Multiplexing and demultiplexing method and equipments measuring transmission quality and locating operation faults on multiplexed digital channels

• US 4,845,711 A
• Filed: 01/15/1987
• Issued: 07/04/1989
• Est. Priority Date: 01/17/1986
• Status: Expired due to Fees

• Current Assignee: Societe Anonyme de Telecommunications (Safran SA)
• Original Assignee: Societe Anonyme de Telecommunications (Safran SA)
• Inventors: Walraet, Jean, Boutmy, Patrick, Liger, Marc, LeFort, Gilbert
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Haseman, Marianne
• Application Number:
  US07/003,594
• Time in Patent Office: 901 Days
• Field of Search: 370/102, 370/17, 370/13, 375/112
• US Class Current: 370/242
• CPC Class Codes: H04J 3/073 Bit stuffing, e.g. PDH
• CPC Class Codes: H04J 3/14 Monitoring arrangements for SDH/SONET rings H04J3/085

Abstract

A predetermined characteristic of each of incoming plesiochronous component signals in a time-division multiplexing equipment is derived at each stuffing time for transmission in the form of a stuffing bit in a respective stuffed signal to be multiplexed in a resulting signal. In a demultiplexing equipment receiving the resulting signal, the stuffing bit in a respective demultiplexed stuffed signal is sampled and simultaneously the predetermined characteristic of the plesiochronous signal outgoing from the demultiplexing equipment is derived at each unstuffing time. The sampled stuffing bit and the derived predetermined characteristic are compared in order to measure the transmission quality of a digital channel carrying the component signal through the two equipments. The predetermined characteristic is preferably the parity of the signal between two consecutive stuffing and unstuffing times. The results of the comparisons, in the form of error signals relating to the component signals, contribute to locating faults in the two equipments, signalled by a checking unit included in the demultiplexing equipment.

Claims

1. A method of measuring the quality of digital channels between a multiplexing equipment and a demultiplexing equipment,

said channels respectively applying digital plesiochronous signals fed to said multiplexing equipment for synchronization by utilizing techniques for pulse stuffing into digital stuffed signals which are multiplexed into a digital resultant signal,

said resultant signal being supplied to said demultiplexing equipment for demultiplexing into digital stuffed signals which are desychronized by utilizing techniques for pulse unstuffing into outgoing plesiochronous digital signals,

said method comprising for each of said digital channels,

in said multiplexing equipment, deriving a predetermined characteristic of the respective incoming plesiochronous signal during signal stuffing times for transmission in the form of stuffing bits in the respective stuffed signal, said predetermined characteristic of the incoming plesiochronous signal being a function of the bits in said incoming plesiochronous signal between two consecutive stuffing times,

in said demultiplexing equipment, sampling each of said stuffing bits in the respective stuffed signal while deriving a predetermined characteristic of the respective outgoing plesiochronous signal during an unstuffing time, said predetermined characteristic of the outgoing plesiochronous signal being a function of the bits in said outgoing plesiochronous signal between two consecutive unstuffing times, and

comparing said sampled stuffing bit and the derived predetermined characteristic of the outgoing plesiochronous signal to provide a measure of the quality of the respective channel.

2. A method of measuring the quality of digital channels between a multiplexing equipment and a demultiplexing equipment,

said channels respectively applying digital plesiochronous signals fed to said multiplexing equipment for synchronization by utilizing techniques for pulse stuffing into digital stuffed signals which are multiplexed into a digital resultant signal,

said resultant signal being supplied to said demultiplexing equipment for demultiplexing into digital stuffed signals which are desynchronized by utilizing techniques for pulse unstuffing into outgoing plesiochronous digital signals,

said method comprising for each of said digital channels,

in said multiplexing equipment, deriving a predetermined characteristic of the respective incoming plesiochronous signal during signal stuffing times for transmission in the form of stuffing bits in the respective stuffed signal, and

in said demultiplexing equipment, sampling each of said stuffing bits in the respective stuffed signal while deriving predetermined characteristic of the respective outgoing plesiochronous signal during an unstuffing time, and

comparing said sampled stuffing bit and the derived predetermined characteristic of the outgoing plesiochronous signal to provide a measure of the quality of the respective channel, said predetermined characteristic being the parity of the incoming and outgoing plesiochronous signals between two consecutive stuffing and unstuffing times.

3. A multiplexing equipment comprising:

a plurality of pulse stuffing means for synchronizing incoming digital plesiochronous signals into corresponding synchronized stuffed digital signals and for deriving a stuffing command signal,

means for multiplexing said stuffed signals into a digital resultant signal, and

associated with each of said synchronizing means;

means for deriving a predetermined characteristic of said respective incoming plesiochronous signal in response to a stuffing command signal deriving by said synchronizing means, and means for inserting a stuffing bit dependent on said characteristic into said respective synchronized signal, said deriving means comprising means for deriving a parity signal from said respective incoming plesiochronous signal, means controlled by said stuffing command signal for storing two states of said parity signal at first and second sequential stuffing times, and means for comparing said two parity signal states simultaneously at said second time to derive a stuffing bit having a state indicating the parity of said respective incoming plesiochronous signal between said first and second times.

4. The multiplexing equipment of claim 3 wherein one of synchronizing means includes a buffer store for receiving the incoming plesiochronous signal associated with said one synchronizing means, said buffer store comprising a cell for transferring said parity signal from said parity signal deriving means to said storing means thereby to phase said parity signal with said synchronized signal deriving from said one synchronizing means.

5. A demultiplexing equipment comprising:

means for demultiplexing a resultant digital signal into synchronous digital stuffed signals,

a plurality of pulse unstuffing means for desynchronizing said synchronous stuffed signals into respective outgoing plesiochronous digital signals and for deriving an unstuffing command signal,

associated with each of said desynchronizing means;

means for sampling a stuffing bit in said respective stuffed signal to be desynchronized in response to the unstuffing command signal derived by said desynchronizing means, means responsive to said unstuffing command signal for deriving a predetermined characteristic of said respective outgoing plesiochronous signal simultaneously with sampling of said stuffing bit, and first means for comparing said predetermined characteristic of said respective outgoing plesiochronous signal with said sampled stuffing bit, thereby measuring the quality of said outgoing plesiochronous signal, said sampling means including means for sampling the state of said stuffing bit in said respective stuffed signal at another unstuffing time in response to said unstuffing command signal, said deriving means comprising means for deriving a parity signal from said respective outgoing plesiochronous signal, means controlled by said unstuffing command signal for storing two parity signal states at a first unstuffing time preceding said second time and at said second time, and second means for comparing said two parity signal states after said second time to detect the parity of said respective outgoing plesiochronous signal between said first and second times, and said first comparing means comparing said outgoing plesiochronous signal parity with said sampled stuffing bit representing an old parity of said plesiochronous signal.

6. The demultiplexing equipment of claim 5, wherein said sampling means comprises means for extracting the contents of a stuffing bit from said respective stuffed signal to be desynchronized, means for delaying said extracted content of said stuffing bit, and means for deriving a gate pulse signal for indicating a location of said stuffing bit in said respective stuffed signal and said stuffing bit content, and said respective desynchronizing means including a buffer store for receiving said respective stuffed signal, said buffer store comprising a cell for transferring said location gate pulse and content signal to said memorizing means and first comparing means so that said stuffing bit location gate pulse controls memorization of two states of said parity signal in phase with said respective outgoing plesiochronous signal.

7. A time-division multiplexing and demultiplexing system comprising:

means for synchronizing incoming digital plesiochronous signals into incoming synchronized respective stuffed digital signals, each of said incoming stuffed signals including stuffing bits, a stuffing bit in a stuffed signal having a state dependent on a function of a predetermined parity characteristic of the respective incoming plesiochronous signal between said stuffing bit and another stuffing bit of said stuffed signal preceding said stuffing bit,

means for multiplexing said incoming synchronized stuffed signals into a digital resulting signals,

means for demultiplexing said resulting signal into outgoing synchronized stuffed digital signals which are normally identical to said incoming synchronized stuffed signals respectively,

means for desynchronizing said outgoing synchronized stuffed signals into outgoing digital plesiochronous signals which are normally identical to said incoming plesiochronous signals respectively, an outgoing stuffed signal being desynchronized for sampling stuffing bits, said means for desynchronizing including means for deriving a predetermined characteristic of an outgoing plesiochronous signal between two consecutive sampled stuffing bits in the respective outgoing stuffed signal, and

means respectively connected to said desynchronizing means for comparing said characteristics of said incoming plesiochronous signals in the form of said sampled stuffed bits with said derived characteristics of said outgoing plesiochronous signals respectively, to thereby provide a measure of the transmission quality of said system.

8. A time-division multiplexing and demultiplexing system interconnected to a plurality of digital channels,

said system comprising:

a plurality of pulse stuffing means for receiving incoming digital plesiochronous signals transmitted from digital channels for synchronizing said incoming plesiochronous signals into incoming synchronized stuffed digital signals respectively, said pulse stuffing means including means for deriving a stuffing command signal and means for stuffing bits at predetermined locations in said incoming stuffed signal in response to the respective stuffing command signal derived by the respective synchronizing means,

a plurality of means for receiving said incoming plesiochronous signals for deriving predetermined characteristics of said respective incoming plesiochronous signals,

means responsive to the stuffing command signal for indicating the characteristic of an incoming plesiochronous signal as determined by the state of a stuffing bit to be inserted in the respective incoming stuffed signal,

means for multiplexing said incoming stuffed signals into a digital resultant signal,

means for demultiplexing said resultant digital signal into outgoing synchronized stuffed digital signals normally identical to said incoming stuffed digital signals respectively,

plural pulse unstuffing means for desynchronizing said outgoing stuffed signals into outgoing digital plesiochronous signals to be transmitted into said digital channels respectively, said outgoing plesiochronous signals being normally identical to said incoming plesiochronous signals respectively, each of said desynchronizing means producing a respective unstuffing command signal in correspondence with stuffing bits included in the respective outgoing stuffed signal,

a plurality of means receiving said outgoing stuffed signals for sampling said stuffing bits in said outgoing stuffed signals to thereby deduce said characteristics of said incoming plesiochronous signals respectively,

a plurality of means receiving said outgoing plesiochronous signals and associated with said digital channels for deriving predetermined characteristics of said outgoing plesiochronous signals simultaneously with samplings of stuffing bits respectively, and

a plurality of means respectively connected to said sampling means and said outgoing plesiochronous signal characteristic deriving means for comparing the sampled stuffing bits with the outgoing plesiochronous signal characteristics respectively thereby to provide a measure of the transmission quality of said digital channels through said system,

said predetermined characteristic of each of said incoming and outgoing plesiochronous signals being the parity of said signal.

9. A time-division multiplexing and demultiplexing system interconnected to a plurality of digital channels,

said system comprising:

a plurality of pulse stuffing means for receiving incoming digital plesiochronous signals transmitted from digital channels for synchronizing said incoming plesiochronous signals into incoming synchronized stuffed digital signals respectively, said pulse stuffing means including means for deriving a stuffing command signal and means for stuffing bits at predetermined locations in said incoming stuffed signal in response to the respective stuffing command signal derived by the respective synchronizing means,

a plurality of means for receiving said incoming plesiochronous signals for deriving predetermined characteristics of said respective incoming plesiochronous signals,

means responsive to the stuffing command signal for indicating the characteristic of an incoming plesiochronous signal as determined by the state of a stuffing bit to be inserted in the respective incoming stuffed signal,

means for multiplexing said incoming stuffed signals into a digital resultant signal,

means for demultiplexing said resultant digital signal into outgoing synchronized stuffed digital signals normally identical to said incoming stuffed digital signals respectively,

plural pulse unstuffing means for desynchronizing said outgoing stuffed signals into outgoing digital plesiochronous signals to be transmitted into said digital channels respectively, said outgoing plesiochronous signals being normally identical to said incoming plesiochronous signals respectively, each of said desynchronizing means producing a respective unstuffing command signal in correspondence with stuffing bits included in the respective outgoing stuffed signal,

a plurality of means receiving said outgoing stuffed signals for sampling said stuffing bits in said outgoing stuffed signals to thereby deduce said characteristics of said incoming plesiochronous signals respectively,

a plurality of means receiving said outgoing plesiochronous signals and associated with said digital channels for deriving predetermined characteristics of said outgoing plesiochronous signals simultaneously with samplings of stuffing bits respectively,

a plurality of means respectively connected to said sampling means and said outgoing plesiochronous signal characteristic deriving means for comparing the sampled stuffing bits with the outgoing plesiochronous signal characteristics respectively, thereby to provide a measure of the transmission quality of said digital channels through said system, each of said comparing means associated with a digital channel including means for deriving an error signal in response to the derived characteristic of the respective outgoing plesiochronous signal differing from the derived characteristic of the respective incoming plesiochronous signal represented by a stuffing bit sampled in the respectively outgoing stuffed signal,

means for receiving the error signal derived by said comparing means for locating operation faults in said synchronizing means, said multiplexing means, said demultiplexing means and said desynchronizing means,

said locating means comprising;

supplementary means for demultiplexing said resultant digital signal into supplementary synchronized stuffed digital signals normally identical to said incoming stuffed digital signals respectively,

switching means for selecting one of said supplementary stuffed signals,

supplementary means analogous to one of said desynchronization means for desynchronizing said selected supplementary stuffed signal into a supplementary digital plesiochronous signal,

supplementary means analogous to one of said sampling means for sampling stuffing bits in said selected supplementary stuffed signal,

supplementary means analogous to one of said characteristic deriving means for deriving the predetermined characteristic of said supplementary plesiochronous signal simultaneously with samplings of said stuffing bits of said selected supplementary stuffed signal,

supplementary means analogous to one of said comparing means for comparing the sampled stuffed bits of said selected supplementary stuffed signal with the supplementary plesiochronous signal characteristic to thereby derive a supplementary error signal, and checking means responsive to all said error signals and said supplementary error signal for comparing said supplementary error signal with the error signal derived by one of said comparing means associated with the desynchronizing means receiving the outgoing stuffed signal normally identical to the selected supplementary stuffed signal, thereby mainly checking the operation of the synchronizing means and desynchronizing means corresponding to the selected supplementary stuffed signal.

10. The time-division multiplexing and demultiplexing system of claim 9, further including means for applying said resultant signal to said supplementary demultiplexing means in response to at least one of said error signals derived by said plural comparing means.

11. The time-division multiplexing and demultiplexing system of claim 9 wherein said checking means includes means for controlling said switching means whereby the selected supplementary stuffed signal corresponds to one of said stuffed signals to be desynchronized by said plurality of said desynchronized means for which an error signal is being received by said checking means.

12. The time-division multiplexing and demultiplexing system of claim 9 wherein said checking means includes means for controlling cyclic selection of several supplementary stuffed signals in said switching means in response to several error signals respectively derived by several of said comparing means, said several comparing means being associated with several desynchronizing means receiving outgoing stuffed signals normally identical to said several selected supplementary stuffed signals, thereby primarily locating an operation fault in said multiplexing means and demultiplexing means.

13. Apparatus for demultiplexing a resultant digital signal comprising

means for demultiplexing the resultant digital signal into N synchronous digital stuffed signals, where N is an integer greater than one,

N pulse unstuffing means for deriving an unstuffing command signal and for desynchronizing said N synchronous stuffed signals into N outgoing plesiochronous digital signals, so that a kth unstuffing means derives a kth one of the synchronous stuffed signal that is desynchronized into a kth one of the outgoing plesiochronous digital signals, where 1≦

k≦

N,

the kth one of said N pulse unstuffing means including;

means responsive to the unstuffing command signal for sampling a stuffing bit in the kth stuffed signal to be desynchronized, means responsive to said unstuffing command signal and the kth outgoing plesiochronous signal for deriving an indication of a predetermined characteristic of the kth outgoing plesiochronous signal simultaneously with sampling of said stuffing bit, and means responsive to said indication and the kth sampled stuffing bit for comparing said predetermined characteristic of the kth outgoing plesiochronous signal with the kth sampled stuffing bit to provide a measure of the quality of the outgoing plesiochronous signal.

14. The demultiplexing equipment claimed in claim 13,, wherein said first comparing means derives an error signal in response to said derived predetermined characteristic of said kth outgoing plesiochronous signal differing from said sampled stuffing bit.

15. The apparatus of claim 13 wherein the indicated characteristic of the kth outgoing plesiochronous signal indicates bit errors in the kth outgoing plesiochronous signal.

16. A time-division multiplexing and demultiplexing system comprising:

means for synchronizing N incoming digital plesiochronous signals into N incoming synchronized stuffed digital signals, incoming stuffed signal k including stuffing bits, where N is greater than one and 1≦

k≦

N, a stuffing bit in stuffed signal k having a state dependent on a function of a predetermined characteristic of incoming plesiochronous signal k between said stuffing bit and another stuffing bit of said stuffed signal preceding said stuffing bit,

means for multiplexing said N incoming sychronized stuffed signals into a resulting digital signal,

means for demultiplexing said resulting digital signal into N outgoing synchronized stuffed digital signals so the kth outgoing synchronized stuffed digital signal is normally identical to said kth incoming synchronized stuffed signals,

means for desynchronizing said N outgoing synchronized stuffed signals into N outgoing digital plesiochronous signals so the kth outgoing digital plesiochronous signal is normally identical to the kth incoming plesiochronous signal, an outgoing stuffed signal being desynchronized for sampling stuffing bits,

said means for desynchronizing including;

means responsive to the kth outgoing plesiochronous signal for deriving predetermined characteristic of outgoing plesiochronous signal k between two consecutive sampled stuffing bits in the kth outgoing stuffed signal, and

means connected to said desynchronizing means for comparing said characteristics of said kth incoming plesiochronous signal in the form of said sampled stuffed bits with said derived characteristics of said kth outgoing plesiochronous signal, to thereby provide a measure of the transmission quality of said system.

17. The system of claim 16 wherein the predetermined characteristic indicates bit errors in incoming plesiochronous signal k and in outgoing plesiochronous signal k.

18. A time-division multiplexing and demultiplexing system interconnected to N digital channels, where N is an integer greater than one, said system comprising:

N pulse stuffing means for receiving N incoming digital plesiochronous signals transmitted from N digital channels and for synchronizing said N incoming plesiochronous signals into N incoming synchronized stuffed digital signals so incoming plesiochronous signal k is synchronized into synchronized stuffed digital signal k, each of said pulse stuffing means including means for deriving a stuffing command signal and means for stuffing bits at predetermined locations in the kth incoming stuffed signal in response to the stuffing command signal derived by the kth synchronizing means, where 1≦

k≦

N,

N means responsive to said N incoming plesiochronous signals for deriving predetermined characteristics of said incoming plesiochronous signals so that an indication of the predetermined characteristic of the kth incoming plesiochronous signal is derived,

means responsive to the stuffing command signal and the indication of the predetermined characteristic for indicating the characteristic of an incoming plesiochronous signal as determined by the state of a stuffing bit to be inserted in the respective incoming stuffed signal,

means for multiplexing said incoming stuffed signals into a digital resultant signal,

means for demultiplexing said resultant digital signal into N outgoing synchronized stuffed digital signals normally identical to said incoming stuffed digital signals so the kth outgoing synchronized stuffed digital signal is normally identical to the kth incoming stuffed digital signal,

N pulse unstuffing means for desynchronizing said N outgoing stuffed signals into N outgoing digital plesiochronous signals to be transmitted to said N digital channels, so the kth outgoing stuffed signal is desynchronized into the kth outgoing digital plesiochronous signal to be transmitted to the kth digital channel, said N outgoing plesiochronous signals being normally identical to said N incoming plesiochronous signals so the kth outgoing plesiochronous signal is normally identical to the kth incoming plesiochronous signal, the kth desynchronizing means producing a kth unstuffing command signal in correspondence with stuffing bits included in the kth outgoing stuffed signal,

N means responsive to said N outgoing stuffed signals for sampling said stuffing bits in said N outgoing stuffed signals to thereby deduce said characteristics of said incoming plesiochronous signals so sampling of the stuffing bits of the kth outgoing stuffed signal results in said characteristic of the kth incoming plesiochronous signal being deduced N, means responsive to said outgoing plesiochronous signals and associated with said N digital channels for deriving predetermined characteristics of said N outgoing plesiochronous signals so that the predetermined characteristic of the kth outgoing plesiochronous signal is derived simultaneously with sampling of the kth stuffing bit, and

N means respectively connected to said sampling means and said N outgoing plesiochronous signal characteristic deriving means for comparing the kth sampled stuffing bit with the predetermined characteristic of the kth outgoing plesiochronous signal thereby to provide a measure of the transmission quality of said digital channels through said system.

20. The system of claim 18 wherein the predetermined characteristic indicates bit errors in incoming plesiochronous signal k and in outgoing plesiochronous signal k.

19. The time-division multiplexing and demultiplexing system of claim 37 wherein each of said comparing means associated with a digital channel includes means for deriving an error signal in response to the derived characteristic of the respective outgoing plesiochronous signal differing from the derived characteristic of the respective incoming plesiochronous signal represented by a stuffing bit sampled in the respective outgoing stuffed signal and means for receiving the error signals derived by said comparing means for locating operation faults in said synchronizing means, said multiplexing means, said demultiplexing means and said desynchronizing means.