TSAT 3000 - Telemetry and data transfer via SATellite
TSAT 3000 Configuration Parameter Description, January 2013 Page 58 of 124
3.8.3 LCC_WINDOW_SIZE
Default 16, Range 2…4096
HUB: Set the maximum number of satellite link packets that may be outstanding before
acknowledge from the remote side is required. The packet sequence numbering is used in
conjunction with the “Secure Link Facility”. See
PORT_MAX_APPL_RETRIES [n].
RT: Not Used.
RT will obtain and use the HUB’s value of
LCC_WINDOW_SIZE when Link is Opened (RT
receive
LINK_RESET or LINK_ACK packet). If you want to change the CURRENT value, you
should therefore change the HUB parameter, and then Close + Open all Links.
Please also note the following:
• The actual number of outstanding packets is 1 less than the value indicated by
LCC_WINDOW_SIZE
.
• To utilise the full satellite link capacity,
LCC_WINDOW_SIZE should be 1 greater than the
Round-Trip delay (measured in number of packets). The Round-Trip delay is approximately
660.000 [us] /
MAC_TIMESLOT_LENGTH [us/packet] (depending on Satellite Link Rate and
Packet Size).
• To utilise the full window size, the
LCC_RETRANS_QUE_SIZE must also be greater or equal
LCC_WINDOW_SIZE.
• Secure-Link packets include Tx-Sequence-number + Piggy-Back-acknowledge. The size of
Link-Header is therefore increased with some bytes (and available room for User-Data
decreased). Number of bytes is dependent of
LCC_WINDOW_SIZE:
LCC_WINDOW_SIZE Extra bytes in Link-Header
2 … 8 1 byte
9 …128 2 bytes
129 …2048 3 bytes
2049 …4096 4 bytes
• Non-Secure-Link packets to/from single RT (i.e. Not Multi destination packets – Broadcast and
Group addressing from HUB to RT) will also by default include Piggy-Back-acknowledge (but
not Tx-Sequence-number). The size of Link-Header is therefore increased with 1 or 2 bytes
(and available room for User-Data decreased). Number of bytes is dependent of
LCC_WINDOW_SIZE
:
LCC_WINDOW_SIZE Extra bytes in Link-Header
2 … 128 1 byte
129 …4096 2 bytes
You may select to not include Piggy-back-acknowledge in non-Secure-Link packets with
option bit 20 (0x0010.0000 –
UTILITY_NO_PIGGYBACK) in UTL_UTILITY_MASK.
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