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1. Broadcast (default): The program sends a ‘limited’ broadcast message on port 5151. It is limited because the message will be restricted to a single subnet (VLAN) and will not get forwarded by routers to other subnets. This can help reduce unnecessary network traffic across subnets and enhance connection security.

2. Multicast: This method sends a multicast message on port 5151 to the network's multicast address. Multicast messages can traverse across subnets (see Subnets to Scan), but you must make sure the routers allow multicasting. This is especially important for Wireless routers as most have multicast turned off by default.

Subnets to Scan:

The control program will automatically scan the current network for computers with the client program installed and running. You can set the program to search deeper into the networks by increasing the number of subnets to scan. (e.g. If you have many small sub-networks controlled by individual network routers, then increase the ‘Subnets to scan’ figure to bridge the routers.)

 If you choose this option, you can leave the default method of scanning for clients as 'broadcast' as this is more efficient. 

Imagine a scenario where a teacher in subnet A needs to connect to a classroom of 10 clients in Lab01 in subnet B.  To be able to do this, the teacher will need to create a classroom group of the clients as follows:

- From subnet A, she should try the first option above (enabling multicast) to scan for machines across subnets.  If there are problems finding the 10 machines in LAB01, she should get a list of the computer names of the 10 clients in that lab. 

If all the clients in LAB01 are visible in the AB Tutor Control window, she should

- select all these clients and go to Groups, Add to New Group. 
- Rename the Group to LAB01 by clicking on 'New Class', right-mouse clicking and selecting Rename.  

If she cannot see the clients in LAB01, she will need to add them to a new group manually:

- Go to Groups, Manage Groups
- Click on Add Classroom and give the Name 'LAB01' to the new group
- Make sure that the new group is selected
- Click on Add Computer
- Add the Computer Name of the first client in Lab01
- Click on Add Computer again to add the second client
- Keep doing this till all the 10 clients have been added
- Click on OK

Now, every time the program launches, or the 'Find' button is clicked, the teacher will be given the option to find all computers or to those in the group LAB01. 

 If you find that when you connect to a classroom group, you do not connect to the clients that you would expect, but seem to connect to machines at random, this may be to do with a problem with DHCP/DNS refreshing.  Please read the related article below - Sometimes ABTC seems to allocate names to machines at random.