CN1719825A - A method and network for realizing link protection switching - Google Patents

Abstract

This invention discloses a network for realizing link protection conversion containing a communication link composed of a working link, a protection link and working link data flow end junctions at both ends of the working link and protection link data flow end junctions at both ends of the protection link, among which, said communication link includes an ATM exchange unit at the either end, each ATM includes a working link logic node and a protection link logic node. This invention also discloses a realization method including: when the working link is fault, the ATM cross connection between the fault working link data flow end junction and the working link logic node is deleted and the ATM cross connection is set up between the fault working link data flow end junction and the protection link logic node.

Description

A method and network for realizing link protection switching

technical field

The invention relates to transmission protection technology, in particular to a method and network for realizing link protection switching.

Background technique

The Asynchronous Transfer Mode (ATM) Protection Switching (APS) mechanism is an ATM link layer protection mechanism, especially applied to the situation where there is no physical layer protection mechanism, that is, the situation where there is no physical link protection. Using the APS mechanism, the network can automatically switch service data flows to another path after detecting a path failure. The specific realization of the APS mechanism can adopt 1:1, 1+1, or 1:N protection mode. Among them, the 1:1 protection mode is to set a protection link for each working link, specifically: there is a dedicated protection link for each working link; when the working link is normal, the working link carries the service ; When the working link fails, the protection link carries the service. 1+1 protection mode refers to setting a protection link for each working link, and the protected service data flow is transmitted by the working link and the protection link at the same time. If any link is cut off, it will be carried by the other link data. 1:N protection mode refers to setting a protection link for N working links. When one of the working links fails, the service data is switched to the protection link. However, if multiple working links fail at the same time, Then only the working link with the highest priority can be protected.

The mechanism for realizing the 1:1 APS protection mode in the prior art is described below. Usually, the system will always monitor whether the working link and the protection link are normal. When the working link is normal, service data is carried on the working link. When the system detects that the working link is faulty and the protection link is normal, the system will automatically perform APS switching. Generally, a link failure refers to a transmission failure, for example, a link transmission failure between A-D or E-H shown in FIG. 1 .

Figure 1 is a schematic diagram of the link structure before 1:1 APS switching in the prior art, and Figure 2 is a schematic diagram of the link structure after the 1:1 APS switching in the prior art. Wherein, in the prior art network for implementing link protection switching, the communication link is composed of a working link and a protection link, and one end of the communication link has a working link data flow termination point A and a protection link data flow termination point E, The other end of the communication link has a working link data flow termination point D and a protection link data flow termination point H; the working link data flow termination points A and D are connected through the working link, and the protection link data flow termination points E and H connected by a protection link. A data stream termination point is an ATM logical entity, for example, may be an ATM Segmentation and Reassembly (SAR) logical entity. Generally speaking, there is no connection relationship between the data flow endpoints A and E, and no information exchange is performed, and there is no connection relationship between the data flow endpoints D and H, and no information interaction is performed. The virtual path identifier (VPI) and the virtual channel identifier (VCI) of the ATM cells passing through the working link data flow termination point A are VPI_W1 and VCI_W1 respectively, and the VPI of the ATM cells passing through the working link data flow termination point D and VCI are VPI_W2 and VCI_W2 respectively, the VPI and VCI of the ATM cells passing through the protection link data flow termination point E are respectively VPI_P1 and VCI_P1, and the VPI and VCI of the ATM cells passing through the protection link data flow termination point H are respectively VPI_P2 and VCI_P2. Here, both the working link and the protection link are bidirectional. The upper-layer application refers to the business undertaken by the ATM.

As shown in FIG. 1 , when the working link is normal, the service data of the upper-layer application is carried on the working links A-D. When the working link fails, if the protection link is normal, APS switching is performed, that is, the logical connection relationship between the upper layer application and the working link A-D is disconnected, and the logical connection relationship between the upper layer application and the protection link E-H is established, and then the business The data flow is switched from the working link A-D to the protection link E-H. Wherein, the APS switching can be controlled and completed by a link monitoring process. The link monitoring process monitors the status of the working link and the protection link in real time. When the working link fails and the protection link is not faulty, the link monitoring process controls and completes the APS switching. As shown in FIG. 2, after the APS switching is completed, the service data of the upper-layer application is carried on the protection link E-H. Since the termination points of the data flow are changed from A and D to E and H, the routing identifiers VPI and VCI of the ATM link carrying the upper-layer application service data are changed from VPI_W and VCI_W to VPI_P and VCI_P.

It can be seen that the APS switching in the prior art is not transparent to the upper layer application, and the service data of the upper layer application needs to be explicitly switched from the working link to the protection link, and certain adaptation and processing are required by the upper layer application. That is to say, upper-layer applications need to receive and process cells through new ATM links, and adapt ATM cell flows to service data flows, thus increasing additional overhead. In addition, because the upper layer application needs to be adapted, this leads to too strong coupling between the ATM layer and the upper layer application, that is, the ATM layer and the upper layer application have too many associations, the system layer is not clear, and it is not conducive to system maintenance.

Contents of the invention

In view of this, the main purpose of the present invention is to provide a method for realizing link protection switching, so that it can shield the details of APS switching from the upper-layer application, and enable the upper-layer application to realize the switching of the service data flow without performing adaptation processing .

Another object of the present invention is to provide a network for realizing link protection switching, so that it can shield the details of APS switching from the upper layer application, and enable the upper layer application to realize the switching of service data flow without adaptation processing.

In order to achieve the above object, technical solution of the present invention is achieved in that way:

The invention discloses a method for realizing link protection switching. An ATM switching unit is added at both ends of the communication link, wherein each ATM switching unit includes a working link logic node and a protection link logic node. Each end of the road respectively establishes the ATM cross-connection between the data flow termination point of the working link and the logical node of the working link of the ATM switching unit, and the data flow termination point of the protection link and the logical node of the protection link of the ATM switching unit ATM cross-connect;

Determine whether the working link is normal, if yes, do not perform APS switching, otherwise perform the following APS switching steps:

Delete the ATM cross-connection between the data flow termination point of the faulty working link and the logical node of the working link of the ATM switching unit at each end of the communication link, and establish a protection chain between the data flow termination point of the faulty working link and the ATM switching unit ATM cross-connect between logical nodes.

The described step of performing APS switching also includes: deleting the ATM cross connection between the protection link logical node of the protection link data flow termination point and the ATM switching unit at each end of the communication link, setting up the protection link data flow termination point and An ATM cross-connection between logical nodes of a faulty working link of an ATM switching unit.

The communication link includes more than one working link, and each ATM switching unit includes the same number of working link logic nodes as the number of working links, then the method further includes: establishing all working links at each end of the communication link One-to-one ATM cross-connection between data stream termination points and working link logical nodes;

If more than one working link fails at the same time, perform the following steps at both ends of the communication link:

Delete the ATM cross-connection between the data flow termination point of the faulty working link with the highest priority and the logical node of the working link of the ATM switching unit, and establish the protection chain between the data flow termination point of the faulty working link with the highest priority and the ATM switching unit ATM cross-connection of road logical nodes.

Correspondingly, the step of performing APS switching also includes: deleting the ATM cross-connection between the protection link data flow termination point and the protection link logic node of the ATM switching unit at each end of the communication link, and establishing the protection link data flow An ATM cross-connection between the termination point and the faulty working link logical node of the ATM switching unit corresponding to the highest priority faulty working link data flow termination point.

In the above scheme, the method for judging whether the working link is normal can be: whether the working link is detected by the ATM OAM CC function of the data flow termination point of the working link.

In addition, before performing the APS switching step, the method also includes:

Judging whether the protection link is normal, if yes, the data flow termination point of the protection link at one end initiates an APS switching request to the data flow termination point of the protection link at the other end through the protection link, and the data flow termination point of the protection link at the other end receives the APS After the switching request, execute the APS switching step; otherwise, report an alarm and end the process.

Wherein, the method for judging whether the protection link is normal may be: detecting whether the protection link is normal by the ATM OAM CC function of the data flow termination point of the protection link.

The invention also discloses a network for realizing link protection switching, which includes a communication link composed of a working link and a protection link, as well as a working link data flow termination point located at both ends of the working link and a communication link located at both ends of the protection link. protection link data flow termination point at the end;

Both ends of the communication link in the network contain an ATM switching unit, and each ATM switching unit contains a working link logical node for establishing an ATM cross-connection with the working link data flow termination point and the protection link data flow termination point and protection link logical nodes;

When the working link is normal, the working link logical node of the ATM switching unit is connected with the working link data flow termination point of this end, and the protection link logical node of the ATM switching unit is connected with the protection link data flow termination point of this end;

When the working link is faulty and the protection link is normal, the logical node of the protection link of the ATM switching unit is connected to the data flow termination point of the working link at this end, and the logical node of the working link of the ATM switching unit is terminated with the data flow of the protection link of this end The dots are connected.

Further comprise more than one working link in the described communication link, then each ATM switching unit comprises the working link logical node identical with the working link number, and each working link logical node respectively when working link is normal connected to a working link data flow endpoint;

When more than one working link fails at the same time and the protection link is normal, the logical node of the protection link of the ATM switching unit is connected to the data flow termination point of the highest priority faulty working link at this end, and the data flow of the highest priority faulty working link The logical node of the working link of the ATM switching unit corresponding to the flow termination point is connected to the data flow termination point of the protection link at this end.

Wherein, the ATM switching unit may be arranged at both ends of the working link or at both ends of the protection link.

As can be seen from the above scheme, the key of the present invention is: add an ATM switching unit respectively at the two ends of the communication link of the network, and each ATM switching unit includes a working link logic node and a protection chain for setting up an ATM cross-connect road logic node. Like this, when working link breaks down, delete the ATM cross-connection between the working link logic node of failure working link data flow termination point and each ATM switching unit, set up failure working link data flow termination point and each The ATM cross-connection between the logical nodes of the protection link of the ATM switching unit realizes APS switching.

Therefore, the network and method for realizing link protection switching provided by the present invention can shield the details of APS switching from the upper-layer application, and enable the upper-layer application to realize the switching of service data streams without performing adaptation processing, thereby increasing network Hierarchical clarity and scalability.

Description of drawings

FIG. 1 is a schematic diagram of a link structure before 1:1 APS switching in the prior art;

FIG. 2 is a schematic diagram of a link structure after 1:1 APS switching in the prior art;

Fig. 3 is a schematic diagram of the link structure before the 1:1 APS switching of the present invention;

Fig. 4 is the link structure schematic diagram after 1:1 APS switching of the present invention;

FIG. 5 is a flow chart of the implementation of the 1:1 APS switching method of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

In the present invention, in order to realize the APS switchover of ATM link, add an ATM switch unit (SWITCH) newly respectively at the two ends of the communication link of the network, each ATM switch unit includes and is used for link data stream termination point and protection Link data flow termination point establishes ATM cross-connected working link logical node and protection link logical node. The ATM switching unit can be set at both ends of the working link, or at both ends of the protection link. No matter which link the ATM switching unit is set on, the working link and the protection link share the two ATM switches. unit. When the working link is normal, the logical node of the working link of the ATM switching unit at each end is connected to the data flow termination point of the working link at this end; When the working link is faulty and the protection link is normal, the logical node of the protection link of the ATM switching unit at each end is connected with the data flow termination point of the working link at this end; the logical node of the working link of the ATM switching unit at each end is connected with the The protection link data flow endpoints are connected.

Based on the above-mentioned network, when the working link fails, delete the ATM cross-connection between the data flow termination point of the failed working link at one end of the communication link and the logical node of the working link of the ATM switching unit at this end, and establish a failure at one end of the communication link The ATM cross-connection between the end point of the data flow of the working link and the logic node of the protection link of the ATM switching unit at this end realizes APS switching.

The ATM switching unit can be implemented using commercially available ATM chips. It is fundamentally to realize the ATM switching function by changing the routing identifier VPI and VCI of the ATM cell. That is to say, the ATM switching unit is used to establish an ATM cross-connection, and complete the exchange of ATM cell header identifiers VPI and VCI. For example, by establishing an ATM cross-connection, the ATM cell header identifiers are changed from VPI1, VCI1 to VPI2, VCI2.

Fig. 3 is the link structure schematic diagram before 1:1 APS switching of the present invention, wherein, ATM switching unit SWITCH1 is connected with one end of working link and protection link, ATM switching unit SWITCH2 is connected with the other end of working link and protection link connected. Logical nodes B, C, F, and G are automatically added with the increase of ATM switching units, and are used to establish ATM cross-connections with data flow termination points. As shown in Figure 3, when the working link is normal, the logical node B of the working link of the ATM switching unit SWITCH1 is connected to the termination point A of the data flow of the working link, and the logical node C of the working link of the ATM switching unit SWITCH2 is connected to the data stream of the working link The flow termination point D is connected, the protection link logic node F of the ATM switching unit SWITCH1 is connected to the protection link data flow termination point E, and the protection link logic node G of the ATM switching unit SWITCH2 is connected to the protection link data flow termination point H.

4 is a schematic diagram of the link structure after 1:1 APS switching of the present invention, showing the link structure after the APS switching is completed when the working link fails and the protection link is normal. Among them, the logical node F of the protection link of the ATM switching unit SWITCH1 is connected to the data flow termination point A of the working link, and the logical node G of the protection link of the ATM switching unit SWITCH2 is connected to the data flow termination point D of the working link; the ATM switching unit SWITCH1 The logical node B of the working link of the ATM switching unit SWITCH2 is connected to the termination point E of the data flow of the protection link, and the logical node C of the working link of the ATM switching unit SWITCH2 is connected to the termination point H of the data flow of the protection link. The connection between the above-mentioned logical nodes and the termination points of the data flow is an ATM cross-connect.

As shown in FIG. 3 , when the working link is normal, service data is carried on the working link A-B-C-D. Among them, ATM cross-connection is between A and B, C and D, E and F, G and H. When the system detects that the working link fails, if the protection link is normal, delete the ATM cross-connection between A and B, C and D, E and F, G and H, and establish A and F, G and D, ATM cross-connect between E and B, C and H. As shown in Figure 4, after the APS switching is completed, the service data is carried on the protection link A-F-G-D. If the protection link is faulty, even if the working link is not normal, APS switching will not be triggered, but an alarm will be reported.

Based on the above network, as shown in Figure 5, the method for realizing link protection switching in the present invention includes the following steps:

Step 501, pre-establish ATM cross-connections between A and B, C and D, E and F, G and H. Wherein, the establishment of the ATM cross-connection only needs to set the ATM switching unit port, VPI and VCI before and after the ATM switching.

Step 502, service data is carried on the working link A-B-C-D; the protection link is E-F-G-H.

Step 503, judging whether the working link is normal, if yes, return to step 502; otherwise, execute steps 504-506.

Wherein, whether it is a working link or a protection link, it is possible to detect whether the link is normal through the ATM operation and maintenance cell (OAM) continuous check (CC, continuous check) function of the data stream termination point. The operation and maintenance cell (OAM) carries the information of link operation and maintenance, such as faults, alarms and other information. The OAM cell is a 48-byte information field that is often sent regularly by the ATM entity, and its content is specified in advance. , the switch that receives these cells judges the line quality according to the code errors of these cells, such as whether there is a fault alarm or not. In this embodiment, it is possible to detect whether the working link is normal through the ATM OAM CC of the data flow termination point A of the working link.

Steps 504-506, judging whether the protection link is normal, if so, the protection link data flow termination point E initiates an APS switching request to the protection link data flow termination point H through the protection link, and then executes steps 507-509; otherwise Report the alarm and end the process.

Similarly, it is possible to detect whether the protection link is normal through the ATM OAM CC function of the protection link data stream termination point E.

Wherein, the link monitoring process may notify the protection link data flow termination point E to initiate an APS switching request. To delete the ATM cross-connect, it is only necessary to delete the ATM switching unit port, VPI and VCI on the logical node side for ATM switching, and retain the ATM switching unit port, VPI and VCI on the data flow termination side for ATM switching.

Steps 507-509, delete the ATM cross-connection between A and B, E and F, set up the ATM cross-connection between A and F, E and B; after the protection link data stream termination point H receives the APS switching request, Delete the ATM cross-connection between C and D, G and H, and establish the ATM cross-connection between C and H, G and D; service data is carried on the protection link A-F-G-D.

At this time, although the current link E-B-C-H cannot work normally due to the link transmission failure between B and C, the ATM cross-connection between E and B and C and H must be established, because if the link between B and C is cleared If the link transmission failure between them, the link E-B-C-H can work normally, and it can also prepare for the next APS switchover.

A specific example is given below to illustrate the method for realizing ATM link protection switching by establishing and deleting ATM cross-connections in the present invention.

Table 1 shows the corresponding relationship between nodes A~H and the ports of the ATM switching unit, and the ATM cell header identification before and after passing through the ATM switching unit. As shown in Table 1, the ports of ATM switching unit SWITCH1 are 1, 2, 5 and 6 respectively, the ports of ATM switching unit SWITCH2 are 3, 4, 7 and 8 respectively, and the data stream termination points A, D, E and H are respectively Connected to ports 1, 4, 5 and 8, logical nodes B, C, F and G connected to ports 2, 3, 6 and 7, respectively. node (PORT, VPI, VCI) A (1, 5, 36) B (2, 6, 38) C (3,6,38) D. (4,8,33) E. (5, 1, 30) f (6, 9, 39) G (7,9,39) h (8,7,35)

Table 1

According to the method of the present invention, when the working link is normal, the ATM cross-connection between A and B, C and D, E and F, G and H is established in advance, and the service data is carried on the working link A-B-C-D. In this way, the ATM cell flow whose routing identifier is VPI=5 and VCI=36 sent from the end point A of the working link data flow enters the ATM switching unit SWITCH1 from port 1, and the ATM switching unit SWITCH1 forwards it to port 2. When the ATM cell leaves the ATM switching unit SWITCH1 from port 2, that is, when the ATM cell passes through the logical node B of the working link, the ATM cell header identifier becomes VPI=6, VCI=38. The ATM cell stream arrives at the logical node C of the working link through the working link. After passing through the logical node C of the working link, the routing identifier is VPI=6, and the ATM cell stream of VCI=38 enters the ATM switching unit SWITCH2 from port 3, and the ATM switching Unit SWITCH2 forwards it to port 4. When the ATM cell leaves the ATM switching unit SWITCH2 from port 4 and arrives at the end point D of the working link data flow, the ATM cell header identifier becomes VPI=8, VCI=33.

When the working link fails, APS switching is required. At this time, first delete the ATM cross-connection between A and B, E and F, C and D, G and H, and then establish the ATM cross-connection between A and F, E and B, C and H, G and D , service data is carried on the protection link A-F-G-D. In this way, the ATM cell flow whose routing identifier is VPI=5 and VCI=36 sent from the end point A of the working link data flow enters the ATM switching unit SWITCH1 from port 1, and the ATM switching unit SWITCH1 forwards it to port 6. When the ATM cell leaves the ATM switching unit SWITCH1 from port 6, that is, when the ATM cell passes through the logical node F of the protection link, the ATM cell header identifier becomes VPI=9, VCI=39. The ATM cell flow reaches the protection link logic node G through the protection link, and through the protection link logic node G, the route identification is VPI=9, and the ATM cell flow of VCI=39 enters the ATM switching unit SWITCH2 from port 7, and the ATM switching Unit SWITCH2 forwards it to port 4. When the ATM cell leaves the ATM switching unit SWITCH2 from port 4 and arrives at the working link data termination point D, the ATM cell header identifier becomes VPI=8, VCI=33.

As can be seen from the foregoing scheme, the realization principle of the inventive method is similar to that of the double-pole double-throw switch, first disconnect two old ATM cross-connects, then set up two new ATM cross-connects to realize the working link Switching with the protection link. In terms of implementation, a new ATM link is established by assigning new unique routing identifiers VPI and VCI to the ATM cell by the logic node inside the ATM link. In this way, before and after the APS switching of the ATM link, the upper-layer application still maintains its logical connection relationship with the working link A-D, so the routing identifier of the ATM link carrying the upper-layer application service data remains unchanged, and the upper-layer application does not need to be adapted and processing to ensure the smoothness of the business. Moreover, the method of the invention shields the implementation details of the bottom layer and is completely transparent to the upper layer application.

The present invention can also be used in 1:N protection mode, and its working principle is similar to that of 1:1 protection mode, the difference is that 1:N protection mode is to set a protection link for N working links to realize link protection switching Each ATM switching unit in the network contains the same number of working link logic nodes as the number of working links. When each working link is normal, the logical node of the working link of the ATM switching unit at each end is correspondingly connected with the data flow termination point of the working link at this end; the logical node of the protection link of the ATM switching unit at each end is connected with the protection link at this end The data flow termination points are connected correspondingly; when one of the working links fails and the protection link is normal, the logical node of the faulty working link of the ATM switching unit at each end is connected to the data flow termination point of the protection link at this end; the ATM switching unit at each end The logical node of the protection link is connected to the data flow termination point of the faulty working link at this end; when multiple working links fail and the protection link is normal, the ATM corresponding to the data flow termination point of the faulty working link with the highest priority at each end The logical node of the working link of the switching unit is connected to the data flow termination point of the protection link at this end; the logical node of the protection link of the ATM switching unit at each end is connected to the data flow termination point of the faulty working link with the highest priority at this end. Wherein, the data flow termination point of the faulty working link with the highest priority refers to the data flow termination point of the working link corresponding to the working link with the highest priority among the failed working links. In this way, when only one working link fails, the service data is switched to the protection link; when multiple working links fail at the same time, only the service data on the working link with the highest priority is switched to the protection link on the way.

In a word, the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in this within the scope of protection of the invention.

Claims (10)

1. A network that realizes link protection switching, including a communication link composed of a working link and a protection link, as well as a working link data flow termination point at both ends of the working link and a protection link at both ends of the protection link road data stream endpoint; It is characterized in that the two ends of the communication link in the network respectively include an ATM switching unit, and each ATM switching unit includes a working link for establishing an ATM cross-connection with the data flow termination point of the working link and the data flow termination point of the protection link. Link Logical Nodes and Protection Link Logical Nodes; When the working link is normal, the working link logical node of the ATM switching unit is connected with the working link data flow termination point of this end, and the protection link logical node of the ATM switching unit is connected with the protection link data flow termination point of this end; When the working link is faulty and the protection link is normal, the logical node of the protection link of the ATM switching unit is connected to the data flow termination point of the working link at this end, and the logical node of the working link of the ATM switching unit is terminated with the data flow of the protection link of this end The dots are connected. 2, the network according to claim 1, is characterized in that, further comprises more than one working link in the described communication link, then each ATM switching unit comprises the working link logic node identical with working link number, And each logical node of the working link is respectively connected to a data flow termination point of the working link when the working link is normal; When more than one working link fails at the same time and the protection link is normal, the logical node of the protection link of the ATM switching unit is connected to the data flow termination point of the highest priority faulty working link at this end, and the data flow of the highest priority faulty working link The logical node of the working link of the ATM switching unit corresponding to the flow termination point is connected to the data flow termination point of the protection link at this end. 3. The network according to claim 1 or 2, characterized in that the ATM switching unit is arranged at both ends of the working link or at both ends of the protection link. 4. A method for realizing link protection switching, characterized in that, An ATM switching unit is added at both ends of the communication link, wherein each ATM switching unit includes a working link logic node and a protection link logic node, and a working link data flow termination point and a protection link logic node are respectively established at each end of the communication link ATM cross-connects between the logical nodes of the working link of the ATM switching unit, and ATM cross-connects between the data flow termination point of the protection link and the logical nodes of the protection link of the ATM switching unit; Determine whether the working link is normal, if yes, do not perform APS switching, otherwise perform the following APS switching steps: Delete the ATM cross-connection between the data flow termination point of the faulty working link and the logical node of the working link of the ATM switching unit at each end of the communication link, and establish a protection chain between the data flow termination point of the faulty working link and the ATM switching unit ATM cross-connect between logical nodes. 5. The method according to claim 4, wherein the step of performing APS switching further comprises: deleting the connection between the protection link data flow termination point and the protection link logic node of the ATM switching unit at each end of the communication link ATM cross-connection between ATM cross-connection, establish ATM cross-connection between protection link data flow termination point and ATM switching unit failure working link logic node. 6, the method according to claim 4 is characterized in that, comprises more than one working link in the communication link, and each ATM exchange unit comprises the working link logic node identical with working link bar number, then this method is further Including: establishing one-to-one ATM cross-connections between all working link data flow termination points and working link logical nodes at each end of the communication link; If more than one working link fails at the same time, perform the following steps at both ends of the communication link: Delete the ATM cross-connection between the data flow termination point of the faulty working link with the highest priority and the logical node of the working link of the ATM switching unit, and establish the protection chain between the data flow termination point of the faulty working link with the highest priority and the ATM switching unit ATM cross-connection of road logical nodes. 7. The method according to claim 6, wherein the step of performing APS switching further comprises: deleting the connection between the protection link data flow termination point and the protection link logic node of the ATM switching unit at each end of the communication link An ATM cross-connection between ATM cross-connections is established, and an ATM cross-connection between logical nodes of the faulty working link of the ATM switching unit corresponding to the data flow termination point of the protection link and the data flow termination point of the highest priority faulty working link is established. 8. The method according to claim 4, wherein the method for judging whether the working link is normal is: detecting whether the working link is normal through the ATM OAM CC function of the data flow termination point of the working link. 9. The method according to claim 4 or 6, characterized in that, before performing the APS switching step, the method further comprises: Judging whether the protection link is normal, if yes, the data flow termination point of the protection link at one end initiates an APS switching request to the data flow termination point of the protection link at the other end through the protection link, and the data flow termination point of the protection link at the other end receives the APS After the switching request, execute the APS switching step; otherwise, report an alarm and end the process. 10. The method according to claim 9, wherein the method for judging whether the protection link is normal is: detecting whether the protection link is normal through the ATM OAM CC function of the data flow termination point of the protection link.

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