Unformatted text preview: an intermediate position to the first position may
be transmitted a number of times greater than the value given by Transmission_Limit.
The value of the Transmission_Limit may be changed using the ‘Set Transmission_Limit’
Directive. CCSDS 232.1-B-2 Page 5-7 September 2010 RECOMMENDED STANDARD FOR COMMUNICATIONS OPERATION PROCEDURE-1 220.127.116.11 Timeout_Type (TT)
The Timeout_Type variable is referred to as ‘TT’. It may take one of two values, ‘0’ or ‘1’.
It specifies the action to be performed when both the Timer expires and the
Transmission_Count (see next variable) has reached the Transmission_Limit (for details, see
The Transmission_Count variable is used to count the number of transmissions of the first
Transfer Frame on the Sent_Queue. The Transmission_Count shall be incremented each
time the first Transfer Frame is retransmitted.
When the AD Service is initiated, Transmission_Count shall be set to ‘1’.
Whenever one or more Transfer Frames are acknowledged and therefore removed from the
Sent_Queue, the Transmission_Count shall be reset to ‘1’. The Transmission_Count shall
also be set to ‘1’ when FOP-1 prepares a Type-AD or Type-BC Transfer Frame for
transmission and the Sent_Queue was previously empty. All of these actions are defined in
detail in 5.2.
For the Expedited Service (BD Service), there is no Transmission_Count variable, because
each Type-BD Transfer Frame is only transmitted once.
18.104.22.168 Actions for Retransmission
There are two different sorts of events which may cause FOP-1 to initiate retransmission of
one or more Type-AD Transfer Frames:
a) a CLCW arrives which negatively acknowledges a Transfer Frame (‘Retransmit Flag’
Whenever a CLCW arrives which negatively acknowledges a Transfer Frame
(‘Retransmit Flag’ = 1), FOP-1 checks whether the value of the Transmission_Count
has reached the value of the Transmission_Limit. If it has not, FOP-1 SHALL
increment the count and initiate retransmission of the Transfer Frames on the
Sent_Queue. If it has, FOP-1 shall generate an ‘Alert’ notification.
b) the Timer expires (a CLCW positively acknowledging that the last Transfer Frame on
the Sent_Queue has not been r...
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