Universal Serial Bus
Frequently Asked Questions

1. What is USB?

• USB stands for Universal Serial Bus. It is a standard that has been adopted by leading manufacturers within the computer industry to define a new type of peripheral connection scheme. It is designed to replace older parallel and serial ports, cables, and connectors with something faster and easier to use.
• USB is made up of a number of parts. At the core, your computer must be running an operating system that supports USB (A PC with Windows 98, a PC with Windows 95 OSR2, or the Apple iMac). Your computer will act as the host for the USB bus. This means that the computer becomes responsible for communicating with all attached USB devices so that it knows what to do with them, what they are doing, etc.
• USB peripherals (like mice, keyboards, joysticks, scanners, printers, cameras, speakers, network adapters, etc.) can be either attached directly to a PC via USB ports built onto your computer or provided by either bus-powered or self-powered USB hubs. The host (your computer) then recognizes the device when attached, loads any necessary drivers, and lets you use the device without even having to reboot. If you decide to attach a different device you can simply unplug the connected device, attach the new one and it too will be automatically recognized repeating the cycle.
• USB will use a single cable and two connector types. The "A" type or downstream connector will always be plugged into the direction of your peripherals. The "B" type or upstream connector will always be plugged in the direction of your computer. For example, in a configuration with a computer, 2 USB hubs, and a USB mouse the connectors will be as follows: the computer's "A" connector will connect to the first USB hub's "B" connector, one of the first USB hubs "A" connectors will plug into the second USB hub's "B" connector, and the mouse will be plugged into the second hub's "A" type connector. ([computer] A -> B [1st Hub] A -> B [2nd Hub] A -> mouse).
• Additionally USB can provide up to 500mA of power to connected devices. This will help to eliminate the need for separate power supplies for peripherals.

2. What are the benefits of USB?

• Easier to add new peripherals -- Windows 98 and Windows 95 R2 will automatically recognize devices when you plug them in.
• Quicker installation of new peripherals -- You won't have to reboot during installation.
• Faster -- Top USB data speed is around 100 times faster than the fastest serial connection.
• Greater Expandability -- Using USB hubs you can connect up to 127 devices to your computer, not just be limited to the number of serial ports, parallel ports, or IRQ's on your computer.
• Hot Swappable -- Changing connected USB devices is as easy as changing a light bulb, just disconnect the old and plug in the new. No need to power down or fumble with drivers. They just plug and go!
• Eliminates need for external power supplies -- fewer plugs to deal with, and lower cost peripherals.
• Meets OnNow industry initiative guidelines -- will help to build a future where the computer will be able to better manage power consumption and more seamlessly integrate into our lives.
• Lower peripheral costs -- will help drive down the cost of computer peripherals by eliminating external power supplies, allowing manufacturers to standardize their products to a single connector, creating a larger customer base by providing the same peripherals for Macs, PCs, and Portables, and reducing returns due to wrong connector types.

3. What is a USB hub?

• A USB hub typically consists of a single upstream port (designed to connect directly to your computer or to another hub) and multiple downstream ports. D-Link provides both 4-port (DSB-H4) and 7-port (DSB-7) models. It allows you to expand the number of devices you can attach to your computer.

4. How Many USB hubs can I connect together?

• In total you should only connect 5 tiers of USB hubs together. A tier is defined by the number of hubs a device's signal must pass through before it reaches the host. For example, using the DSB-H4, D-Link's 4-port USB hub, you could connect a theoretical maximum of 341 hubs in five tiers, this would leave you with an incredible 1024 ports to connect USB devices! But you should only connect 127 devices together at any time.
• Do not add a 6th tier of USB Hubs. This would violate the hub cascading rules, and the signals from any devices attached may not function properly.
• Be careful of any compound devices when attaching USB hubs together, they count as tiers too.

5. What is a compound device?

• Compound devices are defined as a combination of a USB function or functions with a USB hub. A good example would be a keyboard that has an additional USB port for a mouse to be attached. Even though the keyboard is a peripheral (a function), it is also a hub because you can attach another USB device to it. Effectively the keyboard has a hub inside.

6. What is the difference between self-powered and bus-powered USB hubs?

• A self-powered hub plugs into an electrical outlet so that it is better able to provide connected devices with power. Only low power USB devices can be connected to a bus-powered hub (like mice and keyboards). A self-powered hub will allow you to safely connect other devices that require up to the full 500mA outlined in the USB specification. D-Link offers self-powered and user-selectable self- or bus-powered hubs.

7. What kind of cables do I use with USB?

• USB cable will usually have both "A" type (downstream) and "B" type (upstream) connectors. Unshielded USB cables running at 1.5Mb will have a maximum cable length of 3 meters. Shielded USB cables running at 12MB will have a maximum cable length of 5 meters. This simple scheme will ensure that users will not be able to plug cables in wrong, since the connectors are unique in size and shape.

8. Will FirewireT (IEEE 1394) replace USB?

• No. Although IEEE 1394 is a faster standard for connecting peripherals, it is also much more expensive as a technology. In the future both USB and FirewireT will combine to meet the needs of computer users as complimentary technologies. FirewireT will be used to connect high-speed video cameras, external hard-drives, and other devices that need more than 12Mb of bandwidth. USB will survive to support printers, scanners, joysticks, modems, keyboards, mice, and other lower speed devices. At approximately 100 times faster than today's serial ports, USB is in a strong position to give a greater level of speed to users at a much more attractive price.

9. Will USB replace Ethernet as an alternative for home networking?

• No. Although USB is capable of providing a direct connection between multiple PCs, it is not intended as a replacement for networking. It has cable length limitation far shorter than Ethernet or Fast Ethernet at only 5 meters compared to 100 meters for Ethernet. USB networking schemes only connect a limited number of computers. Bandwidth in USB is shared among all connected devices. These are but a few of the issues that still make Ethernet a more desirable choice for home networking.

10. Do I have to replace my existing printer, modem, or other peripheral with a new one that supports USB?

• No. D-Link manufacturers a number of converters that allow you to connect your existing serial or parallel port devices directly to USB. The DSB-S6 and DSB-S15 convert serial to USB and the DSB-P6 and DSB-P15 convert parallel to USB. The DSB-H3SP USB Bay Hub has a parallel printer port and serial port built in to support these legacy devices.

11. Will D-Link make any network products that support USB?

• Yes. Aside from a full line of USB devices that will quickly and easily allow you to connect USB peripherals to your computer, D-Link will begin integrating USB into its networking products as well. USB to Ethernet adapters like the DSB-650 and DSB-650TX will allow you to quickly add Ethernet or Fast Ethernet connectivity to a USB ready computer. In the future, D-Link is planning to provide USB connectors on print servers, access servers, routers and other devices to make it even easier to network with D-Link.

12. How do I add USB support to Windows 95 OSR2?

• A patch is provided here, USBSupp.exe, to add USB support to Windows 95 OSR2. This is an executable installation file that will update your operating system.

13. How can I connect 2 PCs to each other with USB?

• There are a number of USB bridges on the market. These devices allow a direct connection between 2 PCs via their USB ports. However, D-Link recommends using a DSB-650 to add Ethernet networking via USB. Two computers can be connected either via an Ethernet Hub (DE-805TP/C - the "Hubby" is a great choice for a home network) or via a cross-over cable.

  USB bridges are limited in their functionality. They effectively work by accessing a shared piece of memory built into the bridge. Proprietary software is necessary to allow various computer resources to be shared. With Ethernet, native support in Windows 95 and Windows 98 allows you to quickly share printers and CD, DVD, and Hard Drives. With a simple addition of web proxy software, like Midcore's Midpoint Companion, you can also share Internet access.

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