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2. CSE 5231 - Dr. Aydeger - Network Performance Metrics

Course Information

  • Course Name: CSE 5231 Computer Networks

  • Instructor: Dr. Abdullah Aydeger

  • Location: L3Harris Center for Science and Engineering #326

  • Email: aaydeger@fit.edu

  • Department: Electrical Engineering and Computer Science

Network Performance Metrics

  • Overview of key performance metrics used to evaluate network performance.

  • Common metrics include:

    • Bandwidth

    • Throughput

    • Delay

    • Packet Loss

Network Protocols Overview

Layered Architecture

  • Application Layer: End-user applications (e.g., web browsers).

  • Transport Layer: Manages data transfer from end-to-end (TCP/UDP protocols).

  • Internet Layer: Responsible for routing data from the source to the destination (IP protocol).

  • Link (Physical) Layer: Physical media carrying the data (e.g., cables, wireless).

Data Communication Via Networks

  • Application Data: User-generated data inputs.

  • Transport Layer: Adds headers (TCP or UDP).

  • Internet Layer: Adds IP headers or ICMP.

  • Link Layer: Adds error correction and other necessary information.

TCP/IP Protocol Stack

  • The four layers of the TCP/IP reference model enhance:

    • Modularity

    • Flexibility

    • Reliability

Data Handling in Layers

  • Application Layer: Entire files (images, documents) considered as messages.

  • Transport Layer: Divides messages into segments matching packet size limits.

  • Network Layer: Refers to packets, which include data and headers.

  • Data-link Layer: Refers to frames that include packets and additional headers.

Key Network Performance Metrics

Bandwidth

  • Definition: Maximum bits-per-second a communication link can support.

  • Example: 1 Mbps = 1 x 10^6 bits/second.

  • Relationship to Transmission Time: Smaller bandwidth allows for more data in a given timeframe.

Throughput

  • Definition: Actual data transfer performance (measured in bits/sec or packets/sec).

  • Factors: Influenced by input rate and protocol overhead.

Bandwidth vs. Throughput

  • Bandwidth: Represents the capacity of the communication link, ignoring delays.

  • Throughput: Actual performance output, typically lower than bandwidth in real scenarios.

  • Utilization: Ratio of throughput to bandwidth.

Packet Delay and Loss

Delay Sources

  • Queueing Delay: Time packets spend waiting in router buffers.

  • Packet Loss: Occurs when buffers fill up, leading to dropped packets.

Components of Delay

  • Processing Delay (dproc): Time taken by routers to check packet errors and determine output link.

  • Queueing Delay (dqueue): Time spent waiting for transmission.

  • Transmission Delay (dtrans): Calculated as dtrans = L/R (where L = packet length and R = link transmission rate).

  • Propagation Delay (dprop): Calculated as dprop = d/s (where d = link length and s = propagation speed).

Calculating Packet Delay

  • Analogy: Cars waiting at a toll booth symbolize performance at a network link.

  • Total Delay: Latency = Propagation Delay + Transmission Delay + Queueing Delay.

Jitter

  • Description: Variability in packet latency; critical for applications like audio/video conferencing.

  • Application Sensitivity: Different applications may prioritize bandwidth or latency differently.

Real Internet Measurement Tools

Traceroute

  • Measures Internet delay and loss by sending packets to routers and receiving responses to determine the time taken for each hop.

Example: Ping Command

  • Demonstrates the round-trip time for packets sent to a specific destination.

Packet Loss

  • Causes: Arises when incoming packets exceed the buffer capacity at a network link.

Throughput Details

  • Instantaneous vs. Average Throughput: Instantaneous rate is the current transmission rate, while average is measured over time.

  • Bottleneck Link: The link in the path that limits overall throughput.

Network Scenarios

  • Understanding how throughput is constrained by various components of the network and how it is calculated (e.g., min(Rc, Rs, R/10)).

Discussion Topics

  • Critical delays affecting daily web traffic.

  • Strategies for sending optimal data amounts without causing congestion.

  • Calculating delays and throughput in practical scenarios (like the example of Hosts A and B).

Conclusion and Q&A

  • Instructor Contact: Dr. Abdullah Aydeger available for questions.