TCP Probe A TCP with Builtin Path Capacity

TCP Probe: A TCP with Builtin Path Capacity Estimation Anders Persson, Cesar Marcondes, Ling-Jyh Chen, Li Lao, M. Y. Sanadidi, Mario Gerla Computer Science Department University of California, Los Angeles March 18, 2005

Motivation n Knowledge of “narrow link capacity” is important for: q q Optimizing network utilization via better congestion control & adaptive streaming Tracking dynamic changes in capacity due to Vertical Handoffs March 18, 2005 Global Internet 2005 2

Bandwidth Estimation Techniques n Active q Send out-of-band packets into the network n n Cap. Probe [SIGCOMM 04] and Pathrate [INFOCOM 01] Passive q Use ongoing data packets without additional overhead to the network n March 18, 2005 TCP Probe – similar to Cap. Probe technique but uses only “actual” data packets Global Internet 2005 3

Cap. Probe Recap n Packet pair technique q q n Compression & expansion due to cross traffic distorts Tb Filter out distorted samples by using samples with minimum end-to-end delay sum Fast and accurate estimation of bottleneck capacity March 18, 2005 Global Internet 2005 4

TCP Probe n Idea: Use Cap. Probe technique but passively within TCP q n Rely on dispersion of ACK pairs and filter distorted dispersion based on end-to-end delay sum Have to ensure that data packet pairs & corresponding ACK pairs produce accurate capacity estimates March 18, 2005 Global Internet 2005 5

Challenge n TCP implementations try to reduce network overhead by sending one ACK for two data packets, but: q We want an ACK for each data packet! March 18, 2005 Global Internet 2005 6

Solution n n Sender sends inverted data packets Receiver replies a duplicate ACK and an incremental ACK March 18, 2005 Global Internet 2005 7

Packet Size Issue n Probing packet size: q q n forward direction: TCP data 1500 bytes reverse direction: TCP ACK 40 bytes The newly developed Asym. Probe [Networking 05] has shown: q q If , TCP Probe estimates the capacity of the forward direction link If , TCP Probe estimates the capacity of the reverse direction link March 18, 2005 Global Internet 2005 8

Implementation n n Implemented in NS-2 and Linux 2. 4 Network Stack Approach: q q Periodically mark data packet pairs Sender timestamps the data packets and the corresponding ACKs ( sec granularity) March 18, 2005 Global Internet 2005 9

Simulation Scenario n NS-2 simulation n Compare TCP Probe capacity estimation with TCPW BE (bandwidth estimation) q TCPW BE is based on dispersion of ACK packets without filtering samples March 18, 2005 Global Internet 2005 10

TCP Probe vs. TCPW n 20 flows of the same kind q Capacity Estimation (Mbps) q TCP Probe: All flows estimate C=10 Mbps TCPW: Flows estimate BE between 0 to 7 Mbps TCP Probe March 18, 2005 TCPW BE Global Internet 2005 11

TCP Probe vs. TCPW n Capacity Estimation (Mbps) n 1 TCP Probe and 5 TCP New Reno flows 1 TCPW and 5 TCP New Reno flows TCP Probe March 18, 2005 TCPW BE Global Internet 2005 12

Internet Measurement n Three different paths: q q q Los Angeles: 3 Mbps (cable modem) China: 45 Mbps Alabama: 100 Mbps March 18, 2005 Global Internet 2005 13

Cable Modem (3 Mbps) March 18, 2005 Global Internet 2005 14

China (45 Mbps) March 18, 2005 Global Internet 2005 15

Alabama (100 Mbps) March 18, 2005 Global Internet 2005 16

Statistical Analysis n 30 measurements to each destination March 18, 2005 Global Internet 2005 17

Applications n TCP Probe in Vertical Handoff Scenario q n A vertical handoff involves two different network interfaces n Usually represent different technologies and thus result in a drastic change in link capacity n How to get advantage of the extra capacity when we are in congestion avoidance? Revised TCP Probe q Re-initiate the estimation every n samples (n=50) n Detect a huge increase in the capacity estimation q March 18, 2005 Trigger a new slow start phase (i. e. fast rate adaptation) Global Internet 2005 18

Simulation Scenario n n n TCP Probe: 1 → 6 Pareto flows: 7 → 10, 8 → 9, 11 → 14, 12 → 13 Capacity between node 1 and 2 increases from 10 Mbps to 100 Mbps at 80 second March 18, 2005 Global Internet 2005 19

Fast Rate Adaptation March 18, 2005 Global Internet 2005 20

Conclusions n TCP Probe passively provides to a TCP flow sender an accurate estimate of path capacity q q n Estimated capacity can be used as an upper bound on TCP sender rate Vertical Handoff applications can benefit from detecting capacity change Work in progress q q TCP Probe provides improved performance under high loss rate (5%) Astart [INFOCOM 04] can benefit from accurate capacity estimation March 18, 2005 Global Internet 2005 21