rfc2353.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

*------------------------------------------------------------------*
|CS              DLC             LDLC           DMUX            UDP|
*------------------------------------------------------------------*
 .                .                              .               .
 .CONNECT_OUT(RQ) .  create                      .               .
 o--------------->o-------------->o              .               .
 .                |        new LDLC              .               .
 .                o----------------------------->o               .
 CONNECT_OUT(+RSP)|               .              .               .
 o<---------------*               .              .               .
 |               XID              .           XID(CMD)           . XID
 *------------------------------->o----------------------------->o----->

               Figure 3. Regular TG Activation (outgoing)

   In Figure 3 upon receiving START_LS(RQ) from NOF, CS starts the link
   activation process by sending CONNECT_OUT(RQ) to the DLC manager.
   The DLC manager creates an instance of LDLC for the link, informs the
   link demultiplexor, and sends CONNECT_OUT(+RSP) to CS.  Then, CS
   starts the activation XID exchange.

*------------------------------------------------------------------*
|CS              DLC             LDLC           DMUX            UDP|
*------------------------------------------------------------------*
 .                .                              .               .
 . CONNECT_IN(RQ) .          XID(CMD)            .     XID       . XID
 o<---------------o<-----------------------------o<--------------o<-----
 | CONNECT_IN(RSP).    create                    .               .
 *--------------->o-------------->o              .               .
 .                |          new LDLC            .               .
 .                o----------------------------->o               .
 .                |  XID(CMD)     .              .               .
 .                *-------------->o              .               .
 .               XID              |              .               .
 o<-------------------------------*              .               .
 |               XID              .            XID(RSP)          . XID
 *------------------------------->o----------------------------->o----->

               Figure 4. Regular TG Activation (incoming)

   In Figure 4, when an XID is received for a new link, it is passed to
   the DLC manager.  The DLC manager sends CONNECT_IN(RQ) to notify CS
   of the incoming link activation, and CS sends CONNECT_IN(+RSP)
   accepting the link activation.  The DLC manager then creates a new
   instance of LDLC, informs the link demultiplexor, and forwards the
   XID to to CS via LDLC.  CS then responds by sending an XID to the
   adjacent node.




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RFC 2353                APPN/HPR in IP Networks                 May 1998


   The two following figures show normal TG deactivation (outgoing and
   incoming).

*------------------------------------------------------------------*
|CS              DLC             LDLC           DMUX            UDP|
*------------------------------------------------------------------*
 .                .               .              .               .
 .             DEACT              .            DISC              . DISC
 o------------------------------->o----------------------------->o----->
 .             DEACT              .       DM     .       DM      . DM
 o<-------------------------------o<-------------o<--------------o<-----
 | DISCONNECT(RQ) .    destroy    .              .               .
 *--------------->o-------------->o              .               .
  DISCONNECT(RSP) |                              .               .
 o<---------------*                              .               .

              Figure 5. Regular TG Deactivation (outgoing)

   In Figure 5 upon receiving STOP_LS(RQ) from NOF, CS sends DEACT to
   notify the partner node that the HPR link is being deactivated.  When
   the response is received, CS sends DISCONNECT(RQ) to the DLC manager,
   and the DLC manager deactivates the instance of LDLC.  Upon receiving
   DISCONNECT(RSP), CS sends STOP_LS(RSP) to NOF.

*------------------------------------------------------------------*
|CS              DLC             LDLC           DMUX            UDP|
*------------------------------------------------------------------*
 .                .               .              .               .
 .             DEACT              .      DISC    .      DISC     . DISC
 o<-------------------------------o<-------------o<--------------o<-----
 |                .               |             DM               . DM
 |                .               *----------------------------->o----->
 | DISCONNECT(RQ) .    destroy    .              .               .
 *--------------->o-------------->o              .               .
 .DISCONNECT(RSP) |                              .               .
 o<---------------*                              .               .

              Figure 6. Regular TG Deactivation (incoming)

   In Figure 6, when an adjacent node deactivates a TG, the local node
   receives a DISC.  CS sends STOP_LS(IND) to NOF.  Because IP is
   connectionless, the DLC manager is not aware that the link has been
   deactivated.  For that reason, CS also needs to send DISCONNECT(RQ)
   to the DLC manager; the DLC manager deactivates the instance of LDLC.







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RFC 2353                APPN/HPR in IP Networks                 May 1998


2.5.1.1  Limited Resources and Auto-Activation

   To reduce tariff charges, the APPN architecture supports the
   definition of switched links as limited resources.  A limited-
   resource link is deactivated when there are no sessions traversing
   the link.  Intermediate HPR nodes are not aware of sessions between
   logical units (referred to as LU-LU sessions) carried in crossing RTP
   connections; in HPR nodes, limited-resource TGs are deactivated when
   no traffic is detected for some period of time.  Furthermore, APPN
   links may be defined as auto-activatable.  Auto-activatable links are
   activated when a new session has been routed across the link.

   An HPR node may have access to an IP network via a switched access
   link.  In such environments, it may be advisable for customers to
   define regular HPR/IP links as limited resources and as being auto-
   activatable.

2.5.2  IP Connection Networks

   Connection network support for IP networks (option set 2010), is
   described in this section.

   APPN architecture defines single link TGs across the point-to-point
   lines connecting APPN nodes.  The natural extension of this model
   would be to define a TG between each pair of nodes connected to a
   shared access transport facility (SATF) such as a LAN or IP network.
   However, the high cost of the system definition of such a mesh of TGs
   is prohibitive for a network of more than a few nodes.  For that
   reason, the APPN connection network model was devised to reduce the
   system definition required to establish TGs between APPN nodes.

   Other TGs may be defined through the SATF which are not part of the
   connection network.  Such TGs (referred to as regular TGs in this
   document) are required for sessions between control points (referred
   to as CP-CP sessions) but may also be used for LU-LU sessions.

   In the connection network model, a virtual routing node (VRN) is
   defined to represent the SATF.  Each node attached to the SATF
   defines a single TG to the VRN rather than TGs to all other attached
   nodes.

   Topology and routing services (TRS) specifies that a session is to be
   routed between two nodes across a connection network by including the
   connection network TGs between each of those nodes and the VRN in the
   Route Selection control vector (RSCV).  When a network node has a TG
   to a VRN, the network topology information associated with that TG
   includes DLC signaling information required to establish connectivity
   to that node across the SATF.  For an end node, the DLC signaling



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RFC 2353                APPN/HPR in IP Networks                 May 1998


   information is returned as part of the normal directory services (DS)
   process.  TRS includes the DLC signaling information for TGs across
   connection networks in RSCVs.

   CS creates a dynamic link station when the next hop in the RSCV of an
   ACTIVATE_ROUTE signal received from session services (SS) is a
   connection network TG or when an adjacent node initiates link
   activation upon receiving such an ACTIVATE_ROUTE signal.  Dynamic
   link stations are normally treated as limited resources, which means
   they are deactivated when no sessions are using them.  CP-CP sessions
   are not supported on connections using dynamic link stations because
   CP-CP sessions normally need to be kept up continuously.

   Establishment of a link across a connection network normally requires
   the use of CP-CP sessions to determine the destination IP address.
   Because CP-CP sessions must flow across regular TGs, the definition
   of a connection network does not eliminate the need to define regular
   TGs as well.

   Normally, one connection network is defined on a LAN (i.e., one VRN
   is defined.)  For an environment with several interconnected campus
   IP networks, a single wide-area connection network can be defined; in
   addition, separate connection networks can be defined between the
   nodes connected to each campus IP network.

2.5.2.1  Establishing IP Connection Networks

   Once the port is defined, a connection network can be defined on the
   port.  In order to support multiple TGs from a port to a VRN, the
   connection network is defined by the following process:

   1.  A connection network and its associated VRN are defined on the
       port.  This is accomplished by the node operator issuing a
       DEFINE_CONNECTION_NETWORK(RQ) command to NOF and NOF passing a
       DEFINE_CN(RQ) signal to CS.

   2.  Each TG from the port to the VRN is defined by the node operator
       issuing DEFINE_CONNECTION_NETWORK_TG(RQ) to NOF and NOF passing
       DEFINE_CN_TG(RQ) to CS.

   Prior to implementation of Resource ReSerVation Protocol (RSVP)
   support, only one connection network TG between a port and a VRN is
   required.  In that case, product support for the DEFINE_CN_TG(RQ)
   signal is not required because a single set of port configuration
   parameters for each connection network is sufficient.  If a NOF
   implementation does not support DEFINE_CN_TG(RQ), the parameters
   listed in the following section for DEFINE_CN_TG(RQ), are provided by
   DEFINE_CN(RQ) instead.  Furthermore, the Connection Network TG



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RFC 2353                APPN/HPR in IP Networks                 May 1998


   Numbers (X'81') subfield in the TG Descriptor (X'46') control vector
   on an activation XID is only required to support multiple connection
   network TGs to a VRN, and its use is optional.

     *-----------------------------------------------------*
     |   NO                        NOF                CS   |
     *-----------------------------------------------------*
        DEFINE_CONNECTION_NETWORK(RQ)   DEFINE_CN(RQ)  .
          o------------------------>o----------------->o
       DEFINE_CONNECTION_NETWORK(RSP)   DEFINE_CN(RSP) |
          o<------------------------o<-----------------*
     DEFINE_CONNECTION_NETWORK_TG(RQ) DEFINE_CN_TG(RQ) .
          o------------------------>o----------------->o
    DEFINE_CONNECTION_NETWORK_TG(RSP) DEFINE_CN_TG(RSP)|
          o<------------------------o<-----------------*

          Figure 7. IP Connection Network Definition

   An incoming dynamic link activation may be rejected with sense data
   X'10160046' if there is an existing dynamic link between the two
   ports over the same connection network (i.e., with the same VRN CP
   name).  If a node receives an activation XID for a dynamic link with
   an IP address pair, a SAP pair, and a VRN CP name that are the same
   as for an active dynamic link, that node can assume that the link has
   failed and that the partner node is reactivating the link.  In such a
   case as an optimization, the node receiving the XID can take down the
   active link and allow the link to be reestablished in the IP network.
   Because UDP packets can arrive out of order, implementation of this
   optimization requires the use of a timer to prevent a stray XID from
   deactivating an active link.

   Once all the connection networks are defined, the node operator
   issues START_PORT(RQ), NOF passes the associated signal to CS, and CS
   passes ACTIVATE_PORT(RQ) to the DLC manager.  Upon receiving the
   ACTIVATE_PORT(RSP) signal from the DLC manager, CS sends a TG_UPDATE
   signal to TRS for each defined connection network TG.  Each signal
   notifies TRS that a TG to the VRN has been activated and includes TG
   vectors describing the TG.  If the port fails or is deactivated, CS
   sends TG_UPDATE indicating the connection network TGs are no longer
   operational.  Information about TGs between a network node and the
   VRN is maintained in the network topology database.  Information
   about TGs between an end node and the VRN is maintained only in the
   local topology database.  If TRS has no node entry in its topology
   database for the VRN, TRS dynamically creates such an entry.  A VRN
   node entry will become part of the network topology database only if






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RFC 2353                APPN/HPR in IP Networks                 May 1998


   a network node has defined a TG to the VRN; however, TRS is capable
   of selecting a direct path between two end nodes across a connection
   network without a VRN node entry.

*--------------------------------------------------------------------*
|   CS                   TRS                 DLC               DMUX  |
*--------------------------------------------------------------------*
     .            ACTIVATE_PORT(RQ)           .     create
     o--------------------------------------->o----------------->o
     .            ACTIVATE_PORT(RSP)          |                  .
     o<---------------------------------------*                  .
     |  TG_UPDATE         .                   .                  .
     *------------------->o                   .                  .
     .                    .                   .                  .

           Figure 8. IP Connection Network Establishment

The TG vectors for IP connection network TGs include the following