VRNET

Introduction

VRNET is a network emulator that allows programmers to write network protocols and algorithms and test them in a realistic environment. The emulator takes a cluster of computers connected to each other by some real network and arranges them into a virtual network with whatever topology the programmer wants and emulates packet loss, packet corruption, and dynamic traffic across all of its virtual links.

How VRNET emulates packet corruption and loss
VRNET uses a percentage to emulate packet corruption and loss. For each subnet the user defines a transmission reliability between 0.0 and 100.0. The transmission reliability represents the long run percentage of packets that will not be dropped or corrupted. Each time a packet is sent, a random number between 0.0 and 100.0 is chosen and if the random number is greater than the transmission reliability, the packet will either be corrupted or dropped.

How VRNET emulates link failure
VRNET uses a combination of a percentage and normal distribution to emulate link failures. For each subnet the user defines a link reliability, mean link failure period, link failure period standard deviation, and a change rate. The change rate is in seconds and a period is equal to the change rate. The link reliability represents the percent chance the subnet link will fail. When a user configures the subnet with a number less than 100.0, at the specified change rate the emulator will choose a random number between 0.0 and 100.0. If the random number is greater than the link reliability, then the link will go down and a random number of periods the link will remain down is chosen according to the mean link failure period and link failure period standard deviation. The mean link failure period and link failure standard deviation define a normal distribution. The larger the standard deviation the higher the probability the number of periods will vary farther from its mean value. After the random number of periods expires the link will become active again and the process will start all over again. If a link goes down, then all packets sent across that link will be dropped.

How VRNET emulates dynamic traffic
VRNET uses a normal distribution to emulate dynamic traffic. For each subnet the user defines a mean delay, delay standard deviation, and a change rate. The delay is in milliseconds and the change rate is in seconds. The mean delay and delay standard deviation define a normal distribution. The larger the standard deviation the higher the probability the delay will vary farther from its mean value. At the specified change rate a new delay will be chosen according to the normal distribution and all packets leaving a host along that subnet will be physically delayed that many milliseconds.

Compiling Instructions

To compile, use the following commands:

gcc -c vrnet_code.c
		gcc -o executable vrnet_code.o vrnet.a -lpthread -lsocket -lnsl -lm

Function Specification

To use VRNET, the programmer has the following 14 functions. All of their prototypes are defined in vrnet.h. The file vrnet.h should be included in all programs using VRNET.

Configuration file

To configure VRNET, you will need to supply a configuration file that defines the topology of the network and the settings to use for each subnet. The following is an example VRNET configuration file:

                #tag identifier subport simport trans link  mean_link std_link mean_delay std_delay change_rate
                queue 100
                network net1 6100 6101 100.0 100.0 10 2.0 100 30.0 5
                cetus26 alpha1 000afc000102
                cetus27 alpha2 000afc000103
                network net2 6200 6201 100.0 100.0 10 2.0 100 30.0 5
                cetus27 beta1 000afc000104
                cetus28 beta2 000afc000105
                network net3 6300 6301 100.0 100.0 10 2.0 100 30.0 5
                cetus28 gamma1 000afc000106
                cetus29 gamma2 000afc000107
                network net4 6400 6401 100.0 100.0 10 2.0 100 30.0 5
                cetus29 delta1 000afc000108
                cetus30 delta2 000afc000109
                network net5 6500 6501 100.0 100.0 10 2.0 100 30.0 5
                cetus30 epsilon1 000afc00010a
                cetus26 epsilon2 000afc00010b
                trace blah

		

At the top of the configuration file you can specify the send and receive queue sizes, with the line queue [SIZE]. The send queue size is the number of packets per interface that can be waiting for transit. The receive queue size is the number of packets received from other hosts that can be waiting for processing. This is optional and must be defined before any subnets. If you do not define it, then it will be set to its default value. After defining the optional queue size, the rest of the configuration file is basically a series of subnet specifications. Each subnet specification must start with the following line:

network <identifier> <subnet port #> <simulator port #> <transmission reliability> <link reliability> <mean link down period> <link down period std> <mean delay> <delay std> <change rate>

Note: “network” is a literal indicating a new subnet

After defining the subnet, the successive lines are either the hosts on the subnet, routing information, or a trace file to use. The trace file definition should be the last entry in the subnet and the other entries can occur in any order. Note that the trace file and routing information is optional. All that VRNET requires is for you to list the hosts attached to the subnet.

To define a host attached to the subnet use the following line:

<realname> <vrnetname> <vrnetmac>

(ex. cetus2 alpha1 000afc000102)

Finally to define a trace file for VRNET to create use the following line: (this is optional)

trace <filename>

Note: "trace" is a literal indicating that all packets sent and received on this subnet should be written to a tracefile