--- title: "Routing, flow control and dynamic routing" subject: "Telecommunications" chapter: 8 key: "semester_8/telecommunications:routing-flow-control-dynamic" source: https://www.bctengineer.com/q/semester_8/telecommunications/routing-flow-control-dynamic site: BCT Engineering --- # Routing, flow control and dynamic routing Telecommunications · Chapter 8: Data Communication - Asked in: 2071 Shrawan, 2+2+3 marks - Video: [Routing in Computer Networks](https://www.youtube.com/watch?v=duXDA2Rb-68) — Engineering Funda - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/routing-flow-control-dynamic - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-8 ## Question What is the significance of routing and flow control in data communication? Describe briefly about the dynamic routing. ## Short answer Routing determines optimal packet paths for efficiency and reliability, while flow control prevents buffer overflow by matching sender and receiver rates. Dynamic routing automatically adjusts routes based on topology and load; distributed methods include distance vector (RIP) and link state (OSPF). ## Answer #### Significance of routing **Routing** decides the path that packets take from source to destination through the network of switching nodes. - Delivers packets to the correct destination across many possible paths. - Chooses the best path (least delay, cost or hops), so it improves throughput and reduces delay. - Balances load over links and avoids congested parts. - Finds alternative paths when links or nodes fail, so the network is reliable. - Uses network resources efficiently, reducing cost. #### Significance of flow control **Flow control** regulates how fast a sender transmits so that the receiver or an intermediate node is not overrun. - Prevents buffer overflow and the resulting packet loss and retransmissions. - Matches devices of different speeds (e.g. fast server, slow terminal). - Helps avoid congestion and deadlock in the network. - Keeps throughput high and delay stable; ensures fair sharing. - Methods: stop-and-wait, sliding window (HDLC, TCP), XON/XOFF, RTS/CTS, credit and rate (leaky bucket) control. #### Dynamic routing **Dynamic (adaptive) routing** changes routes automatically to follow the current topology and traffic. Routers exchange routing information and recompute their tables periodically or when a change is detected. **Types** - **Centralized:** a Routing Control Centre gathers data from all nodes, computes routes and sends tables. - **Isolated:** each node uses only local information, e.g. hot potato routing (send on the shortest queue). - **Distributed:** - **Distance vector:** each router sends its distance table to neighbours; updates by Bellman-Ford, $D_x(y) = \min_v \{c(x,v) + D_v(y)\}$. Simple, but slow convergence (count-to-infinity). Example: RIP. - **Link state:** each router floods its link costs to all; every router builds the whole map and runs Dijkstra. Fast convergence. Example: OSPF. ```text A ---2--- B ---1--- D \ / 5 3 \--- C -----/ Normal: A->D via B (cost 3) B-D fails: A->D via C (cost 8), learnt automatically ``` **Advantages:** adapts to failures and congestion, no manual work, good for large networks. **Disadvantages:** control traffic overhead, more processing, possible routing loops or oscillation during convergence. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is a main significance of routing? A. Controls the sender speed to protect receiver buffers B. Chooses the best path and finds alternatives when links or nodes fail C. Detects bit errors using CRC D. Assigns MAC addresses Answer: B. Routing selects paths, balances load and provides alternate routes on failure; speed matching is flow control. (Key point: Significance of routing) 2. What does flow control avoid? A. Buffer overflow, packet loss and retransmissions B. Choosing longer paths C. Routing table growth D. Need for acknowledgements Answer: A. By regulating the sender's rate it prevents the receiver or nodes being overrun. (Key point: Significance of flow control) 3. How does a distance-vector router update its table? A. Floods link costs to all routers and runs Dijkstra B. Uses Bellman-Ford: D_x(y) = min over v of c(x,v) + D_v(y), from neighbours' tables C. Asks a central control centre D. Uses only the shortest local queue Answer: B. Distance vector exchanges tables with neighbours and applies Bellman-Ford; it can suffer count-to-infinity. (Key point: Distance vector update) 4. Which is the correct matching? A. Link state - RIP; distance vector - OSPF B. Link state - OSPF with fast convergence; distance vector - RIP with slow convergence C. Isolated - uses whole network map D. Centralized - each node uses only local data Answer: B. OSPF is link state (fast convergence); RIP is distance vector (count-to-infinity, slow). (Key point: Types of dynamic routing) ## Related in Telecommunications - [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 - [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× - [Static and dynamic routing algorithms](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Astatic-dynamic-routing) — 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× - [Adaptive and non-adaptive routing algorithms](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Aadaptive-nonadaptive-routing) — Telecommunications, chapter 8, asked 3× ## Related in other subjects - [Meaning of flow routing](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Aflow-routing-meaning) — Engineering Hydrology, chapter 7, asked 3× - [Why flow routing, time-area method of routing](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Aflow-routing-time-area) — Engineering Hydrology, chapter 7 - [Media Access Control and significance](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Amac-significance) — Computer Networks and Security, chapter 3 - [Static and dynamic data structures; array list](https://www.bctengineer.com/question.md?key=semester_4%2Fdata_structure_and_algorithm%3Astatic-dynamic-ds-array-list) — Data Structure and Algorithm, chapter 3