--- title: "E1 frame, TDM hierarchy and signaling rate" subject: "Communication Systems" chapter: 5 key: "semester_6/communication_systems:e1-frame-hierarchy" source: https://www.bctengineer.com/q/semester_6/communication_systems/e1-frame-hierarchy site: BCT Engineering --- # E1 frame, TDM hierarchy and signaling rate Communication Systems · Chapter 5: Multiplexing Techniques - Asked in: 2074 Asoj (CS II), 3+3 marks - Video: [European E1 TDM Hierarchy](https://www.youtube.com/watch?v=ZS5_Q-Z64Kk) — Aman Dhakal - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/communication_systems/e1-frame-hierarchy - Whole chapter: https://www.bctengineer.com/md/semester_6/communication_systems/chapter-5 ## Question Describe E1 frame and its TDM hierarchy along with signaling rate. ## Short answer The E1 frame has 32 time slots (256 bits) per 125 µs frame, giving 2.048 Mb/s. Signalling uses TS16. Hierarchy: E1 2.048 Mb/s, E2 8.448 Mb/s, E3 34.368 Mb/s, E4 139.264 Mb/s. ## Answer #### E1 frame **E1** is the ITU-T TDM-PCM carrier that carries 30 voice channels. Each voice channel is sampled at 8 kHz and coded with 8 bits (A-law), giving 64 kb/s. One frame takes one byte from each of 32 time slots: ```text |<-------- one frame = 125 us = 256 bits -------->| +-----+-----+-----+-----+------+------+-----+------+ | TS0 | TS1 | ... |TS15 | TS16 | TS17 | ... | TS31 | +-----+-----+-----+-----+------+------+-----+------+ sync voice voice signal voice voice each time slot = 8 bits; 32 slots per frame voice channels: TS1-TS15 and TS17-TS31 (30) ``` - TS0: frame alignment word (0011011) in alternate frames, plus alarm/CRC bits. - TS16: channel-associated signalling. 16 frames form a 2 ms multiframe. - 30 slots carry speech. **Signalling (bit) rate:** $$ \begin{aligned} \text{Bits per frame} &= 32 \times 8 = 256 \\ R_b &= 256 \times 8000 = 2\,048\,000\ \text{b/s} = 2.048\ \text{Mb/s} \end{aligned} $$ Bit duration $T_b = 1/2.048\ \text{MHz} \approx 0.488$ µs. #### E1 TDM hierarchy ```text 30 voice ch x 64 kb/s (+ 2 overhead slots) | [ E1 ] 2.048 Mb/s 30 ch | x4 [ E2 ] 8.448 Mb/s 120 ch | x4 [ E3 ] 34.368 Mb/s 480 ch | x4 [ E4 ] 139.264 Mb/s 1920 ch | x4 [ E5 ] 564.992 Mb/s 7680 ch ``` | Level | Rate | Channels | |---|---|---| | E1 | 2.048 Mb/s | 30 | | E2 | 8.448 Mb/s | 120 | | E3 | 34.368 Mb/s | 480 | | E4 | 139.264 Mb/s | 1920 | Each level combines 4 streams of the level below. A few extra bits are added for framing and justification, so for example $4 \times 2.048 = 8.192$ Mb/s, but E2 = 8.448 Mb/s. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which slots of the E1 frame carry speech? A. TS0 to TS29 B. TS2 to TS31 C. TS1 to TS15 and TS17 to TS31 D. TS1 to TS30 Answer: C. TS0 is for alignment and TS16 for signalling, leaving TS1-TS15 and TS17-TS31 = 30 voice slots. (Key point: Voice channels in E1) 2. How many frames form the E1 multiframe, and how long is it? A. 12 frames, 1.5 ms B. 24 frames, 3 ms C. 16 frames, 2 ms D. 32 frames, 4 ms Answer: C. 16 frames of 125 µs each make a 2 ms multiframe, used for TS16 channel-associated signalling. (Key point: Multiframe) 3. What is the E1 signalling (bit) rate and the bit duration? A. 2.048 Mb/s and about 0.488 µs B. 1.544 Mb/s and about 0.648 µs C. 2.048 Mb/s and about 2.048 µs D. 2.048 kb/s and about 488 µs Answer: A. Rb = 256 x 8000 = 2.048 Mb/s, so Tb = 1/2.048 MHz = 0.488 µs. (Key point: Signalling rate calculation) 4. In the E-hierarchy, how are the levels E2, E3 and E4 built? A. Each combines 4 streams of the level below B. E2 = 7 x E1, E3 = 6 x E2 C. Each combines 2 streams of the level below D. Each combines 24 streams of the level below Answer: A. E2 = 4 x E1 (120 ch), E3 = 4 x E2 (480 ch), E4 = 4 x E3 (1920 ch), with extra stuffing bits. (Key point: Hierarchy multiplexing factor) ## Related in Communication Systems - [T1 and E1 TDM-PCM hierarchy with frame diagrams](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3At1-e1-frame-diagrams) — Communication Systems, chapter 5 - [PCM block diagram; T1 signaling rate and frame](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Apcm-block-t1-rate-frame) — Communication Systems, chapter 5 - [E1 hierarchy; PCM of 4.2 MHz TV signal with 512 levels](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Ae1-pcm-tv-4-2mhz-512) — Communication Systems, chapter 4 - [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 - [E1 hierarchy; PCM SQNR at 32 kbps](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Ae1-pcm-4khz-1-1v-32kbps) — Communication Systems, chapter 5 - [TDM vs FDM for voice; E1 and T1 hierarchies](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Atdm-fdm-voice-e1-t1) — Communication Systems, chapter 5 ## Related in other subjects - [T1 and E1 frame structures and bit rates](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3At1-e1-frame-structures) — Telecommunications, chapter 3 - [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× - [E1 telephone hierarchy](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Ae1-hierarchy) — Computer Networks and Security, chapter 2 - [TDM and T1/E1 carrier standards](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Atdm-t1-e1-carriers) — Telecommunications, chapter 3