What is the maximum number of devices that can be connected using a USB connector?
|
Table of Contents
USB Cable Length LimitationsWith the popularity of USB (it powers everything from our external hard drives to the charging of our
mobile phones), we are constantly amassing USB cables. USB 1.0/1.1 has been almost entirely supplanted by USB 2.0. Since USB 3.0 / USB 3.1 has yet to become as ubiquitous as 2.0 that means that most people have several 2.0 cables lying around. The mistake that most individuals make is when they take a 10 foot cord that came with a device and then purchase a 10 foot extension to make a cable that is 20 feet in total length. This kind of setup will not work and requires the use of
a special type of USB cable known as an active or repeater cable. But before we get to active cables or hubs, how long can a USB cable be? Show
Maximum length of USB 2.0 cable: The 2.0 specification limits the length of a cable between USB 2.0 devices (Full Speed or Hi-Speed) to 5 meters (or about 16 feet and 5 inches). In other words, you cannot just connect a bunch of extension cables together (like taking a 6 foot cord and extending it with 4
other 6 foot extension cords) and run them 30 feet to another room. However, you can connect a 6 foot cable with a 10 foot extension cable for a total of 16 feet, which is below the maximum cable length for USB 2.0. Maximum length of USB 3.0 / USB 3.1 cable:The 3.0/3.1 specification does not specify a maximum cable length between USB 3.0/3.1 devices (SuperSpeed or SuperSpeed+), but there is a recommended length of 3 meters (or about 9 feet and 10 inches). However, the biggest limitation to the length of the cable is the
quality of the cable. Results may vary, but with a high quality cable you should be able to go beyond 3 meters. However, to ensure you achieve the best results possible, use an active cable when going more than 10 feet (3 meters). How to break the USB length limitations:With the USB specs limiting the length of
cables, is there a way to extend those limits? Yes! However, in order to go beyond these cable length limits (or recommended lengths) you need to use self-powered USB hubs or active (repeater) cables; both of which have their own limits as well. Other options such as USB over Ethernet or building your own USB bridge can extend the USB range further. USB Hubs:You can use extension cables and self-powered USB hubs connected together to extend the range of your USB device. However, it is important to remember when using 2.0 hubs and cables that the distance between each powered hub can be no more than 5 meters (16 feet and 5 inches). When using 3.0/3.1 hubs and cables, do not exceed the recommended length of 3 meters (9 feet and 10 inches) between hubs. Note: It is possible to use bus-powered USB hubs, but you will
quickly run out of power as you extend your setup. Active (Repeater) Extension Cables:USB active extension cables contain electronics that regenerate the USB signal. Active cables are essentially 1 port USB hubs. You can use a regular USB cable in conjunction with an active cable as long as the regular cable is not
more than 5 meters (16 feet and 5 inches) long for 2.0 devices and not more than 3 meters (9 feet and 10 inches) long for 3.0 devices. Note: Typically, active cables are bus-powered cables. To ensure you receive the full 500mA power of a USB port, consider purchasing an active cable that includes a separate power adapter. USB Hub Limits and Maximum Length of Active CablesJust like there is a limit on a regular (passive) USB cable, there is also a limit on how long an active cable can be and how many USB hubs you can use. Maximum number of USB Hubs:The USB 2.0/3.0/3.1 specifications call for only 7 tiers of devices to be connected.
When you count the devices on each end (the host and the peripheral device), that only leaves 5 tiers available and a USB hub is considered 1 tier. Thus, only a maximum of 5 USB hubs can be used for a total maximum length of 30 meters (about 98 feet and 5 inches). Maximum length of USB active (repeater) cable:This
number depends if you are using a regular cable with an active cable or not. If you are not using a regular cable, then the maximum active cable length for USB 2.0 is 30 meters (98 feet and 5 inches) and the maximum recommended length for USB 3.0/3.1 is 18 meters (about 59 feet). If you are using a regular cable (max length of 5 meters for 2.0 and max length of 3 meters for 3.0/3.1) with an active cable, then the maximum length for USB 2.0 is 25 meters (about 82 feet) and the maximum recommended
length for USB 3.0/3.1 is 15 meters (about 49 feet). Is there any way to go beyond the limit of active cables or hubs?There are other ways you can extend a USB signal beyond the 30 meter limit. You can use USB over Ethernet to achieve distances up to 100 meters (about 328 feet). Additionally, you can build your
own USB bridge to transmit data over different communication channels such as wireless methods. What about USB 1.0/1.1?USB 1.0/1.1 has been superseded by USB 2.0 and USB 3.0/3.1. In addition, USB 2.0 cables are backward compatible so they will work just fine with any USB 1.0/1.1 devices. However, in case you are using a
1.0/1.1 USB host and device, there are limits to the maximum length of the cable. The limit for USB 1.0/1.1 cable length is 3 meters (about 9 feet and 10 inches) and the maximum total length should not exceed 18 meters (about 59 feet). |
