TCP TRAFFIC CHARACTERISTICS—

DEEP BUFFER SWITCHSTEVE PERRY, DIRECTOR OF NETWORKS UNM

PIYASAT NILKAEW, DIRECTOR OF NETWORKS NMSU

OVERVIEW•NETWORK IP PROTOCOLS•TCP•SWITCH OVERVIEW•DEEP BUFFER SWITCHES•PRECAUTIONS

IP PROTOCOLS•8 BIT FIELD IN PACKET HEADER

•IDENTIFIES SPECIFIC PROTOCOL TO BE USED

•TCP IDENTIFIED BY PROTOCOL 6

TCP•TCP IS CONNECTION ORIENTED•CONSIDERED RELIABLE

•REQUIRES ACKNOWLEDGEMENTS (ACK)•OVERHEAD COSTS•SEQUENCING AND WINDOWING

TCP THROUGHPUT TRANSMISSION

•TCP RELIES ON WINDOWING• RECEIVER WINDOW (RWND)• CONGESTION WINDOW (CWND)

•TCP SLOW START• INCREASE TRANSMISSION RATE ON

RECEIPT OF ACK, UNTIL EVENTUALLY CONGESTION OR LOSS OCCURS, THEN DECREASE TRANSMISSION RATE

Host A

one segment

RTT

Host B

two segments

four segments

ACK

ACKACK

ACKACKACKACK

TCP THROUGHPUT TRANSMISSION

•TCP CONGESTION AVOIDANCE•CONGESTION & PACKET LOSS CAUSE SENDER

TO SLOW DOWN•WINDOWING RAMPS UP AGAIN•CONDITION KNOWN AS GLOBAL

SYNCHRONIZATIONTCP Slow StartACKs being received, so increase rate

X

X

XX

Xloss, so decrease rate

send

ing

rate

time

TCP’s“sawtooth”behavior

TCP EFFECT ON THROUGHPUT

•THE GOAL IS TO ACHIEVE MAXIMUM CAPACITY OUT OF THE INSTALLED BANDWIDTH WITH TCP?

•ALLEVIATE 2 FACTORS•LATENCY•PACKET LOSS

TCP EFFECT ON THROUGHPUT• LATENCY

• TIME FOR A TCP SEGMENT (PACKET) TO TRAVEL TO ITS DESTINATION

• ROUND TRIP TIME (RTT)• SLOW DOWN THE ACKS, HENCE TCP CAN’T

TRANSMIT PROMPTLY• RESTRICTED BY THE LAW OF PHYSICS

• SPEED OF LIGHT

• PACKET LOSS• ERROR ALONG THE PATH• NETWORK CONGESTION

TCP EFFECT ON THROUGHPUT

•CAN BE ALLEVIATED BY •UPGRADE THE BANDWIDTH•REDUCING THE NETWORK HOPS•GUARANTEE A CLEAN & HIGH SPEED PATH

•DEPLOY NETWORK EQUIPMENT WITH DEEP BUFFER

TCP THROUGHPUTTCP Throughput with Increasing network distance and packet loss

R&E TRAFFIC CHARACTERISTICS

1. TYPE OF R&E TRAFFIC – TCP –BASED, MICROBURST TRAFFIC THAT CAN QUICKLY CONSUME ENTIRE AVAILABLE BANDWIDTH

A. SUBJECT TO TCP GLOBAL SYNCHRONIZATION

2. TCP TRAFFIC NEEDS DEEP BUFFER ON PORTS WHEN CONGESTION OCCURS.

3. NO COMMERCIALLY AVAILABLE SECURITY DEVICES CAN SIT IN-PATH WITH LINE-RATE PROCESS SPEED

4. 100 GBPS BACKBONE ACROSS CONTINENTAL US5. THE GENERAL RULE OF THUMB IS THAT YOU NEED 50MS OF

LINE-RATE OUTPUT QUEUE BUFFER FOR A 10G PORT, SO THERE SHOULD BE AROUND 60MB OF BUFFER.

SWITCHES•SCIENCE_DMZ BASED ON 10GBPS ETHERNET•INTERFACE SPEED/FORWARDING FALLACY•AGGREGATE SPEEDS IF MORE THAN ONE LEVEL•TYPICALLY THROUGH LINK AGGREGATION

SWITCHING METHODS

•CUT THROUGH SWITCHING (ERRORS)

•FRAGMENT FREE (ERRORS)•STORE AND FORWARD

•USED WITH BUFFERING MODEL

DEEP BUFFER SWITCHES

•LOADS THE SWITCH WITH ADDITIONAL BUFFER CAPACITY

•HELPS TO SMOOTH SPIKES•PREVENTS DROPS

DEEP BUFFER SWITCHESEXAMPLE

SHORTCUT

•SOMETIMES TOUGH TO GET BUFFER SIZE

•ESNET HAS INFO ON SITE:•HTTP://FASTERDATA.ES.NET/NETWORK-TUNING/ROUTER-SWITCH-BUFFER-SIZE-ISSUES/

PRECAUTIONS

•DON’T BE BOUND BY LARGE BUFFER SWITCHES•CAN BE PRICEY

•DEPENDS ON TRAFFIC (LOCAL OR WAN)

SUMMARY•NETWORK IP PROTOCOLS•TCP•SWITCH OVERVIEW•DEEP BUFFER SWITCHES•PRECAUTIONS

Questions???