rfc2458.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

   majority of terminals are dedicated to carrying speech traffic
   (telephones) or to carrying facsimile data (fax machines). The
   terminals all connect to Central Offices (COs) via access lines, and
   these COs are interconnected into a network.

    /--\
   ()/\()__
    /__\   \       .................................
            \      !             !                 !           /--\
     __      \   [-!-]         [-!-]               !          ()/\()
     \ \      \__[CO ]=========[CO ]==\\           !        ___/__\
    [Fax]________[---]         [---]   \\        [-!-]     /   __
                                        \\=======[CO ]____/    \ \
                                                 [---]________[Fax]
   Key: ___   Access Lines
        ===   Trunk Links (inter-CO user data links)
        ...   Inter-CO signaling network links
        CO    Central Office (Telephone Exchange)

                                 Figure 2






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   Communications between the terminals are all "circuit switched", so a
   dedicated synchronous data path (or circuit) needs to be placed
   between the end terminals for carrying all communications. Arranging
   for such a circuit to be made or removed (cleared) is the
   responsibility of the Central Offices in the network. A user makes a
   request via his or her terminal, and this request is passed on to the
   "local" Central Office. The relationship between the terminals and
   the local Central Offices to which they are connected is strictly
   Client/Server.

   The COs are interconnected using two different types of connections.
   One of these is called a trunk connection (shown as a double line in
   the above figure) and is used to carry the data traffic generated by
   the terminals. The other connection acts as part of a separate
   network (and is shown as a dotted line in the above figure). This is
   the signaling network, and is used by the Central Offices to request
   a connection to be made between themselves and the destination of the
   required circuit. This will be carried across the trunk link to the
   "next" Central Office in the path. The path, once in place through
   the PSTN, always takes the same route. This contrasts with the
   Internet, where the underlying datagram nature of the infrastructure
   means that data packets are carried over different routes, depending
   on the combined traffic flows through the network at the time.

   The call set up process can be viewed as having two parts: one in
   which a request for connection is made, and the other in which the
   circuit is made across the PSTN and call data flows between the
   communicating parties. This is shown in the next pair of figures (3a
   and 3b).


                            /--\
                           ()  ()
                             --____
                            /++\   \
                           /----\   \
                              A      \   [-!-]
                                      \->[CO ]
                                         [---]
                           Time = 13:55

                                 Figure 3a


   Key: ___   Access Lines
        ===   Trunk Links (inter-CO user data links)
        ...   Inter-CO signaling network links
        CO    Central Office (Telephone Exchange)



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    /--\
   ()  ()
     --            .................................
    /  \<---       ^             !                 !           /--\
   /----\   \      !             v                 !          ()  ()
      A'     \   [-!-]         [-!-]               !            --
              \__[CO ]=========[CO ]==\\           v        ->-/  \
                 [---]         [---]   \\        [-!-]     /  /----\
                                        \\=======[CO ]____/     B'
   Time = 14:00                                  [---]

                                 Figure 3b

   Figure 3 shows a particular kind of service that can be provided;
   call booking. With this service, a request is sent for a connection
   to be made between the A and B telephones at a specified time. The
   telephone is then replaced (the request phase is terminated). At the
   specified time, the CO will make a connection across the network in
   the normal way, but will, first, ring the "local" or A' telephone to
   inform the user that his or her call is now about to be made.

   For more complex services, the requesting telephone is often
   connected via its "local" CO to a Service Node (SN), where the user
   can be played prompts and can specify the parameters of his or her
   request in a more flexible manner.  This is shown below, in Figures
   4a and 4b. For more details of the operation of the Service Node (and
   other Intelligent Network units), see the Appendix.

   When the SN is involved in the request and in the call setup process,
   it appears, to the CO, to be another PSTN terminal. As such, the
   initial request is routed to the Service Node, which, as an end
   system, then makes two independent calls "out" to A' and B'.

                             /--\         [---]
                            ()  ()        [SN ]
                              --___       [|--]
                             /++\  \       |
                            /----\  \      |
                                     \     |
                               A      \   [|-!]
                                       \->[CO ]
                                          [---]
                            Time = 13:55

                                 Figure 4a






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   Key: ___   Access Lines
        ===   Trunk Links (inter-CO user data links)
        ...   Inter-CO signaling network links
        CO    Central Office (Telephone Exchange)
        SN    Service Node


    /--\         [---]
   ()  ()        [SN ]
     --          [|--]                                           /--\
    /  \<--       |   ...............................           ()  ()
   /----\  \      |  ^             !                !             --
            \     | /              v                v            /  \
      A'     \   [|-!]            [-!-]            [-!-]     ->-/----\
              \--[CO ]            [CO ]            [CO ]    /
                 [---]            [---]            [---]___/      B'
   Time = 14:00

                                 Figure 4b

   Note that in both cases as shown in Figures 3 and 4 a similar service
   can be provided in which the B' telephone is replaced by an
   Intelligent Peripheral (or an Special Resource Functional entity
   within a Service Node), playing an announcement. This allows a "wake
   up" call to be requested, with the Intelligent Peripheral or Service
   Node Special Resource playing a suitable message to telephone A' at
   the specified time. Again, for more details of the operation of the
   Special Resources (and other Intelligent Network units), see the
   Appendix.

4.2 Pre-PINT Systems

   Although the pre-PINT systems reported here (i.e., those developed by
   AT&T, Lucent, Siemens and Nortel) vary in the details of their
   operation, they exhibit similarities in the architecture. This
   section highlights the common features. Specific descriptions of
   these systems will follow.

   All of the systems can be seen as being quite similar to that shown
   in the following diagram. In each case, the service is separated into
   two parts; one for the request and another for execution of the
   service. Figure 5 summarizes the process.









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                                _____
              __          _____/     \_____
             [__]        /                 \
            [-++-]-.-.>.-.   Internet       .-.-
                         \_____     _______/   .
                               \___/           v
                                       [----]  .
                                       [PINT]-.-
                                       [----]
                                         %
                                         v
                                       [---]
                                       [SN ]
                                       [|--]

                                 Figure 5a

   Key: CO    Central Office (Telephone Exchange)
        SN    Service Node
        PINT  PSTN/Internet Gateway
        .-.-. Internet Access Link
        %%%   Gateway/Service Node Link
        ___   PSTN Access Lines
        ===   PSTN Trunk Links (inter-CO user data links)
        ...   Inter-CO signaling network links

                       _____
     __          _____/     \_____
    [__]        /                 \
   [----]-.-.-.-.   Internet       .-.-
                \_____     _______/   .
                      \___/           |
                              [----]  .
                              [PINT]-.-
                              [-%--]
                                %
                                %
                 /--\         [-%-]
                ()  ()        [SN ]
                  --          [|--]                               /--\
                 /  \<--       |    ....................         ()  ()
                /----\  \      |   ^        !          !           --
                         \     |  /         v          v          /  \
                   A'     \   [|-!]       [-!-]      [-!-]    ->-/----\
                           \--[CO ]=======[CO ]======[CO ]   /
                              [---]       [---]      [---]__/      B'

                                 Figure 5b



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   Comparing Figure 4a with Figure 5a, the differences lie in the way
   that the information specifying the request is delivered to the
   Service Node. In the PSTN/IN method shown in the earlier diagram, the
   user connects to the SN from the telephone labeled A, with the
   connection being routed via the CO. In the latter case, the request
   is delivered from an Internet node, via the PINT gateway, and thence
   to the Service Node over a "private" link. The effect is identical,
   in that the request for service is specified (although the actual
   parameters used to specify the service required may differ somewhat).

   The figures depicting the respective service execution phases
   (Figures 4b and 5b) show that the operation, from the IN/PSTN
   perspective, is again identical. The Service Node appears to initiate
   two independent calls "out" to telephones A' and B'.

   The alternative systems developed by AT&T and by Nortel allow another
   option to be used in which the PINT Gateway does not have to connect
   to the PSTN via a Service Node (or other Intelligent Network
   component), but can instead connect directly to Central Offices that
   support the actions requested by the gateway. In these alternatives,
   the commands are couched at a "lower level", specifying the call
   states required for the intended service connection rather than the
   service identifier and the addresses involved (leaving the
   Intelligent Network components to coordinate the details of the
   service call on the gateway's behalf). In this way the vocabulary of
   the commands is closer to that used to control Central Offices. The
   difference really lies in the language used for the services
   specification, and all systems can use the overall architecture
   depicted in Figure 5; the only question remains whether the
   Intelligent Network components are actually needed in these other
   approaches.




















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