CATNIP – Context Aware Transport/Network

Internet ProtocolCarey Williamson Qian Wu

Department of Computer ScienceUniversity of Calgary

Why CATNIP

• Layered protocol stacks

Good: providing a unifying framework

Bad: compromise performance

vs.

Physical

Link

Network

Transport

Application

Why CATNIP (Cont’d)

• Observations in Web data transfer using TCP/IP Poor protocol interactions;

TCP’s window-based flow control mechanism produces data bursts;

Not all packet losses are created equal. Packet losses are costly for small document transfer;

A TCP source has limited control over packet loss effects;

An IP router has significant control over packet loss effects.

Design of CATNIP•Can we make the TCP/IP protocols “smarter”

about the specific job?

Convey application-layer context information to the TCP and IP layers

Network

Transport

Application

Document Size

Packet Priority

Design of CATNIP (Cont’d)•Adding context-awareness to TCP:

Rate-Based Pacing of the Last Window (RBPLW)

Early Congestion Avoidance (ECA)

Selective Packet Marking (SPM):Use the reserved high-order bit in the TCP header to convey packet priority information

Design of CATNIP (Cont’d)

•Adding context-awareness to IP:

CATNIP-Good

CATNIP-Bad

CATNIP-RED: RED + CATNIP-Good

Evaluation of CATNIP

Evaluation

Simulation: ns-2

Emulation: use WAN emulation to test a prototype implementation of CATNIP in the Linux kernel of an Apache Web server.

Evaluation using simulation

• Network model:

Client 100

Server 1

Server 2

Server 10

Client 1

Client 2

Client 99

1.5 Mbps, 5 ms

10 Mbps, 5 ms 10

Mbp

s, 5 m

s

10 M

bps,

5 m

s 10 Mbps, 5 m

s

RouterS RouterC

Evaluation using simulation (Cont’d)

• Web workload model: 10 Web pages Use empirically-observed distribution to

determine the size, and the number of embedded images

Evaluation using simulation (Cont’d)

• Factors and Levels:Factor Levels

TCP IP

Reno, RBPLW, ECA, ECA+RBPLW, SPM DropTail, RED, CATNIP-Good, CATNIP-Bad, CATNIP-RED

• Performance metrics:

the transfer time for each Web page

the average packet loss

Simulation results• DropTail routers:

Mean and standard deviation of transfer times

Reno/ RBPLW

Reno

ECA

ECA/RBPLW

Packet loss:

Observations:

TCP endpoint control algorithms have little advantage to offer.

Simulation results (Cont’d)• CATNIP-Good routers:

Mean and standard deviation of transfer times

Reno/SPM/Good

Reno/DropTail

Reno/SPM/RBPLW/Good

ECA/SPM/Good ECA/SPM/RBPLW/Good

Packet loss:

Observations:

Adding context-awareness at the IP routers improves the mean Web page transfer times and the standard deviation of the transfer times.

The average packet loss rates with CATNIP-Good are higher than for the DropTail routers.

Simulation results (Cont’d)• CATNIP-Bad routers:

Mean and standard deviation of transfer times

Reno/DropTail

Reno/SPM/BadECA/SPM/Bad

Packet loss:

Observations:

Packet losses are shifted to the high priority TCP packets, that is, throw away the “wrong packet” at the “wrong time”, therefor makes matters worse.

Simulation results (Cont’d)• CATNIP-RED routers:

Mean and standard deviation of transfer times

Reno/DropTail

Reno/REDReno/SPM/CATNIP-RED ECA/RED ECA/SPM/CATNIP-

RED

Observations:

Reno and ECA perform similarly in almost all cases.

The effect of CATNIP-RED is greater than the effect of ECA.

Experimental Implementation and Evaluation

• Experimental environment: WAN emulator: IP-TNE (Internet Protocol Traffic and

Network Emulator)

Web server:Apache Web server (version 1.3.19-5) runs on top of modified Linux 2.4.16 kernel.

Implementation focused on the SPM feature only

Client 100

• Primary Factor:

buffer size of the bottleneck link (64 KB -- 512 KB)

10 M

bps,

5 ms

Endpoint

Client 1

Client 2

Client 99

1.5 Mbps, 5 ms10 M

bps, 5 ms

10 Mbps, 5 ms

• Network model

Server

WAN Emulation

RouterS RouterC

• Evaluation results:

Conclusions

•Not all packet losses are created equal;

•A TCP source alone has limited control over Web data transfer performance, even with application-layer information;

•The IP layer has a significant influence on Web data transfer performance, particularly when application-layer context information is available;

•A simple change to the TCP/IP stack implementation can provide the context information;

•Changes to the queue management at routers can provide significant performance advantages for the context-aware TCP/IP.