Trickles :A stateless network stack for improved Scalability, Resilience, and Flexibility

Alan Shieh ,Andrew C.Myers ,Emin Gun SirerDept. of Computer Science ,Cornell UniversityUSENIX NSDI 2005

Outline

Introduction Stateless Transport Protocol

About “Continuation” Abstraction of Trickle Trickles’s congestion control

Server API Client processing Evaluation

Introduction

A new network protocol stack which system state can be kept entirely on one side of a connection.

Stateless Network Protocol

Continuation: Transport continuation

For shipping Kernel-level state (TCP control block,TCB): Packet number, RTT, ssthresh …

User continuation For supportting stateless user-level server applications.

Trickle abstraction Packets are decomposed into disjoint trickles. One packet is exactly a member of one trickle. Each line pattern corresponds to a trickle.

3 actions when receiving a request packet : Continuing

Trickles permits the srver application to send response. Terminate

Trickles stops sending one response when packet loss. Split

Trickles starts one new response to trigger a new trickle. Using SACK.

Congestion control of Trickles Request number ‘k’

Trickles associates each request packet arrived with a request number ‘ k ’.

new Cwnd = TCPCwnd (K) Trickle updated when each packet ‘k’ received:

TrickleUpdate = TCPCwnd(k) – TCPCwnd(k-1) Generate ‘ TrickleUpdate + 1 ‘ responses.

Slow start and congestion avoidance

Fast retransmit / recovery First packet ‘k’ after losses, retransmitting the lost packets.

If cwndAtLoss – lossoffset < newCwnd Continue the trickle.

For fast recovery : ssthresh = startCwnd = newCwnd

firstLoss = number of first losscwndAtLoss = TCPCwnd (firstloss-1)newCwnd = numInFlight / 2

Retransmit timeout ssthresh = TCPCwnd ( firstloss -1) / 2 newCwnd = InitialCwnd

Server API

an ‘event’ queue Every response generated to client , a event pass

ed to the application. An event includes data of a request that needed f

or application. Minisocket

Each minisocket is associated with one client. Created and destroyed with one event. For optimizations , minisockets caching is used.

Client processing

A Trickles client stack implements a Berkeley sockets interface using Trickles transport protocol. Input continuations:

To help server application to resume accepting client input.

Output continuations: To help server application to resume generate output to

the client.

Evaluation

Trickles protocol stack is implemented in Linux 2.4.26.

Environment Gigabit Ethernet P4 1.7G 512 Mb RAM Intel e1000 gigabit NIC

Throughput Point to point topology, server 100 Mb/sec bottleneck

link.

Memory utilization

CPU utilization

Failover : disconnection occurs at t = 10.

Conclusion

Stateless side has good performance with small memory usage.

Trickles’s scalability is good. Transparent connection migration. Trickles is backward compatible with TCP.