- 2073 Shrawan · 4 marks
E1 telephone hierarchy
Short answer
E1 is a TDM hierarchy with 32 slots per frame, 8000 frames/s, giving 2.048 Mbps; 30 voice channels, one sync, one signalling. Higher levels E2 (8.448 Mbps) to E5 (564.992 Mbps) each multiplex four lower levels.
Explain the E1 telephone hierarchy system.
E1 is the European (ITU-T) standard digital telephone hierarchy based on time division multiplexing (TDM) of 64 kbps voice channels. It is used in Nepal, India and most countries outside North America and Japan (those two use the T1 hierarchy).
E1 frame
- Voice is sampled at 8000 samples/s with 8 bits per sample, giving a 64 kbps channel (DS0).
- An E1 frame has 32 time slots of 8 bits each = 256 bits. Frames are sent 8000 times per second.
- Slot 0 is for frame synchronisation and alarms; slot 16 is for signalling. The remaining 30 slots carry user voice or data.
- Rate = 32 × 64 kbps = 2.048 Mbps.
| TS0 | TS1 ... TS15 | TS16 | TS17 ... TS31 |
| sync| voice | sign.| voice |
Higher levels (each multiplexes four of the lower level)
| Level | Channels | Rate |
|---|---|---|
| E1 | 30 voice | 2.048 Mbps |
| E2 | 4 × E1 = 120 | 8.448 Mbps |
| E3 | 4 × E2 = 480 | 34.368 Mbps |
| E4 | 4 × E3 = 1920 | 139.264 Mbps |
| E5 | 4 × E4 = 7680 | 564.992 Mbps |
The rates are slightly more than 4 times the lower level because of extra framing and justification bits.
✓ Answer checked by Claude Opus 5.5 (high effort)
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