Pulse or digital communications – Transceivers
Reexamination Certificate
1998-10-30
2002-05-21
Ghayour, Mohammad H. (Department: 2734)
Pulse or digital communications
Transceivers
C375S220000, C375S222000
Reexamination Certificate
active
06393050
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to home network computer systems, and more particularly, but not by way of limitation, to a transmit/receive switch utilized in a 10Base-T Ethernet data communications system, that provides data communication between computers and peripherals over a two-wire medium.
BACKGROUND OF THE INVENTION
As more appliances and items in the home become computer controlled, and as more homes obtain multiple computer systems with associated peripherals, the importance of a home network for allowing data communications between computer systems, automated appliances, and peripherals within a home is increasing. While many high speed networking alternatives are available for businesses, which generally have a greater capability for investment in networking resources, choices for a home network are limited by practical and economic factors common to the typical household. Systems designed especially for home networking may require expensive custom hardware having marginal or negligible performance advantages giving rise to unattractive price vs. performance tradeoffs. On the other hand, the cost associated with rewiring a home to provide cable capable of carrying signals at network frequencies typical of existing network technology, such as Baseband Ethernet, using existing network hardware can be prohibitive for most households.
Baseband Ethernet technology is commonly used in businesses for providing network connectivity, and has evolved into successively more robust forms over many years. One commonly used baseband Ethernet technology is know as the 10BASE-T network. The 10BASE-T network has an operating rate of 10 Mbps, is compliant with LAN 802.3 standards and specifications, and thereby provides moderate to high speed interconnectivity between many workstations and peripherals for most applications.
In a conventional business LAN application, workstations and peripherals, such as printers and disk towers are wired together to allow shared access, data transfer, and communication between individual user workstations and network devices. A typical 10BASE-T network interface card (NIC) is located at each workstation and network device and accommodates two pairs of unshielded twisted-pair wire. Under the 10BASE-T standard, one twisted pair is used for data transmission and one twisted pair is used for data reception. Due to the specialized nature of the interface circuitry and the common mode noise rejecting capability of the “twisted” configuration of the actual wire pair or, alternatively, the noise rejecting capability of shielded coaxial cable, relatively high data rates may be achieved. In the typical home however, existing coaxial cables for cable TV service cannot be used to transmit data because of the resulting signal interference, and twisted wires pairs are unavailable. Accordingly, high data rate networks are not possible without expensive rewiring.
One solution to the home networking problem has been to use existing phone lines to transmit data. Conventional subscriber line wire pairs however, are traditionally contemplated for narrow band voice transmission in the range of 0 to 4 KHz. Physical limitations arise related to, for example, signal-to-noise ratio, which have traditionally limited the maximum frequency capable of being transmitted over normal phone lines, making it possible for only relatively low data rate signals to be transmitted. As a result of such limitations, the overall cost and complexity of bringing high data rate network communications to the home environment has typically been prohibitive, although some home network systems have been attempted.
One example of a prior art home network is the TUT Systems, HR1300T. The HR1300T uses a “time modulation line code” to provide an in-home network over existing phone lines with a modulation scheme providing a data rate of 1.3 Mbps. While 1.3 Mbps provides an improvement over the data rates achievable with, for example, standard modem technology, the HR1300T requires a proprietary protocol incompatible with 10Base-T Ethernet standards. Accordingly, CSMA/CD protocols cannot be implemented.
Other proposed solutions to home networking include standard modem technology, digital subscriber line (XDSL) technology, and wireless technology. Standard modem technology has traditionally been limited to data speeds of 56 kbps and requires very complicated circuitry and high quality line characteristics not reliably available in a typical home. Although, xDSL technology can transmit data at a much higher rate than standard modem technology, up to 4 Mbps, the cost of implementation of xDSL is very high and requires very complicated modulation methods. High quality line characteristics, such as signal-to-noise ratio, may also be required with xDSL technology to meet theoretical objectives.
Wireless solutions allow for connectivity between elements, typically using frequencies around 900 MHz, but have certain drawbacks. Since wireless portable phones and are often operated in neighboring bands there is a high likelihood of signal interference between a wireless LAN and portable phones or household devices such as, televisions, computers, garage door openers, alarm systems, and the like. Moreover, CSMA/CD protocols, essential to proper handshaking and collision avoidance between network elements, are far more difficult to implement and more unreliable in a wireless application. Without reliable compliance with CSMA/CD protocols a properly functioning, standards compliant 10Base-T network will not be possible.
CSMA/CD is an acronym for “Carrier Sense Multiple Access with Collision Detection”. In a CSMA/CD network, transmission channels are normally open for transmission on a continuous space available basis. Devices communicate when necessary, subject to whether the transmission media is clear, essentially “competing” for transmission time. Since Ethernet protocols are largely packet based, and packets are generally designed to be relatively small (1Kbyte), a given device is not expected to occupy a channel for an inordinate amount of time. It is still possible, due for example to propagation delay, for collisions to occur even though the protocol is designed to avoid collisions.
A conventional four wire 10Base-T Ethernet network with CSMA/CD typically avoids collisions by sensing the presence of a signal on the receive pair at the network interface controller (NIC) and inhibiting transmissions initiated by the NIC over the transmit pair during such intervals. If a collision occurs, an Ethernet compliant network device immediately stops the transmission of a frame as soon as a collision has been detected. By stopping the transmission, greater efficiency is achieved. To recover from the collision, the network device waits an interval then retransmits. If a collision occurs on the second attempt, the device waits for a longer interval before retransmitting. The process of waiting for progressively longer intervals is called “backoff.” Each time the device senses a collision on a subsequent transmit attempt, the time between making a transmission attempt will be increased by a small constant factor, leading to “exponential backoff.” After a limit is reached, data is simply lost.
Because, a typical Ethernet NIC has four wires, a two wire transmit pair and a two wire receive pair which are wired at all times to the network, the CSMA/CD protocol is active at all times. A problem arises however in the home network environment where only a single pair of wires is available. In such an environment, CSMA/CD has not been possible since only one of the two pairs may be connected to the two wire phone line at one time.
Therefore, as can be appreciated, there is a need to provide a CSMA/CD compliant home network that is easy-to-install-and-use, that is available at a low cost, and that can provide high data rates while taking advantage of existing two wire phone lines.
SUMMARY OF THE INVENTION
The present invention overcomes the above identified problems as well as other shortcomings and deficien
Compaq Information Technologies Group L.P.
Conley & Rose & Tayon P.C.
Ghayour Mohammad H.
LandOfFree
Transmit/receive switch for 10BASE-T home network does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transmit/receive switch for 10BASE-T home network, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transmit/receive switch for 10BASE-T home network will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2907016