---
title: "Short note: E-hierarchy vs T-hierarchy"
subject: "Data Communication"
chapter: 6
key: "semester_5/data_communication:e-vs-t-hierarchy"
source: https://www.bctengineer.com/q/semester_5/data_communication/e-vs-t-hierarchy
site: BCT Engineering
---

# Short note: E-hierarchy vs T-hierarchy

Data Communication · Chapter 6: Multiplexing and Spreading

- Asked in: 2073 Chaitra, 5 marks
- Video: [North American (T1), Europe (E1) System & Hierarchy Principles of Communication Board Soln In Nepali](https://www.youtube.com/watch?v=XiEB5dKF_Ec) — OPengineer
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/data_communication/e-vs-t-hierarchy
- Whole chapter: https://www.bctengineer.com/md/semester_5/data_communication/chapter-6

## Question

Write a short note on E-hierarchy versus T-hierarchy.

## Answer

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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Where is the T-carrier standard used compared with E-carrier?
   A. T in Europe and Nepal; E in North America
   B. T in North America and Japan; E in Europe, Nepal and most of the world
   C. Both are used only in North America
   D. T is used everywhere except Japan
   Answer: B. T-carriers are North American/Japanese; E-carriers (ITU-T) are used in Europe, Nepal and elsewhere. (Key point: Where used)

2. What are the first-level channels and rates?
   A. T1: 24 ch, 1.544 Mbps; E1: 30 ch, 2.048 Mbps
   B. T1: 30 ch, 2.048 Mbps; E1: 24 ch, 1.544 Mbps
   C. T1: 24 ch, 2.048 Mbps; E1: 30 ch, 1.544 Mbps
   D. Both 32 ch, 2.048 Mbps
   Answer: A. T1 carries 24 channels at 1.544 Mbps; E1 carries 30 voice channels at 2.048 Mbps. (Key point: Level 1 rates)

3. How big are the T1 and E1 frames?
   A. T1 256 bits, E1 193 bits
   B. Both 256 bits
   C. T1 193 bits (24x8+1), E1 256 bits (32x8)
   D. Both 193 bits
   Answer: C. T1: 24x8+1 framing = 193 bits; E1: 32x8 = 256 bits; both at 8000 frames/s. (Key point: Frame size)

4. Which companding law does each standard use?
   A. T uses A-law, E uses mu-law
   B. Both use mu-law
   C. Both use A-law
   D. T uses mu-law, E uses A-law
   Answer: D. T-carriers use mu-law and E-carriers use A-law. (Key point: Companding)

## Related in Data Communication

- [Short note: Analog vs digital mux hierarchy](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Aanalog-vs-digital-mux-hierarchy) — Data Communication, chapter 6
- [Packet vs message switching](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Apacket-vs-message-switching) — Data Communication, chapter 7

## Related in other subjects

- [North American T1 vs European E1 hierarchy](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3At1-e1-hierarchy-compare) — Telecommunications, chapter 3, asked 2×
- [DPCM vs delta modulation; E1 hierarchy](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adpcm-vs-dm-e1) — Communication Systems, chapter 4
- [FDMA vs TDMA; T1 and E1 hierarchy](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Afdma-tdma-t1-e1) — Communication Systems, chapter 5
- [FDM vs TDM; FDM telephone hierarchy](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Afdm-vs-tdm-fdm-hierarchy) — Communication Systems, chapter 5