Tony Kerr@ECSOFT
04/06/99 16:43
     
Title:         Re-Use of Transport - 8327-1 Defect 
PDR Reference:                99040003
Originator Reference:         ONS-SV4-02
SARPs Document Reference:     (ISO/IEC 8237-1) 
Status:                  WITHDRAWN
Severity:                D (minor)
PDR Revision Date:       17/05/99 (ACCEPTED -> WITHDRAWN)
                              19/09/99 (SUBMITTED -> ACCEPTED)
PDR Submission Date:          02/04/99 
Submitting State/Organization:     USA 
Submitting Author Name:       Moulton, James
Submitting Author E-mail Address:  moulton@ons.com 
Submitting Author Supplemental Contact Information: 
22636 Glenn Drive Suite 305
Sterling, VA 20164
USA
SARPs Date:              First edition - 1998 
SARPs Language:               English
     
Summary of Defect:
The re-use of transport based upon the text in ISO/IEC 8327-1 fails due to 
improperly specified collision conditions.
The basic problem (referring to the state tables for ease of discussion) is 
in state STA01C.  When one peer state machine is in STA01C, the peer on the 
other end of the transport connection is in STA01C.
Therefore, both peers may issue a SCON_req which will cause an SCN_TD 
(short connect pdu) to be issued by each peer.  Each peer will also 
transition to STA02C.
At this point, each peer will be in STA02C and will receive an SCN-TD for 
which the incoming event is invalid  (not covered in the specification.) 
Hopefully, appropriate error recovery will require a T-DISC to be issued. 
Another issue is how applications are bound to the connection.  The 
transport connection is available for any application and therefore a 
priori knowledge must be in place as to which application will "service" 
the connect request.
     
Proper entries for TDISC-ind must be made in state STA01C and STA02C. 
Proper entries for SUAB-req and -ind must be made for both STA01C and 
STA02C. (Are these in table 16?)
At the present time, there is no way to get out of STA01C execpt by issuing 
an SCON_req or receiving a short connect pdu.
The basic problem is that without procedures for managing who is allowed to 
issue a short connect on an open transport connection, there is no way to 
ensure proper operation.
     
Assigned SME:            SME 4 (A. Kerr)
     
Proposed SARPs amendment:
Make re-use of transport NOT AVAILABLE.
     
SME Analysis:  (See also PDR 99010002). 
ISO/IEC 8327-1 states, in clause 6.2.4:
<<The transport connection may be kept for reuse provided that the 
transport expedited flow is not available, and either:
a) the SPM which established the TC requests retention of the transport 
connection by parameter in an ABORT SPDU or a FINISH SPDU, or
b) the SPM which established the TC receives a REFUSE SPDU or and ABORT 
SPDU which indicates by parameter that the TC is to be retained.
To avoid contention for a retained transport connection, only the TC 
initiator may reuse the TC by sending a CONNECT SPDU to establish a new 
session connection.>>
     
Therefore, there is no collision case to consider, and no defect in 8327-1.
     
Also, as ULCS uses the Short Connect/Null Encoding options, a TC once 
established can never be re-used, as there is no possibility of using ABORT, 
FINISH or REFUSE SPDUs (or their short-encoding equivalents).  The only 
possibility of re-use is when the initial session connection establishment 
is refused.  In such a case, it would indeed be necessary to keep track of 
the TC properties (QoS parameters and associated traffic type) and only 
assign the TC to a suitable application association.  This is an 
implementation matter.  It would be simpler for an implementation not to 
support re-use of a TC, and this is allowed by the current SARPs provisions.
     
WG3/SG3 Palo Alto April 1999:  Base standard covers TC establishment 
collision correctly in text, but some doubt if the State Table reflects 
this correctly.  Need to check whether base standard 8327-1 (as opposed to 
efficiency amendment) has a predicate in the State Table for the collision 
case.  This would be a new meaning of Forwarded status - forwarded to ISO / 
ITU-T defect resolution process.  Also additional GM required on re-use of 
transport connections.
     
On checking the State Table in ISO 8327-1,the collision case is handled by 
predicate p1, which means NOT (Vtca)  where Vtca is a boolean value set 
according to whether this SPM initiated the T-connection.
Also, the PDR is incorrect in the following respects:
SPM State Table does cover TDISC-ind in state STA01C and STA02C, in Table 
A.16.
SUAB-req is not valid in STA01C and is handled in STA02C, in Table A.16. 
There is no SUAB-ind event.  The AB events are handled in Table A.16. 
There are numerous ways to get out of STA01C, as listed in Tables A.8 
through A.16.
     
Impact on Interoperability:  None.
     
SME Recommendation to CCB:    REJECTED, add guidance on re-use of transport 
connections.
     
CCB Decision:        WITHDRAWN (CCB-9, Naples)