1 line (or DS1). For American and Japanese locations, PRI consists of 23 B channels at 64 Kbps and a single D channel of 64 Kbps D, giving a total of 1,544 Mbps is also called T1 line (or DS1). Framing and synchronization are at 8 Kbps or 64 Kbps for T1 to E1. T1 PRI is commonly referred to “23B + D and E1 PRI refers to” 30B + D “.
NB: Actually, E1 PRI has 32 channels with 30 B channels, 1 D channel and a channel Digital Signal Levels (DSx)
The Digital Signal X is used to describe the rates or levels based on DS0 digital transmission standard, which is defined as the ratio of transmission to 64 Kbps channel for voice phone. It is based on guidelines the NSA T1.107, and ITU defined guidelines differ a bit.
PPP
Typically use ISDN protocol tunneling Point-to-Point (PPP) as a basis to send the packages on the ISDN circuit. IP packets are encapsulated in PPP packets before the traffic is transmitted.
PPA provides control functions for the specific link through the Link Control Protocol (LCP), such as Configuration Link and Link Quality Testing & Address Negotiation.
LCP provides advanced features such as Multilink, Header Compression, Callback, Scripting, Demand Dialing, Filtering, Tunnelling and Routing Servers. There are also authentication mechanisms that can help ensure that the ISDN link provided is from a trustworthy source. Authentication is optional, can be done through the use of the PAP, CHAP and EAP (although not used in ‘ ISDN implementation, EAP is a valid method of PPP authentication).
• PAP - Password Authentication Protocol is not particularly “robust” because the password is sent in clear text. PAP occurs during the PPP LCP connection.
• Chap - Challenge Handshake Authentication Protocol. And ‘much stronger than PAP and is much used. It uses a security mechanism like challenge / response using a one-way hash function to ensure that passwords are not transmitted over the link. The password must be the first operation “hashed” and then sent the link. The other side of the connection performs the same hash function on the password configured, then check the link that the two hash values are congruent. This may also provide protection against playback.
• EAP - Extensible Authentication Protocol. Provides the ability to use multiple authentication protocols such as static password, the CHAP, token cards or biometrics. Since CHAP is available by itself and can not work with ISDN cards with biometrics or tokens, is not used ISDN implementation.