Multiplex communications – Network configuration determination
Reexamination Certificate
1999-09-22
2001-11-27
Patel, Ajit (Department: 2662)
Multiplex communications
Network configuration determination
C370S248000, C370S241000, C702S097000, C702S108000
Reexamination Certificate
active
06324168
ABSTRACT:
BACKGROUND OF THE INVENTION
Physically, local area networks (LAN) comprise a transmission medium and network devices that transmit through it. The transmission medium is typically coaxial or twisted-pair wiring. The network devices or nodes are the network cards of computer workstations that utilize the network cabling to communicate with each other. Dedicated network devices such as hubs, repeaters, bridges, switches, and routers are also used to manage or extend a given LAN or act as inter-networking devices.
One of the most common protocols for a LAN is termed carrier sense multiple access with collision detection (CSMA/CD). This protocol is sometimes generically, but incorrectly, referred to as Ethernet, which is a product of the XEROX Corporation. I.E.E.E. has promulgated standards for this protocol; IEEE 802.3 covers 1-persistent CSMA/CD access method and physical layer specification. The protocol comes in various implementations, 10Base(2) and (5) are 10 megabit per second (MBPS) networks using different gauges of coaxial cable (2 and 5) in a bus topology. 10Base(T) also operates at 10 MBPS but uses twisted-pair cabling in a star topology in which each node connects to a hub. Newer 100 MBPS implementations such as 100Base(T) are becoming more common with 1 GigaBPS devices in planning and testing.
A number of problems can arise at a LAN's physical layer. In the case of twisted-pair or coaxial wiring, the electrical conductors may become frayed or broken. The shielding may be damaged, failing to protect the conductors from surrounding electromagnetic interference and changing the cable's characteristic impedance. Moreover, the terminators at the end of the network cables in bus topologies or the terminators in the nodes at the ends of the links in star topologies may be poorly matched to the characteristic impedance of the network's cables or non-existent. This produces signal reflections that can impair the operation of the network.
Another potential problem with a network is the fact that cabling may be too long. The IEEE 802.3 10Base(T) protocol, for example, limits the cable length to 200 meters with repeaters. This restriction is placed on networks because signals require a non-trivial time to propagate through the entire length of a CSMA/CD network relative to the data rate of the network. Network devices, however, must have some assurance that after they have been transmitting for some minimum time that a collision will not thereafter occur. Additionally, the end of each packet transmission must be allowed to propagate across the entire network before the next transmission may take place. If the cabling is long, the time allocated to this may begin to consume too much of the network's potential bandwidth.
A number of techniques exist for validating a network at the physical layer. The most common approach is called time domain reflectometry (TDR). According to this technique, a predetermined signal, typically a step-function, is injected onto the network cabling. The TDR system will then listen for any returning echoes. Echoes arise from the signal passing through regions of the cable where the characteristic impedance changes. Based upon the amplitude of these reflections and the delays between the transmission of the signal onto the cable at the sending-end and the receipt of the reflection back at the sending-end, the location of the impedance change, a frayed portion of cable for example, may be located.
TDR has been used to determine the length of the network cable and thus whether it conforms to the relevant protocol. Prior to testing, the network's terminators are removed and the conductors are shorted together or open circuited. The length of the cable may then be determined based on the time delay between when the TDR signal is placed on the network and when the open- or short-circuit reflection is detected at the sending-end.
SUMMARY OF THE INVENTION
The problem with known cable length detection methods is that they rely on the removal of the terminators or on a reflection producing device. The terminators, however, are necessary to the proper operation of the network. Thus, the cable length can only be determined on a non-operational network. This requirement is not unduly restrictive in the case of validating a newly installed network since the TDR analysis may be performed prior to the installation of the terminators or attachment of the nodes. This requirement, however, negates the periodic monitoring of an operational network and the diagnosis of a previously installed network that is exhibiting problems.
In the invention, the location of a properly configured terminator, i.e., a terminator that has been configured to closely match the nominal characteristic impedance of the network cabling, can be remotely detected by analyzing the network's response to a predetermined signal for skin effects. In more detail, the terminator produces a signature that is detectable at the sending-end when predetermined signal, such as a current step function, is injected onto the network cabling. The magnitude of the voltage at the sending-end will slowly increase. This results from the skin effects and accumulated d.c. resistance across the length of the cable as the step function propagates down its length. After a time corresponding to twice the propagation time between the sending-end and the terminator, the voltage will undergo an inflection. After this inflection, the voltage asymptotically returns to the voltage level initially produced when the step function was generated.
In general, according to one aspect, the invention is directed to a method for analyzing a network link on a computer network. Specifically, it analyzes the link under any one of three criteria. Specifically, a short circuit threshold is applied to the link's response, an open circuit threshold is applied to the response, and a search is performed for a matched termination. A decision is then made based upon the application of these thresholds and the matched terminator search. Then, once the type of termination is found, a determination of the time delay between the generation of the predetermined signal and the located termination is performed.
In general, according to another aspect, the invention is also directed to a network termination analysis device for a digital data network. Specifically, a function generator is provided that injects a predetermined signal onto cabling of a network, a digitizer is provided that then digitally samples the network's response to the predetermined signal. A system processor downloads data from the digitizer to analyze the network's response to the predetermined signal. It then identifies a time between the generation of the predetermined signal and a change in the network's response due to a termination of the network. This analysis comprises applying a short circuit threshold to the response, applying an open circuit threshold to the response, and also searching the response for a matched terminator. The results of these analyses are used to first identify the type of termination and then the time delay to that termination.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.
REFERENCES:
patent: 4580872 (1986-04-01), Bhatt et al.
patent: 4890278 (1989-12-01), Felker et al.
patent: 5062703 (1991-11-01), Wong et al.
patent: 5063353 (1991-11-01), Gubisch
patent: 5245291 (1993-09-01), Fujimura
patent: 5289390 (1994-02-01), Unverrich
patent: 5381348 (1995-01-01), Ernst et al.
patent: 5402424 (1995-03-
Nguyen Hanh
Patel Ajit
Rader & Fishman & Grauer, PLLC
Vigilant Networks LLC
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