ISDN: Integrated Services Digital Network Explained
ISDN: Integrated Services Digital Network
ISDN is an extension of the public network designed to transmit digitized voice or data.
Advantages:
- Better voice quality
- Higher speed
- Lower error rate
- More rapid establishment of calls
- Cost similar to conventional pricing
Objectives: To share information of all kinds (data, audio, text, image, video).
Definition: A network evolved from the ROI that provides end-to-end digital connectivity to support a wide range of services through one interface.
Network structure: Inside installation user (user terminal equipment and internal network) and LAN (digital transmission systems between the user installation and the local exchange).
ISDN Structure: ISDN Channels
Channel B: The basic user channel. Three types of connections can be established:
- Circuit switched (voice connection with another user on the network)
- Packet switching (connection through a switching node, packets, and data exchange)
- Semi-permanent (fixed connection with a previous agreement that does not require call establishment)
Channel D: Used for transmitting signaling information for all B channels and can be used for packet switching or low-speed telemetry.
Channel H: Transmission of information at high speed. H0 is equivalent to 6 channels of 64 kbps, H11 is equivalent to 24 channels of 64 kbps, and H12 is equivalent to 30 channels of 64 kbps.
Access modes:
- Basic access: 2 B + 1 D. The bit rate is 160 kbps, full-duplex transmission, individual users, and small offices, simultaneous use of voice and data.
- Primary Access: 30 B + 1 D. 2048 kbps bit rate, full-duplex transmission, designed for high transmission capacity and users equipped with PABX and LAN.
User Access: Reference Points and Functional Groups
Functional groups: Devices with different functional activities from each other. Types:
- Central Termination (CT): Located in the central adapting communication channels with the corresponding module, processes the signal, and controls the on/off digital line.
- Line Termination (LT): Digital transmission equipment, performs oversight functions online, feeds the local loop (85-90 VDC).
- Network Termination 1 (NT1): Physical completion of the public and private network, controls the transmission quality, synchronizes user signals with the network, and feeds the user network.
- Network Termination 2 (NT2): Performs switching, routing, and concentration, can offer added services, central PBX, router.
- Terminal Equipment type 1 (TE1): Equipment designed to connect directly to ISDN, digital telephones, facsimile group 4.
- Terminal Equipment 2 (TE2): Any terminal not designed for ISDN, analog, facsimile 2 and 3.
- Terminal Adapter (TA): Equipment that allows the connection of TE2 to the S, provides support for non-ISDN equipment.
Reference Points divide separations between functional groups.
Types:
- P. Ref. R: Functional interface between a computer and the TA of TE2, an interim solution (TA migrates to the same terminal).
- P. Ref. S: Defines the interconnection of ISDN terminals, 4 wires at 192 kbits/s, electrical code modified AMI.
- P. Ref. T: Situated between NT1 and NT2, electrically the same as S.
- P. Ref. U: Adapts signals for liaison with the local loop, transforms the circuit from 4 to 2 wires, electrical codes 4B3T and 2B1Q to 160 kbit/s, 80 Kbauds.
- P. Ref. V: Separating line terminal (LT) with the central terminal (CT), separation between transmission and switching functions can be virtual when TL and TC are the same physical machine.