Table Of Contents
Table Of Contents



This chapter describes application models and traffic generators. All applications implement the IApp module interface to ease configuration. For example, StandardHost contains an application submodule vector that can be filled in with specific applications from the INI file.

INET applications fall into two categories. In the first category, applications implement very specific behaviors, and generate corresponding traffic patterns based on their specific parameters. These applications are implemented as simple modules.

In the second category, applications are more generic. They separate traffic generation from the usage of the protocol, Udp or Tcp for example. These applications are implemented as compound modules. They contain separate configurable traffic source, traffic sink, and protocol input/output submodules. This approach allows building complex traffic patterns by composing queueing model elements.

TCP applications

This sections describes the applications using the TCP protocol. These applications use GenericAppMsg objects to represent the data sent between the client and server. The client message contains the expected reply length, the processing delay, and a flag indicating that the connection should be closed after sending the reply. This way intelligence (behaviour specific to the modelled application, e.g. HTTP, SMB, database protocol) needs only to be present in the client, and the server model can be kept simple and dumb.


Client for a generic request-response style protocol over TCP. May be used as a rough model of HTTP or FTP users.

The model communicates with the server in sessions. During a session, the client opens a single TCP connection to the server, sends several requests (always waiting for the complete reply to arrive before sending a new request), and closes the connection.

The server app should be TcpGenericServerApp; the model sends GenericAppMsg messages.

Example settings:


numRequestsPerSession = exponential(3)
requestLength = truncnormal(20,5)
replyLength = exponential(1000000)


numRequestsPerSession = 1 # HTTP 1.0
numRequestsPerSession = exponential(5)  # HTTP 1.1, with keepalive
requestLength = truncnormal(350,20)
replyLength = exponential(2000)

Note that since most web pages contain images and may contain frames, applets etc, possibly from various servers, and browsers usually download these items in parallel to the main HTML document, this module cannot serve as a realistic web client.

Also, with HTTP 1.0 it is the server that closes the connection after sending the response, while in this model it is the client.


Accepts any number of incoming TCP connections, and discards whatever arrives on them.


Generic server application for modelling TCP-based request-reply style protocols or applications.

The module accepts any number of incoming TCP connections, and expects to receive messages of class GenericAppMsg on them. A message should contain how large the reply should be (number of bytes). TcpGenericServerApp will just change the length of the received message accordingly, and send back the same message object. The reply can be delayed by a constant time (replyDelay parameter).


The TcpEchoApp application accepts any number of incoming TCP connections, and sends back the data that arrives on them, The byte counts are multiplied by echoFactor before echoing. The reply can also be delayed by a constant time (echoDelay parameter).


Single-connection TCP application: it opens a connection, sends the given number of bytes, and closes. Sending may be one-off, or may be controlled by a “script” which is a series of (time, number of bytes) pairs. May act either as client or as server. Compatible with both IPv4 and IPv6.

Opening the connection

Depending on the type of opening the connection (active/passive), the application may be either a client or a server. In passive mode, the application will listen on the given local local port, and wait for an incoming connection. In active mode, the application will bind to given local local address and local port, and connect to the given address and port. It is possible to use an ephemeral port as local port.

Even when in server mode (passive open), the application will only serve one incoming connection. Further connect attempts will be refused by TCP (it will send RST) for lack of LISTENing connections.

The time of opening the connection is in the tOpen parameter.

Sending data

Regardless of the type of OPEN, the application can be made to send data. One way of specifying sending is via the tSend, sendBytes parameters, the other way is sendScript. With the former, sendBytes bytes will be sent at tSend. When using sendScript, the format of the script is:

<time> <numBytes>; <time> <numBytes>;...

Closing the connection

The application will issue a TCP CLOSE at time tClose. If tClose=-1, no CLOSE will be issued.


Models Telnet sessions with a specific user behaviour. The server app should be TcpGenericServerApp.

In this model the client repeats the following activity between startTime and stopTime:

  1. Opens a telnet connection

  2. Sends numCommands commands. The command is commandLength bytes long. The command is transmitted as entered by the user character by character, there is keyPressDelay time between the characters. The server echoes each character. When the last character of the command is sent (new line), the server responds with a commandOutputLength bytes long message. The user waits thinkTime interval between the commands.

  3. Closes the connection and waits idleInterval seconds

  4. If the connection is broken, it is noticed after reconnectInterval and the connection is reopened

Each parameter in the above description is “volatile”, so you can use distributions to emulate random behaviour.


This module emulates a very specific user behaviour, and as such, it should be viewed as an example rather than a generic Telnet model. If you want to model realistic Telnet traffic, you are encouraged to gather statistics from packet traces on a real network, and write your model accordingly.


This module hosts TCP-based server applications. It dynamically creates and launches a new “thread” object for each incoming connection.

Server threads can be implemented in C++. An example server thread class is TcpGenericServerThread.

Applications composing TCP traffic

The following TCP modules are provided to allow composing applications with more complex traffic without implementing new C++ modules:

  • TcpClientApp: generic TCP client application with composable traffic source and traffic sink

  • TcpServerApp: generic TCP server application with a TCP server listener to create TCP server connections

  • TcpServerConnection: generic TCP server connection with composable traffic source and traffic sink

  • TcpServerListener: generic TCP server listener for accepting/rejecting TCP connections and for creating TCP server connections

  • TcpRequestResponseApp: generic request-response based TCP server application with configurable pre-composed traffic source and traffic sink

There are some applications which model the traffic of the telnet protocol:

  • TelnetClientApp: telnet client application with configurable pre-composed telnet traffic source and traffic sink

  • TelnetServerApp: telnet server application with pre-configured TCP server listener to create telnet server connections

  • TelnetServerConnection: telnet server connection with configurable pre-composed telnet traffic source and traffic sink

UDP applications

The following UDP-based applications are implemented in INET:

  • UdpBasicApp sends UDP packets to a given IP address at a given interval

  • UdpBasicBurst sends UDP packets to the given IP address(es) in bursts, or acts as a packet sink.

  • UdpEchoApp is similar to UdpBasicApp, but it sends back the packet after reception

  • UdpSink consumes and prints packets received from the Udp module

  • UdpVideoStreamClient,:ned:UdpVideoStreamServer simulates video streaming over UDP

The next sections describe these applications in details.


The UdpBasicApp sends UDP packets to a the IP addresses given in the destAddresses parameter. The application sends a message to one of the targets in each sendInterval interval. The interval between message and the message length can be given as a random variable. Before the packet is sent, it is emitted in the signal.

The application simply prints the received UDP datagrams. The signal can be used to detect the received packets.


This module binds an UDP socket to a given local port, and prints the source and destination and the length of each received packet.


Similar to UdpBasicApp, but it sends back the packet after reception. It accepts only packets with UdpHeader, i.e. packets that are generated by another UdpEchoApp.

When an echo response received, it emits an signal.


This module is a video streaming client. It send one “video streaming request” to the server at time startTime and receives stream from UdpVideoStreamServer.

The received packets are emitted by the signal.


This is the video stream server to be used with UdpVideoStreamClient.

The server will wait for incoming “video streaming requests”. When a request arrives, it draws a random video stream size using the videoSize parameter, and starts streaming to the client. During streaming, it will send UDP packets of size packetLen at every sendInterval, until videoSize is reached. The parameters packetLen and sendInterval can be set to constant values to create CBR traffic, or to random values (e.g. sendInterval=uniform(1e-6, 1.01e-6)) to accomodate jitter.

The server can serve several clients, and several streams per client.


Sends UDP packets to the given IP address(es) in bursts, or acts as a packet sink. Compatible with both IPv4 and IPv6.


The destAddresses parameter can contain zero, one or more destination addresses, separated by spaces. If there is no destination address given, the module will act as packet sink. If there are more than one addresses, one of them is randomly chosen, either for the whole simulation run, or for each burst, or for each packet, depending on the value of the chooseDestAddrMode parameter. The destAddrRNG parameter controls which (local) RNG is used for randomized address selection. The own addresses will be ignored.

An address may be given in the dotted decimal notation, or with the module name. (The L3AddressResolver class is used to resolve the address.) You can use the “Broadcast” string as address for sending broadcast messages.

INET also defines several NED functions that can be useful:

  • moduleListByPath("pattern",...):
    Returns a space-separated list of the modulenames. All modules whose full path matches one of the pattern parameters will be included. The patterns may contain wilcards in the same syntax as in ini files. Example:
  • moduleListByNedType("fully.qualified.ned.type",...):
    Returns a space-separated list of the modulenames with the given NED type(s). All modules whose NED type name occurs in the parameter list will be included. The NED type name is fully qualified. Example:


**.app[0].destAddresses = moduleListByPath("**.host[*]", "**.fixhost[*]")
**.app[1].destAddresses = moduleListByNedType("inet.nodes.inet.StandardHost")

The peer can be UdpSink or another UdpBasicBurst.


The first burst starts at startTime. Bursts start by immediately sending a packet; subsequent packets are sent at sendInterval intervals. The sendInterval parameter can be a random value, e.g. exponential(10ms). A constant interval with jitter can be specified as 1s+uniform(-0.01s,0.01s) or uniform(0.99s,1.01s). The length of the burst is controlled by the burstDuration parameter. (Note that if sendInterval is greater than burstDuration, the burst will consist of one packet only.) The time between burst is the sleepDuration parameter; this can be zero (zero is not allowed for sendInterval.) The zero burstDuration is interpreted as infinity.

Operation as sink

When destAddresses parameter is empty, the module receives packets and makes statistics only.

Applications composing UDP traffic

The following UDP modules are provided to allow composing applications with more complex traffic without implementing new C++ modules:

  • UdpApp: generic UDP application with composable traffic source and traffic sink

  • UdpSourceApp: generic UDP application with a traffic source

  • UdpSinkApp: generic UDP application with a traffic sink

  • UdpRequestResponseApp: generic request-response based UDP server application with configurable pre-composed traffic source and traffic sink

IPv4/IPv6 traffic generators

The applications described in this section use the services of the network layer only, they do not need transport layer protocols. They can be used with both IPv4 and IPv6.

IIpvxTrafficGenerator (prototype) sends IP or IPv6 datagrams to the given address at the given sendInterval. The sendInterval parameter can be a constant or a random value (e.g. exponential(1)). If the destAddresses parameter contains more than one address, one of them is randomly for each packet. An address may be given in the dotted decimal notation (or, for IPv6, in the usual notation with colons), or with the module name. (The L3AddressResolver class is used to resolve the address.) To disable the model, set destAddresses to “”.

The IpvxTrafGen sends messages with length packetLength. The sent packet is emitted in the signal. The length of the sent packets can be recorded as scalars and vectors.

The IpvxTrafSink can be used as a receiver of the packets generated by the traffic generator. This module emits the packet in the signal and drops it. The rcvdPkBytes and endToEndDelay statistics are generated from this signal.

The IpvxTrafGen can also be the peer of the traffic generators; it handles the received packets exactly like IpvxTrafSink.

The PingApp application

The PingApp application generates ping requests and calculates the packet loss and round trip parameters of the replies.

Start/stop time, sendInterval etc. can be specified via parameters. An address may be given in the dotted decimal notation (or, for IPv6, in the usual notation with colons), or with the module name. (The L3AddressResolver class is used to resolve the address.) To disable send, specify empty destAddr.

Every ping request is sent out with a sequence number, and replies are expected to arrive in the same order. Whenever there’s a jump in the in the received ping responses’ sequence number (e.g. 1, 2, 3, 5), then the missing pings (number 4 in this example) is counted as lost. Then if it still arrives later (that is, a reply with a sequence number smaller than the largest one received so far) it will be counted as out-of-sequence arrival, and at the same time the number of losses is decremented. (It is assumed that the packet arrived was counted earlier as a loss, which is true if there are no duplicate packets.)

Ethernet applications

The inet.applications.ethernet package contains modules for a simple client-server application. The EtherAppClient is a simple traffic generator that peridically sends EtherAppReq messages whose length can be configured. destAddress, startTime,waitType, reqLength, respLength

The server component of the model (EtherAppServer) responds with a EtherAppResp message of the requested length. If the response does not fit into one ethernet frame, the client receives the data in multiple chunks.

Both applications have a registerSAP boolean parameter. This parameter should be set to true if the application is connected to the Ieee8022Llc module which requires registration of the SAP before sending frames.

Both applications collects the following statistics: sentPkBytes, rcvdPkBytes, endToEndDelay.

The client and server application works with any model that accepts Ieee802Ctrl control info on the packets (e.g. the 802.11 model). The applications should be connected directly to the Ieee8022Llc or an EthernetInterface NIC module.

The model also contains a host component that groups the applications and the LLC and MAC components together (EthernetHost). This node does not contain higher layer protocols, it generates Ethernet traffic directly. By default it is configured to use half duplex MAC (CSMA/CD).