What is a USB hub?
A USB Hub allows you to connect a number of USB devices, such as mice, keyboards, USB flash drives and Printers to a single USB port on a host computer. They physically come in a variety of shapes and sizes, some are externally powered, and others derive their power from the host to which it is connected.
How Infinity uses USB
By default, an Infinity Transmitter presents itself to the host computer as 13-port USB Hub. The hub size can be reduced to 7, if required for compatiblity with much older host computers. Some older BIOS's will not work if the hub size is 13.
Port 1 of the 13-port USB Hub is taken by the Dummy keyboard (by default, optional). Older hosts will not boot passed the BIOS unless they detect a keyboard. The dummy keyboard tells the host that a keyboard is present even if the Transmitter is not connected to a Receiver.
The diagram shows two RX’s connected to the same TX. Each unique USB device takes a slot on the hub and identifies itself by using a VID and PID. A VID is a 16-bit vendor number (Vendor ID). A PID is a 16-bit product number (Product ID).
If you exceed the 13-port limit, a banner message will tell you that it has not been able to add all of the USB devices.
Port Merging
Infinity allows you to share a single Transmitter with multiple Receivers. As each receiver connects to the same transmitter, the USB devices from each receiver consume a USB hub slot on the transmitter.
It is possible to consume all the 13-ports on the Transmitter when multiple Receivers share the same channel. Therefore, Infinity uses a system called Port Merging, which consolidates USB devices that are identical together to reduce the number of slots required. Port Merging is enabled by default. Merged devices typically remain present on the transmitter's USB hub, even if all the receivers are disconnected. This is to avoid the need to re-enumerate the USB devices again when a receiver with the same device(s) connect, to speed up the channel switching time. However, if all the USB hub slots are taken and another USB device needs to be added, the transmitter will automatically remove identical merged devices that are no longer present to free up a slot.
For example, the diagram shows identical mice and keyboards from each receiver being merged on the transmitter:-
Not only does Port Merging merge USB devices from different receivers, it also merges devices that are identical on the same receiver. This can be a problem where identical devices need to be treated differently.
For example, if you had a dual Infinity transmitter and receiver, and you connected two identical touchscreens to the receiver, by default these devices would merge. This can have unexpected results, where touching one screen actually affects the other. Therefore, it is recommended that Port Merging is disabled on the USB ports where the touchscreens are attached to the Receiver.
Enabling/Disabling Port Merging
Depending on your setup, Port merging can be enabled/disabled in the following ways:-
- Point to Point: When connected point to point without an AIM Manager, you will need to connect directly to the Receiver's web interface. From the available menu options, choose "USB Settings". In the "Host Port Reservation" section there is a checkbox in front of four USB ports on the Receiver, i.e. Top Left, Top Right, Bottom Left and Bottom Right. To disable merging, simply untick the checkbox.
- AIM Manager: When using an AIM Manager, there are two places where the Port Merging can be set, either globally or on an individual receiver. The most common way is to configure the receivers independently as not all receivers may have the same USB devices. On the AIM Manager, navigate to the Receivers tab and click on the edit button for the receiver with devices you do not wish to merge. On the Receivers configuration page, scroll down to the USB Settings link and click it. In the Advanced Port Features section, you untick the merging function on each of the four USB ports on the receiver. Press Save USB Settings to commit the change.
Port Reservation
This is only available under AIM control. You can assign up to 8 of the USB ports on the USB hub (7 or 13 ports) that a transmitter presents to the host computer to dedicated devices. To set the number of reserved ports, on the AIM Manager, navigate to Dashboard, Settings and Transmitters. Scroll down the page and there is an option called "Reserved USB ports" and a drop-down list containing the number of ports that you wish to reserve.
Why would you need to use Port Reservation? Unlike identical keyboards and mice that can be merged and always present on the host, other USB devices are enumerated each time you connect a receiver to a transmitter. Operating systems like Windows, associate a USB port with a particular device and driver. Port reservation ensures that the host sees the device on a particular port allowing the enumeration (e.g., loading the driver) to occur faster.
Port Mapping
The location and mapping of the ports can vary by receiver model. On the AIM Manager, the USB ports are depicted as the layout of the ALIF1000R, ALIF1002R, ALIF2000R, ALIF2020R receivers.
The table below shows you how these ports are mapped on the other Receivers:-
| ALIF1000R, ALIF1002R, ALIF2000R & ALIF2020R | ALiF1100R ALIF2100R | ALIF3000R | ALIF4000R |
| Port | Port | Port | Port |
| Top Left | 3 | 3 | 2 |
| Top Right | 4 | 5 | 3 |
| Bottom Left | 1 | 4 | 4 |
| Bottom Right | 2 | 6 | 5 |
Points of Interest
- When you change this setting and press Save, the USB on all of your active connections will restart and the attached devices will be re-enumerated/setup. There may be a small delay in USB control whilst this occurs, therefore it is recommended that you do not change this setting if the system is currently in use.
- Only reserve the number of ports that you actually need. Unused reserved ports will take away some of the effectiveness of being able to access a transmitter by multiple receivers simultaneously with different keyboards and mice as there may not be enough free ports to accommodate them.
- If you allocate the same reserved port number to more than one receiver and you connect those receivers to the same transmitter, the transmitter will operate on a first come first served basis. Once the port has been occupied, any additional receiver wishing to use the same reserved port will be rejected and therefore the attached USB device will not operate.
To apply a reserved port you can either set this globally or on the individual receivers which will be the most common usage. On the AIM Manager. navigate to the Receivers tab and click on configure the Receiver. Scroll down to the USB Settings option and click on the Configure link.
For each of the four USB ports, the first drop-down list allows you to allocate one of the reserved ports to the receiver's USB port. Assign the reserved port number to the appropriate USB port where your dedicated USB device resides. Press Save USB Settings to commit the change. You may need to disconnect and reconnect the channel for the change to take affect.
Isochronous USB Devices
An isochronous USB device must send and receive a sequence of events regularly, at equal timed intervals. Any delays in receiving the data will cause glitches and/or could cause it to stop functioning. A webcam and USB Audio are examples of devices that are isochronous.
Infinity endpoints do not support isochronous devices. However, you can use our C-USB-LAN product alongside Infinity, which is a dedicated 4-port USB hub that does support isochronous. The C-USB-LAN Transmitters and Receivers can be controlled using an AIM Manger running firmware v4.5 and above.
There are settings that can be applied to the Receivers that can display a banner message should a user connect an isochronous device, to warn them that it is not supported. By default, this setting is disabled. There is also a setting that allows you to connect a mixed USB device that contains an isochronous device. For example, if you had a keyboard with a built-in speaker or microphone. This setting will allow the keyboard element to operate, however, the isochronous component would be ignored. These settings can be found in different locations, depending on your setup. For example, in a simple point to point setup without an AIM, this is configured on the receivers web interface under the USB Configuration section. In an AIM Managed setup, these settings can be either applied Globally (Dashboard -> Settings -> Receivers -> USB Settings) or individually by going into the Receivers tab, clicking edit on an appropriate receiver and then going into the USB Settings.