Bandwidth Metrics and Measurement Tools Xin, Lu High-Performance Computing Group Computer Science University of Windsor

Bandwidth Metrics NMWG divide bandwidth into four sub-metrics: Bandwidth Capacity Achievable Bandwidth Available Bandwidth Bandwidth Utilization FOR MORE INFO... http://www-didc.lbl.gov/NMWG http://www-didc.lbl.gov/NMWG/docs/measurements.pdf

Other Metric Terms Throughput Bulk Transfer Capacity (BTC) Throughput is the same as achievable bandwidth. Bulk Transfer Capacity (BTC) Defined by RFC 3148 BTC = data_sent / elapsed_time The throughput of a persistent TCP transfer. Each of these metrics can be used to describe the entire path (end-to-end) as well as path’s link (hop-by-hop)characteristics.

Bandwidth Capacity vs. Achievable Bandwidth Capacity is the maximum amount of data per time unit that the link or path has available, when there is no competing traffic. Achievable bandwidth is the maximum amount of data per time unit that a link or path can provide to an application, given the current utilization, the protocol and operating system used, and the end-host performance capability and load. (Throughput ) Reference: [2]

Bandwidth Capacity vs. Achievable Bandwidth Cont. If a path consists of several links, the link with the minimum transmission rate determines the capacity of the path. While the link with the minimum unused capacity limits the achievable bandwidth. i.e. at high-speed networks, hardware configuration or software load on the end hosts actually limit the bandwidth delivered to the application.

Available Bandwidth vs. Bandwidth Utilization Available bandwidth is the maximum amount of data per time unit that a link or path can provide, given the current utilization. Utilization is the aggregate capacity currently being consumed on a link or path. Available Bandwidth = Bandwidth Capacity – Bandwidth Utilization Reference: [2]

BTC vs. Available Bandwidth Available Bandwidth is the amount of usable bandwidth without affecting cross-traffic, whereas, the BTC is measured by sending as much packets as possible, limiting other traffic. BTC is simulating “steady state”– persistent flow, taking considerable time and overhead. FOR MORE INFO... RFC 3148 : A Frame Work for Defining Empirical Bulk Transfer Capacity Metrics

BTC vs. Available Bandwidth Cont. The BTC definition assumes an “ideal TCP implementation”, actually, this doesn’t exist, and what BTC measured is the variant of achievable bandwidth. FOR MORE INFO... RFC 3148 : A Frame Work for Defining Empirical Bulk Transfer Capacity Metrics

Passive vs. Active measurement Active measurement means that the tool actively sends probing packets into the network. Passive measurement tools monitors the passing traffic without interfering. Passive measurement is appreciated, however, less reliable than active, as it can’t extract any data pass through it.

Receiver-based vs. Sender-based techniques Receiver-based (end-to-end) techniques usually use the one-direction TCP stream to probe the path bandwidth. Sender-based (echo-based) techniques force the receiver to reply the ICMP query, UDP echo or TCP-FIN.

Sender-based technique Advantage: Flexible deployment. Clock needn’t synchronized at two ends. Disadvantage: ICMP and UDP echo packets usually be rate-limited or filtered out by some routers. Round-trip is much more possibility influenced by cross-traffic than that of one-way delay Response packets may come back through a different path

Receiver-based technique Advantage: More accurate than sender-based technique. Disadvantage: Difficult to deployment. The clock have to be synchronized at two ends.

Bandwidth Measurement Technology Packet Dispersion technology packet pair and packet train Self-Loading Periodic streams (SLOPS) Variable Packet Size (VPS) technology VPS even/odd Tailgating technique

Packet Dispersion Technique Sender sends two same-size packets back-to-back from source to sink. The packets will reach the sink dispersed by the transmission delay of the bottleneck links if there is no cross traffic. Measuring the dispersion can infer the bottleneck link bandwidth capacity. Note: Bottleneck link can refer to the link with smallest transmission rate, it’s also can refer to the link with minimum available bandwidth. We refer the bottleneck link to the first case.

Packet Dispersion Technique Cont. Bottleneck bandwidth = packet size/ t

Packet Dispersion Technique Cont. If sender sends the packets as one observation sample more than two, called packet train. Tools usually apply robust statistical filtering techniques to find valid samples.

Packet pair vs. packet train Packet train is more likely to be interfered by cross traffic than packet pair. Packet train can be used to measure the bottleneck link that is multichannel while packet pair can’t deal with. Packet train can reduce the limitation of clock resolution. Sophisticated tools apply both methods in their implementation. i.e. Pathrate

Packet Dispersion Technique Cont. Tool Name Active/ Passive Method-ology Protocol Metrics Path/Per-link bprobe Active Packet pair ICMP Bandwidth Capacity Path cprobe Bandwidth utilization Netest UDP Bandwidth capacity FOR MORE INFO... Bprobe and cprobe http://cs-people.bu.edu/carter/tools/Tools.html Nettest http://www-didc.lbl.gov/pipechar

Packet Dispersion Technique Cont. Pathrate Active Packet pair, packet train UDP Bandwidth capacity Path Pipechar Packet train Available bandwidth Per-link Sprobe Packet pair TCP FOR MORE INFO... Pathrate http://www.cc.gatech.edu/fac/Constantinos.Dovrolis Pipechar http://www-didc.lbl.gov/pipechar SProbe http://sprobe.cs.washington.edu

Self-Loading Periodic Streams(SLOPS) Sender sends series of packets to the sink at the rate of larger than the bottleneck link available bandwidth. Every packets get a timestamp at sender side. Compare the difference of successive packets timestamp and their arrival times to infer the available bandwidth. Rate-adjustment adaptive algorithm to converge to the available bandwidth.

Self-Loading Periodic Streams Cont. Tool Name Active/ Passive Method-ology Protocol Metrics Path/Per-link pathload Active SLOPS UDP Available bandwidth Path FOR MORE INFO... Pathload http://www.cc.gatech.edu/fac/Constantinos.Dovrolis

Variable Packet Size (VPS) Technique Step1. Sender set TTL=1, send out the packet, and wait for the ICMP TTL-exceeded packet back. Step2. Upon receiving ICMP, estimate the RTT. Estimate the RTT multiple times for various size packets.The minimum RTT of various packets are believed to be the valid sample. Step3. The first link capacity is C=1/b , b is slope of RTT graph. Set the TTL=2,3…n, repeat the process of step1 to 3, to Calculate the C=1/ bi – bi-1

VPS technique cont.

Even-odd VPS The VPS probing technique is not altered, Mathematical ‘trick’ to improve reliability. For each of the probing sizes, divide the set of samples into even and odd numbers. Calculation is based on even-odd samples. i.e. the even sample of link i, the odd sample of link i+1.

Tailgating Technique Tailgating technique divides into two phrase: Phase one: Like VPS probing, but for entire path instead of per link. Phase two: (tailgating phase) The largest possible non-fragmented packet followed by a tailgater which is the smallest possible packet size (i.e 40 bytes). This causes the smaller packet always queue behind the larger packet. Reference: Kevin Lai, Mary Baker “Measuring Link Bandwidths Using a Deterministic Model of Packet Delay” ACM SIGCOMM 2000

Tailgating Technique cont. The following condition should met: The large packet should not be queued due to cross traffic. The large packet should have a TTL field set to L (1…n). The tailgater packet should be queued directly after the large packet on link L. The tailgater packet should not queued after having passing link L.

VPS Technology Tool Name Active/ Passive Method-ology Protocol Metrics Path/Per-link bing Active VPS ICMP Bandwidth capacity, loss, delay Path clink VPS/ even-odd UDP Bandwidth capacity, Loss Pchar UDP, ICMP Bandwidth capacity, Loss, delay Per-link Bing http://www.cnam.fn/reseau/bing.html Clink http://rocky.wellesley.edu/downey/clink/ Pchar http://www.emplyees.org/~bmah/software/pchar

VPS Technology Cont. Tool Name Active/ Passive Method-ology Protocol Metrics Path/Per-link Nettimer Active, Passive VPS/tailgating TCP Bandwidth capacity Per-link pathchar Active VPS/even-odd UDP, ICMP Bandwidth capacity, Loss, delay FOR MORE INFO... Nettimer http://mosquitonet.stanford.edu/~laik/project/nettimer Pathchar ftp://ftp.ee.lbl.gov/pathchar/

TCP Simulation and Path Flooding TCP simulation operates at two mode : UDP/ICMP with low TTL or ICMP echo/reply. It simulates the TCP of using slow-start algorithm. Path flooding method injects TCP/UDP packets into the net as fast as possible within the specific time. To some degree, both TCP simulation and path flooding are associated with Bulk Transfer Capacity (BTC)metrics.

TCP Simulation and Path Flooding Cont. Tool Name Active/ Passive Method-ology Protocol Metrics Path/Per-link TReno Active TCP simulation UDP, ICMP BTC Path ttcp Path flooding TCP, UDP Achievable bandwidth iperf TCP, UDP Bandwidth capacity, Loss Netperf BTC, delay throughput

TCP Simulation and Path Flooding Cont. TReno http://www.psc.edu/networking/treno_info.html Iperf http://dast.nlanr.net/Project/Iperf Netperf http://www.netperf.org/netperf/NetperfPage.html ttcp part of OS ftp://ftp.arl.mil/pub/ttcp/

Bandwidth Measurement Tools Con. Reference : 1.http://www.caida.org/tools/ 2. Bruce Lowekamp, Brain Tierney, Les Cottrell, Richard Hughes-Jones, Thilo Kielmann and Martin Swany. A Hierarchy of Network Measurements for Grid Applications and Services Document (draft) Global Grid Forum NMWG Feb 17, 2003. 3. Rody Schoonderwoerd Network Performance Measurement Tools a comprehensive comparison Nov., 2002