SBP-2 Extended Reconnect Interval proposal

Greg Shue gregs at
Wed Feb 18 16:42:43 PST 1998

* From the T10 (formerly SCSI) Reflector (t10 at, posted by:
* Greg Shue <gregs at>

Hi all,

I have been working with the PWG 1394 group in trying to figure
out whether or not SBP-2 could/should/would be used for a standard
printing transport protocol.  During this work, we recognized the
desire for access control (i.e. logins) to be maintained across
transient link interruptions.  These interruptions include a
person disconnecting and reconnecting the cable.  In trying to
address this, I recognized that this is probably a SBP-2 level
issue.  What follows is a proposal for extending SBP-2 to provide
an extended reconnect interval for asynchronous-only connections.

I know it's very late in the standardization process.
I feel the feature is general enough that I at least want to
hear your comments.

Proposed extension of SBP-2 for

  Programmable reconnect interval proposal for retained access
  control across transient link interruptions

  The SBP-2 proposal 0.3a currently has a reconnect interval
  fixed at one second.  This may be sufficient for resumption of
  access control following a Serial Bus reset where neither the
  initiator, target, nor bus disappeared from the topology.

  Unfortunately it does not address the following situations:

    - the bus is inadvertantly configured in a loop (causing the
	entire bus to disappear)

    - the cable is disconnected along the path between initiator
       and target, and subsequently reconnected.

       (e.g.  a child disconnects a cable in a home-office
       environment while a 1394 printer is in the middle of an
       hour-long print job.)

  These cases typify transient human interaction with the bus
  (which extend for longer than one second) for which access
  control needs to be retained.  Though it is entirely possible
  to build an additional layer of access control on top of the
  SBP-2 protocol, this seems to be much more efficiently
  accomplished by a general extension of the reconnect policy.

Proposed changes to SBP-2, Revision 3a, dated January 23, 1998:

  Section 3.1.2 Glossary:
    Add the following definition.

      transient link interruption:  An interval long enough to
	allow a cable disconnect and reconnect to be performed by
	a human, yet short with respect to an interface access

  Section Login ORB:
    The ORB diagram shall be changed such that the least
    significant 3 bits of the _reserved_ field are labeled as

    Beneath the paragraph describing the _exclusive_ bit, add the
    following text:

      The rcon_to field shall specify, as an enumeration, the
      maximum time a target shall allow for this initiator to
      complete a reconnection before releasing access to the
      interface.  The supported values are enumerated in the
      table below.  A one-second timeout is required for logins
      associated with a Create Stream ORB.

	  Table X - Reconnect Timeout Values

	  rcon_to value               reconnect timeout (seconds)
		0                             1
		1                             5
		2                            10
		3                            30
		4                            60
		5                           120
               6-7                    reserved for future standardization

  Section Query logins ORB:
    The indented NOTE shall be changed to:

      NOTE - A _node_ID_ value of FFFF(16) may be observed only during
      the reconnect interval programmed by the associated initiator.
      After this time the target performs an automatic logout of this
      initiator if it has not reconnected.

  Section 7.4.8 Logical_Unit_Characteristics entry:
    The Logical_Unit_Characteristics entry format diagram shall
    be changed such that the least significant 3 bits of the
    _reserved_ field are labeled as "rcon".

    The following paragraph shall be inserted before the one
    describing the _mgt_ORB_timeout_ field:

      The _max_rcon_to_ field (abbreviated as _rcon_ in the
      figure above) specifies the highest enumerated value
      supported by this implementation for a reconnect interval.
      The target shall support all lower enumerated values beneath
      what is specified in this field.  The values shall match
      those specified for the _rcon_to_ field in section

      All implementations shall support a value of zero.  If this
      entry is missing, the enumerated value of zero shall be

  Section 8.1 Access protocols
    The end of the first paragraph shall be change to read
    "access rights across a Serial Bus reset or transient link

    The first bulletted paragraph shall have "a reconnect timeout
    vairable," inserted before "the base addresses".

    The thired bulletted paragraph shall replace "one second" with
    "the reconnect interval".

  Section 8.2.1 Login
    Paragraph e) shall be changed from "the _lun_ and _status_FIFO_
    fields" to read "the _lun_, rcon_to, and _status_FIFO_ fields"

  Section 8.3 Reconnection
    Paragraph 2 shall be replaced with:

      Subsequent to a bus reset, the target shall retain
      sufficient information to permit an initiator to reconnect
      its login ID (and, implicitly, any associated stream ID's).
      After the programmed reconnect interval, the target shall
      perform an implicit logout of the expired login ID and
      associted stream ID's if a successful reconnection has
      not been established.

    Following NOTE shall be replaced with:

      NOTE - A one second timeout shall be required for
      interfaces which provide isochronous stream control.  This
      interval is to permit initiators to reallocate isochronous
      channels and bandwidth and to reestablish isochronous
      connections.  Interfaces which do not provide isochronous
      stream control may support longer reconnect intervals in order
      to provide transient link interruption tollerance.
      NOTE - The reconnection time-out commences when the target
      observes the first subaction gap subsequent to a bus reset.
      If a bus reset occurs before the time-out expires, the
      timer is zeroed then resetarted upon detection of a
      subaction gap.

Greg Shue
Hewlett-Packard Company
Office Products Division			gregs at
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