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3. LSP Tunnel related Message Formats
//LSP隧道相关消息格式
Five new objects are defined in this section:
Object name Applicable RSVP messages
--------------- ------------------------
LABEL_REQUEST Path
LABEL Resv
EXPLICIT_ROUTE Path
RECORD_ROUTE Path, Resv
SESSION_ATTRIBUTE Path
New C-Types are also assigned for the SESSION, SENDER_TEMPLATE, and
FILTER_SPEC, objects.
Detailed descriptions of the new objects are given in later sections.
All new objects are OPTIONAL with respect to RSVP. An implementation
can choose to support a subset of objects. However, the
LABEL_REQUEST and LABEL objects are mandatory with respect to this
specification.
//对以上新对象的描述，将在后续章节中给出。这些新对象对RSVP都是可选的。
//一个实现可以选择支持这些对象的子集。此外，LABEL_REQUEST和LABEL对象
//对本文档(或RSVP-TE)而言是必须支持的。
The LABEL and RECORD_ROUTE objects, are sender specific. In Resv
messages they MUST appear after the associated FILTER_SPEC and prior
to any subsequent FILTER_SPEC.
//LABEL和RRO对象，与sender有关。它们必须出现在相关的FILTER_SPEC对象后
//且在其他FILTER_SPEC对象之前，当然，是在RESV消息中。
The relative placement of EXPLICIT_ROUTE, LABEL_REQUEST, and
SESSION_ATTRIBUTE objects is simply a recommendation. The ordering
of these objects is not important, so an implementation MUST be
prepared to accept objects in any order.
//ERO，LABEL_REQUEST和SESSION_ATTRIBUTE的位置只是一个建议。这些对象的
//顺序不重要，因此一个实现必须准备好以任何顺序接收这些对象。
3.1. Path Message
The format of the Path message is as follows:
//PATH消息的格式如下：
::= [ ]
[ ]
[ ]
Awduche, et al. Standards Track [Page 15]
RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
[ ... ]
::=
[ ]
[ ]
3.2. Resv Message
The format of the Resv message is as follows:
::= [ ]
[ ] [ ]
[ ... ]
::=
|
::=
[ ]
|
::= [ ]
[ ]
::=
::=
|
::= [ ]
Note: LABEL and RECORD_ROUTE (if present), are bound to the
preceding FILTER_SPEC. No more than one LABEL and/or
RECORD_ROUTE may follow each FILTER_SPEC.
//注意：如果有LABEL和RRO对象，一定要在FILTER_SPEC之后，如果存在，
//每个FILTER_SPEC之后至多只有一个LABEL和RRO。
Awduche, et al. Standards Track [Page 16]
RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
4. LSP Tunnel related Objects
4.1. Label Object
Labels MAY be carried in Resv messages. For the FF and SE styles, a
label is associated with each sender. The label for a sender MUST
immediately follow the FILTER_SPEC for that sender in the Resv
message.
//RESV消息中可能携带标签。对于FF和SE方式，每个sender关联一个标签。与
//sender有关的标签必须紧跟在描述该sender的FILTER_SPEC之后，当然，此
//处说的是RESV消息。
The LABEL object has the following format:
LABEL class = 16, 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (top label) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The contents of a LABEL is a single label, encoded in 4 octets. Each
generic MPLS label is an unsigned integer in the range 0 through
1048575. Generic MPLS labels and FR labels are encoded right aligned
in 4 octets. ATM labels are encoded with the VPI right justified in
bits 0-15 and the VCI right justified in bits 16-31.
//LABEL对象的内容只是一个标签，由4个byte组成。
4.1.1. Handling Label Objects in Resv messages
In MPLS a node may support multiple label spaces, perhaps associating
a unique space with each incoming interface. For the purposes of the
following discussion, the term "same label" means the identical label
value drawn from the identical label space. Further, the following
applies only to unicast sessions.
//一个MPLS节点可能支持多重的标签空间，可能把每个入接口关联一个唯一的
//空间。一下讨论中，"相同标签"表示同一个标签空间内的同一标签值。另外，
//只应用于单播会话。
Labels received in Resv messages on different interfaces are always
considered to be different even if the label value is the same.
//不同接口接受的RESV消息，尽管他们可能标签值相同，但是通常认为是不同
//的标签。(每个接口有其独自的标签空间)
4.1.1.1. Downstream
The downstream node selects a label to represent the flow. If a
label range has been specified in the label request, the label MUST
be drawn from that range. If no label is available the node sends a
PathErr message with an error code of "routing problem" and an error
value of "label allocation failure".
//下游节点选择一个标签以描述该流量。如果在Label request中限定了标签
//范围(label request在PATH中)，标签必须在该范围内分配。如果无合适标签
//可用，该节点发送一个错误码为"routing problem"，错误值为"label
//allocation failure"的PATHERR消息。
If a node receives a Resv message that has assigned the same label
value to multiple senders, then that node MAY also assign a single
value to those same senders or to any subset of those senders. Note
//如果节点收到的RESV消息中，给多个sender分配了相同的标签，那么它可能
//给这些sender(或任意sender的子集)只分配一个标签。
Awduche, et al. Standards Track [Page 17]
RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
that if a node intends to police individual senders to a session, it
MUST assign unique labels to those senders.
//如果节点
In the case of ATM, one further condition applies. Some ATM nodes
are not capable of merging streams. These nodes MAY indicate this by
setting a bit in the label request to zero. The M-bit in the
LABEL_REQUEST object of C-Type 2, label request with ATM label range,
serves this purpose. The M-bit SHOULD be set by nodes which are
merge capable. If for any senders the M-bit is not set, the
downstream node MUST assign unique labels to those senders.
//如果是ATM，一个深层的问题需要考虑。某些ATM节点不能合并stream。这些
//节点可能(可以)设置label request中的一个bit为0以标识。C-Type为2的
//LABEL_REQUEST的M-bit，label request且附带ATM标签范围，服务于该用途(呕)
//那些没有设置M-bit的sender，下游节点必须分配唯一一个标签给这些sender。
Once a label is allocated, the node formats a new LABEL object. The
node then sends the new LABEL object as part of the Resv message to
the previous hop. The node SHOULD be prepared to forward packets
carrying the assigned label prior to sending the Resv message. The
LABEL object SHOULD be kept in the Reservation State Block. It is
then used in the next Resv refresh event for formatting the Resv
message.
//一旦分配好标签，节点构造一个新的LABEL对象。该节点把该LABEL对象作为
//RESV消息的一部分发送给PHOP(上一跳)。该节点应该准备好转发那些打了(发
//往上游的RESV中的)标签的数据包。该LABEL对象应该保存在RSB中。用于下次
//RESV刷新时，解析该RESV消息。
A node is expected to send a Resv message before its refresh timers
expire if the contents of the LABEL object change.
//如果LABEL对象改变，节点应该在刷新定时器到期前发送RESV消息。
4.1.1.2. Upstream
A node uses the label carried in the LABEL object as the outgoing
label associated with the sender. The router allocates a new label
and binds it to the incoming interface of this session/sender. This
is the same interface that the router uses to forward Resv messages
to the previous hops.
//节点使用收到的LABEL对象中的标签作为与sender关联的出标签。该节点为
//该会话/sender分配一个新标签并且与入接口绑定。该接口与发送RESV消息
//的接口相同。
Several circumstance can lead to an unacceptable label.
//某些情况可能导致一个不可接受的标签。
1. the node is a merge incapable ATM switch but the downstream
node has assigned the same label to two senders
//1.
2. The implicit null label was assigned, but the node is not
capable of doing a penultimate pop for the associated L3PID
3. The assigned label is outside the requested label range
//3.标签在请求的标签范围之外。
In any of these events the node send a ResvErr message with an error
code of "routing problem" and an error value of "unacceptable label
value".
//以上任何情况发生，本节点发送一个错误码为"routing problem错误值为
//"unacceptable label value"的RESVERR消息。
Awduche, et al. Standards Track [Page 18]
RFC 3209 Extensions to RSVP for LSP Tunnels December 2001
4.1.2. Non-support of the Label Object
Under normal circumstances, a node should never receive a LABEL
object in a Resv message unless it had included a LABEL_REQUEST
object in the corresponding Path message. However, an RSVP router
that does not recognize the LABEL object sends a ResvErr with the
error code "Unknown object class" toward the receiver. This causes
the reservation to fail.
//通常情况，如果节点在PATH中如果没有携带LABEL_REQUEST对象，则收到的
//RESV消息中不会携带LABEL对象。不支持LABEL对象RSVP节点，发送一个错误
//码为"Unknown object class"的RESVERR给末节点。这将导致预留失败。
本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u/411/showart_389931.html |
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发表于 2007-09-26 00:15