GB2342261A

GB2342261A - Testing connection status

Info

Publication number: GB2342261A
Application number: GB9919501A
Authority: GB
Inventors: Steven R Cole; Marcel B Manzardo
Original assignee: Siemens Information and Communication Networks Inc
Current assignee: Siemens Communications Inc
Priority date: 1998-09-29
Filing date: 1999-08-19
Publication date: 2000-04-05
Anticipated expiration: 2019-08-19
Also published as: GB2342261B; DE19946742A1; GB9919501D0; DE19946742C2

Abstract

A method and apparatus for testing the connection status of a full-duplex voice/data communication link (10) in both directions. The test is performed on a continuous basis running in the background as voice/data elements (12,14) are transmitted over the link. A first level of link testing (16) detects whether or not a signal is being received by the site (A). A second level of link testing (18) uses the transmission and monitoring of a connection status bit (28, 30) that is communicated continuously as overhead in the data transport element. Faults in the connection are isolated and reported. This method does not rely on the two sites (A, B) having microprocessors available to handle the link status functions.

Description

2342261 METHOD AND APPARATUS FOR TESTING THE CONNECTION STATUS OF A

COMMUNICATION LINK

BACKGROUND OF THE INVENTION

I Field of the Invention

The present invention relates to full-duplex voice/data communications systems, and more particularly, to a method and apparatus for testing the connection status of communications links in such systems.

2. Description of the Related Art

There is often a need to test the connection status of fidl-duplex voice/data communications systems. Such communications systems typically connect multiple sites via communications links. Several different types of communications links are widely used, such as for example, twistedpair, coaxial, fiber optic, etc., and the various communications links may utilize many different types of communication protocols, such as for example, Ethernet, Token Ring, High-level Data Link Control (HDLC), etc.

When testing the connection status of full-duplex voice/data communication; systems, it is desirable to have the capability to continually monitor the status, test the connection status in both directions, isolate faults, and report the link status. One conventional technique that has been used to perform these functions is to run manual tests with test equipment on the link. The disadvantage of this technique is that it requires manual intervention with special test equipment to test the link and usually requires the link to be taken out- of-service. Furthermore, this technique does not continually monitor the connection status. Another conventional technique that has been used to test connection status is to use microprocessors to monitor and report the link status. The disadvantage of this technique is that it requires the use of processors which incurs the additional hardware costs of the processors and associated support devices (RAM, ROM, etc.). Furthermore, the technique cannot be used where no processor is available.

Thus, there is a need for a method and apparatus to determine full-duplex link connection status in both directions and to continually monitor, isolate and report the status without requiring intelligent processors.

SLTNUVLARY OFTHE INVENTION The present invention provides a method of testing a connection status of a communication link between a first site and a second site. The method includes the steps of detecting whether an incoming data transport element is received by the first site; setting a connection status bit in an outgoing data transport element to a first state in response to the incoming data transport element being received by the first site; checking a state of a connection status bit in the incoming data transport element; and activating a first status indicator in response to the connection status bit in the incoming data transport element being equal to the first state.

A method in accordance with the present invention may also include the steps of. detecting whether a signal is received by the first site; activating a first status indicator in response to the signal being received by the first site; detecting whether an incoming packet is received by the first site; setting a connection status bit in an outgoing packet to a first state in response to the incoming packet being received by the first site; checking a state of a connection status bit in the incoming packet; and activating a second status indicator in response to the connection status bit in the incoming packet being equal to the first state.

The present invention also provides an apparatus for testing a connection status of a communication link between a first site and a second site. The apparatus includes a signal detector configured to detect whether a signal is received by the first site, and first status indicator circuitry is coupled to the signal detector and responsive thereto. A packet detector is configured to detect whether an incoming packet is received by the first site, and connection status bit circuitry is configured to set a connection status bit in an outgoing packet to a first state in response to the incoming packet being received by the first site. A connection status bit detector is configured to check a state of a connection status bit in the incoming packet, and second status indicator circuitry is coupled to the connection status bit detector and responsive thereto.

A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description of the invention and accompanying drawings which set forth an illustrative embodiment in which the principles of the invention are utilized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. I is a block diagram illustrating two connection status indicators in accordance with the present invention.

FIG. 2 is a flow diagram illustrating the operation of the connection status 10 indicators shown in FIG. 1.

FIG. 3 is a block diagram illustrating in more detail one of the connection status indicators shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. I there is illustrated two connection status indicators A and B in accordance with the present invention. Specificafly, the communication system shown in FIG. I connects two sites, labeled site A and site B, via a full-duplex link 10 transporting data in elements, such as packets 12, 14 as may be the scenario when using Ethernet communication protocol. Site A and site B each include link interface transceivers for 20 interfacing with the full-duplex link 10.

Each of the connection status indicators A and B tests the connection status of the full-duplex communication link 10 in both directions. '17he test is performed on a continuous basis running in the background as voice/data elements are transmitted over the link 10. Faults in the connection are isolated and reported. This method does not rely on 25 sites A and B having microprocessors available to handle the link status functions.

The connection status indicator A includes a light emittifig diode (LED) 16, referred to as uplinkA, and an LED 18, referred to as downlinkA. Similarly, the connection status indicator B includes an uplinkl3 LED 20 and a downlinkB LED 22. The purpose of the LEDs 16, 18, 20, 22 is to indicate the connection status of the full-duplex link 10. The -4..EDs 16, 18, 20, 22 make it possible for a person to determine the connection status by simply viewing the connection status indicators A and B. As shown in FIG. 1 the connection status indicators A and B are coupled to their respective sites A and B via connection means 15 and 19, respectively. It should be understood, however, that the connection status indicators A and B may be incorporated directly into their respective sites A and B and that the connection means 15 and 19 may not be clearly defined. Therefore, the connection means 15 and 19 may include many different types of wiring, bussing, etc.

UplinkA and uplinkB provide a first level of link connection status as a function of the link interface transceivers for site A and site B, respectively. Specifically, uplinkA indicates whether or not a signal is being received by site A. If a signal is being received by site A, uplinkA turns on. Similarly, uplinkB indicates whether or not a signal is being received by site B. If a signal is being received by site B, uplinkB turns on.

DownlinkA and downlinkB provide a second level of link connection status.

The second level of link connection status is provided by the controlling hardware in site A and site B which monitors the received data and transmits the outgoing data. Specifically, site A and site B transmit data to each other in data transport elements, such as packets.

Packet 12 is an example of a packet assembled and transmitted by site A, and packet 14 is an example of a packet assembled and transmitted by site B. A maintenance byte is included in every packet, such as for example, maintenance bytes 24, 26 in packets 12, 14, respectively. Furthermore, each maintenance byte 24, 26 includes a connection status bit 28, 30, respectively.

During operation, if site A is receiving packets (such as packet 14) from site B, then site A sets the connection status bit 28 in the packet 12 that site A transmits to site B. If site A is not receiving packets from site B, then site A clears the connection status bit 28 in the packet 12 that site A transmits to site B. The converse function is performed by site B. Specifically, if site B is receiving packets (such as packet 12) from site A, then site B sets the connection status bit 30 in the packet 14 that site B transmits to site A. If site B is not receiving packets from site A, then site B clears the connection status bit 30 in the packet 14 that site B transmits to site A.

Site A and site B each monitor the received packets and the corresponding connection status bit in each received packet. The state of the connection status bits are used to report the link connection status via the downlinkA and downlinkB LEDs 18, 22. The downlinkA and downlinkB LEDs 18, 22 are activated (i.e., turned on) only when the connection status bit of the received packets are set. Since this operation is done on every packet, the link connection status test is performed continuously as a background fimction.

Site A monitors the connection status bit of incoming packets, such as connection status bit 30 of packet 14. If the connection status bit 30 of packet 14 is set when site A receives packet 14, then site A turns on the downlinkA LED 18. If the connection status bit 30 of packet 14 is not set (i.e., cleared) when site A receives packet 14, then site A turns off the downlinkA LED 18. Similarly, site B monitors the connection status bit of incoming packets, such as connection status bit 28 of packet 12. If the connection status bit 28 of packet 12 is set when site B receives packet 12, then site B turns on the downlinkB LED 22. If the connection status bit 28 of packet 12 is not set when site B receives packet 12, then site B turns off the downlinkB LED 22.

This second layer of link testing, i.e. using the transmission and monitoring of a connection status bit communicated continuously as overhead in the data transport element, is one feature of the present invention which helps to overcome the disadvantages of the conventional link status testing techniques described above.

Isolation of link connection faults is deterTnined from the uplink and downlink LEDs associated with each site. For example, when viewing the connection status indicator A, the uplinkA LED 16 indicates whether or not site A is receiving a signal, and the downlinkA LED 18 indicates whether or not, via the connection status bit, site B is receiving packets from site A. Similarly, when viewing the connection status indicator B, the uplinkB LED 20 indicates whether or not site B is receiving a signal, and the downlinkB LED 22 indicates whether or not, via the connection status bit, site A is receiving packets from site B. Table I below shows the link connection status matrix for connection status indicator A, and Table 11 shows the link connection status matrix for connection status indicator B. CONNECTION STATUS INDICATOR A UplinkA LED 16 DownlinkA LED 18 Link Connection Status On On Communications established in both directions.

Off Off No signal received from site B: Link carrying data from site B to site A is down, or site B controller is not functioning.

On Off Signal received from site B, but site B not receiving data from site A: Link carrying data from site A to site B is down.

TABLEI

CONNECTION STATUS INDICATOR B UplinkB LED 20 DownlinkB LED 22 Link Connection Status On On Communications established in both directions.

Off 0 ff No signal received from site A: Link carrying data from site A to site B is down, or site A controller is not functioning.

On Off Signal received from site A, but site A not receiving data from site B: Link carrying data from site B to site A is down.

TABLE II

Referring to FIG. 2, there is illustrated a state machine flow diagram 40 for the connection status indicator A. Initialization begins in step 42, and in step 44 the uplinkA LED (shown as UP-LED) and downlinkA LED (shown as DN_LED) are turned off.

Furthermore, the transmitted link status bit T_STATUS is initially set to 0, i.e., cleared. The -7lransmitted link status bit T_STATUS corresponds to the state _to which the connection status bit of the transmitted packet, such as connection status bit 28 of packet 12, will be set.

In steps 46 and 48 the receiving portion of the fidl-duplex link 10 is checked to determine, or detect, whether or not a signal is being received by site A. If no signal is received by site A, the uplinkA LED and downlinkA LED are turned off, or deactivated, and the transmitted link status bit T_STATUS is set to 0, all in step 50. Such a scenario indicates that the link carrying data from site B to site A is down or that the site B controller is not functioning.

If a signal is received by site A, the uplinkA LED is turned on, or activated, in step 52. In step 54 the state machine waits a predetermined period of time for a packet to be received by site A, and in step 56 the state machine determines, or detects, whether or not an incoming packet, such as packet 14, has been received by site A. If no incoming packet is received by site A the downlinkA LED is turned off and the transmitted link status bit T_STATUS is set to 0 in step 58. Such a scenario indicates that a signal has been received from site B but that no packets have been received from site B. If it is determined in step 56 that an incoming packet has been received by site A, then the transmitted link status bit T_STATUS is set to 1 in step 60. This will cause the connection status bit of the next outgoing packet transmitted from site A, such as connection status bit 28 of packet 12, to be set.

In steps 62 and 64 the connection status bit R_STATUS of the received incoming packet, such as connection status bit 30 of packet 14, is checked to determine whether or not it is set. If the connection status bit R STATUS of the received packet is not set, the downlinkA LED is turned off in step 66. This scenario indicates that a signal was received from site B but that site B is not receiving data from site A, possibly because the link carrying data from site A to site B is down. If the connection status bit R STATUSof the received packet is set, the downlinkA LED is turned on in step 68. This scenario indicates that communications have been established in both directions.

The state machine flow diagram 40 shown in FIG. 2 is for the connection status indicator A, but it should be understood that the connection status indicator B uses substantially the same state machine flow diagram. Furthermore, the method illustrated by -8he state machine flow diagram 40 can be implemented in hardware that does not require a microprocessor. For example, the state machine flow diagram 40 may be implemented Wifl-I discrete logic circuits, programmable logic circuits, or the like. It should also be understood that the LEDs used for the uplink and downlink indicators may be replaced with various 5 other indication means, such as for example, audible indication means.

FIG. 3 illustrates one example implementation of the connection status indicator A. A signal detector 80 may be used to detect whether or not a signal is received by site A, and a packet detector 82 may be used to detect whether or not an incoming packet is received by site A. The state of the connection status bit R_STATUS of an incoming packet, such as connection status bit 30 of packet 14, may be checked with a connection status bit detector 84. The uplinkA LED 16 is coupled to the output of the signal detector 80. The transmitted link status bit T_STATUS is generated by ANDing the outputs of the signal detector 80 and the packet detector 82 with AND circuit 86. The downlinkA LED 18 is turned on by ANDing the outputs of the signal detector 80, the packet detector 82, and th,,connection status bit detector 84 with AND circuit 88. The inputs of the signal detector 80, the packet detector 82, and the connection status bit detector 84, as well as the transmitted link status bit T_STATUS, are connected to site A via connection means 15. It should be understood that all or part of the signal detector 80, the packet detector 82, and the connection status bit detector 84 may be located, intermingled or incorporated into the circuitry of site A and that connection means 15 represents whatever connections are needed between site A and the connection status indicator A.

The connection status indicator method and apparatus of the present invention is not limited to the specific embodiment shown in FIGS. 1, 2 and 3. For example, the present invention may utilize more than two LEDs or other status indicators.

Such additional LEDs could be used to provide further details of the connection status. For example, a third LED in the connection status indicator A could be used to indicate whether or not site A receives a packet from site B. In this scenario the third LED would be turned on in response to the "yes" branch of step 56 of FIG. 2. This third LED would merely indicate that a packet has been received, in contrast to the downlinkA LED 18 which indicates that the connection status bit R_STATUS in the received packet is set.

An example of another application of the present invention is in pointtomultipoint connections. Specifically, FIG. I illustrates a point-topoint connection. Rather than just being connected to site B, however, site A could be connected to multiple sites, such as for example, sites B, C, D, etc. In this scenario the data transport elements, such as packets 12, 14 shown in FIG. 1, may include unique identifier bits to indicate the specific site they came from and/or the specific site to which they are directed. Such identifier bits may be included in the maintenance bytes 24, 26.

The connection status indicator method and apparatus of the present invention may be employed on any type of link, such as for example, twisted-pair, coaxial, fiber optic, etc. Furthermore, the present invention may be used with any type of communication protocol, such as for example, Ethernet, Token Ring, HDLC, etc. Any fullduplex voice/data communications system connecting multiple sites via a communications link where no processor is available may use the present invention to monitor, isolate faults, and report the link status. By using the present invention, the link connection status is continuously tested and reported without manual operations while the link remains in service. This testing is done entirely in simple hardware without the use of microprocessors.

It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.

Claims

What is claimed is:

1. A method of testing a connection status of a communication link between a first site (A) and a second site (B), comprising the steps of..

detecting whether an incoming data transport element (14) is received by the first site; setting a connection status bit (28) in an outgoing data transport element (12) to a first state in response to the incoming data transport element being received by the first site; checking a state of a connection status bit (30) in the incoming data transport 15 element; and activating a first status indicator (18) in response to the connection status bit in the incoming data transport element being equal to the first state.

2. A method in accordance with claim 1, flirther comprising the steps of.

deactivating the first status indicator in response to the incoming data transport element not being received by the first site; and setting the connection status bit in the outgoing data transport element to a second state in response to the incoming data transport element not being received by the first site.

3. A method in accordance with claims 1 or 2, further comprising the step of- deactivating the first status indicator in response to the connection status bit in the incoming data transport element being equal to a second state.

4. A method in accordance with claims 1, 2, or 3, wherein the first status indicator comprises a light emitting diode (LED).

5. A method in accordance with claims 1, 2, or 3, further comprising the steps of. detecting whether a signal is received by the first site; and activating a second status indicator (16) in response to the signal being received by the first site.

6. A method in accordance with claim 5, further comprising the steps of.

deactivating the first and second status indicators in response to the signal not being received by the first site; and setting the connection status bit in the outgoing data transport element to a second state in response to the signal not being received by the first site.

7. A method in accordance with claims 5 or 6, wherein the second status indicator comprises a light emitting diode (LED).

8. A method in accordance with any of the preceding claims, wherein the data transport elements each comprise a packet.

12 9. An apparatus for testing a connection status of a communication link between a first site (A) and a second site (B), comprising:

a signal detector (80) configured to detect whether a signal is received by the first site; first status indicator circuitry (16) coupled to the signal detector and responsive thereto; a packet detector (82) configured to detect whether an incoming packet (14) is received by the first site; connection status bit circuitry (86) configured to set a connection status bit (2 8) in an outgoing packet (12) to a first state in response to the incoming packet being received by the first site; connection status bit detector (84) configured to check a state of a connection status bit (30) in the incoming packet; and second status indicator circuitry (88) coupled to the connection status bit detector and responsive thereto.

10. An apparatus in accordance with claim 9, wherein the first status indicator circuitry comprises a light emitting diode (LED). 20 11. An apparatus in accordance with claims 9 or 10, wherein the connection status bit circuitry comprises an AND circuit (86) having one input coupled to the signal detector and another input coupled to the packet detector.

12. An apparatus in accordance with claims 9, 10, or 11, wherein the second status indicator circuitry comprises:

13 an AND circuit (88) having a first input coupled to the signal detector, a second input coupled to the packet detector, and a third input coupled to the connection status bit detector; and a light emitting diode (LED) (18) coupled to an output of the AND circuit.