CA2201210A1 - A method of providing continual network access for subscriber communication lines - Google Patents

A method of providing continual network access for subscriber communication lines

Info

Publication number
CA2201210A1
CA2201210A1 CA002201210A CA2201210A CA2201210A1 CA 2201210 A1 CA2201210 A1 CA 2201210A1 CA 002201210 A CA002201210 A CA 002201210A CA 2201210 A CA2201210 A CA 2201210A CA 2201210 A1 CA2201210 A1 CA 2201210A1
Authority
CA
Canada
Prior art keywords
transmission lines
lines
reserved
idle
dsos
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.)
Abandoned
Application number
CA002201210A
Other languages
French (fr)
Inventor
Nagaraja Rao
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens Telecom Networks LLC
Original Assignee
Siemens Stromberg Carlson
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Siemens Stromberg Carlson filed Critical Siemens Stromberg Carlson
Publication of CA2201210A1 publication Critical patent/CA2201210A1/en
Abandoned legal-status Critical Current

Links

Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04MTELEPHONIC COMMUNICATION
    • H04M3/00Automatic or semi-automatic exchanges
    • H04M3/22Arrangements for supervision, monitoring or testing
    • H04M3/26Arrangements for supervision, monitoring or testing with means for applying test signals or for measuring
    • H04M3/28Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor
    • H04M3/30Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for subscriber's lines, for the local loop
    • H04M3/302Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for subscriber's lines, for the local loop using modulation techniques for copper pairs
    • H04M3/303Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor for subscriber's lines, for the local loop using modulation techniques for copper pairs and using PCM multiplexers, e.g. pair gain systems
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04JMULTIPLEX COMMUNICATION
    • H04J3/00Time-division multiplex systems
    • H04J3/02Details
    • H04J3/12Arrangements providing for calling or supervisory signals
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04QSELECTING
    • H04Q3/00Selecting arrangements
    • H04Q3/42Circuit arrangements for indirect selecting controlled by common circuits, e.g. register controller, marker
    • H04Q3/54Circuit arrangements for indirect selecting controlled by common circuits, e.g. register controller, marker in which the logic circuitry controlling the exchange is centralised
    • H04Q3/545Circuit arrangements for indirect selecting controlled by common circuits, e.g. register controller, marker in which the logic circuitry controlling the exchange is centralised using a stored programme
    • H04Q3/54575Software application
    • H04Q3/54591Supervision, e.g. fault localisation, traffic measurements, avoiding errors, failure recovery, monitoring, statistical analysis
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04QSELECTING
    • H04Q2213/00Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13109Initializing, personal profile
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04QSELECTING
    • H04Q2213/00Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13167Redundant apparatus
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04QSELECTING
    • H04Q2213/00Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13348Channel/line reservation
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04QSELECTING
    • H04Q2213/00Indexing scheme relating to selecting arrangements in general and for multiplex systems
    • H04Q2213/13381Pair-gain system, digital loop carriers

Abstract

A method for providing automatic restoration of network access for user lines within a communication system. The user lines interface with groups of transmission lines that include dedicated transmission lines which are connected to the user lines, idle transmission lines and reserved transmission lines. The method includes steps for making a number of transmission lines among the groups of transmission lines available for user lines which have a dedicated transmission line in a group of transmission lines that fails and for coupling each of such user lines to a respective available transmission line. The method may also include steps for delaying the coupling of such user lines if a sufficient number of transmission lines are not available.

Description

f 20 1 2 1 u A M~THOD OF PROVIDING C~N~IN~AL NETWOR~ ACC~SS
FOR 8UBSCRIBER C~M~NICATION LINES

TECHNICAL FIELD
Related applications entitled ~A REPROVISIONING
MONITOR"; "AN IMPROVED DIGITAL LOOP CARRIER SYSTEM'I; and "A METHOD OF MANAGING DIGITAL SIGNAL CARRYING FACILITIES"
by the same inventor, are being filed on the same day herewith and are incorporated by reference herein.
The present invention relates generally to telephone communication systems and more particularly, to a method for providing automatic restoration of network access for user lines in the event of a failure.

BACR~ROUND OF THE INVENTION
In modern telephone networks the use of digital technology has become w despread. Utilizing digital technology in telephone networks has a number of advantages. One advantage is that the digital transmission of data is less susceptible to noise, which improves the quality of the transmission. While another advantage is that the digital format is ideal for being implemented on solid state technology such as integrated circuits. This is siynificant because most of the developments in technology has been in this area.
In crd~r to exploit the advantages of digital technology, new techniques and e~uipment had to be developed. These new developmen's h-:ve included new 22dl21o modulation techniques, digital switches and various digital interfaces.
An example of a system utilized in digital telephone networks is shown in FIGURE 1, which is known as a Digital Loop Carrier or an Integrated Digital Loop Carrier (IDLC) system 10. The IDLC system 10 is utilized to couple subscriber lines 22, 24, 26, 28 to a switching system 12, such as an EWSD~ switching system, which routes calls from the subscriber lines 22, 24, 26, 28 to other parts of the phone network.
The IDLC system 10 includes a remote digital terminal (RDT) 30 which interfaces the subscriber lines 22, 24, 26, 28 to a number of 1.544 MPBS highways 14,18.
The 1.544 MPBS highways 14,18 are also known as Digital Signal Level 1 lines (DSl) and are utilized to carry calls from the subscriber lines 22, 24, 26, 28 to the switching system 12. Each DS1 includes 24 individual 64 K~,PS digital signal carrying facilities, which are also known as Digital Signal Level O lines (DSO). For discussion purposes, only one of the 24 DSOs is shown per each DSl.
The RDT 30 is utilized as an interface to assign and connect the DSOs to the cubscriber lines. The assignment and connection of the DSOs is either accomplished on a per call basis or on a provisioned basis. The per call basis is utilized when a large concentration of subscriber lines are required. This means that the RDT
30 has to dyn~mically assign and connect the DSOs to the i'~

subscriber lines. The subscriber lines utilizing a per call basis interface are known as concentrated lines 24,26. While DSOs assigned and connected on a provisioned basis are known as dedicated DSOs and the connected subscriber lines are known as non-concentrated lines 22,28. The dedicated DSOs 16,20 are nailed up which means semi-permanently connected to the respective subscriber lines 22,2~ at the RDT 30.
A problem with utilizing a provisioned type of interface is that the non-concentrated subscriber lines 22,28 often lose access to the network. Very often this is caused by a failed or blocked DSl, which causes the DSOs to become unavailable to the subscriber lines. This is a serious problem since the subscriber lines connected to the blocked DS1 are unable to be utilized to make calls. The DSls are often blocked due to technical problems or maintenance purposes.
The above discussed problem is partially removed by incorporating DS1 protection switching capability within the RDT 30. An example of a IDLC system having DS1 protection switching is shown in FIGURE 2. In such a system, a standby DSl 36 is reserved in the event one of the other DSls 32,34 fail or is blocked. When a DSl fails, the traffic from that DSl 32 is switched to the standby DSl 36 as shown in FIGURE 3. Thus, the DSl protection switching partially solves the problem of a non-concentrated line losing access. However, the problem remains if a subsequent DSl 34 fails before the ~Oi~ jG

previous failed DSl 32 is repaired as shown in FIGURE 4.
In this situation, the non-concentrated line 40 loses access. Thus, DS1 protection switching is inadequate when there are consecutive DSl failures within a IDLC
system.
It is therefore an object of the present invention to provide a method of providing continual networ~ access to subscriber lines even in the event of consecutive DS1 failures within a Digital Loop Carrier system.

8UMMARY O~ T~E INVENTION
The aforementioned problems are obviated by the present invention which provides a method for enabling automatic re~toration of network access for user lines within a communication system. The communication system includes said user lines interfaced with groups of transmission lines, each of said group of transmission lines including dedicated transmission lines which are connected to said user lines, idle transmission lines and reserved transmission lines. The method comprises distributing said dedicated transmission lines among said groups of transmission lines; providing a number of said reserved transmission lines from among said groups of transmission lines; identifying said user lines which have a dedicated transmission line in a group of transmission lines that fails; and coupling each of said identified user lines to a respective available 22~ 1 2 1 ~
transmission line in another group from the idle and the reserved transmission lines therein.
The method may also include the step of delaying coupling of said identified user lines if a sufficient number of said idle and reserved transmission lines are not available. The method may also include the step of delaying coupling of an identified user line if an idle and reserved transmission line is not available.
Advantageously, the method of the present invention reprovisions the non-concentrated subscriber lines of a Digital Loop Carrier system to the DSOs of the still functioning DSls in the event of a DS1 failure. Thus, the non-concentrated lines have continuous access to switched based services even if the DSls carrying dedicated DSOs fail.

B~IE~ DESCRIPTION OF THE DRA~INGS
For a better understanding of the invention, reference is made to the following description of an exemplary embodiment thereof, and to the accompanying drawings, wherein:
FIGURE 1 is a block diagram of an Integrated Digital Loop Carrier system;
FIGURE 2 is a block diagram of an Integrated Digital Loop Carrier system incorporating DSl protection switching;

22ol2~o FIGURE 3 is a block diagram of an Integrated Digital Loop Carrier system incorporating DS1 protection switching exhibiting a DSl failure;
FIGURE 4 is a block diagram of an Integrated Digital Loop Carrier system incorporating DS1 protection switching exhibiting consecutive DS1 failures;
FIGURE 5 is a block diagram of an Integrated Digital Loop Carrier system according to the present invention;
FIGURE 6 is a block diagram of an Integrated Digital Loop Carrier system according to the present invention exhibiting a DS1 failure;
FIGURE 7 is a block diagram of an Integrated Digital Loop Carrier system according to the present invention exhibiting consecutive DSl failures;
FIGURE 8 is a block diagram of a distributed Integrated Digital Loop Carrier system according to the present invention;
FIGURE 9 is a block diagram of a reprovisioning monitor according to the present invention;
FIGURE 10 is a flow diagram of a repro reserve ~ethod according to the present invention;
FIGURE 11 is a flow diagram of a method for determining the maximum number of DSOs according to the present invention; and FIGURES 12-24 are tables illustrating the operation of a repro reserve method according to the present invention.

22U12f U

DETAILED DESCRIPTION
FIGURE 5 illustrates an IDLC system according to the present invention. The IDLC system 60 has the same basic structure as the systems described in the prior art except that it incorporates a reprovisioning monitor that provides continual switch or network access for the subscriber lines. As can be seen from FIGURE 5, the non-concentrated lines 38, 40 & 44 are connected to respective transmission lines known as Digital Signal Level ls (DSls) 32, 34 & 36, which carry the dedicated Digital Signal Level Os (DSOs).
In the event of a single DSl failure as shown in FIGURE 6, the non-concentrated line 38 is reprovisioned 46 to another dedicated DSO contained in DSl 34. In the event of a consecutive fail~re as shown in FIGURE 7, non-concentrated lines 38, 40 are both reprovisioned 48 to other dedicated DSOs witnin DSl 36. The reprovisioning of the non-concentrated lines in both situations is controlled by the reprovisioning monitor implemented in the IDLC system 60 according to the present invention.
The specific details of the re~rovisioning monitor are discussed below.
The operation of the reprovisioning monitor has a number of advantages over DSl protection switching. DSl protection switching requires a standby DSl to be reserved in case of a failure. In contrast, the reprovisioning monitor does not require an extra DSl to be reserved within an IDLC system. This is because the ~20 ~ o reprovisioning is accomplished by utilizing idle DSOs of other DSls, which enables all of the DSls to be utilized to carry traffic.
The reprovisioning monitor also eliminates the multiple switching required by DSl protection switching.
In a system utilizing DSl protection switching, the traffic must be switched back from the failed DSl when repaired in order to free up the standby DSl in the case of another failure. In contrast, the reprovisioning monitor does not require the switching back of traffic.
Moreover, the reprovisioning of non-concentrated lines does not depend on the failures of other DSls.
Therefore, the non-concentrated lines are capable of re-gaining network access even when multiple DSls fail.
Another advantage of the reprovisioning monitor is that the reprovisioning of non-concentrated lines does not depend on any particular DSl which contains the idle DSOs. Thus, if necessary, the DSls utilized to reprovision a particular~non-concentrated line is capable - 20 of being predetermined. This is beneficial in certain distributed Digital Loop Carrier systems where the dedicated DSOs are required to be served by a pre-selected group of DSls. For example, a distributed Digital Loop Carrier system may require that the DSOs dedicated to an ISDN BA line be served by the same interfacing unit or interfacing unit portion.
Such a distributed system according to the present invention is shown in FIGURE 8. The distributed IDLC

' '~ 220lJ21'' system 58 includes an interface unit 60, DSl groups 62,64,66 and a switching system 68, which functions similarly as previously described for the IDLC system.
In the distributed IDLC system 58, the subscriber lines are Integrated Service Digital Network (ISDN) lines 50,52. The ISDN lines 50, 52 are broadband communication lines that allows the transmission of voice services along with other types of services such as video. The interface 60 has the capability of separating the respective t-~o B and one D channels of ISDN lines 50, 52 so that the ISDN data may be compatible with the rest of the network.
A reprovisioning monitor implemented in the distributed system 58 enables the system to maintain a relationship between two or more dedicated DSOs. In thi,s case, the DSls carrying the DSOs dedicated to the B and D
channels are required to be grouped together. As can be seen, the dedicated DSOs associated with the two B and one D channels of ISDN line 50 can be split into different DSls of the first DS1 group 62. Similarly, the dedicated DSOs associated with the two B and one D
channels of ISDN line 52 can be split into different DSls of the second DSl group 64.
FIGURE 9 shows a block diagram of the reprovisioning monitor according to the present invention. The reprovisioning monitor 70 includes a reprovisioning element 72, a monitoring element 74 and a DSO management element 76, which are preferably implemented as .''' 22~lfi~ia additional software functions within the RDT or the switching system. The elements of the reprovisioning monitor 70 interface with the rest of the switching system, which includes a fault analysis element 76, a call processor 78, a provisioning element 80 and a timing control 82.
When a DSl fails or gets blocked during operation, the number of non-concentrated lines that have to be provisioned is dependent on the number of dedicated DSOs present on the failed DSl. In order to minimize the number of new DSOs required to support this reprovisioning, the DSO management element 76 during normal operation attempts to distribute the dedicated DSOs among all the DSOs serving the IDLC system (preferably, equally or substantially equally), while the non-concentrated lines are provisioned by the provis;oning element 80. The call processor 78 provides information which enables the DSO management element 76 to select the DSOs to be distributed.
The DSO management element 76 also reserves a certain number of DSOs by reducing the number of idle DSOs which are available to the concentrated lines. The reserved DSOs are utilized in order to reduce the situations where the reprovisioning process is deferred.
The DSO management element 76 only reserves the minimum number of DSOs necessary to prevent deferment of the reprovisioning. This is accorlplished by a repro reserve method of the present invention which is invoked , 22ol2lli ll periodically by the DSO management element 76. The timing control 82 provides the timing for when a repro reserve method is invoked.
The DSO management element 76 also provides a method for determining the maximum number of DSOs to be reserved to cover the failure of any one DSl, which will be discussed in detail later.
The fault analysis element 76 is utilized to detect when a DSl fails or is blocked in order to notify the reprovisioning element 72. In response to this, the reprovisioning element 72 first identifies all the non-concentrated lines which have dedicated DSOs on the failed DSl. For each identified non-concentrated line, the reprovisioning element 72 clears the assignment of the dedicated DSO from the failed DSl. The reprovisioning element 72 then reprovisions or connects each identified non-concentrated line to an idle DSO
taken from one of the remaining DSls by way of the DSO
management element 76. This reprovisioning only occurs if there is an idle DSO available at that time.
In order to determine if an idle DSo is available , the monitoring element 74 periodically communicates with the DSO management element 76. The timing of this communication is controlled by the timing control 82. In the event an idle DSO is not available, the monitoring element 74 delays the reprovisioning until one is available. The monitoring element 76 utilizes a polling technique to determine the availability of idle DSOs when ~ 2 0 ~ j the reprovisioning of a few non-concentrated lines are pending. Polling techniques are well known techniques utilized in multi-point line configurations.
As discussed earlier, the DSO management element 76 invokes a repro reserve method of the present invention in order to reserve the minimum number of DSOs necessary to prevent deferment of the reprovisioning process. In order to accomplish this, the repro reserve method operates under a number of rules and maintains a number of counts rel~ted to the IDLC system.
The counts maintained include the number of dedicated DSOs (F~), number of reserved DSOs (R~) and number of idle DSOs (I~). In regard to the above counts, the subscript K associates the counts to a particular DS1. Also, let N identify the number of DSls and M
identify the number of non-concentrated lines within the IDLC system. Let Rtotal identify the total number of reserved DSOs and Ftot~ identify the total number of dedicated DSOs within the IDLC system. It should be noted that M is equal to Ftotal In order to understand the repro reserve method, let the DSls identified with the numbers 1 to N so that the associated F~ values are in descending order. In other words, F~ 2 F~+l.
The repro reserve method operates under the following rules. A DSO can only be reserved on a DSl if the associated number of idle DSOs (I~) is greater than 1.
Reserving a DSO on a DSl implies that the number of reserved DSOs (R~) is increased by 1. Also, each time a ~ 220l230 DSO is reserved on a DS1, the associated number of idle DSOs on that DSl is decreased by 1. The last rule followed by the method requires that when a DSl is selected in order to reserve a DSO, the DSl that has the lowest F~+ R~ value is chosen.
The repro reserve method following the above last rule ensures that the DSOs are not reserved in excess.
This is because when a DSl fails or is blocked, the non-concentrated lines having the dedicated DSOs on the failed DSl are reprovisioned utilizing the DSOs reserved on the remaining DSls. If rkrepresents the excess number of reserved DSOs left immediately after the completion of reprovisioning Fx number of dedicated DSOs due to the failure of the DSl numbered R(where l~K~N), then Fk+ rk = Rtotl - R~ (1) , which is e~uivalent to F~ rk + P~k= Rtot~1 (2) Let rtOt~lidentify the total number of excess reserved DSOs, by extending the above analysis to all the N DSls.
Since the goal of the method is to reserve a minimum number of DSOs I rtOt~l is expected to be O. This is equivalent to saying that each of the rkvalues is expected to be O. This is because, N

rtot~ = ~ r~ = O (3) j=1 is only achieved when each of the r~s is o.
When rk= ~, 14 V~c i~-F~+ r~ = ~ot ~ (4) In other words, the goal of reserving a minimum of DSOs is achieved when the following conditions are met:
Fl+ rl = ~ot~ t5) and, F2+ r2 = ~o~l (6) and, continuing F~+ rN = ~ot~ (7)' which is equivalent to saying:
F1+ r1 = F2+ r2 =.... F~+ r~ = FN + rN (8) In summarizing the above discussion, in order to reserve a minimum but sufficient number of DSOs the repro reserve method attempts to distribute the reserving of DSOs in such a way so that all of the DSls end up having the same Fk+ r~ values.
FIGURE 10 shows a flow diagram of a repro reserve method according to the present invention. Due to its periodic invocation, the methcd 84 starts out assuming it is being invoked for the first time. Thus, the base counts of all of the DSls associated with the IDLC system ~0 are initialized to have O reserved DSOs 86 ~ which means For R = 1 to N
~ + R~ (9) R~ = O
Then the DS1 which has the highest number of dedicated DSOs is identified 88. In this step, this particular DS1 is labeled by DS1~x and the number of dedicated DSOs this DS1 is associated with F~. Finding the DS1 with the highest number of dedicated DSOs is 2~0 ~ 2 i U

important because this determines the minimum number of DSOs that are required to be reserved in case of a failure. Since the number of DSOs reserved must be able to cover the failure of any one of the DSls included in the IDLC system.
The method 84 next determines the number of idle DSOs the remaining DSls are carrying 90 excluding D81~.
This step then associates the number of the idle DSOs with II~ ;nin7~ Determining I~ 1nin~ is important because this enables the method to determine if additional DSOs need to be reserved beyond IL 1n1n~ This is determined indirectly by comparing T~ 1n1n~ with F~92 to see if T~ 1n1n7 2 FmaX~ If this is true, T~,,~l~ is equated with F~ 94 If this is not true, T~1Q is equated with 15 Ir~ 1n1nq 94. Thus, T~,~lQis set to the smaller of either or T~ 1ni~ which is utilized by the method 84 to reserve the proper number of DSO.
The method 84 then sets a variable count equal to T~ 100. The next portion of the method 98 operates in a continuous loop to reserve the number of DSOs in the remaining DSls that corresponds to T~,~ . This is accomplished by first checking to see if the Count=O 102, which enables the loop 98 to be broken. Initially the variable count is not equal to O and then a DS1 is chosen which has both the minimum F~+ R~ value and at least one idle DSO 104. An additional DSO is then reserved in the chosen DS1 106. The variable count is then decreased by one 108 and the method 84 loops back to where it again ' ' ' ' ' 220 ~ o chec~s to see if the count=O 102. The method 84 stays in the loop 98 until the count=O, which means that all of the T~Ja~1enumber of DSOs have been reserved.
The above described loop 98 first reserves DSOs in DSls having minimal F~ + R~ values, in order to evenly distribute the reservation process so that F~ + R~ values of all the DSls are equal. This is desirable because according to equation 8 such a condition ensures that the minimum necessary number of DSOs are reserved.
After the count=O, the DSl is selected which has the maximum F~ + R~ value out of the remaining DSls and designates this value by (F+R)~ 112. Then (F+R)~ is compared to F~ to see if (F~R)~ ~ T~,,~l~ 114. If this is true, a sufficient number of DSOs have already been reserved to cover a failure of one of the DSls and the method then exits 124. If this is not true, additional DSOs are required to be reserved in DS1~, which has the highest number of dedicated DSOs.
The additional DSOs are reserved by first ZO calculating (F+R)~ - T~aa~1e116, which is the number of additional DSOs that are required to be reserved. Then R~ is compared to I~to see if R~ 118, which determines if DSl~xhas a sufficient number of idle DSOs to be reserved. If this is true, then the required number of DSOs are reserved in DS1~ by setting I~
R3~ 122. If this is not true, the number of idle DSOs are increased by setting R~ 120. Then the required ,, ,,, 22l~'2~U

number of DSOs are reserved in DS1~ by setting I~ = I~x-Rm,,C 122. After performing this step the method exits 124.
In regard to the method steps designated by numerals 112-122 of FIGURE 10, the Tpo~Lble number of reserved DSOs are sufficient to cover the failure of any one of the remaining DSls excluding DS1~xonly when TpoJJ~le is greater than or equal to the F~C + R~C values associated with those DSls.
The DSOs reserved on a DS1 are not available when that particular DSl fails. In other words, the number of DSOs available to cover the failure of a DS1 numbered L
(where 2 ~; L ~ N) is equal to TpoJ~ible~ RL. The number of DSOs required when the DS1 numbered L fails is equal to the number of dedicated DSOs on that DSl which is FL.
The TPO~ib1e ~ RL number of reserved DSOs (i.e. reserved on the DSls excluding the DSls numbered 1 and L) are sufficient enough to cover the failure of the DS1 numbered L when TpoJJi'ble~ RI, is greater than or equal to F~,-In other words, no additional DSOs are required to cover the failure of the DS1 numbered L when the following is true:

Tpo~:lLbla ~ RL 2 FL (10), or TpO~ible 2 FL + R~ (11) In the event FL ) TPO~3ib1e ~ R~;, a few additional DSOs are required to cover the failure of the DSO numbered L.
This additional number of reserved DSOs required is equal to FL ~ (TPO33ib1e RL) or FL + RL ~ TPO93ib1e , .,, ~., ~'2V1f'1U

Let P and Q identify two DSOs which have F~+ R~
values greater than Tpo9aible~ The additional number of reserved DSOs required to cover the DS1 P is equal to FP +

RP ~ Tpossible and the additional number of reserved DSOs required to cover the DS1 Q is equal to FQ + RQ - TPO99ib1e~
The additional reserved DSOs are ~ade mutually available to one another when the reservation is made on a DS1 which is different from those two. Generalizing this to the DS1 numbered 2 to N, the desired DSl where the additional number of DSOs have to be reserved is 1.
Accordingly, when Fp + Rp - Tp~99iblenumber of DSOs are reserved on the DS1 numbered 1, these additionally reserved DSOs are available to cover the failure of the DS1 numbered Q. Therefore, the total number of reserved DSOs available to cover the failure of the DS1 numbered Q
is now increased to:
TPO~alb1~ -- RQ + FP + RP ~ Ti,~,,~,1,~ (12), or FP + RP - RQ (13).
Since FQ identifies the total number of reserved DSOs required to cover the failure of the DS1 numbered Q, additional DSOs are not required if:
FQ ~ FP + ~P ~ RQ (14), which is equivalent to saying that additional DSOs are not required to be reserved if:
FQ + RQ ~; FP-- RP (15).
Therefore, by choosing the highest possible F" + Rk value and by reserving the required ~F + R) ~ ~ TP~
number of DSOs on the DS1 numbered 1, all the remaining Z2G l~i ~U' DSls can be covered even if some other DSls have F~+ Rk values greater than T~,,~l~.
In summary, the method steps designated by the numerals 112-122 of FIGURE 10 determines the DSl (from the DSls 2 to N) which has the highest F~ + Rk value. Let (F + R) ~ identify the corresponding F~ + R~ value. As illustrated above, no additional DSOs are required to cover the failure of the associated DSl as long as T~a,~
is greater than or equal to ~F + R)~. When (F + R)~ is greater than T~a,~l~ the additional number of reserved DSOs which are required to cover the failure of the DSl associated with the (F + R)~ is equal to (F + R)~ -~ ~le The method reserves ~F + R)~ - T~aa~l~ number of DSOs on the DSl numbered 1 (i.e., Rl = (F + R)~ - T~aa~lQ) provided enough idle DSOs are available on that DS1. In other words, if (F + ~ - T~aa~l~ is greater than Il then the method reserves an I1 nurlber of DSOs on the DSl numbered 1 (i.e., Rl = Il).
The following are examples of the operation of a repro reserve method according to the present invention.

Example 1:
N=3, F1=6, F2=5, F3=4.
First, 6 (which is F1) DSOs are reserved on DSls 2 and 3. The reservation results in a R2=3, R3=3 or a R2=2, R3=4. In either case, the ~F + R)~ value is 8. Since 8 is larger than 6 (which is Fl), R1=(F ~ R)~- Fl= 8-6 =
2.

When the DS1 numbered 1 fails, there are 6 reserved DSOs to cover the 6 DSOs on the DSls numbered 2 and 3.
When the DSl numbered 2 fails, there are 6 or 5 reserved to cover the 5 DSOs on the DSls numbered 1 and 3. When the DS1 numbered 3 fails, there are 4 or 5 to cover the 4 DSOs on the DSls numbered 1 and 2.

Example 2:
N=3, F1=7, F2=3, F3=2.
First, 7(which is Fl) DSOs are reserved on DSls 2 and 3. The reservation results in ~=3, R3=4. In this case, the ~F+R)~X value is 6. Since 6 is smaller than 7 which is Fl, no additional DSOs are required to be reserved on the DS 1 numbered 1 or R1=O.
When the DS1 numbered 1 fails, there are 7 reserved DSOs to cover the 7 DSOs on the DSls numbered 2 and 3.
When the DSl nur~ered 2 fails, there are 4 reserved DSOs to cover the 3 DSOs on the DS1 numbered 3(note that Rl=O).
When the DSl numbered 3 fails, there are 3 reserved DSOs ~0 to cover the 2 DSOs on the DS1 numbered 2(note that Rl=O).
As noted above, the DSO management element 16 also provides a method for calculating the maximum number of DSOs which have to be reserved. In a Digital Loop Carrier system with N number of DSls and M number of non-concentrated lines, the minimum number of DSOs which haveto be reserved to cover the failure of any (but at most one at any instant of time) of the DS1 is equal to M/(N-1) unless a single DSl has more dedicated DSOs than this.

In the illustrations given below, it is assumed that enough idle DSOs are available to perform the reservation.
Let F1, F2,..., FN identify the number of dedicated DSOs on the DSls numbered 1, 2, ..., N (i.e., F~
represents the number of dedicated DSOs on the DSl numbered R). Let Ftot~l identify the total number of dedicated DSOs within the IDLC system. It has to be noted that Ftot~ is equal to M. Let the DSl numbers be identified in such a way that the corresponding F~ values are in the descending order (i.e., F~ 2 F~+1) .
Let R1, R2-.., RN identify the number of DSOs reserved on those DSls numbered 1, 2, ..., N (i.e., R~
represents the number of ~SOs reserved on the DSl numbered R). Let Rto~ identify the total number of reserved DSOs within the IDLC system.
Let rl, r2, ..., rN identify the number of excessive DSOs left immediately after completing the reprovisioning process due to the failure of one of the DSls numbered 1, 2, ..., N(i.e., r~ represents the number of excess DSOs left immediately after completing the reprovisioning process due to the failure of the DS1 numbered X). In other words, for K=1 to N, F~ +r~= Rto~ - R~ (16), or F~ +R~= Rto~ - r~ ~17).
Utilizing equation 17 for all the DSls, N N N
~Fi+ ~Ri= N * ~ot ~ ~ ~r~ (18) j=l j=l j=1 ' . ' ~'~0,~

Ftot~ + Rtot~= N ~ Rtot~ - Er~ tl9), or N
Rtot~ = tFtot~ /(N-1)) + ((~r~)/(N-l) (20) j=l N

When Er~= 0, j=l Rtotl= Ftot~ /(N-1) (21) Based on the steps and rules of a repro reserve method, Rtotl = F1+ R1 (22) Utilizing equation 22 within the equation 17, r1 = Rtotl - (Fl+R1) = 0 (23) Obviously, when R1= 0, Rtotl= F1 (24) For R1> 0, Rl= (F~R)~- Fl (25) Therefore utilizing equation 22, Rtotl= Fl+ Rl= Fl+ ~F+R)~ - Fl= (F+R)~ (26) Then utilizing the equation 17, the r~ value for the DSl associated with (F ~ R)~ is ~ (27) Due to the rules and steps followed within a repro reserve method, the F~ + R~ values of any two DSls can differ by at most 1. Based on equations 23 and 27 (i.e., at least two of the r~ values are 0), N

Er~ ~ (N-2) (28) j=l Based on equations 18 and 28, . ,,. 2201~jV

~ot 1 S (Ftot 1/ (N~ ((N-2))/(N-1)) (29), or ~o~ s (Ftot~/(N-l))~ 1-(1/(N-1)) (30) Utilizing equations 19 and 30, (Ftotl/(N-1)) ~ ~ot 1 5 (Fto~/(N-1)) ~ 1/(N-11)) (31) Since Rtot~ represents the number of reserved DSOs, it has to be an integer value. Utilizing equation 31, ~0~ has to be an integer which is greater than or equal to (~tota,/(N-1)), but less than or equal to (Ftotl/(N-1)) ~1 - (1/(N-1)). This is equivalent to saying:
0 ~ot~ = Smallest integer 2 (Ftot 1/ (N-1)) (32) In summary, utilizing equations 23 and 32, the maximum number of DSOs which have to be reserved in an IDLC system with N number of DSls and M number of non-concentrated lines so as to allow the reprovisioning process to complete its task successfully, is the larger of the following two values:
a) highest number of dedicated DSOs, a single DS1 has.
b) smallest integer 2 M/(N-1).
FIGURE 11 shows a flow diagram of the method for determining the maximum number of DSOs required according to the present invention. The method 126 includes finding F~ 126, which is the DS1 that has the greatest number of dedicated DSOs. Then an integer value is 25 calculated which is 2 M/(N-1) 128, where M corresponds to the number of non-concentrated lines and N corresponds to the number of DSls the system includes. Finally, F~ is compared to the integer value calculated in step 128 in 24 ~ ~U
order to find the maximum value 130, which corresponds to the maximum number of DSOs which have to be reserved in case of a failure DSl within the system.
The following are examples of the operation of the method described in FIGURE 11.

Example 1:
N=3, F1=62, F2 =5, F3=4.
M=6+5+4=15 Therefore, M/N(-l)= 15/2 = 7.5 Since 6 ~which is Fl) is smaller than 7.5, ~ot~ has to be the smallest integer greater than or equal to 7.5 In other words, the maximum numbers of DSOs which have to be reserved in this IDLC system is equal to 8.

Example 2:
N=3, F1=7, F2=3, F3=2.
M=7+3~2=12 Therefore, M/N-l = 12/2 = 6 Since 7 (which is Fl) is greater than 6, ~0~ = 7.
In other words, the maximum nu~ber of DSOs which have to be reserved in this IDLC system is equal to 7.
It should be specifically noted that the DSOs used during the reprovisioning process are not restricted to the DSOs reserved by a repro reserve method (as a matter of fact, the reprovisioning process needs an idle DSO).
This flexibility enables the reprovisioning monitor to encounter the situation of not having enough reserved ~2~3~-Z1~7 DSOs (this can happen if enough idle DSOs are not available when a repro reserved method is invoked) and complete its task of the reprovisioning process.
In the event the reprovisioning monitor is unable to find an idle DSO, the monitoring element defers the reprovisioning process until idle DSOs are available.
Additionally, it has to be noted that the reprovisioning monitor is able to support multiple DSl failures due to the fact that a repro reserve method is invoked periodically and the monitoring element defers the reprovisioning process when idle DSOs are not available.
The following discussion relates to a model for demonstrating the overall detailed operation of the reprovisioning monitor within a Digital Loop Carrier system according to the present invention. The model uses an IDLC system which has 200 subscriber lines with 5 DSls and which serves 10% of the subscriber lines in a non-concentrated mode. In other words, 20 subscriber lines have dedicated DSOs. Before a repro reserve method is invoked, the number of DSOs available to the 180 concentrated lines is equal to 96 (it is assumed that out of 120 DSOs, 20 are used as dedicated DSOs and 4 are used as the communication channels).
The model considers the failure of two DSls (one after the another) and illustrates the management of DSl based counts. Let the 5 DSls be identified using the symbols DSll, DSl2, DSl3, DSl4, and DSls. Let us assume 2 6 ~ I C ,i (~
that DSll contains the two communication channels (Time Slot Management Channel (TMC) and Embedded Operations Channel (EOC). Further, let us assume that DSl5 contains the backup of those two communication channels (referred to as TMC' and EOC'). Let I1, I2, I3, I4 and I5 identify the 5 DSl based counts indicating the number of idle DSOs. Let F1, F2, F3, F4 and F5 identify the 5 DSl based counts indicating the number of dedicated DSOs. Let R1, R2, R3, R4, and R5 identify the 5 DS1 based counts indicating the number DSOs reserved by a repro reserve method. While provisioning those 20 non-concentrated lines, the DSO management element 76 attempts to distribute the dedicated DSOs among the 5 DSls, preferably equally. The repro reserve method of the present invention reserves the DSOs on the 5 DSls to cover the failure of at most one DSl. FIGURES 12-24 include tables that illustrate the DSl based counts values of the model.
FIGURE 12 illustrates the counts before provisioning the 20 non-concentrated lines. FIGURE 13 illustrates the counts after provisioning the 20 non-concentrated lines, but before reserviny the DSOs (i.e., by the repro reserve method). FIGURE 14 illustrates the counts after reserving the DSOs. The number of DSOs reserved by the repro reserve method is the smallest integer 2 20/4 which is equal to 5.
Now assume that one of the DSls fail and let the failed DS1 be DS12. The reprovisioning monitor 27 22012i o reprovisions the 4 non-concentrated lines which have dedicated DSOs on the failed DSl. The repro reserve method, executed periodically, reserves the DSOs on the 4 DSls to cover the failure of at most one DS1. In this regard, FIGURE 15 illustrates the counts before reprovisioning the 4 non-concentrated lines. FIGURE 16 illustrates the counts after reprovisioning the 4 non-concentrated lines, but before the repro reserve method is invoked again. FIGURE 17 illustrates the counts after the repro reserve method is executed again. The number of DSOs reserved by the repro reserve method is the smallest integer 2 20/3 which is equal to 7.
Now assume that another DS1 fails and let the failed DS1 be DS13. The reprovisioning monitor reprovisions the 5 non-concentrated lines which have dedicated DSOs on the failed DS1. The repro reserve method, executed periodically, reserves the DSOs on the 3 DSls to cover the failure of at most one DS1. FIGURE 18 illustrates the counts before reprovisioning the 4 non-concentrated lines. FIGURE 19 illustrates the counts after reprovisioning the 4 non-concentrated lines, but before the repro reserve method is invoked again. FIGURE 20 illustrates the counts after the repro reserve method is executed again. The number of DSOs reserved by the repro reserve method is the smallest integer 2 20/2 which is equal to 10.
Now assume that the failed DSI2 is repaired. The DS1 based count values for the reserved DSOs change due to ~~12~

the fact that the repro reserve method is executed periodically. FIGURE 21 illustrates the counts before the repro reserve method is executed again. FIGURE 22 illustrates the counts after the repro reserve method is executed again. The number of DSOs reserved by the repro reserve method is the smallest integer 2 20/3 which is equal to 7.
Now assume that the failed DS13 is also repaired.
The DS1 based count values for the reserved DSOs change due to the fact that the repro reserve method is executed periodically. FIGURE 23 illustrates the counts before the repro reserve method is executed again. FIGURE 24 illustrates the counts after the repro reserve method is executed again. The number of DSOs reserved by the repro reserve method is 7 since DS14 and DS1s have more dedicated DSOs than the smallest integer 2 20/4 (i.e., 5).
In summary, the above model illustrates that the non-concentrated lines continue to have network access even when multiple DSls fail. The repro reserve method, executed periodically, redistributes the reserved DSOs based on the current distribution of other counts. For simplicity, this model deliberately neglected the call processing aspects (i.e., in terms of altering the Ik values) of concentrated lines. It has to be noted that in some cases the DSl based counts may be distribu~ed among the DSls in more than one way. For example, the distribution of Rk values in the last table can be ' ~ "' 2~0 ~

reversed between DSl2 and DS13 (i.e., the Rk value for the DSl2 can be 4 and the Rk value for the DSl3 can be 3).
The embodiments described herein are merely illustrative of the principles of the present invention.
Various modifications may be made thereto by persons ordinarily skilled in the art, without departing from the scope or spirit of the invention.

Claims (25)

1. A method for providing automatic restoration of network access for user lines within a communication system, said communication system including said user lines interfaced with groups of transmission lines and each of said group of transmission lines including dedicated transmission lines which are connected to said user lines, idle transmission lines and reserved transmission lines, comprising the steps of:
distributing said dedicated transmission lines among said groups of transmission lines;
providing a number of said reserved transmission lines from among said groups of transmission lines;
identifying said user lines which have a dedicated transmission line in a group of transmission lines that fails; and coupling each of said identified user lines to a respective available transmission line in another group from the idle and the reserved transmission lines therein.
2. The method of claim 1, further comprising the step of delaying coupling of said identified user lines if a sufficient number of said idle and reserved transmission lines are not available.
3. The method of claim 1, further comprising the step of delaying coupling of an identified user line if an idle and reserved transmission line is not available.
4. The method of claim 1, wherein the step of providing comprises providing a number of said reserved transmission lines on a periodic basis.
5. The method of claim 1, wherein the step of providing comprises:
determining which one of said groups of transmission lines has the greatest number of dedicated transmission lines and for counting the number of dedicated transmission lines in said group;
counting the total number of idle transmission lines within said other groups of transmission lines;
comparing the number of dedicated transmission lines in the group with the greatest number of said lines to said total number of idle transmission lines in order to determine a minimum number of idle transmission lines to be reserved; and reserving said minimum number of idle transmission lines within said other groups of transmission lines.
6. The method of claim 5, wherein the step of providing comprises providing a number of said reserved transmission lines on a periodic basis.
7. The method of claim 5, wherein the step of providing further comprises reserving an additional number of idle transmission lines within the group of transmission lines having the greatest number of dedicated transmission lines if the number of dedicated transmission lines in said group is less than said total number of idle transmission lines, said additional number of idle transmission lines corresponding to the difference between the number of dedicated transmission lines in the group with the greatest number of said lines and said total number of idle transmission lines.
8. The method of claim 7, wherein the step of reserving an additional number of idle transmission lines comprises comparing said minimum number of idle transmission lines to the combination of dedicated transmission lines and reserved transmission lines in the one of said other groups of transmission lines having the greatest combination of said lines.
9. The method of claim 6, wherein the step of providing further comprises initially reducing said reserved transmission lines of said groups of transmission lines to zero.
10. The method of claim 6, wherein the step of reserving said minimum number of idle transmission lines comprises continually reserving a single transmission line within said other groups of transmission lines that have an idle transmission line and a certain minimum number of dedicated transmission lines and reserved transmission lines.
11. The method of claim 1, wherein the step of coupling comprises clearing the assignment to a respective identified user line of each said dedicated transmission line in said group of transmission lines that fails.
12. The method of claim 2, wherein the step of delaying comprises determining, via polling, the availability of a sufficient number of idle and reserved transmission lines when said coupling of at least two identified user lines is not accomplished.
13. The method of claim 3, wherein the step of delaying comprises determining, via polling, the availability of a sufficient number of idle and reserved transmission lines when said coupling of at least two identified user lines is not accomplished.
14. The method of claim 1, wherein said communication system is a Digital Loop Carrier system, said user lines are non-concentrated subscriber lines, each said group of transmission lines is a Digital Signal Level 1 line including a plurality of Digital Signal Level 0 lines and said non-concentrated subscriber lines are interfaced with said Digital Signal Level 1 lines by a remote terminal.
15. A method of providing continual network access for user lines in a communication system, comprising the steps of:

a. reserving a number of transmission lines among the groups of transmission lines in the communication system; and b. coupling a user line to a respective available transmission line from the reserved transmission lines and the other idle transmission lines of the system in the event the user line is connected to a transmission line that fails.
16. The method of claim 15, wherein the step of reserving is executed periodically.
17. The method of claim 15, wherein the step of reserving comprises determining and reserving a minimum number of transmission lines.
18. The method of claim 15, wherein the step of reserving comprises determining and reserving the maximum number of transmission lines.
19. The method of claim 15, wherein the step of coupling comprises coupling a user line to a respective available transmission line in a group of transmission lines other than the group with the failed transmission line.
20. The method of claim 15, wherein the step of coupling comprises clearing the assignment of the user line to the transmission line that fails and re-assigning the user line to the coupled available transmission line.
21. The method of claim 15, further comprising the step of re-coupling the user line to a second respective available transmission line from the reserved transmission lines and the other idle transmission lines of the system in the event the coupled transmission line fails.
22. The method of claim 15, further comprising the step of assigning each user line to be coupled to pre-selected available transmission lines.
23. The method of claim 15, wherein the user lines are connected to respective dedicated transmission lines and, further comprising the step of distributing the dedicated transmission lines among the groups of transmission lines in the communication system.
24. The method of claim 23, wherein the distribution of dedicated transmission lines is accomplished substantially evenly among the groups of transmission lines.
25. The method of claim 15, further comprising the step of delaying the coupling of a user line if a transmission line is not available.
CA002201210A 1996-03-29 1997-03-27 A method of providing continual network access for subscriber communication lines Abandoned CA2201210A1 (en)

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US4197427A (en) * 1977-11-11 1980-04-08 Lynch Communication Systems, Inc. Dual-processor line concentrator switching system
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US4511762A (en) * 1983-06-06 1985-04-16 Siemens Corporate Research & Support, Inc. Overload detection and control system for a telecommunications exchange
US5509065A (en) * 1993-11-12 1996-04-16 Teltrend Inc. Dual span monitoring system for maintenance shelf control
US6115355A (en) * 1996-03-29 2000-09-05 Siemens Stromberg-Carlson Reprovisioning monitor
US6084853A (en) * 1996-03-29 2000-07-04 Siemens Information And Communication Networks, Inc. Method of managing digital signal carrying facilities
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