rfc1190.txt
来自「RFC 的详细文档！」· 文本 代码 · 共 1,353 行 · 第 1/5 页
TXT
1,353 行
resources if it wishes to do so and if the possibility is still
available. Third, if the target accepts the connection, it
returns the updated FlowSpec to the origin, so that the origin can
decide if it still wishes to participate in the stream with the
characteristics that were actually obtained.
CIP Working Group [Page 14]
RFC 1190 Internet Stream Protocol October 1990
When the data transmitted by stream users is generated at varying
rates, including bursts of varying rate and duration, there is an
opportunity to provide service to more subscribers by providing
guaranteed service for the average data rate of each stream, and
reserving additional network capacity, shared among all streams,
to service the bursts. This concept has been recognized by analog
voice network providers leading to the principle of time assigned
speech interpolation (TASI) in which only the talkspurts of a
speech conversation are transmitted, and, during silence periods,
the circuit can be used to send the talkspurts of other
conversations. The FlowSpec is intended to assist algorithms that
perform similar kinds of functions. We do not propose such
algorithms here, but rather expect that this will be an area for
experimentation. To allow for experiments, and a range of ways
that application traffic might be characterized, a "DutyFactor" is
included in the FlowSpec and we expect that a "burst descriptor"
will also be needed.
The FlowSpec will need to be revised as experience is gained with
connections involving numerous participants using multiple media
across heterogeneous internetworks. We feel a change of the
FlowSpec does not necessarily require a new version of ST, it only
requires the FlowSpec version number be updated and software to
manage the new FlowSpec to be distributed. We further suggest
that if the change to the FlowSpec involves additional information
for improved operation, such as a burst descriptor, that it be
added to the end of the FlowSpec and that the current parameters
be maintained so that obsolete software can be used to process the
current parameters with minimum modifications.
CIP Working Group [Page 15]
RFC 1190 Internet Stream Protocol October 1990
**** ****
* * ST Agent 1 * * +---+
* *------- o ---------* *-------+ B |
* * * * +---+
* * ****
+---+ * * |
| | * * |
| A +---------* * o ST Agent 3
| | * * |
+---+ * * |
* * ***
* * * * +---+
* * ST Agent 2 * *-------+ C |
* *------- o --------* * +---+
* * * *
**** * *
* *
+---+ * * +---+
| E +--------* *-------+ D |
+---+ * * +---+
***
Figure 2. Topology Used in Protocol Exchange Diagrams
**** ST Agent 1 ****
* +--+---14--- o -----15--+----+--44---+---+
* | +-+--11--- -----16--+-+ * | B |
* | | * * |+-+--45---+---+
* | | * *++*
+---+ * | | * 34 ||32
| +----4----+--+ | * ||
| A +----6----+----+ * o ST Agent 3
| +----5----+---+ * |
+---+ * | * | 33
* | * ST *+*
* | * Agent * | *
* | * 2 -----24-+--+ * +---+
* +--+--23--- o -----25-+-----+--54---+ C |
* * -----26-+---+ * +---+
**** -----27-+-+ | *
* | | *
+---+ * | | * +---+
| E +---74---+-+ +-+--64---+ D |
+---+ * * +---+
***
Figure 3. Virtual Link Identifiers for SCMP Messages
CIP Working Group [Page 16]
RFC 1190 Internet Stream Protocol October 1990
3. ST Control Message Protocol Functional Description
This section contains a functional description of the ST Control
Message Protocol (SCMP); Section 4 (page 75) specifies the formats of
the control message PDUs. We begin with a description of stream
setup. Mechanisms used to deal with the exceptional cases are then
presented. Complications due to options that an application or a ST
agent may select are then detailed. Once a stream has been
established, the data transfer phase is entered; it is described.
Once the data transfer phase has been completed, the stream must be
torn down and resources released; the control messages used to
perform this function are presented. The resources or participants
of a stream may be changed during the lifetime of the stream; the
procedures to make changes are described. Finally, the section
concludes with a description of some ancillary functions, such as
failure detection and recovery, HID negotiation, routing, security,
etc.
To help clarify the SCMP exchanges used to setup and maintain ST
streams, we have included a series of figures in this section. The
protocol interactions in the figures assume the topology shown in
Figure 2. The figures, taken together,
o Create a stream from an application at A to three peers at B,
C and D,
o Add a peer at E,
o Disconnect peers B and C, and
o D drops out of the stream.
Other figures illustrate exchanges related to failure recovery.
In order to make the dispatch function within SCMP more uniform and
efficient, each end of a hop is assigned, by the agent at that end, a
Virtual Link Identifier that uniquely (within that agent) identifies
the hop and associates it with a particular stream's state
machine(s). The identifier at the end of a link that is sending a
message is called the Sender Virtual Link Identifier (SVLId); that
at the receiving end is called the Receiver Virtual Link Identifier
(RVLId). Whenever one agent sends a control message for the other to
receive, the sender will place the receiver's identifier into the
RVLId field of the message and its own identifier in the SVLId field.
When a reply to the message is sent, the values in SVLId and RVLId
fields will be reversed, reflecting the fact the sender and receiver
roles are reversed. VLIds with values zero through three are
received and should not be assigned in response to CONNECT messages.
Figure 3 shows the hops that will be used in the examples and
summarizes the VLIds that will be assigned to them.
CIP Working Group [Page 17]
RFC 1190 Internet Stream Protocol October 1990
Similarly, Figure 4 summarizes the HIDs that will eventually be
negotiated as the stream is created.
**** ST Agent 1 ****
* +>+--1200-> o -------->+--->+-3600->+---+
* ^ * * * | B |
* | * * +->+-6000->+---+
* | * *+**
+---+ * | * ^
| +-------->+-->+ * |
| A | * * o St Agent 3
| +-------->+-->+ * ^
+---+ * | * | 4801
* | * *+*
* V * ST Agent 2 * ^ * +---+
* +>+--2400-> o ------->+->+->+-4800->+ C |
**** * | * 4801 +---+
* | *
+---+ * V * +---+
| E +<-4800--+<-+->+-4800->+ D |
+---+ * * 4801 +---+
***
Figure 4. HIDs Assigned for ST User Packets
Some of the diagrams that follow form a progression. For example,
the steps required initially to establish a connection are spread
across five figures. Within a progression, the actions on the first
diagram are numbered 1.1, 1.2, etc.; within the second diagram they
are numbered 2.1, 2.2, etc. Points where control leaves one diagram
to enter another are identified with a continuation arrow "-->>", and
are continued with "[a.b] >>-->" in the other diagram. The number in
brackets shows the label where control left the earlier diagram. The
reception of simple acknowledgments, e.g., ACKs, in one figure from
another is omitted for clarity.
3.1. Stream Setup
This section presents a description of stream setup assuming that
everything succeeds -- HIDs are approved, any required resources
are available, and the routing is correct.
3.1.1. Initial Setup at the Origin
As described in Section 2.3 (page 11), the application has
collected the information necessary to determine the
CIP Working Group [Page 18]
RFC 1190 Internet Stream Protocol October 1990
participants in the communication before passing it to the host
ST agent at the origin. The host ST agent will take this
information, allocate a Name for the stream (see Section
4.2.2.8 (page 87)), and create a stream.
3.1.2. Invoking the Routing Function
An ST agent that is setting up a stream invokes a routing
function to find a path to reach each of the targets specified
in the TargetList. This is similar to the routing decision in
IP. However, in this case the route is to a multitude of
targets rather than to a single destination.
The set of next-hops that an ST agent would select is not
necessarily the same as the set of next hops that IP would
select given a number of independent IP datagrams to the same
destinations. The routing algorithm may attempt to optimize
⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?