AU7756098A

AU7756098A - Method for changeover to standby of transmission installations for bi-directional transmission of atm cells

Info

Publication number: AU7756098A
Application number: AU77560/98A
Authority: AU
Inventors: Joachim Klink; Andreas Klug; Karl Schrodi
Original assignee: Nokia Solutions and Networks GmbH and Co KG
Current assignee: Nokia Solutions and Networks GmbH and Co KG
Priority date: 1997-04-25
Filing date: 1998-03-18
Publication date: 1998-11-24
Anticipated expiration: 2018-03-18
Also published as: CN1253706A; ATE328453T1; CN1123274C; CA2288291C; DE19717584A1; ES2263207T3; AU745134B2; WO1998049863A1; CA2288291A1; EP0978217B1; DE19717584C2; EP0978217A1; DE59813573D1

Abstract

In prior art, in cases of interference on a service line, the ATM cells routed via this line are changed over onto a standby line provided for this purpose. In accordance with the invention, ABR/UBR special data is transmitted via this standby line in the case of interference-free functioning.

Description

GR 97 P 1525 -1 Description A method for switching transmission devices to an equivalent circuit for the bidirectional 5 transmission of ATM cells. The invention relates to a method according to the preamble of patent claim 1. Such a method has already been suggested in the German patent application DE 19646016.6. 10 This known method relates to transmission devices of the asynchronous transfer mode (ATM). In said mode, transmission devices for bidirectional transmission of ATM cells are provided, in which devices two switching devices which function as 15 terminals are connected to one another via a plurality of service links and only one standby link. The two terminals each contain a plurality of monitoring devices for detecting transmission faults. A switching device which can be controlled by the monitoring device 20 connects a reception device into a first switched state with the service link and in a second switched state with the standby link. Control information is exchanged between the control devices of the two terminals. The switching 25 device is controlled in each case by the local monitoring device as a function of local control criteria which are contained in the control information received from the opposite station. Furthermore, according to this disclosure it is proposed, if 30 appropriate, to feed special data (EXTRA TRAFFIC) to the receiving switching device during the time in which the standby link remains unused.

GR 97 P 1525 - 2 However, this disclosure does not mention what type these special data may be. The invention is based on the object of developing a method of the type mentioned at the 5 beginning in such a way that special data which are transmitted according to an asynchronous transfer mode can be efficiently transmitted via a plurality of network nodes. The invention is achieved on the basis of 10 features specified in the preamble of patent claim 1, by virtue of its characterizing features. An advantage of the invention is, in particular, that just one standby link is provided and it is assigned to a plurality of service links. The ATM 15 cells of the faulty service link are transmitted on this standby link. In a fault-free situation, if appropriate, special data are transmitted via this standby link. Here, the special data are configured as traffic data with which, if appropriate, a minimum bit 20 rate is guaranteed. This entails the advantage of a dynamic relief of the service links. Advantageous developments of the invention are specified in the subclaims. The invention is explained in more detail below 25 with reference to an exemplary embodiment. Figure 1 shows the method according to the invention for the bidirectional transmission of ATM cells in a 1:n structure, 30 Figure 2 shows a specific refinement of the method according to the invention in a 1:1 structure, GR 97 P 1525 - 3 Figure 3 shows a further specific refinement of the method according to the invention in a 1+1 structure. 5 Figure 4 shows the priorities used, in accordance with which the switching to an equivalent circuit is carried out. Fig. 1 shows two nodes of an ATM network which 10 are each embodied as a switching center W, E. In the present exemplary embodiment it is assumed that these switching centers are cross connect switching centers. The use of switching centers of this design does not, however, signify any limitation of the invention; other 15 switching centers can also be used. Fig. la shows the transmission of ATM cells from the switching center W to the switching center E, whereas Fig. lb discloses the reverse direction of this link. The switching centers W, E are connected to one 20 another by means of service links WEi... .WEn (WORKING ENTITY) and just one standby link PE (PROTECTION ENTITY). In addition, switch devices So. . . Sn (BRIDGE) are shown, via which the incoming ATM cells and the associated service links WE 1 .. .WEn are transmitted to 25 the switching center E. The ATM cells are transmitted according to an asynchronous transfer mode and each have a header part and an information part. The header part is used to hold connection information while the information part can be used to hold user information. 30 The connection information contained in the header part is in the form of logic information and is usually embodied as a virtual path number VPI or virtual channel number VCI. In addition, Fig. 1 shows selection devices SN 35 whose function consists in feeding the ATM cells transmitted on the service links WEi.. .WEn to the output of the switching GR 97 P 1525 - 4 center E. According to the present exemplary embodiment, the selection devices SN are embodied as a ATM switching matrix. The ATM switching matrix SN is contained both in the switching center W and the 5 switching center E. In addition, monitoring devices 0EO ... OEn (PROTECTION DOMAIN SINK, PROTECTION DOMAIN SOURCE), which monitor the state or the quality of the ATM cells transmitted on the service links WE 1 ..WEn, are shown in 10 both switching centers W, E. For example, the ATM cells of the link with the number 1 WT 1 are provided, before they are transmitted to the switching center E on the service link WE, with control information in the monitoring device 0Ei of the switching center W, which 15 information is extracted from the receiving switching center E, and checked, by the monitoring device OE 1 . With reference to this control information it is then possible to determine whether or not the ATM cell is being transmitted correctly. In particular, it is 20 possible to determine a total failure (SIGNAL FAIL FOR WORKING ENTITY) of one of the service links WE1... .WEn here. Likewise, degradation of the transmission quality (SIGNAL DEGRADE) can be determined, but also using known methods. 25 The monitoring devices OE,. . .iEn terminate the service links WE 1 .. .WEn at both ends. Further monitoring devices CEO are arranged at both ends of the standby link PE. The latter is intended to serve, in the case of a fault, as a transmission link for the service link 30 WE, which is taken out of operation. In addition, equivalent circuit switching protocols ES are transmitted in this way so that the intactness of the standby link has top priority. In addition, central control devices ZST are 35 arranged in each of the switching centers W, E. Said control devices ZST each contain priority tables PG, PL. The priority tables GR 97 P 1525 - 5 PL are local priority tables in which the state and priority of the local switching center is stored. The priority tables PG are global priority tables in which there is the state and priority of the local, but also 5 remaining, switching center. The introduction of the priorities ensures that when a plurality of equivalent circuit requests occur at the same time it is defined which service link will be switched to an equivalent circuit. Likewise, the equivalent circuit requests are 10 prioritized in the priority tables. Thus, there is, for example, a high priority request by a user. Since this equivalent circuit request is assigned a high priority, it is thus controlled with preference. An equivalent circuit request which is controlled by one of the 15 service links is thus rejected. The individual priorities are shown in Fig. 4. The central control devices ZST of the switching centers W, E exchange information in a standby protocol ES. This protocol is transmitted on 20 the standby link PE and obtained from the associated monitoring device OE 0 of the respective receiving switching center, and fed to the relevant central control device ZST. In addition, measures in the central control device ZST ensure that, in the event 25 of a fault, the switching devices So ... Sn are controlled in a corresponding way. Information K2 is stored in the protocol ES. This is information relating to the instantaneous states of the switching devices. Information Kl is also 30 stored. This is information relating to the generated equivalent circuit request. The protocol is exchanged between the two switching centers whenever the equivalent circuit request is generated. In one specific refinement of the invention it is provided 35 that the ,GR 97 P 1525 - 6 protocol ES be transmitted cyclically between the two switching centers. The way in which the method according to the invention will be carried out will be explained in more 5 detail below with reference to Fig. 1. Fig. la shows the transmission of the ATM cells from the switching center W to the switching center E via the service links WE1... .WE,. The associated opposite direction (bidirectional transmission) is explained in Fig. lb. 10 In the present exemplary embodiment it is then initially assumed that the service links WE 1 .. .WEn are still intact and the incoming ATM cells are transmitting correctly. According to Fig. la, the ATM cells are fed to 15 the switching center W. The ATM cells are associated here with a plurality of links WT1... WTn. The individual links are distinguished with reference to the logic operation number VPI entered in the header part of the ATM cells. 20 The switching devices Si.. .S of the switching center W are switched, in this (still intact) operating situation, in such a way that the ATM cells are fed directly to the monitoring devices OE1...TEn. In the latter devices, the ATM cells are provided with the 25 control information already referred to and fed on the respective service link WE 1 .. .WEn to the monitoring devices CE,... OEn of the receiving switching center E. The control information which is also carried is checked there and, if appropriate, a fault situation is 30 determined. If the transmission has taken place correctly, the ATM cells are fed to the ATM switching matrix SN. Here, the logic operation information VPI is evaluated and the ATM cell is passed on to the ATM network via the respective output of the switching 35 matrix SN in accordance with this evaluation. - T76*n GR 97 P 1525 - 7 The standby link PE can remain unused during this time. However, if appropriate, special data (EXTRA TRAFFIC) can also be fed to the switching center E during this time. The switching device So of the 5 switching center W therefore assumes the positions 1 or 3. The special data are also transmitted in ATM cells. The monitoring device OEo of the of the switching center W feeds control information to the ATM cells in the same way as has already been described for the case 10 of the on the service links WEi.. .WE,. The link is also monitored. It is assumed below that the service link WE 2 has failed. This is determined by the monitoring device 0E 2 , assigned to the latter, of the receiving switching 15 center E. The equivalent circuit request K1 is then transmitted to the respective central control device ZST and stored there in the local priority table PL and the global priority table PG. In accordance with the priorities stored in the 20 global priority table PG it is then determined whether requests with still higher priorities are present. These could be, for example, the user's switchover request (FORCED SWITCH FOR WORKING ENTITY) already mentioned. Even if other fault situations, such as on 25 the service link WEi, for example, occur simultaneously, the equivalent circuit of this service link would be handled with preference since a higher priority is assigned to this service link. In this case, a request with higher priority is handled first. 30 The priorities stored in the local and global priority tables PL, PG are shown in Fig. 4. If there are no requests present with higher priority, the switching device S2 of the switching center E is placed in the remaining operating state, as 35 shown in Fig. lb. The equivalent circuit switching protocol ES is then

R

.GR 97 P 1525 - 8 fed to the switching center W on the standby link PE. The information K1 and K2 already mentioned is contained in this equivalent circuit switching protocol. The central feature is that the local 5 priority logic defines the configuration of the information K1, and the global priority logic defines the position of the switching device So. The equivalent circuit switching protocol ES is then transferred from the monitoring device OEo of the 10 switching center E and fed to the central control device ZST of the switching center W. If there are no further requests with higher priority present in the global priority table PG here either, the switching device S2 is also driven and set here in a 15 corresponding way. In addition, the switching device So of the switching center W is also switched over. The new status of the two switching devices So, S2 is acknowledged to the switching center E and updated in the global priority table PG there. The ATM cells of 20 the link WT 2 are thus fed to the switching center E on the standby link PE. The selection device SN of the switching center E is embodied as an ATM switching matrix. The ATM cells transmitted on the standby link PE are fed to this 25 switching matrix. Here, the logic path number VPI is obtained from the cell header and evaluated and routed through the switching matrix. The driving of switching devices is thus omitted in this case. Since these links are a bidirectional link, it 30 is also necessary to take measures to ensure the transmission of the ATM cells in the reverse direction. This is carried out according to Fig. lb in the same way as has just been described for the transmission of the ATM cells from the switching center W to the 35 switching center E. -c- GR 97 P 1525 - 9 In the exemplary embodiment just described, a 1:n structure was assumed. This means that there is just one standby link available for n service links. It is therefore a special case if n=1. In this case, a 1:1 5 structure is therefore used. The corresponding conditions are shown in Fig. 2. The selection device is also embodied as an ATM switching money in this case so that switching through is carried out in accordance with the VPI number. The 10 switching centers according to Fig. 2 also contain central control devices (not shown) with local and global priority tables. A further refinement of the invention is shown in Fig. 3. This is a 1+1 structure. This structure is 15 obtained from the 1:n structure in that the switching devices S are set permanently and can no longer be controlled by means of the central control devices ZST. In this way, the ATM cells are transmitted both on the service link WE and on the standby link PE, even in a 20 fault-free operating situation. The selection device SN is not embodied here as an ATM switching matrix but rather as a switching device. The equivalent circuit switching protocol ES assumes a simpler form in this case. The information K2 describes the state of the 25 selection device here. Whenever, in the case of the 1:n structure, the switching devices So...S, have been controlled, in the case of the 1+1 structure the selection device SN is controlled instead. As already mentioned at the beginning, there is 30 provision for the standby link PE to remain unused during the time in which there is undisrupted operation. However, if appropriate, special data (EXTRA TRAFFIC) can also be fed to the switching device E during this time. The dynamics of the system are thus 35 increased. ABR (Available Bit Rate) traffic data or UBR cR GR 97 P 1525 - 10 (Unspecified Bit Rate) traffic data are used here as the special data. They are defined, for example, in the ATM forum "Traffic Management Specification", Version 4.0. 5 According to the above, ABR/UBR traffic is understood in particular to be specifically defined classes of traffic. The ABR traffic class is defined here in such a way that the transmission of the associated traffic data is performed under the 10 guarantee of a minimum bandwidth (Minimum Cell Rate, MCR). The remaining bandwidth is, if appropriate, regulated depending on the usage factor of the nodes (quality of servive) . In the case of the UBR traffic class, no guarantee whatsoever is made for the 15 transmission quality (quality of servive) . Likewise, no lower bandwidth is guaranteed. However, the transmission of data traffic of a general type is thus perfectly tolerable. Both traffic classes are also assigned a priority. 20 The transmission of the ABR/UBR traffic data which is controlled by means of the standby link PE in the case of fault-free operation does not necessarily have to be interrupted in the case of standby operation. The reason for this is that the traffic data 25 which is configured in this way have a lower priority than the traffic data which are switched to standby circuits, and are thus automatically moved on depending on their priority. However, in this case, the ABR/UBR traffic which may be present on the service link 30 WE 1 .. .WEn which is not available are no longer treated with higher priority than the ABR/UBR traffic on the standby link PE. Here, in the case of standby operation, it must be ensured that the total of the guaranteed bandwidths including the guaranteed minimum 35 bandwidth does not exceed the capacity of the standby link. The transmission of the ABR/UBR traffic data on the standby link PE does not necessarily have to take 'ace between the switching devices W, E. Instead, the (7, GR 97 P 1525 - 11 transmission could also merely occur over one section of the standby link PE. Such signal injection/extraction could then be performed by means of by means of further switching devices which are 5 designed, for example, as cross-connect switching devices and which are arranged between the switching devices W, E. In addition, the bandwidth of the ABR/UBR traffic data on the standby link PE may be distributed as desired amongst a large number of other virtual 10 paths/channels (route freedom). R4

Claims

1. A method for switching transmission devices to an equivalent circuit for the bidirectional 5 transmission of ATM cells, having at least two switching centers (W, E) which each terminate a transmission section formed from a plurality of service links (WEi.. .WEn), and feed the information in ATM cells to the respective receiving switching center (W, E) on 10 the plurality of service links (WEi ...WE) , and having a standby link (PE) which is arranged between the two switching centers (W, E) and on which the ATM cells which are transmitted on the service links (WEi.. .WE,) are transmitted in the event of a fault on one of said 15 links and on which, if appropriate, special data are transmitted during fault-free operation, characterized in that the special data are configured as traffic data (ABR, UBR) with which, if appropriate, a minimum bit rate is guaranteed. 20

2. The method as claimed in claim 1, characterized in that the transmission of the special data is not interrupted in the case of standby operation.

3. The method as claimed in claim 1 or 2, characterized in that in the case of standby operation 25 it is ensured that the total of the guaranteed bandwidths is not exceeded the capacity of the standby link (PE).

4. The method as claimed in claim 1, characterized in that the traffic data are, if appropriate, 30 transmitted on a section of the standby link (PE). GR 97 P 1525 - 13

5. The method as claimed in claim 1 to 4, characterized in that the bandwidths of the traffic data on the standby link (PE) can be divided in various 5 ways between other virtual paths/channels.

6. The method as claimed in one of claims 1 to 5, characterized in that the switching centers are embodied as cross-connect switching devices.