High impedance probe for monitoring fast ethernet LAN links

A high impedance tap for monitoring traffic over a communication link of a fast Ethernet local area network (LAN). The circuit of the present invention is advantageously used for tapping into a fast Ethernet communication link (e.g., bi-directional communication channel) of a LAN using, for instance, 10/100 BaseT Ethernet communication protocol. The novel circuit is particularly useful in point to point communication links (e.g., supporting fast Ethernet communication) where two communication nodes are coupled together using a bi-directional communication link (e.g., two twisted pair cables). Unlike the prior art monitoring probes, the probe of the present invention does not insert itself in series between the communication link, but rather taps onto the communication link in parallel using a high impedance termination circuit thereby leaving the existing communication link undisturbed electrically. By leaving the communication link undisturbed electrically, the probe of the present invention does not introduce latency into the communication link nor does it interrupt the communication link for any reason (e.g., during auto-negotiation sessions or on power down, power interruption, etc.). The high impedance value selected for the present invention is approximately one order of magnitude greater than the individual termination impedance of the communication nodes. The particular termination circuit used can employ a parallel coupled resistor with optional capacitors coupled to each wire of a twisted pair cable. The probe can be attached to a number of different statistics gathering systems (e.g., of the RMOD and RMOD2 standard) or various types of traffic accounting systems.

BACKGROUND OF THE INVENTION
 1. Field of The Invention
 The present invention relates to the field of local area networks (LANs)
 using the Ethernet communication protocol (e.g., the IEEE 802.3 Standard).
 Specifically, the present invention relates to a probe design for
 monitoring information transmitted over a point to point communication
 link of a fast Ethernet LAN.
 2. Related Art
 Networked communication systems ("networks") are very popular mechanisms
 for allowing multiple computer and peripheral systems to communicate with
 each other. Local area networks (LANs) are one type of networked
 communication system and one type of LAN is the Ethernet communication
 standard (IEEE 802.3). One Ethernet LAN standard, 10 BaseT, communicates
 at a rate of 10 Megabits per second while another Ethernet LAN standard,
 100 BaseT, communicates at a rate of 100 Megabits per second.
 There are many well known reasons for which the traffic over a LAN is
 monitored and monitoring typically uses probes and monitoring equipment.
 FIG. 1A illustrates a prior art Ethernet LAN system 10 using the 10 BaseT
 communication standard in which traffic is monitored. In system 10,
 several communication nodes (e.g., computer systems) 12-18 are
 individually coupled through communication links to ports of a repeater
 hub ("repeater") 20. The repeater hub 20 repeats every communication it
 receives from a node to all other nodes that are coupled to the ports of
 the repeater 20. Therefore, in order to monitor the traffic of the entire
 system 10, a single probe 22 can be coupled to a port of the repeater 20
 and it then receives all messages that are broadcast by any node 12-18.
 Although the monitoring configuration of system 10 is relatively straight
 forward, its communication speed is relatively slow because the technology
 requires that all messages from one node be repeated (e.g.,
 re-transmitted) by the repeater 20 to all communication nodes in system 10
 thereby reducing the overall bandwidth of system 10.
 FIG. 1B illustrates a point to point communication link 40 within a fast
 Ethernet LAN system that allows much faster communication rates compared
 to the 10 BaseT system 10 of FIG. 1A. In fast Ethernet, e.g., of the 100
 BaseT, 100 BaseT2, 100 BaseTX, or 1000BaseT communication standards,
 repeater hubs are replaced by equipment (e.g., switches, managed hubs,
 etc.) that establishes point to point communication links 46 between two
 communication nodes 42 and 44. In this framework, a message sent from one
 node to the switched hub is not automatically repeated to all other nodes
 coupled to the switched hub, but is rather communicated only to a select
 number of other nodes, or, only communicated to a single other node, as
 shown in FIG. 1B. In the system of FIG. 1B, it is not uncommon for one
 communication node 42 to have its own bi-directional communication link 46
 with another communication node 44. In fast Ethernet LAN systems, the only
 way to monitor the traffic over the system is to monitor the communication
 traffic over individual communication links 46 that the system forms
 between the various communication nodes of the LAN.
 As shown in FIG. 1C, within fast Ethernet LAN systems, probe equipment 52
 is inserted between prior art communication link 46. This causes the
 communication link 46 (FIG. 1B) to be separated into two links 46a and 46b
 that individually link the probe 52 to node 42 and the probe 52 to node
 44, respectively. Once inserted between the communication link 46, the
 probe 52 can gather any required traffic information with respect to the
 communication link between nodes 42 and 44. However, probe 52 electrically
 interrupts the communication link 46 because it is inserted in series with
 the nodes 42 and 44.
 There are several disadvantages to the probe configuration shown in FIG.
 1C. The first disadvantage is that power down and power interruption
 protection circuitry must be placed within the probe equipment 52 because
 if a power interruption occurs, communication between links 46a and 46b
 will become broken. This power down and power interruption protection
 circuitry typically includes one or more relays that are used to bypass
 the monitoring circuitry within probe 52 if power should be interrupted or
 removed from the probe 52. The relay circuit within probe 52 then restores
 the communication link 46 during periods of power interruption. However,
 this circuitry is very expensive and adds to the overall cost of the probe
 equipment 52. Further, the power interruption prevention circuitry does
 not switch immediately after the power failure, but rather requires some
 latency period to restore the communication link 46. During this latency
 period, the communication link 46 is broken which can cause data loss
 and/or initiate an auto-negotiation session between node 42 and node 44.
 Both of these factors further delay communication over point to point
 communication link 46. It would be advantageous to provide a probe that
 eliminates the need for power down and power interruption protection
 circuitry.
 The second disadvantage to the probe equipment configuration of FIG. 1C is
 that the probe 52 must act as a repeater in repeating messages received
 from node 42 for node 44 and in repeating messages received from node 44
 for node 42 because the probe 52 is inserted in series between node 44 and
 node 42. The act of repeating these messages introduces unwanted latency
 in the communication between nodes 42 and 44. It would be advantageous to
 provide a probe that eliminates the need to repeat messages between the
 linked nodes of a point to point communication link.
 The third disadvantage to the probe equipment configuration of FIG. 1C
 originates due to auto-negotiation sessions between node 42 and node 44.
 When probe equipment 52 is first placed between communication link 46, the
 link 46a auto-negotiates between probe 52 and the node 42. Simultaneously,
 link 46b auto-negotiates between probe 52 and the node 44. Each
 auto-negotiation session is independent and can, unfortunately, result in
 an auto-negotiated speed of 10 Megabits for one node (e.g., node 42) and
 100 Megabits for the other node (e.g., node 44). This is an impermissible
 result as the probe equipment 52 is not configured to allow split rate
 communication between its two different ends. Therefore, specialized
 software is included within the circuitry of probe 52 to: (1) detect when
 split rate communication is auto-negotiated; and (2) force the higher
 communication rate down to 10 Megabits. This specialized software is
 expensive and adds to the overall cost of the probe 52. Further, the
 auto-negotiation sessions initiated by an inserted probe 52 and the
 specialized software (1) takes time to determine if split rate
 communication was auto-negotiated and also (2) takes time to alter the
 communication rate of one of the links (e.g., link 46b). Each of the above
 further introduces unwanted latency in the communication between nodes 42
 and 44. It would be advantageous to provide a probe that eliminates the
 need to auto-negotiate with each communication node of a monitored point
 to point communication link.
 Accordingly, the present invention provides effective probe and monitoring
 equipment that can be used for monitoring traffic over a point to point
 communication link but eliminates the need for power down and power
 interruption protection circuitry. The present invention further provides
 a probe and monitoring equipment that can be used for monitoring traffic
 over a point to point communication link but eliminates the need to repeat
 messages between the linked nodes. Also, the present invention provides a
 probe and monitoring equipment that can be used for monitoring traffic
 over a point to point communication link but eliminates the need to
 auto-negotiate with each communication node of a monitored communication
 link. These and other advantages of the present invention not specifically
 mentioned above will become clear within discussions of the present
 invention presented herein.
 SUMMARY OF THE INVENTION
 A high impedance tap is disclosed for monitoring traffic over a
 communication link of an Ethernet local area network (LAN). The circuit of
 the present invention is advantageously used for tapping into a fast
 Ethernet communication link (e.g., bi-directional communication channel)
 of a LAN using, for instance, 10/100 BaseT Ethernet communication
 protocol. Fast Ethernet is a network that supports 100 BaseT, 100 BaseT2,
 100 BaseTX, and/or 1000BaseT. The novel circuit is particularly useful in
 point to point communication links (e.g., supporting fast Ethernet
 communication) where two communication nodes are coupled together using a
 bi-directional communication link (e.g., two twisted pair cables). Unlike
 the prior art monitoring probes, the probe of the present invention does
 not insert itself in series between the communication link, but rather
 taps onto the communication link (in parallel using three way connectors)
 and includes a high impedance termination circuit thereby leaving the
 existing communication link undisturbed electrically. By leaving the
 communication link undisturbed electrically, the probe of the present
 invention does not introduce latency into the communication link nor does
 it interrupt the communication link for any reason (e.g., during
 auto-negotiation sessions or on power down, power interruption, etc.). The
 high impedance value selected for the present invention is approximately
 one order of magnitude greater than the individual internal termination
 impedance of the communication nodes. The particular termination circuit
 used can employ a parallel coupled resistor with optional capacitors
 coupled to each wire of a twisted pair cable. The probe can be attached to
 a number of different statistics gathering systems (e.g., of the RMOD and
 RMOD2 standard) or various types of traffic accounting systems.
 Specifically, embodiments of the present invention include a probe for
 monitoring communications over a point to point communication link of a
 fast Ethernet network, the communication link existing between a first
 communication node and a second communication node, the probe comprising:
 a tap for coupling onto the communication link; a receiver magnetics
 circuit coupled to the tap for receiving signals from the communication
 link; a high impedance termination circuit coupled to an output of the
 receiver magnetics circuit, the high impedance termination circuit having
 an impedance 10 to 20 times that of individual internal termination
 impedances of the first and the second communication nodes such that the
 presence of the probe does not disrupt electrical characteristics of the
 communication link; a physical layer circuit coupled to the high impedance
 termination circuit, the physical layer circuit for recovering bits from
 the signals received from the communication link; and a communication
 monitoring circuit coupled to an output of the physical layer circuit for
 gathering and maintaining statistical information regarding the
 communication link.

DETAILED DESCRIPTION OF THE INVENTION
 In the following detailed description of the present invention, a high
 impedance probe for monitoring traffic over a point to point communication
 link of an Ethernet local area network (LAN), numerous specific details
 are set forth in order to provide a thorough understanding of the present
 invention. However, it will be recognized by one skilled in the art that
 the present invention may be practiced without these specific details or
 with equivalents thereof. In other instances, well known methods,
 procedures, components, and circuits have not been described in detail as
 not to unnecessarily obscure aspects of the present invention.
 FIG. 2 illustrates one embodiment of the present invention used in
 conjunction with a point to point communication channel in a fast Ethernet
 communication system 100, e.g., a network including 100 BaseT, 100 BaseT2,
 100 BaseTX, and/or 1000 BaseT and can include a mixed network with one of
 the above standards and 10 BaseT communication. Within this communication
 system 100, there are one or more point to point links, each communication
 link bridges at least two communication nodes together. FIG. 2 shows two
 exemplary communication nodes 110 and 120 coupled together with a point to
 point communication link. The point to point communication link is
 bi-directional and is composed of twisted pair line 150 bridging message
 packets from node 110 to node 120 and also a twisted pair line 160
 bridging message packets from node 120 to node 110.
 It is appreciated that twisted pair lines 150 and twisted pair lines 160
 are each terminated with impedance elements located within each node 110
 and 120. This termination impedance is on the order of 100 ohms, but can
 vary depending on the particular Ethernet standard employed by system 100.
 Within the present invention, the individual internal termination
 impedance of the nodes 110 and 120 is called Z.
 In this configuration of FIG. 2, the present invention includes an external
 three way connector 140 which taps onto lines 150 and lines 160, in
 parallel, to bring lines 150 and lines 160 to probe 130 while not
 disturbing their connection to node 110 or node 120. It is appreciated
 that, in this configuration, the presence of probe 130 does not disrupt
 any communication between nodes 110 and 120. The three way connector 140
 contains three ports into which (1) wires from node 110 are connected, (2)
 wires from node 120 are connected and (3) wires from probe 130 are
 connected.
 Probe 130 of the present invention contains a high termination impedance
 compared to the internal impedance, Z, of nodes 110 and 120. More
 specifically, this termination impedance of probe 130 is on the order of
 10-20 times the value Z. In the above example where Z is 100 ohms, the
 termination impedance of the probe 130 is 1 K ohms. By using this high
 termination impedance, the probe 130 of the present invention is able to
 directly tap onto lines 150 and lines 160 of the point to point
 communication link without altering the electrical characteristics of this
 communication link between nodes 110 and 120.
 Advantageously, probe 130 does not require repeater circuitry as used in
 the prior art because probe 130 is not coupled between the nodes 110 and
 120, as done in the prior art, and further because the electrical
 characteristics of the communication link of FIG. 2 are not altered by the
 presence of the three way connector 140 or the coupled probe 130. Also,
 because the presence of probe 130 does not alter the electrical
 characteristics of the communication link of FIG. 2, probe 130 does not
 introduce any latency in the communications between node 110 and 120.
 Because the presence of probe 130 does not alter the electrical
 characteristics of the communication link of FIG. 2, probe 130 further
 does not require the power down and power interruption protection
 circuitry as required of the prior art. Specifics of the high termination
 impedance configuration of probe 130 are described further below.
 FIG. 3 illustrates another embodiment 200 of the present invention where
 the probe 130 is coupled to the link connection using an internal three
 way connector 140. In this configuration, twisted pair line 150 from node
 110 and twisted pair line 160 to node 110 are coupled to a port 210 of
 probe 130. Likewise, line 160 from node 120 and line 150 to node 120 are
 coupled to another port 210 of probe 130. The probe 130 then internally
 couples to these lines using a parallel three way connection 140 similar
 to the connector shown in FIG. 2. Although it appears to be connected in
 series between lines 150 and 160, probe 130 of the present invention is
 not coupled in series between nodes 110 and 120 in the configuration of
 FIG. 3 due to the presence of the internal three way connector 140. In
 like fashion to the configuration of FIG. 2, the probe 130 of FIG. 3 does
 not disrupt the electrical characteristics of lines 150 and 160 or any
 communication between nodes 110 and 120.
 FIG. 4 illustrates details of the high impedance circuitry within probe 130
 of the present invention. LAN nodes 110 and 120 are shown. Twisted pair
 line 150 as shown includes a (+) line 150b and a (-) line 150a. Twisted
 pair line 160 as shown includes a (+) line. 160b and a (-) line 160a.
 Together, lines 150a-b and 160a-b constitute a point to point
 communication link between nodes 110 and 120. FIG. 4 also shows the
 internal impedance, Z, of nodes 110 and 120; element 122 represents the
 internal impedance, Z, of node 120 and element 112 represents the internal
 impedance, Z, of node 110. In one embodiment, the individual internal
 impedance, Z, of the nodes 110 and 120 is 100 ohms. The three way
 connectors (e.g., connections 390) of the probe 130 of present invention,
 whether external as shown in FIG. 2 or internal as shown in FIG. 3, couple
 in parallel to the lines 150a-b and 160a-b of the communication link to
 supply probe 130 with the traffic information over this communication
 link.
 Probe 130 of the present invention contains a receiver magnetics circuit
 310a which receives both line 160a and line 160b. The receiver magnetics
 circuit 310a is well known in the art and any of a number of well known
 circuits can be used as circuit 310a within the present invention.
 Receiver magnetics circuit 310a outputs modified signals over line 370a
 (+) and line 372a (-) to the high impedance termination circuit 320a of
 the present invention. The high impedance termination circuit 320a
 provides approximately 10 to 20 times the individual internal impedance,
 Z, of the communication nodes 110 and 120. In one embodiment, the high
 impedance termination circuit 320b introduces approximately 1k ohm of
 impedance into the line 160.
 The high impedance termination circuit 320a of FIG. 4 outputs terminated
 signals over line 374a (+) and line 376a (-) to a physical layer receiver
 circuit 330a that is capable of receiving either 100 BaseT Ethernet
 signals or 10 BaseT Ethernet signals. As is well known in the art, the
 physical layer receiver circuit 330a recovers the bits of a message packet
 received over line 160. Any of a number of well known physical layer
 receiver circuits can be used as circuit 330a within the present
 invention. In an alternative embodiment of the present invention, the
 physical layer circuit 330a is also capable of recovering bits from 100
 BaseT2 and/or 100 Base TX communication. The physical layer receiver
 circuit 330a transmits a bit stream over bus 380a to a 10/100M Ethernet
 controller 335.
 Ethernet controller 335 of FIG. 4 includes a processor and memory for
 gathering and maintaining statistical information regarding the message
 packets transmitted over line 160. It is appreciated that the high
 impedance termination circuit 320a of the sent invention can operate in
 conjunction with a number of different statistics gathering devices.
 However, one such statistics gathering technology that can be employed
 within the present invention is the Internet Engineering Task Force's RMOD
 (Remote Monitoring) and RMOD2 standard. According to these well known
 standards, packet based statistics are gathered and can be used for
 diagnostic purposes. Alternatively, Ethernet controller 335 can be used to
 collected and maintain accounting statistics regarding which node sent
 which information and to which destination, etc. One exemplary statistics
 monitoring system that can be employed as circuit 335 is the Superstacks
 II Enterprise Monitor System available from 3COM Corporation of Santa
 Clara, Calif.
 It is appreciated that the present invention includes analogous circuitry
 for receiving message packets from lines 150a-b. Probe 130 of the present
 invention contains a receiver magnetics circuit 310b which receives both
 line 150a and line 150b. Any of a number of well known circuits can be
 used as circuit 310b of the present invention. Receiver magnetics circuit
 310b outputs modified signals over line 370b (+) and line 372b (-) to
 another high impedance termination circuit 320b of the present invention.
 The high impedance termination circuit 320b provides approximately 10 to
 20 times the individual internal impedance, Z, of the communication nodes
 110 and 120. In one embodiment, the high impedance termination circuit
 320b introduces approximately 1 k ohm of impedance into the line 150. The
 high impedance termination circuit 320b outputs terminated signals over
 line 374b (+) and line 376b (-) to another physical layer receiver circuit
 330b that is capable of receiving either 100 BaseT Ethernet signals or 10
 BaseT Ethernet signals. As is well known in the art, the physical layer
 receiver circuit 330b recovers the bits of a message packet received over
 line 150. Any of a number of well known physical layer receiver circuits
 can be used as circuit 330b within the present invention. In an
 alternative embodiment of the present invention, the physical layer
 circuit 330b is also capable of recovering bits from 100 BaseT2 and/or 100
 Base TX communication.
 The physical layer receiver circuit 330b of FIG. 4 transmits a bit stream
 over bus 380b to a 10/100M Ethernet controller 365. Ethernet controller
 365 performs functions analogous to Ethernet controller 335 but is used
 for monitoring message traffic over line 160. It is appreciated that
 Ethernet controller 365 and Ethernet controller 335 can be combined into a
 single statistics gathering and maintenance system that receives message
 traffic from both lines 150 and 160 and differentiates this data
 internally to maintain separate statistics on both lines.
 It is appreciated that the present invention is able to provide the
 parallel three way taps 390 onto the point to point communication link of
 FIG. 4 due to the high impedance termination circuits 320a-b. These
 circuits 320a-b ensure that the taps 390 to not disrupt the electrical
 characteristics of the communication link (lines 150 and 160) in any
 meaningful way. Due to this circuitry, the probe 130 of the present
 invention avoids the requirement of being placed in series with the
 communication link, as done in the prior art point to point monitoring
 equipment. By being removed from the series connection, the probe 130 of
 the present invention advantageously: (1) avoids the unwanted latencies
 introduced by series inserted repeater equipment of the prior art; (2)
 avoids the power down and power interruption protection circuitry required
 of the series inserted prior art; and (3) avoids auto-negotiation sessions
 performed by the prior art that are initiated upon probe insertion.
 FIG. 5A illustrates one particular configuration 400 used with the high
 impedance termination circuit 320a of the present invention. Line 160a (-)
 and line 160b (+) comprise the twisted pair line 160. Line 160a (-) is
 coupled to one end of capacitor 410 and line 160b (+) is coupled to one
 end of capacitor 412, as shown. The other ends of the capacitors 410 and
 412 are coupled to the inputs of receiver magnetics circuit 310a which
 couples these lines to either end of one winding of a coil element 414.
 Each capacitor 410 and 412 is on the order of 1-100 picoFarads. Outputs
 374a and 376a are taken from either end of a second coil element 416 of
 the receiver magnetics circuit 310a. A 1k ohm resistor 418 is coupled
 across lines 374a and 376a. These two lines 374a and 376a are input into
 the physical layer 330a. Alternatively, the capacitors 410 and 412 can be
 eliminated. It is appreciated that FIG. 5B illustrates an analogous
 configuration 400' for twisted pair line 150 which includes line 150a (-)
 and line 150b (+)
 FIG. 6A illustrates another exemplary configuration 500 used with the high
 impedance termination circuit 320a of the present invention. Line 160a (-)
 and line 160b (+) are coupled to receiver magnetics circuit 310a which
 couples these lines to either end of one winding of a coil element 414.
 Output lines from magnetics circuit 310a are taken from either end of a
 second coil element 416 and one output line is coupled to one end of
 capacitor 410 and the other output line is coupled to one end of capacitor
 412, as shown. Each capacitor 410 and 412 is on the order of 1-100
 picoFarads. The other end of the capacitors 410 and 412 have a 1 k ohm
 resistor 418 coupled between them and further are coupled to the inputs of
 physical layer circuit 330a. Alternatively, the capacitors 410 and 412 can
 be eliminated. It is appreciated that FIG. 6B illustrates an analogous
 configuration 500' for lines 150a (-) and 150b (+).
 The preferred embodiment of the present invention, a high impedance probe
 is disclosed for monitoring traffic over a point to point communication
 link of an Ethernet local area network (LAN), is described. While the
 present invention has been described in particular embodiments, it should
 be appreciated that the present invention should not be construed as
 limited by such embodiments, but rather construed according to the below
 claims.