- Asked 2/29
- 2078 Bhadra · 4+4 marks
- 2074 Chaitra · 8 marks
ISDN interfaces and channels
Short answer
ISDN provides digital connections through defined functional groups and interfaces: R, S, T, U. Access interfaces are Basic Rate Interface (BRI: 2B+D at 144 kbps) and Primary Rate Interface (PRI: 30B+D at 2.048 Mbps or 23B+D at 1.544 Mbps). Its channels include B (64 kbps), D (16/64 kbps signalling), and H channels for high bandwidth.
Explain ISDN with different interfaces. Also mention its channels.
ISDN (Integrated Services Digital Network) is a digital network standardised by ITU-T that provides end-to-end digital connections for voice and non-voice services over the subscriber line, through a small set of standard user–network interfaces.
ISDN reference configuration and interfaces
R S T U
[TE2]---[TA]--+
|--[NT2]---[NT1]=======[LT/ET]
[TE1]---------+ (PBX) (NTU) 2-wire exchange
S bus 4-wire loop
Functional groups: TE1 (ISDN terminal), TE2 (non-ISDN terminal), TA (terminal adapter), NT1 (line termination at customer site), NT2 (PBX or controller), LT/ET (exchange side).
Interfaces (reference points)
| Point | Between | Description |
|---|---|---|
| R | TE2 – TA | non-ISDN interface (e.g. RS-232, analog) |
| S | TE1/TA – NT2 | 4-wire bus, up to 8 terminals, 192 kbps (BRI) |
| T | NT2 – NT1 | same electrical form as S; customer–network boundary |
| U | NT1 – exchange | 2-wire local loop, 160 kbps (2B1Q) for BRI |
When there is no NT2, S and T merge into the S/T interface.
User–network access interfaces
- Basic Rate Interface (BRI): 2B + D(16 kbps) = 144 kbps; with framing, 192 kbps at S/T. For homes and small offices.
- Primary Rate Interface (PRI): 30B + D(64 kbps) = 2.048 Mbps (E1) in Europe/Nepal; 23B + D = 1.544 Mbps (T1) in North America. For PBXs and large customers.
ISDN channels
| Channel | Rate | Use |
|---|---|---|
| B | 64 kbps | voice, data, fax (user information) |
| D | 16 kbps (BRI) / 64 kbps (PRI) | signalling (LAPD, Q.931), packet data |
| H0 | 384 kbps | video, high-speed data |
| H11 | 1536 kbps | high-speed data (T1) |
| H12 | 1920 kbps | high-speed data (E1) |
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- Interfaces available in ISDN · Telecommunications, chapter 8
- ISDN architecture, services and channels · Telecommunications, chapter 8 · asked 2×
- ISDN and its channel types · Telecommunications, chapter 8 · asked 2×
- Short note: ISDN structure, services, reference points · Telecommunications, chapter 8