--- title: "Communication protocol and its need" subject: "Telecommunications" chapter: 8 key: "semester_8/telecommunications:communication-protocol-need" source: https://www.bctengineer.com/q/semester_8/telecommunications/communication-protocol-need site: BCT Engineering --- # Communication protocol and its need Telecommunications · Chapter 8: Data Communication - Asked in: 2069 Bhadra (old course), 12 marks; 2065 Magh (old course), 1+11 marks; 2064 Poush (old course), 2+10 marks (asked 3 times) - Video: [Network Protocols & Communications (Part 1)](https://www.youtube.com/watch?v=ly8ikWtAY7s) — Neso Academy - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/communication-protocol-need - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-8 ## Question What is a communication protocol and why is it required in data communication? Explain. ## Short answer A communication protocol is a set of rules governing data format, transmission, and interpretation between devices. It is required because without common rules, devices cannot understand each other. Protocols provide essential functions such as encapsulation, error and flow control, addressing, and synchronization, ensuring reliable data exchange. ## Answer A **communication protocol** is a set of agreed rules and conventions that govern how data are formatted, transmitted, received and interpreted by two or more communicating entities. Without a common protocol, devices can send bits to each other but cannot understand them, just as two people need a common language to talk. #### Key elements of a protocol 1. **Syntax:** the format and structure of data, e.g. first 8 bits are the address, next 8 bits the control field, then data. 2. **Semantics:** the meaning of each field and the action to take, e.g. what a "NAK" means. 3. **Timing:** when data should be sent and how fast; sequencing and speed matching. Example: HDLC frame ```text | Flag | Address | Control | Data | FCS | Flag | 8b 8b 8b var 16b 8b ``` #### Why a protocol is required (functions) 1. **Encapsulation:** adds headers (address, control, error-check bits) to user data. 2. **Segmentation and reassembly:** breaks long messages into blocks of suitable size and rebuilds them at the receiver. 3. **Connection control:** sets up, maintains and releases logical connections (e.g. TCP three-way handshake). 4. **Ordered delivery:** sequence numbers allow the receiver to put data back in the correct order. 5. **Flow control:** prevents a fast sender from overrunning a slow receiver (stop-and-wait, sliding window). 6. **Error control:** detects errors (CRC, checksum) and recovers by retransmission (ARQ) or correction. 7. **Addressing:** identifies source, destination, ports and connections. 8. **Multiplexing:** many connections share one link or one lower-layer connection. 9. **Synchronisation:** both ends agree on timing, state and frame boundaries. 10. **Transmission services:** priority, QoS, security (encryption, authentication). 11. **Interoperability:** equipment from different vendors and countries can work together. #### Layered protocol architecture Because communication is complex, protocols are arranged in layers; each layer uses the services of the layer below and serves the layer above. Peer layers talk using their protocol. ```text Host A Host B Application <-- HTTP --> Application Transport <-- TCP --> Transport Network <-- IP --> Network Data link <-- Eth --> Data link Physical ============ Physical ``` | OSI layer | Function | Example protocol | |---|---|---| | Application | user services | HTTP, SMTP, FTP | | Presentation | format, encryption | TLS, JPEG | | Session | dialogue control | RPC | | Transport | end-to-end reliability | TCP, UDP | | Network | routing, addressing | IP | | Data link | framing, error control | HDLC, Ethernet | | Physical | bit transmission | RS-232, V.24 | #### Types of protocols - **Direct or indirect:** data passed directly between two stations, or through switches/routers. - **Monolithic or structured (layered).** - **Symmetric** (peer-to-peer) or **asymmetric** (client/server, master/slave). - **Standard** (ISO, ITU-T, IETF) or **non-standard** (vendor specific). #### Example When a browser loads a web page, HTTP defines the request and reply format; TCP divides data into segments, numbers them, and retransmits lost ones; IP routes each packet; Ethernet frames carry packets on the LAN with a CRC. If any of these rules were missing, data would be lost, mixed up or not understood. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a communication protocol? A. A set of agreed rules governing how data are formatted, transmitted, received and interpreted B. A hardware cable standard C. A program that encrypts all data D. A device that connects two networks Answer: A. Without common rules devices can exchange bits but cannot understand them. (Key point: Protocol definition) 2. In a protocol, what does 'semantics' specify? A. The meaning of each field and the action to take B. The format and field layout of data C. The physical medium used D. When data are sent and how fast Answer: A. Syntax is format, semantics is meaning/action (e.g. what NAK means), timing is when and how fast. (Key point: Elements of a protocol) 3. Which protocol function prevents a fast sender from overrunning a slow receiver? A. Flow control B. Multiplexing C. Addressing D. Encapsulation Answer: A. Flow control (stop-and-wait, sliding window) matches sender speed to the receiver. (Key point: Flow control) 4. How does a protocol recover from errors found by CRC or checksum? A. By retransmission (ARQ) or error correction B. By ignoring the frame silently always C. By changing the IP address D. By lowering the layer number Answer: A. Error control detects errors and then recovers using ARQ retransmission or correction. (Key point: Error control) ## Related in Telecommunications - [Communication protocol and OSI architecture](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aprotocol-osi-architecture) — Telecommunications, chapter 8 - [Switching techniques in data communication](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aswitching-techniques-data-comm) — Telecommunications, chapter 8, asked 3× - [Short note: Routing algorithm in data communication](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Arouting-algorithm-data-comm) — Telecommunications, chapter 8, asked 2× - [Flow control mechanisms in data communication](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aflow-control-mechanisms) — Telecommunications, chapter 8 - [Flow control in data communication network](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aflow-control-network) — Telecommunications, chapter 8 ## Related in other subjects - [Routing and need of routing protocol](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Arouting-protocol-necessity) — Computer Networks and Security, chapter 4, asked 2× - [Estimating, purpose and data required](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Aestimating-purpose-data-required) — Estimating and Costing, chapter 1, asked 6× - [Estimated cost never actual; data required](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Aest-cost-never-actual-data) — Estimating and Costing, chapter 1 - [Data required for detailed estimate](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Adata-for-detailed-estimate) — Estimating and Costing, chapter 1