Movatterモバイル変換

Network Working Group                                          J. WongRequest for Comments: 117                                         UCLANIC #5826                                                 7 April 1971Some Comments on the Official Protocol               [Categories B.1, C.1, C.2, C.3, C.4, C.5] Document No. 1 and NWG/RFC No. 107 gave a very detailed description ofconnection establishment, connection termination and flow control overthe Network.  Throughout the implementation of the NCP it wasdiscovered that the handling of ERR control commands, messages oftypes other than 0 (regular), 4 (nop), and 5 (rfnm), and messages withthe From-imp bit on are not well discussed so that problems arise whenthey occur.The Protocol is not complete if the above situations are not handledclearly, and the Host-Host Protocol Glitch Cleaning Committee shouldtake this into consideration.  In this document, experience with theseunfavorable situations and suggestions for handling are given:1.  ERR Control CommandsIn Document No. 1, the following error conditions are described:     a.  Illegal Op. code.     b.  End of message encountered before all expected parameters.     c.  Bad socket polarity within commands.     d.  Link number not in the range of 0 <= L < 32.     e.  A request (other than RTS/STR) on a non-existent socket.     f.  A request (ALL, GVB, RET, INR, INS) on a non-existent link         number.     g.  Transmit over non-existent link number.Other error conditions are:     h.  A request (GVB, RET, INR, INS) on an existent link, but         connection is not established.                                                                [Page 1]

     i.  Transmit over an existent link, but connection is not         established.     j.  ALL or GVB on a send connection.     k.  RET on a receive connection.     l.  An attempt to send more than the allocated number of bits or         messages.     m.  ECO, ERP, ERR commands do not have the defined number of bits        of data.In Document No. 1, each site is supposed to document the informationon their ERR command.  No one has done that so far, and the mainreason is we are not sure of what information is important.  InNWG/RFC No. 107, the text portion of the ERR Commands is decided tohave a fixed length of 80 bits because 80 bits is long enough to holdthe longest non-ERR command.  In some of the above error conditions,more information than the command itself is desirable.  It was notedthat these error conditions arise very often in the experimental stageof the NCP.  If every NCP is operating properly, none of them shouldever occur.  The ERR commands are therefore, an excellent debuggingtool for the protocol.  So it is desirable to define a set of possibleerror conditions, and for each condition, define a set of arguments inthe corresponding ERR command so that enough information is given totell what's wrong.  The suggested arguments for each situation (a - m)are listed below:     a.  1.  Op. code in error.         2.  Part of message following op. code (A maximum of 72             bits).     b, c, d, e, f.         1.  The command in error.     g.  1.  Link number,         2.  Beginning of message (A maximum of 72 bits),     h.  1.  Command in error.         2.  Socket numbers for the connection.         3.  Status of the connection.                                                                [Page 2]

     i.  1.  Link number,         2.  Beginning of message (A maximum of 72 bits),         3.  Socket numbers for the connection.         4.  Status of the connection.     j, k.         1.  Command in error.         2.  Socket numbers for the connection.     l.  1.  Link number.         2.  Beginning of message (A maximum of 72 bits).         3.  Number of bits sent.         4.  Number of bits allocated.         5.  Number of messages allocated.     m.  1.  The Command in error.Each of the ERR commands should have a special error code (8 bits) totell the error type, an 80-bits field to store the command in error,and additional fields for socket numbers and other information.2.  Imp-to-host messages of types other than 0, 4, and 5.From the BBN report 1822, the following message types will causedifficulty in the implementation of the Protocol.     a.  Type 2 - Imp going down.     b.  Type 7 - Destination host or imp dead.     c.  Type 9 - Incomplete transmission.It was discovered that on sending a message to a site whose imp orhost is not running, a Type 7 or Type 9 message is returned.  Thiscan happen in two situations:     a.  The foreign host or imp is not up at all.     b.  Some connections have been established, and the foreign host         or imp goes down.                                                                [Page 3]

The first situation does not cause much problem because the NCP has noentry in its table corresponding to this site.The second situation is more complicated, because if the table entriesfor the connections to the dead host are not cleared, by the time thishost comes up again, the table entries still exist and the informationwill be very misleading.  One suggestion to solve this problem is:     a.  Whenever a NCP comes up, it send a RESET Control Command to         every other site.     b.  Associated with each site there is a bit called the up-bit.         If a RESET-reply command is received from some site, the         corresponding up-bit is set to 1.  Race condition can be         avoided by ignoring all messages from sites which have not         returned the RESET-reply command.     c.  Messages can only be sent to sites with the up-bit on.     d.  If a RESET control command is received, the Table entries         corresponding to the site are cleared, a RESET-reply is         immediately returned, and the up-bit for the site is set.     e.  The up-bit is reset to 0 when a Type 7 or Type 9 message is         received from a particular site.The above solution will handle the Type 2 messages also.  When a hostreceives a Type 2 message, there is no way for it to tell the otherNCP's that its imp is going down.  Subsequent messages to this hostwill return a Type 7 or 9 message.  The solution above will then comeinto effect.                                                                [Page 4]

With the introduction of the RESET and RESET-reply Control command,the ECO and ERP control command are no longer important and should beremoved.3.  Messages with the From-imp bit on.These kinds of messages are not discussed at all.  Some statisticalmeasurements have been made on messages with the From-imp bit on.  Weshould classify what these messages represent.       [ This RFC was put into machine readable form for entry ]         [ into the online RFC archives by Randy Dunlap 4/97]                                                                [Page 5]