Method of Assigning Connection Identifier in Asynchronous Transfer Mode Switching System

1. Field of the Invention

The present invention relates to a method of assigning connection identifiers for virtual path connection (VPC) and virtual channel connection (VCC) in an asynchronous transfer mode (ATM).

2. Discussion of Related Art

Connection identifiers (VPI/VCI) are used to discriminate the connection between a subscriber and networks in an ATM switching system. Subscriber interfacing includes digital signal level 1 European (DS1E) supporting 2.048 Mbps, digital signal level 3 (DS3) supporting 44.736 Mbps, synchronous transport module 1 (STM1) supporting 155 Mbps, and STM4 supporting 622 Mbps.

According to the type of subscriber link connected in subscriber interface module (SIM), one subscriber link is interfaced in SIM for STM1, 3 for DS3, and 72 for DS1E. In ITU-T Q.2931 recommending interfacing between the subscriber and network for wideband service, the range of VPI for every subscriber interface is regulated to be within 0-255, the range of VCI inside the VP within 32-65535.

An existing N-ISDN switching system allows a limited number of channels inside the physical link between the subscriber and network. For instance, 2B+D interface has two channels transmitting user data so that only if they are discriminated is the subscriber data easily distinguished. Therefore, interfacing between subscriber and network is simply performed so that channel number allocation is managed only by indicating one being in use.

In B-ISDN switching system employing ATM, information for multiple connections is multiplexed because the broadband offered by one physical link is above 155 Mbps. Here, a connection identifier for discriminating user information is used, whose range is eight bits for VPI, and 16 bits for VCI.

In the ATM switching system, the range of connection identifiers available is wide so that it is almost impossible to indicate whether it is used or not, for every subscriber link. For this reason, contrary to the conventional method, the identifier cannot be limited to a predetermined range of values between subscriber and network when the subscriber link is installed.

Accordingly, the present invention is directed to a method of assigning a connection identifier in an ATM switching system that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a method of assigning a connection identifier in an ATM switching system in which VPI is managed by index to thereby assign as many connection identifiers as a permissible number of connections for every SIM, in which a virtual path connection is enabled only with VPI, and in which the VPI assigned for the virtual path connection is not taken as a connection identifier for virtual channel connection so that user information transmitted by connection identifiers does not collide.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims as well as the appended drawings.

To achieve these and other advantages in accordance with the purpose of the present invention, as embodied and broadly described, herein there is provided a method of assigning a connection identifier for an asynchronous transfer mode switching system, the method comprising the steps of: (a) analyzing a parameter transmitted in a connection identifier allocation request when it is received, analyzing the number of connections in SIM, and confirming a signalling mode between subscriber and network if the input parameter is normal and connection is available; (b) calculating an index value for accessing a VPI management table which stores a VPI usage state if the signalling mode is a coupled signalling mode in which only the same VPI for signalling is used as VPI for user data transmission, VPI or both VPI and VCI are designated in connection identifier allocation request, and the VPI for signalling and the VPI for user data transmission are identical, to thereby check the usage stage of a detected VPI; (c) designating the VPI for user data transmission as the VPI for signalling if the signalling mode is a decoupled signalling mode in which the VPI for signalling and other VPIs are available for VPI for user data transmission, and VPI or both VPI and VCI are not designated, and calculating an index value for accessing the VPI management table which stores a VPI usage state it there is no error in the designated VPI, to thereby check the usage stage of the detected VPI; (d) notifying a connection identifier allocation failure if the VPI is used for virtual path connection, notifying that the virtual path is already established if the VPI is used for a virtual channel, or analyzing the signalling mode if the VPI is not in use; (e) indicating that the VPI selected is in use if the signalling mode is the non-associating mode and the number of VPI used does not surpass the number of VPI assigned to the VPI connection identifier allocation number management table; and (f) indicating that the VPI selected is in use if the signalling mode is the associating mode and a new VPI can be used.

In another aspect of the present invention, there is provided a method of assigning a connection identifier for an asynchronous transfer mode switching system, the method comprising the steps of: (a) analyzing a parameter transmitted in a VPI allocation request when it is received, analyzing the number of connections and the number of VPI used in SIM, and confirming whether a VPI desired to be used in VPI allocation request if the input parameter is normal and connection is available; (b) changing the usage state of VPI assigned to a VPI management table if the VPI is designated and is not in use, increasing the number of VPI and the number of VPI assigned in the connection identifier management table, indicating an assigned VPI, or selecting a VPI in no use in SIM if the VPI is not designated with reference to the VPI management table, and changing the usage state of the VPI assigned in the VPI management table.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the drawings.

In the drawings:

FIG. 1 is a schematic architecture of an ATM switching system to which the present invention will be applied;

FIG. 2 is a block diagram of software function for connection identifier allocation;

FIGS. 3A, 3B and 3C are management tables for connection identifier allocation according to the present invention;

FIGS. 4A and 4B are flowcharts for assigning connection identifiers for virtual channel connection according to the present invention;

FIG. 5 is a flowchart for calculating index values of the VPI managing table according to the present invention;

FIGS. 6A and 6B are flowcharts for assigning VCI inside VPI selected according to the present invention;

FIG. 7 is a flowchart for checking the usage state of VCI selected according to the present invention;

FIG. 8 is a flowchart for inputting a selected connection identifier to the table according to the present invention; and

FIG. 9 is a flowchart for assigning VPI for virtual path connection.

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

In FIG. 1, reference numeral 1 represents ATM local switching subsystem (ALS). Reference numeral 2 is an ATM central switching subsystem (ACS). Reference numeral 3 is a subscriber interface module (SIM). Reference numeral 4 is an access switching control module (ASCM). Reference numeral 5 is an operation & maintenance control module (OMCM). An ATM switching system is divided into independent ALSs (1), which are connected with ACS 2.

ALS 1 includes SIM 3 for performing cell transmission/reception between subscriber and network, and ASCM 4 for controlling subscriber call and connection. ACS 2 has OMCM 5 for performing operator interfacing and system operation and maintenance.

Referring to FIG. 2, a software function block for connection identifier allocation is incorporated in the call connection control processor (CCCP) of the ALS. Semi-permanent PtP virtual connection control function (SPVCF) block 6 controls point-to-point exclusive line service required from management plane function.

Semi-permanent PtMP virtual connection control function (SMVCF) block 7 controls point-to-multipoint exclusive line service required from the management plane function. User protocol control function (UPCF) block 8 controls the subscriber call according to the transmission/reception of Q.2931 message with a subscriber terminal.

After the function of assigning a connection identifier necessary for connection by SPVCF 6, SMVCF 7 and UPCF 8, UNI link resource handling function (ULRHF) block 9 performs call processing library, as a block performing the present invention. SIM 3 receives information for connection from SPVCF 6, SMVCF 7 and UPCF 8 in order to transmit or receive subscriber information cell.

FIG. 3A shows a management table of the number of connection identifiers assigned to interfacing modules. FIG. 3B shows a management table of VPI. FIG. 3C shows a management table of VCI. The elements of the table of the number of connection identifiers assigned to interfacing modules are as follows.

IMNo 11 is the SIM number, having one byte of integer. The maximum number of SIM 3 is determined by the switch architecture of ALS 1. When a switch is 32.times.32, 31 SIMs are ensured for every ALS 1 because SIM 3 can be connected to 32 ports excluding one port for connecting ASCM 4.

VPINum 12 is the number of VPI assigned to SIM 3, having a value between 0 and 127 from one byte of integer. The maximum number of VPI permissible inside SIM 3 is 128.

VPCcnt 13 is the number of virtual path connection assigned to SIM 3, having a value between 0 and 127 from one byte of integer. The maximum number of permissible virtual connections in SIM 3 is 128.

VCCcnt 14 is the number of virtual channel connections assigned to SIM 3, having a value between 0 and 511 from one byte of integer. The maximum number of virtual channel permissible connections in SIN 3 is 512. The management table of FIG. 3A stores the number of VPI, the number of virtual path connections, and the number of virtual channel connections, all being in use. If the virtual path connection is set, then VPCcnt 13 and VPINum 12 both increase by 1. If the virtual channel connection is set, then VCCcnt 14 increases by 1.

If the virtual path identifier assigned for virtual channel connection is newly assigned but not used for virtual channel connection, then VPINum 12 increases by 1. If the virtual path connection is released, then VPCcnt 13 and VPINum 12 both decrease by 1. If the virtual channel connection is released, then VCCcnt 14 decreases by 1.

If there is no other virtual path connection in a VPI to which the released virtual channel connection belongs, then VPINum 12 decreases by 1, and Usage.sub.-- Sts 16 of the VPI management table of FIG. 3B is changed into TRUE. The elements of the VPI management table are shown as below.

IndexNo 15 is an index key for accessing the VPI management table, having four bytes. It is calculated with IMNo 11.times.256 (range of maximum VPI in interface module)+VPI number to be assigned. If there are 31 interface modules, the maximum IndexNo is 7935.

Usage.sub.-- Sts 16 indicates whether the VPI is in use or not. If the value is FALSE in Boolean type, the VPI is indicated to be in use, and vice versa.

HeadConvType 17 is information indicative of whether the VPI is assigned for virtual path connection or for virtual channel connection, having one byte of set type. The information being stored for VP indicates virtual path. The case for VC indicates virtual channel.

VCCcnt 18 is the number of virtual channel connections assigned to VPI of SIM 3, having a value between 0 and 511 from one byte of integer.

NextVCINo 19 is VCI to be next assigned in VPI, having four bytes between 32 and 65535.

The VPI management table enables one approach by calculating IndexNo 15 in order to know whether or not a VPI is used in SIM. In addition, the time to assign a connection identifier can be reduced by maintaining a next-assigned NextVCINo 19 when a VCI is to be assigned in VPI. Whether or not the VPI is used is managed by SIMs. With the allocation and release of VPI, IndexNo 15 is calculated. With reference to the table with the IndexNo calculated, in case of VPI allocation, Usage-Sts 16 is defined as FALSE. In case of VPI release, it is set as TRUE. If the VPI assigned is to be used for virtual path connection, HeadConvtype 17 is stored as VP, but if it is to be used for virtual channel connection, it is stored as VC. For VPI in which HeadConvType 17 is VC, it can be used as a VPI for virtual channel connection. Here, the selection of VCI not used is made easy by storing the number of virtual channel connections within a virtual path in VCCcnt, and storing a VCI assigned next in NextVCINo 19. Finally, the elements of the VCI management table are as follows.

IMNo 20 is the SIM number, having one byte of integer. The maximum number of SIM 3 is determined by the switch architecture of ALS 1. When a switch is 32.times.32, 31 SIMs are ensured for every ALS 1 because SIM 3 can be connected to 32 ports excluding one port for connecting ASCM 4.

VPI 21 is a virtual path identifier assigned for virtual channel connection, having two bytes between 0 and 255.

VCI 22 is a virtual channel identifier of the VPI assigned for virtual channel connection, having four bytes between 32 and 65535.

The VCI management table manages VPI 21 and VCI 22 used by virtual channel connections set by SIMs. VPI/VCI assigned in setting virtual channel connection is stored in SIM number area to which the connection belongs. In case of virtual channel connection release, the stored VPI/VCI is erased.

The management table is characterized in that it includes as many tables as the number of connections permissible by SIMs.times.the number of SIMs. In accessing the table, the number of accessing table in the worst case can be reduced by applying IMNo as the table index. In addition, the time of access can be minimized by accessing only tuple not -1 in table access. This is accomplished by storing -1 as the value of memory not storing its contents yet and packing it. A tuple having -1 is selected when a new VPI/VCI is assigned and then input to the table so that the selection of memory is made easy.

Referring to FIGS. 4A and 4B, when ULRHF block 9 receives a connection identifier allocation request from SPVCF 6, SMVCF 7 and UPCF block 8, IMNo 11, parameters such as signalling mode designation information, signalling VPI are analyzed in step 101. If they are determined to be abnormal, connection identifier allocation impossibility is informed to the block for setting call and connection in step 102, and the step ends.

If the parameters are normal, the number of connection in SIM required to assign connection identifier is analyzed in step 103 by using VPCcnt 13 and VCCcnt 14 of FIG. 3. If the number of connection surpasses a predetermined value allowable value, connection identifier allocation impossibility is informed to the block for setting call and connection in step 102, and the step ends.

If the connection is allowable in step 103, the signalling mode between subscriber and network required when a VPI number is selected in connection identifier allocation is analyzed in step 104. When a coupling mode in which only the same VPI for signalling is used for VPI for user data transmission, it is determined in step 105 whether the VPI or both VPI and VCI are designated.

According to the analysis result in step 105, if they are not designated, the VPI for user information transmission is designated as the VPI for signalling in step 109. If they are designated, it is determined in step 106 whether the VPI for signalling and the VPI for user data transmission are identical. If they are not identical, connection identifier allocation impossibility is informed to the block for setting call and connection in step 107. If the VPI for signalling and the VPI for user data transmission are the same, IndexNo 15 for accessing VPI management table b of FIG. 3 where the usage state of VPI is stored is calculated in step 112.

The signalling mode between subscriber and network is analyzed in step 104. If the mode is a non-associating mode which allows signalling VPI and other VPIs for user data transmission, it is determined in step 108 whether VPI or both VPI and VCI are designated.

According to the result of analysis in step 108, if they are not designated, the VPI for user information transmission is designated as the VPI for signalling in step 109, and then the error of VPI designated for user information transmission is analyzed in step 110 as when they are designated, to thereby decide whether there is an error in VPI in step 111.

If there is a false VPI, connection identifier allocation failure is informed to the block for setting call and connection in step 102. If there is no false VPI, IndexNo 15 for accessing VPI management table b of FIG. 3 where the usage state of VPI is stored is calculated in step 112.

The usage state of VPI detected with the calculated IndexNo 15 as a key is checked in step 113. If the VPI is used for virtual path, connection identifier allocation impossibility is informed to the block for setting call and connection in step 102 because the VPI cannot be used for VPI for VC connection. When VPI is already used for VC connection, a procedure following the step 123 for finding out whether the VCI is not designated is performed including the step. When VPI is not in use, the signalling mode is analyzed in step 114.

In case of non-associating signalling mode, the number of VPI in use in SIM is checked in step 115. If the number does not surpass a permissible value, the VPI selected is changed to be in use in step 116, and it is determined in step 123 whether or not the VCI is designated. If the number of VPI surpasses its limit in SIM, one of VPI being used for VC connection in SIM is selected in step 117, and the selection result of VPI is analyzed in step 118. If the VPI selection fails, connection identifier allocation impossibility is informed to the block for setting call and connection in step 119. If the selection is finished, it is determined in step 123 whether the VCI is not designated.

In case of associating signalling mode, the number of VPI being used in SIM is analyzed in step 120 with reference to VPINum 12 of connection identifier allocation number management table a of FIG. 3. According to the result of analysis in step 120, if the use of a new VPI is not permitted, connection identifier allocation impossibility is informed to the block for setting call and connection in step 102. If a new VPI is allowable, VPINum 12 of connection identifier allocation number management table a of FIG. 3 increases by 1 in step 121, and Usage.sub.-- Sts 16 corresponding to IndexNo 15 of VPI management table b of FIG. 3 is determined to be FALSE. Then, HeadConvType 17 is designated as VC, VCCcnt 18 as 0, and NextVCINo 19 as 32. The VPI is stored to be in use in step 122, and then it is determined in step 123 whether the VCI is not designated.

The step of assigning VCI is carried out in such a manner that the VCI value is designated, and it is determined in step 123 whether or not the connection identifier allocation is required. If the value is not designated, the VCI of VPI selected is assigned in step 124. When VCI allocation fails according to the result of allocation in step 125, connection identifier allocation failure is informed to the block for setting call and connection in step 126. If the VCI allocation is normal, the VPI/VCI assigned is informed to the block for setting call and connection in step 127, and the step ends.

If the VCI is designated in step 123 in connection identifier allocation request, it is confirmed in step 128 whether or not the VCI selected is in use. If the VCI is in use in step 129, allocation impossibility is informed to the block for setting call and connection in step 130 because the connection identifier required for allocation is in use. If the VCI is not in use in step 129, the VCCcnt 14 of connection identifier allocation number management table a and VCCcnt 18 of VPI management table b of FIG. 3 increase by 1 in step 131, and the connection identifier selected is stored in the VCI management table in step 132.

If the storage result ends abnormally in step 133, connection identifier allocation impossibility is informed to the block for setting call and connection in step 130. If the storage is normal, the connection identifier assigned is informed to the block for setting call and connection in step 134.

Referring to FIG. 5, it is determined in step 140 whether IMNo is 0 or not. If IMNo is 0, base index value Base.sub.-- Index is stored as 0 in step 141. If IMNo is not 0, for the base index value, a value in which IMNo is multiplied by the maximum VPI value MAX.sub.-- VPI.sub.-- VAL +1 of the subscriber link is stored in step 142. IndexNo is calculated in step 143 by adding the VPI required for index calculation to the base index value Base.sub.-- Index stored, and the range of the calculated index value is checked in step 144.

If the calculated index value is smaller than 0 but greater than the maximum index value set in table configuration, index error INDEX.sub.-- ERR is informed in step 145. If the calculated index value is not smaller than 0 but smaller than the maximum index value set in table configuration, the calculated index value is informed in step 146, and the step ends.

Referring to FIGS. 6A and 6B, a next VCI value NextVCINo 19 stored in the VPI management table is selected in step 150, and then the range of VCI selected is checked in step 151. If the selected VCI is smaller than 32 but greater than 65535, the maximum VCI value of VPI, 32 is selected as the VCI value in step 152. If the selected VCI is greater than 32 but smaller than 65535, the maximum VCI value of VPI, the usage state of the VCI value selected is confirmed with reference to the VCI management table in step 153.

If the VCI is not in use in step 154, the VCCcnt of the connection identifier allocation number management table a and VPI management table b increases by 1 in step 155, and connection identifier VPI/VCI selected is stored in the VCI management table in step 156.

If the storage result is abnormal in step 157, VCI allocation failure is informed in step 158. If the storage is performed normally, NextVCINo 19, a next selected VCI value stored in the VPI management table, increases by 1 in step 159, and the VCI assigned is informed in step 160.

If the selected VCI is in use in step 154, NextVCINo 19 of the VPI management table for selecting usable VCI in the VPI selected increases by 1 in step 161, and the usage state of VCI increased is confirmed in step 162. If the VCI is not in use, a procedure following the step of increasing by 1 VCCcnt of connection identifier allocation number management table a and VPI management table b is performed. If the VCI is in use, a procedure following the step of increasing by 1 NextVCINo 19 of the VPI management table in order to select usable VCI is performed ten times in step 164. If the usable VCI is not selected despite ten performances, a value in which an index value VCI.sub.-- JUMP.sub.-- INDEX for jumping the next selected VCI is added thereto when the selected VCI is in continuous use is selected as the VCI in step 165, and it is determined in step 166 whether the range of the VCI surpasses a predetermined value.

If the VCI selected is greater than 65535, the maximum VCI, the VCI is designated at 32 in step 167. If this process is not performed more than two times in step 168, a procedure following the step 161 of increasing by 1 NextVCINo 19 of the VPI management table in order to select usable VCI is performed repeatedly. If the VCI selected is smaller than 65535, the maximum VCI of VPI, a procedure following the step 161 of increasing by 1 NextVCINo 19 of the VPI management table in order to select usable VCI is performed repeatedly. If a usable VCI is not found in spite of at least two performances in step 168, VCI allocation failure is informed in step 169.

Referring to FIG. 7, the usage state of VCI is repeatedly performed as many as the number of connections currently set in SIM in order to find out whether the VPI/VCI selected is input in the VCI management table while in use. If the VPI/VCI selected is identical with the VPI/VCI corresponding to the VCIIndex stored in the VCI management table in step 170, it is informed in step 171 that the VCI selected is in use, and the step ends.

If they are not identical, the index value increases by 1 in step 173 when the value stored in the VCI management table is not -1, the final tuple, in order to the value corresponding to the next index value. Then, a procedure following the step 170 of analyzing whether the VPI/VCI selected is identical with the VPI/VCI corresponding to the VCIIndex stored in the VCI management table is performed repeatedly. If the value stored in the VCI management table is the final tuple in step 172, it is informed in step 174 that the VCI selected is usable, and the step ends.

Referring to FIG. 8, a VPI/VCI is stored which is searched until the VPI 21 and VCI 22 of the VCI management table are -1, the final tuple, by taking the IMNo as the index. More specifically, it is determined in step 180 whether the VPI and VCI of the VCI management table are -1. If they are not -1, the index value increases by 1 in step 181. Then the step 180 of deciding whether the VPI and VCI of the VCI management table are -1 is performed repeatedly. If they are -1, the VPI/VCI selected is stored in the buffer of the VCI management table in step 182, and it is informed in step 183 that the VPI/VCI selected is completely input.

Referring to FIG. 9, the VCI may be assigned after the allocation of VPI, but the allocation of VCI will not be described in the description of the present invention.

According to the step of assigning VPI, if a VPI allocation request is received from the SPVCF 6, SMVCF 7 and UPCF 8 for performing semi-permanent connection, in step 200, IMNo 11 transmitted in allocation request and, if the VPI is designated, a parameter indicative of whether the designated VPI is within a normal range are analyzed in step 201. If the result of analysis is abnormal, connection identifier allocation impossibility is informed to the block for semi-permanent connection in step 202, and the step ends.

If the result of analysis is normal, the number of connections in SIM required for VPI allocation is analyzed with reference to VPCcnt 13 and VCCcnt 14 of connection identifier allocation number management table a in step 203. If there are no more connections available, VPI allocation impossibility is informed in step 202 to the block of semi-permanent connection. If there is another connection available, the number of VPI in use in SIM required to assign to virtual path is analyzed with reference to the VPINum 12 of the connection identifier management table in step 204.

If the number of used VPI surpasses its limit, VPI allocation impossibility is informed in step 202. If not, it is determined in step 205 whether or not a VPI desired to be used in VPI allocation request is designated. If the VPI is designated, the usage state of the VPI designated is analyzed in step 206. If the VPI is in use, VPI allocation impossibility is informed in step 202. If the VPI is not in use, the usage state of the VPI assigned in the VPI management table is changed. Usage.sub.-- Sts 16 is stored as FALSE, HeadConvType 17 as VP, and VCCcnt 18 as 0 in step 208. VPCCnt 13 of the connection identifier management table increases by 1 in step 209, and VPINum 12 increases by 1 in step 210. Then, the assigned VPI is informed to the block for semi-permanent connection in step 211, and the step ends.

If the VPI is not designated, a VPI not in use in SIM is selected with reference to the VPI management table in step 212, and if the selection of VPI fails, VPI allocation impossibility is informed in step 214. If the selection is normal, a procedure following the step 208 of changing the usage state of the VPI assigned of the VPI management table is performed.

In this invention as many connection identifiers as the number of connections permissible per SIM are assigned, a virtual path connection is enabled only with assigned VPI, and a virtual channel connection is enabled only with assigned VPI. In addition, the collision of user information transmitted by connection identifiers is eliminated because the VPI assigned for virtual path connection is not assigned for virtual channel connection. The entire range of connection identifiers recommended by ITU-T can be used so that there is no limit in the range of connection identifiers in subscriber terminal connection in accordance with the ITU-T recommendation. Further, the connection identifier management mode for assigning connection identifier is formed with index table so that it can be decided whether to use the VPI only with once selection, and thus the time to assign connection identifier can be minimized. According to management mode of the connection identifier assigned per subscriber link, the number of memories is reduced by setting as many memories as the number of connection permissible in the subscriber link.

It will be apparent to those skilled in the art that various modifications and variations can be made in a method of assigning connection identifier in ATM switching system of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the is appended claims and their equivalents.