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Understanding Available Bandwidth Measurement: Challenges and Tools for Accurate Assessment

Available Bandwidth (AB) defines the rate at which packets can traverse a network, influenced by static bottlenecks and dynamic congestion. Accurate measurement of AB is complicated by factors like system interrupts and traffic congestion, which can lead to distorted results. Common tools for measuring AB include Pathchar, Pathload, and Netest, which offer insights into physical bandwidth and throughput. As network speeds surpass CPU and memory capabilities, there's an increasing risk of hosts becoming the bottleneck. Understanding these challenges is crucial for effective network management.

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Understanding Available Bandwidth Measurement: Challenges and Tools for Accurate Assessment

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  1. Available Bandwidth Measurement and the Obstacles to Overcome Accurate Measurement

  2. Definitions • Available Bandwidth (AB): The rate a which packets can be sent through the network. AB is limited by two factors: • Bottleneck: The minimum rate we can send packets (static) • Congestion: The amount of competing traffic (dynamic) • Throughput: Amount of data actually received

  3. Common Tools for Measuring AB • Pathchar: Estimates physical bandwidth of hop-to-hop links • Pathload: Estimates AB • Netest: Measures end-to-end achievable throughput and AB, also analyzes cross traffic • bprobe/cprobe/tccp: Measure achievable throughput • Ping: First & simplest, measures round trip time

  4. AB Measurement Difficulties • Packet dispersions techniques can be intrusive to a system • Traffic congestion in the network can cause packets to be lost and false measurements • Network bandwidth has become faster than system I/O

  5. More Complex Limitations • System Interrupts • System interrupt flooding • Interrupt coalescence • System Time Resolution • Packets come in faster that the system can time stamp them • System Calls • Overhead time required to do them

  6. Measurement Algorithms & Limitations • Variable Packet Size (VPS) • Use size and hop differential methods to estimate physical bandwidth • Accuracy limited by cross traffic • Packet Pair Dispersion (PPD) • Separation between packets remains after bottleneck • Accuracy limited by cross traffic, no interrupt coalescing • Packet Train • Can determine amount of cross traffic • Measures hop-by-hop link capacity beyond bottleneck (each routers bandwidth)

  7. Future Issue • Network speeds are growing faster than CPU clock speeds and memory speeds • Host will become the bottleneck

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