EIFEL RETRANSMISSION TIMER IMPLEMENTATIONSeth A. Hellbusch

University of California – Santa Cruz

CMPE 257 – Wireless & Mobile Networks

Winter 2011

Eifel Retransmission Timer• Proposed by R. Ludwig & K. Sklower – 2000• Comparison between TCP-Lite & TCP-Eifel• Retransmission Timeout Value (RTO)

• Elapsed time since packet is sent• Upper limit of RTT• |-------RTO-------(packet)---REXMT--|

• TCP-Lite RTO weaknesses• Prediction flaw when RTT drops• Failure of estimator gains• REXMT-restart bug• Timer granularity

• TCP-Eifel RTO address these issues

Lite RTO vs. Eifel RTO

Initial Testing Model• Wrote two OO BASIC macros to auto-populate/calculate

• runTCPlite & runTCPeifel

Authors’ Model

My Model

Qualnet Implementation

• Source files• transport_tcp_input.cpp

• RTT sampling• SRRT, RTTVAR, & REXMT

• transport_tcp_timer.cpp• Heartbeat timer• REXMT updates

• transport_tcp_output.cpp• TCP transmit• Statistics capture

*note - all files located in:

~qualnet/4.0/libraries/developer/src/

• Test Network• Two Qualnet Branches

• Control• Experiment

• Traditional TCP/IP bottleneck• Wireless with multiple subnets

• Multiple TCP flows (FTP)• Increase channel utilization

• Monitored single flow• One flow across two routers• Captured output statistics• Monitored input computations

Simulation Scenario

Focused on Flow 1

Qualnet Analysis Results

50 100 150 200 2500

2

4

6

8

10

12

0

5000

10000

15000

20000

25000

30000

TCP-Lite

cwnd

rxtcur

srtt

rttvar

TX Packet

rxcu

r, s

rtt,

rtt

var

cwn

d

50 100 150 200 25005

1015202530354045

0

5000

10000

15000

20000

25000

30000

TCP-Eifel

cwnd

rxtcur

srtt

rttvar

TX Packet

rxcu

r, s

rtt,

rtt

var

cwn

d

Conclusion• Success

• Spreadsheet model• Matched authors work from scratch• Dynamic data generation and analysis• TCP-Lite RTO & TCP-Eifel RTO

• TCP-Light Flow Capture in Qualnet• Qualnet TCP-Eifel RTO Works

• Follows current data in flight• Transmitted data is the same per time

• Challenges• Valid Experiment Model• Counter Binary Math• TCP Congestion Window

Questions