Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-11-10
2002-05-14
Ngo, Ricky (Department: 2731)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S465000
Reexamination Certificate
active
06389029
ABSTRACT:
FIELD OF INVENTION
The invention relates in general to local area networks and in particular to local area networks incorporating Universal Serial Bus (USB) capabilities.
BACKGROUND OF THE INVENTION
The computer industry has recently formulated a new serial bus standard for interfacing peripherals and devices to computers. The new serial bus standard is known as a Universal Serial Bus (USB). The USB is a four wire bus which supports isochronous and asynchronous communications, multiple sub-channels of varied payload sizes for fan out of up to 127 USB devices (including low power USB devices), integrated powering for low power USB devices, simple connectors and hot plug and play for easy addition and removal of USB devices by a user. The Universal Serial Bus has its own protocol, the USB protocol, which supports two transmission speeds, full speed (12 Mbs) for full speed USB devices and low speed (1.5 Mbs) for low speed USB devices.
FIG. 1
shows a computer network comprising a host computer, a Universal Serial Bus, and a plurality of USB devices. In particular, a USB interface (typically called a root hub interface or root hub device) from the host computer offers at least one USB port but typically offers a plurality of USB ports (e.g. 2 which share a specified bandwidth of the USB interface) to which the USB devices may connect over cables not exceeding 5 meters. Additional USB devices can be supported in the bandwidth through the use of a special type of USB device, a USB hub device. Up to five USB hub devices may be daisy chained. That is, a first USB hub device may be connected, to one of the USB ports of the USB interface with a cable not exceeding 5 meters. The first USB hub device typically provides a number of additional USB ports (e.g. 4) to which additional USB devices may be connected over cables not exceeding 5 meters. A second USB hub device may be connected to one of the USB ports of the first USB hub device by a cable not exceeding 5 meters. Up to 5 USB hub devices may be daisy chained in this way. The length of each cable segment cannot exceed 5 meters (i.e. the reach limitation of each cable segment is 5 meters). Only USB devices, other than a USB hub device, may be connected to the fifth USB hub device. Consequently, the furthest a USB device can be from the host computer is 30 meters (six 5 m cables). i.e. the total reach limitation is 30 meters according to the USB protocol. There are a variety of USB devices that can be connected to a Universal Serial Bus ranging from: printers, scanners, video cameras, keyboards, monitors, telephones, label printers, bar code readers, modems, disk drives, etc. Many of the new computers sold today, (such as personal computers (PC's) and the new iMac*), have at least one USB port.
* Trade-mark
Many of the USB devices which can be connected to the host computer via the Universal Serial Bus can also be advantageously used for applications running over a communications network (such as a local area network (LAN) or a wide area network (WAN)), to allow remote computers, servers or even telephone switches to exploit their functionality. Communication software and hardware within the host computer can mediate the connection between the communications network and the Universal Serial Bus, but this solution has drawbacks. The host computer used to mediate the connection between the communications network and the Universal Serial Bus can suffer from common reliability problems caused by the host computer being crashed, the host computer being infected by a virus, the host computer being powered off or even the host computer being removed (e.g. a notebook PC being used as the host computer). Furthermore, for USB devices placed in conference rooms, reception areas, hotel rooms, etc., deploying at least one host computer (such as a PC) in every such room is usually not practical nor cost efficient. Furthermore, many devices, such as a telephone, do not inherently need or use the functionality of the host computer beyond the network connectivity it provides. The invention disclosed herein will address these drawbacks.
Each USB hub device (including the root hub interface or root hub device) has a hub controller for controlling the USB ports (also called sub-tending ports). The hub controller can be accessed via data transfers on the Universal Serial Bus between the host computer and the USB hub device.
The host computer runs Operating System software (OS) that includes USB host software, client software and device drivers. The USB host software manages the Universal Serial Bus. The client software is typically one or more software programs for one or more applications such as word processing, communications, spreadsheets or software programs (including device drivers) designed to interact with external devices such as printers, scanners, modems, etc. The client software and the USB host software interact with each other. (Discussed in more detail later).
Once a USB device (including a hub device) is first connected to a USB port, the USB host software assigns a unique USB device address to the USB device. A given USB device typically has a plurality of sub-functions contained within it. The host computer interacts with each sub-function by exchanging data with a corresponding unique end point within the USB device. Each end point has a unique end point number.
Every USB device has at least one end point, end point
0
(sometimes called control end point
0
), which is a control end point for the device (e.g. the hub controller for a hub device is addressed through end point
0
). Through interaction with the control end point
0
, the USB host software in the host computer can determine what other end points are available on the USB device for interactions with client software as well as configure these end points or reset the USB device. All the other end points (i.e. all the end points other than the control end point
0
) are sometimes called functional end points. A functional end point can either receive data from the host computer or transmit data to the host computer but not both. Only the control end point
0
can both receive data from the host computer and transmit data to the host computer.
Each USB port uses four wires, two data wires for data transmission and reception and two wires for carriage of power (one 5 volt source power wire and one ground wire).
Each USB hub device detects the connection or disconnection of USB devices from the USB hub device by sensing the amount of current flowing through each USB port. As mentioned earlier, two general types of USB devices can be connected to a USB hub device, low speed USB devices which operate at the low speed (1.5 Mbs) and full speed USB devices which operate at the full speed (12 Mbs). These different USB devices cause different current draw characteristics when attached to a USB port in order that a full speed USB device can be distinguished from a low speed USB device. When a low speed USB device is connected to a USB port, the USB port is sometimes called a low speed port. Similarly, when a full speed USB device is connected to a USB port, the USB port is sometimes called a full speed port.
Every USB hub device manages the status of each of its USB ports. When a USB device is first connected to one of the USB ports of a USB hub device, the USB hub device changes the status of the USB port from a disconnected state to an attached state. In the attached state, regular bus communication does not flow through the USB port to the USB device. When a USB device is disconnected from one of the USB ports of a USB hub device, the USB hub device changes the status of the USB port to the disconnected state. The USB host software polls each hub device periodically and the USB hub device indicates whether the status has changed for any of its USB ports. Once the USB host software has received indication of a status change for one or more USB ports, the USB host software will issue commands to the hub controller of the USB hub device (via its control end point
0
) to determine
Ngo Ricky
Nortel Networks Limited
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