Abstract:
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, {fraction (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.

Description:
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.  1 A. In fast Ethernet, e.g., of the 100 BaseT, 100 BaseT 2 , 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.  1 B. 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  46   a  and  46   b  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.  1 C. 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  46   a  and  46   b  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  46   a  auto-negotiates between probe  52  and the node  42 . Simultaneously, link  46   b  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  46   b ). 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, {fraction (10/100)} BaseT Ethernet communication protocol. Fast Ethernet is a network that supports 100 BaseT, 100 BaseT 2 , 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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a communication system of the prior art using a probe coupled to a standard repeater hub which repeats messages from one communication node to all other communication nodes of the system. 
     FIG. 1B is an illustration of a point to point communication link in a prior art fast Ethernet local area network communication system. 
     FIG. 1C is an illustration of a prior art probe coupled in series in between a communication link of two communication nodes. 
     FIG. 2 is a logical diagram of the high impedance probe of the present invention tapping onto a bi-directional point to point communication link using an external three way connector. 
     FIG. 3 is a logical diagram of the high impedance probe of the present invention tapping onto a point to point communication link using port connectors of the probe equipment and an internal connector. 
     FIG. 4 illustrates a logical block diagram of the internal circuitry of the probe of the present invention including the high impedance termination block. 
     FIG.  5 A and FIG. 5B are circuit diagrams illustrating elements of one embodiment of the high impedance probe of the present invention. 
     FIG.  6 A and FIG. 6B are circuit diagrams illustrating elements of a second embodiment of the high impedance probe of the present invention. 
    
    
     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 BaseT 2 , 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  150   b  and a (−) line  150   a . Twisted pair line  160  as shown includes a (+) line.  160   b  and a (−) line  160   a . Together, lines  150   a-b  and  160   a-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  150   a-b  and  160   a-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  310   a  which receives both line  160   a  and line  160   b . The receiver magnetics circuit  310   a  is well known in the art and any of a number of well known circuits can be used as circuit  310   a  within the present invention. Receiver magnetics circuit  310   a  outputs modified signals over line  370   a  (+) and line  372   a  (−) to the high impedance termination circuit  320   a  of the present invention. The high impedance termination circuit  320   a  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  320   b  introduces approximately 1k ohm of impedance into the line  160 . 
     The high impedance termination circuit  320   a  of FIG. 4 outputs terminated signals over line  374   a  (+) and line  376   a  (−) to a physical layer receiver circuit  330   a  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  330   a  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  330   a  within the present invention. In an alternative embodiment of the present invention, the physical layer circuit  330   a  is also capable of recovering bits from 100 BaseT2 and/or 100 Base TX communication. The physical layer receiver circuit  330   a  transmits a bit stream over bus  380   a  to a {fraction (10/100)}M 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  320   a  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&#39;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  150   a-b . Probe  130  of the present invention contains a receiver magnetics circuit  310   b  which receives both line  150   a  and line  150   b . Any of a number of well known circuits can be used as circuit  310   b  of the present invention. Receiver magnetics circuit  310   b  outputs modified signals over line  370   b  (+) and line  372   b  (−) to another high impedance termination circuit  320   b  of the present invention. The high impedance termination circuit  320   b  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  320   b  introduces approximately 1 k ohm of impedance into the line  150 . The high impedance termination circuit  320   b  outputs terminated signals over line  374   b  (+) and line  376   b  (−) to another physical layer receiver circuit  330   b  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  330   b  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  330   b  within the present invention. In an alternative embodiment of the present invention, the physical layer circuit  330   b  is also capable of recovering bits from 100 BaseT 2  and/or 100 Base TX communication. 
     The physical layer receiver circuit  330   b  of FIG. 4 transmits a bit stream over bus  380   b  to a {fraction (10/100)}M 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  320   a-b . These circuits  320   a-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  320   a  of the present invention. Line  160   a  (−) and line  160   b  (+) comprise the twisted pair line  160 . Line  160   a  (−) is coupled to one end of capacitor  410  and line  160   b  (+) 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  310   a  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  374   a  and  376   a  are taken from either end of a second coil element  416  of the receiver magnetics circuit  310   a . A 1k ohm resistor  418  is coupled across lines  374   a  and  376   a . These two lines  374   a  and  376   a  are input into the physical layer  330   a . 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  150   a  (−) and line  150   b  (+) 
     FIG. 6A illustrates another exemplary configuration  500  used with the high impedance termination circuit  320   a  of the present invention. Line  160   a  (−) and line  160   b  (+) are coupled to receiver magnetics circuit  310   a  which couples these lines to either end of one winding of a coil element  414 . Output lines from magnetics circuit  310   a  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  330   a . Alternatively, the capacitors  410  and  412  can be eliminated. It is appreciated that FIG. 6B illustrates an analogous configuration  500 ′ for lines  150   a  (−) and  150   b  (+). 
     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.