One USB camera will use most of the bandwidth on a USB bus (this is because USB cameras use uncompressed video, as opposed to network cameras, which use compressed video). Therefore, it is not possible to use more than one camera on the same USB bus at full resolution.

Although Mac computers typically have more than one built-in USB port, they vary in how many USB busses they have. In some Macs, all the ports share the same bus, and therefore the same bandwidth. On other Macs there may be multiple busses. To see how many busses your Mac has, open the “System Information” app (“System Profiler” on systems before OS X 10.7) from your /Application/Utilities/ folder. Click the “System Report” button, and locate the USB section on the left side of the window:

The above system report is for a late-2009 Mac Mini. This computer has five USB ports, and as you can see, it actually has four separate USB busses. The first bus powers the built-in IR Receiver and USB port number 2; the second bus powers the built-in bluetooth controller; the third bus powers USB ports number 3 and 4; and the fourth bus powers USB ports 1 and 5. Note that there is no way to tell from the above information which busses power which ports! You either have to find out this information online or through trial and error. Note also that only the second two busses are “High-Speed”, i.e. USB 2.0. The first two are USB 1.1 busses, which are much slower (useful for bluetooth, keyboards, mice and other low-bandwidth devices only).

So, with the above computer, if you wanted to use two USB cameras, you would plug one into port 1 or 5, and the other into port 3 or 4, so that they are on separate high-speed busses. If you were to connect a camera to port 2, it would work poorly, or maybe not at all, because this port is on a USB 1.1 bus.

Similarly, if you use an external USB hard drive, this should be on its own high-speed bus for optimum performance. Therefore, in the above example, we have one camera using one high-speed bus, and one USB hard drive using the other high-speed bus.

If your computer has PCI slots (a Mac Pro for example), you can add extra USB ports using PCI cards. Note however that such cards typically have only one bus, and share this bus between all their ports, so it is likely that you will need one PCI card per USB camera.

Our advice remains: use network cameras, which don’t suffer the same limitations, and are designed for the purpose of video surveillance with typically far superior video quality. SecuritySpy supports a wide variety.

A high-performance switch was required, and a Netgear FS116 was chosen:

This switch supplies power-over-ethernet (PoE) on 8 of the 16 ports, which is supported by both models of camera mentioned above, simplifying the wiring installation.

From my experience, it is not worth economising on such items of network hardware. Netgear is a company with a long history of making high-quality reliable products. You may be tempted by alternative cheaper products from little-known manufacturers but it is generally a false economy. The above switch costs around GBP £150, a small price to pay for such a critical component.

The first setup of the system was laid out as follows:

As you can see, the router connects the Mac Mini and the main switch – the router basically contains its own internal hub/switch that provides four ethernet ports. This setup was chosen because of the close proximity of the router and Mac Mini (therefore easier wiring), and also to implement as short a route as possible from the Mac Mini to the internet. As well as managing the video surveillance system, the Mac Mini is providing some important web server functionality to the internet, and the above layout means that a failure of the main switch would not cause an outage of these functions.

However, this setup was plagued with problems. There were frequent timeouts and disconnections in the communication between the Mac Mini and the cameras. Troubleshooting revealed that the problem was down to the router’s internal hub. As you can see from the above diagram, the traffic from the cameras has to pass through the router to get to the Mac Mini, and apparently the router’s hub wasn’t up to the task. This underlines the point made above about only using high-quality networking hardware – a point apparently ignored by router’s manufacturer. So, the topology was changed as follows:

Now, the Mac Mini connects directly to the main switch. The traffic from the cameras goes straight through the main switch to the Mac Mini, and the router doesn’t see any of this traffic. Since the change, performance has improved and reliability has been flawless.

The above switch works at “fast ethernet” speeds, up to 100Mbps. This works well for the system described above, which has only four cameras. With more cameras, this speed limitation may start to impact on performance (depending of course on the cameras’ resolutions and your desired frame rates). The solution is to to use a gigabit switch, which offers speeds 10 times that of fast ethernet. For this I would recommend the Netgear FS728:

As well as 24 fast ethernet ports (all of which provide PoE), this switch offers four gigabit ethernet ports, one of which you would use to connect the computer. This removes the speed limitation and will allow you to connect many more cameras without any problems of network bandwidth. In addition, this is a managed switch, so has a web interface that has some useful statistics as well as other features such as cable tests – very handy for troubleshooting network connections.