--- title: "Adaptive and non-adaptive routing algorithms" subject: "Telecommunications" chapter: 8 key: "semester_8/telecommunications:adaptive-nonadaptive-routing" source: https://www.bctengineer.com/q/semester_8/telecommunications/adaptive-nonadaptive-routing site: BCT Engineering --- # Adaptive and non-adaptive routing algorithms Telecommunications · Chapter 8: Data Communication - Asked in: 2081 Baisakh, 4+4 marks; 2075 Asoj, 4 marks; 2074 Asoj, 8 marks (asked 3 times) - Video: [Introduction to Routing Algorithms | Types of Routing Algorithms | Adaptive | Non Adaptive | Static](https://www.youtube.com/watch?v=1KGC7Tp6HGo) — Sudhakar Atchala - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/adaptive-nonadaptive-routing - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-8 ## Question Explain adaptive and non-adaptive routing algorithms used in data communication. ## Short answer Non-adaptive routing uses fixed routes (e.g., shortest path, flooding) and cannot react to changes. Adaptive routing dynamically updates routes based on network state, using algorithms like distance vector (RIP) or link state (OSPF), which automatically handle failures and congestion but require routing overhead. ## Answer **Routing** is the process by which a node (router or packet switch) decides the outgoing link for a packet so it reaches its destination. Routing algorithms are of two kinds: **non-adaptive (static)** and **adaptive (dynamic)**. #### Non-adaptive (static) routing Routes are computed in advance (off-line) and loaded into the routers; they do **not change** with current traffic or topology, unless an administrator changes them. **Examples** 1. **Shortest path routing:** the network is a graph with link costs (distance, delay); Dijkstra's algorithm finds the least-cost path from each source, and the tables are fixed. 2. **Flooding:** every incoming packet is sent on every outgoing line except the one it came on; hop counters or sequence numbers stop endless copies. Very robust, used in military networks and for broadcasting link-state updates. 3. **Flow-based routing:** uses known average traffic between node pairs and link capacities to choose routes that minimise mean delay. 4. **Fixed/static routes** configured by hand (e.g. default route). **Features:** simple, low processing and no routing traffic, predictable; but cannot react to failures or congestion. #### Adaptive (dynamic) routing Routes are **changed automatically** in response to changes in topology and traffic load. Routers exchange information and recompute paths periodically or when a change occurs. **Types by where decisions are made** - **Centralised:** a routing control centre collects information and sends tables to all nodes. - **Isolated:** each node decides from local information only, e.g. **hot-potato** routing (send on the shortest queue) or backward learning. - **Distributed:** nodes exchange information with neighbours. **Main distributed algorithms** 1. **Distance vector routing** (Bellman–Ford): each router keeps a table of the best known distance to every destination and the next hop, and periodically sends it to neighbours. Used in RIP. Simple but suffers from the **count-to-infinity** problem and slow convergence. 2. **Link state routing:** each router learns its neighbours and link costs, floods **link state packets** to all routers, builds the full topology and runs Dijkstra. Used in OSPF and IS-IS. Converges fast, larger memory and CPU. ```text A --2-- B --1-- D | | | 5 2 1 | | | C --3-- E ------+ If link B-D fails, adaptive routing finds A-B-E-D; static routing keeps using B-D and the packets are lost. ``` #### Comparison | Point | Non-adaptive | Adaptive | |---|---|---| | Route decision | fixed in advance | changes with network state | | Reaction to failure | none (manual) | automatic | | Overhead | very low | routing messages, CPU | | Complexity | simple | complex | | Examples | static route, flooding, shortest path | distance vector (RIP), link state (OSPF) | | Suited for | small, stable networks | large, changing networks | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the key feature of non-adaptive routing? A. Routes change automatically with load B. Routes are computed in advance and do not change with traffic or topology C. Routers exchange tables every second D. Decisions use link-state packets Answer: B. Static routes are fixed unless an administrator changes them. (Key point: Non-adaptive routing) 2. How does flooding work? A. Sends on the shortest queue only B. Uses Dijkstra's tables C. Sends each incoming packet on every outgoing line except the one it arrived on, with hop counters to stop endless copies D. Uses only the default route Answer: C. Flooding is robust and uses counters or sequence numbers to limit copies. (Key point: Flooding) 3. Which algorithm suffers from the count-to-infinity problem? A. Link state (OSPF) B. Flooding C. Flow-based routing D. Distance vector (RIP) Answer: D. Distance vector (Bellman-Ford) has slow convergence and count-to-infinity. (Key point: Count to infinity) 4. What does a link state router do? A. Floods link state packets, builds the full topology and runs Dijkstra B. Sends its table only to neighbours C. Uses fixed manual routes D. Picks the shortest queue Answer: A. Link state converges fast but needs more memory and CPU; used in OSPF and IS-IS. (Key point: Link state routing) ## Related in Telecommunications - [Static and dynamic routing algorithms](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Astatic-dynamic-routing) — 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× - [Link-state routing as adaptive routing](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Alink-state-adaptive-example) — 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× - [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 - [Adaptive equalization algorithms (any two)](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aadaptive-equalization-algorithms) — Wireless Communication, chapter 5 - [Data types and classification of algorithms](https://www.bctengineer.com/question.md?key=semester_4%2Fdata_structure_and_algorithm%3Adata-types-classify-algorithms) — Data Structure and Algorithm, chapter 1 - [I/O functions used with data files](https://www.bctengineer.com/question.md?key=semester_1%2Fcomputer_programming%3Afile-io-functions) — Computer Programming, chapter 10, asked 2× - [Non-verbal communication and its elements](https://www.bctengineer.com/question.md?key=semester_5%2Fcommunication_english%3Anonverbal-communication-elements) — Communication English, chapter 4