--- title: "Multiplexing techniques and TDM standards" subject: "Telecommunications" chapter: 3 key: "semester_8/telecommunications:multiplexing-techniques-tdm-standards" source: https://www.bctengineer.com/q/semester_8/telecommunications/multiplexing-techniques-tdm-standards site: BCT Engineering --- # Multiplexing techniques and TDM standards Telecommunications · Chapter 3: Signal Multiplexing - Asked in: 2075 Chaitra, 4+4 marks - Video: [Types of Multiplexing | FDM TDM WDM | Analog Digital | Computer Networks](https://www.youtube.com/watch?v=WXof7bg_Zys) — Dr. Ankit Verma - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/multiplexing-techniques-tdm-standards - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-3 ## Question What are the different multiplexing techniques used in telecommunication? Explain briefly. Also discuss the North American and European standard of TDM with their hierarchies and data rates. ## Short answer Multiplexing techniques include FDM, TDM, WDM, CDM/CDMA, and space division multiplexing. NA TDM: T1 1.544 Mbps (24 channels), T2 6.312, T3 44.736, T4 274.176 Mbps. European: E1 2.048 Mbps (30 voice), E2 8.448, E3 34.368, E4 139.264, E5 564.992 Mbps. ## Answer **Multiplexing** is combining several signals for transmission over one shared medium. #### Multiplexing techniques 1. **Frequency Division Multiplexing (FDM):** each signal is placed in its own frequency band by modulation; guard bands separate the bands; all channels are sent together. Used in analogue carrier telephony, radio and TV broadcasting. 2. **Time Division Multiplexing (TDM):** each channel is given a time slot in a repeating frame and uses the full bandwidth during its slot. Synchronous TDM (fixed slots, e.g. T1/E1) and statistical TDM (slots on demand, with addresses). 3. **Wavelength Division Multiplexing (WDM):** in optical fibre, each signal is carried on a different wavelength of light (CWDM, DWDM). 4. **Code Division Multiplexing (CDM/CDMA):** all users share the same band at the same time, each spread by a unique orthogonal code; used in 3G mobile and GPS. 5. **Space Division Multiplexing:** separate physical paths (pairs in a cable, fibres, beams). #### North American TDM standard Basic frame: 24 channels × 8 bits + 1 framing bit = 193 bits per 125 µs. $$ \begin{aligned} \text{Bits per frame} &= 24 \times 8 + 1 = 193\ \text{bits} \\ \text{Frame rate} &= 8000\ \text{frames/s}\ (T = 125\ \mu\text{s}) \\ R_{T1} &= 193 \times 8000 = 1.544\ \text{Mbps} \end{aligned} $$ ```text 24 x DS0 --> [MUX] --> T1 1.544 Mbps (24 ch) 4 x T1 --> [M12] --> T2 6.312 Mbps (96 ch) 7 x T2 --> [M23] --> T3 44.736 Mbps (672 ch) 6 x T3 --> [M34] --> T4 274.176 Mbps (4032 ch) ``` | Level | Made from | Voice channels | Bit rate | Overhead | |---|---|---|---|---| | DS0 | 1 voice channel | 1 | 64 kbps | – | | DS1 (T1) | 24 DS0 | 24 | 1.544 Mbps | 8 kbps (framing) | | DS2 (T2) | 4 DS1 | 96 | 6.312 Mbps | 136 kbps | | DS3 (T3) | 7 DS2 | 672 | 44.736 Mbps | 552 kbps | | DS4 (T4) | 6 DS3 | 4032 | 274.176 Mbps | 5.76 Mbps | #### European TDM standard Basic frame: 32 time slots × 8 bits (TS0 sync, TS16 signalling, 30 voice). $$ \begin{aligned} \text{Bits per frame} &= 32 \times 8 = 256\ \text{bits} \\ R_{E1} &= 256 \times 8000 = 2.048\ \text{Mbps} \end{aligned} $$ ```text 30 x 64k --> [MUX] --> E1 2.048 Mbps (30 ch) 4 x E1 --> [MUX] --> E2 8.448 Mbps (120 ch) 4 x E2 --> [MUX] --> E3 34.368 Mbps (480 ch) 4 x E3 --> [MUX] --> E4 139.264 Mbps (1920 ch) 4 x E4 --> [MUX] --> E5 564.992 Mbps (7680 ch) ``` | Level | Made from | Voice channels | Bit rate | Overhead | |---|---|---|---|---| | E0 | 1 voice channel | 1 | 64 kbps | – | | E1 | 30 voice + 2 TS | 30 | 2.048 Mbps | 128 kbps (TS0, TS16) | | E2 | 4 E1 | 120 | 8.448 Mbps | 256 kbps | | E3 | 4 E2 | 480 | 34.368 Mbps | 576 kbps | | E4 | 4 E3 | 1920 | 139.264 Mbps | 1.792 Mbps | | E5 | 4 E4 | 7680 | 564.992 Mbps | 7.936 Mbps | The European system uses a regular factor of 4 at every level and keeps signalling in a separate slot; the American system uses robbed-bit signalling and factors 4, 7 and 6. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What distinguishes synchronous TDM from statistical TDM? A. Synchronous TDM gives each channel a fixed slot in every frame; statistical TDM gives slots on demand with addresses B. Synchronous TDM uses different wavelengths; statistical TDM uses different codes C. Synchronous TDM needs guard bands; statistical TDM does not D. Synchronous TDM gives slots only to active sources; statistical TDM gives fixed slots Answer: A. In synchronous TDM (T1/E1) slots are fixed and idle ones are wasted; statistical TDM allocates slots only to active sources and tags them with addresses. (Key point: Synchronous vs statistical TDM) 2. How is the T1 rate of 1.544 Mbps obtained? A. 24 x 8 bits = 192 bits per frame x 8000 frames/s B. (24 x 8 + 1) = 193 bits per frame x 8000 frames/s C. 32 x 8 = 256 bits per frame x 8000 frames/s D. (24 x 8 + 1) = 193 bits per frame x 4000 frames/s Answer: B. A T1 frame has 24 channels x 8 bits plus 1 framing bit = 193 bits, sent 8000 times per second, giving 1.544 Mbps. (Key point: T1 frame and rate) 3. Which grouping correctly gives the North American hierarchy above T1? A. 4 T1 = T2, 4 T2 = T3, 4 T3 = T4 B. 4 T1 = T2, 7 T2 = T3, 6 T3 = T4 C. 7 T1 = T2, 4 T2 = T3, 6 T3 = T4 D. 6 T1 = T2, 7 T2 = T3, 4 T3 = T4 Answer: B. The American system uses irregular factors 4, 7 and 6 giving 6.312, 44.736 and 274.176 Mbps. (Key point: North American hierarchy) 4. In the European E1 frame of 32 time slots, how are the slots used? A. 32 voice channels with one framing bit B. TS0 for sync, TS16 for signalling, 30 for voice C. TS0 and TS31 for sync, 30 for voice D. 24 voice slots and 8 signalling slots Answer: B. E1 has 32 x 8 = 256 bits per frame: TS0 sync, TS16 signalling and 30 voice channels, giving 2.048 Mbps. (Key point: E1 frame structure) ## Related in Telecommunications - [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× - [European TDM system](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aeuropean-tdm-system) — Telecommunications, chapter 3 - [Compare multiplexing techniques](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Acompare-multiplexing-techniques) — Telecommunications, chapter 3 - [TDM and T1/E1 carrier standards](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Atdm-t1-e1-carriers) — Telecommunications, chapter 3 - [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 - [Digital carrier system and multiplexing techniques](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Adigital-carrier-multiplexing) — Telecommunications, chapter 3 ## Related in other subjects - [American vs European distribution layout in Nepal](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aamerican-vs-european-distribution-nepal) — Transmission and Distribution System Design, chapter 5, asked 2× - [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 - [Multiplexing; synchronous vs asynchronous TDM](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Amux-compare-sync-async-tdm) — Data Communication, chapter 6, asked 6× - [Multiplexing techniques; analog one explained](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Alist-mux-techniques) — Data Communication, chapter 6