What are common examiner traps in Switching and Performance Metrics?

Failing to convert bytes to bits (1 byte = 8 bits) when bandwidth is specified in bps/Mbps. Forgetting to include per-packet header overhead when calculating packet transmission delay. Multiplying the entire transmission time by the number of hops (m × N × Tt) instead of recognizing link pipelining ([N + m - 1] × Tt). Unit mismatches between seconds, milliseconds (ms), and microseconds ( ). Confusing the number of routers (R) with the number of links/hops (m = R + 1). Double-counting propagation delay for intermediate packets in pipelined transmission instead of applying it to the leading or trailing packet. Unit conversion errors (e.g., kilometers to meters, Mbps vs bps, bytes vs bits). Confusing Go-Back-N sequence number space (2k ≥ Ws + 1) with Selective Repeat (2k ≥ 2 Ws). Using 1 + a instead of 1 + 2a for round-trip channel utilization. Rounding down instead of applying ceiling when determining integer bit-widths ( lceil log2(N) rceil). Confusing symmetric key pairs (N(N-1))/(2) with asymmetric/public-key requirements (2N total keys). Overcounting directed pairs as N(N-1) instead of undirected shared secret keys (N(N-1))/(2). Off-by-one errors like (N-1)2 or failing to account for self-communication exclusion. Confusing TCP and UDP requirements for control/lookup protocols (e.g., DNS typically uses UDP) vs. bulk transfer protocols (e.g., FTP uses TCP). Swapping the sender's private key with the receiver's public key during message signing versus message encryption. Reversing the decryption and verification order at the receiver end (the outermost encryption layer must be decrypted first before verifying the inner digital signature).

GATE CSE Switching and Performance Metrics PYQs

Standard yield8.6% of Computer Networks

In this topic area within Computer Networks, GATE tests foundational conceptual knowledge through direct 1-mark multiple-choice questions. The questions focus o… Read the guide

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Questions: 11
Asked: since 2013
Total marks: 17
Marks / paper: 0.7

11 GATE CSE Switching and Performance Metrics PYQs with solutions, from Computer Networks. Browse all GATE CSE PYQs.

Questions

Every official paper that asked this topic, newest first.

What GATE tests in Switching and Performance Metrics

Concepts, patterns, formulas and traps distilled from past papers.

In this topic area within Computer Networks, GATE tests foundational conceptual knowledge through direct 1-mark multiple-choice questions. The questions focus on matching standard network applications to their corresponding underlying transport layer protocols (TCP vs. UDP) and identifying key-usage sequences in secure transmission protocols involving digital signatures and asymmetric encryption. The emphasis is on testing functional understanding of protocol services and layered security mechanisms.

Core concepts

Store-and-forward packet switching and pipelining
Transmission delay vs Propagation delay distinction
Header overhead trade-off during packet fragmentation/segmentation
Router processing and store-and-forward scheduling delay
Bottleneck link throughput in multi-hop paths
Stop-and-Wait protocol channel efficiency
Propagation delay vs Transmission delay
Bandwidth-Delay Product (BDP)
Channel utilization and efficiency
Go-Back-N window sizing constraints
Sequence number field bit-length requirements
Symmetric key cryptography key management overhead
Full-mesh pairwise communication topology
Combinatorics in network security and connectivity (selecting 2 endpoints out of N)
Transport Layer protocol selection (TCP reliability vs. UDP low-overhead/low-delay)
Application requirements for transport protocols (Real-time streaming, FTP, DNS, SMTP)
Digital signatures for authentication and non-repudiation using sender's private key
Public-key encryption for confidentiality using receiver's public key
Decryption sequence and signature verification using receiver's private key and sender's public key

Recurring question patterns

Pipelined Multi-Hop Store-and-Forward Delay
Commonmixed2 marks2024, 2015, 2014
A file is partitioned into $N$ equal packets (or chunks) and transmitted across $m$ hops (or intermediate routers). Questions require computing total delivery time or comparing how packetization and per-packet headers trade off serialization latency against header overhead.
Point-to-Point End-to-End Latency Calculation
Commonmixed2 marks2022, 2017
Direct single-link or single-hop satellite/terrestrial links where candidates must compute individual transmission delay ( $L/B$ ) and propagation delay ( $D/v$ ) or their sum to find total reception time.
Bottleneck Bandwidth and Throughput
OccasionalMCQ1 marks2026
A multi-hop path with heterogeneous link capacities where candidates compute total transfer time governed by the bottleneck (minimum bandwidth) link.
Protocol Efficiency and Propagation Relationship
OccasionalNAT1 marks2015
Given protocol efficiency (e.g. Stop-and-Wait ARQ) and link transmission parameters, determine link propagation delay or maximum distance.
Optimal Window Size and Sequence Number Header Calculation
OccasionalNAT2 marks2015
Given link distance, propagation velocity, bandwidth, and packet length, compute transmission and propagation delays to find the window size needed for 100% channel utilization ( $W_s = 1 + 2a$ ) and find the minimum number of sequence number bits required by the protocol (e.g., Go-Back-N).
Pairwise Communication and Key/Link Counting
CommonMCQ1 marks2015
Given a network of $N$ entities where every pair requires a dedicated, private symmetric key (or dedicated point-to-point circuit/channel), compute the total number of unique keys/links needed across the entire system.
Application to Transport Protocol Mapping
CommonMCQ1 marks2013
Given an ordered list of common network services (e.g., real-time multimedia, file transfer, DNS, email), identify the correct sequence of transport layer protocols (TCP or UDP) utilized by each.
Asymmetric Cryptography Key Sequence Tracking
CommonMCQ1 marks2013
Given a combined cryptographic workflow involving digital signing and confidential encryption between sender and receiver, identify the exact sequence of public and private keys used for encryption/signing at the sender and decryption/verification at the receiver.

Formulas GATE uses

Transmission Delay ($T_t$)

T_t = \frac{L}{B}

Used whenever a packet of size $L$ bits is pushed onto a link with transmission rate / bandwidth $B$ bps.

Propagation Delay ($T_p$)

T_p = \frac{D}{v}

Used to compute physical travel time of a signal over distance $D$ at propagation speed $v$ .

Total Pipelined Packet Transmission Time (Homogeneous Links)

T_{\text{total}} = (N + m - 1) \times T_t + m \times T_p

Used when sending $N$ store-and-forward packets over $m$ links with identical bandwidth and propagation delay, assuming zero queueing/processing delay.

Stop-and-Wait Link Efficiency

\eta = \frac{T_t}{T_t + 2T_p} = \frac{1}{1 + 2a} \quad \text{where } a = \frac{T_p}{T_t}

Used when analyzing the channel utilization/efficiency of a Stop-and-Wait protocol with negligible ACK transmission delay.

Bottleneck File Transfer Time

T_{\text{transfer}} = \frac{\text{File Size}}{\min(B_1, B_2, \dots, B_m)}

Used for end-to-end file transfer over a path of $m$ consecutive links with negligible propagation and queueing overheads.

Propagation Delay

T_p = \frac{\text{Distance } d}{\text{Propagation Speed } v}

Calculating signal transit time across the physical medium.

Transmission Delay

T_t = \frac{\text{Packet Size } L}{\text{Bandwidth } B}

Calculating time required to push packet bits onto the wire.

Delay Ratio

a = \frac{T_p}{T_t}

Normalizing propagation delay relative to packet transmission time.

Full Utilization Window Size

W_s \ge 1 + 2a

Finding minimum sender window size to achieve 100% channel efficiency.

Go-Back-N Sequence Number Bit-Width

k = \lceil \log_2(W_s + 1) \rceil

Finding the number of bits in sequence number field for Go-Back-N where maximum window size is $2^k - 1$ .

Total Unique Pairs for $N$ Entities (Full Mesh / Symmetric Key Count)

\binom{N}{2} = \frac{N(N-1)}{2}

Used when determining the total number of unique secret keys, connections, or dedicated circuits needed so every pair among $N$ participants can communicate privately in a symmetric system.

Examiner traps in Switching and Performance Metrics

Failing to convert bytes to bits (1 byte = 8 bits) when bandwidth is specified in bps/Mbps.
Forgetting to include per-packet header overhead when calculating packet transmission delay.
Multiplying the entire transmission time by the number of hops (m × N × Tt) instead of recognizing link pipelining ([N + m - 1] × Tt).
Unit mismatches between seconds, milliseconds (ms), and microseconds ( ).
Confusing the number of routers (R) with the number of links/hops (m = R + 1).
Double-counting propagation delay for intermediate packets in pipelined transmission instead of applying it to the leading or trailing packet.
Unit conversion errors (e.g., kilometers to meters, Mbps vs bps, bytes vs bits).
Confusing Go-Back-N sequence number space (2k ≥ Ws + 1) with Selective Repeat (2k ≥ 2 Ws).
Using 1 + a instead of 1 + 2a for round-trip channel utilization.
Rounding down instead of applying ceiling when determining integer bit-widths ( lceil log2(N) rceil).
Confusing symmetric key pairs (N(N-1))/(2) with asymmetric/public-key requirements (2N total keys).
Overcounting directed pairs as N(N-1) instead of undirected shared secret keys (N(N-1))/(2).
Off-by-one errors like (N-1)2 or failing to account for self-communication exclusion.
Confusing TCP and UDP requirements for control/lookup protocols (e.g., DNS typically uses UDP) vs. bulk transfer protocols (e.g., FTP uses TCP).
Swapping the sender's private key with the receiver's public key during message signing versus message encryption.
Reversing the decryption and verification order at the receiver end (the outermost encryption layer must be decrypted first before verifying the inner digital signature).

How questions are asked

Compute total elapsed time across a multi-hop path (NAT/MCQ)
Compare transmission completion times for varying packet sizes with fixed headers (MCQ)
Calculate independent transmission and propagation delays (MCQ)
Derive link propagation delay or distance from ARQ efficiency (NAT)
Determine end-to-end transfer time over heterogeneous link capacities (MCQ)
Numerical calculation of delay metrics and header field sizes (NAT)
Symbolic algebraic formula selection for N communicating nodes
Ordered sequence matching of protocols to application list
Key sequence selection for end-to-end secure transmission pipeline

Paper trends

Shift from purely algebraic/comparative multi-case problems to precise numerical computation with pipelined timelines and router processing delays.
2024, 2015, 2014
Increase in NAT questions requiring exact unit conversions (seconds, milliseconds, microseconds) and decimal rounding.
2022, 2015
Introduction of heterogeneous multi-hop bandwidths highlighting bottleneck link capacity over intermediate router buffering.
2026
Performance metric questions are framed as multi-step numerical calculation problems (NAT) combining physical layer delay parameters with transport/data-link framing constraints.
2015
Questions on basic network counting and fundamental system parameters are presented as direct, conceptual 1-mark multiple-choice questions.
2015
Questions are tested as conceptual 1-mark single-correct MCQs targeting fundamental protocol choices and asymmetric key management workflows.
2013

Difficulty notes

Easy items test standard single-link transmission/propagation delay arithmetic or direct formula application ( $T_t + T_p$ ). Medium items involve multi-hop store-and-forward pipelining, non-zero switch processing delays, packetization with header overhead trade-offs, or bottleneck bandwidth identification with unit conversions.