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ISDN and its channel types
Short answer
ISDN is a fully digital network with separate D-channel signalling for fast call setup. Its channel types include B channels (64 kbps) for user data, D channels (16 kbps for BRI, 64 for PRI) for signalling and low-speed data, and H channels (384-1920 kbps) for high-speed applications like video conferencing.
Explain ISDN (integrated services digital network) and the types of ISDN channels in detail.
ISDN (Integrated Services Digital Network) is a fully digital network defined by ITU-T (I-series Recommendations) in which voice, data, fax and video share the same digital subscriber line. Signalling is carried separately on a D channel, giving fast call setup and many supplementary services.
Main features
- End-to-end digital connection over the existing copper loop.
- Standard user–network interfaces (BRI, PRI) and reference points (R, S, T, U).
- Several devices (up to 8) on one line and simultaneous calls.
- Common-channel signalling: DSS1 (Q.931) on the D channel to the user, SS7 in the network.
Types of ISDN channels
1. B channel (bearer channel), 64 kbps
- Carries user information: PCM voice, circuit-switched data, packet data (X.25), fax.
- Four kinds of connection on B: circuit-switched, packet-switched, semi-permanent (leased), and multiplexed lower-rate data.
- Two B channels can be combined (bonding) to give 128 kbps.
2. D channel (data/signalling channel), 16 or 64 kbps
- 16 kbps in BRI, 64 kbps in PRI.
- Carries common-channel signalling for the B channels using LAPD (layer 2) and Q.931 (layer 3).
- When idle, it can carry low-speed packet data and telemetry.
3. H channels (high-speed)
| Channel | Rate | Equivalent |
|---|---|---|
| H0 | 384 kbps | 6 B channels |
| H11 | 1536 kbps | 24 B (T1 payload) |
| H12 | 1920 kbps | 30 B (E1 payload) |
Used for video-conferencing, high-speed data, LAN interconnection and fast fax.
Channel structures (access interfaces)
BRI: | B1 64k | B2 64k | D 16k | = 144 kbps
PRI: | 30 x B 64k | D 64k | sync | = 2.048 Mbps
| Interface | Structure | Total rate |
|---|---|---|
| Basic Rate (BRI) | 2B + D(16) | 144 kbps (192 kbps line rate at S/T) |
| Primary Rate, Europe | 30B + D(64) | 2.048 Mbps |
| Primary Rate, N. America | 23B + D(64) | 1.544 Mbps |
BRI suits homes and small offices; PRI connects PBXs and large users. B-ISDN (ATM based, 155/622 Mbps) was the broadband extension.
✓ Answer checked by Claude Opus 5.5 (high effort)
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