NS-2 TCP-NS-2 TCP-LinuxLinux

David Wei and David Wei and Pei CaoPei Cao

OutlineOutline

MotivationMotivation Code structure of NS-2 TCP-Linux Code structure of NS-2 TCP-Linux

agentagent Design of Design of Scoreboard1Scoreboard1, a new , a new

module for SACK processingmodule for SACK processing Validation ResultsValidation Results

Why one more TCP agent in Why one more TCP agent in NS-2?NS-2?

TCP Implementations in TCP Implementations in NS-2NS-2

Low simulation accuracyLow simulation accuracy Low simulation performanceLow simulation performance

up to 20 hours to run a simulation of up to 20 hours to run a simulation of 200-second traffic on gigabit links200-second traffic on gigabit links

Poor extensibilityPoor extensibility Much fewer number of congestion Much fewer number of congestion

control algorithms than Linux 2.6control algorithms than Linux 2.6

TCP Implementations in TCP Implementations in Linux 2.6Linux 2.6

Standard interface for congestion control Standard interface for congestion control algorithms: algorithms: void start(struct tcp_sock *tp):void start(struct tcp_sock *tp): init the algorithm init the algorithm u32 ssthresh(struct tcp_sock *tp):u32 ssthresh(struct tcp_sock *tp): called after packet called after packet

lossloss u32 min_cwnd(struct tcp_sock *tp):u32 min_cwnd(struct tcp_sock *tp): called after loss called after loss void cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt, void cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt,

u32 in_flight, int good):u32 in_flight, int good): called after ack received called after ack received void rtt_sample(struct tcp_sock *tp, u32 rtt):void rtt_sample(struct tcp_sock *tp, u32 rtt): called called

after rtt calculationafter rtt calculation set_state(…)set_state(…), , cwnd_event(…)cwnd_event(…), , undo_cwnd(…)undo_cwnd(…), ,

get_info(…)get_info(…) Better SACK processing than NS-2 Better SACK processing than NS-2

implementationimplementation

Narrow the gap between Narrow the gap between NS-2 and Linux 2.6 NS-2 and Linux 2.6 NS-2 NS-2

TCP-LinuxTCP-LinuxDesign goals of Design goals of NS-2 TCP-LinuxNS-2 TCP-Linux:: Accuracy: Accuracy:

Use congestion control algorithm code Use congestion control algorithm code **as-is*as-is* from Linux 2.6 source trees from Linux 2.6 source trees

Improve SACK processingImprove SACK processing Extensibility: Extensibility:

Import the concept of interfaces for loss Import the concept of interfaces for loss detection algorithms detection algorithms

Speed: Speed: Improve event queue schedulerImprove event queue scheduler

Code structureCode structure

An example of congestion An example of congestion control algorithm in control algorithm in NS-2 NS-2

TCP-LinuxTCP-Linux

Status of Status of NS-2 TCP-LinuxNS-2 TCP-Linux

Imported all 9 congestion control algorithms Imported all 9 congestion control algorithms from Linux 2.6.16-3from Linux 2.6.16-3 Reno (FACK), Vegas, HS-TCP, Scalable-TCP, BIC, Reno (FACK), Vegas, HS-TCP, Scalable-TCP, BIC,

Cubic, Westwood, H-TCP, HyblaCubic, Westwood, H-TCP, Hybla Imported 3 experimental congestion control Imported 3 experimental congestion control

algorithms in testing for future Linux versionsalgorithms in testing for future Linux versions Veno, TCP-LP, TCP Compound (MS Windows Vista)Veno, TCP-LP, TCP Compound (MS Windows Vista)

3 bugs were found with Linux 2.6 HighSpeed 3 bugs were found with Linux 2.6 HighSpeed TCP, 1 performance problem is found with TCP, 1 performance problem is found with Linux 2.6 VegasLinux 2.6 Vegas

Using Using LinuxTCPAgentLinuxTCPAgent in in NS-2 SimulationsNS-2 Simulations

Easy usage for all users to migrate TCL Easy usage for all users to migrate TCL scripts:scripts:

……#set tcp [new Agent/TCP/Sack1]#set tcp [new Agent/TCP/Sack1]set tcp [new Agent/TCP/Linux]set tcp [new Agent/TCP/Linux]……#everything else is the same#everything else is the same……ns at 0 “tcp select_ca reno”ns at 0 “tcp select_ca reno”……#everything else is the same#everything else is the same……

Better SACK ProcessingBetter SACK Processing

Scoreboard1: Scoreboard1: Combines Combines NS-2 Sack1 NS-2 Sack1 design and design and

Linux Linux scoreboardscoreboard design design Enable correct implementation of Enable correct implementation of

FACKFACK Simulation speed similar to Simulation speed similar to NS-2 NS-2

Sack1Sack1

SACK Processing in NS-2 SACK Processing in NS-2 Sack1Sack1

Reassembly queueReassembly queue Pro: scans the SACK list very fastPro: scans the SACK list very fast Con: difficult to implement FACK correct, Con: difficult to implement FACK correct,

can’t identify retransmitted packets, etc.can’t identify retransmitted packets, etc.

SACK processing in SACK processing in Linux 2.6Linux 2.6

Per-packet state machinePer-packet state machine Con: slower processing of SACK listsCon: slower processing of SACK lists

ScoreBoard1ScoreBoard1 Combine the Linux design (state Combine the Linux design (state

diagram for each packet) and Sack1 diagram for each packet) and Sack1 design (Reassembly Queue)design (Reassembly Queue)

Validation ResultsValidation Results

Accuracy: Comparable to Linux Accuracy: Comparable to Linux results in the level of congestion results in the level of congestion window trajectorieswindow trajectories

Simulation speed:Simulation speed: Best case: 50 times faster than NS-2 Best case: 50 times faster than NS-2

SACK1 SACK1 Worst case: as fast as NS-2 SACK1 Worst case: as fast as NS-2 SACK1

Memory consumption: very similar Memory consumption: very similar memory usage as NS-2 SACK1memory usage as NS-2 SACK1

Evaluation SetupEvaluation Setup Comparing NS-2 TCP-Linux Results with Comparing NS-2 TCP-Linux Results with

Dummynet Results.Dummynet Results.

Accuracy: Accuracy: window window

trajectorytrajectory

ExtensibilityExtensibility

Accuracy: throughput in Accuracy: throughput in lossy linklossy link

Why use Why use NS-2 TCP-LinuxNS-2 TCP-Linux

NS-2 Analysis community: NS-2 Analysis community: Able to analyze new algorithms without Able to analyze new algorithms without

waiting for the availability of the NS-2 waiting for the availability of the NS-2 versionsversions

Higher accuracy and faster simulationHigher accuracy and faster simulation

Linux Implementation community:Linux Implementation community: Able to run repeatable simulation to test Able to run repeatable simulation to test

new algorithmsnew algorithms A larger user pool to find bugsA larger user pool to find bugs

TCP-LinuxTCP-Linux: a better TCP for : a better TCP for NS-2NS-2

Future works:Future works: D-SACK processing and window D-SACK processing and window

reduction undoreduction undo Support for non-SACK receiversSupport for non-SACK receivers A tutorial for the public: “Tuning A tutorial for the public: “Tuning

TCP in NS-2”TCP in NS-2” A TCP benchmark suite in NS-2A TCP benchmark suite in NS-2

Thank youThank you

Questions ?Questions ?

Example 1: variable overflowExample 1: variable overflowin Linux HS-TCPin Linux HS-TCP

cwnd

rate

Example 2: AI bugs in Linux Example 2: AI bugs in Linux HS-TCPHS-TCP

RTT: 64ms

Flow #: 32

(4 flows are presented)

Capacity: 100Mbps

Buffer size: 220pkt

Acker: Sack1/DelAck

Performance: SpeedPerformance: Speed

Performance: MemoryPerformance: Memory