Communications: electrical – Selective – Interrogation response
Reexamination Certificate
1999-09-27
2004-07-13
Zimmerman, Brian (Department: 2635)
Communications: electrical
Selective
Interrogation response
C340S315000, C379S022010, C713S300000, C713S310000
Reexamination Certificate
active
06762675
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is related to the field of devices used in networks, and more specifically to network nodes that verify the power configuration of a device before supplying power to it.
2. Description of the Related Art
Integrated Services Local Area Networks (ISLANs) include nodes such as switches, gateways, routers, bridges, repeaters, etc. Network nodes are referred to generally below as network switches, but include any device used for processing information in a network. Endpoints connected to the network, such as Internet phones, can receive power along with data from the network switch. Such endpoints are called line powered devices.
An example of a line powered device is described with reference to
FIG. 1. A
network node, such as ISLAN Access Unit (AU)
12
, is connected to two devices
14
and
16
. Device
14
is a line powered telephone. Device
14
is connected to Port A of ISLAN AU
12
by a cable
14
a.
Switch
12
applies power remotely to device
14
. Applied power is depicted by voltage V
N
traveling over cable
14
a.
A serious problem exists when network switch
12
inadvertently applies power to a non-line powered device. In the example of
FIG. 1
, device
16
is unsuitable for remote line powering. Device
16
includes a network card
18
connected to Port B of ISLAN AU
12
by a cable
16
a.
Card
18
is not configured for receiving remote power from switch
12
. If switch
12
applies power over cable
16
a,
the incoming waveform V
N
can damage card
18
, as shown by a flash
18
a.
In conventional circuit switched networks, telephones are often powered through the telephone lines. However, the telephones in packet switched networks may or may not be powered remotely by the network switch
12
over the network cable. In packet switched networks, the switch can detect a device coupled to a port (assuming the device already has power), but does not know whether the device is suitable for remote powering before power is applied to the device. What aggravates the problem is that such devices are often connected to the network switch at remote locations. For example, telephones are typically powered from a central location (e.g. a wiring closet) instead of locally (e.g. in the same office). This makes it hard to configure the network for different line powered devices.
The problem is worsened in the event of loss of power. In the case of telephones, users have come to expect service under all conditions, including loss of power. The device must therefore operate without interruption when local power is not available.
Accordingly, a need exists for identifying line powered devices on a packet switched network.
BRIEF SUMMARY OF THE INVENTION
The present invention ascertains the suitability for remote powering a device from a network switch, before the network switch supplies power to the device. The network switch determines suitability by interrogating all coupled devices.
The switch sends a discovery signal to the ports connected to remote devices and monitors each port for a return signal. If a return signal is received, it is compared to the transmitted discovery signal. If the signals are identical, accounting for the expected signal losses in the wire, the coupled device is deemed suitable for receiving power remotely from the network switch. Accordingly, the network switch then supplies power to the line powered devices. If the network switch fails to discover any device, the switch periodically retries this discovery signal in order to detect new devices that are connected. The network switch also monitors ports that have power applied, looking for loss of signal, indicating that a device has been detached. Power then needs to be removed before another device is connected.
The invention eliminates having to preprogram the network switch with the type of devices connected to each port. This reduces the amount of time required to initially program the switch, and also eliminates having to reprogram the switch every time a new device is connected. The invention also eliminates having to reprogram the switch after loss of power. The invention is particularly useful in network locations without local power, or with a central power distribution facility that uses an uninterrupted power supply.
REFERENCES:
patent: 4173754 (1979-11-01), Feiker
patent: 4419666 (1983-12-01), Gurr et al.
patent: 4703306 (1987-10-01), Barritt
patent: 5544163 (1996-08-01), Madonna
patent: 5668857 (1997-09-01), McHale
patent: 5991885 (1999-11-01), Chang et al.
patent: 6021493 (2000-02-01), Cromer et al.
patent: 6218930 (2001-04-01), Katzenberg et al.
Robert Bell, “P802.9f Draft Standard Local and Metropolitan Area Networks -Supplement to Integrated Services (IS) LAN Interface at the Medium Access Control (MAC) and Physical (PHY) Layers, ”IEEE Standards Project,1997, pp. 1-24.
Cafiero Luca
De Nicolo Maurilio
Edsall Thomas
Hang Soei-Shin
Nakamura Karl
Marger Johnson & McCollom PC
Yang Clara
Zimmerman Brian
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