rfc2067.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

                  +------+-------------------------+------+
                        /                           \
                       /                             \
                      /                               \
                     /                                 \
                    /                                   \
                   +-------+ +-------+ +-------+ +-------+
                   |I-field| |Packet | |Packet | |Packet |
                   +-------+ +-------+ +-------+ +-------+
                            /         \
                           /           \
                          /             \
                         /               \
                        /                 \
                       /                   \
                      /                     \
                     +-----+ +-----+   +-----+
                     |Burst| |Burst|...|Burst|
                     +-----+ +-----+   +-----+

                    HIPPI Logical Framing Hierarchy

   The Source asserts PACKET for the duration of a Packet transmission,
   deasserting it to indicate the end of a Packet.  A sequence of Bursts
   comprise a Packet.  To send a burst, a Source asserts the BURST
   signal for 256 clock periods, during which it places 256 words of
   data on the DATA lines.  The first or last Burst of a Packet may be
   less than 256 clock periods, allowing the transmission of any
   integral number of 32 or 64 bit words in a Packet.




















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RFC 2067                     IP over HIPPI                  January 1997


   The READY signal is a pulse four or more clock periods long.  Each
   pulse signals the Source that the Destination can receive one Burst.
   The Destination need not wait for a burst before sending another
   READY if it has burst buffers available; up to 63 unanswered READYs
   may be sent, allowing HIPPI to operate at full speed over distances
   of many kilometers.  If a Source must wait for flow control, it
   inserts idle periods between Bursts.

                +------------------------------------------------+
      REQUEST---+                                                +----
                      +--------------------------------------------+
      CONNECT---------+                                            +--
                         +---------------------------------------+
      PACKET-------------+                                       +----

                       +-+   +-+   +-+   +-+   +-+   +-+   +-+   +-+
      READY------------+ +---+ +---+ +---+ +---+ +---+ +---+ +---+ +--

                         +-------+ +-------+ +-------+ +-----+
      BURST--------------+       +-+       +-+       +-+     +--------

      DATA------I-field----DATA------DATA------DATA-----DATA----------

                      HIPPI Signal Timing Diagram

Serial HIPPI

   There is no ANSI standard for HIPPI other than the parallel copper
   cable version.  However an implementors' agreement exists, specifying
   a serial protocol to extend HIPPI signals on optical fiber or coaxial
   copper cable.  Serial links may be used interchangeably with parallel
   links to overcome HIPPI distance limitations; they are transparent to
   the Source and Destination, except for the possibility of longer
   propagation delays.

















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RFC 2067                     IP over HIPPI                  January 1997


I-Field and Switch Control

   The REQUEST, CONNECT and I-field features of HIPPI-PH were designed
   for the control of switches as described in HIPPI-SC.  A switch is a
   hub with a number of input and output HIPPI ports.  HIPPI Sources are
   cabled to switch input ports, and switch output ports are cabled to
   HIPPI Destinations.  When a HIPPI Source requests a connection, the
   switch interprets the I-field to select an output port and
   electrically connects the HIPPI Source to the HIPPI Destination on
   that port.  Once connected, the switch does not interact with the
   HIPPIs in any way until REQUEST or CONNECT is deasserted, at which
   time it breaks the physical connection and deasserts its output
   signals to both sides.  Some existing switch implementations can
   switch connections in less than one microsecond.  There is the
   potential for as many simultaneous connections, each transferring
   data at HIPPI speeds, as there are input or output ports on the
   switch.  A switch offers much greater total throughput capacity than
   broadcast or ring media.

      31    28  26    23                      11                     0
      +-+---+-+-+---+-+-----------------------+-----------------------+
      |L|   |W|D|PS |C|    Source Address     |  Destination Address  |
      +-+---+-+-+---+-+-----------------------+-----------------------+

                  HIPPI-SC I-field Format (Logical Address Mode)

           L  = Locally defined (1 => entire I-field is locally defined)
           W  = Width (1 => 64 bit connection)
           D  = Direction (1 => swap Source and Destination Address)
           PS = Path Selection (01 => Logical Address Mode)
           C  = Camp-on (1 => wait until Destination is free)

   HIPPI-SC defines I-field formats for two different addressing modes.
   The first, called Source Routing, encodes a string of port numbers in
   the lower 24 bits.  This string specifies a route over a number of
   switches.  A Destination's address may differ from one Source to
   another if multiple switches are used.

   The second format, called Logical Address Mode, defines two 12 bit
   fields, Source Address and Destination Address.  A Destination's 12
   bit Switch Address is the same for all Sources.  Switches commonly
   have address lookup tables to map 12 bit logical addresses to
   physical ports.  This mode is used for networking.








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RFC 2067                     IP over HIPPI                  January 1997


Control fields in the I-field are:

   L  The "Locally Defined" bit, when set, indicates that the I-field
      is not in the standard format.  The meaning of bits 30-0 are
      locally defined.

   W  The Width bit, when set, requests a 64 bit connection through
      the switch.  It is meaningless if Cable B is not installed at
      the Source.  If W is set and either the Source or the requested
      Destination has no Cable B to the switch, the switch rejects
      the connection.  Otherwise the switch connects both Cable A and
      Cable B if W is set, or Cable A only if W is clear.  This
      feature is useful if both Source and Destination
      implementations can selectively disable or enable Cable B on
      each new connection.

   D  The Direction bit, when set, reverses the sense of the Source
      Address and Destination Address fields.  In other words, D=1
      means that the Source Address is in bits 0-11 and the
      Destination Address is in bits 12-23.  This bit was defined to
      give devices a simple way to route return messages.  It is not
      useful for LAN operations.

   PS The Path Selection field determines whether the I-field
      contains Source Route or Address information, and in Logical
      Address mode, whether the switch may select from multiple
      possible routes to the destination.  The value "01" selects
      Logical Address mode and fixed routes.

   C  The Camp-on bit requests the switch not to reject the
      connection if the selected Destination is busy (connected to
      another Source) but wait and make the connection when the
      Destination is free.

15 Appendix B -- How to Build a Practical HIPPI LAN

   "IP on HIPPI" describes the network host's view of a HIPPI local area
   network without providing much information on the architecture of the
   network itself.  Here we describe a network constructed from
   available HIPPI components, having the following characteristics:

   1.  A tree structure with a central HIPPI-SC compliant hub and
   optional satellite switches

   2.  Each satellite is connected to the hub by just one bidirectional
   HIPPI link.





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RFC 2067                     IP over HIPPI                  January 1997


   3.  Serial HIPPI or transparent fiber optic HIPPI extender devices
   may be used in any link.

   4.  Some satellites may be a particular switch product which is not
   HIPPI-SC compliant.

   5.  Host systems are attached either directly to the hub or to
   satellites, by single bidirectional links in which both HIPPI cables
   go to the same numbered switch port.

Switch Address Management

   Switch addresses use a flat address space.  The 12-bit address is
   subdivided into 6 bits of switch number and 6 bits of port number.

   11                       5                     0
      +-----------------------+-----------------------+
      |     Switch Number     |      Port Number      |
      +-----------------------+-----------------------+

Logical Address Construction

   Switches may be numbered arbitrarily.  A given host's address
   consists of the number of the switch it is directly attached to and
   the physical port number on that switch to which its input channel is
   attached.

   In the singly-connected tree structure, there is exactly one path
   between any pair of hosts.  Since each satellite must be connected
   directly to the hub, the maximum length of this path is three hops,
   and the minimum length is one.  Each HIPPI-SC compliant switch is
   programmed to map each of the host switch addresses to the
   appropriate output port: either the port to which the host is
   directly attached or a port that is linked to another switch in the
   path to it.

Special Treatment of Nonstandard Switches

   There is one commercially available switch that was designed
   before the drafting of HIPPI-SC and is not fully compliant.  It is
   in common use, so it is worth making some special provisions to
   allow its use in a HIPPI LAN.  This switch supports only the
   Source Route mode of addressing with a four bit right shift that
   can be disabled by a hardware switch on each input port.
   Addresses cannot be mapped.  The switch does not support the "W",
   "D", or "PS" fields of the I-field; it ignores their contents.
   Use of this switch as a satellite will require a slight deviation
   from normal I-field usage by the hosts that are directly attached



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RFC 2067                     IP over HIPPI                  January 1997


   to it.  Hosts attached to standard switches are not affected.

   For a destination connected to a non compliant satellite, the
   satellite uses only the least significant four bits of the I-field
   as the address.  Since the address contains the destination's
   physical port number in the least significant bits, its port will
   be selected.  Nonstandard switches should be set to disable I-
   field shifting at the input from the hub, so that the destination
   host will see its correct switch address in the I-field when
   performing self-address discovery.  I-field shifting must be
   enabled on the satellite for each input port to which a host is
   attached.

   Hosts attached to nonstandard satellites must deviate from the
   normal I-field usage when connecting to hosts on another switch.
   It is suggested that all host implementations have this capability
   as long as the nonstandard switches remain in use.  The host must
   know, by some manual configuration method, that it is connected to
   a nonstandard switch, and it must have its "link port" number;
   that is, the number of the port on the satellite that is connected
   to the hub.

   The normal I-field format for a 32-bit connection, per the
   document, is this:

   31        26    23                      11                     0
   +---------+---+-+-----------------------+-----------------------+
   |0 0 0 0 0|x 1|C|        Unused         |  Destination Address  |
   +---------+---+-+-----------------------+-----------------------+

   The special I-field format is:

   31        26  24                15                     4 3     0
   +---------+---+-+---------------+-----------------------+-------+
   |0 0 0 0 0|x 1|C|    Unused     |  Destination Address  | Link  |
   +---------+---+-+---------------+-----------------------+-------+

   This I-field is altered by shifting the lower 24 bits left by four
   and adding the link port number.  Camp-on is optional, and the PS
   field is set to 01 or 11 (the host's option) as if the switch
   supported logical address mode.  All other I-field bits are set to
   zero.  When the host requests a connection with this I-field, the
   switch selects a connection through the link port to the hub, and
   shifts the lower 24 bits of the I-field right by four bits.  The link
   port number is discarded and the I-field passed through to t