Computer Network Important Formulas

Questions and Answers

What does MTBF stand for in network reliability?

Mean Time Between Failures

Calculate the network availability probability when links are arranged in series.

(1-b1)(1-b2)(1-b3)...

What is the formula for normalized propagation delay?

a = Time of Propagation / Time of Frame transmission

What is the formula for Link Utilization (U)?

U = 1 / (1 + 2a) Signup and view all the answers

What is the formula relating window size (N) to sequence bits (K)?

N = 2a + 1 Signup and view all the answers

What is the first step in the Go Back N protocol with sliding window?

N(2 ip interface Signup and view all the answers

What is Distance Vector Routing?

A method to discover neighbors, exchange distance vectors, and compute shortest paths. Signup and view all the answers

What are the stages of Link State Routing?

Discover neighbors, construct link state packets, flood LSA/LSP, construct database, compute shortest path using Dijkstra. Signup and view all the answers

What does BGP stand for and its primary usage?

Border Gateway Protocol; used for exchanging routing information between gateway hosts on the Internet. Signup and view all the answers

Describe UDP.

A connectionless, unreliable, datagram protocol used in real-time applications. Signup and view all the answers

What is the TCP connection management three-way handshake process?

Client sends SYN, server replies SYNACK, client replies ACK. Signup and view all the answers

How does TCP flow control work?

Adjusts the amount of data sent based on the receiver's specified window size. Signup and view all the answers

What is the purpose of delayed ACK in TCP?

Reduces the number of acknowledgment packets and improves flow control. Signup and view all the answers

Explain TCP error control and its scenarios.

Handles segments arriving out of order, duplicated segments, corrupted segments, and segment loss using acknowledgments. Signup and view all the answers

What is the congestion control algorithm in TCP?

It includes Slow Start and Avoidance phases to manage congestion window size. Signup and view all the answers

What is the formula for maximum TCP throughput?

Max Throughput = (cwnd * MSS) / RTT Signup and view all the answers

Study Notes

Network Reliability Parameter

Mean Time Between Failures (MTBF) consists of Mean Time to Failure (MTTF) and Mean Time to Repair (MTTR), expressed as MTBF = MTTF + MTTR.

Network Availability Probability Calculation

For series connections, calculate availability as the product of the probabilities that each link will work: (1-b1)(1-b2)(1-b3)*...
For parallel connections, compute the probability that all links will fail: b1b2b3*...*bn.
In mixed configurations, decompose into paths and convert parallel paths to single paths for series.

Normalized Propagation Delay

Expressed as a = Time of Propagation / Time of Frame Transmission.

Throughput (U) Link Utilization

Utilization (U) is calculated with the formula U = 1 / (1 + 2a).

Sliding Window Protocol

The window size, N, is linked to sequence bits K with the formula N = 2a + 1.
Utilization (U) relates to N as follows: U = 1 when N = 2a + 1; U = N(1-P)/(2a + 1) when N < 2a + 1.

Go Back N Protocol

Employs a sliding window of size N.

Distance Vector Routing

Neighbors are discovered via multicast requests.
Distance vectors are exchanged in response to requests or periodically.
Shortest paths are computed using the Bellman-Ford algorithm.
Addresses the count-to-infinity problem using techniques like Split Horizons and Poison Reverse.

Link State Routing

Involves discovering neighbors through multicast hello messages.
Constructs a Link State Advertisement (LSA) and floods it to all routers.
Builds a link state database to calculate the shortest path using Dijkstra's algorithm.

Border Gateway Protocol (BGP)

Operates between gateway hosts on the Internet to manage routing tables and select optimal routes.
Utilizes TCP for communication between routers.

Transport Protocols

UDP is connectionless, unreliable, and suitable for real-time applications like online gaming.
TCP is connection-oriented, reliable, and stream-focused, commonly used for file transfer (FTP) or video streaming.

UDP Datagram Structure

Header includes source port, destination port, message length, and checksum, totaling a min size of 8 bytes and a max size of 65535 bytes.

TCP Connection Management

Initiated via a three-way handshake involving SYN, SYN-ACK, and ACK segments.
Closing involves a four-step process using FIN segments.

TCP Flow Control

Utilizes a receive window size that adjusts data transmission to optimize bandwidth usage according to the receiver's capacity.

Flow Control Enhancements

Delayed ACK reduces acknowledgment packets by waiting before sending.
Controls silly window syndrome using Clark's solution and the Eagle algorithm to manage small segment transmissions.

TCP Error Control

Different scenarios trigger retransmissions to address out-of-order, duplicated, corrupted, and lost segments.

TCP Timeout Retransmission

Calculates retransmission time using algorithms like Jacobson's and Karn's, adjusting for initial and subsequent Round Trip Times (RTT).

TCP Error Control Enhancement

Implements fast retransmit upon receiving three duplicate ACKs instead of waiting for a timeout.

TCP Congestion Control

Manages the congestion window size with phases of slow start and avoidance; triggers fast recovery upon detecting packet loss.

TCP Throughput

Maximum throughput is achieved when the congestion window (CWND) is at its maximum, calculated as (cwnd * MSS) / RTT.

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Description

This quiz features essential formulas related to computer networks, focusing on network reliability parameters and availability probabilities. Test your understanding of mean time between failures and calculations for network availability based on different configurations. Ideal for students and professionals looking to reinforce their knowledge in networking.