ARPANET short blocking feature
RFC 852

Document Type RFC - Unknown (April 1983; No errata)
Last updated 2013-03-02
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Request for Comments: 852

                    The ARPANET Short Blocking Feature

                                  RFC 852

                              Andrew G. Malis
                       ARPANET Mail: malis@bbn-unix

                       Bolt Beranek and Newman Inc.
                              50 Moulton St.
                           Cambridge, MA  02238

                                April 1983

     This RFC specifies the ARPANET Short Blocking Feature, which will
     allow ARPANET hosts to optionally shorten the IMP's host blocking
     timer.  This Feature is a replacement of the ARPANET non-blocking
     host   interface,  which  was  never  implemented,  and  will  be
     available to hosts using either the 1822  or  1822L  Host  Access
     Protocol.   The  RFC is also being presented as a solicitation of
     comments on the Short  Blocking  Feature,  especially  from  host
     network software implementers and maintainers.




     ARPANET Short Blocking Feature                         April 1983
     RFC 852

     1  INTRODUCTION

     This RFC specifies the ARPANET Short Blocking Feature, which will

     allow a host to shorten the amount of time that it may be blocked

     by its IMP after it presents a message to the network (currently,

     the  IMP  can  block  further input from a host for up to fifteen

     seconds).

     The Feature is an addition to the ARPANET  1822  and  1822L  Host

     Access  Protocols,  and  replaces the non-blocking host interface

     described in section 3.7 of BBN Report 1822 [1], which was  never

     implemented.   This  Feature  will  be available to hosts on C/30

     IMPs only.  This will not present a problem on the ARPANET, which

     only  has  C/30 IMPs, but hosts on non-C/30 IMPs in networks that

     mix C/30 and non-C/30 IMPs will not be  able  to  use  the  Short

     Blocking Feature.

     The RFC's terminology is consistent  with  that  used  in  Report

     1822, and any new terms will be defined when they are first used.

     Familiarity  with  Report  1822  (section  3  in  particular)  is

     assumed.

     This RFC was once part of RFC 802, which is now obsolete and  has

     been  replaced  by  the  combination of this RFC and RFC 851, The

     ARPANET 1822L Host  Access  Protocol  [2].   The  Short  Blocking

     Feature  will  be  available to all hosts on C/30 IMPs, no matter

                                   - 1 -




     ARPANET Short Blocking Feature                         April 1983
     RFC 852

     which (1822 or 1822L) host access  protocol  they  are  using  to

     communicate with the IMP.

                                   - 2 -




     ARPANET Short Blocking Feature                         April 1983
     RFC 852

     2  THE ARPANET SHORT BLOCKING FEATURE

     The Short Blocking Feature of the 1822 and 1822L protocols allows

     a  host to present messages to the IMP without causing the IMP to

     not accept further messages from the host  for  long  amounts  of

     time  (up  to fifteen seconds).  It is a replacement for the non-

     blocking host interface described in section 3.7 of Report  1822,

     and that description should be ignored.

     2.1  Host Blocking

     Usually, when a source host submits a message to an IMP, the  IMP

     immediately processes that message and sends it on its way to its

     destination host.  Sometimes, however, the IMP  is  not  able  to

     process the message immediately.  Processing a message requires a

     significant number of resources, and when the network is  heavily

     loaded,  there can sometimes be a long delay before the necessary

     resources become available.  In such cases, the IMP must  make  a

     decision  as  to  what to do while it is attempting to gather the

     resources.

     One possibility is for the IMP to stop  accepting  messages  from

     the  source  host  until  it has gathered the resources needed to

     process the message just submitted.  This strategy  is  known  as

     blocking  the  host,  and is basically the strategy that has been

                                   - 3 -




     ARPANET Short Blocking Feature                         April 1983
     RFC 852

     used in the ARPANET up to the present.  When  a  host  submits  a

     message  to  an  IMP, all further transmissions from that host to

     that IMP are blocked until the message can be processed.

     It is important to note, however, that not all  messages  require

     the  same  set  of resources in order to be processed by the IMP.

     The particular set of resources needed will depend on the message

     type,  the  message  length,  and  the  destination  host  of the

     message.  Therefore, although it might take a long time to gather

     the  resources  needed  to process a particular message, it might
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