TCP for OMNeT+ + Roland Bless Mark Doll Institute of Telematics - - PowerPoint PPT Presentation

Bless/Doll WSC 2004 1

TCP for OMNeT+ +

Roland Bless Mark Doll Institute of Telematics University of Karlsruhe, Germany

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Overview

Motivation Introduction OMNeT+ + & TCP Concept for integration Implementation problems Evaluation results Summary & Outlook

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Motivation I

Investigation of Network Protocols

Different parameter settings Extreme conditions Scaling properties

Difficult in testbeds Simulation

Expressive simulation results

Require good emulation of real world behavior Protocols we design use or modify TCP/IP stack Emulation of network oriented layers

Transport (TCP) Internet (IP) Network Access (Ethernet)

Need TCP/IP stack implementation for simulation

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Motivation II

Problem

no validated (tested to be compliant to the standard)

TCP/IP implementation for OMNeT+ +

Possible solutions

Choose other simulator

ns-2 OPNET

New implementation Revision of the existing implementation (i. e. from

Communications Engineering Institute, Karlsruhe)

full featured? validated?

Re-use an existing real world implementation

Linux FreeBSD

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OMNeT+ +

Discrete event simulator

hierarchically nested modules communicate with messages through channels

Written in C+ +

Complete source code publicly available

Free for academic use

Commercial version OMNESTTM

Advantages

Very well structured Highly modular Not limited to network protocol simulations (i. e. like ns-2)

Disadvantages

Relatively young: 1997 first public release

Few simulation models

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• system module

top level module

• simple modules

C+ + NED description of interface: parameters and gates

• compound modules

NED only: parameters, gates and connections unlimited nesting

OMNeT+ +

NED

system module compound module simple modules input gates

• utput gates

C++ C++ C++ NED

Hierarchical nested modules

channels

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Transmission Control Protocol

TCP

Transport layer protocol (layer 4) connection-oriented, reliable, stream-oriented flow control, congestion control

Influenced by round trip time, packet loss

Most of today’s internet traffic via TCP

TCP behavior influences behavior of many protocols & applications

API: BSD socket interface (socket type: stream)

FreeBSD‘s TCP/IP implementation

source code freely available well structured code (not as optimized as Linux) 4.x BSD was starting point for many other implementations

MAC OS X essentially is FreeBSD (with additions like Aqua)

Network research was and still is based on (Free)BSD

Mobile IPv6, Protocol Independent Multicast, …

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FreeBSD vs. OMNeT+ +

Function Call One TCP stack per host Multi-tasking, threads, functions are interruptible Messages Many TCP stacks per simulation Messages must be processed in one pass

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Protocol stack of FreeBSD

device driver RX interrupt ether_input() swi_net() ip_input() tcp_input() application rcv_buff snd_buff tcp_output() ip_output() device driver ip_forward() ether_output() TX interrupt

Transport Layer Network Layer Network Access Layer Application Layer

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cHost concept I

Gates to Applications (cAppl)

Multiplexer In/Out Gate SimpleModule

Gates to LANs or other Hosts (cMedium or cHost)

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cHost concept II

Gerätetreiber RX-Interrupt ether_input() swi_net() ip_input() tcp_input() Applikation rcv_buff snd_buff tcp_output() ip_output() Gerätetreiber ip_forward() ether_output() TX-Interrupt

+

= ?

Multiplexer

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cHost concept III

Multiplexer In/Out Gate SimpleModule

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OMNeT+ + classes

cHost

Simulated host with TCP/IP

cMedium

Emulates broadcast medium (Ethernet LAN) Allows for cHost address autoconfiguration

cAppl

Source/sink (sample application)

cRoute

Generates routing tables

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cAppl & cRoute

cAppl

Uses socket interface to cHost

Demonstrates usage of message based socket interface

Can accept and initiate connections Full duplex

cRoute

Manual routing table set up

Time consuming Configuration Errors Often routing table details unimportant

Use cRoute class to generate routing tables for FreeBSD

Utilizes standard OMNeT+ + class cTopology Computes shortest path (Dijkstra)

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cHost < -> FreeBSD I

TCP stacks must be independent No global and static variables possible Access via C macro

#define D ( (struct private_data*)bsd_data)

Usage: replace xyz with D->xyz

FreeBSD: same identifier for types and variables

• i. e. ifnet

Simple substitution of xyz with macro impossible However changes to FreeBSD source minimal

Avoid bugs Allow for easier re-porting of future FreeBSD releases

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cHost < -> FreeBSD II

Switch to BSD via C macro (simplified)

#define ENTER_BSD() { \ bsd_data=data; \ host_class=this; \ host_id=id(); \ }

Calling BSD functions from OMNeT+ +

Enclose call by ENTER_BSD and LEAVE_BSD

Calling OMNeT+ + functions from BSD

OMNeT+ + function exported with C calling conventions Function then uses host_class to access instance data

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Technical Problems

Include files

• FreeBSD and OMNeT+ + (host OS) need their own include files
• i. e. struct sockaddr and struct sockaddr_in

Socket interface

• Function calls replaced by OMNeT+ + messages

read(), write(), listen(), connect(), ...

• Blocking functions emulated by non-blocking + self message

Memory (shared)

• Differences between libc of FreeBSD and host OS running

OMNeT+ +

• mbufs & mclusters mapped on malloc

Timers

• Access to BSD ticks variable redirected to

gettick_toomnet() which uses OMNeT+ + ’s simtime()

startup added individually per cHost to prevent synchronization

• One timer for all hosts where appropriate, i. e. ip_slowtimo

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Evaluation

Memory usage per Host

• FreeBSD: 19 KiB
• + cHost class
• + Receive-/Send buffer 64 KiB (default) per connection

Run time in seconds for 1 hour of simulated time

• Time consuming insertion/removal of timer events in OMNeT+ + ’s

event queue (heap)

59.638 30.575 3.361 100 823.019 434.724 64.233 1000 4.196 2.199 0.467 10 2 1 Hosts/Conn.

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Summary

First validated and complete TCP implementation for OMNeT+ + Realized by adapting FreeBSD‘s TCP/IP stack Message-based implementation of the BSD socket interface Routing module automates routing table setup

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Outlook

Performance

hide certain messages in OMNeT+ + dedicated timer module for OMNeT+ +

Improve adaption process

Perl script/parser for (semi)automatic global variable

replacement

Support further protocols

IPv6 System call interface for routing deamons Mobile IPv6 patches

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Thanks to Jérôme Freilinger (diploma student) Thank You for your attention!