US 7,603,486 B2
Network management system providing logic signals over communication lines for detecting peripheral devices
Linh My Le, Mundelein, Ill. (US); Dwight D. Dipert, Fox River Grove, Ill. (US); and Ellen Oschmann, Winnetka, Ill. (US)
Assigned to 3Com Corporation, Marlborough, Mass. (US)
Filed on Nov. 26, 2002, as Appl. No. 10/304,218.
Prior Publication US 2004/0101133 A1, May 27, 2004
Int. Cl. H04L 29/00 (2006.01); H04J 99/00 (2009.01)
U.S. Cl. 710—7  [710/15; 710/17; 455/133; 379/414; 379/377] 26 Claims
OG exemplary drawing
 
26. A system for indicating and detecting the presence of at least one network device on a communications network, the at least one network device comprising a transmission line interface, the system comprising:
a first transformer circuit connected between a transmission line and a management device transceiver, wherein data signals are transmitted and received through the first transformer circuit;
at least one pull-up resistor connected between a first defined voltage and the transmission line, wherein the first defined voltage imparts a DC voltage component onto the transmission line, and wherein the magnitude of the DC voltage component is determined by a current flow through the at least one pull-up impedance;
a presence detector for detecting a presence of the at least one network device;
a low-pass filter coupled between the transmission line and the presence detector for generating an output from the DC voltage component and the data signals, the low-pass filter substantially eliminating the data signals while passing the DC voltage component;
a second transformer circuit connected between the transmission line interface and a network device transceiver, wherein the data signals are transmitted and received through the second transformer circuit; and
at least one pull-down resistor connected between a second defined voltage and the transmission line, the at least one pull-down resistor reducing the magnitude of the DC voltage component when the at least one network device transceiver is coupled to the management device transceiver, wherein the presence detector detects the presence of the at least one network device based on the output of the low-pass filter.