The Enterprise structure

As mentioned in 4.1 section the enterprise is composed by four sites. The corporate site and the three remote sites that are connect in a star topology [9]. The main advantage of this topology is that the remote sites are independent from each other. So if a site encounters problems doesn’t affect the others. On the other hand it introduces a single point of failure which is the corporate site. If this site has problems then the remote sites have problems too. The components of each site can be seen in the figures 7 and 8.

The central site is composed by the corporate Lan1 (implementing 10baseT technology which means 10Mbps over twisted pair cable [9] and 25 users), a switch (Cisco Catalyst 3550 of 48 interfaces at selectable data rates), the router (a CISCO7000 supporting 10 and 100Mps, along with ATM, Frame Relay and serial interfaces) and two servers (supporting database, printing, http and email services).

The other three sites which connect to the corporate Lan1 are composed by a lan (implementing 10baseT technology which means 10Mbps over twisted pair cable and 15 users), a switch (Cisco Catalyst 3550 of 24 interfaces at selectable data rates), the router (a CISCO3660 supporting 10Mbps along with serial interfaces).

The selected routers have integrated firewall and security capabilities and for this reason there is no need for a separate firewall unit. The firewall protects the sites from unauthorized access while providing encryption features for protection of sensitive data.

Figure 7: The Corporate Site Figure 8: The Remote Site

The internal components of the networks are connected with 10baseT links and the remote sites are connected to the corporate LAN with ISDN lines at 128kbps (between the routers, R1 with R2, R3 and R4 in a star topology).

The components of the scenario are easily inserted from large libraries that OPNET maintain. These components are inserted into the scenario by simple drag and drop in the graphical environment. This makes OPNET very easy for use even from less experienced users. The elements have default configurations set show anyone can built a scenario without special knowledge, while it can be used from professionals due to advanced features that it support.

After building thr network the next step is to configure the services that the network will provide and the profiles, indicating which services each LAN will use. As we can see at the top right corner of Figure 6 I have inserted (just the same as with the other components) an application and a profile definition node. In the application node I will configure the services that the network will support and in the profile node I’ll configure the profiles with the services that each profile will have.

Figure 9: Configured Services

As presented from Figure 9 I have configured the four services Database, Printing, Http and Email which are the most common among the enterprise’s users. Along with the services I define and the load that each service introduce into the network. As displayed in Figure 9 I chose the High Load for all the services. The reason for this decision is that if the network manages to function with the worst scenario of data traffic then it will have no problem in any other traffic situation.

With the same procedure I configure the profile that each LAN will adopt. There will be four profiles one for every service. It is simple, I first create the profiles and then I assign the appropriate service to each profile. As we can see from Figure 10 along with the service the profile can be configured with the time that it will be active. In this case the profiles are active from the start until the end of simulation.

Figure 10: Configured Profiles

The last step that remains before I simulate the scenario is to apply the profiles on each LAN and the destination server to each profile. All the LANs in the corporate and in the remote sites are configured with the four profiles which means that the users are work with all the services (database, printing, http, email) and also that the traffic in the network will be as heavy as it gets.

The database and print services will have as destination the DB_Print_Server. The http and email services will have the Http_Email_Server as their destination server. This is done by assigning to each of the application a destination server from those that are present in the network. The same configuration as with the corporate LAN will be applied to the remote LANs. This assignment is very important for the simulation because if there is no server assigned to the applications, after the simulation there will be no results presented. In the following figures we can see the configuration:

Figure 11: Supported Profiles

Figure 12: Destination Server

Now that I have the scenario build and configured I can advance to the simulation. The main approach is to first simulate the network with the configured basic services (database, print, http and email) and acquire the delay time of each service to use it as a reference point. Next I will introduce IP telephony into our network and examine the delay responses again and based on the delays, take the appropriate actions in order for the network to compensate the changes.