EINTE LAB EXERCISES LAB EXERCISE #5 - SIP PROTOCOL

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EINTE LAB EXERCISES

LAB EXERCISE #5 - SIP PROTOCOL PREPARATIONS

STUDYING SIP PROTOCOL

The aim of this exercise is to study the basic aspects of the SIP protocol. Before executing the exercise you should familiarize yourself with SIP protocol specification.

LABORATORY CONFIGURATION

In order to perform the exercise you must create the VoIP system by installing 3CX VoIP Server and 3CX soft-phones using at least two PC computers. The recommended system configuration is shown on the figure below. Install the VoIP server and VoIP client on one PC and the second VoIP client on another PC. Optionally you may install the VoIP clients on dedicated computers using 3 PCs (if available). Install the Wireshark program on the server PC.

The 3CX VoIP software is available for free from the following web page: http://www.3cx.com/. Move to the download section and then select the Free Edition version. To be able to download the 3CX software you must fill in a short registration page (see figure below), provide the required information and click the Submit&Download button.

 VoIP Client 1 (3CX Softphone)

 VoIP Client 2 (3CX Softphone)

 VoIP Server (3CX Softswitch)

 VoIP Client 2 (opt.)

 wireshark

PC 1 PC 2 PC 3

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After submitting the registration form you will be redirected to the download page. Select the current 3CX version and download the following components:

 VoIP server software – „Download 3CX Phone System for Windows”

 VoIP client software (soft-phone) - „Download the Windows Client (3CXPhone for Windows)”

INSTALLING AND CONFIGURING 3CX VOIP SERVER

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Run the 3CX setup program and follow the instructions provided by the installation program. Pay special attention to the system requirements and in particular to the availability of the required port numbers.

After successful installation of the server software, the 3CX setup Wizard will be launched automatically. The Wizard will guide you through the initial system configuration. you may also setup/modify these settings later using the 3CX management console.

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Using the configuration Wizard setup the following configuration options of your VoIP system (see the provided screenshots):

 Language – setup your desired language version

 Public IP – select “No I don’t have a static public IP address” if you don’t have or don’t want to use your public IP address

 Settings – select “Create new PBX” to create new VoIP server instance

 Extension Digits – select the number of digits for your extension numbers (select any settings you like).

 Mail Server – enter your email account settings (optionally). Setting email account will easy the 3CX client configuration task.

 Administrator Login – enter the user name and password for the administrator account that will be used to manage your VoIP server.

 Region – enter the region settings (select any region you like)

 General settings – enter the internal operator extension (select any number you like)

 Allowed Countries – use default settings

At this point, the wizard will create and configure the VoIP system. The following step (registration) can be skipped.

After installation is completed the login page should be displayed in your browser. The default login page is https://localhost:5001/management/MainForm.wgx. Login into the 3CX management console and configure two extensions.

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Configure two extensions for your soft-phones. In the 3CX management console select the Extension option and then click on the Add Extension button. Enter the following configuration options:

 Extension Number

 Email address

 ID

 password

If you configure the email address you will be able to send a welcome message containing client provisioning information (the mail server must be configured for this option to work).

In order to send configuration email select the extension by clicking on it and click on the Send welcome message button (right most button on the menu toolbar above the extension list).

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INSTALLING AND CONFIGURING 3CX VOIP CLIENT

Install the 3CX client software on two PCs. Run the setup program and follow the provided instructions.

When the client is started for the first time, the following screen is displayed informing about the lack of client configuration. Follow the provided instructions to configure the client (using the welcome message).

If you didn’t configure the mail server option in the 3CX system you must configure the client manually. Click on the Settings button (mark by red circle) and on the next screen select the Configure Accounts option.

Click the Add Account button (plus sign on the bottom of the window) and enter the required information according to the extension configuration done in the 3CX system, namely enter: extension number, extension ID, password and 3CX server IP address. After configuring the client switch the soft-phone to the 3CX mode.

From this point the soft-phone should register with the 3CX server (verify this under Extension Status in management console.

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WIRESHARK SNIFFER

WireShark is a free and powerful protocol analyzer available under the GNU license for most popular operating systems (Windows, Unix, Linux, OS X). It allows observing and recording data units transmitted over the network interfaces of a computer. The WireShark main window is divided into three parts: frame list (top panel), frame decode view (middle panel) and frame hex view (bottom panel). You can edit columns displayed in the frame panel. In order to add new column, for example to add the TCP sequence number, right click on the parameters of interest and select Apply as Column option. This will add new column to the frame panel, showing TCP segment send sequence number. You may add parameters as required.

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The link http://www.wireshark.org/docs provides extensive documentation to the program. The basic options that may come in handy during the exercise are mostly related to packet filtering, for example by IP addresses:

== ip.src 194.29.169.x

== ip.dst 194.29.169.x

Expressions may be combined using Boolean operators. Filtering allows to simplify the view by removing the information that is not important for current context. However, please be aware that by filtering one may not see some important messages, such as queries for host address etc.

For further processing you may export data to the text file (or other file format). This may be useful if you want to perform analysis other then provided by the WireShark or save filtered packets in the separate pcap file. To export data to a file select the option Export Packet Dissections or Export Specified Packets form the File menu.

TESTING SIP PROTOCOL

CLIENT REGISTRATION

Using WireShark capture the SIP messages used for registering the user agent (client) in the SIP server. Start the WireShark capture process and then start the 3CX client. Notice that the 3CX client mustn’t run in the background prior to starting it up.

Explain in the report the registration procedure used by the 3CX system, does it follow the SIP specification?

Draw the SIP message sequence diagram. Include the decoded SIP messages in the report. Explain the meaning and usage of the SIP headers observed in the decoded messages. Include the relevant screenshots from WireShark showing the captured packets.

SETTING UP SIP CONNECTION

Using WireShark capture the SIP messages used for setting and disconnecting SIP session between client 1&2.

Check the following cases:

 Called client answers the call

 Called client blocks the call

 Called client dose not answer the call (ignores alerting signal)

 Calling client stops the call before the called client answers

 Calling or called client disconnects

HOLDING SIP CONNECTION

Using WireShark capture the SIP messages used for holding active SIP connection. Check the following cases:

 Hold the connection

 Activate back the connection

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FINAL REPORT

Please prepare a document (in PDF format) containing the description of actions taken during the exercise, your observations and conclusions. The report should clearly describe your results, analysis methodology etc.

Attach the WireShark dumps (in .pcap format) collected during the exercise to the report. The pcap files should contain only filtered SIP messages (frames relevant to the exercise that contains the SIP messages).