WO2009052720A1 - Upstream node label allocating method, device and system for point to multi-point tunnel - Google Patents

Abstract

An upstream label allocating method for point to multi-point tunnel in communication filed ensures that repetition will not occur when a plurality of upstream nodes allocate labels to the same downstream node. The upstream label allocating method for point to multi-point tunnel applies negotiation mechanism between the upstream nodes and the downstream nodes, if an upstream node receives the label information returned by a downstream node after allocating a label to said downstream node, said upstream node re-allocates a label to said downstream node according to the label information returned by said downstream node. There is also an upstream label allocating system for point to multi-point tunnel.

Description

 Method, device and system for upstream node label allocation for point-to-multipoint tunnel

 The present invention relates to the field of communications technologies, and in particular, to a method, device, and system for allocating an upstream node label for a point-to-multipoint tunnel. Background technique

 Multi-Protocol Label Switching (MPLS) is an efficient forwarding technology applied to IP backbone networks. Label Switched Path (LSP) established by MPLS technology can support point-to-point (Point to Point). , P2P ) and point to multi-point (P2MP) and other tunnels. Currently, the signaling protocols used by MPLS to establish LSPs are mainly Resource Reservation Protocol-Traffic Engineering (RSVP-TE) and Label Distribution Protocol (LDP). Unlike traditional IP forwarding technology, MPLS decides to forward based on the label.

 Currently, the LSP tunnel mainly uses a downstream distribution label, that is, the downstream node allocates labels for the upstream nodes.

 However, if the downstream node is used to assign tags in a point-to-multipoint tunnel, there are problems in the following situations:

 Broadcast network. Figure 1 is a schematic diagram of packet forwarding for a broadcast network that uses a downstream node to assign labels. In the broadcast network, multicast traffic is sent from node A to node C, node D, and node E. Because the downstream node assigns labels, node C, node D, and node E give the upstream node B different labels, resulting in node B. To copy three streams to node C, node D, and node E, increase the burden on node B, and cause bandwidth waste between node B and node C, node D, and node E. Because it is a broadcast network, node C will also The traffic sent to the node D and the node E is discarded by the forwarding layer, and the load of the node C is increased. The same problem exists in the node D and the node E.

Bypass tunnel. FIG. 2 is a schematic diagram of forwarding of Bypass tunnel texts by using a downstream node to assign labels. In the MPLS network, the Bypass tunnel of the node A-Node B is the node A-node F. After the primary tunnel passing through the node A-Node B fails, the traffic is forwarded through the bypass tunnel. Nodes C, D, and E assign different labels to the node F, and the bypass tunnel uses the label stack technology to request packets destined for node C, node D, and node E. The label needs to be encapsulated at node A, which causes three traffic to be transmitted between node A and node F, resulting in wasted bandwidth.

 To solve the above problem, as shown in FIG. 3, FIG. 3 is a schematic diagram of packet forwarding of a broadcast network that uses a label assigned by an upstream node. The upstream B node assigns the same label to node C, node D, and node E, so node B only needs to send a multicast traffic; because it is a broadcast network, node C, node D, and node E can all receive it.

 As shown in FIG. 4, FIG. 4 is a schematic diagram of a Bypass tunnel 4 packet forwarding with an upstream node assigning a label. Node F assigns the same label to node C, node D, and node E, so that node A can transmit a traffic to node F, which greatly saves bandwidth.

 In a point-to-multipoint tunnel, after an upstream node assigns a label, when there are multiple upstream nodes, different upstream nodes may assign the same label to the same downstream node, causing forwarding errors on the downstream node.

 In order to avoid forwarding errors, in the prior art, the upstream node allocates labels using the neighbor label space, that is, the downstream node records the labels allocated by the upstream nodes, and records the addresses of the respective upstream nodes. For example, on the Ethernet link, the upstream node A and the upstream node B simultaneously assign the same label L1 to the downstream node C. The records of the downstream node are:

 MAC A L1 → forwarding behavior of node A 1;

 Node B's MAC + L1 → forwarding behavior 2;

 When receiving the MPLS packet from the upstream node, the node C searches the forwarding table according to the source MAC address and label of the packet. Since the current MPLS forwarding process directly searches the forwarding table according to the label, this method requires a large modification of the existing forwarding process of the MPLS, and the complexity of the algorithm search and the hardware implementation is greatly increased, and the search efficiency is also slow. ^艮多多.

In order to avoid forwarding errors, another method for assigning labels by an upstream node in the prior art is to statically specify a label allocation space. For example, the label of the specified node is assigned to L1 to L50, and the label allocation space of the specified node B is L51 to L100. There are many restrictions on the use of statically allocated label space. Firstly, the entire network is required to be uniformly planned. If the planning is not good, there may be overlapping of label spaces, which will inevitably lead to forwarding errors. Secondly, the static allocation of label space is not flexible. In the range, the adjustment may fail because some labels have been allocated. Third, the static allocation must be a period of allocation. Usually, the label space cannot be accurately planned. For example, this label is assigned to node A, and other nodes. Can not be used, and node A may not actually need so many tags, resulting in tag resources Waste. Summary of the invention

 An object of the present invention is to provide an upstream node label allocation method, device, and system for a point-to-multipoint tunnel, which solves the problem that multiple upstream nodes assign duplicate labels to the same downstream node.

 To achieve the above objective, the technical solution of the embodiment of the present invention is implemented as follows:

 An upstream node label allocation method for a point-to-multipoint tunnel, the method comprising:

 After the upstream node assigns a label to the downstream node, if the label information fed back by the downstream node is received, the upstream node re-assigns the label to the downstream node according to the label information fed back by the downstream node;

 The downstream node feeds back label information to the upstream node because the label allocated by the upstream node cannot be accepted.

 An upstream node device, the device comprising:

 a label receiving unit, configured to receive label information fed back by the downstream node;

 a node allocating unit, configured to allocate a label to the downstream node, and re-allocate the label to the downstream node after the label receiving unit receives the label information fed back by the downstream node.

 An upstream node label distribution system for a point-to-multipoint tunnel, the system comprising an upstream node device and a downstream node device:

 The upstream node device is configured to allocate a label to the downstream node device; and re-allocate the label to the downstream node device according to the label information fed back by the downstream node device;

 And the downstream node device is configured to receive the label allocated by the upstream node device, and if the label allocated by the upstream node device is not accepted, feed back label information of the downstream node device to the upstream node device.

It can be seen that, by adopting the technical solution of the embodiment of the present invention, a label negotiation mechanism is introduced between the upstream node and the downstream node to ensure that multiple upstream nodes do not duplicate when assigning labels to the same downstream node, thereby solving the prior art. Duplicate problems occur when multiple upstream nodes assign labels to the same downstream nodes. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in the claims Other drawings may also be obtained from these drawings without the inventive labor.

 FIG. 1 is a schematic diagram of packet forwarding of a broadcast network that uses a downstream node to allocate labels;

 FIG. 2 is a schematic diagram of forwarding of a bypass tunnel using a downstream node to assign a label;

 FIG. 3 is a schematic diagram of packet forwarding of a broadcast network that uses a label allocated by an upstream node;

 Figure 4 is a schematic diagram of a Bypass tunnel >3⁄4 text forwarding with an upstream node assigned label;

 5 is a flow chart of assigning labels to an upstream node in a point-to-multipoint tunnel established by RSVP-TE according to a preferred embodiment of the method of the present invention;

 6 is a flow chart of an upstream node allocation label in a point-to-multipoint tunnel established by using LDP according to a preferred embodiment of the method of the present invention;

 7 is a structural diagram of a point-to-multipoint tunnel system established by using RSVP-TE according to a preferred embodiment of the present invention;

 FIG. 8 is a structural diagram of a point-to-multipoint tunnel system established by using LDP according to a preferred embodiment of the present invention. detailed description

 In order to make the objects, technical solutions and advantages of the present invention more comprehensible, the present invention will be further described in detail below with reference to the accompanying drawings.

 FIG. 5 is a flow chart of assigning labels to an upstream node in a point-to-multipoint tunnel established by RSVP-TE according to a preferred embodiment of the method of the present invention. As shown in FIG. 5, the method includes the following steps:

 Step 501: The upstream node A sends a PATH (Path) message to the downstream node B, where the PATH message carries the label assigned by the upstream node A to the downstream node B. The upstream node A records the upstream node A carried in the PATH message. a label assigned to the downstream node B;

Step 502: The downstream node B determines whether to accept the label allocated by the upstream node A, for example, whether the label allocated by the upstream node A belongs to its own acceptable label range, or whether the label allocated by the upstream node A is upstream with other labels. The label assigned by the node is repeated; if the label assigned by the upstream node A is accepted, step 509 is performed; if the label assigned by the upstream node A is not accepted, step 503 is performed; Step 503: The downstream node B sends a PATHERR (Path Error) message to the upstream node A, where the PATHERR message carries a label set object, and the object carries the following label information:

 TYPE (type);

 Length (length);

 Action

 Acceptable label;

 Unacceptable label;

 Acceptable label range;

 Unacceptable range of labels;

 Step 504: The upstream node A receives the PATHERR message sent by the downstream node B, records the acceptable label range of the downstream node B, and re-selects a new label acceptable to the downstream node B according to the acceptable label range;

 Step 505: The upstream node A determines, according to the recorded label information, whether the new label belongs to other downstream node label ranges except the node B; if the new label does not belong to other downstream node label ranges except the node B (ie, other The downstream node can not accept the new label), step 506 is performed; if the new label belongs to other downstream node label ranges except B (ie, other downstream nodes can accept the new label), step 507 is performed;

 Step 506: The upstream node A assigns a label to the downstream node B again, and step 505 is performed. Step 507: The upstream node A sends a PATH message to all the downstream nodes, where the PATH message carries the upstream node A and is allocated to the downstream node. New tag information; at the same time, the upstream node A updates the tag information assigned to the downstream node;

 Step 508: After receiving the PATH message carrying the new label information, the downstream node B installs the new label to the forwarding layer; the other downstream nodes except the downstream node B receive the PATH message carrying the new label information. After that, the forwarding layer label information is updated;

 Step 509: Enter the normal process of establishing a point-to-multipoint tunnel by using RS VP-TE.

 After the above process, the label range of the downstream node has changed. When the next upstream node assigns a label to the downstream node, the above process is repeated, and the label information of the downstream node recorded by the upstream node can be updated.

According to the description of the above preferred embodiments, those skilled in the art may know that the upstream node label allocation method for the point-to-multipoint tunnel provided by the above embodiment may also be applied to the point established by using LDP. Go to a multi-point tunnel.

 FIG. 6 is a flow chart of an upstream node allocation label in a point-to-multipoint tunnel established by LDP according to a preferred embodiment of the method of the present invention. As shown in Figure 6, the method includes the following steps:

 Step 601: The downstream node B sends a label request message to the upstream node A.

 Step 602: The upstream node A sends a label mapping message to the downstream node B, where the label mapping message carries the label information allocated by the upstream node A for the downstream node B. The upstream node A records the upstream node A carried in the label mapping message. Tag information assigned to the downstream node B;

 Step 603: The downstream node B determines whether to accept the label allocated by the upstream node A, for example, whether the label allocated by the upstream node A belongs to its own acceptable label range, or whether the label allocated by the upstream node A and other upstream The label assigned by the node is repeated; if the label assigned by the upstream node A is accepted, step 610 is performed; if the label assigned by the upstream node A is not accepted, step 604 is performed;

 Step 604: The downstream node B sends a Notify message to the upstream node A, where the Notify message carries a label set object, and the object carries the following label information:

 TYPE (type);

 Length (length);

 Action

 Acceptable label;

 Unacceptable label;

 Acceptable label range;

 Unacceptable range of labels;

 Step 605: The upstream node A receives the Notify message sent by the downstream node B, records the acceptable label range of the downstream node B, and reselects a new label that the downstream node B can accept according to the label range acceptable to the downstream node B. ;

 Step 606: The upstream node A determines, according to the recorded label information, whether the new label belongs to other downstream node label ranges except B; if the new label does not belong to other downstream node label ranges except B (ie, other downstream nodes) If the new label belongs to other downstream node label ranges other than B (ie, other downstream nodes can accept the new label), step 608 is performed;

Step 607: The upstream node A again assigns a label to the downstream node B, and step 606 is performed; Step 608: The tour node A sends a label mapping message to all the downstream nodes, where the label mapping message carries the new label information, and the upstream node A updates the label information allocated to the downstream node.

 Step 609: After receiving the label mapping message carrying the new label information, the downstream node B installs the new label to the forwarding layer; and the other downstream nodes except the downstream node B receive the label carrying the new label information. After the message is mapped, the forwarding layer label information is updated;

 Step 610: Enter a normal process of establishing a point-to-multipoint tunnel by using LDP.

 After the above process, the label range of the downstream node has changed. When the next upstream node assigns a label to the downstream node, the above process is repeated, and the label information of the downstream node recorded by the upstream node can be updated.

 FIG. 7 is a structural diagram of a point-to-multipoint tunnel system established by using RSVP-TE according to a preferred embodiment of the present invention. As shown in FIG. 7, the system of this embodiment includes upstream node devices (including A and B) and downstream node devices (including C, D, and E).

 The upstream node device is configured to allocate a label to the downstream node device, and re-allocate the label to the downstream node device according to the label information that is fed back by the downstream node device. The upstream node device in this embodiment may include :

 a label receiving unit, configured to receive label information fed back by the downstream node;

 a node allocating unit, configured to allocate a label to the downstream node for the first time, and re-allocate the label to the downstream node after the label receiving unit receives the label information fed back by the downstream node.

 a label recording unit, configured to record label information allocated to the downstream node device when the node allocating unit allocates a label to the downstream node device for the first time; when the node allocating unit is at least a second time When the downstream node device allocates a label, the label information allocated for the downstream node device is recorded to update the label information of the downstream node device recorded by the label recording unit before the label is allocated.

 And the downstream node device is configured to receive the label allocated by the upstream node device, and if the label allocated by the upstream node device is not accepted, feed back label information of the downstream node device to the upstream node device.

Specifically, the upstream node device A sends a PATH message to the downstream node devices C and D, where the PATH message carries the label L1 allocated by the upstream node device A to the downstream node devices C and D; and the upstream node device A records the upstream The tag information assigned by the node device A to the downstream node devices C and D. The acceptable label range of the downstream node device C is LI ~ L100, the acceptable label range of the downstream node device D is LI ~ L200; the downstream node devices C and D are judged to accept the label L1.

 When the downstream node device E is added, the upstream node device A assigns the label L1 to the downstream node device E; the downstream node device E determines that the label L1 does not belong to its own acceptable label range; the downstream node device E moves to the upstream node device A. The PATHERR message is sent, and the PATHERR message carries the acceptable label range of the downstream node device E is L50 ~ L100.

 The upstream node device A receives the PATHERR message sent by the downstream node device E, records the label range of the downstream node device E, and the upstream node device A re-grants the downstream node devices C, D, and E according to the acceptable label range of the downstream node device E. The label L50 is allocated; according to the label range of the downstream node devices C and D originally recorded, the label L50 belongs to the label range of the downstream node devices C and D (ie, the downstream node devices C and D can accept the label L50); the upstream node device A goes downstream The node devices C, D, and E send the PATH message carrying the new label L50; after receiving the PATH message carrying the new label L50, the downstream node device E installs the new label L50 to the forwarding layer; the downstream node devices C and D receive After carrying the PATH message of the new label L50, the forwarding layer label information is updated.

 When the upstream node device B is added, the upstream node device B allocates the label L50 to the downstream node devices (D, E, and records the label information assigned to the downstream node devices C, D, and E; the downstream node devices (, D, and E) After the judgment, the L50 overlaps with the label assigned by the upstream node device A, and is unacceptable; the downstream node device C sends a PATHERR message to the upstream node device B, which carries the label information of the downstream node device C: The label range acceptable to the downstream node device C It is L1 ~ L100, but it cannot be L50. The downstream node device D sends a PATHERR message to the upstream node device B, which carries the label information of the downstream node device D: The label range acceptable to the downstream node device D is L1 ~ L200, but cannot It is L50; the downstream node device E sends a PATHERR message to the upstream node device B, and the message carries the label information of the downstream node device E: The label range acceptable to the downstream node device E is L50 ~ L100, but cannot be L50.

The upstream node device B receives the PATHERR message sent by the downstream node devices C, D, and E, records the label range of the downstream node devices (, D, and E, and re-based the acceptable label range of the downstream node devices (, D, and E). The label L51 is selected; the upstream node device B sends the PATH message carrying the new label L51 to the downstream node device (, D and E, and updates the label information assigned to the downstream node devices C, D and E; the downstream node device C, After receiving the PATH message carrying the new label L51, D and E update the forwarding layer label information. When the next upstream node device allocates a label to the downstream node device, if the downstream node device cannot accept the label assigned by the upstream node device due to the change of the label range of the downstream node device or other reasons, the downstream node device will forward the label to the downstream node device. The PATHERR message is sent, and the label carries the label information of the downstream node device. In this way, the label information of the downstream node device recorded by the upstream node device can be updated.

 FIG. 8 is a structural diagram of a point-to-multipoint tunnel system established by using LDP according to a preferred embodiment of the present invention. As shown in Fig. 8, the system of this embodiment includes upstream node devices (including A and B) and downstream node devices (including C, D, and E).

 The upstream node device is configured to allocate a label to the downstream node device, and re-allocate the label to the downstream node device according to the label information that is fed back by the downstream node device. The upstream node device in this embodiment may include :

 a label receiving unit, configured to receive label information fed back by the downstream node;

 a node allocating unit, configured to allocate a label to the downstream node for the first time, and re-allocate the label to the downstream node after the label receiving unit receives the label information fed back by the downstream node.

 a label recording unit, configured to record label information allocated to the downstream node device when the node allocating unit allocates a label to the downstream node device for the first time; when the node allocating unit is at least a second time When the downstream node device allocates a label, the label information allocated for the downstream node device is recorded to update the label information of the downstream node device recorded by the label recording unit before the label is allocated.

 And the downstream node device is configured to receive the label allocated by the upstream node device, and if the label allocated by the upstream node device is not accepted, feed back label information of the downstream node device to the upstream node device.

 Specifically, the downstream node devices C and D send a label request message to the upstream node device A. After receiving the label request message, the upstream node device A sends a label mapping message to the downstream node devices C and D, where the label mapping message is sent. The tag L1 assigned by the upstream node device A to the downstream node devices C and D is carried; and the upstream node device A records the tag information allocated by the upstream node device A to the downstream node devices C and D. The label range of the downstream node device C is LI ~ L100, the label range of the downstream node device D is LI ~ L200, and the downstream node devices C and D are judged to accept the label L1.

When the downstream node device E is added, the downstream node device E sends a label request message to the upstream node device A. After receiving the label request message sent by the downstream node device E, the upstream node device A goes downstream. The node device E sends a label mapping message, and the label mapping message carries the label L1.

 The downstream node device E determines that the label L1 does not belong to its own acceptable label range; the downstream node device E sends a Notify message to the upstream node device A, and the Notify message carries the acceptable label range of the downstream node device E from L50 to L100.

 The upstream node device A receives the Notify message sent by the downstream node device E, records the label range of the downstream node device E, and the upstream node device A re-grants the downstream node devices C, D, and E according to the acceptable label range of the downstream node device E. The label L50 is allocated; according to the label range of the downstream node devices C and D originally recorded, the label L50 belongs to the label range of the downstream node devices C and D (ie, the downstream node devices C and D can accept the label L50); the upstream node device A goes downstream The node device (D, E, and E sends a label mapping message carrying the new label L50; after receiving the label mapping message carrying the new label L50, the downstream node device E installs the new label L50 to the forwarding layer; the downstream node devices C and D After receiving the label mapping message carrying the new label L50, the forwarding layer label information is updated.

 When the upstream node device B is added, the downstream node devices C, D, and E send a label request message to the upstream node device B; the upstream node device B assigns a label L50 to the downstream node devices C, D, and E, and records the allocation to the downstream node. Label information for devices C, D, and E.

 The downstream node devices C, D, and E are judged that the L50 is duplicated with the label assigned by the upstream node device A, and is unacceptable; the downstream node device C sends a Notify message to the upstream node device B, which carries the label information of the downstream node device C: downstream The label range acceptable to the node device C is LI ~ L100, but cannot be L50; the downstream node device D sends a Notify message to the upstream node device B, the message carrying the label information of the downstream node device D: the label acceptable to the downstream node device D The range is LI ~ L200, but not L50; The downstream node device E sends a Notify message to the upstream node device B, which carries the label information of the downstream node device E: The label range acceptable to the downstream node device E is L50 ~ L100, but Can't be L50.

 The upstream node device B receives the Notify message sent by the downstream node devices C, D, and E, records the label range of the downstream node devices C, D, and E, and reselects according to the acceptable label ranges of the downstream node devices (, D, and E). The label L51; the upstream node device B sends the label mapping message carrying the new label L51 to the downstream node devices C, D and E, and simultaneously updates the label information assigned to the downstream node devices C, D and E; the downstream node device C, After receiving the label mapping message carrying the new label L51, D and E update the forwarding layer label information.

When the next upstream node device assigns a label to the downstream node device, if it is due to the downstream node device The change of the label range or other reasons causes the downstream node device to fail to accept the label assigned by the upstream node device, and the downstream node device sends a Notify message to the downstream node device, where the message carries the label information of the downstream node device. In this way, the label information of the downstream node device recorded by the upstream node device can be updated.

 In the foregoing technical solution, a label negotiation mechanism is introduced between the upstream node and the downstream node to ensure that no more upstream nodes assign labels to the same downstream node, and the downstream node does not need to modify the current forwarding process, and can continue to The label is forwarded; the complexity of the hardware implementation is reduced, and the forwarding efficiency is improved; the label is allocated on demand, which effectively saves the label resource.

 A person skilled in the art can understand that all or part of the process of implementing the above embodiment method can be completed by a computer program to instruct related hardware, and the program can be stored in a computer readable storage medium. In execution, the flow of an embodiment of the methods as described above may be included. The storage medium may be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM).

 The above are only the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Claims

Rights request An upstream label allocation method for a point-to-multipoint tunnel, comprising: after an upstream node assigns a label to a downstream node, if the label information fed back by the downstream node is received, the upstream node according to the The tag information fed back by the downstream node re-assigns the label to the downstream node;  The downstream node feeds back label information to the upstream node because the label allocated by the upstream node cannot be accepted.  2. The method of claim 1 wherein:  If the upstream node allocates a label to the downstream node for the first time, the upstream node records label information allocated by the upstream node for the downstream node;  If the upstream node allocates a label to the downstream node at least a second time, the upstream node records a label allocated by the upstream node to the downstream node, to update the location recorded by the upstream node before the allocation label The label information of the downstream node.  3. The method of claim 1 wherein:  If the label assigned by the upstream node is accepted by the downstream node, the normal point-to-multipoint tunnel establishment procedure is entered.  4. The method of claim 1 wherein:  The point-to-multipoint tunnel is established by using a resource reservation protocol-traffic engineering or by using a label distribution protocol.  5. The method of claim 4, wherein:  In a point-to-multipoint tunnel established using a label distribution protocol,  Before the upstream node assigns a label to the downstream node, the method further includes:  The upstream node receives a request from the downstream node to request the upstream node to assign a label to the downstream node.  6. An upstream node device, comprising:  a label receiving unit, configured to receive label information fed back by the downstream node;  a node allocating unit, configured to allocate a label to the downstream node, and re-allocate the label to the downstream node after the label receiving unit receives the label information fed back by the downstream node. 7. The upstream node device of claim 6, further comprising: a label recording unit, configured to record label information allocated to the downstream node device when the node allocating unit allocates a label to the downstream node device for the first time; when the node allocating unit is at least a second time When the downstream node device allocates a label, the label information allocated for the downstream node device is recorded to update the label information of the downstream node device recorded by the label recording unit before the label is allocated.  The upstream node device of claim 6, further comprising:  And a request receiving unit, configured to receive, by the downstream node device, a request for the upstream node to allocate a label to the downstream node.  9. An upstream node label distribution system for a point-to-multipoint tunnel, characterized in that it comprises an upstream node device and a downstream node device:  The upstream node device is configured to allocate a label to the downstream node device, and re-allocate the label to the downstream node device according to the label information fed back by the downstream node device;  And the downstream node device is configured to receive the label allocated by the upstream node device, and if the label allocated by the upstream node device is not accepted, feed back label information of the downstream node device to the upstream node device.  An upstream label allocation method for a point-to-multipoint tunnel, comprising: when a downstream node receives a label allocated by an upstream node, if the label allocated by the upstream node cannot be accepted; The upstream node feeds back label information of the downstream node;  And causing the upstream node to re-allocate the downstream node with a label acceptable to the downstream node according to the label information fed back by the downstream node.