Post on 19-Dec-2015
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