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

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

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

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

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

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

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