M3SR Series 4100 Selecting the xDL Mode
4.96 Operating Manual 6175.4760.02 – 01
4.4.5.7 Selecting the xDL Mode
Softkey Selection / Editor Description
Listbox 1. Press 'xDL Mode' softkey.
2. Select desired value from listbox.
3. Press 'ENT' to confirm.
The new value is now effective.
Possible values:
• LDL (Low Data Rate Link Protocol)
• HDL (High Data Rate Link Protocol)
• adaptive xDL
If adaptive xDL is selected, the ALE 3G auto-
matically chooses the best xDL selection
based on the measured channel conditions
and the used packet size.
If LDL is selected, the LDL ARQ (Automatic
Repeat Request) protocol is used with prese-
lected number of bytes per Tx-Frame (see
sect. 4.4.5.9 Selecting the LDL Number of
Bytes per Tx Frame).
If HDL is selected, the HDL ARQ protocol is
used with preselected number of packets per
Tx-Frame (see sect. 4.4.5.8 Selecting the
HDL Number of Packets per Tx Frame).
xDL ARQ protocols which allow an acknowl-
edged point-to-point delivery of datagrams. In
case of an erroneous transmission, single
packets are repeated with changed FEC (For-
ward Error Correction) coding so that code
combining techniques can be used for error
correction.
Differences between HDL and LDL
The HDL protocol is best suited for delivering
relatively large datagrams under good to fair
HF channel conditions, while the LDL protocol
provides better performance for smaller data-
gram lengths under fair to very poor HF chan-
nel conditions. The HDL achieves a highest
possible data throughput of approximately
4 kbps under very good channel conditions.
Packet Sizes
LDL / HDL offers predefined packet sizes as
listed below which can be preconfigured via
R&S RNMS or selected manually by the user.
Due to traffic management capabilities the
packet size can be changed during an estab-
lished link.
To reach the best performance in changing
channel conditions it is recommended to use
the adaptive xDL mode.
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