Network Designer (NetDes)

Click here to start the applet. For the documentation please read below.

Overview
Add (Create) Object
Update Object
Delete Object
Load Examples
Simulation
Limitations
Supported Platforms and Known Bugs

1. Overview

The Network Designer (NetDes, for short) is a Java applet which allows to interactively design simple communication networks and simulate them in ns-2. The goal is to give the user possibility to compare the performances of Core-Stateless Fair Queueing (CSFQ) to other buffer management and scheduling disciplines, such as Random Early Detection (RED), Flow Random Early Drop (FRED) and Deficit Round Robin with dropping from the longest queue (DRR). A comparison of these disciplines is given in Table 1, where n represents the total number of flows.

	Time Complexity	Space Complexity	Congestion Control Support	Comments
FIFO	O(1)	O(1)	no	-
RED	O(1)	O(1)	no	-
FRED	O(1)	O(n)	yes	-
DRR	O(log n)	O(n)	yes	Implements Fair Queueing
CSFQ	O(1)	O(n) - edge node O(1) - core node	yes	Approximates Fair Queueing

Table 1. Disciplines that can be simulated with NetDes.

1.1. Architecture

As any web application this is a client-server application. The client runs NetDes, which provides a friendly user interface to design simple networks. The server runs a dispatcher process that handles client requests by invoking ns-2 to simulate user's networks. The overall architecture is shown bellow.

Figure 1. System architecture.

A typical client/server interaction consists of three steps:

Once the network design is completed, the user starts simulation by clicking on the Execute button (see Section 6 ). As a result a request containing all the relevant information about user's network is transmitted to the dispatcher process. In turn the dispatcher creates a corresponding tcl file that describes the network topology and invokes ns-2.
When the simulation completes, the dispatcher assembles the results into a web page, and acknowledges the user by sending back the address of this web page.
By using the returned address, the user loads the result page through her/his browser.

1.2. User Interface

NetDes manipulates three types of objects: nodes, links, and flows. All links are duplex and all flows are unicast. Figure 2 shows the NetDes user interface displaying a simple network consisting of two nodes (node_1 and node_2), one link, and five flows (UDP, TCP-1, TCP-2, TCP-3, and TCP-4).

Figure 2. The NetDes user interface.

The editor has three modes. Each mode is activated by making the corresponding selection in Control Area. The three modes are:

Add - create a new object. The object type is specified by the selection at the right-hand side of Add, i.e., node, link, or flow. When node is selected the user can move a node by dragging it.
Update - update the information of an existing object.
Delete - delete an object. When a node is deleted all links that are incident to the node, and all flows that have either the source or the sink at that node are also deleted.

The window located at the right-hand side of the Control Area is called Information Window. In the Add mode, this window displays the next action to be performed. In the Update and Delete modes, the Information Window indicates the current object as the user moves the pointer.

Action Area contains usually three buttons. However, if the browser allows a Java applet to write on your disk, then the Action Area will display three additional buttons: Load, Save, and Save as. This allows the user to save/load her/his work. The three buttons which are always displayed are:

New - delete the current network.
Load Examples - load one of the network examples which come with NetDes.
Execute - simulate the network that is currently displayed in the Drawing Area.

The next sections describes in detail how to design and simulate a network.

2. Add (Create) Object

An object can be a node, link, or flow. This section describes how to create a new object.

2.1. Create Node

The steps to create a new node are the followings:

Select Add and node in the Control Area (see Figure 2).
Move the pointer over the Drawing Area at the location you wish to create the node and click the left-button of the mouse.
As a result a dialog box pops up asking for the node label/name. Fill the name you wish and press "OK".

2.2. Create Link

In NetDes all links are duplex. Thus, when a link is created the user needs to specify parameters in both directions, more precisely, the buffer management and/or the scheduling discipline employed by the output queue of each end node and the capacity of the link in each direction. The steps to create a new link are given below.

Select Add and link in the Control Area.
Click over the node from which you want the link to start. As a result the following dialog pops up.

The parameters in this dialog box are associated to the output queue of the selected node, and they are:
- Scheduler type - the type of scheduler and/or the buffer management policy employed by the output queue. Current supported types are FIFO, RED, FRED, FREDL, CSFQ, and DRR.
- Rate (Mbps) - the capacity of the output link.
- Delay (ms) - the propagation delay along the link.
- Buffer size (bytes) - the size of the output buffer.
- Max. packet size (bytes) - the maximum packet size along the link. This parameter together with Buffer size are used to express the size of the output buffer in terms of the number of packets of maximum size that can be stored. More precisely the output buffer capacity in packets is computed as (Buffer size) / (Max. packet size).
- Ka - fair rate const. (ms) - the constant used to estimate the fair rate along the outgoing link. This parameter is used only by CSFQ.
- Kf - flow rate const. (ms) - the constant used to estimate the rate of the incoming flows. This parameter is used only by CSFQ.
- Trace link's traffic - the flag that indicates whether the traffic on the outgoing link is to be traced. Only the results for the marked links will be returned.
- Edge node - the flag that indicates whether the outgoing link belongs to an ingres node (at the edge of the cloud or not). This parameter is used only by CSFQ.
In addition, the following parameters are specific to RED and FRED(L):
- Min. threshold (bytes) - the output buffer minimum threshold. When the average queue length exceeds this threshold packets start to be probabilistically dropped.
- Max. threshold (bytes) - the output buffer maximum threshold. When the average queue length exceeds this threshold all incoming packets are being dropped.
Select the second end-node of the link. As a result an identical dialog box pops up. The parameters in this dialog box are associated to the output queue of the second node.
Thus, while the first dialog box specifies the parameters associated to the simplex link from the first to the second node, this dialog box specifies the parameters of the simplex link from the second to the first node.

2.3. Create Flow

Flows are of two types: UDP and TCP. The steps to create a flow are the followings.

Select Add and Flow in the Control Area.
Select the node to be the source of the flow. As a result the following dialog box pops up.

The meaning of the parameters in this dialog box is the following:
- Label - the label/name to identify the flow. This name will be associated to both source and the sink of the flow.
- TCP/UDP - the flags that specifies the type of the flow: UDP or TCP.
- Packet size (bytes) - the size of the flow's packets. In the current implementation all packets of a flow have the same length.
- Window Size (packets) or Rate (Kbps) - the window size if the flow is TCP, and the transmission rate of the source if the flow is UDP. The interdeparture time between UDP's packets is uniformly distributed between 0.5 and 1.5 of the average value.
- Start time (sec) - the time when the flow becomes backlogged, i.e., when the first packet of the flow is sent.
- Finish time (sec) - the time when the flow becomes un-backlogged, i.e., when the last packet of the flow is sent.
Select flow's destination node.

3. Update Object

3.1. Update Object Information

The steps to update the information associated to an object are given below:

Select the Update mode in the Control Area.
Select the object you want to update by clicking on it. As a result a dialog box will show up. Set the desired values and then press "OK".

While in the Update mode, the Information Window in the Control Area shows the object which will be selected if you press the left mouse button. The node and flow objects are identified by their labels. A link is identified by the two end nodes. The order in which these nodes appear is important. For example, in Figure 2, (node_1 -> node_2) identifies the simplex link from node_1 to node_2 and the corresponding output queue of node_1. Link (node_1 -> node_2) is selected when you are closer to node_1, while (node_2 -> node_1) is selected when you are closer to node_2.

3.2. Update Object Position

In the current implementation only the node position can be changed. The flows' and links' positions are automatically computed based on the nodes' positions and the order in which they were created.

To move a node perform the following steps.

Select Add and node in the Control Area.
Select the node you want to move and drag it to the new position.

4. Delete Object

The steps to delete an object are given below:

Select Delete in the Control Area.
Select the object you want to delete by clicking on it. As a result a dialog box asking for confirmation is displayed. If you want to continue press "OK".

Note: When a node is deleted all flows that have either the source or the sink at that node, as well as all incident links are also deleted.

5. Load Examples

To load an example click Load Examples button in the Action Area. As a result the following dialog box in which the user can select the example, the scheduling discipline and the TCP type is displayed.

Currently there are two examples available. In both of them all links have 10 Mbps capacity. The first example consists of a single link shared by one UDP flow that blast at the link capacity and four TCP flows (see Figure 2). The second example represents a scenario in which one TCP traverses two congested links. Each congested link is traversed by four other UDP flows, each of them sending at twice its fair rate. The parameters associated to all links and flows can be visualized/changed as described in Section 3.1.

6. Simulation

To simulate the network that is currently displayed in the Drawing Area the user needs to perform the following steps:

Click Execute button in the Action Area. As a result a dialog box containing the list of all (simplex) links in your topology is displayed. An example is shown below.

You can select one or more links to be traced. As an example, above only the link (node_1 -> node_2) will be traced. Then click "OK".
Once you select "OK" you have to wait until the simulation is completed. Depending on the size of the network the simulation may take up to several minutes. Once the simulation is completed, you will get the address of the web page containing the results as shown below:

Note that you need to copy this address and use explicitly your browser to download it. When you press "Cancel" the window will simply disappear; the address is not stored anywhere else.

The result web page obtained by simulating the network shown in Figure 2, which is the Single Link example using the CSFQ discipline, is shown here.

In general, the result web page gives for each traced link the following information:

The average bandwidth of each flow along that link.
A plot representing the throughput of each flow along the link.

In addition, the web page shows the parameters associated to all links and flows in the simulated network.

7. Limitations

Since currently we perform simulation on one machine, to limit the simulation time we have imposed the following limits:

The link capacity cannot exceed 45 Mbps.
The flow rate cannot exceed 10 Mbps. (This limit applies to UDP only.)
The duration of a flow cannot exceed 20 seconds simulation time.

In addition, for simplicity many of the parameters that can be set in ns-2 are left out. For example, in the TCP case only the window size and the type can be set.

Finally, as described in Section 4, when designing a network only the nodes can be moved around. The positions of flows and links are implicitly determined by the nodes' positions.

8. Supported Platforms and Known Bugs

NetDes was tested on the following configurations:

FreeBSD 2.7, NetBSD 1.2.1, and Solaris (SunOS 5.5) with Netscape 3 and Navigator 4.05
AIX 2.3 with Netscape 3.
Windows NT 4.0 with both Navigator 4.05 and Microsoft Explorer 3.0/4.0

Following is the list of known bugs or inconsistent behaviors:

With AIX 2.3 and Navigator 3.0, the fonts are not correctly displayed. Also, when dialog boxes are displayed the "OK" button is not visible. To correct this you need to stretch the dialog box on the horizontally until you see the "OK" button.
With Windows NT 4.0 and Explorer 4.03 the first object on the dialog box may not be displayed. To correct this you need to stretch the dialog box vertically.
With Windows NT 4.0 and Navigator 4.05 the applet terminates occasionally after the results are returned. This makes impossible to go back, change the topology, and then re-run the simulation. We do not have a fix for this problem yet.

Ion Stoica

Last modified: Sat Oct 31 11:09:36 EST 1998