changes

REAL 5.0 Changes S. Keshav Cornell University skeshav@cs.cornell.edu August 13^th 1997

1. Introduction

This document outlines the changes made in REAL 5.0 compared to REAL 4.0. I released 4.0 in October 1993, and in the last four years, have made many changes. These include
1. many new simulation modules
2. a Java-based GUI.
3. faster, smaller, cleaner simulation engine
4. ports to FreeBSD, Solaris, and Digital Unix (OSF/3)
5. simulation exercises based on my book
6. minor bug fixes

I'm finally releasing all of these together in Real v5.0. Suggestions for changes are welcome. In the rest of this document, I will describe these changes in more detail.

2. New modules in the simulator

The table below summarizes all the modules being released as part of Real 5.0.

FILE	DESCRIPTION
background.c	sends background traffic on-off at a nominal rate
coder.c	MPEG coder that adapts its rate to the currently available rate (needs pp.c as transprt layer)
controlled_rate.c	sends on-off traffic and also does call setup
dec.c	obeys DECbit flow control
ecn_error.c	template for error control assignment
ecn_flow.c	template for flow control assignment
ecn_master.c	simulates shared channel for CSMA/CD (Ethernet)
ecn_receiver.c	generic receiver for assignment 3
ecn_router.c	really tiny router, but it works
ecn_sender.c	sources to test the router
ecn_simple.c	template for simple source assignment
ecn_slave.c	simulates Ethernet card for CSMA/CD
ftp_vegas.c	untested code for FTP with TCP vegas flow control
generic.c	generic transport layer with windowing, timeouts, acks
jk_reno.c	implements flow control scheme of 4.3BSD-Reno
jk_tahoe.c	implements flow control in 4.3BSD Tahoe
mmpp.c	something like a markov modulated poisson source
mpeg.c	uncontrolled mpeg coder (reads values from file)
onoff.c	ON OFF source
onoff_closed.c	ON OFF source, off time starts when all packets generated during on time have been acked
onoff_closed_gbn.c	same as above, but does go-back-n retransmission
playout.c	plays out MPEG video, complains if frame misses its end-to-end delay bound
poisson.c	poisson source
pp.c	packet pair flow control
random_rate.c	sends data at random intervals, but conforms to peak/ave description
send.c	implements packet transmission functions
sink.c	universal receiver function
telnet.c	flow controlled poisson source (with windowing)
trace.c	reads a trace from a file and sends packets according to that description

The simulator now has code for packet-pair flow control. The work is described partly in my Sigcomm'91 paper ("A Control theoretic approach to flow control"), and the code implements all the details described in my unpublished (and very long) paper "Packet pair flow control" as well as my recent work on retransmission described in "SMART: Retransmission: Performance with Random Losses and Overload". The pp.c source provided implements a transport layer that does both flow control and error control. Error control is with SMART retransmission, but no flow control. The pp.c source can also act like a 'transport layer', expecting another node to provide it with packets that it sends to the destination. When the option is set, each source requires a pair of nodes: one generates traffic from an arbitrary distribution (or reads it from a trace file), and the pp node performs error control, and optionally, flow control. This provides a very flexible environment for testing out packet-pair flow control in a wide range of scenarios.

A set of sources with the name ecn_*.c contain templates for simulation exercises based on my book.

TCP flow control is available, as before, in both Tahoe and Reno flavors.

The coder.c source shapes a video source's rate based on feedback from a packet-pair transport layer.

The playout.c node replaces a sink, and complains if a packet is received beyond its deadline.

The sink.c node stores individual packet delays in a file called e2e<node-number>. This can be postprocessed to obtain the delay-jitter and delay distribution.

The trace.c file allows a source to read a trace from a file and generate packets according to it.
I am also providing TCP Vegas code which I did not write, and will not support.

3. GUI

There is finally a GUI for REAL. It was written in Java by Hani Jamjoom at Cornell University. The GUI is meant to be used in conjunction with a simulator server, currently real.cs.cornell.edu. The idea is that users can create a simulation scenario using the GUI, then send it to the simulation server. The server connects to the GUI over a socket and sends simulation results in the form of plot files, that are displayed dynamically as the simulation proceeds. For more information, go the the RealEdit home page.

For users who do not want to use a GUI, the simulator continues to support an ASCII input file format. The only change is that the plot files are all lumped together into a single file called "plot". The file sim/kernel/demux demultiplexes this file into a bunch of plot files. This also makes the simulator much more efficient, since the number of disk writes is dramatically reduced. If you want to continue using the old style of simulation, then you should do

simulate foo.l
cd foo
../kernel/demux plot

You will then not be required to use the GUI. Incidentally, v5 will continue to parse NetLanguage files supported by older versions of Real.

4. Simulation Engine

The simulation engine in Real 4.0 was essentially the one I got from NEST 2.5 from Columbia. I have rewritten the code to make it less general, cleaner, and faster. I also added lots of comments, so that the code is finally somewhat understandable (I never fully understood it till now !).

5.Ports

I have ported the simulator to Solaris and Digital Unix (OSF). Elan Amir ported it to FreeBSD, and I have added his changes to my distribution, though I have not tested it. A Linux port was done by Cheryl Pope, and I have added the changes she made, though, again, this hasn't been tested. I am looking for volunteers to port to Windows NT/95. The Installation Manual has a full list of supported architectures.

6. Things to add

I'm porting the FreeBSD2.2.2 TCP kernel code, and will release it when I'm done. I would like help in adding multicast to the simulator and in porting it to Windows NT. Any volunteers?