POWER AND DATA TRANSMISSION OVER ETHERNET NETWORK

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to telecommunications, and particularly to the transmission of power and data between electronic devices over Ethernet networks.

BACKGROUND OF THE INVENTION

The IEEE 802.3 standard for Ethernet type local area networks (LANs) has been universally adopted by the network industry. A relatively recent addition to the IEEE 802.3 standard is the IEEE 802.3af standard, which specifies the delivery of power over Ethernet. Particularly, the IEEE 802.3af standard describes the use of two pairs of four- pair Ethernet cables for the delivery of power, and includes specifications for power sourcing equipment ("PSE") and powered devices ("PD").

Powered Ethernet networks conforming to the IEEE 802.3 standard typically use a star- connected topology, with each networked device connected separately to a central core device, such as a hub or switch, as illustrated in Figure 1 , which supplies power to each of the devices over an Ethernet cable connecting the networked device to the core device. As a star-connected topology requires a separate cable for each networked device, the cost of multiple cables for multiple networked devices can be considerable. Also, the addition of any new connected device to the network requires installation of a new cable from the core device to the networked device, unless cabling has already been provided to the intended location of the new connected device.

Multidrop Ethernet networks have the advantage that multiple networked devices can be connected in a daisy-chain arrangement. However, this arrangement suffers the disadvantage that each networked device must be independently powered.

SUMMARY OF THE INVENTION

Although a star-connected topology is for various reasons regarded as the network configuration of choice for many applications, there are applications where a multidrop bus structure offers advantages - particularly in terms of cost and flexibility.

The invention therefore provides a multidrop Ethernet network, wherein both data and power according to the IEEE 802.3af standard are provided to networked devices. The invention also extends to devices configured for operation in such a network.

According to a first aspect of the invention, there is provided a multidrop Ethernet network, including a first device; a second device; and a third device; the devices being connected in a daisy-chain arrangement by means of a first Ethernet cable connecting the first device to the second device and a second Ethernet cable connecting the second device to the third device; and wherein the first device supplies power to the second device via the first Ethernet cable; and characterized in that the second device supplies power to the third device via the second Ethernet cable.

The first device may be powered from an external power source, such as electrical mains.

The first device may be a PSE as defined in IEEE 802.3af.

At least one of the second device and the third device may be a PD as defined in IEEE 802.3af. At least one of the second device and the third device may be a PD substantially complying with IEEE 802.3af. Each of the second device and the third device may be a PD as defined in IEEE 802.3af.At least one of the first Ethernet cable and the second Ethernet cable may be a Category 5 cable. At least one of the first the network cable and the second network cable may be a Category 5e cable.

According to a second aspect of the invention, there is provided a device, having a first port and a second port, and configured to both receive and transmit data in an Ethernet network via each of the first port and the second port, and to receive power provided according to IEEE 802.3af via the first port from an upstream device connected to a first Ethernet cable connected to the first port; characterized in that the device is configured to feed power received via the first port to provide power to the second port so as to power a downstream device via a second Ethernet cable connected to the second port.

The device may include a switch, configured to identify data intended for the device and to route such data to an application associated with the device.

The device may include data format conversion means, by way of any of a variety of well known such conversion means, configured to convert TCP/IP data to serial data.

The device may include power connections and data connections, which may be connected to the first port and the second port via magnetics.

The device may include a power acceptor controller unit, such as the Linear LTC4257 manufactured by Linear Technology, or a similar unit.

The device may include a power deliverer controller unit, such as the Maxim MAX5922A manufactured by Maxim Integrated Products, Inc., or a similar unit.

The device may include a power supply unit, configured to draw power from the power received via the first port and to supply power to an application associated with the device.

At least one, and preferably both, of the first port and the second port is an RJ-45 port.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates a block diagram of an exemplary, prior art data-only Ethernet network system having a star-connected topology;

Fig. 2 illustrates a block diagram of an exemplary prior art data and powered Ethernet network system having a star-connected topology;

Fig. 3 illustrates a block diagram of an Ethernet network in accordance with the invention; and

Fig. 4 illustrates a block diagram of the design of an example connecting device in accordance with the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

The invention will be described using the network 1 illustrated in Fig, 3.

The network 1 comprises a powered core device, which in the illustrated embodiment is an injector hub 2 (but could equally be a switch); and a plurality of networked devices 3.1 to 3.4.

The injector hub 2 is provided with AC power, and includes both data-only ports and data- and-power ports, which in addition to permitting the transmission of data provide DC power to the connected devices 3.1 to 3.4. In the illustrated embodiment, these ports are RJ-45 ports.

The devices are daisy-chained, and DC power and data for all of the networked devices is sent along a single, standard CAT5 cable 4 with RJ-45 connectors (not shown), running between the injector hub and the first networked device 3.1.

Each of the networked devices 3.1 to 3.4 is provided with a transmitter-receiver, such as the one described more fully below with reference to Fig. 4, capable of both the receipt and onward-transmission of both data and power according to the IEEE 802.3af standard. The transmitter-receiver may be built into the device, or may be provided by way of a separate transmitter-receiver unit.

A transmitter-receiver unit 10 for a networked device in accordance with the invention is illustrated in Fig. 4. The transmitter-receiver unit 10 includes a first, upstream port 1 1 and a second, downstream port 12. The unit 10 is configured such that each of the ports 1 1 and 12 is capable of receiving and transmitting data, and such that the upstream port 11 is capable of receiving DC power from an upstream device (not shown), and in turn delivering DC power to both the associated networked application 13 and the downstream port 12, so as to power a downstream networked device (not shown).

In the unit 10 shown, the upstream port 11 is connected through an RJ-45 connector and Ethernet magnetics 14, and power is provided to a power acceptor controller unit 15, such as the Linear LTC4257 manufactured by Linear Technology or a similar unit. Power is fed

from the power acceptor controller unit 15 to a power supply unit 16 for powering the connected networked application 13, and to a power deliverer controller unit 17, such as the Maxim MAX5922A manufactured by Maxim Integrated Products, Inc. or a similar unit. The power deliverer controller unit 17, in turn, delivers power to the downstream port 12 via Ethernet magnetics 18 and an RJ-45 connector.

Data is transmitted to and received from each of the RJ-45 Ethernet ports (through magnetics 14 and 18 to an Ethernet switch 19; in the illustrated embodiment a Micrel KS8993M Layer 2 Ethernet switch, or similar.

The Ethernet magnetics 14 and 18 may be integrated within the RJ-45 connectors, or may be discreet components.

All data messages sent on the network comply with the IEEE 802.3 standard, which provides that the basic data frame format includes a 6 byte destination address field, identifying the addressed device.

Accordingly, the transmitter-receiver associated with each networked application 13 is configured to listen for data messages addressed to that networked device, and to transmit an accordingly addressed data message to the networked application 13, and onwardly transmit data messages not addressed to the associated networked application 13.

It will be appreciated that numerous embodiments of the invention could be made without departing from the invention as described and claimed herein.