GB2158679A - Testing a local area network - Google Patents
Testing a local area network Download PDFInfo
- Publication number
- GB2158679A GB2158679A GB08500762A GB8500762A GB2158679A GB 2158679 A GB2158679 A GB 2158679A GB 08500762 A GB08500762 A GB 08500762A GB 8500762 A GB8500762 A GB 8500762A GB 2158679 A GB2158679 A GB 2158679A
- Authority
- GB
- United Kingdom
- Prior art keywords
- transmission line
- transceivers
- testing
- frame
- transceiver
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000012360 testing method Methods 0.000 title claims description 38
- 230000005540 biological transmission Effects 0.000 claims abstract description 54
- 230000004044 response Effects 0.000 claims abstract description 3
- 238000012544 monitoring process Methods 0.000 claims description 29
- 238000000034 method Methods 0.000 claims description 11
- 101100172132 Mus musculus Eif3a gene Proteins 0.000 claims description 9
- 238000010998 test method Methods 0.000 claims description 8
- 238000009434 installation Methods 0.000 description 9
- 238000013101 initial test Methods 0.000 description 5
- 206010003402 Arthropod sting Diseases 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 239000004020 conductor Substances 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000012956 testing procedure Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/40—Bus networks
- H04L12/40006—Architecture of a communication node
- H04L12/40032—Details regarding a bus interface enhancer
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/28—Data switching networks characterised by path configuration, e.g. LAN [Local Area Networks] or WAN [Wide Area Networks]
- H04L12/40—Bus networks
- H04L12/407—Bus networks with decentralised control
- H04L12/413—Bus networks with decentralised control with random access, e.g. carrier-sense multiple-access with collision detection [CSMA-CD]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L43/00—Arrangements for monitoring or testing data switching networks
- H04L43/50—Testing arrangements
Landscapes
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Small-Scale Networks (AREA)
Abstract
The transmission system of a local area network comprising a transmission line having transceivers connected to it at spaced apart positions is tested by connecting monitor stations to two of the transceivers. One of the monitor stations is operating, on receipt of a first frame of data from the transmission line, to transmit a second frame of and the other monitor station is data operable to transmit a first frame of data and thereafter is operative to determine if the second frame of data is successfully received in response to its transmission of the first frame. <IMAGE>
Description
SPECIFICATION
Improvements in or relating to the testing of the transmission system of a local-area-network
This invention relates to the testing of the transmission system of a local area network, especially of the type that uses an access protocol of the kind known as carrier- sense multiple-access with collision detection (CSMA/ CD).
The invention provides a method of testing the transmission system of a local-area-network which system comprises a transmission line terminated at each end by a terminating impedance and having, in use, a plurality of transceivers connected to the transmission line at positions spaced apart therealong, the method comprising: - connecting a first monitoring station to a first transceiver connected to the transmission line, the first monitoring station being operable to transmit over the transmission line using a CSMA/CD protocol and being operative on receipt of a first frame of data from the transmission line to transmit, or attempt to transmit, a second frame of data to the transmission line; - and successively for each of the remaining transceivers connected to the transmission line carrying out a testing stage comprising connecting a second monitoring station to the appropriate one of said remaining transceivers, the second monitoring station being operable to transmit, or to attempt to transmit, over the transmission line using a CSMA/CD protocol the first frame of data and thereafter being operative to determine if the second frame of data is successfully received in response to transmission of the first frame.
Preferably the first instance of a testing stage occurs with all transceivers in place and the first monitoring station attached to a first (preferably an end) transceiver and the second monitoring station attached to a second (preferably the next) transceiver to that end transceiver along the transmission line. Then, if a second frame is received successfully it is assumed that the transmission line and those two transceivers are functioning correctly and preferably the second monitoring station is moved to be attached to each remaining transceiver in turn, each testing stage then indicating whether the transceiver it is connected to is functioning correctly.
If on the other hand the first testing stage fails, the faulty component must be identified. if the transceivers are of the type that comprise an inline component, identification is preferably done by repeatedly carrying out a testing stage with the first monitoring station connected to an end transceiver and the second monitoring station connected to each remaining transceiver in turn in the order they are connected along the line starting with the one nearest the said end transceiver, the transmission line being broken and reterminated on the side of the transceiver concerned remote from the said end station for each testing stage, and the testing stages being carried out until a failure to receive an expected second frame occurs.
The failure indicates that a faulty component is present in the most recently added components.
If the transceivers are of the bee-sting type, if the initial testing stage fails, transceivers are disconnected, the transmission line tested and then, if it is functional, transceivers are successively reconnected and tested by a testing stage.
Examples of testing methods according to the invention will now be described in greater detail with reference to the accompanying drawings, in which
Figure 1 illustrates an installation to be tested,
Figure 2 is a block diagram of a monitoring station,
Figures 3 to 8 illustrate testing procedures.
Transmission system to be tested
The transmission system to be tested is the transmission backbone of a network using the
CSMA/CD protocol. This protocol is used, for example, in the well-known Ethernet system. Briefly in a CSMAICD network, a station that wishes to transmit listens to the transmission line to detect if any message is already being transmitted. If any message is being transmitted, the station waits until the line is silent before starting to transmit; otherwise it starts at once. Owing to propagation delays it is possible for more than one station to detect silence and start to transmit at the same time. If that happens each station detects the resulting collision, ceases to transmit and makes another attempt after a random interval chosen to give a good chance of ensuring that only one station succeeds.
Referring to Figure 1, the system to be tested consists essentially of the cabling and transceivers of the network. It will be assumed first that the transceivers are of the in-line type. Thus the system to be tested, indicated generally by the reference numeral 1 and shown solid in the figure, consists of sections 2 of coaxial cable, transceivers 3 inserted between pairs of cable sections, and terminating resistors 4 at the ends.
Each transceiver 3 connects the two sections 2 of the cable between which it is connected so as to provide a through signal path. There is thus a single transmission line extending between the two terminating resistors 4, which have a resistance equal to the characteristic impedance of the cabling and prevent reflection.
In use, each of the devices 5 which is to communicate over the network (one is shown dotted in
Figure 1) is connected to a transceiver 3. Each transceiver 3 includes a receiver, a transmitter and a collision detector, which indicates when data is being received while a message is being transmitted.
One problem with a decentralised network such as a CSMA/CD network is that faults can be very difficult to locate. The method to be described is applied to test the installation 1 before any devices are attached, to ensure that this installation is functioning correctly. It may also be used subsequently, after disconnecting the devices, if an unidentifiable fault occurs in the completed network.
Monitoring station
Referring to Figure 2, the installation is tested using a pair of monitor stations 10. Each contains a local- area-network controller 11 and a microcomputer 12 connected by a bus 13. The controller 11 can be connected to one of the transceivers 3 by coupling a connector 14 to a corresponding connector 15 from the transceiver 3. An operator's console 16 is connected to the microcomputer 12.
Transceivers such as the transceivers 3 and controllers such as the controller 11 are commercially available. For transmitting, the controller 11 is passed a frame, adds a starting preamble and sync pattern and a closing frame-check sequence and transmits the frame when it is able in accordance with the CSMA/CD protocol. For receiving it receives all frames from other stations transmitted over the network and recognises if they are addressed to that station, either by its unique address or because the frame has a broadcast address or a multicast address defining a set of stations of which it is a member.
If a frame is addressed to the station' the controller removes the added preamble and sync patterns and frame check sequence and, provided the latter is correct, passes the frame to the remainder of the station. It may also be set to pass all received frames, whoever they may be addressed to.
The microcomputer 12 is programmed to formulate and transmit frames over the network under the control of the operator at the console 16, who indicates the destination address to be used and the data to be sent. The values of these variables can if desired be selected from stored values heid in the microcomputer 12. The microcomputer 12 then formulates a frame with the correct header and data and, on command from the operator, passes it to the controller 11 for transmission.
The microcomputer 12 can cause all received frames to be displayed on the console. It can also be instructed to reflect all frames addressed to it.
That is, on receiving such a frame from the controller 11 it outputs a frame to be transmitted which has the same data content as the frame just received but contains the address of the source of that frame as the destination and its own address as the source address.
The monitoring station has a number of functions with which this invention is not concerned, such as displaying all frames transmitted over the network, collecting statistics, and sending frames intended to assist in testing higher level characteristics of the network. This invention is concerned with the use of a pair of such stations to test the physical level of the network consisting of the transmission system 1 (Figure 1).
Testing method
The testing method is carried out in a number of stages. Referring to Figure 3, in the first test stage, one monitoring station 10a is attached to the transceiver 3a at one end of the line. This station is set to reflect. The other monitoring station 10b is connected to the next transceiver 3b. A test frame is then sent from the station 10b, and, if the system is functioning correctly, is reflected by the station 10a, returned to the station 10b and itself displayed for operator comparison and/or compared in the microcomputer 12 with the expected value and in indication of match displayed. In this case the first stage has been successful.However, if a transceiver 3a or 3b is faulty or if there is a fault in the transmission line caused by a cable or transceiver fault the expected frame will not be returned and the test stage will fail.
Referring to Figure 4, if the first test stage is successful, the remaining transceivers 3 are tested in turn by moving the monitoring station 10b to each remaining transceiver 3c etc. in turn and repeating the test stage with the monitoring station 10b connected to that transceiver. If any test fails the transceiver 3 implicated is replaced.
If the initial test stage fails, possible reasons are that one of the transceivers 3a and 3b is failing to transmit or receive correctly, or that there is a discontinuity in the transmission line in either a cable section or a transceiver. Such a discontinuity (e.g.
a short or open circuit) causes a signal to be reflected, which in a CSMAiCD system causes a collision. Since a collision will occur on any attempt to transmit, if the cause of a reflection is present no transmission will be possible.
Referring to Figure 5, if the initial test stage fails, the next step is to disconnect the cable 2c connected to the side of the transceiver 3b away from the end of the line. A new end assembly 20 consisting of a cable section and terminating resistor is then connected in its place and the test stage repeated for this isolated end section. If the test stage now succeeds, it is known that the fault is in the remainder of the installation and the procedure to be described with reference to Figure 6 is carried out. If on the other hand the test stage on the end section fails, it has been discovered that there is at least one faulty component in this end section and the various components are replaced individually or if necessary in combination by known working examples to identify the faulty component(s).With the faulty component(s) replaced the cable section 2c is reconnected so that the installation 1 is again whole, and, because there may also be faults in the remainder of the installation, the initial test stage is repeated with the monitoring stations 10a and 10b attached to the end two transceivers 3a and 3b. If the test is now successful the transmission line is functioning correctly and the procedure already described with reference to
Figure 4 is carried out to test the remaining transceivers.
If the test stage now fails, there is still at least one fault in the remainder of the installation. This state of affairs may alternatively have been established earlier if the first test of the isolated end section described above with reference to Figure 5 succeeded.
Referring to Figure 6, in either case the line is broken immediately beyond the next transceiver, 3c, and the end assembly 20 substituted. The monitoring station 10b is now attached to the trans ceiver 3c and the test stage repeated for this longer end section. If the test succeeds the added components 2c and 3c are shown to be functioning. If it fails, the location of a faulty component has been narrowed down to one or both of this pair and can be replaced in turn and if necessary together by known working examples to ensure they both function. Once the tested section is working the line is reconnected and the test stage repeated to check if the remainder of the installation still includes a fault.
While the transmission line still includes a fault the procedure described with reference to Figure 6 is repeated, moving the point at which the break is made and also the monitoring station 10b successively along the line. As soon as the line is shown to be functioning the procedure described with reference to Figure 4 is followed to check the remaining transceivers.
Modifications
It has so far been assumed that the transceivers are of the type that are completely inserted between sections of cable. The same procedure may be used for the type in which the transceiver is attached to a T-piece which is then inserted between cable sections, this transceiver and its T-piece together being treated as the transceiver in the method so far described.
However, an alternative type of transceiver is of the bee-sting type and is used with a transmission line formed of coaxial cable not broken into sections at each transceiver. Instead, the transceiver has contact-points which pierce the cable to make contact with the conductors of the cable. With this type of transceiver, the initial test stage described with reference to Figure 3 is carried out as before, and, if it succeeds,the individual transceivers are tested as described with reference to Figure 4. If it fails, all the transceivers are removed and the cabling tested on its own, for example with a resistance meter, and replaced if necessary.Then referring to Figure 7, a pair of transceivers 3a and 3b are reconnected to the cabling, a cable 30, the monitoring stations 10a and 10b are connected to the transceivers 10a and 10b and the test stage carried out. If that reveals faulty components they are replaced and, referring to Figure 8, each subsequent transceiver 3c etc. is reconnected, tested by moving the monitoring station 10b to it and carrying out the testing stage, and replaced if necessary.
It will be realised that the console 16, while used in the case of the monitoring station 10b by the operator who moves it from transducer to transducer, is not needed in the station 10a, and may be omitted from it.
It has so far been assumed that the frames sent by the station 10b and 10a are uniquely addressed to the destinations. However, since no other communicating devices are present, if desired broadcast of multicast addresses, or random addressess with promiscuous reception may be used.
The network itself need not necessarily use a
CSMA/CD protocol, even though the monitoring stations do. But it may then be necessary to carry out the collision- detection function in the monitoring stations themselves if that is not done in the transceivers.
Claims (7)
1. A method of testing the transmission system of a local-area-network which system comprises a transmission line terminated at each end by a terminating impedance and having, in use, a plurality of transceivers connected to the transmission line at positions spaced apart therealong, the method comprising: - connecting a first monitoring station to a first transceiver connected to the transmission line, the first monitoring station being operable to transmit over the transmission line using a CSMA/
CD protocol and being operative on receipt of a first frame of data from the transmission line to transmit, or attempt to transmit, a second frame of data to the transmission line; - and successively for each of the remaining transceivers connected to the transmission line carrying out a testing stage comprising connecting a second monitoring station to the appropriate one of said remaining transceivers, the second monitoring station being operable to transmit, or to attempt to transmit, over the transmission line using a CSMA/CD protocol the first frame of data and thereafter being operative to determine if the second frame of data is successfully received in response to transmission of the first frame.
2. A method of testing as claimed in claim 1 in which, in a first testing stage, the second monitoring station is connected to one of the remaining transceivers which is connected to the transmission line next to the first transceiver.
3. A method of testing as claimed in claim 1 or 2 in which the transceiver, to which one of the monitor stations is connected, is connected to the transmission line next to the terminating impedance.
4. A method of testing as claimed in claim 2 in which, in successive stages of testing, one monitor station is connected to transceivers connected successively further along the transmission line from the other transceiver to which the other monitor station is connected.
5. A method of testing a transmission system in which the transceivers constitute links between adjacent sections of transmission line, the method including the steps of disconnecting a section or sections of transmission line, from the transceiver to which one of the monitor stations is connected, other than the transmission line interconnecting those transceivers to which the monitor stations are connected and connecting a terminating impedance in place of the disconnected line.
6. A method of testing a transmission system in which the transceivers are connected to a continuous length of transmission line, the method including disconnecting transceivers from the transmission line beyond the transceivers to which the monitor stations are connected.
7. A method of testing a transmission system substantially as hereinbefore described with reference to Figures 1 to 6 or with reference to Figures 1, 2, 7 and 8 of the drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB848401000A GB8401000D0 (en) | 1984-01-14 | 1984-01-14 | Testing of transmission system |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8500762D0 GB8500762D0 (en) | 1985-02-13 |
| GB2158679A true GB2158679A (en) | 1985-11-13 |
| GB2158679B GB2158679B (en) | 1987-05-07 |
Family
ID=10555003
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB848401000A Pending GB8401000D0 (en) | 1984-01-14 | 1984-01-14 | Testing of transmission system |
| GB08500762A Expired GB2158679B (en) | 1984-01-14 | 1985-01-11 | Testing a local area network |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB848401000A Pending GB8401000D0 (en) | 1984-01-14 | 1984-01-14 | Testing of transmission system |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8401000D0 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4775983A (en) * | 1987-09-28 | 1988-10-04 | Ncr Corporation | High speed logic analyzer |
| US5091870A (en) * | 1988-05-27 | 1992-02-25 | Ncr Corporation | Apparatus for measuring the speed of transmission of digital characters |
| EP0520787A1 (en) * | 1991-06-28 | 1992-12-30 | Hewlett-Packard Company | System and method for detecting an improper termination and a short circuit in a network |
-
1984
- 1984-01-14 GB GB848401000A patent/GB8401000D0/en active Pending
-
1985
- 1985-01-11 GB GB08500762A patent/GB2158679B/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4775983A (en) * | 1987-09-28 | 1988-10-04 | Ncr Corporation | High speed logic analyzer |
| WO1989003144A1 (en) * | 1987-09-28 | 1989-04-06 | Ncr Corporation | Data link monitoring system |
| US5091870A (en) * | 1988-05-27 | 1992-02-25 | Ncr Corporation | Apparatus for measuring the speed of transmission of digital characters |
| EP0520787A1 (en) * | 1991-06-28 | 1992-12-30 | Hewlett-Packard Company | System and method for detecting an improper termination and a short circuit in a network |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8500762D0 (en) | 1985-02-13 |
| GB8401000D0 (en) | 1984-02-15 |
| GB2158679B (en) | 1987-05-07 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5381348A (en) | Token ring local area network testing apparatus using time delay reflectory | |
| EP0307461B1 (en) | Lan communication system and medium adapter for use therewith | |
| EP0416942B1 (en) | Method of detecting a cable fault and switching to a redundant cable in a universal local area network | |
| US5309428A (en) | Token ring local area network testing apparatus for phase jitter testing | |
| US4159470A (en) | Data communications systems employing redundant series transmission loops | |
| US5444695A (en) | Token ring local area network testing apparatus providing station history information | |
| US5363366A (en) | Token ring local area network testing apparatus for obtaining beacon domain information | |
| US4385384A (en) | Modem diagnostic and control system | |
| US5365513A (en) | Token ring local area network testing apparatus for matching its speed to ring speed | |
| US5115449A (en) | Data networks | |
| US5586251A (en) | Continuous on-local area network monitor | |
| JP3716359B2 (en) | Control method of input signal transmission in communication network, connector therefor and separation circuit built therein | |
| US5425017A (en) | Token ring local area network testing apparatus inserted in an active "T" co | |
| US5329519A (en) | Lan monitoring method and apparatus | |
| JP2001505731A (en) | Physical layer monitoring provided by computer network cross-connect panel | |
| JPH08510615A (en) | Communication network having a plurality of stations and operating method thereof | |
| GB2158679A (en) | Testing a local area network | |
| WO2000054419A1 (en) | Automatic crossover system for a media dependent interface with hysteresis | |
| US4654807A (en) | Method of measuring communication channel impairement in polling applications | |
| US6922742B2 (en) | Node device for a serial databus connecting a number of devices | |
| US4760488A (en) | Transmission control apparatus for duplex loop type transmission system | |
| JP2530771B2 (en) | Transmitter / receiver line switch | |
| US5504779A (en) | Redundancy modem | |
| JPS60251751A (en) | Digital suscriber line test system | |
| EP0338126A2 (en) | Method and apparatus for testing twisted-pair interconnections of a local area network |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |