- 2073 Chaitra · 5 marks
Short note: E-hierarchy vs T-hierarchy
Write a short note on E-hierarchy versus T-hierarchy.
Both are digital TDM hierarchies that combine 64 kbps PCM voice channels (DS0), but they differ in standard and rates. T-carriers are used in North America and Japan, E-carriers in Europe, Nepal and most of the world (ITU-T).
| Level | T-carrier (channels, rate) | E-carrier (channels, rate) |
|---|---|---|
| 1 | T1: 24, 1.544 Mbps | E1: 30, 2.048 Mbps |
| 2 | T2: 96, 6.312 Mbps | E2: 120, 8.448 Mbps |
| 3 | T3: 672, 44.736 Mbps | E3: 480, 34.368 Mbps |
| 4 | T4: 4032, 274.176 Mbps | E4: 1920, 139.264 Mbps |
| 5 | none | E5: 7680, 565.148 Mbps |
Other differences
- Frame: T1 frame = 24 × 8 + 1 framing bit = 193 bits. E1 frame = 32 × 8 = 256 bits, of which 30 slots carry voice, 1 slot is for frame alignment and 1 for signalling.
- Companding: T uses µ-law; E uses A-law.
- Both use 8000 frames per second.
- T1: 8000 × 193 = 1.544 Mbps. E1: 8000 × 256 = 2.048 Mbps.
- At higher levels, extra bits are added for synchronisation (bit stuffing), so rates are slightly above a plain multiple.
- The two standards are not directly compatible, so conversion gateways are used between them.
✓ Answer checked by Claude Sonnet 5.5
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