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Versions: 00                                                            
        INTERNET DRAFT                                  expires March 1997



                TITLE:  A MODEL FOR SECURE CALL-LIKE SESSIONS
                              WITHIN THE INTERNET
         <draft-davies-broker-model-00.txt>

                              - September 1996 -


                AUTHORS:                P.J.Williams) GPT Limited, UK.
                                        Ian Davies  )


        Status of this document

          This document is an Internet-Draft.  Internet-Drafts are
          working documents of the Internet Engineering Task Force
          (IETF), its areas, and its working groups.  Note that other
          groups may also distribute working documents as
          Internet-Drafts.

          Internet-Drafts are draft documents valid for a maximum of
          six months and may be updated, replaced, or obsoleted by
          other documents at any time.  It is inappropriate to use
          Internet-Drafts as reference material or to cite them other
          than as ``work in progress.''

          To learn the current status of any Internet-Draft, please
          check the ``1id-abstracts.txt'' listing contained in the
          Internet-Drafts Shadow Directories on ftp.is.co.za (Africa),
             nic.nordu.net (Europe), munnari.oz.au (Pacific Rim),
             ds.internic.net (US East Coast), or ftp.isi.edu (US West
             Coast).


        ABSTRACT

        The Internet is increasingly being used for commercial and
        industrial purposes which, apart from causing an explosion in
        traffic, will require that the future network provides a
        highly efficient "on-demand" service.  The provision of an
        efficient on-demand service will require Internet "sessions"
        to use virtual-message-paths that must be opened and closed in
        a manner similar to the establishment of calls in a telephone
        network; enabling the network to refuse traffic which exceeds
        the available capacity and ensuring that established sessions
        will not be violated.  It is felt that the RSVP mechanism will
        not fully meet these requirements for the commercial services
        described below, and this paper describes an alternative.

        As the Internet becomes the ultimate source of information,
        the "Global Net", users will need intermediary "Broker"
        services to clarify their requirement, select the appropriate
        service and arrange delivery of the information.  It is
        proposed that Broker-type "special-service" sessions should be



        established in reverse. The Broker or Receptionist will be
        given identifiers enabling the virtual-message-path to the
        user to be picked-up at the user's Internet Router.  As the
        user's requirements are recognised, these identifiers can be
        passed from Broker to Broker and from Server to Server
        enabling other Brokers or Servers to join the session, or
        enabling the user to be transferred from one to the other
        until service delivery is complete.

        The proposed method of service delivery is very user-friendly.
        From the user's point of view, every session appears to be a
        simple session with a single Internet host. Whatever starting
        point is chosen (even the wrong one), the transfer activity
        will eventually deliver the required information.  The method
        is also commercially secure. The user does not participate in
        the transfer activity and cannot short-circuit the Broker on
        future occasions. Servers deliver information directly to the
        user - whose identity is verified, thereby easing if not
        completely eliminating the "hacking" problem.

                              TABLE OF CONTENTS.

        1.      INTRODUCTION . . . . . . . . . . . . . . . . . . .0004

        2.      REQUIREMENTS OF THE FUTURE INTERNET. . . . . . . .0004
          2.1.  The "connection-oriented" requirement. . . . . . .0004
          2.2.  The simple-session requirement . . . . . . . . . .0005
          2.3.  The "special-service" requirement. . . . . . . . .0005

        3.      OUTLINE OF SPECIAL-SERVICE IMPLEMENTATION. . . . .0006

        4.      INTERNET NAMES AND ADDRESSES . . . . . . . . . . .0006
          4.1.  Internet names . . . . . . . . . . . . . . . . . .0006
          4.2.  Internet addresses . . . . . . . . . . . . . . . .0007
            4.2.1.  User addresses . . . . . . . . . . . . . . . .0007
            4.2.2.  Service-delivery addresses . . . . . . . . . .0007
            4.2.3.  Special-service networks . . . . . . . . . . .0008

        5.      TRANSPORT LAYER PROTOCOL MIGRATION STRATEGY. . . .0008

        6.      CREATING A VIRTUAL-MESSAGE-PATH. . . . . . . . . .0008
          6.1.  The host/Router link . . . . . . . . . . . . . . .0008
            6.1.1.  The host/Router link header. . . . . . . . . .0009
          6.2.  The OPEN message . . . . . . . . . . . . . . . . .0009
          6.3.  The message-path through the Internet. . . . . . .0010
            6.3.1.  VCN allocation . . . . . . . . . . . . . . . .0010
            6.3.2.  Switching tables . . . . . . . . . . . . . . .0010
            6.3.3.  The OPEN_DONE message. . . . . . . . . . . . .0011
            6.3.4.  Reserving capacity . . . . . . . . . . . . . .0012
            6.3.5.  Using the message-path . . . . . . . . . . . .0012
            6.3.6.  Diverting a message-path . . . . . . . . . . .0013
            6.3.7.  Closing the message-path . . . . . . . . . . .0013

[page 2



        7.      SPECIAL-SERVICES . . . . . . . . . . . . . . . . .0013
          7.1.  Invoking special-service delivery. . . . . . . . .0013
            7.1.1.  The SERVICE_ACK message. . . . . . . . . . . .0014
            7.1.2.  The SERVICE_REQUEST message. . . . . . . . . .0014
          7.2.  Establishing the service delivery path . . . . . .0015
            7.2.1.  The OPEN_SERVICE message . . . . . . . . . . .0015
            7.2.2.  The OPEN_DONE messages . . . . . . . . . . . .0016
              7.2.2.1.  OPEN-DONE to the Server. . . . . . . . . .0016
              7.2.2.2.  OPEN_DONE to the user. . . . . . . . . . .0017
            7.2.3.  Control message interface. . . . . . . . . . .0017
            7.2.4.  The REQUEST_DONE message . . . . . . . . . . .0018
          7.3.  Delivering the service . . . . . . . . . . . . . .0018
          7.4.  Service transfer . . . . . . . . . . . . . . . . .0018
            7.4.1.  The TRANSFER_REQUEST message . . . . . . . . .0018
            7.4.2.  The OPEN_TRANSFER message. . . . . . . . . . .0018
            7.4.3.  The OPEN_DONE and CLOSE_REQUEST messages . . .0018
            7.4.4.  The REQUEST_DONE message . . . . . . . . . . .0019
          7.5.  Subsequent transfers . . . . . . . . . . . . . . .0019

        8.      ACCOMMODATING EXISTING EQUIPMENT . . . . . . . . .0021
          8.1.  A simple session in the unknown Internet . . . . .0021
            8.1.1.  The OPEN message . . . . . . . . . . . . . . .0022
            8.1.2.  The OPEN_OLD message . . . . . . . . . . . . .0022
            8.1.3.  Conducting the session . . . . . . . . . . . .0023
              8.1.3.1.  Forward messages . . . . . . . . . . . . .0023
              8.1.3.2.  Backward messages. . . . . . . . . . . . .0023
              8.1.3.3.  Closing the session. . . . . . . . . . . .0024
          8.2.  A special-service session in the unknown Internet.0024
            8.2.1.  Invoking the service . . . . . . . . . . . . .0024
            8.2.2.  SERVICE_REQUEST via old network. . . . . . . .0024
              8.2.2.1.  UDP/IP header. . . . . . . . . . . . . . .0024
              8.2.2.2.  The ACK_OLD message. . . . . . . . . . . .0024
            8.2.3.  Service delivery via old network . . . . . . .0025
              8.2.3.1.  The OPEN_SERVICE message . . . . . . . . .0025
              8.2.3.2.  The OPEN_OLD message . . . . . . . . . . .0025
            8.2.4.  Conducting the session . . . . . . . . . . . .0027
              8.2.4.1.  Forward messages . . . . . . . . . . . . .0027
              8.2.4.2.  Backward messages. . . . . . . . . . . . .0028
              8.2.4.3.  Closing the previous message-path. . . . .0028
            8.2.5.  Closing the session. . . . . . . . . . . . . .0028

        9.      MULTI-SESSIONS . . . . . . . . . . . . . . . . . .0029

        10.     THE FUTURE INTERNET - CHARGING . . . . . . . . . .0029
          10.1. Basic charges. . . . . . . . . . . . . . . . . . .0029
          10.2. Special-service charges. . . . . . . . . . . . . .0029
          10.3. Collecting Service Providers charges . . . . . . .0030

        11.     SECURITY . . . . . . . . . . . . . . . . . . . . .0030
          11.1. User identity verification . . . . . . . . . . . .0030
          11.2. Breeching security . . . . . . . . . . . . . . . .0030

[page 3



         1. INTRODUCTION.

        This paper describes a very simple, very user-friendly and
        commercially secure means of providing access to the endless
        variety of services and sources of information that is and
        will be available via the Internet. The proposals are an
        adaptation of the principles employed in the "Enhanced
        Intelligent Network" proposed for the telephone network and
        are equally applicable to ATM, X25 or similar networks.

        To gain access to even the most remote and obscure source of
        information, a user simply opens a session with a Broker or
        Enquiry type service. As the user's needs are identified, the
        session will be transferred from Broker to Broker and from
        Server to Server until the final objective is reached. The
        user is not required to participate in the transfer activity.

        Brokers do not reveal any information to their client users as
        they transfer sessions to other Brokers or Servers. Having
        gained access to a service via a Broker, a user cannot regain
        access to that service without again going via the Broker.

        Servers deliver information directly to the user whose
        identity is verified. The Broker cannot copy the information.

        The paper also shows how the proposals can interwork with the
        existing Internet architecture and protocols.

        2. REQUIREMENTS OF THE FUTURE INTERNET.

        The Internet is increasingly being used for commercial and
        industrial purposes which, apart from causing an explosion in
        traffic, will require that the future network provides a
        highly efficient and commercially secure "on-demand" service.

        The current arrangement, in which users benevolently handle
        and switch one-another's traffic (and do not quarrel about the
        performance), cannot continue. Internet Providers must be
        independent of and impartial to the users. Users must know
        that their messages are not handled in a competitor's network.

        The future Internet Providers will be similar to the telephone
        network Providers. Users will pay a fixed charge for Internet
        access and will almost certainly pay an additional usage
        charge. In some cases, a further charge may be levied by the
        distant terminal for the actual information delivered. The
        charging arrangements are reviewed in Section 10.

        2.1. The "connection-oriented" requirement.

        The provision of an efficient on-demand service will require
        Internet "sessions" to use virtual-message-paths that must be
        opened and closed in a manner similar to the establishment of
        calls in a telephone network; enabling the network to refuse

[page 4



        traffic which exceeds the available capacity and ensuring that
        established sessions will not be violated.

        Charging is another aspect of the future Internet that will
        require sessions to be opened and closed. Internet Providers
        will record the traffic at network terminals and at gateways
        to other networks for charging purposes, but will need to know
        which terminal originated the session to which the messages
        belong; - that is "which end is paying?"

        2.2. The simple-session requirement.

        Perhaps the majority of Internet usage will continue to be
        where a user establishes a virtual-message-path to another
        user to conduct a simple one-to-one session.

        The present method of gaining access to remote information
        during a simple session is for the terminating end to open a
        session with the remote source and relay information as
        required. This method is known as "chaining".

        Alternatively, the terminating end may send to the user the
        address of the remote information. The user is required to end
        the current session and open a session with the new address to
        obtain the information, Returning an Internet address in this
        manner is known as "referral".

        "Chaining" and "referral" will continue to be used in the
        future but in many cases it will be preferable to use the
        proposed means of "special-service" delivery.

        2.3. The "special-service" requirement.

        In many cases, an Internet user may merely know that he wishes
        to buy software, insurance, or contact a large multi-national
        business organisation and will need to open an initial session
        with a broker or receptionist in order to proceed.

        Having interrogated the user to identify the service required,
        the Broker/Receptionist may not need to participate in the
        ensuing activity but may be unwilling to use "referral" as
        this would give information to the user that could be used, or
        misused on future occasions.

          e.g.  the user could bypass the Broker on future occasions.

                the user could pass the information to other users.

                the user could amend the information to gain access to
                other services provided by the Server.

                the information may enable privileged access to the
                service and privileged charges to be applicable.

[page 5]


        "Chaining" may also be unacceptable. Apart from the additional
        handling and resources involved, the Server may be unwilling
        to deliver its service via a Broker and may require to deal
        directly with the user.
        Service delivery requires that the user can be transferred
        from Broker to Broker and from Server to Server as service
        delivery proceeds, without being involved in the transfer
        activity.


        3. OUTLINE OF SPECIAL-SERVICE IMPLEMENTATION.

        "Special-service" sessions will be established in reverse.

        When a user attempts to open a session with a special-service,
        the special-service Server will be given identifiers enabling
        it to establish a virtual-message-path through the Internet to
        pick-up the virtual-message-path from the user at the user's
        Internet Router (a message switching node of the Internet).

        As the session proceeds, the identifiers may be passed from
        Server to Server enabling the user to be transferred from one
        Server to another, or enabling other Servers to be brought
        into the session.

        This basic concept of special-service delivery is very simple,
        but because the present Internet is not connection-oriented, a
        detailed description of its implementation requires that the
        creation of a virtual-message-path for a simple session is
        described and that the method of interworking with existing
        equipment is included.

        Consequently, the implementation is detailed in three parts.

                Part 1. Creating a virtual-message-path. (Section 6.)

                Part 2. Special-service delivery. (Section 7.)

                Part 3. Accommodating existing equipment. (Section 8.)



4. INTERNET NAMES AND ADDRESSES

        4.1. Internet names.

        To send a message or open a session in the Internet, a user
        provides the Internet name of the distant end. The initial
        task in any activity is to consult a cache or Domain Name
        Server to obtain the Internet address. As a result the choice
        of an Internet name is, and will remain, rather arbitrary.

[page 6]


        4.2. Internet addresses.

        4.2.1. User addresses. (See Figure 1)

        For the majority of Internet users, the more significant bits
        of the user's address (netID) will identify the user's Router;
        the lesser bits (hostID) identifying the user's terminal.

        The user's Internet address will not identify a particular
        Router if the user is connected to an elongated private
        network that gains access to the Internet via several Routers.

 host                                                        host
   1                                                           n
   +   +   +   +   +   +   +   +   +   +   +   +   +   +   +   +
   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
 +-+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+-+
 |                   ELONGATED PRIVATE NETWORK                   |
 |                      netID d; hostID 1-n                      |
 +---------+---------------------+---------------------+---------+
       +   |   +             +   |   +             +   |   +
       |   |   |             |   |   |             |   |   |
     +-+---+---+-+         +-+---+---+-+         +-+---+---+-+
 +---+ ROUTER A  +---+ +---+ ROUTER B  +---+ +---+ ROUTER C  +---+
     |           |         |           |         |           |
 +---+  netID a  +---+ +---+  netID b  +---+ +---+  netID c  +---+
     | hostID 1-n|         | hostID 1-n|         | hostID 1-n|
 +---+           +---+ +---+           +---+ +---+           +---+
 host+-----+-----+host host+-----+-----+host host+-----+-----+host
  1        |       n    1        |       n    1        |       n
           |                     |                     |
      +----+---------------------+---------------------+----+
      |               I  N  T  E  R  N  E  T                |
      +-----------------------------------------------------+

                         FIGURE 1. INTERNET ADDRESSES


        Such users present no problems for simple Internet sessions;
        whichever Router is used to establish a virtual-message-path
        at the start of a session will be the Router used throughout
        the session. However, when users have to be picked-up for
        special-service delivery, the address used must identify the
        Router that invoked the service.

        4.2.2. Service Delivery addresses.

        To deliver a "special-service", a Server establishes a virtual
        message-path through the Internet to pick-up the message-path
        to the user at the user's Internet Router. To establish the
        path, the Server uses a "service delivery address" allocated
        by the Router at the time of service invocation. The netID
        part of the address identifies the Router, the hostID part
        enables the Router to identify the current session-record.

[page 7




        4.2.3. Special-service networks.

        The future Internet address structure will include "networks"
        (netIDs) that identify Brokers and Services but have no
        relation to the location of the Routers and Servers. A single
        address (hostID) within such a network might identify all the
        worldwide services provided by General Motors of America,
        adjacent addresses identifying Siemens of Germany, Reuters
        News Agency or Mitsubishi of Japan.

        Thus, the netID part of the address is merely a "special-
        service" identifier and the hostID part is no more than an
        index number identifying the service.



        5. TRANSPORT LAYER PROTOCOL MIGRATION STRATEGY.

        In order to accommodate existing Internet equipment, all new
        equipment (hosts and Routers) will continue to handle the
        existing protocols (IP/TCP,etc.).

        As the penetration of new style equipment increases, new
        transport layer protocols will be introduced which are more
        suited to a connection-oriented environment, but some time
        will elapse before such protocols are universally available.

        The old protocols will continue to be used when no other
        protocol is mutually available. When old protocols are used in
        a connection-oriented manner, the IP header is redundant and
        should be ignored or even omitted. (It would be used only to
        make a checksum?)

        To accommodate the introduction of new protocols, when opening
        a session, a user will indicate in the OPEN message the old
        and new protocols available for the transport layer session.
        The distant end will indicate in the OPEN_DONE message the
        chosen mutually available protocol. (If old network equipment
        is encountered, the session will use old network protocols.)



        6. CREATING A VIRTUAL-MESSAGE-PATH. (SEE FIG.2, page 11)

        6.1. The host/Router link.

        Internet terminals are called "hosts". A host may be a PC
        capable of little more than one task at a time; an ISDN type
        terminal with several ports, each capable of several sessions;
        or a mainframe computer with innumerable hardware and software
        "ports", each capable of countless simultaneous sessions.

        Whatever the configuration, a session within a host can be

[page 8



        uniquely identified by a "port" and "session" number.

        A session-reference number identifies a session on the link
        between a host and its parent Router. All messages sent or
        received during a session will have the session-reference
        number in the host/Router link header. The reference may be
        supplemented by a sub-session number during multi-sessions.

        The host relates the session-reference to the appropriate port
        and session, the Router relates the host/session-reference to
        the route and virtual-channel-number (VCN) that forms the next
        link in the chain toward the distant end.

        The session-reference number will be allocated by the host on
        originating sessions or by the Router on terminating sessions.

        A host passes control messages (OPEN/CLOSE) received from the
        Internet to its control port. On hosts which deliver special-
        services, this port will require a standard port number in
        order to allow new version SERVICE-REQUEST messages to be
        received via old version Internet equipment. (See 8.2.2.1.)

        6.1.1. The host/Router link header.

        The host/Router link header might appear as follows:
                 +-------------------------------+\
                 |to host/Router|from host/Router||
                 |Control flags|SESSION-REFERENCE|)Link Header
                 | Sub-session  |  TOTAL LENGTH  ||
                 +-------------------------------+/
                 |           MESSAGE             |
                 |                               |
        The control flags may be used as follows:
                00 - ordinary message packet (new version),
                10 - session control message (OPEN/CLOSE etc.)
                01 - (not used)
                11 - old version message packet (no session-reference)

        6.2. The OPEN message.

        To open a virtual-message-path through the Internet, a host
        sends an OPEN message to its Internet Router. The message
        contains the distant host's address and port number which are
        derived from the Internet name and protocol indicator (ftp,
        http, etc) specified by the user.

        As new transport layer protocols are introduced, more than one
        protocol indicator might indicate the same port (ftp, newftp).
        The OPEN message will list the different protocols that are
        available at the user end and the distant end will indicate
        the chosen protocol in the OPEN_DONE message.

[page 9]


                            +--------------------+
                            | VERSION |  LENGTH  |
                            |   Function - OPEN  |
                            |DISTANT_HOST_ADDRESS|
                            |        PORT        |
                            |  User's protocols  |
                            | (with "more" flag) |
                            |         "          |
                            |      CHECKSUM      |
                            +--------------------+

                             TYPICAL OPEN MESSAGE

        6.3. The message-path through the Internet.

        6.3.1. VCN Allocation.

        Each Router uses the distant-host-address in the OPEN message
        to identify the route towards the destination and allocates a
        VCN to identify the session on the link to the next Router.
        The OPEN message is then passed on the control channel (VCN
        0000?) to the next Router in a message packet carrying the
        allocated VCN where the process will be repeated.

        At the link level, an OPEN message being passed from Router to
        Router might appear as follows:

                 +-----------------------------------------+
                 +  VIRTUAL CHANNEL 0000 (control channel) +
                 +          TOTAL MESSAGE LENGTH           +
                 +-----------------------------------------+
                 | ALLOCATED VCN (changed by each Router)  |
                 +-----------------------------------------+
                 |              OPEN  MESSAGE              |
                 |                                         |
        Messages received on a link's control channel (VCN 0000) will
        be passed to the Router's session processer for attention.

        To avoid VCN collisions, the Router at one end of a link may
        allocate VCNs in the range 0001 - 7FFF while the Router at the
        other end allocates 8000 - FFFF. (This assumes that VCN 0000
        is used in both directions for control messages.)

        To accommodate the existing and other network-layer protocols,
        link implementation may find it convenient to allocate a
        separate control VCN for each protocol. Messages received on
        such VCNs will be passed directly to the appropriate handler.

        6.3.2. Switching tables.

        As sessions are opened and closed, Routers will update tables
        which, for each incoming route (link) and VCN, will indicate
        the corresponding outgoing route, VCN and message switching
        priority. Each session will have two complimentary entries in

[page 10



        the tables; one for each direction of transmission.

        For charging or traffic recording purposes, Routers will also
        record which party established each session (which party is
        paying). Whilst this information could be derived from the
        session records, it may be convenient to have a flag in the
        switching tables.

        6.3.3. The OPEN_DONE message.

        When the message-path is complete, the distant host will
        return an OPEN_DONE message indicating the chosen protocol,
        and the capacity and message switching priority to be reserved
        in the network in both directions.

                        +----------------------------+
                        |   VERSION   |    LENGTH    |
                        |    Function - OPEN_DONE    |
                        |       CHOSEN PROTOCOL      |
                        | Forward priority & capacity|
                        |Backward priority & capacity|
                        |          CHECKSUM          |
                        +----------------------------+

                          TYPICAL OPEN_DONE MESSAGE








             (1)                (2)                (1)
         >  OPEN   >        >  OPEN   >        >  OPEN   >
         >SESS-REFa>        >   VCNx  >        >SESS-REFb>
  +-----+>to Host n>+------+>to Host n>+------+> to Host n>+------+
  |USER +-----------+ROUTER+-----------+ ROUTER+-----------+HOST n|
  +-----+    (3)    +------+    (3)    +-------+    (3)    +------+
         <SESS-REFa<        <  VCNx   <        <SESS-REFb<
         <OPEN_DONE<        <OPEN_DONE<        <OPEN_DONE<

                                                No.     Refer to text
                                                (1)      6.1. & 6.1.1.
                                                (2)         6.3.1.
                                                (3)     6.3.3.& 6.3.4.

                  ESTABLISHING A VIRTUAL-MESSAGE-PATH


                               FIGURE 2


        The OPEN_DONE or FAILURE message will be returned link by link

[page 11



        using the control channel (VCN 0000); each Router amending the
        RELEVANT VCN to indicate the session to which the message
        applies.

        At the link level, an OPEN_DONE message being passed from
        Router to Router might appear as follows:

                 +-----------------------------------------+
                 +  VIRTUAL CHANNEL 0000 (control channel) +
                 +          TOTAL MESSAGE LENGTH           +
                 +-----------------------------------------+
                 |  RELEVANT VCN (changed by each Router)  |
                 +-----------------------------------------+
                 |            OPEN_DONE MESSAGE            |
                 |                                         |

        To accommodate hosts which require use of a wake-up procedure,
        the final Router may return an OPEN_ACK message indicating
        that the message-path is complete but that there will be a
        delay before the OPEN_DONE message can be sent.

        All subsequent control messages - in either direction - will
        be sent on the control channel in a similar manner, with the
        link header being followed by the RELEVANT VCN and the control
        message itself.

        6.3.4. Reserving capacity.

        Routers will reserve capacity (in terms of anticipated mean
        bits per second) on the links employed as indicated in the
        OPEN_DONE message, and will refuse traffic which exceeds the
        capacity available.

        A Router will convert an OPEN_DONE message into a FAILURE
        message if it finds that it cannot provide the capacity
        indicated in the OPEN_DONE message. Upon receiving a FAILURE
        message the originating host will be required to send a CLOSE
        message to release the established part of the message-path.

        6.3.5. Using the message-path.

        Once a message-path is established, the originating host will
        open a transport layer session. Message packets will be passed
        from Router to Router with the Link Header indicating the
        allocated VCN. Each Router will replace the incoming VCN with
        the outgoing VCN as the message packet is switched.

                 +-----------------------------------------+
                 +  ALLOCATED VCN (changed by each Router) +
                 +          TOTAL MESSAGE LENGTH           +
                 +-----------------------------------------+
                 |             MESSAGE  PACKET             |
                 |                                         |


[page 12




        6.3.6. Diverting a message-path. (2nd OPEN_DONE message.)

        To OPEN a simple Internet session, a user may need to OPEN an
        initial session with the distant host's Port Mapper in order
        to learn the appropriate port number.

        With new version equipment, the distant host should be able to
        divert the Port Mapper session to the required port without
        requiring the user to re-open the session.

        There may then be need for a control message to change the
        chosen protocol and reserve appropriate network capacity.

        The message content will be seen to be identical to the
        OPEN_DONE message. Users and Routers should be prepared to
        accept a second such message, including that a Router may
        change the message to a FAILURE message if it finds that it
        cannot provide the required capacity.

        An OPEN_DONE message may also be sent to a user more than once
        during special-service delivery when a session is transferred
        from one Server to another.

        6.3.7. Closing the message-path.

        When the session ends, the transport layer session will be
        closed followed by closure of the virtual-message-path.

        Message-paths are controlled by the originating terminal and
        closed by the exchange of CLOSE and CLOSE_ACK messages. The
        CLOSE_ACK message being returned on a per link basis. The
        terminating end may invite closure with a CLOSE_REQUEST
        message.

        7. SPECIAL-SERVICES. (See Figures 3 & 4. PAGES 16 & 17)

        7.1. Invoking special-service delivery.

        To open a special-service session in the Internet, a host
        sends an OPEN message to its Internet Router as normal. The
        message includes the distant-host-address derived from the
        Internet name specified by the user.

        When the user specifies the name of a special-service, the
        netID part of the distant-host-address will be a "special-
        service" identifier. (See 4.2.3.)

        Upon receiving a "special-service" address, the Router returns
        a SERVICE_ACK message to the host and sends a SERVICE_REQUEST
        message to the nearest SORTER. (A Sorter is located with any
        convenient Router and has an address in the range used by any
        other host connected to that Router.)

[page 13



        The SORTER opens the SERVICE_REQUEST message to identify the
        special-service address and uses a look-up table to re-address
        the message to the appropriate Broker or Server.


        In the case of services which are provided by other network
        operators or in other countries, the Sorter will re-address
        the message to a Sorter in that network or country; there is
        no need for internetwork management of Sorters.

        7.1.1. The SERVICE_ACK message.

        The SERVICE_ACK message contains no parameters. It informs the
        user that the session may involve more than one transport
        layer session and that the initiative to open and close those
        sessions will be at the distant end. The user must assume the
        default situation, - that messages will be sent and received
        via old network equipment and will have IP/TCP type headers.

        All messages sent or received during the session (old protocol
        or otherwise) will use the current message-path; link headers
        quoting the SESSION_REFERENCE and the control bits set to 00
        (or 10 for new version session control messages). See 6.1.1.

          +-------------------------+     +--------------------------+
          |   VERSION  |   LENGTH   |     |   VERSION  |   LENGTH    |
          |Function -  SERVICE_ACK  |     |Function - SERVICE_REQUEST|
          |         CHECKSUM        |     |  *SORTER/SERVER ADDRESS  |
          +-------------------------+     |  SPECIAL-SERVICE ADDRESS |
                                          | SERVICE DELIVERY ADDRESS |
                                          |REFERENCE No.(SEE OPTIONS)|
        * The Service-Request message is  |   USER'S INTERNET NAME   |
          initially addressed to a Sorter |   AVAILABLE PROTOCOLS    |
          which re-addresses the message  |   (with "more" flags)    |
            to an appropriate Server.     |         CHECKSUM         |
                                          +--------------------------+

                TYPICAL SERVICE_ACK & SERVICE_REQUEST MESSAGE

        7.1.2. The SERVICE_REQUEST message.

        The SERVICE_REQUEST message contains;
        (i)   the special-service address
        (ii)  the service-delivery address & reference no. See OPTIONS
        (iii) the user's Internet name (prime user's name)
        (iv)  the transport layer protocols available.
                Items i and iv are taken from the OPEN message,
                items ii & iii are provided by the Router.
        OPTION 1  This option enables the service-delivery address to
                be used as the DESTINATION-ADDRESS in IP headers when
                services are delivered via old network equipment, but
                requires a block of hostIDs to be reserved for this
                purpose. The SERVICE DELIVERY ADDRESS is an ordinary
                Internet address, the netID identifies the Router, the

[page 14



                hostID is a reference number enabling the Router to
                identify the active session-record.
        OPTION 2  Enables address economy by using a single SERVICE
                DELIVERY ADDRESS and placing the reference number in
                another field. This requires a field to be found in IP
                Headers to carry the reference when services are
                delivered via old network equipment. (Not difficult?)


        SERVICE_REQUEST messages use the control channel like any
        other control message and create a message-path as they are
        passed via Routers and Sorters to the Server; each Router and
        Sorter allocating a VCN or session reference as necessary.

        The message-path created by the SERVICE_REQUEST message is
        used only to return a REQUEST_DONE or FAILURE message from the
        Server via the Sorter to the originating Router. The Router
        will CLOSE the path when the returned message is received. No
        capacity is reserved for the SERVICE_REQUEST session.

        7.2. Establishing the service delivery path.

        7.2.1. The OPEN_SERVICE message.

        Upon receiving the SERVICE_REQUEST message, the Server will
        choose the protocol to be used and open a message-path to the
        user via the Internet with an OPEN_SERVICE message containing:
          (i)   the SERVICE-DELIVERY ADDRESS as DISTANT-HOST-ADDRESS
           (ia) the REFERENCE NUMBER (OPTIONAL. See 7.1.2. OPTIONS)
          (ii)  the USER'S INTERNET NAME
          (iii) the transport layer protocol to be used
          (iv)  the capacity and switching priority to be reserved
             Items iii and iv are valid only if a complete virtual-
             message-path can be established and are used only after
             being transferred to an OPEN_DONE message.

                         +----------------------------+
                         |     VERSION  |  LENGTH     |
                         |   Function - OPEN_SERVICE  |
                         |  SERVICE_DELIVERY_ADDRESS  |
                         | REFERENCE NUMBER(OPTIONAL) |
                         |    USER'S INTERNET NAME    |
                         |       CHOSEN PROTOCOL      |
                         | Forward capacity & priority|
                         |Backward capacity & priority|
                         |          CHECKSUM          |
                         +----------------------------+

                          TYPICAL OPEN_SERVICE MESSAGE

        The OPEN_SERVICE message will be treated as a normal OPEN
        message by all Routers except the final Router, which uses the
        SERVICE_DELIVERY_ADDRESS (and REFERENCE NO.? See 7.1.2.) to
        find the session record, verify the USER'S INTERNET NAME and

[page 15



        pick-up the message-path to the user.

        7.2.2. The OPEN_DONE messages.

        7.2.2.1. OPEN_DONE to the Server.

        The Router sends an OPEN_DONE message to the Server using the
        protocol, capacity and priority fields from the OPEN_SERVICE
        message. It is used by all Routers to reserve capacity. To the
        Server, it confirms the protocol to be used and indicates that
        a complete virtual-message-path has been established.



                            +------+
                            |SORTER|
                    (2b)    +-+--+-+     (3)
               SERVICE_REQUEST^  v SERVICE_REQUEST
                  to Sorter +-+--+-+    to Server    +------+
                        + ->+ROUTER+ - - - ->- - - - +ROUTER+ ->+
                        ^   +------+                 +------+   v
              (2b)      |                                  (3)  |
      SERVICE_REQUEST                            SERVICE_REQUEST
            to Sorter   |                              to Server|
                        ^        (4)                 (4)        v
+----+   (1) >OPEN>  +--+---+OPEN_SERVICE+------+OPEN_SERVICE+--+---+
|USER+------->-------+ROUTER+------<-----+ROUTER+------<-----+SERVER|
+----+ <SERVICE_ACK< +------+            +------+            +------+
                        (2a)
                                 No.      Message     Refer to Text
                                (1)       OPEN           7.1
                                (2a)   SERVICE_ACK      7.1.1.
                                (2b) SERVICE_REQUEST    7.1.2.
                                (3)  SERVICE_REQUEST    7.1.2.
                                (4)   OPEN_SERVICE      7.2.1.

      - ->- - path of SERVICE_REQUEST message
      ---<--- virtual-message-path & direction of establishment

                    CREATING A SPECIAL-SERVICE MESSAGE-PATH

                                            FIGURE 3.







[page 16




                         +------+
                         |SORTER|
                   (6)   +-+--+-+  (6)
              REQUEST_DONE v  ^REQUEST_DONE
                         +-+--+-+                 +------+
                     +<- +ROUTER+ - - - -<- - - - +ROUTER+ -<+
                     v   +------+ REQUEST_DONE (6)+------+   ^
             (6)     |                                       |    (6)
         REQUEST_DONE                            REQUEST_DONE
                     |                                       |
                     v                                       ^
+----+            +--+---+            +------+            +--+---+
|USER+------------+ROUTER+------------+ROUTER+------------+SERVER|
+----+<OPEN_DONE< +------+>OPEN_DONE> +------+>OPEN_DONE> +------+
      to user (5b)       to Server(5a)       to Server(5a)

                            No.      Message         Refer to Text
                           (5a) OPEN_DONE to Server    7.2.2.1.
                           (5b)  OPEN_DONE to User     7.2.2.2.
                           (6)     REQUEST_DONE         7.2.4.

- - - - - - - - - - SERVICE_REQUEST message path
 ----------------- established virtual-message-path

         After receiving REQUEST_DONE the user's Router closes the
SERVICE_REQUEST message path


                            PATH-COMPLETE MESSAGES

                                          FIGURE 4.


        7.2.2.2. OPEN_DONE to the user.

        The same OPEN_DONE message will be sent to the user but with
        the forward and backward capacity and priority fields reversed
        (the capacity and priority may be required by a LAN Gateway?)

        The message tells the user which transport layer protocol will
        be used for service delivery and overrides the default old
        network protocol established by the SERVICE_ACK message. At
        the end of the transport layer session, the user must revert
        to the default. (See 7.1.1.)

        7.2.3. Control message interface.

        The user's Internet Router will be required to provide an
        interface for subsequent control messages as both the user and
        Server will consider themselves to be the session originator.
        For charging purposes, the session must be considered to be
        originated by the Server.

[page 17



        7.2.4. The REQUEST_DONE message.

        Having received OPEN_DONE indicating that the message-path is
        complete, the Server will return a REQUEST_DONE message to the
        originating Router using the message-path created by the
        SERVICE_REQUEST message; the Router will then CLOSE that path.

        7.3. Delivering the service.

        Using the established message-path, the Server will open a
        transport layer session with the user to commence service
        delivery. This will often involve interrogating the user to
        further identify the service required after which the user may
        be transferred to another Server.

        7.4. Service Transfer. (See Figures 5 & 6, pages 20 & 21)

        7.4.1. The TRANSFER_REQUEST message.

        A Server transfers a user to another Server by closing the
        transport layer session and sending a TRANSFER_REQUEST message
        to the other Server. The TRANSFER_REQUEST message contains the
        same information as the original SERVICE_REQUEST message, but
        indicates that the existing message-path must be diverted.

        The message will usually be addressed directly to the other
        Server but may be addressed via a Sorter as before, in which
        case the SPECIAL_SERVICE_ADDRESS field must be updated.

        The message packet may include information for the new Server
        obtained during the earlier session (regarding payment etc.).
        All such information is of no consequence to the Internet.

        The TRANSFER_REQUEST message will be forwarded to the new
        Server and a message-path created to return the REQUEST_DONE
        or FAILURE message. (Similar to a SERVICE_REQUEST message.)


        7.4.2. The OPEN_TRANSFER message.

        The new Server will use a OPEN_TRANSFER message to establish a
        message-path via the Internet to the user. The message content
        is the same as an OPEN_SERVICE message and is treated as an
        ordinary OPEN message by all Routers except the final Router
        that connects to the user or user's LAN. This Router uses the
        SERVICE_DELIVERY_ADDRESS (and REFERENCE_NO. See 7.1.2.) to
        find the session record, verify the USER'S NAME and complete
        the virtual-message-path to the user.

        7.4.3. OPEN_DONE and CLOSE_REQUEST messages.

        Having completed the new message-path, the Router will send an
        OPEN_DONE message to the new Server and to the user as before
        (See 7.2.2) and will send a CLOSE_REQUEST message to the old

[page 18



        Server on the old message-path. (If the previous session used
        old network procedure, no CLOSE_REQUEST message can be sent.)

        The previous Server will CLOSE the old message-path when the
        CLOSE_REQUEST message is received. (See also 8.2.4.3.)

        Upon receiving the OPEN_DONE message, the user will cancel the
        default situation (restored when the previous transport layer
        session was closed. See 7.2.2.2) and await the opening of a
        new transport layer session using the protocol indicated in
        the OPEN_DONE message.

        7.4.4. The REQUEST_DONE message.

        When the new Server receives the OPEN_DONE message, it will
        send REQUEST_DONE to the old Server on the TRANSFER_REQUEST
        message-path and will commence service delivery.

        After receiving REQUEST_DONE, the old Server will close the
        TRANSFER_REQUEST message-path.

        7.5. Subsequent transfers.

        The session transfer activity may be repeated any number of
        times.























[page 19]

                                                   +- -- -+
                                                    SORTER
                                                   +- -- -+
                                                   +------+
                                                   |ROUTER+ -<- +
                                                   +---+--+     ^
                                             (1)       |        |  (1)
                                       TRANSFER_REQUEST|      TRANSFER
                                                       v      _REQUEST
                            +------+      (2)       +--+---+    ^
                (2)      +--+ROUTER+-------<--------+ NEW  |    |
           OPEN_TRANSFER v  +------+ OPEN_TRANSFER  |SERVER|
             +------+    |                          +------+ +--+---+
+----+       |      +-<--+  +------+                         | OLD  |
|USER+-------+ROUTER+/-/-/-/+ROUTER+/-/-/-/-/-/-/-/-/-/-/-/-/+SERVER|
+----+       +------+       +------+                         +------+



                                  No.      Message       Refer to text
                                  (1)  TRANSFER_REQUEST     7.4.1.
                                  (2)   OPEN_TRANSFER       7.4.2.

- - ->- -path of TRANSFER_REQUEST message
-----<---new virtual-path & direction of establishment
-/-/-/-/-old virtual-path

                            INITIATING SERVICE TRANSFER

                                              FIGURE 5.

















[page 20




                                                    +- -- -+
                                                     SORTER
                                                    +------+
                                                    |ROUTER+ - >+
                                                    +--+---+    v
                                                (5)    ^        |
                                           REQUEST_DONE|        | (5)
                                                       ^      REQUEST
                       (3a)      +------+ OPEN_DONE +--+---+    _DONE
                    OPEN_DONE  +-+ROUTER+------->---+ NEW  |    |
                    to Server  ^ +------+ to Server |SERVER|    v
                    +------+   |                    +------+ +--+---+
+----+(3b) OPEN_DONE|      +->-+  <(6) CLOSE<  +------+      | OLD  |
|USER+------<-------+ROUTER+/-/-/-/-/-/-/-/-/-/+ROUTER+//-/-/+SERVER|
+----+   to User    +------+>(4) CLOSE_REQUEST>+------+ >(4)>+------+

                               No.      Message        Refer to text
                              (3a) OPEN_DONE to Server   7.4.3.
                              (3b)  OPEN_DONE to User    7.4.3.
                              (4)     CLOSE_REQUEST      7.4.3.
                              (5)     REQUEST_DONE       7.4.4.
                              (6)         CLOSE          7.4.3.

- - - - - path of TRANSFER_REQUEST message
--------- new virtual-path
-/-/-/-/- old virtual-path

              After receiving REQUEST_DONE the old Server closes the
REQUEST message-path

                                        PATH-COMPLETE MESSAGES

                                              FIGURE 6.


        8. ACCOMMODATING EXISTING EQUIPMENT.

        To interwork with existing equipment, new version hosts and
        new version Routers must be able to handle the existing
        procedures and must be able to receive and send old version
        messages. Control flags indicate the presence of old version
        messages on host/Router links (See 6.1.1.); on links between
        Routers, old version messages use a special VCN. (See 6.3.1)

        8.1. A simple session in the unknown Internet. See Fig 7, p22)

        Although capable of old network procedures, new version hosts
        will never initiate old version sessions. Even when a session
        is known to involve old version equipment, a new version host
        will attempt to establish a virtual-message-path; ensuring as
        far as possible, the continuity of the session. (If only the
        distant host were old version equipment a virtual-message-path
        could be established right across the Internet.)

[page 21




        8.1.1. The OPEN message.

        When a new version host sends an OPEN message into the
        Internet, a message-path will established to the distant host
        or to the point that the path meets old version equipment.

        If the path meets old version equipment, the Router at the
        interface to the old equipment completes the path to the old
        network route and returns OPEN_OLD to the originating end.

        8.1.2. The OPEN_OLD message.

        The OPEN_OLD message informs the user that the message-path is
        open but is not complete and that old network procedures must
        be used. The message includes a SOURCE_ADDRESS for use in the
        IP Headers; it identifies the interface Router and its active
        session-record. (An "option" achieves address economy by using
        an additional REFERENCE_NO field. See SERVICE_DELIVERY_ADDRESS
        in SERVICE_REQUEST messages. Section 7.1.2.)

        The OPEN_OLD message also indicates nominal capacities and
        priorities to be reserved by the Routers.

                        +----------------------------+
                        |   VERSION   |    LENGTH    |
                        |   Function -   OPEN_OLD    |
                        | Forward capacity & priority|
                        |Backward capacity & priority|
                        |SOURCE_ADDRESS (and REF.NO?)|
                        |         CHECKSUM           |
                        +----------------------------+

                           TYPICAL OPEN_OLD MESSAGE

        Once an interface to old version equipment has been provided,
        it is not possible to return to the new version procedures if
        later equipment has new version capability.


            (1)                  (1)
      >    OPEN    >        >   OPEN   >
      > SESS._REFa >        >   VCNx   >          (         )
+----+>  to HOSTn  >+------+> to HOSTn >+------+  (   OLD   )
|USER+--------------+ROUTER+------------+ROUTER+--( NETWORK )
+----+< SESS._REFa <+------+<   VCNx   <+------+  (         )
      <  OPEN_OLD  <        < OPEN_OLD <          (         )
            (2)                  (2)


 No.         Refer to text
(1)   OPEN      8.1.1.     ESTABLISHING AN INCOMPLETE MESSAGE-PATH
(2) OPEN_OLD    8.1.2.                  FIGURE 7.

[page 22




            (3)                 (3)
      | SESS._REFa |        |   VCNx   |
      |   TCP/IP   |        |  TCP/IP  |
+----+|  MESSAGES  |+------+| MESSAGES |+------+
|USER+----->--<-----+ROUTER+---->--<----+ROUTER|
+----+              +------+            +---+--+
                                            |
                 +--------->----<-----------+
                 |
                 |
                 |  (      (4,5)      )              (4,5)
                 |  (  |  TCP/IP  |   )           |  TCP/IP  |
                 |  (  | MESSAGES |   )  +------+ | MESSAGES | +-----+
                 +--(- - ->- -<- - - -)--+ROUTER+----->--<-----+HOSTn|
                    (                 )  +------+              +-----+
                    (       OLD       )
                    (     NETWORK     )


       No.     Refer to text
      (3)        8.1.3.
      (4)        8.1.3.1.
      (5)        8.1.3.2.

                        USING AN INCOMPLETE MESSAGE-PATH

                                  FIGURE 8.


        8.1.3. Conducting the session. (See Figure 8)

        The user will send and receive messages with IP/TCP type
        headers on the established message-path. (i.e. With the
        link-header using the SESSION-REFERENCE and the control bits
        set to 00.) The DESTINATION_ADDRESS in the IP header will be
        the same as the distant-host-address in the OPEN message, the
        SOURCE_ADDRESS (and REFERENCE NO?) will be that provided in
        the OPEN_OLD message.

        8.1.3.1. Forward messages.

        Upon receiving forward messages from the user, the Router at
        the interface will pass the messages to the old network route.
        The messages will continue to their destination using old
        network procedures.

        8.1.3.2. Backward messages.

        Messages returned from the distant end will be addressed to
        the SOURCE_ADDRESS given in the forward messages, which (with
        an optional REFERENCE NO.?) identifies the interface Router
        and its session-record.

        Upon receiving the returned messages, the interface Router

[page 23



        will find the session-record and return the messages, with
        headers, to the user on the established message-path.

        8.1.3.3. Closing the session.

        When the session ends, the originating host will CLOSE the
        message-path to the interface Router in the normal manner.

        8.2. A special-service session in the unknown Internet.

        8.2.1. Invoking the service.

        When a new version host attempts to OPEN a session with a
        special-service address, the Internet Router addresses a
        SERVICE_REQUEST message to the nearest Sorter which
        re-addresses the message to an appropriate Server.

        If an old version host attempts to gain access to such a
        service, the special-service address will appear in the
        DESTINATION_ADDRESS of an IP header. A variety of treatments
        are possible; but are not detailed in this document.

        8.2.2. SERVICE_REQUEST via old network. (See Figure 9, p 26)

        8.2.2.1. UDP/IP Header.

        If the message path from the Router via the Sorter to the
        chosen Server encounters old version equipment, the Router at
        the interface will prefix the SERVICE_REQUEST message with an
        IP/UDP Header and forward it via the old version equipment.


        For this purpose, new version Routers will have a ready-made
        IP/UDP Header. The Router will be required to complete the
        DESTINATION_ADDRESS, CHECKSUM and LENGTH fields each time the
        header is used. The ready-made header may also be used to
        forward TRANSFER_REQUEST messages.

        A Sorter will be required to accept IP/UDP messages only when
        old network equipment exists in the path between the Sorter
        and the Routers which it serves; or when SERVICE_REQUEST
        messages are received from Sorters in other networks or other
        countries (See 7.1. last para). Having received a request
        message using IP/UDP, the message should be forwarded to the
        Server in the same manner.

        The SERVICE_REQUEST message will be delivered using the IP/UDP
        protocol to the Server's control port (a standard port number
        on special-service equipment. See 6.1. last para.).

        8.2.2.2. The ACK_OLD message.

        Servers do not acknowledge SERVICE_REQUEST messages delivered
        by IP/UDP. Having forwarded the message, the interface Router

[page 24



        will return ACK_OLD to the originating Router.

        The ACK_OLD message has no parameters. The originating Router
        will CLOSE the partly established REQUEST message-path (used
        only to return DONE or FAILURE messages from the Server) and
        await the commencement of service delivery; a time-out and
        escape procedure being available if no response arises.

        8.2.3. Service delivery via old network. (See Figure 10, p26)

        8.2.3.1. The OPEN_SERVICE message.

        Having received the SERVICE_REQUEST message (by whatever
        means), the Server will attempt to open a message-path to the
        user by sending a OPEN_SERVICE message into the Internet.

        If the message-path meets old version equipment, the Router at
        the interface to the old equipment will complete the path to
        the old network route and return OPEN_OLD to the Server.

        8.2.3.2. The OPEN_OLD message. (See 8.1.2. )

        The OPEN_OLD message informs the Server that the message-path
        is not complete and that old network procedure must be used.

        The message gives nominal capacity and priority reservations
        and includes a SOURCE_ADDRESS to be used by the Server in the
        IP Headers. The address (including an optional REFERENCE_NO.)
        identifies the interface Router and its session-record.

        Upon receiving the OPEN_OLD message, the Server will return
        REQUEST_DONE to the request message source. (If the request
        message delivery had also encountered old-network equipment,
        it will not be possible to return a REQUEST_DONE message.)


















[page 25




           (1)                 (1)
      > SESS_REFa >        >  VCNx   >
      >   OPEN    >        >SVCE_REQ >
+----+> to Svce n >+------+>to Sorter>+------+
|USER+-------------+ROUTER+-----------+ROUTER|
+----+     (1)     +------+    (3)    +---+--+
      < SESS_REFa <        <  VCNx  <     |
      <SERVICE_ACK<        < ACK_OLD<     |
                                          |
               +---------<---------<------+
               |
               |
               |                      +------+
               |    (      (2)      ) |SORTER|      (2)
               |    (  |  UDP/IP  | ) +-+--+-+  |  UDP/IP  |
               |    (  | SVCE_REQ | )   ^  v    | SVCE_REQ |
               |    (  | to Sorter| ) +-+--+-+  | to Server| +------+
               +----(-------->------)-+ROUTER+-------->------+SERVER|
                    (       OLD     ) +------+               +------+
                    (     NETWORK   )

  No.    Refer to text
 (1) 7.1; 7.1.1; & 7.1.2.
 (2)       8.2.2.1.
 (3)       8.2.2.2.

FIGURE 9.      SENDING SERVICE_REQUEST VIA OLD NETWORK





    No.    Refer to text
    (1)      8.2.3.1.        (               )
    (2)      8.2.3.2.        (               )
+-  -+             +- -- -+  (               )
|USER+ - - - - - - +ROUTER+ -(               )------+
+-  -+             +- -- -+  (      OLD      )      |
                             (    NETWORK    )      |
                                                    |
              +-------------------------------------+
              |
              |               (1)                    (1)
              |          <   VCNn    <          < SESS_REFx <
              |          < OPEN_SVCE <          < OPEN_SVCE <
              | +------+ <  to User  < +------+ <  to User  <+------+
              +-+ROUTER+---------------+ROUTER+--------------+SERVER|
                +------+      (2)      +------+     (2)      +------+
                          >   VCNn   >           > SESS_REFx >
                          > OPEN_OLD >           > OPEN_OLD  >

FIGURE 10.   ESTABLISHING AN INCOMPLETE SERVICE-DELIVERY MESSAGE-PATH

[page 26



          (1,2)
       | SESS_REFa|          (     (1,2)     )
       |  IP/TCP  |          ( |  IP/TCP  |  )
+----+ | Messages |+------+  ( | Messages |  )
|USER+---->----<---+ROUTER+--(---->----<-----)------+
+----+             +------+  (      OLD      )      |
                             (    NETWORK    )      |
                                                    |
              +-------------->---------<------------+
              |
              |
              |              (1,2)                  (1,2)
              |           |   VCNn   |          | SESS_REFx|
              |           |  TCP/IP  |          |  TCP/IP  |
              |  +------+ | Messages | +------+ | Messages | +------+
              +--+ROUTER+---->----<----+ROUTER+---->----<----+SERVER|
                 +------+              +------+              +------+


                  No.   Refer to text
                 (1)     8.2.4.1.
                 (2)     8.2.4.2.

FIGURE 11.   DELIVERING SERVICE VIA INCOMPLETE MESSAGE-PATH


        8.2.4. Conducting the session. (See Figure 11, above)

        8.2.4.1. Forward messages.

        The Server will commence service delivery using the part
        established message-path. (i.e. The link header will hold the
        session_reference number with the control bits set to 00.)

        Each message packet will have an old version IP/TCP header.
        The SOURCE_ADDRESS (and REFERENCE NO.?) in the header will be
        as received in the OPEN_OLD message, identifying the interface
        Router and its session-record. The DESTINATION_ADDRESS (and
        REFERENCE NO.?) will be the SERVICE_ DELIVERY_ADDRESS from the
        SERVICE/TRANSFER_REQUEST message, identifying the originating
        Router and its session-record.

        The interface Router passes messages received from the Server
        into the old network which forwards the messages to the
        originating Router as identified by the DESTINATION_ADDRESS.

        The originating Router recognises that the DESTINATION_ADDRESS
        in the forward messages is a SERVICE_DELIVERY_ADDRESS. It uses
        the address (and REFERENCE_NO?) to find the session-record and
        send the messages to the user on the established message-path,
        albeit only one link. (Link headers hold the session-reference
        number with the control bits set to 00.)

        The user will be in the default situation and will be

[page 27



        expecting service delivery using old network protocols. The
        port and session to which the messages belong will be
        identified by the session-reference number in the link header;
        the IP Header in the forward messages will be used only for
        checksums and to provide the address for returned messages.

        8.2.4.2. Backward messages.

        To simplify the handling of backward messages, the originating
        Router may record in its switching table the route from which
        forward messages are received. The table must be updated each
        time a forward message is received as the route may change
        without notice if service delivery is transferred to a Server
        which also needs to use old network procedure.

        Messages returned to the Router from the user will have IP/TCP
        type headers and will use the established message-path (the
        link-header holding the session-reference and the control bits
        set to 00). The DESTINATION_ADDRESS will be the SOURCE_ADDRESS
        from the forward messages, which (with a REFERENCE NO.?)
        identifies the interface Router and its session-record.

        The Router processes the messages using old-network procedure.

        When the interface Router receives the messages it uses the
        DESTINATION_ADDRESS (and REF.NO?) to find the session-record
        and return the messages to the Server on the established
        message-path.


        8.2.4.3. Closing the previous message-path (if any).

        If the service delivery were the result of a service transfer,
        the originating Router's records would hold references to the
        path used for the earlier session. The records will be updated
        and a CLOSE_REQUEST message sent on the previous message-path.

        The previous Server will CLOSE the previous message-path when
        it receives the CLOSE_REQUEST message.

        If the previous session encountered old-network equipment, no
        CLOSE_REQUEST message could be sent. The previous Server would
        CLOSE the previous incomplete message-path after receiving
        REQUEST_DONE from the new Server; or after receiving ACK_OLD
        in response to its TRANSFER_REQUEST message indicating that
        REQUEST_DONE would not be received.

        8.2.5. Closing the session.

        When service-delivery is complete, the final Server will CLOSE
        the part established message-path in the normal manner. The
        user will CLOSE the host/Router link when no more transfers
        are expected.

[page 28



        9. MULTI-SESSIONS

        A user may establish several simultaneous sub-sessions in the
        pursuit of a session. No special handling is required in the
        Internet as the user would be able to relate the different
        Internet sessions as being part of one master-session.

        A multi-session may also be formed by a special-service Server
        adding other Servers instead of transferring to other Servers;
        or by a mixture of user and Server created sub-sessions.

        A Server adds another Server by sending an ADD_REQUEST message
        to the new Server containing the same information that would
        be contained in a TRANSFER_REQUEST message.

        The new Server will establish a message-path to the user with
        an OPEN_ADD message containing the same information that would
        be contained in an OPEN_TRANSFER message.

        The user's Router will return an OPEN_DONE message to the new
        Server which will send REQUEST_DONE to the Server that
        initiated the ADD.

        The user's Router will also allocate a sub-session number
        before sending an ADD_DONE message to the user containing
        similar information to that contained in the OPEN_DONE
        message. (See 7.2.2.2.)

        Upon receiving the ADD_DONE message, the user's host will open
        a sub-session as indicated by the SESSION_REFERENCE and
        sub-session number in the link header.


        The ADD facility is dependant upon new version equipment.
        There is no means of separating the different sub-session
        windows if old version equipment is encountered.

        10. THE FUTURE INTERNET - CHARGING.

        10.1. Basic charges.

        Internet users will pay a fixed-fee to their Internet Provider
        and will probably pay an additional usage charge, each session
        being charged to the session originator.

        Session charges will depend upon the time that a session
        remains open (and upon the number and size of the messages
        carried?). Session charges should be sufficient to deter users
        from blocking network resources by keeping sessions open
        unnecessarily.

        10.2. Special-service charges.

        Sessions originated by Brokers or Servers in response to

[page 29



        service or transfer request messages will be charged to the
        Broker or Server. Some Service Providers may choose to pay the
        session charges (like Freefone in the telephone network) while
        others may not only pass-on the session charges to the user
        but levy an additional charge for the actual service delivered
        (like Premium Rate services).

        10.3. Collecting Service Provider's charges.

        To deliver special-services, Brokers and Servers are given the
        USER'S INTERNET NAME. Most simply, the charge for the service
        should be collected from that name.

        Collecting service delivery charges on behalf of the Service
        Providers could be a very attractive and very profitable
        service provided by the Internet Operators.

        Recording the charges levied by Servers for service delivery
        will be the responsibility of the Service Providers, - not a
        problem for the Internet! (A Broker may elect to pay for a
        session between a Server and a user - then add commission
        before charging the user.)

        11. SECURITY.

        11.1. User identity verification.

        The user-friendliness and commercial security of this proposal
        are interdependant and lie in the fact that services are
        delivered directly to the user who has no knowledge of the
        service's source or the detail of its invocation. The Server
        is given the user's identity which is verified by the user's
        Internet Router from the session records. (See 7.2.1.)


        11.2. Breeching security.

        The commercial security of this proposition is in part
        attributable to the fact that services are delivered to a
        verifiable user name.

        This verification is not possible when services are delivered
        via old version equipment as the DESTINATION_ADDRESS in the IP
        header is an address which identifies a session-record and the
        user's identity is not included.

        Also, when message-paths are established via old version
        equipment, the user is given an address which identifies a
        session-record to use as the SOURCE_ADDRESS in IP headers.

        Having established a message-path via old version equipment, a
        knowledgeable and meddlesome user could extricate this number
        and use it to build SERVICE or TRANSFER_REQUEST messages with
        a bogus user-name.

[page 30




        The user may also cheat the system when services are known to
        be delivered via old version equipment, by sending REQUEST
        messages to Servers containing a false user's name but with
        the true user's address in the SERVICE_DELIVERY_ADDRESS field.
        This method may not be so attractive to a dishonest user as it
        requires revealing the true address.

        Consequently, Servers must be aware that the user's identity
        cannot be verified when services are delivered via old network
        equipment.


        ********DOCUMENT EXPIRES MARCH 1997**********


Authors' addresses


P.J. Williams                   Ian Davies
IN / R&S                                Central Engineering
GPT Limited                     GPT Limited
PO Box 53                               PO Box 53
New Century Park                        New Century Park
Coventry   CV3 1HJ              Coventry CV3 1HJ
UK                                      UK



Please note - Pip Williams (who did all the work!) is now a consultant
to GPT and not usually available except on Wenesdays.  He is not
directly accessible by e-mail.  Please address comments to Ian Davies
(daviesic@ncp.gpt.co.uk) tel. +44 1203 562755 or fax +44 1203 562566.