Access Link Capacity Monitoring with TFRC Probe Ling-Jyh Chen, Tony Sun, Dan Xu, M. Y. Sanadidi, Mario Gerla Computer Science Department, University of California at Los Angeles

Oct. 3, 2004E2EMON Motivation Knowledge of link capacity is important for network management, pricing, and QoS support. The link capacity of a network connection may vary dramatically due to vertical handoff, dynamic channel allocation, and wireless channel quality. Knowing the link capacity will permit the source to rapidly and appropriately adapt the outbound data transmissions rate.

Oct. 3, 2004E2EMON Access Link Capacity Monitoring Requirements provide correct information work passively without adding excess overhead promptly react to occurrences in network events maintain end-to-end semantics Our approach: TFRC Probe embed CapProbe algorithm within TFRC simple, accurate, passive, timely, and end-to-end extensible to other protocols and applications

Oct. 3, 2004E2EMON Potential Applications Adaptive multimedia streaming Congestion control Overlay network structuring Wireless link monitoring Mobility detection

Oct. 3, 2004E2EMON Estimate minimum link capacity on an Internet path, as seen at the IP level Design Goals End-to-end: assume no help from routers Inexpensive: Minimal additional traffic and processing Fast: converges to capacity fast enough for the application 100 Mbps 50 Mbps 10 Mbps (Link Capacity) The Capacity Estimation Problem

Oct. 3, 2004E2EMON T3T3 T2T2 T3T3 T3T3 T1T1 T3T3 Narrowest Link 20Mbps10Mbps5Mbps10Mbps20Mbps8Mbps Packet Pair Dispersion

Oct. 3, 2004E2EMON Ideal Packet Dispersion No cross-traffic Capacity = (Packet Size) / (Dispersion)

Oct. 3, 2004E2EMON Compression and Expansion First packet queueing → compressed dispersion → Over- estimation Second packet queueing → expanded dispersion → Under- estimation

Oct. 3, 2004E2EMON CapProbe Filter PP samples that do not have minimum queuing time Dispersion of PP sample with minimum delay sum reflects capacity CapProbe combines both dispersion and e2e transit delay information CapProbe is simple, fast, and accurate

Oct. 3, 2004E2EMON TFRC: TCP-Friendly Rate Control TFRC is an equation based unicast multimedia streaming protocol. TFRC mimics the TCP long-term throughput by utilizing the function: The receiver is responsible for calculating the loss event rate p and sending the information back to the sender once per round-trip time. The sender is responsible for adjusting its sending rate T actual to be close to T.

Oct. 3, 2004E2EMON TFRC Probe Embedding CapProbe within TFRC Three design issues: 1. Accurate capacity estimation 2. Fast estimation process 3. Minimal traffic overhead and modification to the original TFRC Two design options: 1. One-way estimation 2. Round-trip estimation

Oct. 3, 2004E2EMON TFRC Probe Accurate Capacity Estimation Embed CapProbe algorithm within TFRC by sending two packets back-to-back every n packets

Oct. 3, 2004E2EMON TFRC Probe Fast Link Capacity Estimation Fast in estimating link capacities from samples CapProbe has been shown to be a fast and accurate technique for link capacity estimation. Fast in getting samples The speed of sampling will increase/decrease when the packet sizes decrease/increase.

Oct. 3, 2004E2EMON TFRC Probe R send is the sending rate of data packets S is the number of samples needed to get a reliable capacity estimation P is the data packet size t is the expected time to get one capacity estimation. n is the number of data packets between samples Packet size adaptation

Oct. 3, 2004E2EMON Simulation The monitoring ability of TFRC Probe is verified using NS-2 simulator The bottleneck link (between node 3 and 4) is shared by all the data flows and configured as an asymmetric link with various capacities in the forward direction and fixed capacity (100Kbps) in the backward direction.

Oct. 3, 2004E2EMON Simulation Cross Traffic Description Type I 4 FTP flows (from node 7 to 10, 8 to 9, 11 to 14, and 12 to 13); 1500 bytes/packet Type II 4 CBR flows (from node 7 to 10, 8 to 9, 11 to 14, and 12 to 13); 500 bytes/packet; 80% load on the bottleneck Type III 16 Pareto flows with alpha = 1.9 (4 flows from node 7 to 10, 4 flows from 8 to 9, 4 flows from 11 to 14, and 4 flows from 12 to 13); 1000 bytes/packet; 80% load on the bottleneck Three type of cross traffic are employed in the simulaiton. The link capacity estimation results are collected after 20 and 50 samples.

Oct. 3, 2004E2EMON Simulation Results TFRC Probe CapProbe TFRC Probe CapProbe TFRC Probe CapProbe TFRC Probe CapProbe no cross traffic 20 samples100 K 500 K100 K1 M100 K5 M100 K 50 samples100 K 500 K100 K1 M100 K5 M100 K cross traffic type I 20 samples100 K 500 K100 K1 M100 K5 M100 K 50 samples100 K 500 K100 K1 M100 K5 M100 K cross traffic type II 20 samples100 K 500 K100 K1 M100 K5 M100 K 50 samples100 K 500 K100 K1 M100 K5 M100 K cross traffic type III 20 samples100 K 500 K100 K1 M100 K5 M100 K 50 samples100 K 500 K100 K1 M100 K5 M100 K bottleneck capacity of the forward direction link 100 Kbps500 Kbps1 Mbps5 Mbps bottleneck capacity of the backward direction link 100 Kbps

Oct. 3, 2004E2EMON Experiments Implementation: based on the original TFRC codes (Linux platform) Experiments: Without packet size adaptation Evaluate the effectiveness of TFRC Probe in wired Internet links (symmetric and asymmetric links) and wireless links (1xRTT and b) With packet size adaptation Evaluate the feasibility of monitoring wireless link capacity using TFRC Probe.

Oct. 3, 2004E2EMON Experiment Results 1 Run 1Run 2Run 3Run 4Run 5 CapacityTimeCapacityTimeCapacityTimeCapacityTimeCapacityTime Ethernet 100Mbps 20 samples samples samples DSL DownLink 2Mbps 20 samples samples samples DSL UpLink 128Kbps 20 samples samples samples Wired Internet links (no pkt size adaptation)

Oct. 3, 2004E2EMON Experiment Results 2 Run 1Run 2Run 3Run 4Run 5 CapacityTimeCapacityTimeCapacityTimeCapacityTimeCapacityTime 1xRTT 150Kbps 20 samples samples samples b 1Mbps 20 samples samples samples b 2Mbps 20 samples samples samples b 5.5Mbps 20 samples samples samples b 11Mbps 20 samples samples samples Wireless links (no pkt size adaptation)

Oct. 3, 2004E2EMON Experiment Results b link with varying data rate (with pkt size adaptation)

Oct. 3, 2004E2EMON Conclusion TFRC Probe is simple, accurate, passive, timely, and end-to-end. The evaluation of TFRC Probe is performed by both simulation and testbed experiments. The same concept can be applied to other UDP based application protocols (e.g. RAP, RTP, UDP based FTP and P2P file downloading) and other emerging data transmission protocols (e.g. DCCP). CapProbe website:

Oct. 3, 2004E2EMON Thanks!