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2007-11-03 00:27:15
4.2. Label Request Object
The Label Request Class is 19. Currently there are three possible
C_Types. Type 1 is a Label Request without label range. Type 2 is a
label request with an ATM label range. Type 3 is a label request
with a Frame Relay label range. The LABEL_REQUEST object formats are
shown below.
//Label Request类为19.当前有3中C-Type。1为没有标签范围的Label Request。
//2为有ATM标签范围的Label Request。3为有帧中继标签范围的Label Request。
4.2.1. Label Request without Label Range
Class = 19, C_Type = 1
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | L3PID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
This field is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt.
//该字段保留。必须设置为0，接收方必须忽略该位。
L3PID
an identifier of the layer 3 protocol using this path.
Standard Ethertype values are used.
//确定一个该LSP使用的3层协议号。填写标准以太网值(呕)。
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RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
4.2.2. Label Request with ATM Label Range
Class = 19, C_Type = 2
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | L3PID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M| Res | Minimum VPI | Minimum VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res | Maximum VPI | Maximum VCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved (Res)
This field is reserved. It MUST be set to zero on transmission
and MUST be ignored on receipt.
L3PID
an identifier of the layer 3 protocol using this path.
Standard Ethertype values are used.
M
Setting this bit to one indicates that the node is capable of
merging in the data plane
//设置为1，表示本节点可以合并数据流。
Minimum VPI (12 bits)
This 12 bit field specifies the lower bound of a block of
Virtual Path Identifiers that is supported on the originating
switch. If the VPI is less than 12-bits it MUST be right
justified in this field and preceding bits MUST be set to zero.
//VPI的下限，如果少于12bit，左边填充0.
Minimum VCI (16 bits)
This 16 bit field specifies the lower bound of a block of
Virtual Connection Identifiers that is supported on the
originating switch. If the VCI is less than 16-bits it MUST be
right justified in this field and preceding bits MUST be set to
zero.
//VCI的下限，如果少于16bit，左边填充0.
Awduche, et al. Standards Track [Page 20]
RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
Maximum VPI (12 bits)
This 12 bit field specifies the upper bound of a block of
Virtual Path Identifiers that is supported on the originating
switch. If the VPI is less than 12-bits it MUST be right
justified in this field and preceding bits MUST be set to zero.
//VPI的上限，如果少于12bit，左边填充0.
Maximum VCI (16 bits)
This 16 bit field specifies the upper bound of a block of
Virtual Connection Identifiers that is supported on the
originating switch. If the VCI is less than 16-bits it MUST be
right justified in this field and preceding bits MUST be set to
zero.
//VCI的上限，如果少于16bit，左边填充0.
4.2.3. Label Request with Frame Relay Label Range
Class = 19, C_Type = 3
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | L3PID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |DLI| Minimum DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Maximum DLCI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Reserved
This field is reserved. It MUST be set to zero on transmission
and ignored on receipt.
L3PID
an identifier of the layer 3 protocol using this path.
Standard Ethertype values are used.
DLI
DLCI Length Indicator. The number of bits in the DLCI. The
following values are supported:
//DLCI长度标识。DLCI的bit数。支持一下值：
Len DLCI bits
0 10
2 23
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RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
Minimum DLCI
This 23-bit field specifies the lower bound of a block of Data
Link Connection Identifiers (DLCIs) that is supported on the
originating switch. The DLCI MUST be right justified in this
field and unused bits MUST be set to 0.
//DLCI的下限，如果少于23bit，左边填充0.
Maximum DLCI
This 23-bit field specifies the upper bound of a block of Data
Link Connection Identifiers (DLCIs) that is supported on the
originating switch. The DLCI MUST be right justified in this
field and unused bits MUST be set to 0.
//DLCI的上限，如果少于23bit，左边填充0.
4.2.4. Handling of LABEL_REQUEST
To establish an LSP tunnel the sender creates a Path message with a
LABEL_REQUEST object. The LABEL_REQUEST object indicates that a
label binding for this path is requested and provides an indication
of the network layer protocol that is to be carried over this path.
This permits non-IP network layer protocols to be sent down an LSP.
This information can also be useful in actual label allocation,
because some reserved labels are protocol specific, see [5].
//首节点发送一个携带LABEL_REQUEST对象的PATH以创建LSP隧道。LABEL_REQUEST
//对象表明需要为本LSP绑定标签，且指出本LSP传送的业务的L3协议号。这
//可以允许LSP传送协非IP业务。该信息在标签分配时也可以使用，因为某些预留
//标签具有协议特殊性。
The LABEL_REQUEST SHOULD be stored in the Path State Block, so that
Path refresh messages will also contain the LABEL_REQUEST object.
When the Path message reaches the receiver, the presence of the
LABEL_REQUEST object triggers the receiver to allocate a label and to
place the label in the LABEL object for the corresponding Resv
message. If a label range was specified, the label MUST be allocated
from that range. A receiver that accepts a LABEL_REQUEST object MUST
include a LABEL object in Resv messages pertaining to that Path
message. If a LABEL_REQUEST object was not present in the Path
message, a node MUST NOT include a LABEL object in a Resv message for
that Path message's session and PHOP.
//LABEL_REQUEST应该存储在PSB中，因此PATH刷新消息也应包含LABEL_REQUEST，
//当PATH消息抵达目的节点，因LABEL_REQUEST的存在触发末节点分配一个标签，
//且将其填写在相关的RESV消息的LABEL对象中。如果指定了标签范围(ATM/FR)，
//标签必须在该范围之内分配。末节点收到LABEL_REQUEST对象的PATH消息，必
//须在回应的RESV消息中包含一个LABEL对象。否则，对于该会话,RESV消息不能
//包含LABEL对象。
A node that sends a LABEL_REQUEST object MUST be ready to accept and
correctly process a LABEL object in the corresponding Resv messages.
//节点如果发送LABEL_REQUEST对象，必须准备好接收且正确的处理一个带LABEL
//对象的RESV消息。
A node that recognizes a LABEL_REQUEST object, but that is unable to
support it (possibly because of a failure to allocate labels) SHOULD
send a PathErr with the error code "Routing problem" and the error
value "MPLS label allocation failure." This includes the case where
a label range has been specified and a label cannot be allocated from
that range.
//节点能够识别LABEL_REQUEST对象，但是不能处理好它(可能因分配标签失败)，
//应该发送一个错误码为"Routing problem"错误值为"MPLS label allocation
//failure"的PATHERR。这包括设定标签范围，但是在范围内分配标签失败。
Awduche, et al. Standards Track [Page 22]
RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
A node which receives and forwards a Path message each with a
LABEL_REQUEST object, MUST copy the L3PID from the received
LABEL_REQUEST object to the forwarded LABEL_REQUEST object.
//节点收到和转发的PATH消息都包含LABEL_REQUEST，必须把收到的
//LABEL_REQUEST对象的L3PID拷贝到转发的LABEL_REQUEST对象中。
If the receiver cannot support the protocol L3PID, it SHOULD send a
PathErr with the error code "Routing problem" and the error value
"Unsupported L3PID." This causes the RSVP session to fail.
//如果末节点不支持该L3PID协议，它应该发送一个错误码为"Routing problem"
//错误值为"Unsupported L3PID"的PATHERR，这将导致会话建立失败。
