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⟦056ff294e⟧ Wang Wps File
Length: 4369 (0x1111)
Types: Wang Wps File
Notes: FIX/1000/PSP/038
Names: »5201A «
Derivation
└─⟦e48583e73⟧ Bits:30006141 8" Wang WCS floppy, CR 0514A
└─ ⟦this⟧ »5201A «
WangText
…0f…
5201A/bna…02…FIX/1000/PSP/0038
…02…JL/840726…02……02…
FIKS SYSTEM SPECIFICATION
…02……02…FK7809…0e…
4.1.1.2 I̲n̲b̲o̲u̲n̲d̲ ̲M̲e̲s̲s̲a̲g̲e̲ ̲P̲r̲o̲c̲e̲s̲s̲i̲n̲g̲
Narrative and control messages arrive at the black
TDX interface simultaneously from up to 7 internodal
trunk lines. On a given trunk, as illustrated in Figure
4.1.2.4.1-1, messages are intermixed, arriving in packets
by precedence level.
Message packets are variable in length up to a maximum
size, whose value is a system parameter. The message
data portion of the packet currently is set at a maximum
of 512 bytes.
4.1.1.2.1 N̲o̲d̲a̲l̲ ̲M̲e̲s̲s̲a̲g̲e̲ ̲S̲w̲i̲t̲c̲h̲i̲n̲g̲
Employing X.75 Level 3 protocol, the NSS buffers the
packets of an incoming message (1). Buffers may be
temporarily unavailable, possibly due to a bottleneck
at the File Processor interface. If so, acknowledgement
of packet receipt to the sending node is withheld.
This action inhibits further input of message packets.
The first packet of a message indicates a new transmission
serial number. If this number is not greater in value
than the serial number of a previous message received
from the internodal trunk, then the message is assumed
to be a duplicate and is discarded, but acknowledged,
as its packets are received. If the serial number is
greater by 2 or more than the previous value, then
a negative acknowledgement is sent to the sending node
reporting a m̲e̲s̲s̲a̲g̲e̲ ̲t̲r̲a̲n̲s̲m̲i̲s̲s̲i̲o̲n̲ ̲s̲e̲r̲i̲a̲l̲ ̲n̲u̲m̲b̲e̲r̲ ̲e̲r̲r̲o̲r̲
(1a).
The binary header which is contained in the first packet
of the message is referenced to obtain the routing
information. These data provide identifiers of the
appropriate MEDE, SCC or NICS which will receive a
copy of the message.
This information is entered into a Message Transition
Control Block (MTCB) which is requested from the MTCB
Monitor.
Acknowledgement to the sending node, on receipt of
the first packet, is withheld pending the reservation
of the MTCB and its associated file (3).
The header of each incoming packet is then referenced
to determine its sequence number and if it is the last
packet comprising the message.
As packets are written to the IMF (4), their headers
are removed. If packet sequence numbers indicate transmission
errors, then the sending node is requested to r̲e̲t̲r̲a̲n̲s̲m̲i̲t̲
̲t̲h̲e̲ ̲m̲e̲s̲s̲a̲g̲e̲ (4a). Otherwise, each packet is acknowledged
by the NSS by transmitting the appropriate X.75 control
message response.
If the NSS receives a status indication of t̲r̲u̲n̲k̲ ̲f̲a̲i̲l̲u̲r̲e̲
from the I/O System, it reports the failure to the
Supervisory Function Subsystem (4b).
After the last packet has been written to the IMF of
the message, the Nodal Switch acknowledges the receipt
of the message to the sending node (5).
If the message is intended for relay to another node,
then its orbit control count is decremented. If the
count becomes zero, then the MTCB of the message is
updated to indicate that an o̲r̲b̲i̲t̲ ̲e̲r̲r̲o̲r̲ has occurred.
This overrides the internodal relay indicator of the
binary header, as specified by the routing mask, to
direct the message to the MEDE for disposal (6a).
The QACCESS Monitor is then invoked to make an entry
in the Nodal Switch's Transport queue for outbound
transmission of the message to be relayed (6).
The entry is time-stamped by QACCESS and entered in
the queue which is designated for outbound messages
of the requested precedence level. QACCESS also updates
the MTCB of the message to indicate that further use
of the message's file is pending. The message may be
intended for delivery to the SCC which is collocated
with the NODE/MEDE. In this case, QACCESS is requested
to enter the message's MTCB index number in the input
queue served by the SCC Interface Process (SIP).
If the message is intended for delivery to the MEDE,
then QACCESS is requested to enter the message's MTCB
reference into the appropriate precedence-level input
queue of the Message Distribution Subsystem (7).
QACCESS notifies the MDS that a message awaits distribution
if the MDS's input queue is empty when the enqueue
request was made. A logical "signal" is sent to the
MDS interface through the AMOS' interprocess communication
facility.
