rfc705.txt

RFC 相关的技术文档

When the Host sets up a path(s) (with a BEGIN or LISTEN command) it identifies
what type of translation or data-mapping it requires the FE to perform on all
data transmitted on this path(s).  This is specified by two values - one
giving the format of the data transmitted between the FE and the network,
the other giving the format of the data between the Host and the FE. [4]

Flow Control								3i

All commands (except REPLYs) must be REPLYED to by the receiver.  The sender
is blocked from sending more commands on the same path until a REPLY has been
received.  The REPLY command serves two functions:  it indicates the
success/failure of the last transmission on the path, and it also indicates
a willingness of the receiver to accept more data on that path.  Receipt of
any valid REPLY on an open path is sufficient to unblock it for END or
INTERRUPT commands.  Thus a receiver who will not (or can not) accept more
data (MESSAGE commands) on a given path need not block the sender from
ENDing the path if he desires.  An indication of "READY" in the reply serves
to unblock the path for MESSAGE commands also.

In the normal case, the REPLY performs both functions concurrently.  However,
when the receiver is not ready to accept more data, he can REPLY indicating
only success/failure of the last command which should be sufficient to
allow the sender to free the transmission buffer, requeue the command for
retransmission if necessary, etc. and wait for another REPLY command 
announcing the receiver's ability to accept more data.

Exceptional Conditions							3j

When a command is received and can not be executed, the REPLY command is used
to notify the sender of the command.  To do this, the bits of CODE field of
the REPLY are set to show the CATEGORY of the error and its TYPE within that
category (see Section 3h).



                        ***WORKING DOCUMENT***


                                 7


RFC 705
Front-End Protocol


                        ***WORKING DOCUMENT***



                               COMMANDS					4


Introduction								4a

All communications between the Host and the FE is performed by means of
commands.  The commands are given names for documentation purposes but are
distinguished by the binary value of the first field of the command string.
Command strings will be padded with zeros up to the next multiple of an
installation defined parameter.  (This value will be dependent on the 
capabilities of the hardware interface between the Host and the FE.)

Field lengths within a command string are specified as some number of bits.
These information bits will be right-justified within the least number of
bytes needed to hold them.  The size of a byte will be an installation
parameter which will normally be 8 bits but other values will be accommodated
as necessary.

The values and meanings of the CODE field of the REPLY command are given for
each command within the following descriptions:

1:  BEGIN								4b

Format

       	BEGIN INDEX PATH HOST SOCKET TRANS-TYPE CONN-TYPE NPATHS

Use

This command is sent only from the Host to the FE.  Its function is to direct
the FE to establish one or more logical connections (paths) on the specified
index between the Host and the FE.

Its use has three different modes (depending on the value of the PATH field) :

	mode (a) - to set up a new index and to direct the FE to attempt
	to establish network connections for the one or more paths
	specified within this index.



                       ***WORKING DOCUMENTS***


                                 8


RFC 705
Front-End Protocol


                        ***WORKING DOCUMENT***



	mode (b) - to attempt to establish network connections for an
	existing (but at present closed) path within the already set-up
	index.

	Mode (c) - to attempt to establish network connections for
	one or more new paths within the already set-up index.

Parameters

	a)  BEGIN is an 8-bit field with the value 1.

	b)  INDEX is a 16-bit field, specifying the index.  Note that
            the value 0 is reserved for special use (see Section 4).

	c)  PATH is an 8-bit field, specifying the path(s) which are
	    to be established.  Its value identifies the mode of the
	    BEGIN (see above) :

		mode (a) - its value must be 1.

		mode (b) - its value must be that of the path to be
		"re-opened."

		mode (c) - its value must be exactly one greater than
		the current number of paths defined within this index.

	d)  HOST is a 32-bit field specifying the foreign host with
	    which connections are to be established.

	e)  SOCKET is a 32-bit field, specifying the first or only
	    socket at the foreign host to which connections are to 
	    be made.

      	f)  TRANS-TYPE is a 16-bit field which directs the FE to
	    perform this type of translation on all data (i.e. TEXT
	    in the MESSAGE command string) sent on every path being
	    established by this command.  The first 8 bits specify
	    the format of the data on the network side; the second 
	    8 bits specify the format of the data on the Host side.	 
	    The values assigned to the particular formats (eq. ASCII,
	    EBCDIC etc.) are installation parameters; however, the


                        ***WORKING DOCUMENT***


                                 9


RFC 705
Front-End Protocol


                        ***WORKING DOCUMENT***


	    value 0 will always mean "bit string" and thus if either
	    of the 8-bit sub-fields contains 0, then no mapping will
	    be performed.

        g)  CONN-TYPE is an 16-bit field, specifying the type and mode
	    of connection(s) to be established for the specified path(s).
	    Its value informs the FE how to associate sockets with
	    indexes/paths (see Sections 2f and 2g).

		Value		 Type		 Mode

		  7		Duplex		via ICP
		  6		Duplex		direct
		  5		Receive		via ICP
		  4		Receive		direct
		  3		Send		via ICP
		  2		Send		direct

        h)  NPATHS is an 8-bit field, specifying the number of paths which
	this command directs the FE to attempt to establish connections
	for.  If the BEGIN is of mode (b) then its value must be 1.
	Otherwise the sum of its value and the value of the PATH field
	is the new current number of paths plus one.

Error CODES in REPLY

	Category   Type			Meaning
			
	   3	     1		PATH invalid for new index
	   3	     2		PATH invalid for old index
	   3	     3		PATH already open
	   3	     4		HOST unknown
	   3	     5  	TRANSLATION-TYPE invalid
	   3	     6		CONNECTION-TYPE invalid
	   3	     7		NPATHS invalid for old path on old index
	   3	     8		Specified socket inconsistent with CONN-TYPE
	   3	     9		INDEX invalid, not ready for business
	   4	     1		No new connections - FE full
	   4	     2		No new connections - closing down soon


                        ***WORKING DOCUMENT***


                                  10


RFC 705
Front-End Protocol


                        ***WORKING DOCUMENT***


2:  LISTEN								4c

Format

	LISTEN INDEX PATH HOST SOCKET TRANS-TYPE CONN-TYPE NPATHS

Use

This command is sent only from the Host to the FE.

Its function is to direct the FE to "listen," i.e., to hold the specified paths
pending until such time as a request for connection (RFC) is received from the 
network to the specified local socket. then to set up connections and to 
respond with a RESPONSE command for each path.

Its use has three different modes (depending on the value of the PATH field) :

	mode (a) - to set up a new index and to listen on the specified local
	socket in order to establish connections for the specified paths.

	mode (b) - to listen on the specified socket in order to establish
	connections for the specified, existing (but at present closed)
	path within the already set-up index.

	mode (c) - to listen on the specified socket in order to establish
	connections for the specified new path(s) within the already set-up
	index.

By use of the HOST parameter, the FE can be directed to accept RFCs from any
host or only from the specified host.

Parameters

	a)  LISTEN is an 8-bit field with value 2.

	b)  INDEX is a 16-bit field specifying the index.

	c)  PATH is an 8-bit field specifying the first of the one or more
	    paths which are to be held pending receipt of a RFC.  Its 
	    value identifies the mode of the LISTEN (see above) :



                        ***WORKING DOCUMENT***


                                  11


RFC 705
Front-End Protocol


                        ***WORKING DOCUMENT***


		mode (a) - its value must be 1.

		mode (b) - its value must be that of the existing path.
		
		mode (c) - its value must be exactly one greater than
		the current number of paths within this index.

	d)  HOST is a 32-bit field specifying the host from which RFCs
	    are to be accepted; a value of 0 implies from any host.

	e)  SOCKET is a 32-bit field specifying the local socket on which
	    the FE is to listen for RFCs.

	f)  TRANS-TYPE is a 16-bit field specifying the type of translation
	    the FE is to perform on all data sent on every path established
	    as a result of this command.  Its values are the same as in the
	    BEGIN command.

	g)  CONN-TYPE is an 16-bit field specifying the type and mode of the
	    connection(s) to be established for the specified path(s) when
	    an RFC is received.  Its values are the same as in the BEGIN
	    command.

	h)  NPATHS is an 8-bit field specifying the number of paths which
	    this command associates with the specified index and which are
	    to be established.  If the LISTEN is of mode (b) then its value 
	    must be 1.  Otherwise the sum of its value and the value of the
	    PATH field is the new current number of paths plus one, within
	    this index.  Thus its value is the number of extra RFCs for
	    which the FE is listening on this socket.

Error CODEs in REPLY

	Category      Type			Meaning

	   3		1	PATH invalid for new index
	   3		2	PATH invalid for old index
	   3		3	PATH already open
	   3		4	HOST unknown
	   3	        5	TRANSLATION-TYPE invalid
	

                        ***WORKING DOCUMENT***


                                  12


RFC 705
Front-End Protocol


                        ***WORKING DOCUMENT***


	   3		6	CONNECTION-TYPE INVALID
	   3		7	NPATHS invalid for old path on old index
	   3		8	Specified socket inconsistent with CONN-TYPE
	   3		9	INDEX invalid, not ready for business
	   3	       10	Socket already in use.
	   4		1	No new listens - FE full
	   4		2	No new listens - closing down soon

3:  RESPONSE								4d

Format

	RESPONSE INDEX PATH CODE HOST SOCKET

Use

This command is sent only from the FE to the Host - once per path specified in
a BEGIN or a LISTEN command.

For paths specified in a BEGIN, it is sent to indicate the success or failure
of the connection attempt.  For paths specified in a LISTEN, it is sent at
the time when the FE has received a matching RFC and has established the
connection.

The HOST and SOCKET parameters are purely informational which the Host can 
ignore if it so desires.  Their contents are only guaranteed if the connection
attempt succeeded.

Parameters

	a)  RESPONSE is an 8-bit field with value 3.

	b)  INDEX is a 16-bit field specifying the index.

	c)  PATH is an 8-bit field specifying the particular path.

	d)  CODE is a 16-bit field indicating the outcome of the
	    connection attempt:


                        ***WORKING DOCUMENT***


                                  13


RFC 705
Front-End Protocol


                        ***WORKING DOCUMENT***


		Value			Meaning

		  0		Path successfully established.
		  1		Local IMP dead.
		  2		Foreign IMP inaccessible.
		  3		Foreign Host dead.
		  4		Foreign Host not responding.
		  5		Connection refused.

	e)  HOST is a 32-bit field specifying the foreign host to which the
	    connection has been made.

	f)  SOCKET is a 32-bit field specifying the socket at the foreign
	    host.  If the connection type is simplex, then it is the only
	    foreign socket for this path; if duplex, then it is the lower