Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus expansion or extension
Reexamination Certificate
2000-02-18
2002-04-30
Etienne, Ario (Department: 2155)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus expansion or extension
C710S100000, C710S305000, C710S316000, C710S062000
Reexamination Certificate
active
06381666
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and apparatus for transmitting signals between devices using Universal Serial Bus ports, and, in particular, to an method for allowing communications between devices using such ports over an extended range.
DESCRIPTION OF THE RELATED ART
Universal Serial Bus (USB) is a technology designed to permit a wide range of peripherals to be attached to personal computers by the average user. Since the technology supports all of the common peripheral devices such as keyboards, mice, speakers, modems, joysticks, cameras and many others, it will replace the serial and parallel ports in use today. The Apple iMac (Trade Mark), for example, supports only USB ports. In addition, almost every personal computer (PC) manufactured since 1997 has been equipped with USB ports.
USB was created by an alliance of seven of the largest companies in the computer and communication markets. Those companies were Intel, Compaq, Microsoft, NorTel, NEC, Digital and IBM. The specifications defining USB (e.g. Intel et al., Universal Serial Bus Specification, Revision 1.0, January 1996; and updated as Revision 1.1 in Sep. 23, 1998, and subsequent updates and modifications (such as draft Revision 2.0)—hereinafter collectively referred to as the “USB Specification”, which term can include future modifications and revisions) are non-proprietary and are managed by an open industry organization known as the USB Forum. The USB Specification establishes a number of criteria which must be met in order to comply to USB standards. The USB Specification also defines a number of terms, which definitions are adopted for the purposes of this specification.
For example, it is a requirement of Revision 1.0 of the USB Specification that a single USB domain shall support up to 127 devices operating over a shared medium providing a maximum bandwidth of 12 Mbps. Draft Revision 2.0 allows, however, a bandwidth of 480 Mbps, thus demonstrating modification of the USB Specification.
All known USB Specifications, however, currently limit the distance that a device can be separated from its host PC to 5 meters. By using a series of USB Hubs—devices that are intended to support increased populations rather than increased distances—this distance limitation can be increased, in theory, to 30 meters. This multiple hub solution is both expensive and clumsy. For example, to support a single device at a range of 30 meters the consumer must purchase five hubs at a current cost of about $50 US each. In addition, at least two of these hubs must be provided with electrical power. Since the individual cables between hubs are limited to 5 meters each, it is also likely that some of the hubs would have to be positioned in very inconvenient and insecure locations.
There is therefore a need for methods and apparatus to allow USB devices to be positioned at greater distances from the host PC. For example, an uninterrupted distance of at least 100 meters is required for compatibility with the standards governing the cabling of commercial buildings (see, for example, TIA/EIA-568-A, Commercial Building Telecommunications Cabling Standard, Telecommunications Industry Association, October 1995). Meeting this standard must be accomplished without the need for intermediate repeaters since distribution cabling is not normally accessible between its end-points at, for example, the Telecommunications Closet and the Work Area. Furthermore, even if the cable were to be accessible, the cabling standard does not allow active devices to be inserted other than at the end-points.
Providing for an extended range capability would also create new applications for USB devices as well as facilitating existing ones. For example, a simple residential or SOHO (small office, home office) surveillance system could be constructed by connecting consumer quality cameras to a central PC. An overhead mounted monitor could be controlled by a remote keyboard or mouse. A door-phone entrance system could be monitored from any office in a commercial building. Many other applications are possible.
Currently, however, the USB Specifications do not permit the use of extended ranges. For example, it is a further requirement of the USB Specification that the access of each device to the shared communications bus is controlled by a single Host Controller. It is also specified that when the Host Controller instructs a particular device to place its information onto the shared bus, the requested information must be received by the Host Controller within sixteen (16) “bit-times” of said Host Controller issuing said instruction. In practise, this ensures that the USB Specification provides for a high efficiency of bandwidth utilization by limiting the period during which no information is being transmitted. However, these requirements also limit the physical range of USB devices since one bit-time at 12 Mbps is equivalent to the time taken for an electronic signal to traverse approximately 17 meters of copper cable, and an even shorter distance for one bit-time at 480 Mbps. Further, although the USB device must respond to a request from the Host Controller within 16 bit-times, 7.5 bit-times is allocated for delay within a USB device and its associated 5 meter cable. This allocation retains only 8.5 bit-times at 12 Mbps for additional cable delay. The time represented by 8.5 bit-times is equivalent to the delay incurred by electronic signals in traversing approximately 144 meters of cable. However, this cable length is insufficient to satisfy the round-trip cable length of 200 meters required by the premise cabling specification.
Thus, it is not currently possible to provide USB devices which are separated over an extended distance.
However, it is a further feature of the USB Specification that the USB Specification (or protocol) segregates access to the shared bus into discrete units known as “frames”. Each frame is designed to last for a period of 1 ms.
Further, the USB Specification also requires that at least four separate types of data streams or “traffic” are recognized, namely isochronous transfers, control transfers, interrupt transfers and bulk transfers.
Isochronous data transfer is characterised as being a data transfer wherein data flows essentially continuously, and at a steady rate, in close timing with the ability of the receiving mechanism to receive and use the incoming data.
In particular, it should be noted that it is an aspect of isochronous transfers that timely delivery of information is ensured at the expense of potential transient losses in the data stream. In particular, there is no attempt to retransmit any data that may have been lost in previous transmissions. For example, With an isochronous video signal, loss of one frame of information is generally not significant, and there is no interest in retrieving the lost frame. Instead, the host controller is typically more concerned with transmitting or receiving the current frame. Accordingly, isochronous data transfer is said to be a “time-relevant” data transfer system.
This type of data transfer is distinguished from asynchronous data transfer, which pertains to processes that proceed independently of each other until a dependent process has to “interrupt” the other process, and synchronous data transfer, which pertains to processes in which one process has to wait on the completion of an event in another process before continuing. Accordingly, these data transfer methods are said to be non-time-relevant. Instead, a correct response to any request is required.
The current invention therefore uses the fundamental characteristics of isochronous and asynchronous data transfer, and more generally any time relevant or non-time-relevant data transmission, and the existence of regular protocol frames in order to provide methods and apparatus to enable data transmission over extended distances
SUMMARY OF THE INVENTION
Accordingly, while USB technology has proven to be useful, it would still be desirable to provide improvements to the technology by providing a method and appara
Kejser Keith
Krajci Juraj
(Marks & Clerk)
Etienne Ario
Igron Systems Inc.
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