rfc1190.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

         allocated depends on the details of the networks involved, and
         is not specified here.

         If an ST agent must send data across a network to a single
         next-hop ST agent, then only the point-to-point bandwidth needs
         to be reserved.  If the agent must send data to multiple next-
         hop agents across one network and network layer multicasting is
         not available, then bandwidth must be reserved for all of them.
         This will allow the ST agent to



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RFC 1190                Internet Stream Protocol            October 1990


         use replication to send a copy of the data packets to each
         next-hop agent.

         If multicast is supported, its use will decrease the effort
         that the ST agent must expend when forwarding packets and also
         reduces the bandwidth required since one copy can be received
         by all next-hop agents.  However, the setup phase is more
         complicated.  A network multicast address must be allocated
         that contains all those next-hop agents, the sender must have
         access to that address, the next-hop agents must be informed of
         the address so they can join the multicast group identified by
         it (see Section 4.2.2.7 (page 86)), and a common HID must be
         negotiated.

         The network should consider the bandwidth and multicast
         requirements to determine the amount of packet switch
         processing bandwidth and buffer space to reserve for the
         stream.  In addition, the membership of a stream in a Group may
         affect the resources that have to be allocated;  see Section
         3.7.3 (page 56).

         Few networks in the Internet currently offer resource
         reservation, and none that we know of offer reservation of all
         the resources specified here.  Only the Terrestrial Wideband
         Network (TWBNet) [7] and the Atlantic Satellite Network
         (SATNET) [9] offer(ed) bandwidth reservation.  Multicasting is
         more widely supported.  No network provides for the reservation
         of packet switch processing bandwidth or buffer space.  We hope
         that future networks will be designed to better support
         protocols like ST.

         Effects similar to reservation of the necessary resources may
         be obtained even when the network cannot provide direct support
         for the reservation.  Certainly if total reservations are a
         small fraction of the overall resources, such as packet switch
         processing bandwidth, buffer space, or network bandwidth, then
         the desired performance can be honored if the degree of
         confidence is consistent with the requirements as stated in the
         FlowSpec.  Other solutions can be designed for specific
         networks.


      3.1.4.        Sending CONNECT Messages

         A VLId and a proposed HID must be selected for each next-hop
         agent.  The control packets for the next-hop must carry the
         VLId in the SVLId field.  The data packets transmitted in the
         stream to the next-hop must carry the HID in the ST Header.

         The ST agent sends a CONNECT message to each of the ST agents
         identified by the routing function.  Each CONNECT message
         contains the VLId, the proposed HID (the HID Field option bit


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RFC 1190                Internet Stream Protocol            October 1990


         must be set, see Section 3.6.1 (page 44)), an updated FlowSpec,
         and a TargetList.  In general, the HID, FlowSpec, and
         TargetList will depend on both the next-hop and the intervening
         network.  Each TargetList is a subset of the received (or
         original) TargetList, identifying the targets that are to be
         reached through the next-hop to which the CONNECT message is
         being sent.  Note that a CONNECT message to a single next-hop
         might have to be fragmented into multiple CONNECTs if the
         single CONNECT is too large for the intervening network's MTU;
         fragmentation is performed by further dividing the TargetList.

         If multiple next-hops are to be reached through a network that
         supports network level multicast, a different CONNECT message
         must nevertheless be sent to each next-hop since each will have
         a different TargetList;  see Section 4.2.3.5 (page 105).
         However, since an identical copy of each ensuing data packet
         will reach each member of the multicast group, all the CONNECT
         messages must propose the same HID.  See Section 3.7.4 (page
         58) for a detailed discussion on HID selection.

         In the example of Figure 2, the routing function might return
         that B is reachable via Agent 1 and C and D are reachable via
         Agent 2.  Thus A would create two CONNECT messages, one each
         for Agents 1 and 2, as illustrated in Figure 5.  Assuming that
         the proposed HIDs are available in the receiving agents, they
         would each send a responding HID-APPROVE back to Agent A.


         Application  Agent A                    Agent 1    Agent 2

    1.1. (open B,C,D)
               V
    1.2.       +-> (routing to B,C,D)
                         V
    1.3.                 +->(reserve resources from A to Agent 1)
                         |  V
    1.4.                 |  +-> CONNECT B --------->>
                         |      <RVLId=0><SVLId=4>
                         |      <Ref=10><HID=1200>
                         V
    1.5.                 +->(reserve resources from A to Agent 2)
                            V
    1.6.                    +-> CONNECT C,D ------------------>>
                                <RVLId=0><SVLId=5>
                                <Ref=15><HID=2400>

               Figure 5.  Origin Sending CONNECT Message







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RFC 1190                Internet Stream Protocol            October 1990


      3.1.5.        CONNECT Processing by an Intermediate Agent

         An ST agent receiving a CONNECT message should, assuming no
         errors, quickly select a VLId and respond to the previous-hop
         with either an ACK, a HID-REJECT, or a HID-APPROVE message, as
         is appropriate.  This message must identify the CONNECT to
         which it corresponds by including the CONNECT's Reference
         number in its Reference field.  Note that the VLId that this
         agent selects is placed in the SVLId of the response, and the
         previous-hop's VLId (which is contained in the SVLId of the
         CONNECT) is copied into the RVLId of the response.  If the
         agent is not a target, it must then invoke the routing
         function, reserve resources, and send a CONNECT message(s) to
         its next-hop(s), as described in Sections 3.1.2-4 (pages 19-
         20).


       Agent A                   Agent 1                      Agent B

    [1.4] >>-> CONNECT B -------->+--+
               <RVLId=0><SVLId=4> |  V
2.1.           <Ref=10><HID=1200> |  (routing to B)
                                  |  V
2.2.                              V  +->(reserve resources from 1 to B)
2.3.       +<- HID-APPROVE <------+     V
2.4.           <RVLId=4><SVLId=14>      +-> CONNECT B ---------->>
               <Ref=10><HID=1200>           <RVLId=0><SVLId=15>
                                            <Ref=110><HID=3600>

       Agent A                   Agent 2                      Agent C

    [1.6] >>-> CONNECT C,D ------>+-+
               <RVLId=0><SVLId=5> | V
2.5.           <Ref=15><HID=2400> | (routing to C,D)
                                  | V
2.6.                              V +-->(reserve resources from 2 to C)
2.7.       +<- HID-APPROVE <------+ |   V
2.8.           <RVLId=5><SVLId=23>  |   +-> CONNECT C ---------->>
               <Ref=15><HID=2400>   |       <RVLId=0><SVLId=25>
                                    |       <Ref=210><HID=4800>
                                    |
                                    |                         Agent D
                                    V
2.9.                                +->(reserve resources from 2 to D)
                                        V
2.10.                                   +-> CONNECT D ---------->>
                                            <RVLId=0><SVLId=26>
                                            <Ref=215><HID=4800>

         Figure 6.  CONNECT Processing by an Intermediate Agent




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RFC 1190                Internet Stream Protocol            October 1990


         The resources listed as Desired in a received FlowSpec may not
         correspond to those actually reserved in either the ST agent
         itself or in the network(s) used to reach the next-hop
         agent(s).  As long as the reserved resources are sufficient to
         meet the specified Limits, the copy of the FlowSpec sent to a
         next-hop must have the Desired resources updated to reflect the
         resources that were actually obtained.  For example, the
         Desired bandwidth might be reduced because the network to the
         next-hop could not provide all of the desired bandwidth.  Also,
         the delay and delay variance are appropriately increased, and
         the link MTU may require that the DesPDUBytes field be reduced.
         (The minimum requirements that the origin had entered into the
         FlowSpec Limits fields cannot be altered by the intermediate or
         target agents.)


      3.1.6.        Setup at the Targets

         An ST agent that is the target of a CONNECT, whether from an
         intermediate ST agent, or directly from the origin host ST
         agent, must respond first (assuming no errors) with either a
         HID-REJECT or HID-APPROVE.  After inquiring from the specified
         application process whether or not it is willing to accept the
         connection, the agent must also respond with either an ACCEPT
         or a REFUSE.

         In particular, the application must be presented with
         parameters from the CONNECT, such as the Name, FlowSpec,
         Options, and Group, to be used as a basis for its decision.
         The application is identified by a combination of the NextPcol
         field and the SAP field in the (usually) single remaining
         Target of the TargetList.  The contents of the SAP field may
         specify the "port" or other local identifier for use by the
         protocol layer above the host ST layer.  Subsequently received
         data packets will carry a short hand identifier (the HID) that
         can be mapped into this information and be used for their
         delivery.

         The responses to the CONNECT message are sent to the previous-
         hop from which the CONNECT was received.  An ACCEPT contains
         the Name of the stream and the updated FlowSpec.  Note that the
         application might have reduced the desired level of service in
         the received FlowSpec before accepting it.  The target must not
         send the ACCEPT until HID negotiation has been successfully
         completed.

         Since the ACCEPT or REFUSE message must be acknowledged by the
         previous-hop, it is assigned a new Reference number that will
         be returned in the ACK.  The CONNECT to which the ACCEPT or
         REFUSE is a reply is identified by placing the CONNECT's
         Reference number in the LnkReference field of the ACCEPT or
         REFUSE.


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RFC 1190                Internet Stream Protocol            October 1990


           Agent 1                    Agent B       Application B
 3.1.                                             (proc B listening)
         [2.4] >>-> CONNECT B ---------->+------------------+
                    <RVLId=0><SVLId=15>  |                  |
 3.2.               <Ref=110><HID=3600>  V          (proc B accepts)
 3.3.           +<- HID-APPROVE <--------+                  |
                    <RVLId=15><SVLId=44>                    |
                    <Ref=110><HID=3600>                     V
 3.4.                       (wait until HID negotiated) <---+
                                         V
 3.5.       <<--+<- ACCEPT B <-----------+
                    <RVLId=15><SVLId=44>
                    <Ref=410><LnkRef=110>

           Agent 2                    Agent C       Application C
 3.6.                                             (proc C listening)
         [2.8] >>-> CONNECT C ---------->+------------------+
                    <RVLId=0><SVLId=25>  |                  |
 3.7.               <Ref=210><HID=4800>  V          (proc C accepts)
 3.8.           +<- HID-APPROVE <--------+